Society&’s energy challenge is a formidable one: we need to produce more energy for a growing world population and at the same time research, develop and build a more sustainable energy system for the future. The challenge requires that we make as efficient as possible use of hydrocarbon resources that we have. Selective catalytic conversions are doubtlessly among the best tools that science can offer to that end.
In a nutshell, catalysis has a lot of work to do in the changing energy landscape: where, in the long term, and with interruptions from time to time, the feedstock base is shifting towards heavier oil and more gas, products are required to become cleaner and shifting towards more distillates (so, less gasoline and less heavy product). Our Pearl gas-to-liquid project in Qatar meets that challenge excellently, at both ends. In refining, the more complex picture consists of: growing importance of hydrocracking and hydrotreating; a stronger economic incentive for upgrading heavy feeds into transportation fuel-range products generally; a need to make the FCC process more flexible; continuing interest in upgrading of residue, non-conventional crude oils and oil sands, opportunities for synergy with Gas to Liquid (GTL) processes, and the challenge to sustainably produce fuels from biomass.
Here we will highlight recent developments in catalysis and discuss some examples of how the above challenges are being addressed through improved catalysts, and improved understanding of catalysis, with an emphasis on hydroprocessing and acid catalysis.

Fuel production and development of new routes to base chemicals from renewable resources are currently drawing much attention worldwide. The production of synthesis gas (CO + H₂), e.g., from biomass-derived feedstock and its conversion to methanol, dimethyl ether (DME), or gasoline provides an attractive option. Recently, DME has attracted a lot of interest not only as liquefied petroleum gas for domestic applications and intermediate product for various base chemicals but also as a clean diesel substitute. Traditionally, DME is obtained in a two-step process, where methanol is produced from syngas with a Cu-based catalyst in the first stage, followed by methanol dehydration to DME with an acidic catalyst in the second stage. Alternatively, methanol synthesis is coupled in situ with the condensation to DME and immediately removed from the equilibrium in the single-step, syngas-to-DME (STD) process. The STD process has several advantages, e.g. the reduction of investment costs and a lower optimum CO/H₂ ratio, which favors the use of biomass-derived syngas. The design of STD catalysts remains a crucial issue for enhancing the catalytic performance. In this context, model systems based on well-defined nanoparticulate precursors may contribute to a more fundamental understanding of structure-property relationships for future design of highly effective catalysts.
Here, we address the design of bifunctional STD catalysts. Well-defined colloidal Cu/Zn-based nanoparticles were applied as precursors for the methanol active component. Different synthetic pathways were developed for synthesizing colloidal Cu/Zn-based nanoparticles, while ensuring close contacts between the Cu nanoparticles and the Zn phase. Pure Cu nanoparticles were used as a reference. A series of bifunctional STD catalysts was prepared, where the nanoparticles were either directly supported on the dehydration catalyst or integrated into the STD catalyst by physical mixing. Catalytic tests were performed in a single continuous-flow laboratory reactor, using simulated biomass-derived, CO-rich syngas (H₂:CO ratio of 1:1). By using this approach, active catalysts for the STD reaction with high DME selectivity were obtained.

Conventional microporous zeolites have long been utilized as solid-acid catalysts capable of cracking hydrocarbon molecules of particular importance to the petrochemical and chemical industries. However, large and bulky hydrocarbons are typically unable to access the zeolite framework and are restricted by strong diffusion limitations, ultimately resulting in their inability to access the active sites of microporous zeolites. Within the last decade, hierarchical zeolites with secondary porosity have been investigated for their ability to accommodate these bulkier hydrocarbon chains. Previous top-down approaches utilizing alkaline treatments (desilication) on MFI type zeolites with wide ranges of Si/Al ratios (15-1000) have been demonstrated to be successful in generating mesoporosity, while preserving the acidity found in conventional zeolites In this work, we utilize a series of different treatment protocols, such as traditional and modified alkaline treatments, and pre-fluorination and desilication techniques, in order to optimize the generation of mesopores in less stable BEA and FAU type zeolites. The material properties of these zeolites are investigated and reported by conventional techniques, including N₂ physisorption, XRD, Ammonia-TPD, SEM, TEM, and NMR. The catalytic cracking performance of the modified zeolites will be discussed.

The possibility of in situ doping during electrochemical anodization of titania nanotube arrays is demonstrated and the mechanism and variations in structural and electronic characteristics of the nanotube arrays as after doping is systematically explored. In the presence of strontium as the dopant, bulk analysis shows strontium mainly incorporated into the lattice of TiO₂. Surface analysis, however, reveals phase segregation of SrO in the TiO₂ matrix at high Sr doping levels. The near edge X-ray absorption fine structure (NEXAFS) spectroscopy analysis reveals that Sr²⁺ doping only alters the Ti and O ions interaction in the TiO₂ lattice on the surface with no effect on their individual charge states. An in-depth understanding of the dopant incorporation mechanism and distribution into TiO₂ nanotube arrays is achieved using high resolution transmission electron microscopy (HRTEM) and the high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) coupled with the electron energy loss spectroscopy (EELS) measurements on the surface and bulk of the nanotubes. Upon their use to photoelectrochemically split water, the Sr-doped TiO₂ nanotube film shows incident photon conversion efficiencies (IPCE) as high as 65%. The enhanced light activity in conjunction with the ordered one-dimensional morphology makes the fabricated films promising candidates for water photoelectrolysis.

Catalytic conversion of alcohols is nowadays of topical interest, as some of them are readily obtained from bio resources. Among them, ethanol is now massively produced for biofuels needs, but it is also being more and more considered as a platform molecule from which families of chemicals can be derived. For instance, ethanol can be used as a starting material in the synthesis of different byproducts such as aldehydes¹, acetals², ethers, esters or alcohols with longer carbonated chains through the Guerbet chemistry³. Such products are then of high importance in the context of the biorefineries development, as intermediate reactants in the downstream production of alternative fuel or chemicals. Within this frame, FeMo-based mixed oxides⁴ (namely Fe₂(MoO₄)₃) are known for their specific redox behavior making them good catalysts for alcohols oxidation.
In order to enhance the redox property of the catalyst, the introduction of lanthanum was checked. Among several syntheses, the second new lanthanum iron molybdenum oxide referenced to date was stabilized and fully characterized. Its crystal structure is original and built of chains of FeO₆ octahedron sharing corners with MoO₄ tetrahedra and surrounded by La³⁺ cations. Its stability under both air and reductive atmosphere was checked prior to further catalytic tests. Also the sample was grinded in a planetary mortar to modify its microstructure and increase its specific area.
On a mechanically milled compound, a conversion of 97 % was observed at 650K with a selectivity to acetaldehyde of 62 %.This clearly outperforms the conventional FeMo catalyst, which exhibits a much lower selectivity to acetaldehyde due to uncontrolled ethanol reaction from ca. 575K. A comparison of both catalysts will be done in this talk as well as the nature of products obtained from ethanol reaction.
References
1- I.-C. Marcu, D. Tichit, F. Fajula, and N. Tanchoux,” Catal. Today, vol. 147, no. 3-4, pp. 231-238, Oct. 2009.
2- K. Thavornprasert, B. de la Goublaye de Ménorval, M. Capron, J. Gornay, L. Jalowiecki-Duhamel, X. Sécordel, S. Cristol, J.-L. Dubois, and F. Dumeignil, Biofuels, vol. 3, no. 1, pp. 25-34, Jan. 2012.
T. Tsuchida, J. Kubo, T. Yoshioka, S. Sakuma, T. Takeguchi, and W. Ueda, J. Catal., vol. 259, no. 2, pp. 183-189, Oct. 2008.
3- K. Thavornprasert, M. Capron, L. Jalowiecki-Duhamel, O. Gardoll, M. Trentesaux, A.-S. Mamede, G. Fang, J. Faye, N. 4- Touati, H. Vezin, J.-L. Dubois, J.-L. Couturier, and F. Dumeignil, Appl. Catal. B Environ., vol. 145, pp. 126-135, février 2014., N. Pernicore, F. Lazzerin, G. Liberti, and G. Lanzavecchia, Journal of Catalysis, p. 293, 1969.

The search for suitable cathode materials for intermediate temperature solid oxide fuel cells has led to the study of complex oxide perovskites such as LaCoO₃ doped with Sr and Fe. To understand the ionic and electronic transport properties of this material, it is essential to model accurately the relevant defect structures. Moreover, LaCoO₃ has a complicated magnetic structure, where transitions from diamagnetic insulator to paramagnetic semiconductor to metal occur as one varies the temperature from close to zero to above 500 K. Building a consistent theoretical framework to model this material has proved highly challenging. We apply a range of computational modelling approaches to study the electronic, magnetic and crystal structure of LaCoO₃, determining optimum methods for the different properties. We then study defect structures in the material, both intrinsic and extrinsic as well as complexes, showing how the magnetic structure is highly sensitive to the local defect configurations. Our results agree well with relevant experiment.

Sr-doped lanthanum manganite (LSM) is the most commonly used cathode material in solid oxide fuel cells (SOFC). Nevertheless, many aspects including the oxygen reduction at LSM electrodes are not yet fully understood. Particularly important in this respect are oxygen reduction (ORR) kinetics, that often exhibit the highest losses in thin film electrolyte-supported SOFCs. By identifying the rate limiting steps and obtaining a fuller understanding of the catalytic reaction mechanisms at the cathode, further optimization becomes possible.
Much attention has recently been focused on the oxygen reduction reaction on dense LSM thin films shown to be dominated by grain boundaries. Instability and degradation is often implicated and correlated to preferential grain boundary cation diffusion. The influence of heterogeneous doping on cation segregation and on the transport properties of anions and cations in LSM was studied by combining operando impedance spectroscopy (IS) and ¹⁸O tracer exchange measurements. LSM thin film electrodes were deposited by pulsed laser deposition (PLD) and analyzed by time of flight secondary ion mass spectrometry (ToF-SIMS), transmission electron microscopy (TEM), scanning tunneling microscopy (STM) and IS. Tracer exchange measurements, on both the polarized and non-polarized polycrystalline thin film microelectrodes, with and without heterogeneous doping, reveal contributions from diffusion and surface exchange kinetics of both grains and grain boundaries. These investigations showed that grain boundaries facilitate a nearly 1000 times faster oxygen diffusivity, as well as oxygen exchange kinetics. Additionally the impact of grain boundaries on LSM thin film oxygen reduction kinetics could be varied by nano-engineering the thin film microstructure by varying the deposition conditions. Cathodically polarized microelectrodes in SOFC operation conditions showed a large increase in ¹⁸O concentration in the LSM films with an apparent uphill diffusion. This could be understood by 3D finite element simulations of the two parallel and interacting diffusion pathways, via grains (D_b and k_b) and grain boundaries (D_gb and k_gb). By heterogeneous doping the total polarization resistance could be dramatically enhanced in the low temperature regime. This shows, that with appropriate optimization of microstructure and microchemistry, suitable cathodes for reduced temperature SOCF operation become possible.

This study investigates surface segregation phenomenon and phase formation in La_(1-x)Sr_xCo_0.2Fe_0.8O_3-δ (LSCF, where x=0.2, 0.3, 0.4), a typical perovskite material used as cathode in solid oxide fuel cells (SOFCs). (001)-oriented LSCF thin films were deposited on (110)-oriented NdGaO₃ (NGO) substrates by pulsed laser deposition (PLD) technique. Upon annealing at 800°C, it was found that Sr content increases in the near surface region in LSCF thin films measured by synchrotron-based total reflection x-ray fluorescence (TXRF). Secondary phases were observed on post-annealed samples by atomic force microscope (AFM), which phases were confirmed to include SrO and SrCO₃ by synchrotron-based hard x-ray photoelectron spectroscopy (HAXPES). An Omniprobe supported focused ion beam (FIB) lift-out technique was successfully applied to preparing site-specific cross-section thin specimens. High resolution transmission electron microscopy (HRTEM) was used to characterize the specimens and TEM-based energy dispersive spectroscopy (EDS) was used to analyze the film/substrate interface as well as film/precipitate interface. The kinetics and thermodynamics of the segregation and phase formation phenomena are discussed in this presentation.

Chemical-electrical energy conversion and storage are greatly attractive for the development of sustainable energy. Catalytic processes are heavily involved in such energy conversion and storage. Development of high-performance catalyst nanomaterials relies on tuning material structures at nanoscale. This is in particular manifested in the design of catalysts demanding both high activity and durability. In this talk, I will present a research system that connects fundamental investigation on well-defined extended surfaces (e.g. single crystal surfaces), extrapolation onto nanocrystals with highly controlled shape and size, exploration of interfacial interaction using novel nanocrystal superlattices as platform, and finally design of high performance catalysts in which all the possible beneficial properties from complex functional structures are implemented. Using recent published results (ref.1-11), I will demonstrate that optimal and fine balanced activity and durability, as well as tunable functionality, can be achieved by carefully tailoying the nanostructure of catalytic nanomaterials.
References:
1. Kang et al.Science,2014, 343, 1339
2. Kang et al.ACS Nano, 2013, 7(1), 645
3. Kang et al.Angew. Chem. Int. Ed., 2010, 49(35), 6156
4. Kang et al.J. Am. Chem. Soc.,2010, 132(22), 7568
5. Kang et al.ACS Nano, 2012, 6 (6), 5642
6. Kang et al.Angew. Chem. Int. Ed.,2011, 50(19), 4378
7. Kang et al.J. Am. Chem. Soc.,2013, 135 (4), 1499
8. Kang et al.J. Am. Chem. Soc.,2013, 135 (1), 42
9. Kang et al.J. Am. Chem. Soc.,2013, 135 (7), 2741
10. Kang et al.Nano Lett.,2014, 14, 6361
11. Kang et al.ACS Nano, 2012, 6 (3), 2818

Oxide semiconductors have attracted widely attention in the past decades. However, its applications are still limited because of its inherent defects involving wide band gap and results in low light utilization efficiency. In order to overcome these disadvantages, many processes have been proposed in the last several years involving compounds, metal and nonmetal doping, surface modifications. Generally, coupling with oxide semiconductor is a simple and efficient method to improve photocatalytic efficiency. That is to say, a heterojunction is introduced between different oxide conductors for enhancing utilization of solar energy and also reducing the recombination ratio of photo induced electron-hole pairs simultaneously.
In this paper, we introduce a novel physical route for preparing heterojunction composites via high temperature treatments. The general process is as follows: 1) preparation of the substrate; 2) pulse plating a metal layer on the substrate; 3) thermally treating the composite and “in situ” to obtain the metal oxide on substrate composite. Four kinds of heterojunction composites were prepared base according to this route, including ZnO/TiO2 heterojunction fibres, ZnO/graphene composite, ZnO/TiO2 vertical- nanoneedle-on-film heterojunction, and porous micro-nano-structure NiO/ZnO heterojunction.
Comparing with the other heterojunction from regular chemical routes, the present process provided a tight contact and combination between the components, which eventually led to a heterojunction between the two kinds of components. The most important was that a full lattice coherent or partial lattice coherent heterojunction was formed between the components in the elevated conditions through short atom diffusion at the interface, and the formation mechanism was different from the chemical route. This kind of heterojunction exhibited great improvement for separation efficiency of photo-generate electron-hole pairs. Experimental results of ultraviolet-visible light catalysis demonstrated that the photocatalytic activity of the heterojunction composite had been greatly improved. The photocatalytic efficiency of the heterojunction composites has been improved for over 2 times higher than that of pure TiO2 or ZnO.

Oxygen reduction reaction (ORR) is crucial in conversion of chemical to electrical energy (fuel cells and batteries), corrosion science and bio-catalysis. The mechanism of the multi-electron and multi-step ORR reaction, involving a set of reaction intermediates is still controversial and not well resolved. Poor understanding of the mechanism limits the development of efficient, inexpensive and improved fuel cell electrocatalysts.
Platinum is still one of the best available catalysts for the ORR at fuel cell cathodes but is unattractive because of its high cost, scarcity and the high loadings required to overcome its sluggish ORR kinetics. Various other noble (e.g. Pd, Ru) and non-noble metals have been used as an alternative to Pt, but shows diminished efficiency. Hence, efforts have been devoted to developing cheaper Pt-based bimetallic alloy catalysts. Unfortunately, this strategy presents a big challenge in synthesis as the nanoparticles (Np) required are thermodynamically unfavourable and their crystal shape is dominated by the slow-growth facets that have low surface energy. Moreover, the synthesis of Pt-based core-shell structures in the sub-15 nm regime with a thin Pt atomic monolayer as a shell on a definite metal core poses difficulty and is scientifically challenging.
In this work, we develop and investigate cost-effective core-shell electrocatalysts PtX, featuring Pt as an outer shell with a core of non-noble and inexpensive metals (X=Ni or Co). Our strategy is to increase the surface energy of ORR electrocatalysts by building in strain to the exposed subsurface region of the Pt skin. Scanning Tunnelling Electron Microscopy (STEM) and Extended X-ray Absorption Fine Structure (EXAFS) is used to investigate structural changes in the strained catalyst at the atomic level, both for the core and for the surface. Electrochemical rotating ring disk electrode (RRDE) measurements are carried out to check the ORR activities and stabilities of unsupported and carbon-supported PtCo and PtNi catalysts under different reaction conditions (pH and under gas flow). Both the carbon supported catalysts show good stabilities and higher activities compared to commercial Pt catalyst.

Recent advance in nano-fabrication has made it possible to design and synthesize nanoparticles with nearly precise controls on nanoparticle size, shape, composition and structure for catalytic applications. In this talk, I will summarize the common methods we used to synthesize monodisperse nanoparticles, especially intermetallic nanoparticles, core/shell nanoparticles, nanowires and their self-assemblies on graphene (or N-doped graphene) surface. I will use Au-, Pt-, and Cu-based elemental and alloy nanoparticles as examples to demonstrate the rational tuning and enhancement of nanoparticle catalysis for selective electrochemical reduction of proton, oxygen, and carbon dioxide for renewable energy applications.

Alternative energy technologies are in need of efficient and stable yet inexpensive components for practical devices. In addition, the syntheses of these catalytic materials need to be scalable and sustainable by using non-precious elements. The petaled MoS₂ electrode, which has been previously reported by our group as a highly active QDSSC cathode, is a candidate to meet this challenge, showing promising results as an HER electrocatalyst as well as a lithium ion battery electrode. We have developed a simple, highly scalable, hydrothermal preparation of nanostructured MoS₂ grown directly from Mo foil. This self-supported MoS₂ material exhibits a petaled morphology that preferentially exposes the catalytically active S-Mo-S edge sites of its layered crystalline structure, leading to increased performance towards a variety of reactions. Our more recent studies have revealed a large, intermediate MoS_xO_y layer between the Mo substrate and the petals which plays an important role in the overall electrochemical performance. A new methodology for growing petaled MoS₂ from alternate substrates will be presented, as well as the results of electrochemical impedance spectroscopic studies and lithium ion battery testing of the electrode. We hope these studies will aid in the development of a new class of self-supported TMDCs which can be fine-tuned for specific applications.

Efficient yet, low-cost electrocatalysts are indispensable for electrochemical oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) in low-temperature proton exchange membrane fuel cell (PEMFC). Here we present laser ablation synthesis in solution in tandem with galvanic replacement reaction (LASiS-GRR), for the first time, as a facile route to synthesize nanocomposites (NCs) of PtCo nanaoalloy (NA) embedded in CoO_x matrices as bifunctional electrocatalysts. Our results from high resolution TEM imaging reveals PtCo NAs of mean sizes ~8.5-17.7 nm embedded in sponge-shaped CoO_x matrices. Electron diffraction and X-ray diffraction data along with energy dispersive X-ray spectrometry (EDX) confirm the NC compositions and crystalline structures. Detailed electrochemistry data indicates outstanding ORR and OER activities for the PtCo/CoO_x NCs while exhibiting better stability than the respective standard nanocatalysts. Such activities are ascribed to the shrunken lattice constants of alloyed PtCo that promote oxygen adsorption and the synergic “spillover” effect from high surface area CoO_x matrices that accelerate both ORR and OER through symbiotic adsorption/desorption of intermediate species. Furthermore, the CoO_x matrix prevents aggregation and/or dissolution of the embedded NAs in alkaline medium. We report a combined overpotential of 756 mV vs. RHE for the PtCo/CoO_x NC with 33.3 % (molar) Pt content which is the best value ever reported for catalysts supported by carbon black. The enhanced bifunctional catalytic activities of the NCs are attributed to their unique heteronanostructures tailored by our one-pot, “green” synthesis route of LASiS-GRR.

The major barriers to broad commercialization of technologies such as fuel cells, metal-air batteries and electrolyzers are the cost, performance and durability of currently employed materials. Improvements in materials design at atomic scale are expected to bring substantial change in their functional properties. It has been demonstrated that tuning of surface and bulk properties such as composition, structure, and electronic properties are critical aspects toward novel electrocatalysts. For instance, an increase in catalytic activity of almost two orders of magnitude compared was reported for well-ordered single crystalline surfaces. That finding inspired the design of nanoscale catalysts with more active and durable performance. For that reason a synergy between well-defined extended surfaces and corresponding nanoscale materials has been in focus of our research and will be presented as a potent approach in development of functional materials for electrochemical applications.

Carbon nanostructures are essential for numerous energy conversion and storage applications including fuel cells, supercapacitors, and batteries. Nevertheless, current technologies face challenges such as long-term durability at high potentials (fuel cells), low energy/power density (supercapacitors), and metal intercalation issues (batteries). State-of-the-art devices have been typically synthesized from highly heterogeneous precursors leading to amorphous carbon materials. Current efforts focus on the development of carbon nanostructures utilizing graphene/graphene oxide materials with superior structural and functional properties. Nanostructured carbon electrocatalysts derived from graphene/graphene-oxide materials are inherently more homogeneous and possess desired properties, such as good chemical stability, excellent conductivity, and more importantly, the ability to be functionalized in a controlled manner. These unique properties have led to the increased interest in graphitic materials as catalyst/catalyst supports in electrocatalysis for energy-related applications. In particular, carbon electrocatalysts for the oxygen reduction reaction (ORR) are of significant interest for the replacement of expensive Pt-based catalysts in the polymer-electrolyte fuel cell cathode.
In this study, we report the synthesis of highly ordered carbon nanostructures derived from graphene oxide (GO). GO inherently possesses a high density of defects, including moieties such as carboxyl, hydroxyl, and epoxy groups, which may serve as niches for the chemical doping of heteroatoms, such as nitrogen, which have been proven to play a critical role in the overall performance of non-precious metal electrocatalysts. Furthermore, despite the widely known fact of the presence of residual water between GO layers, no reports exist about the role of intercalated water on the precursor morphology and the resulting ORR activity of GO electrocatalysts. We report the control of the density of functional groups and inter-lamellar spacing of GO materials via low temperature drying treatments, which when subjected to reduction and nitrogen doping, resulted in improved ORR electrocatalysts. Therefore, our results demonstrate that the structure formed following the effective removal of intercalated water is crucial in the formation of active sites caused by the nano-confinement of water. Lastly, we also demonstrate a systematic improvement in half-wave potential and significant decrease in peroxide production depending upon the GO pretreatment.

In alkaline media, as the oxygen reduction reaction (ORR) kinetics are much faster, alternative non-platinum group metal electrocatalysts to compete with platinum in terms of the performance and durability have been extensively investigated; one of the most popular being Fe/N/C-based electrocatalysts. Here, we explore the ORR of crumpled graphene impregnated with iron-based nanoparticles. The structured materials are prepared by pyrolyzing graphene-wrapped microsized iron oxide particles with melamine, which lead to crumpling of graphene with its N-doping while transforming microsized iron oxide particles to nanosized iron species. Iron loadings are controlled while maintaining well-dispersed iron nanoparticles with as-produced crumpled graphene surface areas up to ~650 m²/g. The resultant nitrogen-doped crumpled graphene containing well-dispersed iron nanoparticles exhibits superior electrocatalytic activity and durability and further displayed fast and selective four electron transfer kinetics for the ORR, as evidenced by various electrochemical experiments. High loading of well-dispersed iron nanoparticle has been proposed to play a key role in facilitating the desired ORR reaction.

Dealloyed nanoporous Ni/Pt (np-NiPt) has emerged as a highly active and useful catalyst for electrochemical oxygen reduction. With ~5 nm diameter pores, a Pt-rich surface skin, and high specific surface area, np-NiPt has the physical and chemical properties of nanoparticle catalysts, with the additional feature that the pores of this material can be filled with a secondary phase that can moderate reactant transport to the catalyst, and product transport away from it. Here, we present results of studies of model electrochemical reactions in ionic liquid (IL)-filled np-NiPt. Specifically, protic and aprotic hydrophobic ILs were used to examine mechanisms of enhanced oxygen reduction activity in composite catalysts, clarifying how both oxygen and water solubility in the IL phase is the primary determinant to enhance activity. In addition, we will discuss how hydrogen evolution can be suppressed using IL + np-NiPt composite catalysts, facilitating electrocatalytic reactions at extremely reducing potentials.

Photoelectrochemical water splitting is a promising way of using solar energy to generate hydrogen fuel and it has been widely studied since the discovery of photocatalytic activity of TiO₂ [1]. The efficiencies of photocarrier generation and separation in a semiconductor photoelectrode are key parameters that determine the photoelectrochemical activity. Nanoscale structural design of photoelectrodes is an effective method for improving the photogenerated charge separation. Morphology control in the form of nanowires [2] or nanotubes [3] and the use of composite materials that combine a metal with a semiconductor [4] or different semiconductors [5] have been shown to improve the photocarrier migration rate from bulk to surface either by decreasing the charge transport distance or by creating internal electric fields. In this study, we propose a new concept of the nanoscale design to enhance photoelectrochemical activity by implantation of metal nanopillars in semiconducting oxide photoelectrodes. The enhancement is attributed to increased photocarrier separation efficiency in the Schottky junction space charge region that surrounds the metal nanopillars. In particular, Ir-doped SrTiO₃ with embedded Ir metal nanopillars showed good stability in water, nearly 100% absorbed photon-to-current efficiency under visible light in the 400 to 600 nm wavelength range, and the ability to utilize light up to a wavelength of 700 nm.
Metal-doped SrTiO₃ (M = Ir, Pt, Pd, etc.) epitaxial thin films were grown on SrTiO₃ (001) substrates by pulsed laser deposition at various temperatures and oxygen pressures. Metal nanopillars were found to form spontaneously in epitaxial SrTiO₃ films under suitable deposition conditions, driven by thermodynamic metal segregation. The metal nanopillar formations were investigated by high-resolution transmission electron microscopy, atomic force microscopy, and X-ray diffraction. Transport analysis using a conductive AFM tip showed that the metal nanopillars form Schottky junctions with SrTiO₃ with a built-in voltage corresponding to the work function difference between the metal and SrTiO₃. The metal nanopillars thus enhance photocarrier transport from bulk SrTiO₃ to the surface. The photoelectrochemical properties were evaluated under visible light illumination in a conventional three-electrode system containing a Pt counter electrode and a Ag/AgCl reference electrode. We discuss the mechanism of spontaneous metal nanopillar formation during film growth and the photoelectrochemical activity enhancement related to the metal nanopillar implantation.
[1] A. Fujishima and K. Honda, Nature 1972, 238, 37. [2] C. Liu, N. P. Dasgupta, and P. Yang, Chem. Mater. 2014, 26, 415. [3] G. K. Mor et al., Nano Lett. 2005, 5, 191. [4] Z. Zhang and J. T. Yates, Jr., Chem. Rev. 2012, 112, 5520. [5] O. Khaselev and J. A. Turner, Science 1998, 280, 425.

Bimetallic nanoparticles have been widely used in a variety of catalytic reactions. The physical and chemical properties of the surface largely depend upon the surface compositions as well as compositional distribution and hence have effects on catalytic performances. One of the challenges in the rational design of more efficient bimetallic heterogeneous catalysts is the ability of predicting the morphologies and elemental distribution (i.e. surface segregation) by understanding the underlying thermodynamics and kinetics. In this work, we focus on studying the surface segregation in multiply-twinned alloy Pt/Pd particles. The Pt/Pd alloy multiply-twinned particles with different Pt/Pd ratio are synthesized using a method developed by Lim et al. (Lim et al., 2009), and the structure of the nanoparticles and the elemental distribution of Pt and Pd within the particles are studied via Energy-dispersive X-ray Spectroscopy (EDX) in Scanning Transmission Electron Microscope (STEM). We observe the surface segregation of Pt, which is most significant at the corners, and it is universal as the same phenomena are observed in particles with different sizes and Pd/Pt ratios. The characterization and theoretical models describing this phenomenon will be discussed.
Lim, B., Wang, J., Camargo, P. H., Cobley, C. M., Kim, M. J., & Xia, Y. (2009). Twin-induced growth of palladium-platinum alloy nanocrystals. Angew Chem Int Ed Engl, 48(34), 6304-6308. doi: 10.1002/anie.200902235

As important industrial materials for energy conversion, microporous zeolites are necessarily synthesized in the presence of templates and solvents under hydrothermal conditions. This hydrothermal synthesis of zeolites is not green, due to the use of organic templates, the presence of high pressure, low efficiency, and production of polluted waters. In our cases, at first it is successful to synthesize zeolites in the absence of organic templates (template-free), later it is demonstrated a green route for synthesizing zeolites under solvent-free conditions [1]. Recently, the combination of template-free and solvent-free routes for synthesizing zeolites is also successful [2]. These approaches in the synthesis not only signi#64257;cantly reduces the waste production, but also greatly increases the yield of zeolite products.
References: [1] L.M. Ren, Q.M. Wu, C.G. Yang, L.F. Zhu, C.J. Li, P.L. Zhang, H.Y. Zhang, X.J. Meng, and F.-S. Xiao, J. Am. Chem. Soc., 134 (2012) 15173.[2] Q.M. Wu, X. Wang, G.D. Qi, Q. Guo, S.X. Pan, X.J. Meng, J. Xu, F. Deng, F.T. Fan, C. Li, S. Maurer, U. Muller, and F.-S. Xiao, J. Am. Chem. Soc. 136 (2014) 4019.

The oxidative coupling of methane (OCM) is a chemical process involving heterogeneous catalytic and homogeneous non-catalytic reactions for directly converting methane into value-added C₂ hydrocarbons, mainly ethylene and ethane:
2CH₄ + O₂ → C₂H₄ or C₂H₆ + 2H₂O [Eq. 1]
Due to the high temperatures required for initiating the reaction and the limited reactivity of methane, a highly active and stable catalyst is required. Furthermore, aside from the C₂-selective reactions, nonselective oxidation of hydrocarbons to CO_x takes place, demanding the use of a highly selective catalyst [1]. The Na-W-Mn/SiO₂ catalytic systems have shown promising performance in this respect [2]. Recent investigations have demonstrated that using ordered mesoporous silica (OMS) as the catalyst support greatly enhances the performance of the Na-W-Mn/SiO₂ system, probably due to the fine dispersion of catalytic components on the surface [3].
Here we report the outstanding catalytic performance of a Na₂WO₄-Mn/SiO₂ catalyst supported on an OMS similar to SBA-15.
Powder OMS was prepared via a room temperature buffered soft-templating synthesis using the amphiphillic triblock copolymer Pluronics P123 as a structure-directing agent and sodium silicate as the silica source [4]. The synthesis was modified in order to yield larger monolithic granules that can be ground into the size range required for different reactor concepts.
Both powder and monolithic OMS syntheses were successfully upscaled to batches 25 times that of the original synthesis, yielding between 60 and 65g of OMS per batch. By upscaling the batch synthesis, we avoid inconsistencies in the quality of the material for comparative studies. Due to the facile nature of the OMS synthesis, the installation and start-up of a large-scale (300g/run) semi-continuous powder OMS production unit is underway.
All supports were loaded with the catalytic components via incipient wetness impregnation, and then calcined in air. Testing of the catalysts was done in various OCM reactors, and exceptional performance was observed in comparison with the standard OCM catalyst.
We are also investigating the variation of the OMS pore size and shape by incorporation of hexane, p-xylene and polypropylene glycol as pore swelling agents. Studies regarding the effect of these modifications on the performance of the catalyst in OCM are currently underway.
References
[1] U. Zavyalova, M. Holena, R. Schlögl, M. Baerns. ChemCatChem, 2011, 3, 1935-1947.
[2] S. Arndt, T. Otremba, U. Simon, M. Yildiz, H. Shubert, R. Schomäcker. Appl. Catal., A. 2012, 425-426, 53-61.
[3] M. Yildiz, Y. Aksu, U. Simon, K. Kailasam, O. Görke, F. Rosowski, R. Schomäcker, A. Thomas, S. Arndt. Chem. Commun., 2014, 50, 14440-14442.
[4] J. Jammaer, A. Aerts, J. D&’Haen, J.W. Seo, J.A. Martens. J. Mater. Chem. 2009, 19, 8290-8293.

Low-temperature total oxidation of propane is becoming increasingly important in the context of cleaning air and lowering automotive emissions. Highly dispersed platinum nanoparticles were synthesized and supported on home-made mesoporous silica (SBA-15 and KIT-6) with well-ordered mesopores. The platinum catalysts were used for the total oxidation of propane and compared with the conventional Pt/Al₂O₃ catalyst. The synthesized materials were characterized through XRD, N₂-adsorption/desorption, CO titration, transmission electron microscope (TEM), H₂ temperature-programmed reduction (TPR), C₃H₈ temperature-programmed desorption (TPD) and in-situ DRIFTS analytic techniques. The influences of pore structure and size of the mesopores as well as of different Pt loading ratio (in the range 0.1-1 wt %) on the catalytic activity have been investigated. The results indicated that the parent 2D-hexagonal and 3D-cubic ordered mesoporous structures in SBA-15 and KIT-6, respectively, were well-maintained during the synthesis process. The spherical Pt nanoparticles were fabricated within the channels of SBA-15 and KIT-6. The diameters of the Pt nanoparticles were effectively controlled by the mesopores of the mesoporous silica host, and the population of the Pt nanoparticles could be tuned by the metal loading amount. Platinum supported on mesoporous silica exhibited better propane oxidation activity than the conventional Pt/Al₂O₃ catalyst in the following order: Pt/KIT-6 > Pt/SBA-15 > Pt/Al₂O₃. The difference between Pt/KIT-6 and Pt/SBA-15 was related to the different pore structures of the supports, which in turn affected the nanostructure of platinum and the adsorption-desorption properties during the reaction process. All this makes the mesoporous silica support, especially KIT-6 with 3D-cubic mesopores, a promising candidate in the application of propane abatement in exhaust control.

The dry reforming of CH₄ using CO₂ rather than steam represents a quite attractive alternative route to syngas or hydrogen. It produces in a sustainable manner, through the consumption of greenhouse gases, energetically useful gases. As for the steam reforming of methane, side reactions occur leading in particular to the formation of carbon, i.e. cocking. Ni-based catalysts have developed because they represent cheaper and abundant alternatives compared to noble metals catalysts [1]. However, Ni-based catalysts are very easily deactivated by coking [2]. This phenomenon blocks active sites through the formation of carbon deposits. In this undesired reaction, larger Ni metal particles enhance the obstruction of the support pores. One direction to overcome such difficulties is to produce supported catalyst based on nickel nanoparticles.
In that context, we have evidenced a new Ni-based catalyst obtained from the complex oxide precursor BaNi₂V₂O₈. A very good catalytic activity with very limited side reactions and an excellent stability is observed [3]. BaNi₂V₂O₈ is a two dimensional antiferromagnet known from a fundamental point of view for its peculiar structure in which Ni atoms are arranged in a 2D honeycomb lattice [4]. Its catalytic properties were investigated in the reforming of methane with CO₂ to hydrogen gas. The in situ treatment at 800°C in 50%H₂ gas atmosphere lead to its decomposition into a complex mixture dominated by the phases Ba₃(VO₄)₂ and Ni. The quite good catalytic activity rises from this decomposition product. The conversion of CH₄ and CO₂ is quite honorable compared with efficient catalysts in the literature: the conversion at 800 #9702;C amounted to 85 % for both CH₄ and CO₂, with H₂/CO=0.9. The untreated precursor, however, does not show any significant activity. In another hand, the direct conception of Ni-Ba₃(VO₄)₂ through the impregnation in Ni based solutions of the oxide with subsequent heat treatment in reducing conditions was carried out. It produced samples with a support loaded with nickel nanoparticles of ~30-40 nm and homogeneously distributed. Surprisingly, no catalytic activity occurs in the later, and only the supported catalyst generated through the destructive reduction of the precursor BaNi₂V₂O₈ led to efficient reactions. In this communication, the catalytic activity for dry reforming of CH₄ will be detailed, together with the characterizations through X-rays powder diffraction; transmission electron microscopy etchellip;. A comparison with Ni-Ba₃(VO₄)₂ will be presented to understand the origin of such different reactivity. In summary, we present new efficient catalysts candidates for the dry reforming of methane which we believe open new perspectives in this field.
[1] R. Benraba, A. Löfberg, A. Rubbens, E. Bordes-Richard, R.N. Vannier, A. Barama. Catalysis Today 203 (2013) 188- 195
[2] J.R. Rostrup-Nielsen, Catalysis Today 18 (1993) 305.
[3] Manuscript submitted
[4] N. Rogado et al.PRB 65, 144443 (2002)

The more efficient use of our energy reserves relies on the productive use of otherwise undesirable materials as a way to limit waste. One method is to take advantage of underutilized components of the refinement processes for the on-purpose synthesis of high demand commodity chemicals. Demand for propylene is expected to outpace the quantity produced through conventional cracking processes. Thus, the on-purpose synthesis of this valuable commodity chemical via metathesis from underutilized feedstocks, such as 2-butene, is being investigated. Current methods for the on-purpose synthesis of propylene rely on the cross metathesis of 2-butene with ethylene, which is itself a highly desired commodity chemical.
The development of olefin metathesis catalysts for the production of propylene typically depends upon a relatively small selection of commercially available tungsten or molybdenum oxides and various silica and/or alumina supports. While processing methods are sometimes considered in the analysis of structure-property relationships for these catalysts, control over the morphology, size, shape, and surface area of these materials is seldom explored. For this reason, improving the yield and selectivity of such catalyst materials is often viewed as a largely empirical process where transition metal precursors are developed independently from the support material.
The objective of this work is to combine the support and precursors into a single reactor with well-controlled, highly tunable synthesis. Through a high temperature aerosol process, group 6 metal oxides are simultaneously synthesized on silica-alumina supports in one step. Synthesizing these materials in such a fashion allows for fine tuning of the chemical composition of the active metal species, as well as controlling the silica and alumina interaction. With this control, we will show relevant correlations between catalyst synthesis and processing in an effort to affect the surrounding environment of the active sites and control the resulting catalytic activity. Catalytic testing results from a fixed-bed reactor will be used to correlate acidity/basicity measurements (TPD), reduction potential measurements (TPR), porosity (BET), particle shape and morphology (FESEM), and the distribution of active sites (EDS) with the synthesis and processing variables. Ultimately, this work will enable the rapid development of novel catalysts with optimized activity and selectivity for the conversion of specific feed streams.

As oil reserves shrink and the world moves towards a low-carbon economy, valuable chemicals traditionally refined from crude oil will need to be derived from alternative resources. The methanol to hydrocarbons (MTH) process is an attractive method of producing liquid fuels and olefins such as ethylene and propylene from methanol, which can be derived from coal, natural gas, or biomass. The zeolite ZSM-5 is one of the two catalysts used commercially for MTH. Zeolites are microporous aluminosilicates with defined pore networks, with their exceptional thermal stability, strong acidity and molecular shape-selectivity making them highly successful heterogeneous catalysts. However, for complex systems such as MTH, rationalising catalyst activity and selectivity in terms of material characterisation remains challenging. The MTH mechanism involves many steps and intermediates, but can be broadly separated into two catalytic cycles: an aromatic-based cycle producing mainly ethylene, and an olefin-based cycle producing larger olefins, alkanes and aromatics [1]. Understanding how these mechanisms are catalysed is fundamental to designing catalytic materials that yield the desired products.
One aspect of MTH that remains contentious is the role of the external surface of the zeolite particles. Passivating the external surface of MTH catalysts typically leads to an increase in selectivity to ethylene, which has been attributed either to the loss of external active sites [2] or pore mouth narrowing [3]. The outer surface may also be susceptible to carbon deposition leading to catalyst deactivation. In this contribution, we studied the effect of external surface passivation via silica deposition of ZSM-5 used in the MTH reaction. We examine in detail the activity of external active sites and also changes in mass transport, using a combination of established material characterisation techniques including infrared spectroscopy, temperature-programmed desorption of bases, solid-state NMR, and nitrogen sorption, and also novel approaches such as pulsed field gradient diffusion NMR, NMR relaxometry, and tapered element oscillating microbalance techniques. The passivation procedure deactivated approximately 75 % of active sites on the external zeolite surface, while also significantly altering the diffusion properties via pore mouth narrowing. These changes lead to an increased ethylene yield and reduced catalyst lifetime. We show that the olefin-based cycle is catalysed by the external zeolite surface, whereas the aromatic-based cycle produces ethylene within the catalyst pores, and discuss the role of the external surface in catalyst deactivation.
[1] S. Ilias and A. Bhan, J. Catal., 2012, 290, 186-192.
[2] Z. Zhu et al., J. Energy Chem., 2014, 23, 771-780.
[3] P. Tynjälä and T. Pakkanen, J. Mol. Catal. A Chem., 1997, 122, 159-168.

Metal on oxides have received significant attention in the past few decades because of their importance in a variety of applications, including those involving heterogeneous catalysis ^[1], electronic devices, and recently in proton exchange membrane fuel cell (PEMFC) catalyst materials.
Although, the existing PEMFC catalysts that are mainly composed of carbon supported Pt nanoparticles (Pt/C) exhibit high surface to volume ratio, they are prone to activity losses in the fuel cell operation due to carbon corrosion, Pt aggregation driven by Ostwald ripening, dissolution and migration from the catalyst layer ^[2]. To overcome this issue, conductive oxide supports have started to gain importance due to their stability in acidic and alkaline media. It has been also demonstrated that extended surface Pt catalysts have about an order of magnitude higher specific activity compared to nanoparticles. However, in order to deposit a monolayer of Pt on a conductive oxide support, the surface of the oxide needs to be reduced to lower the interfacial energies between the substrate and the Pt film, otherwise, Pt island formation takes place on the oxide surface ^[1].
In the work we are presenting here, we show a unique method that we have developed to reduce the oxide thin films on metallic surfaces and bulk oxide materials. This oxide thin film reduction was achieved by the polyol method ^[3], and the reduction process was monitored by an electrochemical means. We have investigated the reduction of Sn oxide thin film on a Sn metal substrate as well as the surface reduction of antimony doped tin oxide particles (ATO).
The reduction of oxide thin film on a Sn metal ^[4] substrate was indicated by a sudden change in the Sn electrode potential when measured vs. a reference electrode (Ag/AgCl). Ethylene glycol (EG), a well-known polyol, was used as a reducing agent in this process. The reduction capabilities of EG at high temperatures was used to reduce the oxide thin films. In the surface reduction of bulk ATO, there was no considerable potential drop observed for this system through the electrochemical measurements, but the surface reduction was confirmed by RAMAN spectroscopy.
Further details about the oxide reduction along with preliminary results of the platinum deposition will be provided in the presentation.
References:
[1] Zhang, L., Persaud, R., and Madey, T. 1997. Ultrathin metal films on a metal oxide surface: Growth of Au on TiO2 (110). Phys. Rev. B 56, 16, 10549-10557.
[2] Alia, S.M., Yan, Y.S., and Pivovar, B.S. 2014. Galvanic Displacement as a route to highly active and durable extended surface
[3] Preparation of Metallic Powders and Alloys in Polyol Media: A Thermodynamic Approach. In Journal of Solid State Chemistry 154 (2), pp. 405-411. DOI: 10.1006/jssc.2000.8802.
[4] B.-S. Kim, J.-c. Lee, H.-S. Yoon, S.-K. Kim, Materials Transactions 52 (2011) 1814-1817.

Platinum is a ubiquitous catalyst in the chemicals and energy production sectors, however, its scarcity in nature and high price will limit future proliferation of current and new Pt-catalyzed reactions. One promising approach to conserve Pt involves understanding the minimal number of Pt atoms needed to catalyze a desired reaction and then designing catalysts with the smallest necessary Pt ensembles. Guided by surface chemistry and microscopy studies we designed and tested a new generation of Pt/Cu nanoparticle catalysts for the selective hydrogenation of butadiene to butene, an industrially important reaction. An isolated Pt atom geometry enables H₂ activation and spillover but is incapable of C-C and C-H bond scission that leads to loss of selectivity and catalyst deactivation. Nanoparticle Pt/Cu catalysts with ~1 at. % Pt were found to exhibit high activity and selectivity for butadiene hydrogenation to butene under mild operating conditions.

Manganese dioxide (MnO₂) nanomaterials with multiple structures have emerged as an increasingly important type of photo- and electrocatalysts for water oxidation and oxygen reduction reactions (WORs and ORRs). Current studies identify that the doping of gold nanoparticles (AuNPs) on nanostructured MnO₂ can largely enhance the electrocatalytic activities of MnO₂. In this contribution, we demonstrate a feasible but efficient hydrothermal method to synthesize AuNP@MnO₂ nanosheets that possess uniform structure with a GNP as a central core surround by two-dimensional multilayered MnO₂ nanosheet shells (Figure 1a), and systemically investigate the unconventional structural and morphological transitions of AuNP@MnO₂ nanosheets to MnO₂ monolayered nanoflakes (Figure 1b), finally to single-crystal nanorods (Figure 1c). We further investigate the electrocatalytic (ORRs) properties of these nanomaterials, and found ORR activities are strongly dependent on the morphologies and structures in an order of AuNP@MnO₂ nanosheets > nanoflakes > nanorods. Especially, the ORR activity of our AuNP@MnO₂ nanosheet is found to better than that of conventional Pt/C catalyst. Our studies provides insight on the mechanism behind efficient electrocatalysts for the future development of novel and facile electrocatalysts with high performance in water splitting, fuel cells, and metal air batteries.

Carbon supported bimetallic and trimetallic nanoparticle materials have been attracting much attention as fuel cell catalysts. It is well known that appropriate choice of constituent phases and morphology enhances functional diversity of the materials. But it is not an easy task to prepare samples with controlled structure, furthermore to synthesize advanced materials for practical uses. Therefore, it is still required to try various synthesis methods and conditions to find out appropriate samples.
Electron beam irradiation method is a novel method for synthesizing catalyst nanoparticles. We have synthesized various carbon supported bi- and tri-metallic nanoparticles using this method. Adding different second and third metal to platinum alters the nanoparticle structures. However, the formation mechanism is not clear and needs more research to synthesize nanoparticles with the aimed structure. In this work, we are reporting the formation mechanism of electron beam irradiation method in case of platinum based catalysts supported on carbon.
We synthesized carbon supported PtCu, PtRu, PtRh, PtSn, PtRhSn nanoparticles using electron beam irradiation method. A glass vial containing water together with support carbon powder and metal source ions is irradiated with a high energy electron beam (4.8 MeV, 20 kGy) for several seconds. Radiation induced radicals reduces the aqueous metal ions and induces precipitation of composite phases on the support. 2-propanol, tartaric acid, and/or NaOH were also added in some samples. Ar gas was bubbled to purge air from the solution as necessary. These samples were characterized by techniques of ICP-AES, XRD, XAFS, TEM, and LSV.
The chemical analyses indicated all kinds of metal (Pt, Rh, Ru, Cu, and Sn) precursors have been reduced and found in the powder. TEM observation revealed that Pt nanoparticles have particle size of 2-5 nm in all systems. XRD and XAFS study revealed that Pt formed a uniform alloy structure with Rh. PtCu and PtRu were more likely to form core-shell structure rather than a uniform alloy. PtSn did not form an alloy and existed as Pt and SnO₂. These results show that various types of bi- and tri-metallic nanoparticles could be synthesized with the one-pot process. The difference in the structures is discussed with their thermodynamic properties. According to the phase diagrams, Pt is completely miscible with Rh and Cu but partially miscible with Ru and Sn. Considering together their standard electrode potentials, PtRh is the easiest and PtSn is the most difficult system to form an alloy. However, under some experimental conditions, nanoparticles did not follow this thermodynamic discussion. This is explained by the variation of metal ion location. The formation mechanism must differ whether the metal ions locate in the solution or on carbon support. We report the correlation between nanoparticles&’ formation mechanism and their fine structures, also referring to their catalytic activities.

Transition metal containing mixed metal nitrides are emerging as excellent catalyst for reactions such as electro- chemical redox processes and ammonia synthesis reaction. The catalytic activity of these materials is often found to be comparable with precious metal containing materials [1] and thereby providing an opportunity of having low-cost catalysts. However, the origin of such remarkable activity is least understood and also found to vary in similar samples prepared using varying synthetic routes. [2]
We have developed a citrate-gel dervied route for the synthesis of high quality Ni_2-xCo_xMo₃N (x = 0.0-0.6). The materials have been characterised with Rietveld refinement, pair distribution function and X-ray absorption spectroscopy (XAS) analysis methods with the use of synchrotron X-ray radiation. The end member Ni₂Mo₃N crystalises in filled β-manganese structure. It has been demonstrated that the use of mild sol-gel process enables one to incorporate Co into Ni₂Mo₃N maintaining β-manganese type structure when synthesised at much lower temperature than used in conventional solid state methods.[3] These materials show hydrogen evolution activity in the range of 4-6 mA/cm² (at -0.4V SHE under electrochemical conditions) at room temperature and 150-300 µmol/h/g activity towards synthesis of ammonia from N₂ and H₂ at 400 ^omicron;C.
References
(1) J. S. J. Hargreaves, Coord. Chem. Rev. 2013, 257, 2015-2031.
(2) N. Bion, F. Can,J. Cook, J.S.J. Hargreaves, A.L. Hector, W. Levason, A.R.McFarlane, M. Richard, K. Sardar, Applied catalysis A 2015 (in press)
(3) T.J. Prior and P.D. Battle, J. Solid State Chem. 2003, 172, 138-147.

Dopants have often been used to optimize, enhance, or tailor the behavior of a parent material in many situations ranging from material strengthening to electronics to electrochemistry to catalysis. The search and identification of suitable dopant candidates has been laborious though, and dominated either by lengthy trial-and-error strategies (guided by intuition) or plain serendipity. As we enter the data-driven era, such traditional Edisonian approaches are being augmented (and sometimes, replaced) by rational strategies based on advanced computational screening. In this contribution, we offer such a paradigm for the selection of suitable dopants in metal oxides for catalytic reactions involving oxygen. As an example, we explore dopants across the periodic table for enhanced thermochemical splitting of water on doped ceria surfaces. Using ab initio methods the oxygen vacancy formation energy was identified as the suitable descriptor, and used to develop screening criteria based on Sabatier&’s principle. Sc, Cr, Y, Zr, Pd and La were identified as the best candidates, and in good agreement with past experimental data. However, owing to slow predictive capability of ab initio methods, machine-learning methods (specifically feature selection techniques) were employed to mine and discover patterns amongst the spectrum of dopants, to quickly classify a dopants impact on activity. By using methods such as principal component analysis and random forest methods, we identified the key properties of dopants that make them most attractive. A dopant&’s oxidation state, ionic radius and electron affinity were found to correlate strongly with enhanced activity. Thus, by combining the power of ab initio with speed of machine learning methods, we can therefore quickly pre-screen dopants simply based on their properties, and further expand the dopant chemical space by searching for those elements with the desired properties. Though, the framework was developed for thermochemical dissociation of water, we believe it can be applied to several other processes, e.g. CO oxidation, chemical looping and solid oxide fuel cells, etc.

The efficient removal of poisonous carbon monoxide (CO) gas at ambient pressures and temperatures for applications in fuel-cell technology, respirators and catalytic converters is an area of active research in heterogeneous catalysis and surface science. Until recently, the discovery and development of catalysts for the oxidation of CO has remained largely serendipitous and empirical, while relying heavily on high-throughput combinatorial approaches. Thus, mixed-oxide materials such as copper(II) oxide on cerium(IV) oxide (CuO/CeO₂) have been found to be promising candidates for low-temperature CO oxidation, but what is lacking is a fundamental understanding of the atomic and electronic structure of the sites responsible for catalytic rate enhancement. We have developed a generalizable synthetic route towards phase-pure, monodisperse (d = 30 ± 5 Å) transition-metal substituted ceria nanoparticles (M_0.1Ce_0.9O_2-x, M = Mn, Fe, Co, Ni, Cu) in order to elucidate the atomic and electronic structure and role of the transition-metal species in these materials for CO oxidation catalysis. In conjunction with powder X-ray diffraction (PXRD), high-resolution transmission electron microscopy (HRTEM) and DFT slab studies performed at the GGA+U level, X-ray absorption spectroscopy (XAS) demonstrates that the aliovalent transition-metal species (M³⁺ and M²⁺) substitute directly onto the {111} and {100} surfaces of the host CeO₂ lattice, where they serve as the active sites for CO oxidation catalysis. The low-temperature CO oxidation activity for M_0.1Ce_0.9O_2-x demonstrates a clear trend with transition-metal substitution; catalysis is a function of the oxygen-ion vacancy formation energy of the embedded transition-metal, with enhancement by over three orders of magnitude originating in more reducible transition metal species such as Cu³⁺. In-situ XAS and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) supports a Mars-van Krevelen mechanism, illustrating the unique reversibility of Cu_0.1Ce_0.9O_2-x. DFT slab studies suggest that the vacancy formation energy serves as a suitable semi-empirical descriptor for CO oxidation, thereby adding predictive power to the design of the next generation of CeO₂-based catalysts.

Electrocatalysis is controlled by the elementary reactions that occur at the interface between the electrode and the solution phase along with the electrochemical potential that results across this interface. Elucidating the electrochemical behavior at this interface, however, presents a considerable challenge due to complexity of the surface chemistry, the explicit atomic and molecular structure of the solution phase at the interface, the presence and formation different ions and their specific location in solution or on the surface, and the surface potentials and electric fields that results as a function of the surface reactivity. While theory has become an invaluable partner together with in-situ experiment, there are still a number of challenges in simulating more realistic materials and interfaces and modeling constant potential systems. Herein, we present an approach to simulate the elementary pathways and kinetics for constant potential systems and highlight the opportunities and challenges of this approach. The results are used to construct first principles based kinetic Monte Carlo simulations to model different electrochemical systems. We discuss the application of the approach to simulate the electrocatalytic reduction of oxygen over transition metal surfaces as well as nitrogen doped carbon-based substrates as well as the reduction of CO2 on metal surfaces. The results are used to compare with those proposed for enzymatic systems reported in the literature.

The ability to exploit the structure-function relationship of peptide-decorated metal nanoparticles (NPs) in solution offers a promising method for the green production of catalytically-active nanomaterials with controllable functionality.[1] A recently synthesized series of peptide-promoted catalytic Au nanoparticles (PEPCANs) is one example of these promising new nanomaterials.[2] However, to fully realize the potential of these materials, clear connections between the catalytic performance of the systems and their structure, at both the biological and metallic level, must be established. Experimental studies have determined the structure of these peptide-grown metallic NPs, as well as investigating their catalytic ability,[2,3] but elucidation of the structure of the adsorbed peptide overlayer via experimental techniques alone is challenging. Molecular simulation provides a complementary approach to predicting the structure(s) of biomolecules adsorbed at aqueous inorganic interfaces.[4,5] Here we employ advanced simulation techniques to predict the structure(s) of the peptide overlayer of the PEPCANS under aqueous conditions, based on the structure of the underlying AuNP provided from high energy X-ray diffraction data.[3] Ten different PEPCAN systems have been investigated, allowing connections between the structure and catalytic behavior of the different systems to be revealed.
[1] Bhandari, R., et al., Structural Control and Catalytic Reactivity of Peptide-Templated Pd and Pt Nanomaterials for Olefin Hydrogenation, J. Phys. Chem. C, 2013, 117, 18053-18062.
[2] Li, Y., et al.; Peptide-mediated synthesis of gold nanoparticles: effects of peptide sequence and natre of binding on physiochemical properties, Nanoscale, 2014, 6, 3165-3172.
[3] Bedford, N.M., et al.; Sequence-Dependent Structure Function Relationships of Bio-Enabled Au Nanoparticles, Energy Environ. Sci., 2015, In Preparation.
[4] Tang, Z., et al.; Biomolecular recognition principles for bionanocombinatorics: an integrated approach to elucidate enthalpic and entropic factors, ACS Nano, 2013, 7, 9632-9646.
[5] Hughes, Z.E. and Walsh, T.R.; What makes a good graphene-binding peptide? Adsorption of amino acids and peptides and aqueous graphene interfaces, J. Mater. Chem. B, 2015, 3, 3211-3221.

Zinc oxide is an important wide-gap n-type semiconductor with uses ranging from electronics to catalysis. One of the most puzzling features of this material is the stability of its polar surfaces -the Zn-terminated (0001) and the O-terminated (000-1), which is not evidenced in other oxides. Understanding the stability of ZnO polar surfaces will help to improve its performance, e.g. identifying the active sites of the Cu/ZnO catalyst which used in the synthesis of methanol.
We investigate the origin of the stability of the ZnO polar surface using global search techniques coupled with methods of interatomic potentials and density functional theory. Morphology and mechanisms of the stabilisation of the polar surfaces are related to thermodynamic and optical properties of ZnO, the latter characterised using hybrid QM/MM simulations.
To model a ZnO polar surface it is essential to remove the inherent dipole, which is typically achieved in simulations by altering the number of atoms in the terminating layers. We employ one-sided 2D-periodic slab surface models, with the reconstruction done by removing Zn or/and O atoms from the surface and spreading compensating charge uniformly over the slab bottom. According to our calculations, the optimum ratio of Zn (or O) vacancies is very close to |V_Zn - V_O| = 6 (the remaining dipole is compensated by the use of point charges). A cell size of (5x5) was chosen because of both: findings in STM images and our dipole calculations with respect of the cell size.
The global search using Monte Carlo routines, as implemented in our in-house Knowledge-Led Master Code, probed more than 500, 000 different reconstructions using different Zn/O stoichiometries at the top layers, in both polar surfaces. The lowest energy configurations reveal definitively triangular patterns on the Zn-terminated surface in excellent agreement with experiment and DFT. We calculated big surface energy differences among different stoichiometries in the Zn side, which might be an explanation of the well-defined patterns observed in STM images. The variation in the surface energy among the different stoichiometries at the O-terminated side is smaller when compared to the Zn-terminated side, which explains the difficulty to attribute one single reconstruction pattern to the (000-1) surface.

We have been using well-validated first principles quantum mechanics schemes combined with continuum solvation to explore mechanisms associated with carbon dioxide reduction. We will first briefly review our work in this area to provide context for presentation of our latest findings on the roles played (or not) by aromatic amines and water during the photoelectrochemical reduction of CO₂ to methanol at a p-GaP electrode surface. We will discuss our first principles quantum mechanical simulations aimed at understanding fundamental aspects of:
(i) semiconductor-solution interfacial structure from Pourbaix diagrams from density functional theory
(ii) semiconductor surface acidity from solvated embedded cluster models
(iii) semiconductor surface thermodynamics (reduction potentials) and kinetics (barriers) of CO₂ reduction from a combination of the above approaches.

The application of proton exchange membrane fuel cells (PEMFCs), a promising energy conversion technology, in transportation sectors is beneficial to alleviate societal problems related to energy shortage and environment pollution. However, the wide scale commercialization of PEMFCs is largely limited by the current requirement of expensive Pt group metals as their electrocatalysts. To advance PEMFC technology, it is of great interests to develop earth-abundant, non-precious metal catalysts in replacement of Pt, in particular, for oxygen reduction reaction (ORR) occurring at the cathode of PEMFCs. To accomplish this goal, we have performed both electrochemical measurements, such as the rotating disk electrode and the rotating ring-disk electrode techniques, and density functional theory (DFT) calculations to investigate oxygen reduction reaction (ORR) on non-precious transition metal (TM)/Nitrogen doped carbon nanofiber (Fe/N/C and Co/N/C) catalysts in acid medium. The nanofiber catalysts were synthesized by electrospinning and subsequent heat treatment procedures. Our electrochemical measurements showed that the pyrolyzed Fe/N/C catalyst possesses higher activity for ORR than the pyrolyzed Co/N/C catalyst and could promote four-electron (4e^-) ORR. In comparison, O₂ electroreduction was found to proceed mainly with 2e^- pathway on the Co/N/C catalyst. To gain insights into underlying catalytic mechanisms, we calculated the adsorption energies of all the possible chemical species and the activation energies for O-O bond dissociation reactions involved in ORR on the FeN₄ and CoN₄ active sites embedded in graphene. Our DFT calculations predicted that the ORR could happen through 4e^- associative pathway on the FeN₄ site, whereas might end with a 2e^- pathway on the CoN₄ site due to high activation energy for O-O bond splitting and extremely weak adsorption of H₂O₂ on the CoN₄ site. Complementary experimental and theoretical results suggest that the FeN₄ and CoN₄ clusters might be the main active sites for promoting ORR on the transition metal/Nitrogen doped carbon nanofiber catalysts in acidic medium. Furthermore, we identified that the ORR activity of the TM-N₄ clusters could be gauged by an electronic descriptor related to the d-electron orbitals of the central TM atom. Consequently, our results suggest a catalyst with optimal performance can be developed by tuning ligands that gives delicate balance between the adsorption of ORR species O₂ and OH.

We investigated the application of 1Tprime;-MX2 (M = Mo, W; X = S, Se, Te) 2D materials as hydrogen evolution reaction (HER) catalysts using density functional theory. Our results show that 1Tprime;-MX2 have lower energies and are dynamically more stable than their 1T counterparts, therefore likely more relevant to previous experimental findings and applications. We found that sulfides are the better catalysts, followed by selenides and tellurides. Specifically, 1Tprime;-MoS2 and WS2 are the best HER catalysts among MX2. We proposed a mechanism, rather than the metallicity surmised previously, based on the calculated density of states. On the other hand, the effectively stretched (compressed) X site of the 1Tprime; 2 × 1 reconstruction from 1T is shown to be more (less) active for HER. We further exploited application of external strain to tune and boost HER performance. Our findings are of significance in the elucidation of previous experimental works and exploration of potential materials for clean energy applications.

The ability to design oxides expressly tuned for electrochemical applications is rooted in fundamental understanding of the relationships between structure, chemical composition, electronic properties, and electrochemical functionality. In particular, the perovskite family has been a central focus for studying oxygen evolution reaction (OER) electrocatalyst design due to its chemical flexibility and diverse electronic properties. Previous computational work suggested that the position of the O 2p-band center relative to the Fermi level performs well as an OER descriptor among cobalt perovskites. In this study, we examined a range of perovskite compositions to understand the relationships between composition and electronic structure, and its corresponding influence on OER activity and mechanism. Using synchrotron spectroscopy, we studied the origin of O 2p-band center shifts among 11 perovskite chemistries and identified the charge-transfer energy - a fundamental electronic parameter of oxides - as a unifying, physical underpinning of many electronic descriptors to date. We further elucidated the manner in which the charge-transfer energy leads to mechanistic differences across this chemical space. Our experimental finding that the charge-transfer energy is a descriptor that highly couples to factors that dictate OER mechanism and kinetics also provides materials chemists new intuition for developing novel oxide chemistries for the OER.

Cheap, readily available metal oxides are desirable for catalysis. The reactions that occur at the metal oxide water interface include acid-base, oxidation and dehydrogenation reactions. Coupling these gives the familiar Proton Coupled Electron Transfer reactions. Using Density Functional Theory based Molecular Dynamics, the thermodynamic contributions can be analysed in an uncoupled way. This method also allows calculating the position of the valence band maximum and the conduction band minimum of the interface.
The dehydrogenation of a water molecule on a surface is an important first step for catalyzing reactions such as water splitting. The thermodynamic quantities for this reaction are calculated on the rutile TiO₂ surface and are compared with the isostructural MnO₂ surface. We show how a difference in the electronic structure of the material results in a difference in the catalytic activity of the reaction.

The position of semiconductor band edges relative to the redox levels of water is a crucial criterion for the selection of photocatalytic materials. Owing to the dynamic nature of liquid water and the generally unknown interface structure motifs, this is a particularly challenging structure-function problem. Quantitatively predicting this band alignment is not trivial. However, such predictions are valuable as a test of computational techniques and as a means of screening for new materials. Although bulk semiconductor properties can be used to provide an estimate of relative band edge positions, the empirical accuracy of such approaches is no better than 0.5 eV [1]. The role of important interface effects such as local water dissociation and dynamical fluctuations in the interface structure remain to be understood. Here we describe our recently developed, fully first-principles approach to the energy level alignment at an aqueous/semiconductor interface [2] and extend its application to more semiconductors.
In our approach, the explicit interface is calculated using ab initio molecular dynamics, providing the physical structure at the specific interface and the resultant change in electrostatic potential. Next the GW approach from many-body perturbation theory, which corrects the errors associated with Kohn-Sham eigenvalues, is utilized to determine the semiconductor band edges relative to the centroid of the occupied 1b₁ energy level of water. The connection to electrochemical levels is completed with the known relationship between the 1b₁ energy level and the normal hydrogen electrode.
Using this approach, we determine the water/semiconductor band alignments of a set of relevant photocatalytic materials, including GaN and ZnO non-polar (10-10) facets as well as the most stable (101) anatase and (110) rutile facets of those polymorphs of TiO₂. For each material, we examine how the dynamics and dissociation of water affect these offsets. We find that water spontaneously dissociates fully on the GaN surface, while ZnO exhibits a mixed molecular and dissociative adsorption state. These structural motifs have significant impact on the interface dipole, an effect that can be partially understood by considering a single water monolayer. For rutile and anatase, we also observe interface water dissociation events, allowing us to study their impact in this case as well. Interestingly, for the anatase case, we observe a higher density of water near the interface, which also affects the alignment. In all cases we can identify a role for dynamical effects. Finally, these results will be compared with available experimental data.
This research was carried out at Brookhaven National Laboratory (BNL) under Contract No. DE-SC0012704 with the U.S. Department of Energy.
[1] V. Stevanovic, et al., Phys. Chem. Chem. Phys 16, 3706 (2014).
[2] N. Kharche, J. T. Muckerman, M. S. Hybertsen, Phys. Rev. Lett. 113, 176802 (2014).

Biomass derived molecules are being converted catalytically to useful products. However, many of these reactions are conducted under harsh conditions such as the hydrogenation of furfural to furfuryl alcohol over copper nanoparticles dispersed on alumina particles in water. The copper particles will rapidly sinter and the reactivity is reduced quickly. It has been shown that over coating with alumina the metal nanoparticles using atomic layer deposition (ALD) will reduce the sintering and if the overcoated particles are thermally treated at 700 ^oC, the lifetime and reactivity of catalyst increase dramatically compared to the catalyst without ALD over coating. Understanding the mechanism of the pore formation and further controlling the pore size are crucial for the development of the ALD overcoated catalyst. This work demonstrates that SAXS is very powerful technique to characterize these ALD overcoated catalysts. From SAXS analysis it was found that ALD filled the pores of the particles and the thermal treatment resulted in the formation of ~ 3.5 nm pores, which agrees with the BET analysis. It is possible to control the size of the pores in the overcoat by following in situ pore formation by SAXS as a function of heating rates, final temperature and gas used. The porosity can be tuned to a desired size by using these three variables during heating. Simulation studies suggest that this pore forming process is due to stresses induced because of thermal expansion and densification of the film and surface energy. To better understand the pore formation of ALD overcoats, GISAXS was used to study ALD over coating and thermal treatment on flat substrates as a function of over coat and substrates.
The SAXS and GSAXS studies were done at beamline 12-ID-B at the APS. For the in situ measurements, samples were heated as a 1 mm thick pellet under the appropriate gas with a Linkam stage. The data was fitted with a spherical shape model using Modeling II tool in the Irena package within the IgorPro application.

It is well established that the size, shape, composition and atomic structure of supported metal catalysts impact reactivity and selectivity. However, there remains limited quantitative understanding of how environmental influences modity these attributes in operando conditions. This limited understanding largely arises from the lack of operando charaterization methods that can determine the atomic-scale changes in these morphological features in complex, heterogeneous catalytic systems.
In this work, we will describe the complex structural dynamics exhibited by a common catalytic reaction—ethylene hydrogenation carried out over supported Pt catalysts. We utilize a newly developed catalytic microreactor that is designed for correlated use with both synchrotron x-ray absorption spectroscopy and scanning transmission electron microscopy. By quantifying the reaction products at each stage of the reaction, we can directly correlate the results efrom each approach, and thus gain a deeper understanding of the structural changes that occur through the reaction sequence.
We will show how measurements of the size distribution obtained by atmospheric pressure measurements in the scanning transmission electron microscope can be reconciled with extened x-ray absorption fine structure determination of the average coordination number. The resulting interpretation allows us to quantify the changes that occur in distinct groups of particles sizes, from atomic scale clusters, to nanometer scale particles to agglomerates resulting from sintering, at each stage of the reaction. This information is both distinct from and much more complete than would be obtained from the utilization of either technique alone. Additionally, we will briefly describe how data obtained from infrared spectroscopy obtained from the same microreactor can deepen our understanding of the surface species that form during the reaction.
Finally, we will describe how this operando characterization approach is generalizable to quantitative operando studies of complex systems using a wide variety of x-ray, photon and electron based experimental probes.

Nanoalloy catalysts exhibit enhanced catalytic and electrocatalytic activities in energy production, conversion and storage comparing with pure noble metal catalysts. However, the ability to determine the atomic arrangement in nanoalloy catalysts and reveal the detailed structural features responsible for the catalytically active sites remains exclusive for the understanding of the correlation between atomic structure and catalytic properties, thus enabling the preparation of efficient nanoalloy catalysts by design. This report describes findings of a study of CO oxidation over PdCu nanoalloy catalysts aiming at gaining insights into the correlation between nanoalloy&’s atomic structures (e.g. phase state in nanoscale) and catalytic activity. The catalytic synergy of PdCu alloys was revealed to reach a maximal at 50:50 atomic ratio largely dependant on synthetic protocols and the thermochemical treatment conditions. Both ex-situ and in-situ synchrotron X-ray diffraction characterization reveals the phase structure type features a chemically ordered, body centered cubic (B2) type and a chemically disordered, face-centered cubic (fcc) type coexistng at PdCu nanoalloys with ~50:50 ratio thus the catalytic synergy diminished. This finding provides a rational basis for streamlining the design and preparation of nanoalloy catalysts in terms of atomic structure and phase state.

Sufficient and sustainable energy supply is probably the most important demand for our future. An attractive way to solve this problem would be the production of H₂ by photocatalytic water splitting by visible light. A wealth of semiconductor-based photocatalysts has been tested for this purpose so far, yet significant quantum yields could only be obtained with UV light. Effective design of suitable photocatalysts requires rational improvement of charge separation, stabilization and transport, the peculiarities of which can only be understood in detail by monitoring such processes with suitable spectroscopic in situ methods. In this work, we demonstrate the potential of in situ EPR, XANES and UV-vis spectroscopy for visualizing electron transport and its relation to catalytic performance in plasmonic M/TiO₂ (M = Au and/or Cu) water reduction catalysts in dependence on the metal deposition method and the nature of the support phase as well as in Y₂Ti₂O₇ and CsTaWO₆ semiconductors of pyrochlore structure.
Using in situ-EPR spectroscopy, we could for the first time directly evidence that irradiation with visible light of different, but distinct wavelength generates an EPR signal, the amplitude of which correlates roughly with the maximum of the d-d-interband and surface plasmon resonance (SPR) absorption of Au nanoparticles, indicating that the SPR effect indeed promotes transfer of electrons from the Au conduction band to the TiO₂ support surface where they are trapped in vacancies close to the Au-TiO₂ interphase. Furthermore, it was found that the TiO₂ support phase as well as the method of Au deposition sensitively influence structure and size of the metal nanoparticles and, consequently, the activity of plasmonic metal/TiO₂ catalysts. Highest catalytic performance was found for Au deposited on mixed anatase/rutile phases by deposition-precipitation which led to abundant surface vacancies and surface OH groups that stabilize separated electrons and holes, while the enrichment of Ti³⁺ in the support lattice of less active catalysts hampers an efficient electron transport. With the aim to reduce the noble metal content, pure Cu as well as mixed Au/Cu particles were supported on the most active TiO₂ support. Best catalytic results with visible light were obtained with catalysts in which Au and Cu formed alloyed structures while those containing separate Au and Cu particles were less active.
In the case of Y₂Ti₂O₇ and CsTaWO₆ pyrochlores, we could show by in situ EPR that electrons after light-induced charge separation are preferentially trapped at the B-sites of the pyrochlore structure in the form of Ti³⁺ or W⁵⁺, respectively. From these active sites electrons are transferred via the metal co-catalyst to the protons, thus forming H₂.
In summary, we have shown that spectroscopic in situ techniques that can directly visualize charge separation and transfer are inevitable tools to elucidate photocatalytic mechanisms and the role of active sites in semiconductor photocatalysts for solar H₂ production. The combination of (partly) complementary techniques such as EPR, XANES and UV-vis spectroscopy that can detect electron traps and metal ions in a wide range of valence states is very helpful to derive reliable and comprehensive information about complex photocatalytic systems.

Zinc Oxide (ZnO) is an efficient photocatalyst for water splitting and cleaning organic waste despite its UV bandgap due to a high absorption coefficient. However, ZnO is chemically unstable and undergoes photocorrosion under UV illumination in electrochemical solutions, which hinders its application. This research is focused on preparing ultrathin dielectric layers on ZnO which are chemically stable and limit photocorrosion while providing a significant photocurrent. In this study, we have compared the passivation performance of plasma enhanced atomic layer deposited (PEALD) Al₂O₃ and SiO₂ films (1, 2 and 4 nm thick) prepared on plasma cleaned O-face ZnO or PEALD ZnO/Si. The bandgap of PEALD Al₂O₃ is 6.7 eV and SiO₂ is 8.8 eV. In situ XPS and UPS were used to determine the ZnO/Al₂O₃ and ZnO/SiO₂ band alignment. The wide bandgap of the dielectric layers and band alignment of ZnO with Al₂O₃ and SiO₂ suggests electron tunneling is a possible pathway for photoexcited electrons to flow from ZnO to the passivation layer surface. According to photocurrent measurements, Al₂O₃ is chemically unstable for all three thicknesses. In contrast, photocurrent degradation was not observed for (4nm) SiO₂/ZnO. AFM was used to characterize the heterostructure surfaces prior to and after photocurrent measurements. The RMS roughness of the as-deposited surfaces is ~0.7 nm while after photocurrent measurements, AFM images of 4 nm Alshy;₂O₃ on ZnO display the presence of pits which increase in size with measurement time. Conversely, photocurrent measurement and AFM images of SiO₂ on ZnO indicate that films > 2 nm resist ZnO photocorrosion while providing photocurrent. The results are related to the nanoscale morphology of the films and the electrochemical properties of the materials.
This research is supported by the Arizona Board of Regents and the NSF through grant DMR- 1206935.

Understanding the evolution of composition, activity and atomic-scale structure of nanoalloy (NA) catalysts aged under realistic oxygen reduction reaction (ORR) conditions is essential for the ongoing effort to make fuel cells commercially viable. We will present results from recent in situ high-energy (110 keV) synchrotron x-ray diffraction (HE-XRD) and atomic pair distribution functions (PDFs) studies on binary (Pd-Ni) and ternary (Pt-Ni-Co) NAs used as catalysts at the cathode of a fully functional Proton Exchange Membrane Fuel Cell (PEMFC). HE-XRD data both for binary and ternary NA catalysts was collected at 75 ^oC in intervals of 3 min while the cell was cycled in the range of 0.6 - 1.2 V at a scan rate of 100 mV/s for 12 h, amounting to about 3,000 cell cycles. Studies showed that when exposed to corrosive ORR conditions NAs undergo selective dissolution of less noble metallic species, in particular Ni and Co transition metal ones, leading to a significant decrease in NA&’s catalytic activity and, hence, a significant deterioration of PEMFC performance. Also, the loss of transition metal species was found to be much faster and larger with binary Pd-Ni than with ternary Pt-Ni-Co NAs indicating that the latter outperform the former in terms of stability. To rationalize the finding we focused on resolving two important questions: how does the change in NA&’s composition affects NA&’s atomic-scale structure ? and ii) how, in turn, changes in NA&’s atomic structure affect NA&’s electrocatalytic activity and stability ? For the purpose we built realistic 3D models both for binary and ternary NA catalysts by reverse Monte Carlo simulations using experimental PDF data as a guide. Models were queried against two, highly debated as of now, scenarios for the evolution of NA catalysts during PEMFC operation: a preservation of the fcc-type alloy character of NAs due to continuous re-alloying of noble and transition metal species left in NAs and a phase segregation of the initially fcc-type alloy NAs into distinct transition metal core- noble metal shell structures. Outcomes of the inquiry will be discussed and their relevance to the ongoing search for better and cheaper NA catalysts for ORR in PEMFCs - discussed.

Oxide supported catalysts have attracted great attention not only due to their wide applications in industrial reactions, but also due to their versatile activities that can be altered by 3 orders of magnitude when different substrates are used. It is important to understand how the activity is influenced by catalyts&’ atomic-structure and chemistry during reactions. However, such studies are not easy, particularly on practical powder materials that are polycrystalline. To achieve this goal, we combine in situ X-ray absorption spectroscopy (XAS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to study the chemical and atomic-scale structural changes of a real catalytic system, VO_X supported on powder α-Fe₂O₃, during a redox reaction. We found that the V oxidation state changes between +5 and +4, and structurally VO_X is converted from a two-dimensional chain to a well-connected V-O-V network. This is a combination of different VO_X species that have different redox energy barriers. These redox-driven atomic-scale changes are reversible through the reaction cycles, and are also associated with the breaking and formation of the V=O vanadyl group, observed by in situ DRIFTS. This combined study leads to proposed atomic-scale models for the redox-induced catalysts&’ dynamics, which serves as guidance for the design of highly efficient real catalysts for industrial applications.

In situ monitoring the electrochemical interfaces during electrocatalysis is crucial for the fundamental understanding and continued optimization of electrocatalysts, which will benefit the future energy technologies. To date, conventional spectroscopic techniques are generally employed for this purpose, yet it is considerably challenging. We have developed an alternative on-chip electrical transport spectroscopy (ETS) approach for directly probing the electrochemical surfaces of metallic nanocatalysts under in operando conditions. Exploiting the well-known electron scattering effect on the metallic surfaces, we show that electrical transport properties of ultrafine metal nanowires are highly sensitive to electrochemical surface states, and can be used to create a nanoelectronic signaling pathway that reveals electrochemical interface information during in-device voltammetry. Our results not only show a high degree of consistency with generally accepted conclusions in platinum electrochemistry, but also provide important insights on various technically important electrocatalytic reactions. This study defines a novel nanoelectronic on-chip characterization strategy for in situ electrochemical surface studies with high surface sensitivity and surface specificity.

Nowadays, considerable efforts have been directed to the realization of a low-carbon society in response to concerns about a depletion of fossil fuel, environmental destruction, and human health damage. Hydrogen has attracted much attention as a promising energy carrier because the power generation by fuel cells can achieve high energy conversion efficiency. However, the low volume density and the difficulty in storage and transportation are raised as obstacles for the practical utilization of hydrogen fuel. Moreover, hydrogen is mainly produced from the reforming of fossil fuel accompanied with the CO₂ emission. Thus, the production of hydrogen carrier with the use of CO₂ as a reactant and the on-site generation of hydrogen from it are regarded as an effective technology to overcome these problems.
CO₂ methanation reaction is known to be the most advantageous with a respect to thermodynamics among the production reactions of hydrocarbon and alcohol. Ru, Rh, and Ni catalysts have been developed for this reaction. In this study, then, we focused on Ni catalysts in consideration of the limited availability and cost of noble metals. The Ni catalysts supported on various metal oxides were fabricated and their catalytic activity for the CO₂ methanation was investigated. Moreover, the correlation between the results of catalytic performance test and characterization was examined.
The metal oxides of Al₂O₃, Y₂O₃, ZrO₂, La₂O₃, CeO₂, and Sm₂O₃ were selected as supporting materials of Ni catalysts. The CO₂ methanation activity of 10wt.% Ni/metal oxide catalysts was evaluated with a supply of 10% CO₂-40% H₂-50% N₂ at 200-450 0C in the heating process. The methane yield for most of catalysts drastically increased at 225-275 0C and reached a maximal value at 300-350 0C. The order of methane yield at 275 0C was as follows; Ni/Y₂O₃ > Ni/ZrO₂ > Ni/Sm₂O₃ > Ni/CeO₂ > Ni/Al₂O₃ > Ni/La₂O₃. The absorption species over Ni/Y₂O₃ and Ni/La₂O₃ were studied by in situ DRIFT with a supply of CO₂ and H₂ at 250 0C. The absorption bands derived from carbonate and/or formate species were observed at 1320-1600 cm^minus;1 in a CO₂ atmosphere for both catalysts. Subsequently, the supplied gas was switched from CO₂ to H₂. In response to this operation, the observed bands at 1320-1600 cm^minus;1 fairly disappeared within 2 h for the Ni/Y₂O₃ catalysts, while the spectra for Ni/La₂O₃ remained almost unchanged. This implied that the carbonate and/or formate species could readily decompose over the highly-active catalyst. Accordingly, the ease in the decomposition reaction over the catalysts should be one of the factors for determining the CO₂ methanation activity.

We present the electrochemical reduction of CO₂ using biological catalysts. Processes in nature to reduce CO₂ with the aid of enzymes and microorganisms are known for the conversion to several products with high efficiencies and mild reaction conditions. In non-living approaches reduction reactions of CO₂ to e. g. acids, aldehydes and alcohols can be catalyzed by dehydrogenase enzymes.^1,2 In comparison living systems such as microorganisms reduce CO₂ in multistep reactions with the corresponding enzymes obtaining products like butanol, methane or acetate.^3,4,5 However, for both approaches electrons and protons have to be added artificially in the form of co-enzymes or nutrients to reduce CO₂. In a previous work we showed the direct electron injection from a carbon based electrode into alcohol dehydrogenase without any co-factor added artificially.⁶ Here we show the direct electron injection into methanogenic microorganisms. The experiment was conducted continuously over several months with steady production of methane from CO₂. This method offers the opportunity for a highly selective reduction of CO₂.
All electrochemical measurements were performed at ambient conditions in two compartment cells using carbon felt electrodes modified with microorganisms as working electrode. Cyclic voltammograms were recorded for electrochemical characterization. Results from CO₂ saturated samples are compared to N₂ purged setups to proof product generation from CO₂ reduction. Product generation was obtained by long-term electrolysis at a constant potential and was detected steadily during the months of performance. Liquid and gaseous products were analyzed in ion chromatography and gas chromatography.
This bio-electrochemical method shows high potential to approach the energy storage problem. Combining bio-compatibility and power supply from renewable energy sources like sun or wind enables chemical storage of renewable energy and CO₂ reduction at the same time in the form of valuable fuels and chemicals.
The authors acknowledge the European Union and the county of Upper Austria for funding the Regio 13 project “REG-STORE”, Austrian Science Foundation FWF within
the Wittgenstein Prize [Z222-N19] and the Austrian research funding association (FFG) under the scope of the “Energieforschung” program within the CO2TRANSFER project (848862).
¹ U. Ruschig, U. Müller, P. Willnow, T. Höpner, Eur. J. Biochem., 70, 325-330, (1976).
² M. Aresta, A. Dibenedetto, Ref. Mol. Biotechnol., 90, 113-128(2002).
³ B. P. Tracy, S. W. Jones, A. G. Fast, D. C. Indurthi, E. T. Papoutsakis, Curr. Opin. Biotechnol., 23, 364-381 (2012).
⁴ Y. Jiang, M. Su, Y. Zhang, G. Zhan, Y. Tao, D. Li, Int. J. Hydrogen Energy, 38, 3497-3502, (2013).
⁵ H. Li, P. H. Opgenorth, D. G. Wernick, S. Rogers, T-Y. Wu, W. Higashide, P. Malati, Y.-X. Huo, K. M. Cho, J. C. Liao, Science, 335, 1596, (2012).
⁶ S. Schlager, H. Neugebauer, M. Haberbauer, G. Hinterberger, N. S. Sariciftci, ChemCatChem, 7, 967-971 (2015).

Carbon dioxide abatement has become a matter of critical importance to the developed as well as developing nations. The carbon dioxide level in the atmosphere has recently crossed the 400 ppm mark. The world is becoming increasingly aware of the environmental impact of this greenhouse gas. The International Panel on Climate Change (IPCC) in its 2014 report to United Nations categorically stated: “Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased”. On the other hand, meeting world&’s energy needs is also of paramount significance. Fuel production by recycling CO₂ using sunlight is a promising pathway to address both these issues. Photocatalytic reduction of carbon dioxide is such a technology that facilitates direct production of fuels from CO₂ at ambient conditions using solar energy. This technology, often called artificial photosynthesis, has the potential to yield sunlight to fuel conversion efficiency up to about 17%. The technology, however, has so far offered efficiency lower than that of natural photosynthesis in normal plants. Different technologies available for producing fuels from CO₂ using sunlight will be reviewed in the presentation. The focus of the talk will be on the strategies employed for enhancing the efficiency of photocatalytic COshy;₂ conversion process. The performance of nanostructured semiconductors as photocatalysts for converting solar energy into chemical energy will be discussed in detail.

We present development of a 3D photocatalytic device containing a nanostructured photoelectrocatalyst, capable of converting CO₂ to O₂. A combination of TiO₂ and transition metal co-catalysts provide an ideal photoelectric catalyst for reacting CO₂ with H₂O, which produce oxygen and hydrocarbons at a rate of at least 622 mu;L per hour for every gram of catalyst present. This significantly improves upon current technology in published literature. In addition to the high rates of production, the composition of the catalysts can also be tuned to produce a range of hydrocarbons.
The device operates at ambient pressure and concentration and uses only energy from sunlight, eliminating the need for an external power source. This enables the placement of devices in locations that are not easily connected to power, or in environments where electrical power is a limited resource. The device has broad applications in life support systems for space travel, as well terrestrial solutions to a range of heavy CO₂ emitters from large-scale power plants to vehicles.
The device design uses acrylic waveguide materials and transparent origami structures to deliver solar radiation to the entire available surface area of the catalyst, allowing maximization of the catalyst efficiency. 3D printing techniques are used to accomplish a catalytic ink coating upon the waveguide substrate. The printing strategies allow for a high tortuosity design to allow efficient mass transport of CO₂, as well as high reaction surface areas.

The sustainable development of the society mainly relies on the security of energy. The electrochemical synthesis of renewable fuels from water and carbon dioxide offers a promising solution to address the contemporary energy crisis and environmental issue. However, the energy efficiency and process sustainability so far is limited by the scarcity of both active and stable electrocatalysts. Here we develop two-dimensional (2D) materials, including nitrogen-doped graphene and metallic transition metal dichalcogenide, as an active and stable catalyst system with affordable cost for the low temperature electrolysis of water and carbon dioxide. We synthesized three dimensional highly nitrogen doped graphene (NG) foam as metal-free catalysts for efficient, selective and sustainable electroreduction of carbon dioxide into carbon monoxide. The NG foam exhibits activity towards carbon dioxide reduction exceeding the most active noble metals like Au and Ag.
The catalyst development for hydrogen production from electrochemical water splitting is focusing on the earth abundant materials to replace platinum-group metals. Recently, layered molybdenum and tungsten disulfide have attracted substantial interest to catalyze hydrogen evolution reaction (HER) with their suitable differential free energies for intermediate adsorbed *H at the edge sites. The activity, however, is restricted due to limited number of edge sites. Under a systematic screening of materials by density functional theory calculation, we aimed to develop a series of novel metallic 2D transition-metal dichalcogenides with surface activity for HER. Our novel 2D transition-metal dichalcogenides, for example vanadium disulfide, have shown self-enhanced cathodic current density of HER resulted from the surface activity and the overall performance is comparable to Pt reference catalyst. Meanwhile these 2D transition-metal dichalcogenides exhibit promising activity towards oxygen evolution reaction in acidic medium, making them bifunctional catalysts for water splitting. Our research opens a door to explore novel earth abundant 2D materials for the green energy synthesis from water and carbon dioxide.

The goal of our research is the direct conversion of carbon dioxide and water with visible light to a liquid fuel on the nanoscale under product separation. Closing of the photosynthetic cycle under membrane separation on the length scale of nanometers, inspired by Nature&’s design, minimizes efficiency degrading side and back reactions. To develop photocatalytic units consisting of a heterobinuclear light absorber such as ZrOCo^II or TiOCo^II anchored on high surface area silica coupled to multi-electron catalyst for CO₂ reduction, we have introduced photodeposition methods for the directional assembly of a nanometer sized cuprous oxide catalyst coupled to the Zr acceptor center. Photo-driven CO₂ reduction by at the Cu_xO_y cluster upon excitation of the ZrOCo unit was demonstrated.¹ Using a similar method, an Ir oxide nanocluster coupled to the Co donor center was assembled. Photoexcitation of the resulting ZrOCo^II-IrO_x unit in the presence of a gas mixture of CO₂ and H₂O evolved CO and O₂ thereby demonstrating the complete photosynthetic cycle on the nanoscale by this robust, all-inorganic oxide based assembly.²
For developing a viable photosystem, the Ir oxide catalyst is replaced by Earth abundant Co₃Oshy;₄ catalyst, and the water oxidation chemistry separated from the light absorber and CO₂ reduction reaction by a nanoscale silica layer that acts as a gas impermeable, proton conducting membrane. The nanoscale photosynthetic unit consists of a Co₃O₄ nanotube surrounded by a few nanometer thick silica shell with embedded molecular wires of type oligo(paraphenylene vinylene) for controlled charge (hole) transport from the light absorber on the outside to the Co oxide catalyst on the inside.^3,4 Macroscale arrays (cm² sized) of the core-shell nanotubes prepared by sacrificial Si nanowire array method and atomic layer deposition methods are designed to separate the CO₂ reduction in the space between the nanotubes from the water oxidation catalysis inside each tube. Planar Co oxide/silica layers with embedded wires allowed us to quantify photo-electrochemically the charge and proton transport properties of the membrane, while nanosecond optical absorption spectroscopy was used for monitoring charge injection from the visible light sensitizer into the silica embedded molecular wires.^5,6 Detailed structural characterization of the planar and nanotube arrays is based on TEM imaging, XPS, and grazing angle ATR FT-IR spectroscopy. Latest results on this photocatalytic assembly will be presented.
References:
(1) Kim. W.; Frei, H., ACS Catal., submitted
(2) Kim, W.; Yuan, G.; McClure, B. A.; Frei, H. J. Am. Chem. Soc.2014, 136, 11034.
(3) Soo, H. S.; Agiral, A.; Bachmeier, A.; Frei, H. J. Am. Chem. Soc.2012, 134, 17104.
(4) Agiral, A.; Soo, H. S.; Frei, H. Chem. Mater.2013, 25, 2264.
(5) Yuan, G.; Agiral, A.; Pellet, N.; Kim, W.; Frei, H. Faraday Discuss.2014, 176. 233.
(6) Edri, E.; Frei, H., to be submitted

Electrochemical reduction of CO2, an artificial way of carbon recycling, represents one promising solution for energy and environmental sustainability. By using electricity generated from solar cells and wind turbines, electrochemical CO2 reduction can store these renewable but intermittent energies in chemical forms. With water as the reducing agent, this process can generate a wide range of reduced carbon compounds, ranging from carbon monoxide (CO) and formic acid to methane, methanol and ethanol. These chemicals can either be directly used as fuels, such as ethanol being used to partially substitute gasoline for internal combustion engines, or be converted into liquid fuels and other valuable chemicals through further processing (e.g., Fischer-Tropsch process for CO). Despite the many advantages, electrochemical reduction of CO2 is challenged by the absence of efficient catalysts for this reaction. Copper (Cu) is the most studied material capable of catalyzing CO2 reduction at significant rates, but it still requires large overpotentials; e.g., to reach a current density of 1 mA/cm2 on polycrystalline Cu electrode, it typically requires an overpotential of >0.5 V for producing CO and HCOOH (two-electron processes) and >0.8 V for further reduced products such as CH4 and C2H4. Moreover, hydrogen evolution competes with CO2 reduction, reducing the Faradaic efficiency (FE) towards carbon-containing compounds.
Here we report the synthesis of highly dense Cu nanowires and tailoring of their surface structures to achieve superior performance for electrocatalytic CO2 and CO reduction, with particular attention to low-overpotential conditions. CuO nanowires were first grown by oxidizing Cu mesh in air which were then subjected to electrochemical reduction or annealing in a reducing atmosphere to form Cu nanowires. By tailoring the conditions for the reduction, high activity and selectivity were achieved for the production of CO from CO2, and ethanol/acetate from CO, at E < 0.4 V. It was found that the catalytic performances of the Cu nanowires are strongly correlated to the crystalline and surface structures in the nanoscale, based on which the active sites capable of selective reduction of CO2 and CO were identified. Our work indicates the great potential of electrochemical conversion of CO2 for synthesis of fuel molecules and production of chemical feedstocks.

The reduction of carbon dioxide (CO₂) into hydrocarbons and liquid fuels is drawing increasing attention as a prominent method of recycling atmospheric CO₂. Thus far, recycling CO₂ into renewable carbon-based fuels has been solely dependent on biomass, which has inherent problems of low productivity and limited product. To produce various chemicals with high yield, the direct conversion of CO₂ by simply applying electric power is more feasible. However, achieving high selectivity with low overpotential remains challenging in CO₂ reduction due to the closely positioned thermodynamic energies required for each reaction and the kinetic barrier to activation of the CO₂ molecule. Although rare-earth metals such as Au, Re and Rh as well as their complexes, have been intensively studied to achieve those requirements, their application on the industrial scale is difficult. With respect to cost and environmental ramifications, developing an efficient and inexpensive CO₂-reducing catalyst has a great impact on CO₂ utilization. One possible solution is to use the combination of an earth-abundant electrocatalyst with a photoelectrode powered by solar energy. This strategy for CO₂ photoreduction can significantly lower the overpotential, allowing the solar energy sources to be converted into useful chemicals with low cost. Herein, for the first time, we demonstrate a p-type silicon nanowire electrode with nitrogen-doped graphene quantum sheets (N-GQSs) as a heterogeneous electrocatalyst for selective CO production. The photoreduction of CO₂ into CO on the silicon nanowires decorated with N-GQSs was achieved at a potential of -1.53 V vs. Ag/Ag⁺, providing 0.15 mA/cm² of current density, which is 130 mV higher than that of a p-Si nanowire decorated with a well-known Cu catalyst. The faradaic efficiency for CO production from CO₂ was 95%, which demonstrates significantly improved selectivity for solar-to-fuel conversion compared with that of bare planar Si. By measuring the amount of gas produced against the number of coulombs of electron passed, we have also verified the stability of our catalyst. Additionally, the isotope tracing performed with ¹³CO₂ successfully verified that our N-GQSs did not decompose during electrolysis and that carbon residues do not contribute to the CO conversion. We also performed density functional theory (DFT) calculations, which provided an atomistic level of understanding of the reaction mechanism. The results suggest that N-GQSs larger than 3 nm can efficiently take electrons from the conduction band of p-type Si. Among the various possible types of N-doping sites, pyridinic N lowers the binding energy for CO₂ the most and is considered to be the primary active site of the studied system. The demonstrated high efficiency and good selectivity of the catalytic system provides new insights for the development of non-precious, environmentally benign CO₂ photoreduction systems, which have great potential for realizing CO₂ utilization.

The electroreduction of carbon dioxide (CO₂) has the potential of generating a sustainable supply of chemical feedstocks for our industries and fuels to meet our energy needs. Among all the products formed on copper electrodes, C₂ products such as ethylene and ethanol have higher energy densities and commercial value than their C₁ counterparts. In this talk, we present our recent work using Cu(I)-derived catalyst for the reduction of CO₂ to C₂ products. We studied CuCl-derived Cu mesocrystals and found this catalyst highly selective and stable for ethylene formation. TEM demonstrates the presence of (100) crystal planes and atomic steps, which we believed to be key in selective ethylene formation. We will also present our work on electrodeposited Cu₂O films. A remarkable finding is that the faradic yields of ethylene and ethanol can be systematically tuned by changing the thickness of the deposited overlayers. 1.7-3.6 mm thick films exhibited the best selectivity for ethylene and ethanol with respective faradic efficiencies (FE) of 34-39 and 9-16%. Less than 1% methane was formed. A high C₂H₄/CH₄ products&’ ratio of up to ~100 could be achieved. Scanning electron microscopy, X-ray diffraction and in-situ Raman spectroscopy revealed that the Cu₂O films reduced rapidly and remained as metallic Cu⁰ particles during the CO₂ reduction. They are therefore the catalytically-active Cu species. The effect of local pH on the selectivity is also evaluated by using phosphate buffer and KHCO₃ electrolytes.
References:
(1) Ren, D.; Deng, Y.; Handoko, A. D.; Chen, C. S.; Malkhandi, S.; Yeo, B. S. ACS Catal.2015, 5, 2814. (2) Chen, C. S.; Handoko, A. D.; Wan, J. H.; Ma, L.; Ren, D.; Yeo, B. S. Catal. Sci. Technol.2015, 5, 161. (3) Ren, D.; Huang, Y.; Yeo, B. S. Chimia2015, 69, 131.

Realization of electrochemical reduction of CO₂ to useful hydrocarbons is highly expected from the point of the alternative fossil-fuel-based energy and chemical product sources, and reduction of global warming gas. The current technology of CO₂ electrochemical reduction in aqueous solution is, however, not the level for the industrial use. The technology has the problems, especially a large amount of H₂ generation by water reduction and uncontrollability of CO₂ reduced materials. In order to improve the problems, knowing the electroactive species of CO₂ reduction is important to design the electrochemical reaction. In this report, Cu electrodes and KHCO₃ aqueous solutions are used as electrochemical catalysts and electrolytes, respectively, to evaluate the electroactive species for CO₂ reduction. The Cu is famous metal electrode which can reduce CO₂ to various hydrocarbons like CO, CH₄ and C₂H₄. The electrolyte of KHCO₃ aqueous solution is also often used electrolyte for the CO₂ reduction in aqueous solutions [1].
The chemical forms of CO₂ in aqueous solutions are CO₂, H₂CO₃, HCO₃^-, and CO₃^2-, and the dominant species depends on its equilibrium at the pH. The electroactive species are reported to be CO₂ and HCO₃^- because of this complex pH dependence [2,3]. The reaction is usually performed at pH 8 - 9 in KHCO₃ aqueous electrolyte, where the HCO₃^- ion is the dominant. Our experiments of the changing of KHCO₃ concentration and the electrolyte temperature indicate that HCO₃^- ion is not and CO₂ molecule is the electroactive species. The confusion of CO₂ or HCO₃^- electroactive species is probably due to the interesting property of HCO₃^- decomposition to CO₂. The decomposition is easy to be observed at the higher concentration KHCO₃ and relatively high solution temperature over 40 0C from our experiments.
The results, which the electroactive species is CO₂ molecule and not its ion, are quite interesting for CO₂ reduction. That is, the electrochemical reaction occurs with a straight-line-shaped non-charge-distribution molecule of CO₂, although the reaction occurs on Cu electrode surface and electron transfer plays an important role. This probably means that the activation of the CO₂ molecule at the surface of catalytic electrode is the key and the charge distribution of the ion molecules is not suitable for the CO₂ reduction. The activation mechanism of CO₂ molecule is not clear but the results shows an important role of the electrochemical catalyst.
[1] H. Zhong, et al., J. Phys. Chem. C, 119 (2015) 55.
[2] Y. Hori, et al., Electrochimica Acta 39 (1994) 1833.
[3] B. Innocent et al., App. Catal. B-Environ., 94 (2010) 219.

Fossil fuels have become increasingly scrutinised due to their environmental impact, extraction risks, and the depletion of resources. An alternative to fossil fuels is presented by the usage of CO₂ as a source for the production of carbon based fuels, including methanol. The development of an efficient CO₂ reduction catalyst necessary for fuel production yet faces many research challenges, in particular the development of a catalyst able to direct reactions through stable intermediates, e.g. CO.
Nanoscale copper is an ideal candidate; however, high overpotentials have to be used to overcome the competition with H₂O reduction to H₂. Recently, so-called “oxide-derived” copper has been shown to overcome this problem, working at moderate overpotentials of around -0.2 V vs. RHE. This system is complicated by the fact that most oxide-derived Cu samples still show a considerable amount of Cu₂O present at the surface. Therefore, it is not clear if the increase in catalytic activity originates solely in the change in surface morphology of the Cu or also in the presence of the oxide. As this system promises to be an excellent catalyst for the reduction of CO₂ a detailed understanding of the basis of its catalytic activity is essential and absolutely necessary for any further development.
Photoelectron spectroscopy (PES) is used widely in the solid-state sciences but due to its nature as an ultra high vacuum technique understanding the solid-gas interface, intrinsic to CO₂ reduction catalysis, is not possible. High-pressure PES (HiPPES) is an advanced method which allows the measurement of solid samples at elevated pressures of between 1 and 30 mbar (in comparison to 10^-9 mbar in conventional PES). Using this method a study of the surface chemistry of the solid state catalysts as a function of sample preparation, the presence of oxide, temperature, and the influence of co-adsorbates (O₂/H₂O) becomes possible.
This work presents results on the interaction of CO₂ with the surface of oxide-derived Cu foil and nanoparticles used in actual catalysis processes. In addition, the results of CO₂ interaction with Cu single crystals as well as Cu₂O thin films are presented to pinpoint differences between metallic and oxidic surfaces. The measurements are conducted both at room temperature as well as at elevated temperatures to investigate possible temperature dependence. Cu 2p and 3p core levels, as well as the Cu LMM Auger lines are used to investigate the state of the copper surfaces. The C 1s and O 1s core levels are used to track free CO₂ gas passing over the sample surface as well as CO₂ adsorption. Furthermore, valence band spectra of the as-presented samples and samples under the presence of CO₂ are compared and contributions of CO₂ identified.
Ultimately, the presented results provide a starting point for the detailed understanding of these catalysts and lead to the identification of possible ways to further improve and develop their catalytic characteristics.

Size matters in catalysis. The number of exposed surface atoms increases with decreasing size and, in many cases, the activity per exposed site changes with particle size. Therefore, the control of particle size is essential to regulate catalytic activity and selectivity. Generally, metal catalysts consist of nano-sized particles attached to a support. SBA is an attractive silica-based support, because of its large surface area and large ordered pores, which enable achieving high weight fractions of active material and avoiding diffusion limitation. Gold is an active element for many catalytic reactions and it is a typical element, which shows a strong size dependence. Massive gold particles are completely inactive; decreasing the size below a few nanometer yields high activity in hydrogenation and especially oxidation reactions. Combining the unique properties of SBA and nano-sized gold is desired, however, hampered by the inability to synthesize gold particles of one nanometer and below in a controlled fashion on a silica surface. Through surface modification with amine-functionalized alkyl groups and strict pH control during deposition, we were able to synthesize gold particles smaller than one nanometer with a very narrow size distribution. These particles showed unique performance in the dehydrogenation of formic acid, which is a possible hydrogen storage medium. Decomposition without undesired formation of carbon monoxide was observed. The functionalized catalysts not only yielded smaller particles, they also showed higher stability during the harsh conditions of formic acid decomposition.

Chemical production accounts for a large proportion of the worldwide energy consumption and there is great potential in reduction of energy cost through the development of new efficient, highly selective catalysts. Oxide-supported nanoparticulate and unsupported nanoporous gold demonstrate exceptional efficiency and selectivity for the catalysis of oxidation reactions. We present a fundamental study of adsorption of reactants and intermediates using scanning tunneling microscopy (STM). We show how our model system, the Au(110) single crystal surface is particularly well adapted to atomically resolved investigations. Moreover, the (1x2) missing row reconstruction observed on the pristine surface exhibits a high density of undercoordinated atoms, making this system relevant as a model for gold nanostructures.
First, the STM contrast associated with chemisorbed oxygen is interpreted using density functional theory simulations. The elementary adsorption site and multi-oxygen structures are identified. Adsorption of oxygen occurs without reconstruction of the gold itself. Oxygen tends to form chains along the row direction and evidence of stabilization and increased electronic hybridization is provided. The oxygen species observed are reactive to CO oxidation at ~200K and the pristine surface is recovered after reaction.
Additionally, room-temperature acetate adsorption is considered. Acetate is an intermediate in ethanol oxidation that leads to combustion. We show that acetate adsorbs into ordered islands even at low coverages. Saturation coverage is obtained at 0.25ML acetate density. In the process of acetate adsorption, deconstruction of the missing-row structure is observed. By investigating the low coverage surface, we provide some local information on the adsorbate-induced deconstruction mechanism. Importantly, we show that the deconstruction of the substrate does not take place in the presence of coadsorbed oxygen and the ordered structure of acetate is not observed. Our results thus further demonstrate that the combination of reactants present on the surface has to be considered in structural studies.

Multi-electron transfer processes, such as ascorbic acid decomposition and hydrogen and oxygen evolution reactions, are important areas of research for energy and biological applications. These processes require the use of favorable catalysts to achieve the fast kinetics rates necessary for practical purposes. Nanostructured catalysts offer promise in this regard having shown improved activity, stability, and diverse properties relative to their bulk counterparts. However, several theoretical challenges such as understanding the strain and size dependent thermodynamics, and characterization challenges such as imaging catalytic activity at the single particle level still remain.
In this work, we use ascorbic acid decomposition facilitated by a gold nanoparticle as a model multi-electron transfer process to investigate the strain field evolution in the nanocrystal lattice during catalysis. Integrating ultrafast imaging with molecular dynamics (MD) modeling can provide crucial insights on the catalytic activity of gold in such processes.
Recently, experimental techniques have evolved to conduct time-dependent lattice dynamics measurements in nanomaterials. As part of this work, coherent x-ray diffractive imaging (CXDI), with sub twenty nanometer resolutions, was used to observe reversible lattice distortions in gold nanocrystals upon exposure to ascorbic acid solutions. Here, the lattice displacement dynamics are primarily concentrated on the surface of the gold nanoparticle during catalysis and are strongly size dependent. However, the magnitude of the observed effects is larger than predicted by electrowetting theory.
Reactive MD is a suitable simulation model to capture the reaction chemistry near the gold-acid interface and to precisely determine lattice distortions in the gold lattice. Here, we present results from a series of reactive MD simulations, complementing the CXDI measurements. We reveal co-adsorbed acid-aided dissociation of water near the edges and corners of the nanocrystal facets. The local straining in the gold lattice originates from the chemisorption of the resultant hydroxyl ions. The magnitude of the simulated local lattice displacement is commensurate with experimental observations, indicating an alternate paradigm for lattice dynamics in addition to electrowetting theory. The results show the utility of characterizing the 3D displacement field evolution in identifying catalytically active nanoparticles during redox catalysis processes.

One of the main challenges in photoelectrochemical water splitting is to develop new materials and device concepts that enable direct water splitting at a cost (per kg of H₂ produced) that is competitive with conventional photovoltaic/shy;electrolyzer systems. Many research efforts in this field have been focused on the development of new and improved metal oxide-based photoelectrodes. As a result of these efforts, there are now a handful of metal oxides that show photocurrents in excess of 4 mA/cm² under simulated sunlight, most of which have been developed in the last 5 years. Well-studied examples of such materials are Cu_shy;2O and BiVO₄. One of the main challenges for these and most other materials is to protect them against photocorrosion. Several recent reports have shown that thin films of TiO₂ deposited by ALD can serve as either electron- or hole-conducting protection layers. To achieve the desired functionality, detailed understanding of the growth mechanism is essential. We have developed a home-built ALD system that is connected to a UHV XPS/UPS system, allowing us to study how the surface chemistry of the film evolves with each successive monolayer. For films grown from a TiCl₄ precursor, we find an accumulation of Ti³⁺ species in the first few atomic layers. Furthermore, we find that exposure times beyond those needed for saturated growth significantly affect the nucleation density and impurity content. The implications of these findings will be discussed. In the second part of the talk, we will show recent work on n-type Fe₂WO₆ and p-type CuBi₂O₄, two photoelectrode materials with a bandgap smaller than 2.0 eV. We have studied the mobility and lifetime of the photogenerated charge carriers, as well as the band positions and basic photoelectrochemical properties. Based on these results, we will critically discuss whether or not these materials merit further study.

Since the early development of microscopy, many advanced techniques have been used to get a better understanding of catalytic systems. Previous studies focus either on the catalytic reaction or on the catalyst itself and allow analysing the morphological reconstructions as well as changes in the chemical composition of the catalyst. Atom probe tomography (APT) is a powerful tool for the characterization of both the three-dimensional structure and composition of catalysts at the atomic-scale. Recently, this technique has been used on various catalytic systems to study the atomic distribution as well as the surface segregation in alloys after reaction (see [1] and references therein).
Our current research focuses on the use of nanostructured materials for sustainable catalysis applications: nanoporous catalysts are used as both active catalysts with high surface area and supports, which make them attractive for industrial applications. Specifically, we studied nanoporous gold (npAu) catalysts, which exhibit a high activity and selectivity for selective methanol oxidation. The catalytic performance has been attributed to the presence of traces of silver, originating from the sample preparation by dealloying. In order to improve both the efficiency and selectivity, it is crucial to understand the behavior of Ag during the reaction.
In this study, atom probe tomography (APT) will be used to provide new insights into these materials with atomic resolution compositional analysis. However, the complex morphology and the presence of pores make the APT analysis and the reconstruction impossible via traditional techniques. The sample preparation thus requires new developments. Using a combination of in situ e-beam-directed chemical vapor deposition in the FIB and lift-out techniques, we were able to successfully image npAu samples by atom probe tomography. These analyses provide better insights into the Ag distribution within the nanoporous Au structure. Future work will focus on the analysis of npAu samples at different stages of the catalytic reaction to trace the evolution of the catalyst&’s structure from its initial state through its final form.
[1] C. Barroo, P. A. J. Bagot, G. D. W. Smith, T. Visart de Bocarmé, “Investigating Nano-structured Catalysts at the Atomic scale by Field Ion Microscopy and Atom Probe Tomography”, in Atomically-Precise Methods for Synthesis of Solid Catalysts; RSC Catalysis Series, 2015, pp. 248-295
[2] This work was supported as part of the Integrated Mesoscale Architectures for Sustainable Catalysis - IMASC, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012573. C.B. acknowledges postdoctoral fellowships through the Belgian American Educational Foundation (BAEF) as well as Wallonie-Bruxelles International (Excellence grant WBI.WORLD) foundations.

Reducing and replacing precious metal catalysts in proton exchange membrane fuel cells (PEMFCs) is key to lowering their costs to promote adoption in applications such as transportation. Efforts to reduce catalyst loading have been hindered by performance losses at high power, possibly due to oxygen transport resistance, which remain unexplained by current models. [1] Understanding transport pathways and optimizing the fuel cell catalyst layer design requires characterization of the microstructure of the catalyst and support. We use electron tomography to analyze and compare the nanoscale 3D structure of platinum nanoparticle catalysts on carbon supports, comparing results for different catalyst loadings (10 wt%, 50 wt%) and support types (high surface area carbon (HSC) and Vulcan carbon black).
The position of catalyst on the carbon support (e.g. embedded in the carbon or exposed on its surface) plays a critical role in the accessibility of the catalyst surface for proton and gas transport. We make quantitative statistical measurements of catalyst particle size and surface area, correlating these properties with the local carbon support morphology. In HSC a majority of the catalyst surface is embedded in the porous carbon interior. In HSC, catalyst particles on the surface are larger than those in the interior. At higher loadings, the size difference between interior and exterior particles is more dramatic with exterior particles accounting for an increased fraction of the total catalyst surface area.
We combine tomographic and electrochemical measurements to understand the relationship between catalyst microstructure and fuel cell performance. We find that tomography measures values for the specific surface area that are consistent with measurements by rotating disk electrode (RDE) hydrogen adsorption-desorption (HAD). HAD measurements on the membrane electrode assembly (MEA) are significantly lower because of the impacts of transport limitations. Because the HAD measurements for HSC in both MEA and RDE cannot be accounted for by only catalyst on the carbon exterior, we conclude that particles in the carbon interior must be participating.
[1] T.A. Greszler, et al, J. Electrochem. Soc. 159, F831 (2012).

The application of electron tomography (ET) to materials studies has made considerable strides recently, with atomic resolution 3D imaging and spectral mapping now attainable. This capability is possible due to advancements in aberration-corrected scanning transmission electron microscopy, multi-tilt sample holders, large solid-angle energy dispersive X-ray spectrometers (EDS), and algorithms for reconstruction and image processing. Coupled with increased processing performance, complete datasets up to 5D can now be acquired and analyzed rapidly to obtain precise quantitative information about structure, composition, porosity, and the operando evolution of these properties. This is in contrast to the qualitative information gained from the interpretation of traditional 2D images and elemental maps.
These advances in ET are particularly important for detailed analysis of the structure of catalytic materials for energy research. We take advantage of this in characterization of electrocatalysts for PEM fuel cells, a sustainable energy technology with applications in transportation. The compositional and structural analyses of nanostructured thin film catalyst electrodes, in addition to non-traditional catalyst geometries, are demonstrated using ET. Strategies to overcome the barrier of low contrast electrode constituents, such as carbon and ionomer, to produce high quality 3D tilt-series tomograms by alignment and registration of bright and dark field images, will be presented. Prospects for 4D electron energy loss spectroscopy and EDS spectroscopic datasets of thin ionomer layers are also evaluated. Strategies for mitigating beam damage of soft ionomer films will be presented, with the goal of providing a 3D view of the evolution of ionomer and catalyst distribution over the fuel cell lifetime.
Research supported by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (DOE) and as part of a user project through Oak Ridge National Laboratory&’s Center for Nanophase Materials Sciences, which is a U.S. DOE Office of Science user facility.

Cobalt oxides are among the best performers as future alternative electro-catalysts for the water splitting reaction, with attractive properties in terms of stability, efficiency, abundance and low cost. However, fundamental understanding of the catalytic properties of cobalt oxides is still limited. To elucidate the fundamental structure, composition and surface chemistry of a CoO_x based catalysts, we characterize here the surface of a model catalyst consisting of CoO_x nanoislands (0.66 < x < 2) under ultra-high vacuum conditions by high-resolution Scanning Tunneling Microscopy (STM) and X-Ray Photoelectron and Absorption Spectroscopies (XPS and XAS) together with density functional theory. The Au(111) surface is used as a growth template and the effects of varying synthesis conditions on the resulting CoO_x nanostructures are explored [1]. This allows for an atomic-scale investigation of the correlation between Co oxidation state and the adsorption of water, water dissociation and synergistic effects with the Au(111) substrate, as gold has been observed to strongly enhance the catalytic activity [2].
We find that the oxygen pressure has a profound effect on the CoO_x structure, accompanied by changes in the cobalt oxidation states. The structure at low pressure is a rock-salt Co-O bilayer exposing the (111) plane with cobalt in the +2 oxidation state. However, this can be converted into a more oxygen rich stoichiometry with cobalt in the +3 state, accomplished by intercalation of an additional oxygen layer in the island/gold interface. Both structures exhibit a strong activity towards water dissociation at room temperature, leading to hydroxylation of up to 50% of the island basal plane oxygen atoms as observed in-situ by both dynamic STM movies recorded during H₂O dosing and by corresponding analysis of the hydroxyl component in the O1s core-level XPS spectrum. The reactivity towards water dissociation is measured as function of island edge concentration, revealing the CoOx edges to host the most active sites in the model catalyst.
[1] A. S. Walton, J. Fester, M. Bajdich, et al., ACS Nano 9, 2445 (2015).
[2] B. S. Yeo and A. T. Bell, Journal of the American Chemical Society 133, 5587 (2011).

The combination in the same electrode of Pt and OER particles allows, depending on the conditions, the oxidation of either hydrogen or water molecules. These hybrid electrodes could be of use for both polymer electrolyte membrane (PEM) electrolyser or/and fuel cell applications [1]. Typically, these electrodes are fabricated by mechanical mixing of dispersions of carbon/Pt particles and OER catalyst particles with an ionomer matrix for to use with a PEM. Currently, there is strong need for a method to characterize the electrode structure and composition on the scale on 1 um and below allowing “to see inside” the electrode. In this study we applied STXM to visualize each chemical constituent of the electrode [2]: carbon, ionomer, Pt, and OER catalyst. Combining the 50 nm resolution 5x30 um image stacks recorded for C1s, N1s, O1s, and F1s edges in the soft X-ray energy interval 280-740 eV, after the material decomposition with respect to the standard spectra collected for isolated materials, we are able to map the component distributions with 50 nm resolution through the electrode and measure their content.
1. S.A. Grigoriev, K.A. Dzhus, D.G.Bessarabov, P.Millet, International Journal of Hydrogen Energy, 39, 20440-20446, 2014
2. D. Susac, V, Berejnov, A.P. Hitchcock, J. Stumper, ECS Transaction, 41(1), 629-636, 2011

Oxygen evolution reaction (OER) is the key reaction in the water splitting process, since this half reaction is in charge of high overpotential. Over the years various attempts have been made to develop the effective OER catalyst using earth-abundant materials. Among them, manganese oxide draws massive interests as the strong candidate of the new generation OER catalyst, since there already exists an outstanding OER catalyst based on manganese oxide in nature. Oxygen evolving complex (OEC) in photosystem II, CaMn4O5 cluster, shows amazing efficiency and stability in the water oxidation. We newly developed manganese oxide/nickel oxide heterostructure catalyst that allows for OER to occur at much lower overpotential than other manganese oxide catalysts. (490mV of overpotential @5mA/cm2 under neutral condition and 350mV of overpotential @10mA/cm2 under basic condition) Moreover, this catalyst shows the great stability such that nearly constant current was observed during the 40,000 sec of electrolysis. These experimental results present that synergetic effects are formed by constructing the heterostructure. Therefore, understanding the effects of heterostructure is significantly important to develop the new kinds of improved OER catalyst. Here, we investigated the electronic structure of the manganese oxide/nickel oxide catalyst using scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). We found that the manganese oxide over nickel oxide underlayer is more oxidized than its original state. Furthermore, the new electronic structure which is different from that of both manganese oxdie and nickel oxide is observed at the interface of heterostructure.

Developing earth-abundant, active, and stable electrocatalysts operated in the same electrolyte for water-splitting, including oxygen evolution reaction and hydrogen evolution reaction, is important to many renewable energy conversion processes. Here, we demonstrate the drastic improvement of catalytic activity when transition metal oxide (Fe, Co, Ni oxides and their mixed oxides) nanoparticles (~ 20 nm) are electrochemically transformed into ultra-small diameter (2 to 5 nm) nanoparticles through lithium-induced conversion reactions. Different from most traditional chemical synthesis, this method maintains excellent electrical interconnection among nanoparticles and creates large surface areas and many catalytically active sites. We discover that lithium-induced ultra-small NiFeO_x nanoparticles are excellent bifunctional catalysts exhibiting high activity and stability for overall water-splitting in base. We achieve 10 mA cm^-2 water-splitting current at only 1.51 V for over 200 hours without degradation in a two-electrode configuration and 1 M KOH, better than the combination of Ir and Pt as benchmark catalysts.

We have successfully developed a facile solid-state reaction method to synthesize novel VN/C and WC/C nanocomposites using melamine and corresponding metal oxides as precursors under inert atmosphere. The characterization results obviously suggest that high crystallization and purity VN and WC nanoparticles are encased or supported by few carbon layers with average sizes of 10-15 nm. The nitridation and carbonization process can be ascribed to the pyrolysis of melamine, which will generate a series of chemically reactive hydrogen-, carbon- and nitrogen-containing atomic species such as C₃N₃⁺, C₂N₂⁺, C₃N₂⁺ and CN₂H⁺ at certain temperatures. However, no products can be obtained in the controlled test of pyrolysis of melamine tablets at same condition, suggesting that the dangling bonds on V and W atom are beneficial to the immobilization of carbon layers. Moreover, the electrocatalytic performance of VN/C and WC/C towards oxygen reduction reaction (ORR) in alkaline electrolyte has also been investigated by cyclic voltammetry (CV), rotating disk electrode (RDE) and chronoamperometry test with or without 3M methanol. The results show that both VN/C and WC/C have considerable ORR activity, stability and excellent methanol-tolerance, and the calculated electron transfer numbers according to K-L theory have also demonstrated that WC/C exhibits a two steps of ORR process while VN/C undergoes a direct 4-electron reduction process. Considering their unique structures and electrochemical results, VN/C nanocomposite can be regarded as a promising non-precious metal methanol-tolerant candidate as ORR electrocatalyst while WC/C can further serve as a kind of suitable catalyst support or co-catalyst to develop high-efficient low Pt-loaded ORR catalysts for alkaline fuel cells. In addition, this facile preparation route is also applicable to fabricate other metal carbides and nitrides such as NbC, TaC, V₆C₅ and TiN, NbN, AlN.

This work reports a new method for the fabrication of mesoscopic hollow-structured silver-doped nickel(III) oxyhydroxide (NiOOH) and its use as an efficient electrocatalyst in the electrolysis of urea in alkaline aqueous solution for hydrogen production.
Urea, (NH₂)₂CO, has been recognized as a chemical hydrogen carrier with a material-based gravimetric hydrogen content of ca. 6.7%. Urea appears to be a very attractive potential chemical hydrogen storage material because of its good stability in ambient condition, very low toxicity, high solubility in water, and most of all, the availability of huge quantity produced by both fertilizer industry and human urine. The production of hydrogen fuel from urea aqueous solution has been demonstrated by both direct and indirect catalytic electrolysis as well as by photo-electrolysis. Urea itself as a fuel was also demonstrated in both direct fuel cell and solid oxide fuel cell. Although several types of electrocatalysts based on both supported noble metals and transition metal oxides were examined for electrolysis of urea, Ni(II)oxide/hydroxide stands out to be the most promising contender taking into the consideration of both the cost and efficiency. The catalytic active species of Ni(II)oxide/hydroxide catalyst in electrolysis of urea in aqueous solution was identified to be nickel(III) oxyhydroxide (NiOOH) generated either by electrochemical oxidative(anodic) activation or chemical oxidation. It has been well established that, for a solid state heterogeneous catalyst of given chemical composition, the hollow and/or porous structures are often desirable for maximizing the catalytic efficacy. However, the fabrication of nano-/mesoscopic hollow-structured NiOOH turned out to be challenging.
In this work, we devised a two-step approach for the fabrication of mesoscopic hollow-structured NiOOH electrocatalyst. In step-1, an electrochemical method was used to fabricate a high-valent silver oxide template with well-defined particle size, shape and dispersity. In step-2, a galvanic displacement reaction was employed to fabricate hollow NiOOH by reductively sacrificing the template. The shape and size of the mesoscopic hollow-structured NiOOH are therefore controllable by that of the template in the first step whereas the thickness and the composition of the NiOOH shell is controllable in the second step. We systematically explored the conditions for both step-1 and step-2, and achieved a broad range of structural and chemical tunability for the fabrication of mesoscopic hollow-structured NiOOH. We also demonstrate the high activity and durability of the as-fabricated NiOOH in the catalytic electrolysis of urea in alkaline aqueous solution at the anode and the concomitant production of hydrogen gas at the cathode.

Electrolyzer and fuel cells based on proton-conducting oxides (PC-SOEC/FCs) are gaining grounds in the energy conversion scenario thanks to the high proton conductivity of protons at intermediate temperatures.^1,2 Major advances on PC-electrolytes (e.g. BaCeO₃ and LaNbO₄ derivatives)³ have not been sufficient to bring PC-SOEC/FCs to an applicative stage because of the severe limitations of electrodes, which must comply a list of requirements: high catalytic activity, high electron and proton conductivity. Current electrodes are mostly composites, made of mixed ionic and electronic conductor (MIEC) oxides and the PC-electrolyte. Only recently, triple (e^-/O^2-/H⁺) conducting oxides (TCOs), i.e. MIEC with enhanced proton transport capability, have been proposed as single-phase electrodes instead of composites.⁴
In this work, we evaluated the TCO properties of the double perovskite Sr₂Fe_1.5Mo_0.5O_6-δ (SFMO) with state-of-the-art DFT+U calculations. SFMO has been proposed as anode and cathode material for symmetric oxide-conducting SOFCs because it pairs good catalytic activity, excellent MIEC properties and remarkable stability in both oxidizing and reducing environment.⁵ SFMO is inherently non-stoichiometric,⁶ which turns this MIEC into a good candidate for proton conduction provided that oxygen vacancies allow the incorporation of protons via water dissociative incorporation into the lattice. Thus, we analyzed hydration properties and proton migration barrier heights in SFMO and in two derivatives, namely Sr_0.875Ba_0.125Fe_1.5Mo_0.5O_6-δ and Sr_0.875K_0.125Fe_1.5Mo_0.5O_6-δ.
Ba and K substitutions at the A-site of SFMO perovskite affect both the structural and electronic features, boosting the proton transport of SFMO. In particular, aliovalent K doping results in a higher concentration of oxygen vacancies and in a lower migration barrier. From analysis of our ab initio results, we identified key structural parameters that promote the proton transport between oxygen sites and we designed new promising TCO candidates for PC-SOEC/FC electrodes.
1- Bi et. al. Chem. Soc. Rev.43, 8255 (2014).
2- Fabbri et. al. Chem. Soc. Rev. 39, 4355 (2010).
3- Malavasi et. al. Chem. Soc. Rev. 39, 4370 (2010).
4- Kim et. al. ChemSusChem 7, 2811 (2014).
5- Q. Liu et. al. Adv. Mater.22, 5478 (2010).
6- Muñoz-García et. al. J. Am. Chem. Soc. 134, 13600 (2012).

Reversible electroactivities for oxygen reduction reaction (ORR) and its backward counterpart (oxygen evolution reaction; OER) are required for electrocatalysts of rechargeable metal-air batteries. In this work, a double perovskite oxide (NdBa_0.25Sr_0.75Co₂O_5.9 or NBSCO) is presented as the bifunctional catalyst, which is characterized distinguishably from previously reported perovskite catalysts by its high electrical conductivity (5,400 S cm^-1). With the help of nitrogen-containing conducting polymer (polypyrrole or pPy), the highly conductive double perovskite oxide catalyst showed smaller overpotential with more facile kinetics in ORR as well as OER when compared with a simple perovskite counterpart. Two to three order higher ORR exchange current densities were obtained with NBSCO while the 4-electron transfer process was dominantly favored (number of electron transfer, n = 3.84 ~ 3.95). Also, OER stability was secured with no current loss at least during 100 cycles. The improved catalytic activities were expected from the viewpoint that facile supply of electrons to active sites drives surface peroxide as the intermediate product of 2-electron ORR to go forward to complete 4-electron ORR.

Layered HNb₃O₈/graphene hybrids with numerous heterogeneous interfaces and hierarchical pores are fabricated via the reorganization of exfoliated HNb₃O₈ nanosheets with graphene nanosheets (GNs). The interfaces and pores are created by the alternative stacking of HNb₃O₈ nanosheets with limited size and GNs with a buckling and folding feature.The photocatalytic conversation of CO₂ into renewable fuels by optimized HNb₃O₈/G hybrids yields 8.0-fold improvements in CO evolution amounts than that of commercial P25, and 8.6-fold improvements than that of HNb₃O₈ bulk powders. The investigation on the relationships between microstructures and improved photocatalytic performance demonstrates that the improved photocatalytic ability is further attributed to the exotic synergistic effects via the combination of enhanced specific BET surface area, increased strong acid sites and strong acid amounts, narrowed band gap energy, and heterogeneous interfaces.A thorough understanding the structure-activity relationships is helpful for for rational design and exploiting novel synthetic protocol of 2D nanohybrids.

The nanostructured materials have received much attention over the past decade owing to their chemical, physical, and optical properties when compared to those of the bulk state. In this regards, the controlled synthesis of nano- and meso-porous metal-oxide catalysts is of great interest from the viewpoints of fundamental and industrial chemistry. Particularly, porous metal oxides based on abundant 3d transition metals (Mn, Fe, Co, Ni, and Cu) are prime candidates in terms of durability, activity, and cost.
A wide variety of synthetic method has been applied to fabricate transition metal oxides. Most recently, solvothermal (or hydrothermal) method is under intense investigation to obtain fine nanocrystals. However, the situation is considerably more complex in the case of the mixed-metal oxides including multiple transition metal components. Because of differences in intrinsic redox reactivity of each transition metal, the nucleus formation and particle growth of metal oxide often proceed independently in each metal component, resulting in segregated mixtures of metal oxides including an each single metal component. Despite extensive studies, substantial progress in synthetic methodology is still needed in preparing mixed-metal oxide system, such as binary or trinary mixed-metal oxide. To overcome the synthetic limitations in traditional solution-based synthesis, here, we demonstrate a novel synthetic approach based on the ultra-rapid heating technique for preparing the porous metal oxides with multiple transition metal species.
Typically, two or three kinds of transition metal salts (nitrate salts of Mn, Fe, Co, Ni, and Cu) and solvent (methanol/diethylene glycol) were mixed in an SUS-316 stainless steel tubular reactor, and sealed by a screw cap. Then, the reactor was heated up to 300 0C at 500 0C/min heating rate by using molten-salt bath. After 10 min, the reaction was immediately quenched by immersing the reactor into an ice-water bath. The resulting powdery products were centrifuged, washed with methanol several times, and dried in vacuum, and then, they were well-characterized by using TEM, STEM/EDX, X-ray diffraction (XRD), and nitrogen adsorption/desorption measurements. Judging from the systematic synthesis and structural analysis of a series of mixed-metal oxides (CoMnO_x, NiMnO_x, CoNiMnO_x, etc.), the present approach using the concept of ultra-rapid heating is a simple but potent process, which allows various metal combinations in the reaction to afford porous mixed-metal oxides. Notably, according to the STEM/EDX and XRD analysis, the all transition metal species used in the reaction were completely and homogeneously blended in the resultant mixed-metal oxide with fine nanocrystals. Additionally, they afforded extraordinary high specific surface area (>200 m²/g). These investigations demonstrate the broad applicability of this ultra-rapid heating technique to access highly-integrated metal-oxide catalysts.

Demand on the efficient synthetic approach to highly active and durable electrocatalyst is rapidly increasing for the fuel cell industrialization. Platinum has been regarded as efficient electrocatalyst for oxygen reduction reaction, however its high cost and lack of abundancy impeded the application to fuel cell. Here, we suggest novel approaches to synthesis of Pt-based alloy electrocatalyst with high activity and durability. By encapsulating carbon and inorganic materials, agglomeration and coalescence of nanoparticles during heat treatment can be inhibited. Moreover, these encapsulating layer can also inhibit the particle growth during electrochemical reaction, simultaneously. We confirmed both high mass and specific activity and also confirmed superior long-term stability through accelerated durability test. We also conducted in situ analysis to reveal the high durability accompanied with density functional theory analysis.

Complex perovskite oxides with A_1-xA&’_xB_1-yB&’_yO_3-δ structure as a kind of mixed ionic and electronic conductor (MIEC) have acquired extensively attention as a potential cathode to overcome cathodic polarization at the lower temperature. Ce-doped SrMnO₃ (SCM) has received interest as a cathode material for intermediate temperature (600 - 800 °C) solid oxide fuel cell (SOFCs). Although SCM has lower oxygen ion conductivity at intermediate temperature it has similar thermal expansion coefficient to ceria-based electrolytes as well as its high electrical conductivity (over 300 S cm^-1 at 800 #730;C). The insufficient oxygen ion conductivity in this material is primarily attributed to a decrease in oxygen vacancy concentration with Ce doping due to the strong hybridization between the Ce 4f and O 2p orbital.
We designed and prepared Sr_0.9Ce_0.1Mn_1-xCo_xO_3-δ (SCMCo, x=0.1, 0.3) to enhance oxygen ion conductivity, which is characterized by electrochemical performances. The effects of cobalt ions on the oxygen conductivity were also investigated in terms of oxygen vacancy concentration and their geometric mobility. The in-situ structural analyses, such as high temperature XRD and x-ray absorption spectroscopy using synchrotron radiation, were applied to investigate improved oxygen ion mobility due to relaxation of octahedral distortion.

Reduction of oxygen transport resistance in cathode catalyst layers is one of key issues to increase the power density of polymer electrolyte fuel cells in the direction of reducing total amount of Pt used in the system. It has been reported that the molecular structure of ionomer influences on oxygen transport properties in the catalyst layers. However, the direction of molecular structure design of ionomers has not been cleared, especially for aromatic polymer electrolytes showing lower gas permeability than that of perfluorinated electrolytes. Sulfonated poly(p-phenylene)-based diblock copolymers having aliphatic side chains (SBuH) has been studied as the cathode ionomer for the increase in gas permeability by introducing aliphatic side chains on the polymer backbones. MEAs composed of SBuH cathode ionomer showed an equivalent gas transport properties to those of Nafion® ionomer.
In this study, oxygen reduction reaction (ORR) activity of the cathode catalyst layers composed of SBuH ionomer was investigated in comparison with Nafion^® ionomer. ORR activity was evaluated as the current density at 0.9 V (I_0.9) and the electrochemically active surface area (ECA). In addition, the influence of aging conditions of MEAs (potential cycling, constant current holding) and sweep ratio on the ECA and the charge density of Pt oxide were also investigated. The I_0.9 and ECA values of the catalyst layers composed of SBuH ionomer were lower than those of Nafion^® ionomer. On the other hand, the area specific ORR activity estimated as the current per Pt surface area was almost the same regardless of the ionomer species. The ECA value of the catalyst layers composed of SBuH ionomer was recovered by potential cycling or constant current holding and was an equivalent to that of Nafion^® ionomer. The charge density of Pt oxide in the catalyst layers composed of SBuH ionomer exhibited a steady value despite changing the aging conditions but increased with decreasing the sweep ratio. These results suggested that SBuH ionomer deactivated the effective surface area in terms of the reaction rate of ORR.

The water electrolysis has been refocused in the recent years as a key process in hydrogen production from renewable energy. The efficiency of hydrogen production is mainly dominated by the overpotential of the oxygen evolution reaction (OER) at the anode, and the most widely used anode catalysts are composed of precious metals such as iridium oxide. The design of cost-effective, highly active catalysts for the OER by using of non-precious transition metal oxides is a critical issue. Suntivich et al. reported [1] that a perovskite oxide (ABO₃) catalysts shows high catalytic OER activity and indicates a strong correlation between the catalytic activity and the e_g orbital occupancy of the surface transition metal defined by the X-ray absorption spectroscopy.
Delafossite oxides (ABO₂), which is one of the transition metal oxides and has octahedral coordination as with perovskite oxides, have been widely studied for their application to electronic devices as a transparent conductive film and a thermoelectric material, but has never been examined as the OER catalyst except the precious metal delafossite (ABO₂; A=Pt, Pd) [2] Previously, we reported Copper Delafossite oxides (ABO₂; A=Cu) as active OER catalysts and evaluated the correlation between the catalytic activity and the e_g or t_2g orbital occupancy estimated by density-functional theory (DFT) calculations.[3,4]
In this study, we have examined Silver Delafossite oxides (ABO₂; A=Ag) in order to comprehend the effect of the kind of A-site on the catalytic activity.
From our DFT calculations, it was expected that AgCoO₂ and AgRhO₂ have high catalytic activity as well as CuCoO₂ and CuRhO₂. We confirmed this prediction experimentally.
Several Silver Delafossites (AgBO₂; B=Co, Rh, Fehellip;) were synthesized by hydrothermal reaction or ion-exchange method. Synthesized delafossite particles were deposited on a conductive carbon substrate and used as working electrodes (WE) for electrochemical measurement. The OER activity was evaluated in 1.0 M [M = mol / L] KOH aqueous solution using Rotating Disk Electrode (RDE) method. High OER activity was observed on AgCoO₂ and AgRhO₂ from the electrochemical measurements, as it was expected.
We also evaluated the correlation between the OER activities and the e_g / t_2g orbital occupancy at the B site of each delafossite. It was found that the OER activity is strongly correlated with those electronic structures of B-site metal of delafossite, with no relation to the kind of the A-site metal. The details will be discussed at the presentation.
[References]
[1] J. Suntivich, et al., Science 334 (2011) 1383.
[2] P.F. Carcia, et al., J. Electrochem. Soc. 127 (1980) 1974.
[3] R. Hinogami, et al., Electrochem. Comm. 35, (2013) 142.
[4] K. Toyoda, et al., J. Phys. Chem. C., 119 (2015) 6495.

Three-dimensionally (3D) ordered macro-/mesoporous (3DOM/m) Ni is fabricated by chemical reduction deposition method using lyotropic liquid crystals (LLC) to template the mesostructure within the regular voids of a colloidal crystal (opal). The thereby achieved structural advantages of combining well-ordered bicontinuous mesopores with 3D interconnected periodic macropores, such as abundant exposed catalytic active sites, efficient mass transport, and high electrical conductivity make this non-noble metal structure an excellent hydrogen evolution reaction (HER) electrocatalyst. The 3DOM/m Ni exhibits a low onset overpotential of 63 mV (vs. RHE) and a small Tafel slope of 52 mV per decade, as well as a long-term durability in alkaline medium. These distinct features of the 3DOM/m Ni render it a promising alternative to Pt-based HER electrocatalysts.

Analogues to graphene, graphitic carbon nitride (g-C₃N₄) which contains C, N, and H in trace amount have fascinated scientists to consider as a catalyst for many applications. It is a medium bandgap semiconductor, which can be efficiently used as a catalyst for photochemical splitting of water. The world&’s biggest energy problem will be solved if we can succeed in the splitting of water into H₂ and O₂ gas using solar energy and by using suitable semiconductor photocatalysts. Domen et al showed g-C₃N₄ is a good visible light absorber with proper band gap and have capability to dissociate water molecule. It is stable in water as well as non-toxic, cheap and easily available.^[1] Another report from Zheng et al showed the synthesis of g-C₃N₄ with nitrogen-doped graphene (N-Gr), showed excellent electrocatalytic Hydrogen Evolution Reaction (HER) application since this composite possesses unique molecular structure and electronic properties.^[2] Still this composite has not beaten the best Pt catalyst, it showed to be similar electrocatalytic HER activity with the well-known metallic catalysts like nanostructured MoS₂ materials. These significant reports along with many other reports underline the importance of the non-metal/metal-free based systems in the area of catalysis. Particularly g-C₃N₄ is being explored recently although its basic structure has been know from very long time. Along with this, g-C₃N₄ can act as a catalyst for broad variety of reactions like electrocatalyst for Oxygen Reduction Reaction (ORR), Oxygen Evolution Reaction (OER) in fuel cells, oxidation reactions (alkanes, olefins, alcohols, heteroatoms, photodegradation of pollutants), many hydrogenation reactions and as a basic catalyst for NO decomposition, activation of bonds, F-C reactions as well as. We have synthesized g-C₃N₄ nanostructures by a novel method which has been used for various electrocatalytic reactions such as HER, OER and ORR. The nano-structuring of g-C₃N₄ has improved the electrocatalytic activities compared to bulk g-C₃N₄. To further improve the conductivity and catalytic properties, these nanostructures of g-C₃N₄ have been doped with heteroatoms. It has been already well known that doping of particular heteroatom like Phosphorus (P), Iodine (I), Fluorine (F), Sulfur (S) can alter many properties.^[3] Heteroatom doped g-C₃N₄ nanostructures has showed excellent electrocatalytic performances. Heteroatom doping in g-C₃N₄ nanostructures has been proven by many techniques/characterizations.
References:
1. Xinchen Wang, Kazuhiko Maeda, Arne Thomas, Kazuhiro Takanabe, Gang Xin, Johan M. Carlsson, Kazunari Domen and Markus Antonietti, Nat. Mater. 2009, 8, 76- 80.
2. Yao Zheng, Yan Jiao, Yihan Zhu, Lu Hua Li, Yu Han, Ying Chen, Aijun Du, Mietek Jaroniec and Shi Zhang Qiao Nat. Commun. 2014, 5, 3783-3791
3. Yuanjian Zhang, Toshiyuki Mori, Jinhua Ye, and Markus Antonietti J. Am. Chem. Soc. 2010, 132, 6294-6295

Sodium titanate nanotubes doped with potassium were synthesized by the Kasuga method and tested as catalysts for biodiesel production. Potassium was added to the nanotubes in order to increase their basicity and, consequently, improve their performance in the transesterification of soybean oil with methanol. The synthesis temperature and NaOH:KOH molar ratio used in the preparation were changed in order to define the best experimental conditions leading to solids with nanotubular morphology and improved potassium loading. Synthesized catalysts were characterized by N₂ physisorption, powder XRD, scanning electron microscopy (SEM-EDX), transmission electron microscopy (TEM), FT-IR, FT-Raman and CO₂ temperature-programmed desorption (CO₂-TPD). Obtained results showed that the optimal synthesis temperature was 140 ^oC. At this temperature, sodium trititanate nanotubes containing 1.5 wt. % of potassium were obtained when 10 M alkali solution with NaOH:KOH molar ratio of 9:1 was used. In this case, the proportion of sodium and potassium in the synthesized material was similar to that used in the synthesis. An increase in the proportion of KOH to 20 and 30 molar % in the NaOH-KOH solution used in the synthesis allowed obtaining sodium titanate nanotubes with larger potassium loadings (3.2 and 3.3 wt. %, respectively). Sodium titanate nanotubes doped with potassium showed a higher amount of medium and strong basic sites than the pure sodium counterpart (NaTNT) used as a reference. Their catalytic activity in the transesterification was also higher than that of the reference NaTNT sample. The best results were obtained with the samples containing 3.2-3.3 wt. % of potassium. Conversions of soybean oil to methyl esters obtained with these catalysts at 80 ^oC and 1 h reaction time were about 94-96 %.

Low temperature (< 250 °C) fuel cells continue to be one of the central areas of energy research due to high demand for transportation applications that are conducive to clean energy initiatives. However, sluggish oxygen reduction reaction (ORR) catalysis at the cathode remains problematic from a performance and cost standpoint, with benchmark catalysts being limited to expensive noble metals. Therefore, extensive research has been devoted towards the discovery of alternative, less expensive ORR catalyst materials. Over the years, metal oxides have garnered a lot of interest for electrocatalysis, which has spawned a number of ORR catalyst studies on conductive pyrochlore systems. Many have reported (Bi,Pb)₂(Ir,Ru)_2-x(Bi,Pb)_xO_7-y (0 le; x le; 1, 0 le; y le; 1) pyrochlores as exhibiting fast, stable oxygen reduction kinetics, as well as exceptional catalysis for oxygen evolution reactions (OER), making them ideal bi-functional catalysts. The present study takes a combinatorial, high-throughput approach in rapidly evaluating composition libraries of pyrochlore and doped rutile oxide systems in order to identify characteristics (e.g. composition, structure, defect states, etc.), and trends that may further optimize ORR and OER catalysis. Combinatorial evaluation of pyrochlore and doped rutile oxides is facilitated by the fabrication of ternary and quaternary oxide composition spread thin films through off-axis reactive co-sputtering, which forms a continuous composition gradient (90-10 at %) across a single substrate. The films were then characterized and electrochemically screened for both ORR and OER catalysis using custom and standard electrochemical techniques, revealing optimal pyrochlore compositions, as well as novel oxides that, when doped, also exhibit strong bi-functional catalytic activities.

Over the past decade, replacing fossil fuels by renewable sources of energy has become a major research goal. Hydrogen produced from water using solar energy is clearly the ultimate source of clean renewable energy. Traditionally, H₂ is generated from water using Pt electrodes, and several catalysts have been used for electrocatalytic, photocatalytic or photoelectrocatalytic production of hydrogen. MoS₂, which is one of the transition metal dicalcogenide materials (TMD), has proven to be a good catalyst for electrochemical as well as photochemical hydrogen evolution reaction (HER). In this presentation, we focus on catalytic activity for HER of TMD materials such as MoS₂, WS₂, MoSe₂ and WSe₂. We found that sulfur vacancy is catalytic active site for HER. The range of hydrogen adsorption energies on sulfur vacancies of TMDs is under 1000 meV and the adsorption energy on sulfur vacancy of 2H-MoS₂ is lower than 10 meV which value is comparable to Pt electrode. Detailed analysis of electronic structure and mechanistic studies also will be presented.

Understanding the adsorption and desorption energetics of atoms and molecules on surfaces and the chemical reactions between them during catalytic processes is important for the development of new and more effective catalysis. Presently, the importance of oxygen exchange materials (e.g. CeO₂, perovskites) for thermochemical splitting of H₂O is in focus. In the present study, the effect of Nd³⁺ on the water adsorption and surface energetics of CeO₂ was investigated. Nanoscale Nd doped CeO₂ powders have been synthesized by a surfactant-based method. The as synthesized nano powders were found to be homogeneous solid solutions with a fluorite structure, where the lattice parameters increase linearly with Nd content. The water adsorption enthalpy and coverage found to increases with the dopant level, which implies on increasing surface enthalpies and production of hydrogen. Interestingly, the measured surface enthalpies via differential scanning calorimetric method found to decrease with Nd content, and the grain size after coarsening decreased as well. The reasons for this behavior will be discussed.

Recently, hydrogen has attracted a lot of interest as a promising energy carrier. However, the storage and transportation of hydrogen are difficult issues because of its low volumetric density and boiling point. Thus, ammonia has received much attention as the alternative fuel source due to its high hydrogen capacity and ease in liquefaction. In addition, the hydrogen generation via ammonia decomposition does not emit CO and CO₂. In previous reports, Ru catalysts are known to be the most active for the ammonia decomposition [1]. However, the availability of precious metal is limited. Then, nickel is regarded as a prospective catalyst in recent years.
In this work, we developed Ni catalysts supported on rare-earth oxides (Ni loading: 10-40wt.%) by the impregnation method, and evaluated their catalytic activity for the ammonia decomposition. As the characterization, CO pulse measurement, XRD analysis, and NH₃ temperature programmed surface reaction (NH₃-TPSR) were conducted.
Among the Ni catalysts supported on various metal oxides, the Ni/Y₂O₃ catalyst exhibited the highest activity (conversion: 85% at 5500C). The CO pulse measurement elucidated the Ni/Y₂O₃ catalyst had relatively high Ni surface area despite the small surface area of Y₂O₃ support (7 m²/g). This indicated that the Y₂O₃ support was highly effective for the Ni dispersion. The dependence of the reaction rate on hydrogen partial pressure was investigated by the kinetics analysis since hydrogen atoms adsorb on the active sites of Ni surface [2]. The reaction order of hydrogen partial pressure was negative for all the catalysts, implying the lowering of the performance by the hydrogen atoms adsorbed on the active sites. The absolute value of hydrogen order for rare-earth oxide-supported Ni catalysts was relatively small. This suggests the negative effect of hydrogen would be effectively alleviated in these Ni catalysts. This should be one of the important factors derived from the support effect of rare-earth oxide. Besides, the hydrogen desorption behavior of Ni/Y₂O₃ and Ni/Al₂O₃ by NH₃-TPSR measurement demonstrated that the amount of hydrogen atoms strongly-adsorbed on Ni surface was smaller for Ni/Y₂O₃. This phenomenon supported the result of the kinetics analysis.
[1] S. F. Yin, B. Q. Xu, X. P. Zhou, C. T. Au, Appl. Catal. A: Gen. 277 (2004) 1-9.
[2] M. C. J. Bradford, P. E. Fanning, M. A. Vannice, J. Catal. 172 (1997) 479-484.

Complex oxide perovskites such as LaCoO₃/LaFeO₃ solid solutions doped with Sr are highly promising materials for mixed ionic and electronic conducting cathodes in intermediate temperature solid oxide fuel cells. To improve the efficiency of the catalytic oxygen reduction reaction, nano-structured materials are advantageous as they increase the surface area to volume ratio and facilitate oxygen ion diffusion to the electrolyte. One problem in understanding this class of material is that their structure is not accessible by experiment. In light of this shortfall, theoretical studies prove invaluable as they provide essential structural data to be utilised. Using our in-house developed Knowledge-Led Master Code (KLMC) program suite we have predicted the lowest energy structures of LaCoO₃ and LaFeO₃ nanoclusters over a range of particle size. We determined the structures using the global optimisation module of KLMC, employing our innovative Genetic Algorithm, and characterised them according to their electronic properties. Our results provide a suitable framework to allow the development of more realistic catalytic models.

The Born-Oppenheimer approximation has been widely used in molecular dynamics to obtain insight into processes in heterogeneous catalysis for a broad range of surfaces and reactants. In transition metal catalysis, however, the large density of states at the Fermi level and rapid changes in ground-state electronic character due to bond cleavage/formation can give rise to significant electronic excitations in the metal, violating the Born-Oppenheimer approximation. These effects alter adsorbate motion and change the potential energy surface. We explore the extent of this energy transfer and the effects on the potential energy surface for molecular processes relevant to sustainable catalysis, including H₂ dissociation on Cu(111).
Our calculations use real-time propagation of the Kohn-Sham equations from density functional theory (DFT). Based on the SIESTA DFT code, numeric atomic orbital basis sets and the frozen core approximation are used for computational efficiency. The KS equations are integrated self-consistently by calculating the time evolution operator using Padé approximants. Atomic motion is handled using Ehrenfest dynamics, with forces calculated from the self-consistent electronic density at each time step. This ab initio approach can handle both strong nonadiabatic effects and the full details of atomic motion. Due to the efficiency of SIESTA's basis set and the Padé approximants, as well as MPI parallelization, we can carry out these calculations with many hundreds of atoms with relatively modest computational resources.

Direct use of natural gas as fuel has been a grand challenge in the field of low-temperature solid oxide fuel cells (LT-SOFCs). In addition to high electronic conductivity and stable morphology, an ideal anode for direct methane oxidation must also have a high catalytic activity for C-H bond breaking and a high resistance to coke formation. Here we present results from on-going studies on non-noble carbide-based systems for catalyzing methane-rich fuels in LT-SOFCs. The chemical stability of carbides under methane-rich fuels was investigated from thermodynamic analyses and correlated to experiments by X-ray photoelectron spectroscopy. The electrochemical performance of LT-SOFCs with carbide-based anodes under methane-rich fuels was evaluated, and we will present a critical discussion on the use of carbides as electrodes under extreme chemical potential gradients including in the presence of steam.

As a precursor to fabricate many other materials, methanal (CH₂O) is one of the most important chemical compounds in industry. Currently the large consumption of methanal synthesis mainly relies on the catalytic oxidation of methanol (CH₃OH) by employing metal catalysts: 2 CH₃OH + O₂ → 2 CH₂O + 2 H₂O. In this reaction, the resultant of water is indeed undesirable. It is notable that ethanol (CH₃CH₂OH) can decompose with two H atoms removed while no water produced on Cu; however, such decomposition reaction cannot happen for methanol on Cu at similar experimental conditions. In this work, by using density functional theory calculations, we carefully investigate the activation energies for ethanol and methanol, and thus identify the possible mechanisms for their contrasting decomposition behaviors. We find that the van der Waals interactions play a significant role in the corresponding thermodynamic and kinetic processes. Based on the above understanding, we further discuss the feasible reaction pathways for the industrial fabrication of methanal with lower cost. The present study provides insight into the design of cheap metal catalysts for their future applications in energy.

New catalysts capable of selective conversion under mild conditions could dramatically decrease the energy demands of the chemical industry. Nanoporous Au, a nanostructured material with 2 to 3% Ag, is capable of highly selective (~100% in some cases) oxidation under mild conditions with high stability. The dissociation of O₂ is the most critical step in many oxidation processes on nanoporous Au, yet the active site for O₂ dissociation is unknown. Here, we performed a careful search for structures that can both form under reaction conditions and are able to dissociate O₂.
We predict that the terraces are Au-terminated under reaction conditions, and hence are unlikely to dissociate O₂. However, step sites likely can dissociate O₂: under reaction conditions, Ag is most stable in the rows next to the step sites, and the barrier to O₂ dissociation on these structures is lower than on pure Au. Our findings may explain the high activity and high selectivity of nanoporous Au, as these mixed-metal step sites can likely dissociate O₂ (unlike pure Au) but are likely to remain selective for oxidation processes (unlike pure Ag).

Currently, energy resource is depending on the fossil fuels. So, the dispersion of energy resource for electricity or vehicle is required. Polymer electrolyte fuel cell is an expected source for residential energy and vehicle power because of its low operation temperature and non-toxic property. However, a catalyst is necessary for the oxygen reduction reaction (ORR) at the cathode. Platinum-group metals are critical to catalyzing reactions in the PEFC, but they are rare metal. So, the non-platinum group metals are required for the alternative catalyst. In order to develop the novel catalyst, the guideline for novel catalyst design is necessary, however it has not been clear yet. Then specific guideline based on electric theory should be proposed by the theoretical calculation.
In this study, we suggest new catalyst for ORR by the first principle analysis about the electric states unique to platinum. The 13-atom metal nanocluster of platinum, gold, copper are calculated by Density Functional Theory (DFT) calculation. Unrestricted DFT calculation was conducted by Gaussian09 program. All calculations were performed based on PW91 exchange-correlation functional. The basis set for metal atoms was LanL2DZ, and for oxygen and hydrogen was 6-311+G(2df,2p).
The electric states of the oxygen adsorbed structures are greatly different by the elements. In the case of copper, oxygen made strong bonds, on the other hand, gold did not make bond with oxygen. In the case of platinum, platinum also form bonding orbital, but electric states between platinum and oxygen is different from other elements in that the bonding orbital electrons are delocalized, then the oxygen electrons interact with many electrons. In addition, we analyzed density of states of various metal nanocluster with different element and categorized it into some groups by its electric states. From this classification, we suggest some niobium compounds as alternative catalyst.

The development of new technologies for sustainable energy production has received increasing attention due to the need for energy gain and reduction of environmental impacts. In this context, hydrogen production by water electrolysis is a promising route for green energy production. Hydrogen Evolution Reaction (HER) is normally catalyzed by noble metals as platinum (Pt), and the replacement of Pt by inexpensive and abundant catalysts compound is desirable. One non-precious-metal alternative to Pt is nickel phosphide (Ni₂P) that has good catalytic activity for HER. In this work, we synthesized Ni₂P nanoparticles in a reaction assisted by microwave (MW), decreasing the temperature and the reaction time when compared with traditional methods reported in the literature. The reaction was performed in a microwave oven and the solution was heated at 300 °C during 28 min. X-ray diffraction analysis of the as-prepared material showed the Ni₂P phase formation, and the transmission electron microscopy analysis confirmed the presence of this phase with nanometric characteristics. We have investigated also the electrocatalytic HER activities of the Ni₂P. A primary and qualitative analysis reveals an overpotential of 150 mV at cathodic current densities of 10 mA/cm² for Ni₂P obtained by microwave heating. In conclusion, we have developed a very selective synthetic route to process nickel phosphide (Ni₂P) under milder conditions than others works, by using MW heating. Finally, the Ni₂P exhibited high electrocatalytic activity in HER. We have shown that the synthetic route is simple, versatile and can be extended to other transition metal on synthesis of phosphides.

Lithium oxygen batteries are devices based on lithium conversion chemistries that offer higher energy densities than lithium ion batteries. However, existing lithium oxygen batteries with carbon electrodes in ether based electrolytes only allow for battery operation with limited capacities, exhibit poor stabilities and feature low round-trip efficiencies. Solving these challenges requires detailed understandings of the mechanisms underlying various degradation chemistries, including those of the electrolyte and the carbon support. It is also equally important to understand potential synergistic effect between electrolyte decomposition and the electrode decomposition. We show in this presentation that such goal is possible by protecting the carbon support with a conformal coating of stable inorganic thin film. More specifically, we designed, synthesized, and studied three dimensionally ordered mesoporous (3DOm) carbon by growing a thin layer of FeO_x using atomic layer deposition (ALD). When compared to bare carbon, electrodes with uniform coating of FeO_x proved highly effective in minimizing parasitic reactions, reducing operation overpotentials and boosting battery lifetimes. For enhanced oxygen reduction activities, Pd nanoparticles were also added by a separate ALD process. Collectively, the FeO_x protection and Pd catalyst improved the cyclability from 16 to 68, representing one of the best carbon-based electrode systems tested with proven evidence of O₂ reduction and oxidation.
A second strategy we present is to introduce an electrolyte more stable than traditional ether based ones. Ionic liquids were employed for this purpose. The superior stability and binding ability of ionic liquids permits the formation and decomposition of Li₂O₂ to take place following a highly unique 1-electron mechanism. As a result, significant improvement in round trip efficiencies and cycle lifetime was measured. This body of research highlights the importance of detailed studies of the catalysis on a nanometer scale for advanced energy storage applications.

Alloy nanoparticles are an important class of heterogeneous catalysts due to their remarkable catalytic performance that arises from the synergy between multiple metal components. Despite the fact that most alloy nanoparticles are synthesized in solution, the catalytic application of alloy nanoparticles often requires their integration on surfaces. Herein, we present a method that utilizes scanning probe block copolymer lithography (SPBCL) to make and position alloy nanoparticles on surface. The scope of this method was studied with combinations of Au, Ag, Pd, Ni, Co, and Pt. Specifically, we find that if the metals are miscible, alloy nanoparticles with a well-defined elemental ratio and even distribution of atoms can be synthesized. If the metals are immiscible, phase-segregated binary particles of well-defined and deliberately controlled size are obtained. The catalytic activity of one class of AuPd alloy nanoparticle made via this method was evaluated with respect to the reduction of 4-nitrophenol. In addition to being the first catalytic studies of particles made by SPBCL, this work sets the stage for using SPBCL as a novel method for studying the fundamental science and potential applications of alloy nanoparticles in areas such as heterogeneous catalysis.

Several parameters control the transport of photogenerated charges in a semiconductor, such as, light absorption, interface charge transfer, electron hole couple recombination, surface area and porosity. The pulsed electron deposition technique (PED) allow to obtain films without porous and with good semiconductor/conductor interface. We used PED, spin coating and doctor blade technique to obtain TiO₂ films with different thickness and porosity. Films were studied in a photoelectrochemical cell, under radiation AM1.5G, for water splitting. We have observed that, the photocurrent density is 40 higher for a compact and planar films prepared by PED than for a mesoporous films prepared by spin coating of a solution or dispersion.
Theses results suggest that the photocurrent in the water splitting process is controlled by electron-role recombination process. Besides, the use of high surface area is not a good way to improve the photocurrent in the TiO₂ photoanode.

Proton exchange membrane fuel cells have drawn great attention and been taken as a promising alternated energy source because of the high power output density, low operation temperature and “green” byproduct. One of the reasons that hamper the wider application of PEM fuel cell is the catalytic poison effect from the impurity of the gas flow, like CO. Haruta and Yates have predicted that gold nanoparticles that are platelet shaped and have direct contact with the metal oxide substrate to be the perfect catalysts of the CO oxidization, yet the synthesis method is difficult to apply in the Fuel Cell.
In our experiment, hydrophobic, thiol-functionalized gold nanoparticles were synthesized through two-phase method developed by Brust et al. We previously developed a technique to reproducibly form an Au nanoparticles layers with three atomic layers thick at the air water interface. Then we deposit these Au particles with stepped surface directly onto the Nafion membrane in the PEM fuel cell by Langmuir-Blodgett method, resulting in over 50% enhancement of the efficiency of the fuel cell. Furthermore, DFT calculation demonstrate this kind of enhancement occurs only when the particles are in direct surface contact with the membrane, where they work together with sulfonic groups to oxidize CO back to CO₂, and does not occur when the Nanoparticles are incorporated into the electrodes.

Electrocatalysis plays a key role in the renewable energy technologies that have been developed to lessen our reliance on fossil fuels¹. However, the best electrocatalysts for these processes—which include the hydrogen evolution reaction (HER), the oxygen reduction reaction (ORR), and the oxygen evolution reaction (OER)—often contain scarce and expensive noble metals, substantially limiting the potential for these technologies to compete with fossil fuels. The considerable challenge is to develop robust electrocatalysts composed exclusively of low-cost, earth-abundant elements that exhibit activity comparable to that of the noble metals. Herein, we report, cobalt selenide based nanostructured catalyst which exhibits significant catalytic activities towards ORR, OER and HER and is much more cost-effective that the precious metals and their oxides.
The Co-selenide based electrocatalysts were prepared by electrodeposition² on various conducting electrodes including Au-coated glass, Au-coated Si, and glassy carbon (GC). Bulk quantities of Au-CoSe nanostructures were also synthesized through high temperature CVD reactions. These catalysts were found to be highly active for the ORR, OER and HER reactions in alkaline media showing onset potential at 1.56 V, 0.78 V and -0.08 V (vs RHE) for OER, ORR and HER, respectively. The catalysts were characterized using TEM, SEM, EDX, XRD and XPS for structure, morphology, elemental compositions, and electronic states. Catalytic activity was studied from detailed electrochemical measurements including linear sweep voltammetry, chronopotentiometry, rotating disk electrode and electrochemical surface area. The detailed results will be presented in the meeting.
References:
1. H.J. Choi, S.M. Jung, J.M. Seo, D.W. Chang, L. Dai, J.B. Baek, Nano Energy, 2012, 1, 534.
2. Z. Zhang, S. Pang, H. Xu, Z. Yang, X. Zhang, Z. Liu, X. Wang, X. Zhou, S. Dong, X. Chen, L. Gud and G. Cui, RSC Advances, 2013, 3, 16528.

The (GaN)_1-x(ZnO)_x solid solution is one of the most effective single particle semiconductor systems for driving overall water splitting using visible light. However, the maximum quantum reported efficiency for overall water splitting with visible light is still low (~6%), even after extensive studies to optimize synthesis conditions and co-catalyst usage [1]. We have therefore reinvestigated this system in order to systematically investigate the influence of composition on the key physical properties that most strongly influence the photoelectrochemical performance of this system. Homogenous powders were synthesized and characterized over a much wider range of compositions (0.2 < x < 0.95) than in previous studies. Furthermore, our synthesis methods minimize Zn evaporation and can be used to “dial in” specific target compositions, in contrast to prior work. The dependence of band gap on composition has been investigated through diffuse reflectance measurements, and it is found that the minimum band gap for this system occurs near x = 0.60. Using newly developed methods, we are for the first time able to estimate the absolute absorption coefficient of this system from diffuse reflectance data. Furthermore, the below-gap optical response associated with free carriers has been identified and is found to be strongest in the most Zn-rich samples. Appropriate annealing conditions suitable for gradually suppressing the free carrier response have been identified. This suggests that it is should be possible to systematically control the free carrier concentration within this system.
[1] Xiong, Anke, et al. European Journal of Inorganic Chemistry 2014.4 (2014): 767-772.

The Sabatier reaction is a promising route to the large-scale production of synthetic methane, either as a long-term perspective aiming at converting hydrogen produced with renewable energies and CO₂ captured from the processes or even from the atmosphere, or as a short-term approach consisting in upgrading the composition of biogas to natural gas standards. Although this reaction is thermodynamically feasible with a high yield, kinetic barriers hinder its effectiveness. The catalysis method considered must fulfill durability criteria, one of the most critical being the recurrent problem of deterioration of the Ni catalyst by coking [1] and sulfur poisoning [2]. Particularly the first aspect - the coking - is a challenge when using the so-called sorption enhanced CO₂ methanation process. Here, the Sabatier reaction catalyzed by Ni nanoparticles is enhanced by the active removal of one product, i.e. by absorbing water due to Le Chacirc;telier&’s principle. Such a sorption catalyst consists of Ni nanoparticles in a nanoporous water sorbent (zeolite 5A), which removes water from the reaction centers [3]. The sorption catalyst shows superior activity but deactivates due to coking, both effects due to the fact that the water partial pressure is low. The effect is studied in-situ under different reaction conditions, by means of gravimetric measurements using a magnetic suspension balance in combination with infrared gas analysis. These experiments - combined with a thorough characterization of the coked catalysts (SEM, EDX, X-ray, XPS) - enabled optimizing the reaction conditions and studying the coking phenomenon with respect to parameters such as gas composition, operation time and temperature. To overcome the degradation of the catalysts, we utilize redox cycles leading to a restructuring of the surface and removal of the contaminants. The redox-regeneration is easily implemented in the water desorption step required for sorption catalysts.
The output of this fundamental study led to the design of a portable, lab-scale multi-bed reactor stack, with a target of 1 kW power.
[1] J. Goacute;ralski, J. Grams, T. Paryjczak and I. Rze#378;nicka, Carbon 40 (2002) 2021-2040.
[2] J. K. Dunleavy, Platin. Met. Rev. 50 (2006) 110.
[3] A. Borgschulte, N. Gallandat, B. Probst, R. Suter, E. Callini, D. Ferri, Y. Arroyo, R. Erni, H. Greeling and A. Züttel, Phys. Chem. Chem. Phys. 15 (2013) 9620-9625.

Renewable energy technologies, such as fuel cells and metal-air batteries, are promising for clean energy sources. In these energy devices, oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are crucial to the efficiency of the energy conversion and storage. However, these two reactions are sluggish; catalysts are needed to catalyze these reactions. Currently, platinum is used to catalyze these reactions in fuel cells and metal-air batteries, but the high cost and scarcity of the platinum hinder their commercialization. Doped graphene is a new option for the catalysts since it is much cheaper than Pt and among the earth-abundant elements. A number of elements (N, P, S, B and the like) were used to dope graphene to tailor its electronic structure and electrocatalytic properties. In this study, the first-principles simulations were performed for N, and P single doped and N,P co-doped graphene. We simulated the elementary reactions on different doped graphene structures with different dopant positions The results show that N-doping can lower the overpotentials of the OER and ORR, while N and P co-doping can further lower the overpotential of OER and ORR. Adsorption energies plots were drawn to derive the ideal minimum overpotentials. Their relationship clearly shows a volcano shape, from which the best catalyst can be identified. Effective charge distribution was also analyzed to show how charge density difference can influence the active sites on the graphene. The co-doped graphene has more charge transfer inside graphene thus generate more active sites. In addition, the distance from the dopant to the edge, as well as that from the active sites to the edge, play an important role in OER and ORR. The dopant and active sites near the edges show the better catalytic activities. The predictions were compared with experimental work.

The application of a protective coating on metallic interconnections is necessary to prevent Cr-poisoning in solid oxide fuel cells (SOFCs). In this study, nano-sized powders of copper manganese spinels were synthesized by glycine nitrate combustion process (GNP) and then were deposited on Crofer 22 APU by electrophoretic deposition (EPD) method. During the EPD deposition process, the effects of different parameters (concentration of the charged particles, voltage and time) and subsequent reduction and compaction process were studied. The effectiveness of the coating layer as a barrier to prevent the outward diffusion of chromium and inward diffusion of oxygen was evaluated by energy dispersive spectroscopy (EDS) and thermo-gravimetric measurements. A DC four-probe setup was used to measure the area specific resistance (ASR) of the coated samples.

Pt catalysts have been extensively employed in the electrode of electrocatalytic energy-conversion devices. However, the use of Pt catalysts is severely limited because of high cost and limited resources. Consequently, the design of novel catalysts requires not only reducing the amount of Pt used but also enhancing catalytic activity. The stability for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) on both anode and cathode of proton exchange membrane fuel cells is critical. It has been recognized that metallic core@shell nanostructures have numerous advantages, including distinctly different properties and potential uses in electronics, magnetics, catalysts, optics, and sensors. Their versatility in a wide range of applications stems from their unique physical and chemical properties. Composites consisting of polymers and metal nanoparticles are of great interest due to their combined properties with improved dispersion of metal nanoparticles and high surface area. Conducting polymers can be widely used in many applications because of their unique π-conjugated structure, which lead to electrochemical stability, high stability, high conductivity, easy synthesis, higher hydrophilic property, reversible electrochemical and physical properties controlled by its oxidation state and protonation.
In this presentation, we suggest a unique strategy to generate core@shell nanoparticles based on AuNPs decorated with polymer layer which can serve as templates for tailored nanostructures. Concretely, AuNPs having electroactive polymer shell on the surface were first fabricated. Then, they were mixed with selected transition metal precursors and platinum precursor solutions followed by reduction using reducing agent. The metal NPs thus incorporated were distributed uniformly in the polymer shells. We systematically investigated the structural development during the sequential synthetic process and compared the performance with respect to metal-decorated core-shell nanostructures. The core-shell nanostructures showed a viable and efficient bifunctional electrocatalytic activity for both ORR and MOR in electrodes of fuel cell or battery.

The molybdenum sulfide for electrochemical hydrogen evolution reaction (HER) is the most promising material to replace Pt catalyst. In this work, we synthesized MoS₃ nanoparticles by facile solution process at room temperature and simultaneously reduced the graphene oxide (GO). As synthesized MoS₃ nanoparticles having approximately 40 nm diameter were decorated to the reduced graphene oxide. The GO/MoS₃ nanocomposite shows excellent electrochemical HER activity with low overpotential (~0.1 V), high current density, and Tafel slope as small as 41 mV/decade, because of its highly exposed edges of amorphous MoS₃ and great electrical conductivity of reduced graphene oxide.

Splitting water to generate hydrogen fuel and oxygen through hydrogen evolution (HER) and oxygen evolution (OER) reactions, respectively, is considered to be clean and sustainable energy technology and an alternative for fossil fuels. However, large scale elctrochemical water splitting is a kinetically sluggish mainly because of the slow OER process which necessitates 4 electron conversion and O=O bond formation. Typically, catalysts are used to address this great challenge and make the process more efficient. Herein we report, identification of a highly active Ni₃Se₂ electrocatalyst for oxygen evolution in alkaline condition. The Ni₃Se₂ phase has a structure similar to the sulfur mineral Heazlewoodite, which contains metal - metal bonding. The electrocatalytic activities of Ni₃Se₂ towards OER was seen to be at par with or even superior to the transition metal oxide based electrocatalyst in terms of onset overpotential for O₂ evolution as well as overpotential to reach a current density of 10 mA/cm² (observed at 220 mV).
The electrocatalytic Ni₃Se₂ were grown by electrodeposition on conducting substrates and the deposition parameters including pH of the electrolytic bath, deposition potential, and substrate composition, as well as choice of Ni- and Se-precursors were seen to have some influence on the catalytic activity. In addition to low overpotentials, these Ni₃Se₂ electrodeposited films were seen to be exceptionally stable under conditions of continuous O₂ evolution for period (~24 h). The structure and morphology of these films has been characterized with powder X-ray diffraction, Scanning and Transmission electron microscopy, Raman, and X-ray photoelectron spectroscopy. We will discuss in detail the electrochemical and structural characterizations of these films along with catalytic activities.

Over the last several decades water oxidation has been investigated in pursuit of clean, sustainable and efficient energy conversion and a substitute for fossil fuels. During water oxidation, oxygen evolution reaction (OER) plays a critical role in the advancement of renewable energy technologies like metal-air batteries or solar-to-fuel energy production. However, OER involving a complex 4 electron process, has several steps that have large reaction barriers, which lead to large required overpotentials.¹ Recently we have observed that the family of Ni-chalcogenides can function as more-efficient, stable, earth-abundant electrocatalysts for the OER reaction in alkaline medium with low overpotential thus enhancing the energy conversion efficiency.¹ Interestingly, Ni is always found in combination with iron (Fe) on earth and Fe impurities in the nickel hydroxide (Ni(OH)₂) electrodes can cause destructive effects on Ni-based alkaline batteries by greatly lowering the OER overpotential.³ This phenomenon inspired us to investigate the influence of Fe content and synthesizing a NiFe-composite compounds in order to obtain better OER electrocatalysts. Here we report, for the first time, a nickelminus;iron selenide (Ni_1-xFe_xSe_y) thin film with high OER catalytic activity and stability.
The electrocatalysts Ni_xFe_1-xSe_y were grown by electrodeposition on conducting substrates and detailed electrochemical studies with stationary as well as rotating disc electrodes were performed to investigate the catalytic efficiencies. The deposition parameters including pH of the electrolytic bath, deposition potential were seen to have some influence on the catalytic activity. In some compositions these transition metal mixed chalcogenides even outperform the noble metal and oxide based catalysts like IrO₂, RuO_x and NiO_x. Our studies indicate that the overpotential for producing 10 mA/cm² current density under oxygen evolution conditions can be achieved to be as low as 210 mV by optimizing the ternary composition of the selenide films and tuning the structural details. In addition to low overpotentials, these Ni_xFe_1-xSe_y electrodeposited films were seen to be exceptionally stable under conditions of continuous O₂ evolution for extended period (>24 h). We will present a systematic study of investigating the OER catalytic efficiencies of the ternary chalcogenides, Nishy;_1-xFe_xSe_y and their detailed characterization with powder X-ray diffraction, scanning and transmission electron microscopy, Raman, and X-ray photoelectron spectroscopy.
References:
1. E. Mirzakulova, R. Khatmullin, J. Walpita, T. Corrigan, N. M. Vargas-Barbosa, S. Vyas, S. Oottikkal, S. F. Manzer, C. M. Hadad, and K. D. Glusac, Nature Chem. 2012, 4, 794.
2 McCrory, C. C. L.; Jung, S. H.; Peters, J. C.; Jaramillo, T. F. J. Am. Chem. Soc. 2013, 135, 16977.
3. Munshi, M. Z. A.; Tseung, A. C. C.; Parker, J. J. Appl. Electrochem. 1985, 15, 711.

Carbon Dioxide (CO₂) is one of the major greenhouse gases and its amount in the atmosphere is sharply increasing due to the extensive use of the fossil fuels. In recent years, photocatalytic reduction of CO₂ is of great interest because of its ability to convert CO₂ in to valuable energy products such as CO, CH₄ and other hydrocarbons. Because of the well-known superior photocatalytic properties, titanium dioxide (TiO₂) nanostructures have shown great promises in several green energy applications, such as hydrogen generation by water splitting, water purification and CO₂ photoreduction. Fabrication of TiO₂ nanostructures in a controllable manner is very important to understand the photocatalytic properties of such nanostructures. In this research work, we have fabricated TiO₂ nanorods samples on glass substrates using glancing angle deposition (GLAD). GLAD is a physical vapor deposition (PVD) technique, known for high reproducibility of nanostructured samples. After annealing these samples for half an hour at 500 ^oC, the XRD spectra confirms the presence of anatase phase. Photocatalytic reactions on the TiOshy;₂ nanorods samples were carried out in the presence of CO₂ and water vapors in a small chamber. It has a quartz window for UV illumination with a UV lamp of 100 W. The reaction products were analyzed using a gas chromatograph equipped with thermal conductivity detector (TCD). Carbon monoxide (CO) was found to be the major product of the photocatalytic reaction. Significant conversion rate was found ~ 43 µmol-hr^-1 for nanorods of length 1.2 µm and diameter ~ 130 nm on the samples with area 3.75 cm².
References:
1. Varghese, O. K.; Paulose, M.; La Tempa, T. J.; Grimes, C. A. Nano Lett. 2009, 9, 731-737.
2. Liu, L. J.; Zhao, H. L.; Andino, J. M.; Li, Y. ACS Catal. 2012, 2, 1817minus;1828.
3. Dhakshinamoorthy, A.; Navalon, S.; Corma, A.; Garcia, H. Energy Environ. Sci. 2012, 5, 9217-9233
4. Wang, W. N.; An, W. J.; Ramalingam, B.; Mukherjee, S.; Niedzwiedzki, D. M.; Gangopadhyay, S.; Biswas, P. J. Am. Chem. Soc. 2012, 134, 11276-11281
5. Fang, B.; Bonakdarpour, A.; Reilly, K.; Xing, Y.; Taghipour, F.; Wilkinson, D. P. ACS Appl. Mater. Interfaces 2014, 6, 15488minus;98.

Development of metal-free catalysts is of huge interest for photocatalytic water splitting using solar energy. Here, we report a composite nano-material consisting of sulfur-incorporated graphitic carbon nitride grown on the surface of sulfur/selenium co-doped graphene (CNS:S-Se-Gr) hybrid as a high-performance metal-free photocatalyst for the degradation of methylene blue (MB) and hydrogen evolution (by water splitting) under visible light illumination in the presence of sacrificial donors. The photocatalytic H₂ evolution activity of the projected CNS:S-Se-Gr hybrid was tested and compared in sodium sulfite and lactic acid solutions. The achieved highest hydrogen evolution rates for CNS:S-Se-Gr hybrid in sodium sulfite and lactic acid solution are about 1.58 and 2.59 mmol#8729;g^-1#8729;h^-1 respectively. This hybrid material exhibits significantly enhanced photocatalytic H₂ evolution activity compared with that of pristine g-C₃N₄ and Pt/g-C₃N₄. Also, we proposed a possible mechanism for charge separation and transfer in CNS:S-Se-Gr hybrid catalysts to explain the enhanced photocatalytic HER performance. These results suggest that the CNS:S-Se-Gr metal-free hybrid has great potential as a promising photocatalyst for the water splitting.

Photocatalytic activity draws much attention because it can generate useful chemical fuel using sunlight. Artificial photosynthesis usually turns one of the greenhouse gases, CO₂ gas into methane, carbon monoxide and so on. CO₂ is quite stable molecule and its reduction process requires several steps in the plants' photosynthesis. TiO₂ is one of the abundant material in Earth, and its photocatalytic activity is widely used for various applications. Using Aerosol-Assisted Chemical Vapor Depostion (AACVD), structured TiO₂ thin film can be easily fabricated. Adding colloidal self-assembly technique to those film making process, we can generate hiearchical structure of TiO₂. Sphere particle monolayer can be a template for such structure.
Colloidal solution of sherical particle in several micrometer size was prepared. Solution evaporation occurs when the colloidal solution is casted on proper substrate. Hexagonal-closed packed structure arises after the evaporation. AACVD of TiO₂ over the template shows hiearchical structure with ease. Around 400°C, the substrate was heated to develop culumnar crystal structure of metal oxide. In this experiment, anatase[101] was most dominant crystal orientation as XRD analysis. Upon Xe lamp radiation during CO₂ gas injection to the substrate, CH₄ was observed during supplying H₂O vapor to the chamber.
Applying these combination of techniques, we can easily obtain metal oxide nanostructure other than TiO₂ with proper metal oxide precursor. Precursor flowrate, deposition temperature, and deposition time are experimental variables for obtaining proper characteristics of fabricated film. Ion injection to the AACVD chamber can also change film morphology. Complicated structure of TiO₂ can be applied to generate superhydrophilic property.
Utilizing CO₂ gas is important because we can reduce greenhouse gas and we can obtain energy simultaneously by using sustainable energy, sunlight. Recently, various research were reported to enhancing the efficiency of photocatalytic reaction. These approach to solar energy would give us great chance to have sustainable energy cycle.
Acknowledgement
This research is supported by the Eco-Innovation Project operated by the Korea Ministry of the Environment, as well as supported by Internal Research Funding Program of Korea Institute of Machinery and Materials (KM3410).

Solid-state electrochemical devices such as fuel cells, water-splitting electrolysis cells, and metal-air batteries have received much attentions as alternative clean power generators with renewable fuel productions. However, there is still strong demand for improving cell performances in terms of the efficiency and stability. In particular, slow kinetics of oxygen reduction (ORR) and evolution reactions (OER) are one of the significant technical issues for fuel cells and water-splitting cells, respectively. In order to improve catalytic activity of oxygen electrodes of electrochemical cells, perovskite structure-based oxides have been considered as candidate materials for oxygen electrodes due to high oxygen ion diffusivity and surface exchange coefficient. For example, single perovskite-structured materials including Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ and La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ present the high performance for solid oxide fuel cells (SOFCs) at the intermediate temperature (IT). Furthermore, these materials are chosen as the oxygen electrode for water-splitting electrolysis cells and provide sufficient possibility to produce both oxygen and hydrogen. However, they still need to improve for making commercialization of electrochemical devices in terms of durability and performance. Recently, double perovskite structured materials have much attentions due to their excellent catalytic properties such as oxygen ion diffusivity and surface exchange coefficient for IT-SOFCs and water-splitting electrolysis cells.
For these reasons, in this work, several single and double perovskite-structured materials investigate and compare to improve performance and durability of electrochemical cells. Electrochemical cell performances in power density and durability are measured at intermediate temperature (550-650^oC) by using anode supported-type cells under both fuel cell and electrolysis cell modes. For the SOFC mode, humidified H₂ and dry air are supplied into each chambers and then electrochemical performance such as I-V characteristic is measured under different operating temperatures by Potentiostat/Galvanostat instrument (SP150, BioLogic).

Fuel cells are a promising candidate to emerge as an environmentally friendly alternative to internal combustion engines in applications such as automobiles; however, there are several materials-related challenges that still need to be addressed in order to improve cost, performance and durability of fuel cells. Currently, proton-exchange membrane fuel cells (PEMFC) use carbon black as a catalyst support, but carbon is not thermodynamically stable at operating conditions leading to corrosion at rates determined by the specifics of use. In addition, the carbon support can be oxidized on the anode side in the case of fuel starvation. Corrosion of the carbon support results in issues such as detachment and coalescence of catalyst particles lowering the efficiency and lifetime of fuel cell stacks.
Mesoporous mixed metal oxynitrides of various compositions (Ti_xTa_yAl_zN_1-δO_γ) were prepared by a co-precipitation method and subsequent ammonolysis at 800 - 950 ^oC. The products crystallized in the rock salt structure over wide range of compositions. It was shown that addition of secondary metals to TiN, is beneficial in improving chemical and electrochemical stability without significant decrease of the electrical conductivity of the pressed powders. Platinum particles were successfully dispersed and bound to these oxynitrides and they were shown to be viable catalyst support for the oxygen reduction reaction under acidic condition.

Composites of Pd-Cu bimetallic nanoparticles were used as counter electrodes for dye-sensitized solar cells. These composites show good electrocatalytic acivity toward the catalyzing the Co³⁺ reduction at the counter electrode/electrolyte interface. Simple solution coating followed by a post thermal treatment was employed for the preparation of the counter electrodes. Cyclic voltammmograms and Tafel polarization measurements revealed the excellent electrocatalytic activity of bimetallic Pd-Cu composite electrode than that of standard Pt electrode. Electrochemical Impedance study showed that the comparable charge transfer resistance of Pd-Cu electrode compared to Pt based counter electrode. Scanning electron microscopy characterizations showed that FTO layer was covered by Pd-Cu nanoparticle composite and the distribution of PdCu nanoparticle was uniform. Under AM 1.5 simulated solar light (100 mW/cm²), the dye-sensitized solar cell fabricated with PdCu bimetallic nanoparticles counter electrodes exhibited a power conversion efficiency which is comparable to that of the cell based on the sputtered Pt counter electrode.

Zinc oxide is a semiconductor whose properties make it an attractive material for potentially used in microelectronics, optoelectronics and laser technology. Upon alloying with Co and other transition metals ZnO also exhibits room temperature ferromagnetic properties with enhanced functionalities when used in thin film devices. Zinc oxides-supported cobalt (Co⁰) nanocomposites are important materials with excellent catalytic properties making it an interesting material for use as an efficient catalyst in many important reactive processes such as Fischer Tropsch synthesis (FTS)[1], photocatalysis [2] and steam reforming [3].
In the present work, we report on the preparation of Co:ZnO thin films nano-composites via pulsed electron beam ablation (PEBA) from a single target (Co:ZnO) containing 20% Co and on Al₂O₃ (0001) and Si (100) substrates. To the best of our knowledge, no study on the synthesis and characterization of Co:ZnO nano-composites has been carried out so far using PEBA. The films have been deposited at various temperatures (350⁰C, 400⁰C, 450⁰C) and pulse frequencies (2 Hz, 4 Hz), and under a background Ar pressure of 3 mtorr and an accelerating voltage of 14 kV. The prepared nano composites have been characterized via a variety of analytical techniques in order to assess the quality of the films. The thickness of the deposited films is in the range of 100-250 nm as revealed through visible reflectance spectroscopy. The surface morphology has been examined by SEM and AFM and shows particles with size in the range of 40-250 nm. The Co 2p3/2 peaks reveal that the deposited films contain CoO (binding energy = 780 eV) as well as metallic Co (binding energy = 778.1 to 778.5 eV). XRD analysis also supports the presence of metallic Co hcp phase (2#1012; = 44.762) in the films. The SEM-EDX analysis reveals that deposition is congruent and the prepared films contain ~19 % cobalt. It is anticipated that the deposited nano-composites will prove to be efficient nano-materials for the synthesis of substituted liquid fuels from syngas via FTS.
Keywords: Co:ZnO nano composites, pulsed electron beam ablation, model catalyst.
[1] X. Wang et al., Catalysis communications 2012, 24, 61.
[2] G. Poongodi, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 2015, 148, 237.
[3] J. Llorca et al., Journal of catalysis 2004, 227, 556.

Ce_1-xSm_xO₂ (x = 0, 0.2, 0.5 and 0.8) nanofibers (NFs) were synthesized by coupling sol-gel method with electrospinning technique and using poly-vinylpyrrolidone (PVP) as polymer medium, in ethanol/water mixture. Optimization of the fabrication conditions was achieved through analysis of the most critical synthetic parameters, which include: (i) the applied field strength, (ii) the solution feed rate and (iii) the PVP content in the electrospinning solution. Suitable microstructural fiber morphology could be achieved with 18.5 kV of applied voltage, 7 ml/hr of solution feed rate and 12% (w/w) of PVP composition in the electrospinning mixture. Morphological features of resulting fibers were examined by scanning electron microscopy (SEM). The fiber diameter was typically found to be in the ranges of 200 - 1100 nm and 50 - 300 nm, before and after calcination at 500 ^oC, respectively. X-ray diffraction (XRD) studies proved the preservation of the fluorite cubic structure for the entire compositional range of Ce_1-xSm_xO₂ studied, while elemental analysis (EDX) and X-ray photoelectron spectroscopy (XPS) confirmed the purity of the surface and bulk of the fibers. High Resolution Transmission Electron Microscopy proved that the NFs are highly crystalline. The thermal stability of the polymer/inorganic nitrate salts was further investigated in inert atmosphere (N₂) using thermogravimetric analysis (TGA), where the phenomena that are linked with the transformation from composite towards oxide nanofibers were monitored as well. The reducibility of the nanofibers (mobility of oxygen species in the fluorite cubic lattice) as well as their thermal stability in successive oxidation-reduction cycles was also evaluated using Temperature-programmed reduction technique in H₂ atmosphere (H₂-TPR). Acidic-basic features of the nanofibers surfaces were studied by employing NH₃ and CO₂-TPD techniques, where weak, medium and strong acid sites were successfully probed.

Oxynitrides of d⁰/d¹⁰ metal cations are an emerging group of materials showing promising capabilities as visible light driven water splitting photocatalysts. The most common approach used to synthesize oxynitrides is the ammonolysis of oxide precursors at ambient pressure. High pressure synthesis is an alternative approach which can be advantageous over ambient pressure synthesis as high pressure tends to stabilize the nitride reactants at higher temperatures by suppressing the decomposition, allowing for a direct solid-state reaction between nitrides and oxides. Incorporating in situ X-ray scattering can mitigate the disadvantage of low throughput associated with exsitu high pressure synthesis reducing the time required to study a single system from weeks to hours enabling practical utilization in exploratory synthesis research. We have concentrated on the GaN-ZnO solid solution, an oxynitride system extensively studied for its promising ability as a photocatalytic water-splitter.[1] Previous in-situ high pressure experiments has shown that GaN-ZnO solid solutions can be synthesized by solid state reactions of GaN and ZnO including samples with high ZnO (>50%) content which is difficult to achieve via ammonolysis.[2] In our studies a piston cylinder apparatus was utilized to synthesize solid solutions at 1 GPa and 1150°C to cover the entire compositional range of the solid solutions in sufficient quantities (1g per sample) for optical and H₂ evolution studies. It was observed that samples with ZnO percentages of 10, 25, 50, 75, and 90% have direct band gaps of 2.89 eV, 2.78 eV 2.65 eV, 2.83 eV and 2.82 eV respectively. The highest rate of photocatalytic H₂ evolution under visible light was achieved by the solid solution with 50% ZnO at 2.3 mu;mol/h without any co-catalyst loading, while solid solutions of ZnO contents of 10, 25 and 75% showed evolution rates of 1.8, 1.1, 0.9 mu;mol/h respectively. The 90% ZnO solution had no activity on H₂ evolution. This corresponds to a pattern of decreasing activity and visible light absorption when the solution compositions shift away from 50% ZnO.
1. K. Maeda, T. Takata, M. Hara, N. Saito, Y. Inoue, H. Kobayashi and K. Domen, J Am Chem Soc 127 (23), 8286-8287 (2005).
2. H. Y. Chen, L. P. Wang, J. M. Bai, J. C. Hanson, J. B. Warren, J. T. Muckerman, E. Fujita and J. A. Rodriguez, J Phys Chem C 114 (4), 1809-1814 (2010).

Residual and waste drugs are discarded into environmental waters through sewers with human waste or direct disposal causing serious contamination. One-dimensional Titanium Dioxide (TiO₂) nanofibers have attracted considerable attention as an efficient photocatalyst due to their strong oxidative power, folded surface morphology and being good substrates for preparation of hybrid materials. Mixed-phase TiO₂ nanofibers have been prepared via a sol-gel technique followed by electrospinning and calcination. By adjusting the calcination temperature, rutile phase fraction in TiO₂ nanofibers can be tuned relative to the anatase phase from 0% to 100%. The effect of rutile phase fraction on grain sizes and specific surface area as well as their sequent influence on the photocatalytic activity is investigated. In order to further increase the electron-hole separation, hole conducting poly(3,4-ethylenedioxythiophene) (PEDOT) is introduced onto TiO₂ nanofibers via vapor phase polymerization (VPP) method. Hybrid PEDOT/TiO₂ nanofibers leads to a second-order reaction for the degradation of phenazopyridine instead of a first-order reaction using pure TiO₂ nanofibers. This study provides a further understanding towards the degradation mechanism of TiO₂-based nanofibers.

Lanthanum nickelate, La₂NiO₄ (LNO), is a mixed ionic and electronic conductor that has competitive surface oxygen transport properties and good electrical conduction. This makes it an excellent candidate for solid oxide fuel cell applications as well as oxygen permeation membranes, sensors and high temperature gas electrolyzers. It has been previously shown that LNO with doped-ceria composites as cathode materials lead to higher performance than LNO by itself. However, at low rare earth dopant concentrations of ceria, mixtures of rare-earth doped ceria and La₂NiO₄ results in an equilibrium phase composition of La₂O₃-Ce₂O₃ solid solution and NiO. This instability of LNO -SDC composites has the potential to result in lowering the performance of SOFCs.
In this study, strategies to stabilize two-phase mixtures of La₂NiO₄ and doped-cerium oxides are being explored through judicious choice of the starting compositions. The properties of such electrodes are being studied through electrical conductivity measurements, dilatometry analysis, and X-ray diffractometry as functions of temperature and oxygen partial pressure.

Gadolinium Doped Ceria (GDC) thin films find applications as electrodes and electrolyte materials in Intermediate Temperature Molten Carbonate and Solid Oxide Fuel Cells due to their relatively high ionic conductivities in the temperature range 300-700°C. The performance of GDC is dictated primarily by the film thickness, morphology and porosity. These characteristics depend critically on the synthesis/deposition route. GDC materials are often produced via multi-step and relatively expensive routes such as hydrothermal, sol-gel, homogenous precipitation and glycine-nitrate processes. Reactive Spray Deposition Technology (RSDT) is a single step, cost-effective method for depositing materials on to metal, ceramic or polymer-based substrates. RSDT is a direct flame-based deposition technique that gives a high degree of control over the thickness, porosity, morphology and composition of the material being deposited.
In this study we have deposited Gd_0.1Ce_0.9O_1.95 anode functional layers onto La-doped SrTiO₃ substrates using RSDT. The morphology, crystal structure and composition of the films were analyzed using a combination of X-Ray diffraction, scanning electron microscopy and transmission electron microscopy techniques. The effect of RSDT deposition parameters on the structural characteristics will be discussed, with particular emphasis on the exclusion of carbonaceous residues due to incomplete combustion of the organic solvents used as fuels and transport media in the RSDT process.

We describe a new class of catalysts that uses an epitaxial monolayer of a transition metal oxide on a ferroelectric substrate^{1, 2}. The ferroelectric polarization enables us to switch the surface chemistry between strongly adsorptive and strongly desorptive regimes. We show that cycling between positive and negative polarization states of the ferroelectric makes these monolayers display catalytic behaviors that avoid the familiar limitations and compromises stemming from the Sabatier principle. This method is general and can, in principle, be applied to many reactions, and for each case the choice of the transition oxide monolayer can be optimized. Here, as a specific example, we show how simultaneous NO_x direct decomposition into N₂ and O₂ (which is an open challenge in automotive emission control industry) and CO oxidation can be achieved efficiently on CrO₂ terminated PbTiO₃, while circumventing oxygen (and sulfur) poisoning issues. We show that by inserting a thin SrTiO₃ buffer layer between PbTiO₃ and transition metal oxide monolayer this class of systems can become thermodynamically stable toward bulk crystallites formation and interdiffusion, so in principle, can be fabricated experimentally. Our method can expand the range of catalytically active elements to those which are not conventionally considered for catalysis and which are more economical, e.g., Cr (for NO_x direct decomposition and CO oxidation) instead of canonical precious metal catalysts².
[1] Kevin Garrity, Arvin Kakekhani, Alexie Kolpak, and Sohrab Ismail-Beigi. Ferroelectric surface chemistry: First-principles study of the PbTiO3 surface. Phys. Rev. B, 88(4):045401, July 2013.
[2] Arvin Kakekhani and Sohrab Ismail-Beigi. Ferroelectric based catalysis: Switchable surface chemistry. ACS Catal., June 2015 (Just accepted article on June 18).

Sodium borohydride (NaBH₄) is widely regarded a potential hydrogen storage candidate due to its high gravimetric capacity of 10.8 wt%, low costs and good stability in air [1]. However, thermal decomposition of NaBH₄ requires temperature as high as 550^oC and the reversible hydrogen absorption cannot be achieved. In the present work, reversible hydrogen storage composites of NaBH₄ with the addition of rare earth fluorides (REF₃) and 3d transition metal fluorides, were prepared through ball milling method [2]. Their reversible hydrogen sorption properties and re-/dehydrogenation reactions were systematically investigated. Experimental results revealed that: (i) The dehydrogenation temperature of the NaBH₄-Transition metal fluorides composites is much lower than that of pure NaBH₄; (ii) The composites have outstanding reversible hydrogen sorption performances at moderate temperatures (300^oC-420^oC) and under quite low hydrogen absorption/desorption plateau pressures (0.1-2 MPa) with favorable thermodynamic properties [3]. In particular, through the co-addition of rare earth fluorides (REF₃) and 3d transition metal fluorides, the reversible hydrogen sorption in NaBH₄ can be achieved at temperatures lower than 100^oC [4]. During de-/rehydriding cycles, NaBH₄ reacts with transition metal fluorides to produce metal borides after dehydrogenation and can be regenerated after hydrogenation [2-5]. Our results have shown that through the addition of the transition metal fluorides into NaBH₄, reversible hydrogen storage composites can be obtained with significantly improved thermodynamic and kinetic properties.
References
[1] S. I. Orimo, Y. Nakamori, et al., Chem. Rev., 2007, 107, 4111
[2] L. N. Chong, J. X. Zou, et al., J. Mater. Chem. A, 2013, 1, 3983
[3] L. N. Chong, J. X. Zou, et al., J. Mater. Chem. A, 2013, 1, 13510
[4] L. N. Chong, J. X. Zou, et al., J. Mater. Chem. A 2014, 2, 8557
[5] L. N. Chong, J. X. Zou, et al., Advanced Mater., 2015, In press

CAD/CAM printable, thin film, flexible perovskite ceramic devices have received recent attention for their applicability in novel energy production technology. Hydrogen fueled, clean energy devices have high efficiencies (50-60%), lack hazardous byproducts and can be used to generate electricity from thermal gradients. These technologies require a thermally stable, catalytic conductor, such as nickel, to efficiently produce conductive protons. Increasing demand for streamlined and cost effective device fabrication techniques necessitates a novel approach to the deposition and processing of this catalytic layer. Precise control over the morphology and surface structure of these films increases overall efficiency and can be used to manipulate interfacial interactions between the catalyst, fuel and ion conductor. Ideally, a hierarchal structure should be formed, forming a large pore layer, allowing for a mass transport of hydrgen gas, and a highly dense barrier layer to prevent backflow. As conventional sintering techniques have global effects on devices, they are unable to produce heirarchal structures. Flash lamp annealing, allows users to treat thin (<500 nm) layers independently when combined with additive manufacturing techniques. Through utilizing a UV-active organo-metallic nickel ink, nickel electrodes could be formed when printed onto proton exchange membrane materials. Furthermore by tailoring the discharge parameters of the PulseForge photonic curing system, the morphology could be controlled ranging from large pore, highly porous films to highly dense conductive nickel. It was found that as the curing fluence increased, the film density and conductivity increased as nanoparticles formed in situ experienced higher degrees of sintering. XRD scans showed that the cured nickel layers were phase pure with no NiO contamination. FTIR and Raman scans were used to confirm that organic precursors were removed during the drying and curing steps.

Fuel cells, including proton-exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC), have recently been considered as potential power sources for both electric vehicles and portable electronics since they could potentially fulfill the requirements of high energy and power density, high efficiency and low or zero emission simultaneously. One current bottleneck for building high energy-conversion efficiency fuel cells lies on the sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode side.^[3] Therefore, development of efficient electrocatalysts for ORR becomes the focal task and main challenge in fuel cells research. Traditionally, platinum (Pt) and Pt-based alloys have been intensively investigated as the most active ORR electrocatalysts. However, Pt-based electrocatalysts suffer from various limiting factors including prohibitive cost, element scarcity and the declining activity caused by methanol crossover, which highly hinder the scalable applications of fuel cells. Therefore, it is highly desirable to develop efficient ORR electrocatalysts based on non-precious metals and with high methanol-tolerance.
Mixed valence oxides involving transition metals have been considered as an important class of possible alternatives that exhibit high ORR catalytic activity in alkaline medium.^[15] In particular, cobalt-based oxides have recently attracted growing interests due to their potentially high activity and relatively easy preparation. For example, Dai et al. fabricated the Co₃O₄/N-doped graphene hybrid structure and observed an enhanced catalytic activity for ORR.^[17] Recently, the partial substitution of cobalt with low cost and environmentally benign elements such as Ni, Cu and Mn has been shown potentially advantageous, while the progress is still quite slow. Moreover, the substituted metal oxides can only deliver much lower mass activity compared with Pt-based materials in most of previous studies. Undoubtedly, it will be of great significance to develop substituted metal oxide electrocatalysts having comparable catalytic performance with Pt-based materials.
In this work, we develop a cost-effective and environmentally benign solution phase method to synthesize hybrid nanosheets by growing well crystalline NiCo₂O₄ nanoparticles on reduced graphene oxide (rGO) sheets through based on a polyol process together with a subsequent thermal annealing treatment. Remarkably, the NiCo₂O₄-rGO hybrid nanosheets exhibit very high catalytic activity for ORR in terms of high current density and low over-potential. More importantly, the NiCo₂O₄-rGO hybrid nanosheets possess very high methanol-tolerance, which is very important for practical applications. The high quality NiCo₂O₄-rGO hybrid nanosheets could find promising use as a noble-metal-free and methanol-tolerant electrocatalyst for fuel cells.

The increasing concern over the global energy crisis has been an important driving force for the exploration of alternative energies. Hydrogen energy as a high efficiency, clean and abundant source is one of the most important choices of future energies, which could address the global energy problems. One area of research interests focuses on hydrogen gas produced by water splitting whose bottle neck is the oxygen evolution reaction (OER). A key component is the catalyst for OER. This report describes the synthesis of AuCo nanoparticles prepared by a facile one pot method as a high efficient catalyst for OER. The composition and size of AuCo nanoparticles depends on the feeding ratio of Au and Co precursors in the synthesis. Electrochemical characterization of the catalyst shows that the redox reaction of Co species in the catalyst is dependent on the cycle number while the composition remains changed. Interestingly, the OER activity is shown to depend on the total amount of AuCo species being oxidized or reduced. Implications of the findings to the electrocatalytic synergy will be discussed.

Heterogeneous photocatalysis is a valuable alternative for many technological processes of great interest on the current context of energy generation and environmental remediation. Besides the advances in efficiency and comprehension of the different phenomena involved in photocatalysis, the recombination of photogenerated charges is still a challenge for the photocatalytical processes. It is known that the formation of heterojunctions between TiO₂ anatase and other photocatalysts, like TiO₂ rutile and SnO₂, enhances the photocatalytic activity compared to the pure phases by reducing the recombination rate. Thus, the formation of heterostructures is an alternative to minimize the deleterious effects of charge recombination. The heterostructure Nb₂O₅/SnO₂ is particularly interesting due to the proximity of their bandgap values and the relative position of their valence and conduction bands, which is supposed to form an heterojunction type 2. These heterostructures were formed from hydrothermal annealing of preformed nanocrystals of Nb₂O₅ and SnO₂, obtained previously as colloidal suspensions. The colloidal heterostructures were obtained by varying the ratio of both semiconductors and conditions of hydrothermal treatment, and characterized by X-ray diffraction, Raman spectroscopy, electronic spectroscopy (TEM and SEM-FEG), photoluminescence, X-ray fluorescence and N₂ physical adsorption. Photocatalytic activity was evaluated under UV light through the photodegradation of different dyes and the formation of hydroxyl radicals by using terephtalic acid for fluorometric detection. The formation of heterojunctions was also evaluated by comparison with physical mixtures of pure Nb₂O₅ and SnO₂ submitted to the same hydrothermal treatments.

Uranium oxide materials have attracted much attention not only in the context of nuclear energy generation but also for their application in catalysis such as for the destruction of chlorine-containing organic pollutants. UO₂, U₃O₈ and UO₃ are semiconducting materials with band-gap energies in the range of 2.0 - 2.7 eV and exhibit unique electrical and catalytic properties. However, only little is known on how the size and shape effects their physical and chemical properties. Herein, we report the synthesis of novel uranium (IV) compounds and the generation of high-quality, uranium-oxide nanocrystals for application in heterogeneous catalysis.

The development of direct alcohol fuel cells (DAFCs) as a power source has drawn a surge of interest in recent years because of its high energy density, bio-renewable nature, and ease of storage and transportation. One of the key problems is the limited knowledge on how to design highly e#64256;ective, robust and low-cost catalysts, due to lack of fundamental understanding of the mechanisms into the Cminus;C bond cleavage for the complete oxidation of ethanol. To address this problem, we aim to develop effective strategies for nanoengineering the composition and structure of noble metal containing nanoalloy catalysts. In this work, several new and refined nanoalloy catalysts have been prepared as catalysts for electrocatalytic ethanol oxidation reaction. This presentation describes recent findings of an investigation of the correlation between the catalyst composition, atomic scale structure and the electrocatalytic performance, aiming at providing a new fundamental insight into the role of the detailed atomic alloying and the interaction structure in the electrocatalytic mechanism. Examples of binary and ternary nanoalloy catalysts will be discussed to highlight the importance of controlling composition and structure for the design and preparation of active electrocatalysts.

Anatase TiO2 is an effective photocatalyst for water splitting and oxidation of organics. Photogenerated electron and hole trap sites in polycrystalline anatase are central to this photocatalytic behavior. In this work, anatase TiO₂ films with strong <001> texture and {001} facets at the surface were studied by electron paramagnetic resonance (EPR) spectroscopy after UV photolysis at low temperature. The goal of the study was to study trap state behavior at the surface and within the bulk of the <001> oriented thin films. The films prepared from a hydrothermal fluoride synthesis route express strong <001> texture with the c-axis normal to the substrate. Scanning electron microscopy (SEM) and grazing incidence-X-ray diffraction (GIXRD) show that crystal grains grow upward and away from the substrate along the <001> direction with an in-plane diameter of ~300 nm at the surface of the film. The angular dependence was measured by cw-EPR between 4 - 77 K after in-situ irradiation with 365 nm light. The unique feature of this work is the characterization of the angular dependence of the EPR signals of the electron (Ti³⁺) and hole (O^-) trap states. While Ti³⁺ exhibits the expected axial g-tensor, the oxygen radical centers have rhombic character. These measurements were conducted on as-synthesized, annealed, and thermally reduced films and the differences in g-tensors will be reported in the anatase frame of reference.

Anatase TiO₂ is still receiving a great attention as an excellent candidate for dye-sensitized solar cells (DSSCs) since it was first developed. This is due to its abundant availability and economical processes with respect to single and amorphous Si-based materials. However, due to its wide bandgap of 3.2 eV, it preforms excellent photoelectric activity with UV light absorption and hence shift of its absorbance edges toward the visible region is required. In this work we report synthesis and characterization of carbon-doped TiO₂ synthesized using low-pressure premixed flat flame.
The synthesis of C-TiO₂ powders was carried out in a novel low-pressure premixed flat flame from metal-organic precursors. After vaporization, dried powders were collected on temperature controlled substrate with a stagnation geometry. Methane gas was utilized as a source of carbon doping in ours samples. Speed of gas carrier was used to control the amount of dopants in TiO₂ samples. In-situ laser diagnostics techniques were utilized to determine chemistry of gas species and to detect phase transformations occurring while deposition. Photocatalytic activity with standard Pt-FTO (fluorine-doped tin oxide) electrodes and ruthenium base electrolyte was measured. Structural and chemical analysis were utilized using TEM, electron diffraction, EDS and EELS.
Photocatalytic activity measurements show an increase in visible light absorption which result in ~17% increase in the photocurrent density and ~23% increase in the efficiency with respect to commercially available anatase, Degussa P-25. This improvement is explained due to the increase of absorption cites. Work is underway to examine the C-TiO₂ and its polymorphs for the catalysis of water oxidation/oxygen evolution (OER). Additionally understand possible locations occupied by the carbon and other dopant atoms the TiO₂ structure and their role in photocatalytic and water splitting activities.

Although the heterojunction catalysts using CNTs as supports such as CdS/CNTs, WO₃/CNTs, and TiO₂/CNTs can enhance the activity of photocatalysis due to the combination of shifting absorbance to visible light and lowering electron-hole recombination rate, the performance is still low. In order to improve the quantum efficiency of heterojunction catalyst, loading with platinum is a good approach because Pt provides additional reactive sites in photoreaction. In this study, TiO₂/CNTs hierarchical nanowires were prepared by first functionalizing CNTs (f-CNTs) with nitric acid etching at 140 ^oC. Coating of a TiO₂ shell layer on the f-CNTs at 300 ^oC was then conducted by atomic layer deposition (ALD) using TiCl₄ and H₂O as precursors. After the TiO₂/CNTs shell-core structure was fabricated, Pt nanoparticles were then deposited on the TiO₂ surface at 250 ^oC as co-catalyst by plasma-enhanced ALD (PEALD) with trimethyl(methylcyclopentadienyl)platinum(IV) (MeCpPtMe₃) and oxygen plasma as precursors. The saturated deposition rate of TiO₂ on f-CNTs is 0.55 Å/cycle and the saturated deposition rate of Pt on TiO₂ is 0.54 Å/cycle. The particle size of Pt is approximately 1 nm to 5 nm that vary in different cycle number of PEALD. The photo-induced current of Pt/TiO₂/CNTs multilayer structure is higher than those without Pt co-catalyst. The particle size of Pt on TiO₂/CNTs was a key factor to determine the efficiency of methylene blue (MB) degradation. The TiO₂ particles around 2 nm exhibited the best efficiency of MB degradation.

The rational design of novel catalysts is crucial for more efficient oxygen evolution reactions (OERs) and oxygen reduction reactions (ORRs), both known as important energy conversion processes between O₂ and H₂O for renewable energy technologies. The earth-abundant, inexpensive manganese oxides (MnO_x) have emerged as an intriguing type of catalysts for OERs/ORRs, inspired by the photosystem II water-oxidizing complex of CaMn₄O_x clusters. In this contribution, we report, i) a facet-dependent catalytic activity of MnO nanocrystals for OERs/ORRs using halite MnO nanocrystals; and ii) the enhancement of catalytic activity MnO₂ polymorphs via the slight doping gold nanoparticles (AuNPs). In the first study, the design and synthesis of three-dimensional complex anisotropic MnO nanoflowers, polypods, polyhedra and octahedral with selectively oriented MnO crystals were prepared using a limited ligand protection method. MnO polypods exposed (100) planes on their branched MnO nanorods; while, MnO octahedral nanocrystals exposed (111) planes on all surfaces. The theoretical and experimental studies indicated that MnO (100) planes with higher adsorption energy of O species could largely promote the electrocatalytic activity for OERs/ORRs. In the second study, we demonstrate that the addition of AuNPs to MnO_x polymorphs can result in a strong enhancement of catalytic activity for OERs. Using five different MnO_x materials doped with AuNPs, i.e., cryptomelane-type α-MnO₂, birnessite-type δ-MnO₂, amorphous MnO₂, cobalt doped α-MnO₂, and cubic bixbyite Mn₂O₃, a strong correlation between the catalytic activity of MnO_x/AuNPs for OERs and the valence of Mn centers is presented. Our study highlights the importance of physical states and properties of MnO_x for the catalytic activity for OERs/ORRs and presents new opportunities to prepare highly active transitional metal oxide catalysts for OERs/ORRs.

The Ca₂Al₂SiO₇: Ce³⁺ (gehlenite) long-lasting phosphor is successfully synthesized via a sol-gel approach. The phosphor exhibits a strong emission at 410 nm as well as a long-lasting luminescence. After decorating AgCl nanoparticles, the luminescent intensity is substantially quenched with the quantum yield decreased from ~40% to ~10%. The long-lasting luminescence is also weakened accordingly. Such Ca₂Al₂SiO₇: Ce³⁺ - AgCl composites could efficiently degrade methyl orange under solar irradiation, and this degradation can be carried on after the removal of irradiation because of the long-lasting luminescence of the phosphors. Around 19 % of methyl orange can be degraded after light cutoff. Moreover, it appears that AgCl is more suitable to compose with Ca₂Al₂SiO₇: Ce³⁺ rather than TiO₂ since its broad wavelength light absorption. In addition, the Ca₂Al₂SiO₇: Ce³⁺ shows a better stability in water than the commercially violet-emitting long-lasting phosphor, indicating that Ca₂Al₂SiO₇: Ce³⁺ - AgCl is more suitable in water treatment application.

Conversion of CO₂ to valuable chemical and fuel has attracted worldwide interests due to the significant environmental and economic benefits. Electrochemical reduction of CO₂ is considered as a simple, environmentally friendly and well controllable approach. To achieve efficient and stable electrocatalysts, a series of metal catalysts have been exploited in the past decades. Among them polycrystalline Cu has been demonstrated to catalyze the reduction of CO₂ to hydrocarbons. However, despite of the high catalytic activity of such Cu catalysts, they suffer from poor stability and large reaction overpotentials. Moreover, the catalytic mechanisms of Cu in CO₂ reduction process are still unclear. Therefore, a better design of Cu catalysts and improved understanding of its catalytic mechanisms are highly desired. Several studies have shown that the selectivity of Cu catalyst towards CO₂ reduction was dependent highly on its surface structure, more specifically the crystal facets. This finding has inspired intensive interests in surface modification techniques, such as electrochemical deposition, alloying, ligand stabilization and other approaches. Although the product selectivity was altered in these approaches, they also led to an increased hydrogen production. Moreover, how to maintain a long-term stability, i.e., robust surface structure, of Cu-based catalyst remains a severe challenge..
In this study, we demonstrate the novel method to implement of 3-dimensional (3D) hierarchical Cu as a highly efficient and stable catalyst for electrochemical reduction of CO₂ in aqueous solution. We make the 3D hierarchical Cu using laser interference lithography (LIL). The periodic nano pattern was implemented on Si wafer using the LIL and subsequently deep reactive-ion etching (DRIE) to form the periodically aligned nano rods. HMDS and PR are sequentially spin-coated on Si wafer of which native Si oxide is removed by buffered oxide etchant. 2nd exposure of 325nm laser on 90#730; rotated Si substrate after 1st exposure makes it able to develop hole patterns with period of 250nm to 1um depending on the incident angle of the laser beams. The holes on photoresist is transferred to Si wafer by Bosch process, the commercially known DRIE method. Electron-beam evaporated Cu seed layer is deposited on the hole structure. Branched Cu nanowires are produced by hydrothermal growth of branches on pre-formed vertically aligned Cu nano rods by delamination of Cu layer which fills the holes by electroplating method. The as-prepared 3D hierarchical Cu exhibited much lower overpotentials and higher Faraday efficiency for the CO₂ reduction compared to Cu foil. Nearly no detection of CO₂ reduction was found in Cu foil, but the CO₂ reduction was dramatically enhanced in the 3D hierarchical Cu. The recycle stability for the detection was also increased in prolonged electrolysis. From this results, the mechanism for the CO₂ reduction on 3D hierarchical Cu nanostructures is discussed.

With ever increasing demand for energy and limited availability of fossil fuels, there is an unprecedented urgency in developing high performance and durable materials for energy production as well as energy storage. Presently, platinum is one of the most effective and durable catalyst for hydrogen evaluation reaction (HER), but its wide spread use is precluded due to high costs as well as limited availability. Therefore, it is essential to develop low-cost and earth-abundant materials to replace precious-platinum based catalysts. Recently, transition metal dichalcogenides such as MoS₂ have been shown to possess good catalytic activity towards hydrogen evolution, however the performance and durability is still poor as compared to platinum. In this work, we report a simple solvo-thermal technique to synthesize Cu₂MoS₄ platelets. Synthesis conditions can be altered to achieve various allotropes of Cu₂MoS₄. Electrochemical measurements are performed in acid media, and Cu₂MoS₄ possess excellent catalytic activity for HER and exhibit a Tafel slope of 50 mV per decade at extremely low-loading. We report for the first time that the electrochemical activity as well as the durability of Cu₂MoS₄ depends on its allotropy. The I-phase shows the highest catalytic activity, where as P-phase possess lower catalytic activity. Furthermore, we have successfully intercalated these 2D materials with both hydrazine and lithium that has a direct impact on the of the electrocatalytic activity. Possible origin of the catalytic site will be discussed.

Highly active, durable and cost-effective catalysts for water oxidation are critical to efficient solar energy conversion and storage. Here, we report solution-processed NiFeCo oxide/carbon nanotubes (CNTs) hybrids which are highly active and stable in oxygen evolution reaction (OER), and are comparable to the benchmark noble metal oxide, IrO₂/carbon catalyst. The key features of the designed catalyst are the formation of nanopore in highly OER-active NiFeCo amorphous metal oxide with optimized composition and the synergistic effect between NiFeCo and CNTs. Amorphous NiFeCo oxide exhibited a small overpotential of about 250 mV at 10 mA/cm² and Tafel slope of 85 mV/decade in alkaline media. Combining this amorphous metal oxide with CNTs forms an electrically interconnected conducting networks and changes the modulated electronic structures of catalytic centers. Thus, resulting NiFeCo/CNTs hybrids exhibited an overpotential as low as 210 mV and Tafel slope of 60 mV/decade. In addition, the OER turnover frequency (TOF) at an overpotential of 350 mV of NiFeCo /CNTs hybrids improved to 0.09 S^-1, campared to 0.025 S^-1 of NiFeCo oxide. The NiFeCo/CNTs hybrids also showed no obvious decline in performance over a course of 400-hour test using an applied voltage of 1.8 V, indicating the high stability of the catalyst. Although NiFeCo mixed oxide/hydroxide has been made for OER previously, this is the first time amorphous NiFeCo metal oxide with nanoporous structure and highly active for OER has been achieved by a facile chemical method. Finally, we demonstrated a 6% solar-to-hydrogen integrated system by coupling three ZnO/PbS photovoltaic devices in series with designed NiFeCo/CNTs oxygen evolution catalyst and a bimetallic Ni-Mo hydrogen evolution catalyst.

The scale of renewable energy challenge not only calls for highly efficient technologies but also abundant, inexpensive, and robust materials. Nanomaterials can help to mitigate the poor properties of earth-abundant semiconductors and catalysts to enhance solar energy conversion. We have controlled the nanostructures and polymorphs of layered MS₂ (M = Mo, W) materials and other earth-abundant metal chalcogenides, such as metallic cobalt pyrite (CoS₂), to significantly enhance their catalytic activity in hydrogen evolution reaction (HER). We further tuned the electronic structure of pyrite compounds and established ternary pyrite-type cobalt phosphosulfide (CoPS) as a high-performance earth-abundant HER. These earth-abundant catalysts and semiconductors have been integrated to enable efficient photoelectrochemical solar energy conversion. Integrated photocathodes of the novel earth-abundant catalysts on n⁺-p-p⁺ silicon micropyramids achieved high photocurrents up to 35 mA/cm² and onset photovoltages as high as 450 mV vs RHE, and 5-6% solar-to-hydrogen conversion efficiency.

The structural and electronic properties of the aqueous interface are highly important in determining the microscopic mechanisms of heterogeneous catalysis for solar fuel generation; for example, water splitting into molecular hydrogen and oxygen. In this work, we investigate the microscopic structural motifs that occur at aqueous interfaces of TiO₂, a key prototypical photocatalytic material [1,2]. We employ density functional theory based ab initio molecular dynamics (AIMD), and follow the same simulation protocol used previously for the aqueous interfaces of the GaN/ZnO alloy [3]. Specifically, we study the aqueous interfaces of the most stable anatase (101) and rutile (110) surfaces.
Despite several experimental and computational studies, the nature of the aqueous interfaces of pristine anatase (101) and rutile (110) surfaces - as to whether the adsorbed water molecules dissociate or remain intact - is a matter of controversy. Our AIMD simulations based on the optB88-vdW functional that includes the long-range van der Waals interactions show mixed molecular and dissociative water adsorption on both anatase (101) and rutile (110) surfaces, in agreement with more recent experimental and theoretical studies [4,5]. The AIMD simulations reveal water dissociation and re-association events mediated through the water molecules in the first hydration shell of the hydroxylated surface. These events lead to the formation of transient hydroxide ions adsorbed on the surface Ti sites.
Using the model hydroxylated TiO₂ surfaces obtained from the AIMD simulations, we then investigate the trapping of photogenerated holes, which is a crucial step in the oxygen evolution reaction (OER) in water splitting as shown in our previous studies on OER at the aqueous GaN interface [6]. For this analysis we use hybrid functionals, which are more accurate in describing hole localization owing to their reduction of self-interaction errors. The hydroxide ions resulting from the dissociation of the adsorbed water molecules are found to be the most energetically favorable trapping sites for the photogenerated holes, suggesting a critical role for the adsorbed hydroxide ions in the photo-oxidation of water.
This research was carried out at Brookhaven National Laboratory (BNL) under Contract No. DE-SC0012704 with the U.S. Department of Energy.
[1] A. Fujishima, K. Honda, Nature 238, 37 (1972).
[2] S. Hu, M. R. Shaner, J. A. Beardslee, M. Lichterman, B. S. Brunschwig, N. S. Lewis, Science 344, 1005 (2014).
[3] N. Kharche, M. S. Hybertsen, J. T. Muckerman, Phys. Chem. Chem. Phys. 16, 12057 (2014).
[4] D. A. Duncan, F. Allegretti, D. P. Woodruff, Phys. Rev. B 86, 045411 (2012).
[5] L. E. Walle, A. Borg, E. M. J. Johansson, S. Plogmaker, H. Rensmo, P. Uvdal, A. Sandell, J. Phys. Chem. C 115, 9545 (2011).
[6] M. Z. Ertem, N. Kharche, V. S. Batista, M. S. Hybertsen, J. C. Tully, J. T. Muckerman, ACS Catal. 5, 2317 (2015)

Here we investigate the oxygen reduction reaction electrocatalytic activity and the corrosion stability of several ternary Pt-Au-Co and Pt-Ir-Co alloys, with Pt-Au-Co having never been previously studied for ORR. The addition of Au fine-tunes the lattice parameter and the surface electronic structure to enable activity and cycling stability that is unachievable in Pt-25at.%Co (state-of-the-art binary baseline). The ternary alloys exhibit a volcano-type dependence of catalytic efficacy on the content of Au or Ir. Pt-2.5at.%Au-25at.%Co alloy shows a specific activity of 1.41 mA cm^-2 at 0.95 V, which is 16% and 404% higher than identically synthesized Pt-Co and pure Pt, respectively. This enhancement is promising as compared to a range of previously published Pt "skeleton" and Pt "skin" alloys, and is in fact the most optimum reported for a skeleton-type system. The catalysts exhibit dramatically improved corrosion stability with increasing levels of Au or Ir substitution, with the specific activity of all the ternary alloys being superior to that of Pt-Co after 100,000 potential cycles of 0.6 - 1.0 V. For instance, post-cycled Pt-10at.%Au-25at.%Co shows a specific activity of 0.63 mA cm^-2, which is 140% higher than Pt-Co and 439% higher than Pt. HRTEM and XPS shows that Au alloying promotes the formation of an atomically thin Pt-Au-rich surface layer, which imparts kinetic stabilization against the dissolution of the less noble solute component.

High cost and poor durability are limiting the commercialization of light-duty passenger vehicles powered by Proton Exchange Membrane Fuel Cells (PEMFCs). These limitations are directly related to the high precious metal loading and poor durability of oxygen reduction reaction (ORR) catalysts. The cost can thus be reduced by optimizing the use of platinum group metals in the catalyst. An ORR catalyst is generally made up of 3-7nm platinum particles dispersed by solution based methods on a high surface area carbon powder. This carbon support creates an electronically conductive, porous structure for the transfer of electrons, protons, gases, and water from the catalytic sites. A drawback of the solution-deposited platinum nanoparticles on carbon is the corrosion of carbon in the PEMFC under vehicle operation. Carbon corrosion and Pt dissolution intensify the agglomeration of Pt nano-particles. The reduction in the electrode voltage performance loss over time or loss of durability is a main focus for automotive PEMFC research. Ford Motor Company has developed novel, low loaded, durable, Pt-based ORR catalyst via vapor phase processing technologies. Electronically conductive amorphous metal oxides are coated onto the carbon supports followed by platinum deposition. This Ford ORR catalyst possesses a mass activity greater than 2.5 times current catalyst powder with exceptional stability. The Ford ORR catalyst is potentially the first of many catalysts produced through this new technology that will further reduce cost and extend the service life of PEMFC passenger vehicles.

Investigation of the hydrogen oxidation reaction (HOR) in alkaline media has been pursued in the past few years side by side with the development of alkaline membrane fuel cells (AMFCs), also called anion exchange membrane fuel cells (AEM-FCs). In this communication, we present the best liquid electrolyte-free AMFC performance reported so far for a platinum-free HOR catalyst (550 mW/cm2 peak power), prepared by growing palladium nanoparticles onto nanoparticles of an oxophilic metal (nickel), resulting in nano-dispersed, interconnected crystalline phases of Ni and Pd. When used in the anode of a hydrogen/air AMFC, such Pd/Ni catalyst exhibits high HOR activity, resulting in record high performance of a platinum-free AMFC. The enhancement of HOR catalytic activity vs. that observed at Pd (or Ni) alone was revealed directly in rotating disc electrode tests of this Pd/Ni catalyst that showed a significant negative shift of the onset potential for the HOR current vs. the case of Pd.

Among the disadvantages of proton exchange membrane fuel cells are the high cost of a common cathode catalyst, platinum (Pt), and the sluggish reaction kinetics of the oxygen reduction reaction (ORR) that occurs there. Recent advances in anion exchange membranes have allowed for the development of alkaline fuel cells (AFC), which enable the use of metals other than Pt as ORR catalysts because of the less oxidizing environment of AFCs. This work uses sputtered thin films as electrodes to screen new metal compositions for alkaline ORR catalysts. The catalysts were made by co-sputtering two different metals at a time onto glassy carbon electrodes, which were then inserted into a Teflon holder so that they could be used to perform rotating disk electrode voltammetry (RDE). The use of RDE allows for the determination of mechanistic information, such as the number of electrons involved in the reaction, as well as of kinetic information, given by the onset potential of the reaction. For this work, we selected several metals for screening (Au, Ag, Pd, Rh, Cu) because of the catalytic activity of those individual metals under alkaline conditions.

In order to enable the scale up of low-temperature fuel cells, more active and stable materials are required to catalyse oxygen reduction. This could be achieved by alloying Pt with transition metals [1]. However, commercial alloys of Pt and late transition metals, such as Ni, Co or Fe, are typically unstable under fuel-cell conditions [2]. On the other hand, the highly negative enthalpy of formation of alloys of Pt and rare earths may provide them with greater long term stability than Pt and late transition metals.[3] It turns out that Pt_xY and PtxGd exhibit catalytic activity approaching the highest reported in the literature, both on extended surfaces [3,4]and in the nanoparticulate form.[5,6]
I will present a series of investigations that we have undertaken in order to elucidate the factors controlling the performance of these catalysts.These incoroporate experiments on smooth polycrystalline surfaces,[1,3,4] well-defined mass-selected nanoparticles[5,6] and single crystals of Pt-rare earth alloys.[7] We complement our electrochemical measurements in liquid half cells with a wide range of ex-situ characterisation techniques, including X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, transmission electron microscopy and surface X-ray scatterring. We provide microscopic insight into our experiments using density functional theory. I will show why the activity and stability and activity of these catalysts is closely related to the nearest neighbour Pt-Pt distance in the bulk. This insight should allow for the development of improved, more efficient materials to drive oxygen electroreduction in low temperature fuel cells.
[1] Stephens, I. E. L., Bondarenko, A. S., Groslash;nbjerg, U., Rossmeisl, J. & Chorkendorff, I. Energy Environ. Sci. 5, 6744, (2012).
[2] Chen, S., Gasteiger, H.A., Hayakawa, K., Tada, T., Shao-Horn, Y., J. Electrochem. Soc. 1571, A82 (2010).
[3] Greeley, J., Stephens, I. E. L., Bondarenko, A. S., Johansson, T. P.,Hansen, H. A., Jaramillo, T. F., Rossmeisl, J., Chorkendorff, I. & Noslash;rskov, J. K. Nature Chemistry 1, 552, (2009).
[4] Escudero-Escribano, M., Verdaguer-Casadevall, A., Malacrida, P.,Groslash;nbjerg, U., Knudsen, B. P., Jepsen, A. K., Rossmeisl, J.,Stephens, I. E. L. & Chorkendorff, I. J. Am. Chem. Soc. 134, 16476, (2012).
[5] Hernandez-Fernandez, P., Masini, F., McCarthy, D. N., Strebel, C. E., Friebel, D., Deiana, D., Malacrida, P., Nierhoff, A., Bodin, A., Wise, A. M., Nielsen, J. H., Hansen, T. W., Nilsson, A., Stephens, I. E. L. & Chorkendorff, I. Nature Chemistry 6, 732, (2014).
[6] Velázquez-Palenzuela, A., Masini, F., Pedersen, A. F., Escudero-Escribano, M., Deian, D., Malacrida, P., Hansen, T. W., Friebel, D., Nilsson, A., Stephens, I. E. L. & Chorkendorff, I. J. Catal. In press DOI: 10.1016/j.jcat.2014.12.012, (2015).
[7] Johansson, T. P., Ulrikkeholm, E. T., Hernandez-Fernandez, P.,Escudero-Escribano, M., Malacrida, P., Stephens, I. E. L. &
Chorkendorff, I. Physical Chemistry Chemical Physics 16, 13718, (2014).

Transition metal oxides offer a low-cost, earth abundant alternative to noble metals for catalysis of the oxygen reduction and evolution reactions (ORR and OER), the kinetics of which limit the efficiency of fuel cells and electrolyzers. However, fundamental understanding of electrocatalysis in these systems is often hampered by heterogeneity of oxide powder surfaces and the composite nature of electrodes used for electrochemical measurements. Surfaces of epitaxial thin films, with well-defined crystallographic orientations and strains offer an excellent opportunity to develop insights into what parameters can govern catalytic activity and deduce active sites for oxygen electrocatalysis.^1,2 In addition, these surfaces allow spectroscopic study of the chemical speciation and electronic structure in an aqueous reaction environment, using ambient pressure X-ray photoelectron and absorption spectroscopy coupled with mass spectrometry to analyze the reaction productions.³ Here, control of the surface homogeneity is critical for quantifying the affinity toward adsorbed intermediates and comparing the reactivity between surfaces. The study of these epitaxial surfaces builds fundamental understanding of the mechanisms of oxygen electrocatalysis, and furthermore guides the rational design of high surface area oxide catalysts for technical application.
1. Stoerzinger, K.A. Liang, Q. Biegalski, M.D. Shao-Horn, Y. J. Phys. Chem. Lett. 5 (2014) 1636-1641.
2. Stoerzinger, K.A. Choi, W.S. Jeen, H. Lee, H.N. and Shao-Horn, Y. J. Phys. Chem. Lett. 6 (2015) 487-492.
3. Stoerzinger, K.A. Hong, W.T. Crumlin, E.J. Bluhm, H. Biegalski, M.D. Shao-Horn, Y. J. Phys. Chem. C 118 (2014) 19733-19741.

BiVO₄ exists in three different crystalline phases which are two tetragonal structures (zircon and scheelite types) and one monoclinic structure (scheelite type). Among them, the monoclinic phase shows a better photocatalytic performance under visible-light radiation, probably due to the lower and suitable band gap of around 2.4 eV. However, its use is limited due to the fast electron/hole pair recombination, which significantly decreases the efficiency of the photocatalytic reaction. Thus, different strategies have been proposed to improve the photocatalytic performance of the BiVO₄ which include the introduction of impurities into the structure of a semiconductor (doping), co-catalysts loading, and heterostructures formation. Heterostructures formation between different phases of the same semiconductor have attracted more attention due to the great potential to provide a viable alternative to increase the lifetime of charge carriers. Therefore, this paper studied the influence of two kinds of vanadium precursor (NH₄VO₃ and V₂O₅) and the H₂O₂ concentration in the formation of monoclinic-tetragonal BiVO₄ heterostructure by the OPM synthesis method with crystallization under hydrothermal conditions. The photocatalytic efficiency of the as-synthesized BiVO₄ pure and heterostructure samples was probed by MB dye photodegradation under visible-light. All of materials synthesized using NH₄VO₃ precursor showed only the monoclinic phase independent of another synthesis conditions. On the other hand, when V₂O₅ was used, the obtained crystallite BiVO₄ phase was dependent of H₂O₂ concentration and crystallization time. To molar ratio of 10:1 H₂O₂:(Bi + V) was obtained the pure monoclinic phase, however, when the molar ratio decreased to 5, a small amount of tetragonal phase was also identified by X-ray diffraction. Additionally, the amount of tetragonal phase increased as the crystallization time increased from 12 to 24 h. The samples containing monoclinic and tetragonal BiVO₄ phases, showed better photocatalytic performance in MB degradation under visible light radiation compared to isolated phases. It indicates the formation of a suitable heterojunction between both BiVO₄ phases, promoting an effective separation of the photogenerated charges. Indeed, the species scavengers trapping experiments reveal that the hydroxyl radical (^bull;OH) was the major active species for the samples formed by only monoclinic BiVO₄ phase. However, to samples with monoclinic and tetragonal BiVO₄ phases was verified the formation of a type-II heterostructure and the holes (h⁺) and superoxide anion radical (O₂^-bull;) were the main active species responsible for the methylene blue dye degradation. In summary, we clearly show that the heterojunctions formation between different phases of the same semiconductor presented the great potential to provide a viable alternative to improve the photocatalytic properties.

Nitrogen is a close chemical analogue of oxygen in ionic solids. Intriguingly, the somewhat lower electronegativity of nitrogen relative to oxygen allows important properties (such as light absorption and bond strength) to be effectively tuned without necessarily compromising the overall material stability. Some recent successes of ours in preparing highly active and stable oxynitride and nitride compounds for photoelectrochemical and for electrocatalytic applications will be discussed in the context of both the advantages and challenges of moving away from pure oxide compounds based on structural and activity data for a number of chemical compounds prepared as powders, thin films, and/or single crystals.

One of the major challenges in heterogeneous catalysis is the preparation of highly selective and robust catalysts. The goal is to be able to synthesize solids with stable surfaces containing a large number of specific surface sites designed for the promotion of a particular reaction. Synergies between surface-science studies and novel nanosynthesis methodology promise to afford new ways to design such highly selective catalysts in a controlled way. Here we provide a progress report on a project ongoing in our laboratory based on this approach. New metal@TiO₂ yolk-shell nanomaterials have been conceived for both regular and photo-induced catalytic applications. These catalysts can promote CO oxidation at cryogenic temperatures, and suggest that in photocatalysis the role of the metal may not be to scavenge the excited electrons produced in the semiconductor upon absorption of light, as commonly believed, but rather to promote the recombination of the adsorbed atomic hydrogen initially produced by reduction of H⁺ on the surface of that semiconductor.

The development of efficient catalysts represents one of the most important and challenging issues for the electrochemical hydrogen production. Learning from the biomolecular catalysts such as an enzyme or photosystem in nature provides clues to resolve the related kinetic issues. For example, hydrogenase, which occurs in bacteria, archaea, and some eukarya, catalyzes a proton into a hydrogen evolution reaction (HER) with high activity very near the thermodynamic efficiency limit. The reaction takes place at a specialized metal active center. Functional protein assemblies surrounding a metal active site act as ligands for the metals, pockets for the catalytic reaction, and pathways for reactants and products. Inspired by biomolecular system, we have designed enzyme-mimetic carbon-based catalyst for HER and investigated the effect of each component with a systematic approach.
As the simplest model carbon-based platform, 2D monolayer graphene is chosen as a HER catalyst. Graphene possesses excellent transmittance and superior intrinsic carrier mobility. For the first time, we have investigated new possibilities of monolayer graphene as the efficient HER catalyst. The catalytic activity can be further enhanced by generating more active sites. Treatment with N₂ plasma also induces N doping and abundant defects. The catalyst exhibits a lower Tafel slope (45 mV/decade) and a higher exchange current density (7.1×10^-5 mA/cm²) than those of other previously reported carbon-based HER catalysts, indicating performance comparable to that of Pt catalyst. Based on the electrochemical analysis, the active sites of the N-doped graphene have been identified and quantified.
As an intermediate stage of extension from the single 2D platform to a complicate 3D structure, we have stacked graphene layer-by-layer as a well-defined model of the pseudo-3D system and investigated the layer dependence of catalytic activity. Comprehensive electrochemical analysis shows that there is an optimized structure of stacked graphene for the best catalytic activity and the highest charge transfer rate. Based on the understanding of the optimized carbon platform, metal active sites have been incorporated with high controllability and tunability. Moreover, another type of the biomimetic carbon-based nanosheets will be addressed as a new HER catalyst.
Our synthetic bioinspired HER catalyst is also highly transparent and is applicable to the co-catalyst for the Si photoelectrochemical (PEC) cell. The results indicate the applied bias photon-to-current efficiency of 2.29%, which is higher than that of any other carbon-based PEC catalysts reported to date. Controlling a surface structure of the light-absorbing photoelectrode and the deposition with the co-catalyst represent a significant step toward enhancing the hydrogen production.
[References]
Uk Sim et al., Energy Environ. Sci. 8, 1329 (2015)
Uk Sim et al., Adv. Mater. 26, 3501 (2014)
Uk Sim et al., Energy Environ. Sci. 6, 3658 (2013)

Electrochemistry- the manipulation of electrical charge to drive chemical change- is central to applications in the field of energy conversion and storage. Despite its reach and importance, electrochemistry has advanced far more slowly over the last two decades, in large parts due to the lack of suitable and affordable catalysts. Recently, apart from the expensive noble metal catalysts, 2-dimensional materials, such as molybdenum disulfide (MoS₂) and its allotropes have shown great potential as high-performing and cost-effective catalysts for the electrochemical reactions.
Here, for the first time, we report the synthesis of layered highly crystalline 3D MoS₂ structures on monolayer graphene film with high density of active edge atoms using chemical vapor deposition method and demonstrate its remarkable performance for Hydrogen evolution reaction (HER). Our results indicate that 3D MoS₂ on graphene exhibit a low onset potential (70 mV vs RHE) and a high turnover frequency (> 4 S^-1) for HER. The TOF of the 3D MoS₂ grown on graphene is superior to all of the non-noble metal catalysts produced by scalable methods^2,6. The exceptional activity of this catalyst is attributed to (i) higher number of active sites due to 3D structure of MoS₂ and (ii) the presence of graphene between catalyst and substrate which enhances charge transfer and consequently accelerates electron mobility toward active edge sites.
An easily scalable and robust growth process of highly crystalline layered 3D MoS₂ on a wide variety of substrates together with prolonged stability suggests this material as a key catalyst in energy related applications.

Hydrogen as clean energy fuel has great potential in powering automobiles, yet it is highly flammable and will burn at very wild volume concentrations mixed in air. Single palladium (Pd) nanowires modified by different platinum (Pt) coverages (Pd@Pt nanowires) are prepared, and the properties of these nanowires for detecting hydrogen gas mixed in air are reported. Pd nanowires with dimensions of 40 nm (height) 100 nm (width) 50mu;m (length) are first prepared by using lithographically patterned nanowire electrodeposition (LPNE). Then a thin Pt surface layer is electrodeposited onto a Pd nanowire at coverages, theta;_Pt, of 0.10 monolayer (ML), 1.0 ML, and 10 ML. X-ray photoelectron spectroscopy (XPS) coupled with scanning electron microscopy (SEM) indicates that the deposition of Pt occurs by a layer-by-layer mechanism. The resistance of single Pd@Pt nanowires is measured upon exposure to pulses of hydrogen gas mixed in air at concentrations ranging from 0.05 to 5.0 vol%. Both Pd nanowires and Pd@Pt nanowires show a prompt increase in resistance upon exposure to hydrogen in air, caused by the conversion of Pd to more resistive palladium hydride (PdH_x). The Pt layers existing at Pd@Pt nanowires&’ surfaces modify the response to hydrogen in two ways: First, the amplitude of the resistance change is reduced as theta;_Pt is increased, and second, the rate at which the nanowire resistance attains a new steady-state value upon a change in the hydrogen concentration - characterized by the response time and the recovery time - is accelerated. For theta;_Pt= 1.0 ML, the response rate is accelerated by a factor of 2-3 while the recovery rate is faster by a factor of 10 as compared to single Pd nanowire operating at the same elevated temperature.

Spontaneous photoelectrochemical (PEC) water splitting, compared with water electrolysis with a solar cell and an electrolyzer, is inherently more cost-efficient and convenient to implement. However, presently, the combined challenges of solar conversion efficiency and overall cost still impede its large scale applications. Further, as the overall cost is defined not only by material and fabrication costs, but also the operating lifetime, it is therefore of the highest priority to exemplify comparable stabilities to that of solar cells for PEC photoanodes. BiVO₄, a promising semiconductor composed of earth-abundant elements, is responsible to visible light with an on-set potential as low as 0.2 V vs RHE. Although the stability of BiVO₄ has been extended to 40 hours due to recent research efforts, it is still far away from the standard lifetime of ~1000 hours for solar cells.
In this work, we present the fabrication of highly efficient BiVO₄ based photoanodes from low-cost particles with well defined Mo doping concentration and particle size. More importantly, we demonstrate, for the first time, that BiVO₄-based photoanode is capable of stably oxidizing water for a total time of over 1000 hours, a milestone breakthrough brought by a self-generating and self-preparing co-catalyst on the basis of a new concept of OEC co-catalyst precursor integration.
The Mo-doped BiVO₄ particles were synthesized by liquid solid reaction method and then treated with ball-milling and post-annealing to give an average particle size of 200~300 nm and good crystallinity. Pristine BiVO₄ showed significant performance drop if being heated over 450 0C, while the Mo-doped one can survive as high as 800 0C, enabling facile particle size control. Electrodes were prepared with a modified particle transfer method using low-cost Ni-Sn dual layer thermal vapor deposition. The Sn layer is stable and highly conductive for electron transportation. The relatively thin Ni layer serves two important roles: an adhesion layer for firmly holding BiVO₄ particles; a precursor for in-situ formation of Ni co-catalyst and catalyst repairing after corrosion. Compared with electrodes prepared on expensive ITO or FTO substrates, the current method has a great advantage of reduced production and maintenance cost. The whole fabrication process is atomic- and cost-efficient and can be easily scaled-up for mass production. BiVO₄ electrode with optimized conditions showed a photocurrent of nearly 3 mAcm^-2 under AM1.5 1 sun irradiation, which is comparable to the state-of-the-art film-type electrodes. As the Sn conductive layer is soft, when stick to a back-supporting plastic sheet, the electrode can possess an important feature of flexibility. This represents the first example of flexible photoanodes. Flexibility can bring a lot of advantages, e.g., the electrode can be curved into a parabola to utilize reflected sunlight for higher conversion efficiency.

The electrochemical splitting of water offers an attractive way to provide a carbon-free source of hydrogen. However water splitting efficiency is limited primarily by the high overpotentials required by the anodic oxygen evolution reaction (OER, 4OH^-→ 2H₂O + 4e^- + O₂). In alkaline electrolyte, nonprecious metals such as Ni, Co, and their alloys (NiFe, CoFe, etc.) are used as electrocatalysts for the OER, since they are abundant, cheap, and exhibit high corrosion resistance. However, Ni and Co still require high overpotentials of 350-450 mV relative to the thermodynamic value of 1.23 V vs RHE to yield 1mA/cm² OER current density.^1,2
One way to increase activity of Ni and Co-based materials is to fabricate them into nanoparticles to increase the number of active sites per geometric area. Currently, most high activity catalysts for the OER in alkaline electrolyte are nanostructured Ni(OH)₂ and Ni_xFe_y(OH)₂ powders,^3,4 which are coated onto an electrode with the aid of a polymeric binder such as Nafion. However, these ‘glued&’ nanoparticles for OER exhibit poor stability, especially under conditions of high OER current density where vigorous gas evolution occurs. Additionally, the utilization of polymeric binders decreases contact area of the active material and electrolyte. Binders also decrease conductivity of electrode, leading to diminished catalytic activity.
In this talk, we present simple a electrodeposition technique with which to fabricate nanostructured Ni, and Ni-Fe catalysts to increase OER activity. The origin of this increased activity is roughening of the Ni film via Ni electrodeposition in the presence of 3,5-Diamino-1,2,4-triazole (DAT). DAT inhibits Ni electrodeposition, consequences of which are: dramatic roughening of the film at the nano-scale, an increase the amount of Ni active sites produced, and stable, high current OER activity. A NiFe film electrodeposited in the presence of DAT yields an OER current density of 100 mA/cmshy;² at an overpotential of 300 mV (1.53V vs RHE) which is, to the best of our knowledge, the most active OER electrocatalyst in alkaline electrolyte reported to date. We find that we can tune this activity to nearly any arbitrary current density by changing the amount of NiFe electrodeposited. Interestingly, we found that electrodeposition of Ni in the presence of DAT onto steel produced a Ni/Fe film exhibiting very high activity without any further Fe incorporation.
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(3) Gao, M. R.; Sheng, W. C.; Zhuang, Z. B.; Fang, Q. R.; Gu, S.; Jiang, J.; Yan, Y. S. J Am Chem Soc2014, 136, 7077.
(4) Gong, M.; Li, Y. G.; Wang, H. L.; Liang, Y. Y.; Wu, J. Z.; Zhou, J. G.; Wang, J.; Regier, T.; Wei, F.; Dai, H. J. J Am Chem Soc2013, 135, 8452.

The oxygen evolution reaction (OER), in which water is oxidized to molecular oxygen, is an important part of many technologies including the photoelectrochemical splitting of water. There is much interest in the development of earth-abundant, affordable electrocatalysts for OER. In this talk, we describe the use of atomic layer deposition (ALD) to deposit highly active, earth abundant catalysts for OER based on manganese oxide (MnO_x) and nickel oxide (NiO). ALD is a vapor phase deposition technique capable of forming highly uniform conformal thin films with fine control over film thickness and film composition. It is becoming an attractive method for synthesizing catalytic thin films, opening new avenues for advanced catalytic designs. Using ALD, we synthesize MnO_x- and NiO-based catalysts; the catalysts are characterized using a variety of techniques and their OER activity is measured by cyclic voltammetry. We show that as-deposited MnO catalysts are highly active for OER, approaching the activity of the most active MnO_x catalysts known. We also study ALD-NiO as an OER catalyst. We use an Fe-rich electrolyte to activate the catalyst for OER, and compare it to catalysts tested in Fe-trace electrolyte. Using a two-step electrolyte conditioning procedure, we are able to create NiO_x based catalysts with both high turn-over frequency (TOF) and high surface area. Finally, we explore ternary oxide electrocatalysts, in which mixtures of metal oxides are deposited by ALD, and the activity over the span of compositions is characterized for the films. In the case of ternary Mn-Ti oxides, we find that the activity increases monotonically with increasing Mn concentration. At concentrations between ~10 to ~60 % Mn, a suppression in the activity of individual Mn active sites is observed, consistent with theoretical predictions. The results show that ALD is a useful method for growing compositionally-controlled, ultrathin metal oxide catalysts.

A practical solar fuel device will be made of several electrocatalyst and photoelectrode materials, with different requirements for activity and stability. In particular, the pH of the electrolyte can essentially determine the activation and performance of a (photo)catalyst. In addition, the electrolyte composition and pH should also be compatible with the counter electrode, so the overall water splitting reaction can take place. In this talk, I will discuss our recent work on three different materials that highlight the need for material/pH compatibility in a solar fuel device.
First, we have used three in-situ spectroelectrochemical techniques to probe the structural, optical, and electronic properties of Ni-based oxygen evolution catalysts during electrochemical oxidation of water. Our results indicate that a change in the pH of the electrolyte significantly affects the catalysts ability to de-protonate, and thus become catalytically active. The consequences of these results indicate that the activity and performance of a catalyst is strongly determined by the electrochemical environment it is operated in.
Second, we investigate the photoelectrochemical performance of so-called ‘photocharged&’ BiVO₄photoanodes in a pH range from 4-10. It is apparent that the enhancement in performance of the BiVO₄photoanodes is strongly correlated to the pH of the electrolyte, indicating that the mechanism for photocharging is strongly related to the OH^- concentration in the electrolyte, which can either aid in self-doping the material, or creating a stronger electric field at the semiconductor-electrolyte interface.
Finally, I will discuss our recent progress on using bipolar membranes in photoelectrochemical water splitting systems. Bipolar membranes allow the operation of two different pH solutions in separate compartments without adding any thermodynamic losses across the system. In particular, we can operate a cathode in pH 0, while having a (photo)anode operate in pH 7 or 14, and maintain stability over 100 hours.

This study describes the synthesis of nano-catalysts for methanol steam reforming and preferential oxidation (PROX) of carbon monoxide and their combination with a non-concentrating solar-thermal collector and a polymer electrolyte membrane (PEM) fuel cell. The solar collector is used to capture thermal energy at sufficient temperature to drive hydrogen production by steam reforming of methanol. The PROX catalyst oxides the CO within the H₂-rich reformate gas mixture, produced in an undesired side-reaction in the fuel reformer. Once the CO level is reduced below 20 ppm, the clean hydrogen gas mixture is fed into a low-temperature fuel cell.
In conventional fuel reforming systems, the thermal energy required to preheat water and fuel to the reaction temperature, evaporate liquid water and fuel, compensate heat losses, and overcome the reaction enthalpy of the catalytic steam reforming is generated by burning part of the initial fuel. This typically costs approximately half of the fuel. In the solar-powered system of this study, all fuel can be converted to hydrogen, since the heating requirement is fulfilled by solar power.
The methanol steam reforming catalyst consists of nano-scale CuO/ZnO/Al₂O₃ particles made by a novel flame spray pyrolysis method resulting in a highly active catalyst with high surface-to-volume ratio compared to commercially produced catalyst. Reaction temperatures between 220 and 295 °C, methanol-water inlet flow rates between 2 and 50 mu;l/min, and reactor masses between 25 and 100 mg are tested for their effect on methanol conversion and the production of undesired carbon monoxide. 100% methanol conversion can be easily achieved within the operational conditions mentioned for this flame-made catalyst - at reactor temperatures of 255 °C more than 80% methanol conversion can be reached for methanol-water inlet flow rates as high as 10 mu;l/min.
Au/Fe₂O₃ nanoparticles are synthesized by a modified co-precipitation method. By controlling the pH during the synthesis, an inverse catalyst can be generated: The catalyst support material, Fe₂O₃, is present in smaller particles (5-7 nm) than the active catalyst Au (~15 nm), leading to increased Fe₂O₃ surface area with higher oxygen adsorption and transport capabilities. This results in a catalyst with unprecedented CO conversion even under harsh conditions with significant amounts of CO₂ and H₂O in the gas mixture, as it is typical for realistic reformate mixtures. CO conversion above 99.85% for the necessary system operation can be achieved.
Finally, the hydrogen-rich gas mixture with marginal CO is fed into a conventional PEM fuel cell, resulting in methanol-to-electric efficiencies above 60% and solar-to-electric efficiencies above 50%. The long-term stability of all catalysts and the fuel cell are demonstrated.

Non-platinum group metal (non-PGM) catalysts are under development as an alternative electrode structure to costly Pt-based cathodes for automotive fuel cell systems. In order to become competitive, novel non-PGM catalysts with much improved activity and durability must be developed. Analytical characterization plays a critical role in advancing the understanding of these catalysts, with the aim to identify ORR active sites at the atomic scale as well as to explore electrode morphology at the mm level.
In this work, a hybrid non-PGM catalyst created at Los Alamos National Laboratory is under investigation. This promising catalyst, branded CM-PANI-Fe-C, is based on a mixture of heat-treated carbon-supported catalysts derived from polyaniline (PANI) and cyanamide (CM). The nanoscale morphology and atomic nature of the active sites in CM-PANI-Fe-C is being investigated by analytical scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy (XPS). The catalyst is comprised of fibrous carbonaceous agglomerates intermixed with few-layer graphene sheets. Atomic resolution electron energy loss spectroscopy (EELS) is utilized to identify single Fe atoms coordinated with nitrogen on the few-layer graphene, corroborating the hypothesized Fe-N active sites which exhibit high four-electron selectivity.
Beyond fundamental studies of the electrochemical activity and durability for these non-PGM catalysts, the thick electrode structures required to accommodate high non-PGM loadings play a critical role in fuel cell performance. Energy-dispersive X-ray spectroscopy (EDS) will be utilized to study the bulk electrode structures in order to optimize the electrode architecture. Further, these analytical studies will be extended to understand the role of different process parameters on catalyst and electrode structures at multiple length scales.
Research sponsored by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (DOE), and through a user project supported by ORNL&’s Center for Nanophase Materials Sciences (CNMS), which is a DOE Office of Science User Facility.

The degradation of surface chemistry of perovskite (ABO₃) oxides is a critical factor in determining their performance in energy conversion systems such as solid oxide fuel/electrolysis cells (SOEFC), splitting of H₂O and CO₂ to produce fuels, as well as in information processing devices such as superconductors and memristors. The surface degradation is typically in the form of segregation and phase separation of A-site dopant cations, driven by elastic and electrostatic energy minimization. In the field of SOEFC, the extent of lowering in oxygen exchange kinetics on perovskite oxides because of their surface chemical degradation is very significant, often higher than one order of magnitude. Perovskite oxides recently attracted significant interest also as catalysts for thermochemical H₂O/CO₂ splitting due to their fast oxygen exchange and diffusion kinetics, and large oxygen non-stoichiometry.
In this study, we have assessed the effect of surface chemistry of perovskite catalysts on the kinetics of water splitting for the first time. We compared the catalytic performance of La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) perovskite with CeO₂, which is regarded as the state-of-art material for thermochemical water splitting. Isothermal redox cycles of catalyst powders were carried out in a button cell reactor in the temperature range of 500-1000 ^oC. H₂ production yield during the oxidation cycle, when a mixture of H₂O vapor and Ar was flown over the samples, was measured by mass spectrometer connected to the reactor. During the reduction cycle, a mixture of Ar with H₂ or CH₄ was used. At the low (500-600 ^oC) temperature regime, the highest H₂ production rate was achieved with a “fresh” LSCF, in comparison to CeO₂ and in comparison to the LSCF whose surface was segregated at 1000 ^oC. This indicates that if pristine perovskite surfaces can be retained, they promise fast kinetics at reduced temperatures. In general, we have shown that the H₂ production rate of the LSCF is higher than that of CeO₂, at the temperatures below 700 ^oC. However, at temperatures higher than 700 ^oC under reducing conditions, LSCF decomposed into Sr-rich Ruddlesden-Popper phase and Co oxide, and lost its performance significantly.
In order to improve the stability of LSCF surface chemistry, and prevent phase decomposition, we decorated the LSCF surface with more oxidizing cations (in comparison to Fe and Co), such as with Zr, Ti or Hf. These more oxidizing cations lower the concentration of positively charged oxygen vacancies at the LSCF surface. The decrease of the net positive charge suppresses the electrostatic attraction of point defects to the surface of the LSCF and, consequently, diminishes the segregation of the Sr-rich phases.

Recently, GaN has been attracting considerable interest in photo-electrochemistry and photocatalysis due to the favorable energy position of its band edges with respect to many redox levels [1,2]. Additionally, the flexibility in alloying and doping of III-nitrides is expected to provide an unprecedented control over the electronic properties of the surface. In general, hybrid systems investigated in heterogeneous photocatalysis consist of a semiconductor with a co-catalyst, such as Pt, located on its surface [3]. Here, GaN is also advantageous because of the favorable alignment between the Fermi level of many co-catalysts and the GaN energy band edges, which are relevant e.g. for water splitting [4]. From the point of view of the semiconductor substrate, transport and recombination kinetics of photo-generated charge carriers are particularly important for efficient photocatalytic activity. Here, we investigate GaN with different deposited Pt nano-structures as a model system for the kinetics of photo-generated charge carriers in hybrid photocatalysis. For this purpose we vary the thickness and coverage of Pt on intrinsically n-type (0001) GaN layers. Experimental data from contact potential difference (CPD) and photoconductivity (PC) measurements will be presented for, both, the turn-on and turn-off kinetics upon irradiation with above-bandgap light. The obtained results will be discussed in the context of a recently developed model for the kinetics of photo-induced charges of intrinsic GaN surfaces [5]. In the presence of Pt nano-structures, the photo-excitation processes are similar to those found in Pt free GaN surfaces [5]. However, in GaN with Pt nano-structures, photo-generated holes are preferentially trapped by the Pt and lead to an accumulation of positive charge there, whereas negative charge is accumulated in defect states of the GaN below the Pt. This preferential accumulation of photo-generated electrons close to the surface is responsible for a significant acceleration of the turn-off kinetics observed for the CPD, when compared to Pt free GaN surface. Conductive atomic force microscopy and Kelvin probe force microscopy measurements reveal that Schottky contacts develop in the vicinity of the Pt nano-structures. Our systematic study provides insight into the influence of Pt on the processes involved in the rise and decay of photo-generated charge carriers on a macroscopic scale.
[1] J. Howgate et al., Adv. Mater. 22, 2632 (2010)
[2] S. Schäfer et al., J. Am. Chem. Soc. 134, 12528 (2012)
[3] Z. Zhang and J. T. Yates, Chem. Rev. 112, 5520 (2012)
[4] D. Wang et al., Nano Lett. 11, 2353 (2011)
[5] A. Winnerl et al., Phys. Rev. B 91, 075316 (2015)

Methanotrophic organisms “activate” methane by first converting it to methanol using the Methane Monooxygenase (MMO) enzymes. MMOs perform this difficult partial oxidation under mild conditions, suggesting a biochemical process for methane conversion could be more efficient, less capital intensive, and more easily downscaled compared to current industrial practice. However, the industrial use of enzymes for large-scale applications, especially with reactions involving gases, has been limited by the low enzyme loading and poor mass transfer characteristics of stirred-tank reactors. Here, we demonstrate a new bioreactor design based on enzymes embedded in 3D printed polymer materials. Incorporating MMO enzymes in a polymeric material allows higher enzyme loading per volume, separates reactants from products, and enhances mass transfer compared to stirred tanks. We describe several methods for stabilizing the MMO in the polymer environment and demonstrate 100% of native MMO activity inside a polymer matrix, a major step toward new bioreactor designs and materials. The selection of the polymer is discussed, including an investigation of block co-polymers with hydrophobic and hydrophilic domains for transport of gas phase reactants and aqueous-phase products, respectively. Finally, the structure of the bioreactor for enhanced mass transfer is described.

Due to its high energy density, 2,5-dimethylfuran (DMF) has become one of the most promising biofuel materials. DMF can be obtained through the hydrodeoxygenation (HDO) of 5-hydroxymethylfurfural (HMF) and achieving high conversion and DMF selectivity is essential in preparing catalysts. There have been several reports about this process using various catalysts such as Pd,¹ Ru,² Pt,³ CuRu,⁴ PdAu,⁵ and PtCo.⁶ Among these, alloy catalysts are reported as the most efficient catalysts with high DMF selectivity. Even though many types of catalyst preparation have been studied, the HDO catalytic activity of colloidal nanocrystal based catalysts has been rarely reported. In this work, 3-4 nm Pt and PtCo with controlled Pt to Co ratio are prepared through high temperature metal precursor decomposition process. Nanocrystalline catalysts are prepared by depositing the nanocrystals on carbon support. Organic ligands on the nanocrystal surface are removed using rapid thermal annealing and plasma cleaning. The HDO activity was tested using a continuous flow reactor system.³ The catalytic activities of nanocrystals are not only dependent on the composition of nanocrystals but also on how the surface ligands are treated. Pt and PtCo nanocrystals show similar catalytic activity, but PtCo nanocrystals exhibit higher DMF selectivity over Pt nanocrystals. Finally, the effect of Pt to Co ratio on the conversion ratio and DMF selectivity is discussed.
This work was supported by the Catalysis Center for Energy Innovation, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award no. DE-SC0001004.
References
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One of the most promising technologies for Carbon Dioxide Capture and Sequestration is oxyfuel combustion, i.e. the use of pure oxygen in the combustion of fossil fuels. The current technology uses cryogenic methods for the separation of oxygen from air, however this process comes with a significant energy penalty required for the oxygen separation. Ion transport membranes (ITMs) can serve as a better substitute. They require a difference in the chemical potential of oxygen between the two sides for oxygen to transport from the oxygen rich to the oxygen lean surface. In addition, due to both oxygen separation and reaction, chemical processes become simpler and this leads to a lower operation cost. Especially when fuel is introduced at the sweep side of the membrane, it is expected that the oxygen flux increases significantly. However, the mechanism that leads to this oxygen flux enhancement has yet to be determined and modeled properly.
The objective of this work is to elucidate the mechanism leading to oxygen flux increase when fuel is introduced at the sweep side of an La_0.9Ca_0.1FeO_3-δ (LCF) membrane. Our experimental measurements show that the oxygen flux increases by an order of magnitude in a hydrogen-argon mixture compared to inert argon cases. Surface measurements using probe techniques and numerical simulations coupled with detailed gas-phase chemistry suggest that an LCF membrane exhibits a strong surface activity when a fuel reaches the permeate side. In addition, significant effort has been given to the modeling of this surface oxidation process. A new multistep, thermodynamically consistent and constraint by material properties reaction mechanism is proposed. This mechanism accounts for the membrane&’s electroneutrality, for Iron (Fe) site conservation and preserves microscopic reversibility.

Hydrogen is one of the most promising clean-energies for replacing petroleum fuels in the future. Searching for materials that can separate hydrogen from water by electrochemical process is of great interests [1]. The current most effective catalysts for the electrochemical hydrogen evolution reaction (HER) are all from Pt-group metals, which are quite expensive and rare in the earth. Thus a new and less expensive material with high effective HER catalyst is required. Molybdenum disulfide (MoS₂), a graphene-like two-dimensional transition metal dichalcogenides (TMDCs), has attracted lots of attentions due to its excellent electronic and optical properties [2]. Many potential application fields of MoS₂ have been proposed, such as semiconductor and photovoltaic fields. Recently, considerable efforts have shown that MoS₂ is also a promising electrocatalyst for HER [3], where the edge and the surface of MoS₂ are believed to be the catalytic active centers. Many nano-architectures for the HER have been fabricated by using solvothermal synthesis, chemical intercalation method and template-assisting process [4]. However, a simple method to synthesis MoS₂ catalytic nanostructure is still desired. In this work, we showed a facile and interesting MnO₂ powder-assisted synthesis of MoS₂ microstructures composed of few-layered nanosheets on silica substrate. The MoS₂ nanosheets was synthesized by simple chemical vapor deposition (CVD) method. The precursor MoO₃ powder and aided material MnO₂ powder were placed at the heating zone of the furnace in a sulfur reductive atmosphere at 850 #8451; under the protection of Ar gas. The synthesized lamellar MoS₂ nanosheets randomly stacked and formed large-area flocculose microstructure, which favored the high catalytic activity for HER. The microstructure of the as-prepared MoS₂ was analyzed by high-angle angular dark field imaging. HER measurements were conducted using a three-electrode cell with a 0.5 M sulfuric acid electrolyte. The as-prepared flocculose-like MoS₂ microstructure exhibited a high HER electrocatalytic activity with a low overpotential and a small Tafel slope.
Reference
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The development of efficient and cost-effective materials for polymer electrolyte fuel cells (PEFC) is a key area of scientific research which promises to drastically reduce our dependence on fossil fuels [1]. After decades of research, platinum-based nanoparticles on a conductive carbon support are the most commonly used electrocatalysts due to their exceptional performance when compared to other materials. However, platinum electrochemical surface area degradation during operation as result of sintering, agglomeration/coalescence, dissolution, or detachment of the particles owing to support corrosion, results in performance losses. Therefore, extensive research efforts are underway to optimize the catalyst, either to reduce the cost (by reducing Pt loading) or to improve its activity and durability (by optimizing composition). As an example, Pt deposited on hybrid support materials, such as niobium oxide-carbon, demonstrates enhanced oxygen reduction reaction (ORR) activity together with improved durability [2].
In these experiments, platinum nanoparticles with variable NbO_x content were deposited via sol-gel synthesis onto high surface area carbon support to investigate their electrochemical behaviour and durability. Then, chemical mapping of the catalysts by electron energy loss spectroscopy spectrum imaging in an aberration-corrected scanning transmission electron microscopy was used to understand the links between fuel cell performance and changes in the structure, composition, and morphology of the catalysts under various operating conditions. The changes between BOL (beginning of life) samples and EOL (end of life) samples after electrochemical cycling were studied.
The advanced transmission electron microscopy studies reveal fine details of the spatial distribution of the noble metal components in hybrid catalysts. The results show the presence of isolated Pt atoms, 1-5 nm Pt-rich or 1-20 nm NbO_x particles, and Pt-Nb bimetallic nanoparticles (both alloy and Pt-core/Nb-shell structures). In the EOL samples, the Pt particle size increased marginally with an associated decrease in the exposed metal fraction with respect to a monometallic reference. Moreover, when a near-edge fine structure for the niobium oxides phases, such as the O-K edge, was used to study the oxidation state of the niobium particles, a heterogeneous distribution of niobium in different oxidation states was found both before and after cycling. The electrochemical results reveal the synergistic interaction of NbO_x species with Pt, enhancing the catalyst activity and partially mitigating the Pt dissolution and agglomeration. These findings demonstrate that highly dispersed Pt/NbO_x on carbon supports is a promising electrocatalyst for PEFC.
[1] M. K. Debe, Nature, 2012, 486, 43-51.
[2] T. Trefz et al., 224th ECS Meeting, 2013, No.1501.
Acknowledgments: This work was supported by NSERC and AFCC under a NSERC Collaborative Research and Development Grant.