Symposium EC5 : Proton Transfer and Transport---From Biological Systems to Energy Applications

The development of new membranes cheaper than Nafion®, with similar conductivity and lower hydrogen/methanol cross-over, is crucial for widespread commercial applications of Polymer Electrolyte Membrane Water Electrolysers (PEMWEs) and Direct Methanol Fuel Cells (DMFCs) [1, 2]. This study reports on the synthesis and development of PEMs based on sulfonated polysulfone (sPSf) for application both in WEs and DMFCs at different operating temperatures. The sPSf was synthesized by using trimethyl silyl chlorosulfonate as sulfonating agent in a homogeneous phase of chloroform [3]. In order to try to reduce methanol crossover in DMFCs, functionalized silica was prepared (by reacting silica with neat chlorosulfonic acid at room temperature) and added as a filler in the sPSf membrane. The prepared membranes were physico-chemically characterized and used as electrolytes in PEMWEs and DMFCs [4, 5].
Besides, the transport properties of water and methanol through the electrolyte membranes as a function of methanol concentration (e.g. 1M - 5M CH₃OH) and temperature (from room temperature up to 80°C) were analyzed by using Pulse Field Gradient (PFG) NMR technique.

References
[1] A. S. Aricò, S. Siracusano, N. Briguglio, V. Baglio, A. Di Blasi, V. Antonucci, J. Appl. Electrochem. 43 (2013) 107–118.
[2] F. Lufrano, V. Baglio, P. Staiti, V. Antonucci, A.S. Aricò, J. Power Sources 243 (2013) 519-534.
[3] F. Lufrano, V. Baglio, P. Staiti, A. Stassi, A.S. Aricò, V. Antonucci, J. Power Sources 195 (2010) 7727-7733.
[4] S. Siracusano, V.Baglio, F.Lufrano, P.Staiti, A.S.Aricò, Journal of Membrane Science 448 (2013) 209–214.
[5] F. Lufrano, V. Baglio, O. Di Blasi, P. Staiti, V. Antonucci, A. S. Aricò, Phys. Chem. Chem. Phys. 14 (2012) 2718–2726.

Various ionomers and polymers have been synthesized and evaluated for use as the proton conducting electrolytes in proton exchange membrane (PEM) fuel cells. Electrospinning of polymeric nanofibers is presently of significant interest as it provides a means of controlling polymer morphology. To this end, Nafion, the benchmark perfluorosulfonic acid (PFSA) membrane, has been electrospun with carrier polymers including PAA or PEO to produce mechanically stable nanofibrous membranes.
We have recently undertake an investigation to determine the structural and morphological aspects of composite systems consisting of either fibers or particles of polybenzimidazole (PBI) with PFSA ionomers through coarse-grained classical simulations. Our approach has been to utilize dissipative particle dynamics (DPD) simulations to systematically model the PBI/PFSA systems as a function of water content. Our focus has been identifying how the nature of the interactions of the components results in different morphologies and distinctions in the connectivity of the proton conducting pathways as the ratio of PFSA ionomer to PBI matrix is varied.

Protons in solids are not always welcome. They can cause brittleness in pressure vessels. They can make electric shorts in semiconductors. They can promote dielectric breakdown in insulators. Because of the abundance of humidity (H₂O) in ambient environment and the crystalline imperfections (defects) in materials, water molecules like to enter some materials and settle as hydrates or hydrides structures. Oxygen and protons become part of the structure. Upon thermal excitation, the hydroxyl bonds may become hydrogen bonds which eventually “melt”. The protons may then liberate and become electric charge carriers, which lend them a particular new function in solid electrolytes as proton conductors.
We have in the last couple of years observed and investigated the biography and lifestyle of such protons from localization to de-localization. The proton is an elusive player and not always easy to make out. With a combination of neutron and synchrotron based scattering and spectroscopy methods, along with electroanalytical techniques, we have increased our understanding of the proton dynamics and its structural origin, which is important for super-protonic conductivity.
We have investigated the oxygen vacancy filling of engineered oxygen deficient BCY by water molecules with impedance spectroscopy and ambient pressure XPS [1], which enabled us to sketch a detailed picture of the correlation of molecular and electronic structure changes, with concomitant onset of proton conductivity at higher temperatures. We thus could design experiments, where the proton-phonon coupling was quantitatively investigated with high p-T impedance spectroscopy combined with quasi-elastic neutron scattering [2,3]. Supported by pressure dependent XRD and Raman scattering data [4,5] we correlated the proton jumping parameters with the temperature and found that the proton jump times follow a polaron relation [6,7].
[1] Q. Chen et al., Chem. Mater. 25 (23), 4690 (2013).
[2] Q. Chen et al., Solid State Ionics 252, 2 (2013).
[3] Q. Chen et al., High Pressure Research 32(4), 471 (2012).
[4] Q. Chen et al., J. Phys. Chem. C 115 (48), 24021 (2011).
[5] Q. Chen et al., J. Eur. Ceram. Soc. 31 (14), 2657 (2011).
[6] Q. Chen et al., Appl. Phys. Lett. 97, 041902 (2010)
[7] A. Braun et al., Appl. Phys. Lett., 95, 224103 (2009).

Redox flow batteries, solar-fuel generators, and polymer electrolyte membrane fuel cells and electrolyzers all rely on the use of a solid polymer electrolyte for ion selective transport and electrolyte separation. In these applications, the membrane is typically Nafion®, a commercially available perfluorinated sulfonic-acid (PFSA) ionomer. PFSA is characterized by a strongly hydrophobic polytetrafluoroethylene (PTFE) backbone, and randomly attached pendant side chains of perfluorinated vinyl ethers terminated with hydrophilic sulfonic acid functional group. The performance in terms of ion conductivity, water uptake, durability, and strength have all been related to the structure and morphology of the membrane^1,2. Significant work has been devoted to understanding the structure of Nafion as a solid material with a specific emphasis on understanding how material properties alter with scale (bulk-to-thin films)³. Less attention has been focused on the manufacturing process of PFSA membranes, which involves a phase transition from a polymer colloidal solution to a solid state form. During this transition the colloidal material system is exposed to shear dynamics as well as a solvent evaporation process, both of which can induce structural transformations in the cast materials. Thus, it is of great interest to understand how the structure of the membrane can be controlled either by novel colloidal ‘ink’ design or controlled manufacturing processes. Herein, we directly examine membrane processing conditions utilizing a slot-die printer with GISAXS to observe the structural and morphological evolution during the solvent evaporation process. Moreover, we utilized Rheo-SANS methods to understand how PFSA in different solvents (water, NMP, and isopropyl-alcohol) align and aggregate under shear. Results indicate that solvent properties directly affect the ionomer morphology in the solution as well as the cast form, and shear induced alignment of PFSA occurs in concentrated dispersions (>2 wt%).
[1] Kusoglu, Ahmet, et al. "Role of mechanical factors in controlling the structure–function relationship of pfsa ionomers." Macromolecules 45.18 (2012): 7467-7476.
[2] Kusoglu, Ahmet, and Adam Z. Weber. "Electrochemical/Mechanical Coupling in Ion-Conducting Soft Matter." The journal of physical chemistry letters 6.22 (2015): 4547-4552.
[3] Kusoglu, Ahmet, et al. "Impact of substrate and processing on confinement of nafion thin films." Advanced Functional Materials 24.30 (2014): 4763-4774.

The promising characteristics of redox flow batteries (RFBs) for large scale energy storage are well known. The vanadium redox flow battery, VRFB, is currently the closest to commercialization, and employs a mixed acid electrolyte with dissolved vanadium ions (V^2+/3+/4+/5+) as the redox active species. Many other chemistries are being considered for flow batteries in an attempt to optimize the cost-performance benefit of this technology. However, in almost all cases, the electrolyte consists of an acidic solution containing dissolved ionic reactants. Optimal performance of an RFB therefore relies on membrane separator technology that can achieve facile proton transport to minimize ohmic losses, while at the same time minimizing the transport of the redox active species to minimize loss of the energy stored on charge. In most applications, cation exchange membranes such as DuPont’s Nafion have been employed in an attempt to meet this challenge. However, their performance characteristics are not ideal.

We are considering flow battery membranes that resemble nanofiltration (NF) membranes with a pore size on the order of 1 nm where polyvalent inorganic ions (eg., Fe⁺³) and organic molecules with molecular weights greater than ca. 200 Da (quinones and other redox active organic molecules) are substantially rejected while monovalent ions (e.g., H⁺, K⁺) remain permeable. Fundamentally, polymeric materials need to be selected which will exhibit NF membrane characteristics resulting in low redox species crossover, high ionic conductivity with acidic electrolytes, and low hydraulic permeability due to the absence of larger pores. We will present results for composite membranes we are developing based on this principle.

Supercapacitors (SCs) are playing a key role for the development of next generation technologies that should address sustainability in terms of components, materials processing and energy impact.

Self-powered and self-sustaining integrated systems are of great interest for different fields ranging from remote sensing, robotics and medical devices. SC miniaturization and integration into more complex systems that include energy harvesters and functional devices are valuable strategies that address system autonomy.

Here, the practical energy and power performance of aqueous SCs developed by sustainable processes and materials and implemented into energy harvesters and function devices (e.g. sensors) are reported.

Specifically, the integration of nanostructured carbon electrodes obtained by additive printing into microbial fuel cells (MFCs) and electrolyte-gated transistors is discussed. The study focuses on the use of aqueous NaCl and phosphate buffer (PBS) solutions that are typically used in bio-electrochemical devices, like bio-sensors and MFCs with the purpose of showing novel and sustainable approaches for the design of miniaturized autonomous systems.

References:
J. Sayago, U. Shafique, F. Soavi, F. Cicoira, C. Santato, TransCap: a monolithically integrated supercapacitor and electrolyte-gated transistor, J. Mater. Chem. C, 2 (2014) 10273-10276.

C. Santoro, F. Soavi, A. Serov, C. Arbizzani, P. Atanassov, Self-powered supercapacitive microbial fuel cell: The ultimate way of boosting and harvesting power, Biosens. Bioelectron, 78 (2016) 229-235.

F. Soavi, L. Bettini, P. Piseri, P. Milani, C. Santoro, P. Atanassov, C. Arbizzani, Miniaturized supercapacitors: key materials and structures towards autonomous and sustainable devices and systems, J. Power Sources, 326 (2016) 717-725.

J. Houghton, C. Santoro, F. Soavi, A. Serov, I. Ieropoulos, C. Arbizzani, P. Atanassov, Supercapacitive Microbial Fuel Cell: Characterization and analysis for improved charge storage/delivery performance, Bioresource Technol., 218 (2016) 552–560.

Recent development of resonant soft x-ray scattering (RSoXS) at the Advanced Light Source (ALS) has enabled its applications to many critical research areas of materials research.^1,2 Combining conventional x-ray scattering with soft x-ray absorption spectroscopy, RSoXS is a unique chemical sensitive structure probe that provides a novel route to unambiguously decipher the complex morphologies of mesoscale materials. Tuning x-ray photon energies to match the absorption spectrum of the different chemical components, the scattering contributions from the different components can be selectively enhanced, enabling a glimpse into these complex morphologies with unprecedented details. Applications of RSoXS have been extended to the areas of structured polymer assemblies, organic electronics, functional nano-composites, as well as liquid crystals. The overarching challenge now across various disciplines is to investigate the interfacial phenomenon of new and complex materials in their operational conditions, including batteries, catalysts, gas separations, fuel cells and water desalination, and bio-hybrid systems. In order to achieve comprehensive understanding of the in-operando process, we need multimodal research tools that provide information from different perspectives in order to discover, understand, and control the interfacial phenomena and architectures. This will require combining different in situ probes, such as x-ray scattering and electron microscopy, simultaneously in the same operating condition. We will discuss the recent development of customized instrumentation, multimodal characterization methods, as well as comprehensive theory for the extraction of the chemical distribution and spatial arrangement at multiple length scales in the application of membrane materials.
1 Liu, F., Brady, M. A., & Wang, C. (2016).. European Polymer Journal. 88, 555-568
² Su, G. M., Cordova, I. A., Brady, M. A., Prendergast, D., & Wang, C. (2016). Polymer, 99, 782-796.

Titanium dioxide has been studied extensively as a promising, low cost (photo)catalyst for water splitting. The well-documented activity of TiO₂ towards oxygen evolution led us to examine its catalytic activity for the oxygen reduction reaction on the solid acid electrolyte CsH₂PO₄. Specifically, titania, created by partial oxidation of titanium metal particles, has been incorporated into the cathodes of solid acid fuel cells. Additional cathode components are the electrolyte itself and a carbon-based interconnect. It is found that the activity of such composite cathodes depends on the relative amounts of rutile and anatase polymorphs generated from titanium partial oxidation, in turn controlled by the temperature and time of the oxidation treatment. When fully oxidized, the rutile polymorph is found to be more active than the anatase analog. Indeed, activity is counter-correlated with anatase content, irrespective of the total extent of oxidation (i.e. conversion of titanium to titania). In addition, control of the oxidation treatment provides control over the average oxidation state in the oxide, and thereby another means by which to control electrochemical activity. While the activity of these titania catalysts do not yet rival that of Pt for oxygen electroreduction on proton conducting electrolytes, these results suggest strategies for minimizing and potentially eliminating Pt in high-performance fuel cells.

Cathode materials for proton conducting ceramic fuel cells should exhibit a proton conductivity exceeding about 10^-5-10^-4 S/cm to extend the reactive zone for oxygen reduction to water beyond the gas/electrode/electrolyte three phase boundary [1]. Proton uptake into (Ba,Sr,La)(Mn,Fe,Co)O_3-d cathode materials can occur by incorporation of H₂O similar to the hydration reaction of proton conducting electrolytes (for ), or by incorporation of only H () assuming ideally dilute defect concentrations [2,3].
From thermogravimetry in different pH₂O (including the transient behavior yielding the proton mobility) [4], for Ba_0.5Sr_0.5Fe_0.8Zn_0.2O_3-d a proton conductivity of » 10^-3 S/cm at 350-450 °C can be estimated, which suffices to transport protons from the electrolyte through a thin dense cathode film to the gas interface. This makes the whole surface active for oxygen reduction to water, which can in principle proceed without oxygen incorporation into the cathode material. However, the pO₂ and pH₂O dependences from microcontact impedance spectroscopy indicate that for Ba_0.5Sr_0.5Fe_0.8Zn_0.2O_3-d and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-d the oxygen reduction to water proceeds via intermediate uptake of O into surface oxygen vacancies [5].
Generally, the proton concentrations in (Ba,Sr,La)(Fe,Co)O_3-d cathode materials were found to be less than 3 mol% at 250 °C [3,6], which is much lower than for acceptor-doped Ba(Zr,Ce)O_3-x electrolytes (remaining fully hydrated up to 400-500 °C). The origin for this behavior and correlations of cation composition and proton uptake will be discussed.[6] While the basicity of the oxide ions is known to favour proton uptake, other factors such as the nature and charge of the B cation are also relevant. The thermogravimetric results furthermore point towards pronounced interactions between protons and electron holes.

[1] R. Merkle, D. Poetzsch, J. Maier, ECS Transact. 66(2) (2015) 95
[2] D. Poetzsch, R. Merkle, J. Maier, Adv. Funct. Mater. 25 (2015) 1542
[3] D. Poetzsch, R. Merkle, J. Maier, Faraday Discussions 182 (2015) 129
[4] D. Poetzsch, R. Merkle, J. Maier, Phys. Chem. Chem. Phys. 16 (2014) 16446
[5] D. Poetzsch, R. Merkle, J. Maier, J. Electrochem. Soc. 162 (2015) F939
[6] R. Zohourian, R. Merkle, J. Maier, Solid State Ionics (2016) submitted

Ionic transport dynamics underpin the functionality of most energy storage and conversion technologies. Perovskite-structured, Yttrium doped barium zirconate (Y-BZO) has been widely studied as a promising electrolyte for proton-conducting solid oxide fuel cells, due to its high proton conductivity and excellent chemical stability at intermediate operating temperatures (400-700 °C). Literature reports focusing on approaches to enhance conductivity in Y-BZO are mostly based on developing new processing methods as well as new sintering aids, with macroscopic characterization such as X-ray diffraction and impedance spectroscopy. In order to identify the fundamental role of dopants on the proton transport mechanisms, it is vital to understand the defect distribution and dopant-induced lattice distortion at the atomic scale, thereby elucidating the correlation between point defects and lattice distortions and their role on proton conduction.

In this study, a series of epitaxial Y-BZO thin films (Y = 0 to 20 %) were prepared on (100) oriented MgO substrates by pulsed laser deposition. Time resolved Kelvin probe force microscopy was used to obtain the surface potential mapping in both the space and time domains, from which the activation energy for proton transport was calculated. It was found that the activation energy increases from 0.45 V to 0.64 V with increasing dopant concentration, which is consistent with the impedance spectroscopy measurements. A Nion UltraSTEM was used to acquire fast, frame-averaged, scanning transmission electron microscopy images of the Y-BZO lattice, and distortion analysis on each B-site atom was performed on these images. Both bond angle and displacement distortion increases with increasing dopant concentration, which is consistent with the density functional theory (DFT) predictions. Furthermore, DFT calculations suggest that upon increasing the dopant concentration, an increased density of Y-Y pairs would trap more protons owing to the increased local lattice distortion, thereby explaining the observed monotonic increase in activation energy with dopant concentration. This finding provides new ways of designing new proton conducting oxides by inhibiting dopant clustering and lattice distortion.

The research was sponsored by the Laboratory Directed Research and Development Program fund at the Oak Ridge National Laboratory. Computations were performed at National Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy.

The scarcity of fossil energy and the decrease in affordable energy sources in association with increasing pollution rate in environment due to the strong industrial activity represent driving forces in direction to the development of alternative and clean energy resources. Microbial and yeast fuel cells (MFCs and YFCs) are electrochemical devices that have been progressively reported in the literature as potential candidates for sustainable production of energy due to the electricity generation in association with water treatment. MFCs and YFCs make use of microorganisms as biocatalysts, which provides the conversion of chemical energy to electrical energy. Biologic organisms oxidize organic compounds such as glucose, sucrose and fructose and produce electrons in anolyte (connected to cathode via external electric circuit). The mechanisms involved in external electron transfer (transport of intracellular electrons – produced by electron donors present in substrate - anode) introduce a key role in the production of more efficient electrochemical devices. The optimization in this process requires the introduction of additives, which improve drastically the electron transfer to the electrode while represent a contamination source for environment. Particularly, mediators are typical artificial redox molecules such as bromocresol green, neutral red, methyl red, methyl orange and methylene blue. The key role for convenient activity of mediators is based on its low redox potential, which enables the electron shuttle during microbial respiration without additional oxidation process for electron transportation. In this work, we have explored the activity of biologic fuel cells based on Escherichia coli and Saccharomyces cerevisiae under different operation conditions, viz. type of organic mediator, electron acceptor, anion exchange membrane and electrodes with the aim of improving the power generation and minimizing the production of hazardous residues. Based on these experiments, it was verified promising results for S. cerevisiae feed by glucose under anaerobic conditions, which returns power 10x higher than corresponding experiment for E. coli . Resulting power of 400 μW and voltage in order of 0.6 V is obtained after four hours of continuous growth of yeast in buffer solution. The kinetics of power generation is in agreement with data from absorbance of resulting solution (turvation degree) and dissolved oxygen. This result indicates that solution aeration and continuous insertion of substrate for yeast growth and reproduction at fixed interval of four hours represent critical condition for continuous production of electricity at optimized level in S. cerevisiae-based fuel cells devices.

Many of the issues associated with traditional oxide conducting solid oxide fuel cells can be related to the high operating temperature (800-1000 °C) of the fuel cell. This high operating temperature can lead to accelerated degradation of the cell and will increase the overall cost due to the need to use expensive super alloys in construction. In order to alleviate these issues, research is being conducted to lower the operating temperature to ~500 °C. This can be achieved by using proton-conducting perovskites in the fuel cell rather than traditional oxygen anion conducting materials. One example of a proton-conducting material that has been studied is yttrium-doped barium zirconate (BaY_0.2Zr_0.8O₃), BYZ20. BYZ20 has been shown to have a comparable ionic conductivity to yttria-stabilized zirconia, YSZ, at much lower temperatures. The presented work uses a Ni-BYZ20 cermet as the anode, lanthanum strontium cobalt ferrite (La_0.6Sr_0.4Co_0.2Fe_0.8O₃) as the cathode, and BYZ20 as the electrolyte. Cell fabrication is performed using Reactive Spray Deposition Technology (RSDT), a flame-based one-step process which reduces manufacturing costs and avoids the need for separate pellet fabrication and sintering steps. By adjusting several process parameters, RSDT can create porous anodes and cathodes with a thickness of about 10 μm or dense electrolytes with a thickness of about 2 μm. This work focuses on optimizing RSDT deposition parameters to deposit a full cell on a porous metal support. Characterization of the cells using SEM, XRD, and STEM techniques is presented as well as initial electrochemical performance data.

Proton conducting ceramic membranes have received significant scientific and technological attention in recent years due to their potential for use in a number of electrochemical devices for energy conversion and storage. Of particular note are protonic ceramic fuel cells (PCFCs), which have great potential to be operated at temperatures (350-600^oC) much lower than traditional oxygen-ion solid oxide fuel cells (SOFCs, 600-1000^oC). However, commercial viability of the PCFCs crucially hinges on overcoming several challenges: 1) fully dense thin proton conducting ceramic membranes with low area specific resistance and proton transference number must be achieved, 2) stable and compactible cathode materials must be discovered, and 3) cost-effective techniques for fabrication of single cells must be discovered. In order to address these challenges, we have successfully developed 1) large-grained proton conducting membranes, 2) triple conducting (electron, proton, and oxygen ion) oxide cathodes, and 3) solid-state reactive sintering fabrication of PCFC button cells, which allowed to demonstrate the cost-effective low-temperature PCFCs with promising performance. For the representative single cells, the high power densities of ~450mW/cm² and ~140mW/cm² were obtained at 500^oC under air/H₂ and air/CH₄ gradients, respectively, and the long-term operation of more than 1000h did not show obvious performance degradation.

Much investigation has been devoted to the study of proton conducting thin films, especially trivalently doped perovkites for use in intermediate temperature solid oxide fuel cells. While considerable attention has been given to yttrium as a doping agent in barium zirconate, little has been reported experimentally concerning other choices of dopant such as gadolinium and ytterbium. In addition to this, most of the conductivity values reported are from the so called in-plane experiments on thin films, due to the more favorable experimental conditions and choice of superior substrates to facilitate highly crystalline growth. We report on progress in using pulsed laser deposition on substrates of platinum, MgO, and NiO-BZO cermets in order to compare the differences in conducivity values in-plane and through-plane geometries. Films were deposited with a substrate temperature of 600-800^o C and a background 0₂ pressure of 50 mtorr. Laser fluence was varied from 1-3 J/cm². The targets for pulsed laser deposition were made from mixtures of commercially available BaZrO₃ and Ga₂O₃ powders by pressing at 2800 psi and sintering for 12 hours at 1400^o C. Based on calibration, films thicknesses were in the 1-2 μm range. X-ray diffraction analysis showed polycrystalline films as-deposited for temperatures over 600^o C. Conductivity was measured in the temperature range of 100-500^o C by electrochemical impedance spectroscopy on samples with Ni contacts deposited by d.c. magnetron sputtering. Results obtained and comparison of through plane and in plane measurements will be discussed.

The electronic transport properties of strongly correlated electron systems may be modified drastically by phase transitions under external stimuli such as temperature, electric field and carrier doping. We show in a rare earth nickelate (SmNiO3), spontaneous incorporation of hydrogen can happen at the triple phase boundary near catalytic electrodes and dope electrons into the nickelate lattice. The doped electron modifies the valence state of Ni as verified by X-ray spectroscopy, and induces a filling-controlled Mott transition, which is manifested as greater than eight orders of magnitude decrease in the electronic conductivity. At the same time, the proton conductivity in the nickelate is relatively high. The suppression of the electronic conduction allows us to utilize the initially metal-like material as an electrolyte for solid oxide fuel cells. We will discuss these results in this presentation and highlight the potential for exploiting strong correlation effects in electrochemical energy conversion.

Many point defects including aliovalent dopants in ionic crystals are effectively charged either negatively or positively. As a result, both repulsive and attractive electrostatic interactions stemming from the effective charge are present between point defects. Even if the total concentration of added dopants and compensating defects is already determined, the overall mass and charge transport in crystals can be significantly altered, depending on how the defects are locally distributed. By using simple manipulation of the defect distribution in this work, we demonstrate that the proton conductivity can be notably enhanced by dopant–vacancy association in the proton-conducting perovskites BaZrO_3-δ and BaCeO_3-δ. To suppress the high-temperature entropy and thus make oxygen vacancies cluster with acceptors, post-annealing was adopted at substantially lower temperatures than those employed for sintering processes. The acceptor−vacancy clustering was verified to be remarkably efficient against proton trapping by theoretical DFT calculations and experimental measurements based on impedance spectroscopy along with atomic-scale direct visualization. In particular, to ensure the acceptor-vacancy association is effective against proton trapping, the valence electron density of acceptors should not significantly vary when the oxygen vacancies cluster, based on the weak hybridization between the valence d or p orbital of acceptors and the 2p orbitals of oxygen. As a result, this study demonstrates that the strong electrostatic trapping of protons to neighboring acceptors in perovskite oxides can be remarkably overcome via control of oxygen-vacancy distribution in the lattice. Although the present study deals with two perovskites, we believe that the major conception and the strategy used in this work are reasonably applicable to other oxides in general, emphasizing the impact of control of the defect distribution on the transport behavior.

Water oxidation remains as the more challenging half reaction in water splitting due to inherently high endothermic reaction barrier, multiple electron transfer, and proton-coupled electron transfer (PCET). In natural photosystem II, water oxidation at the oxygen evolving manganese oxo-cluster is mediated by the redox-active tyrosine Z. Inspired by the natural catalytic system, we design a redox-active polydopamine (pD) layer for a cobalt-based water oxidation catalyst, Co-OEC. Since pD contains multiple phenolic moieties, e.g., catechol, (hydro)quinone, and their derivatives, it is expected that pD can also mediate PCET for water oxidation. In addition, pD can be easily coated onto a wide range of substrates as a thin film by a simple solution-based coating process, enabling us to expand our approach to various catalytic electrodes. Co-OEC is prepared by electrodeposition of cobalt ions in the presence of phosphate ions. The pD layer, located between Co-OEC and ITO (or stainless steel) electrode, can readily accept, store, and donate proton-electron pairs through the reversible redox reaction of catechol and (hydro)quinone, increasing the rate of water oxidation reaction. Tafel slope of Co-OEC/pD/ITO (185 mV decade^-1) is much lower than that of Co-OEC/ITO (261 mV decade^-1). Co-OEC/pD/ITO exhibits the lower oxidation potential (1.114 V) compared to Co-OEC/ITO (1.171 V), which indicates that the redox-active pD interlayer reduces the reaction barrier and promotes water oxidation reaction rate through PCET. In addition, the adhesive property of the pD interlayer can lead to form a mechanically stable contact between the catalyst and the electrode. Without the pD layer, Co-OEC is delaminated from the electrode under 0.54 V due to the dissolution of cobalt ions and phase transformation, leading to serious degradation of catalytic activity. However, the pD layer significantly increases the structural stability by suppressing the dissolution and delamination of the Co-OEC via the redox mediation. The Co-OEC/pD/ITO anode maintains its catalytic activities even applied at 0 V for 30 min. Our study suggests that the bio-inspired design of the redox-active polydopamine layer can greatly increase the catalytic activity and structural stability of the Co-based catalyst, and possibly other aqueous PCET catalysts, through the unique redox and metal-ligand coordination chemistry of polydopamine. This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2016R1A2B4013045).

Mixed conducting perovskites containing oxygen vacancies, holes and protons are important as potential cathode materials for protonic ceramic fuel cells (PCFC). The proton uptake in such materials can occur through hydration (acid-base reaction) and hydrogenation (redox reaction) depending on the nature of the material and conditions [1,2].
Experimentally, one-fold or two-fold conductivity relaxation is observed after stepwise pH₂O changes and diffusion-limited conditions.[3-5] Exact analytical relations for these processes were derived in ref. [2]. For a complete description, four diffusion coefficients are required. The complex non-monotonic kinetic behavior is related to the fact that in a three carrier system there is no simple coupling between the carrier fluxes, because the electroneutrality condition holds only fur the sum of all three carriers. In the present contribution, numerical simulations for a wide range of materials and conditions are presented.[2,6] They allow us to identify the conditions for the transition from one-fold to two-fold relaxation. Furthermore, they demonstrate that the time constant for the H concentration change does not necessarily match the "fast" time constants from conductivity relaxation (which probes mainly hole concentration changes).
The simulations also show that the interpretation of the temperature dependence of the effective diffusivities for acceptor-doped (Ba,Sr)(Zr,Ce)O_3-d perovskites (experimental data compiled in [7]) is far from trivial. When the transference number of oxygen vacancies exceeds that of the protons, the fast diffusion coefficient extracted from conductivity relaxation approaches the oxygen chemical diffusion coefficient (not the hydrogen chemical diffusivity as one might expect intuitively). Finally, the effect of trapping reactions on the relaxation kinetics is investigated.

[1] D. Poetzsch, R. Merkle, J. Maier, Faraday Discussions 182 (2015) 129
[2] D. Poetzsch, R. Merkle, J. Maier, Adv. Funct. Mater. 25 (2015) 1542
[3] J. H. Yu, J. S. Lee, J. Maier, Angew. Chem. Int.Ed. 46 (2007) 8992; Solid State Ionics 181 (2010) 154
[4] H. I. Yoo, J. Y. Yoon, J. S. Ha, C. E. Lee, Phys. Chem. Chem. Phys. 10 (2008) 974
[5] E. Kim, H. I. Yoo, Solid State Ionics 252 (2013) 132
[6] R. Merkle, R. Zohourian, J. Maier, Solid State Ionics 288 (2016) 291
[7] G. R. Kim, H. H. Seo, J. M. Jo, E. C. Shin, J. H. Yu, J. S. Lee, Solid State Ionics 272 (2015) 60

Hematite (α-Fe₂O₃) is a canted anti-ferromagnet and a highly insulating semi-conductor at room temperature. Its resistance can be suppressed by chemically doping donor (Ti, Zr, Si, Ge) or acceptor (Mg) elements at the Fe-site; however this process is irreversible. Here we show that hydrogen doping, achieved via a catalytic spill-over method, induces an unprecedented ferromagnetic conducting phase in α-Fe₂O₃ in a reversible manner. In particular, we observe that the magnetism is enhanced 5 fold and the conductivity is increased by more than 4 orders of magnitude at room temperature. The novel phase is further characterized by X-Ray Diffraction, Raman Spectroscopy, Optical Microscopy and Elastic Recoil Detection Analysis. Furthermore hydrogen, owing to its light mass, can be excorporated easily form the host lattice allowing the doping process to be reversible. Our work paves way for engineering novel properties in hematite thin films opening up their applicability to novel protonic and spintronic devices.

Uncovering the details of proton transport mechanisms in high-temperature protonic conductors may enable a new generation of solid oxide fuel cells capable of efficient operation in the intermediate temperature range (500-750°C). Thin film proton conducting electrolytes based on yttrium-doped barium zirconate deposited by pulsed laser deposition (PLD) have yielded high protonic conductivity consistent with this goal. Epitaxial growth of BaZr_0.8Y_0.2O_3-δ films with high protonic conductivity on lattice-matched single crystal substrates such as MgO, SrTiO₃ and LaAlO₃ is now established. While epitaxy on more practical electrode systems, such as BaZrO₃/Ni cermets, is not practical, PLD offers the opportunity of depositing films with high crystallographic texture on substrates with large lattice mismatch and even on amorphous materials. Although not expected to achieve the same performance of epitaxial films, these highly textured proton conductors, if properly engineered in their microstructure and degree of texturing, may deliver acceptable levels of protonic conductivity and enable fundamental proton transfer studies on a variety of thermally matched, porous, and conductive substrates amenable for applications. In this work we explore how to control of crystallographic texture in films of gadolinium-doped barium zirconate, a system that has not yet been fully investigated. Films are deposited by PLD and studied for the effect of texture on their ionic conductivity. Gd-doped BaZrO₃ deposition is carried out using ablation targets prepared from commercially available barium zirconate (BaZrO₃) and gadolinium oxide (Gd₂O₃) powders. The masses of the constituent powders are adjusted in suitable mixtures to yield targets containing 5, 10, and 15 mol. % of Gd in BaZrO₃. Targets of pure BaZrO₃ are also prepared for comparison. Targets are pressed at 2800 psi and sintered at 1400°C for 12 hours in air. PLD is carried out using a KrF excimer laser (248 nm) with energy density between 0.5 and 5 J/cm² and pulse repetition rates between 10 and 30 Hz. Three different types of substrates are used: plain (100) MgO, Pt-coated (100) MgO, and BaZrO₃/Ni cermets. Substrates are maintained at temperatures between 650°C and 800°C. Deposition takes place in O₂ atmosphere at pressures between 50 and 300 mTorr in a vacuum system with base pressure below 7.0×10⁻⁷ Torr. Based on deposition rate calibration data, PLD was carried out for sufficient times to achieve film thicknesses in the 1-2 mm range. Using X-ray diffraction pole figure measurements, we study the effect of laser energy density, plume direction of incidence, background pressure, and choice of substrate on the crystallographic texture of the polycrystalline Gd-doped BaZrO₃ films obtained. Electrochemical impedance spectroscopy measurements on textured samples is carried in an environment with controlled partial pressure of water in an effort to correlate crystallographic texture and protonic conductivity.

Diamond has outstanding bulk physical (super hardness, chemical inertness, biocompatibility, optical luminescence, just a few) properties. In the nanoworld, to exploit these outstanding bulk properties, the surfaces of nanodiamond (ND) particles are accordingly engineered targeting specific applications. Modification of a conductive diamond electrode (heavily boron doped diamond; BDD) with an immobilized layer of diamond is found to significantly enhance the recorded currents for reversible oxidation of ferrocene methanol (FcMeOH). Electrochemical measurement current enhancement is related to nanodiamond diameter, with enhancement increasing in the order <<1000 nm < 100 nm < 10 nm < 5 nm. We attribute the current enhancement to two electrocatalytic processes: (1) electron transfer between the solution redox species and redox-active groups on the nanodiamond surface; (2) electron transfer mediated by FcMeOH⁺ adsorbed onto the nanodiamond surface. The first process is pH dependent as it depends on nanodiamond surface functionalities for which electron transfer is coupled to proton transfer. The adsorption mediated process is observed most readily at slow scan rates and is due to self-exchange between adsorbed FcMeOH⁺ and FcMeOH in solution. Alternatively, it is proposed that surface functionalities, defect sites and unsaturated bonding give rise to surface electronic states with energies within the band gap of undoped diamond. It is known that these surface states act as both electron donors and acceptors and can support electrocatalytic redox processes in the presence of specific redox-active molecules via a feedback mechanism. FcMeOH⁺ has a strong electrostatic affinity for the nanodiamond surface, as confirmed by Raman spectroscopy experiments. Likewise, a model metalloprotein i.e. cytochrome c (Cyt c) on nanodiamond is used to demonstrate the biocatalytic process and investigating interfacial electron transfer kinetics. We gratefully acknowledge financial support from NSF KY EPSCoR, NASA KY EPSCoR and WKU Research Foundation grants.

Hydrogen is ubiquitous in electronic devices due to processing conditions and is known to both passivate the existing and induce new structural defects. Recently it has been demonstrated that atomic hydrogen (H) can break strained Si–O bonds and induce new defects in amorphous SiO₂ [1,2]. Here we investigate the interaction of atomic H with amorphous hafnium oxide (a-HfO₂). To study the distribution of defect properties, ten defect-free a-HfO₂ structures with 324 atoms were produced by molecular dynamics simulations using the force field [3] and further optimised using Density Functional Theory (DFT) calculations. The average density of these structures is 9.6 g cm^-3.
Our results indicate that atomic H occupies an interstitial position in a-HfO₂ and prefers to be in the positive or negative charge state depending on the system’s Fermi level. Atomic H in the neutral charge state can diffuse and interact strongly with the strained Hf–O bonds in the a-HfO₂ networks. The calculations show that H atom can break the strained Hf–O bonds, creating structures which consist of a 5-fold coordinated Hf atom facing a hydroxyl group. To study the distribution of these defects, up to 70 configurations were calculated. This defect introduces a one-electron level at 2.4 eV below the a-HfO₂ conduction band, ranging from 2.1 to 2.7 eV dependent on the sample density and local environment. We show that the hydroxyl center can be thermodynamically stable in the neutral charge state.
These results are discussed in conjunction with the experimental data using the exhaustive photo-depopulation spectroscopy of a-HfO₂ samples to investigate the temperature dependence of deep electron trapping states [4].

[1] A.-M. El-Sayed, Y. Wimmer, W. Goes, et al., Phys. Rev. B 92(1) 014107 (2015)
[2] Al-Moatasem El-Sayed, Matthew B. Watkins, Tibor Grasser, et al., PRL 114, 115503 (2015)
[3] G. Broglia, G. Ori, L. Larcher, and M. Montorsi, Model. Simul. Mater. Sci. and Eng., 22 (6), 065006 (2014)
[4] F. Cerbu, O. Madia, V. Afanasiev, et al., ECS Transactions, 64 (8), 17-22 (2014)

Eumelanin is a brown-black biopigment present in flora and fauna, exhibiting a number of functional properties, such as metal chelation, free radical scavenging, antioxidant and electronic-ionic hybrid conductive behavior. Like other electronic-ionic hybrid conductive biomolecules, eumelanin has hydration-dependent electrical conduction properties [1][2]. The possibility to exploit these hydration dependent properties to design novel technologies, e.g. moisture sensors, is the key motivation of the present work.

We report on the behavior of 60 nm-thick films of synthetic eumelanin
(Sigma) used as the moisture-sensitive material in planar devices, making use of pairs of photolithographically patterned Pt electrodes, with interelectrode distances at the micrometric scale. We observed changes in the behavior of the electrical current vs time plots, according to different relative humidity (RH) of the atmosphere (ranging from 90% to 50% relative humidity, RH).

In consistency with the hypothesis of a comproportionation equilibrium in eumelanin [2], which describes the regulation of the distribution of the redox states of the pigment as a function of the humidity conditions, we observe an increase of the electrical current with RH.
In particular, at a sweeping rate of 0.05 mV/s in the interval of 0.05 V – 0.6 V we observe a current of ~ 15 nA at 90% RH and current of 1 nA at 50% RH (interelectrode distance 10 microns and width 4 mm). Only within the range 0.05 V - 0.2 V a linear behavior is observed. Unlike other ionic-electronic hybrid conductive biomolecules, the current exhibits a hysteresis behavior [3]. Through nano IR investigations, we investigate chemical changes resulting from faraday interfacial processes.

Efficient and directional proton transport is a very necessary energy conversion step whatever in biochemical process and artificial electrochemical energy systems. Microbial rhodopsins photosynthesis is an extremely simple but efficient natural light-driven proton pump energy conversion system. With advanced materials science and manufacturing engineering, the biohybrid nanosystems based on microbial rhodopsins and functional materials have been paid much attention.
In past five years, we devote ourselves on hybrid nanosystem through the integration of proton pump microbial rhodopsin, bacteriropoin(bR) and proteorhodopsin (pR), with functional materials for energy conversion, sensoring and artificial version studies. We focus on the artificial use of bR and pR photoelectric energy conversion through enhancing photocurrent density and enriching photocurrent waveform. Surface plasmonic effect of Au nanoparticles and proton conductor assisted 3D proton transfer have successfully improved bR and pR photocurrent, and greatly ameliorate the photoelectric performance [1, 2]. Inspired by the plasma membrane capacitor-like behavior, we developed a pR bio-capacitor system and regulated photocurrent duration time (PDT) through nanochannel resistance. Consequently, pR original transient photocurrent has been transformed into square-like waveform, which would be of broad use in further nanoenergy conversion [3, 4]. Taking advantage of pR pH-dependent photoelectric characteristics, a pR-hybrid pH sensor has achieved real-time pH detection with quick response and high sensitivity [5]. Recently, bR and pR frequency-responsive characterization was identified in the as prepared photoelectric system and further introduced to construct artificial vision [6]. Moreover, particular effort has been paid on the cooperation and adjustment between bio-components and functional materials. These original findings improve the perception on rhodopsin protein and provide mechanism insights from pure biophysical studies into the design and regulation of artificial biohybrid devices.
References:
1. Z. Guo, D. Liang, S. Rao and Y. Xiang, Nano Energy, 2015, 11, 654-661.
2. S. Rao, Z. Guo, D. Liang, D. Chen and Y. Xiang. Advanced Materials, 2015. 27(16): 2668
3. S. Rao, S. Lu, Z. Guo, Y. Li, D. Chen and Y. Xiang, Advanced Materials, 2014, 26, 5846-5850.
4. S. Rao, K. J. Si, L. W. Yap, Y. Xiang, and W. Cheng, ACS Nano, 2015, 9 (11), 11218–
11224
5. S. Rao, Z. Guo, D. Liang, D. Chen, Y. Wei and Y. Xiang, Physical Chemistry Chemical Physics, 2013, 15, 15821-15824.
6. S. Lu, Z. Guo, Y. Xiang, L. Jiang, Advanced Materials, DOI: 10.1002/adma.201603809

In a classic paper, Miller and Abrahams (M-A) showed that at modest temperatures, a kinetic process with low activation energy, ΔΕ , in a solid, for example, will take place by the annihilation of a phonon or IR vibration of almost exactly the energy needed for the process, to that the process takes place at a rate, ν , given by (the Arrhenius equation) ν = ν_oe —ΔΕ / kT,
where is the attempt frequency. There is a strong natural tendency to believe that this is all we need to know. However, what happens at that large ΔΕ compared to excitation or thermal energies, is quite different. In that case, the entropy, ΔS , in the free energy of excitation includes a contribution, ΔS_M , which we call multi-excitation entropy (MEE), and which increases with ΔΕ. ΔS_M is proportional to ΔΕ in the simplest cases, and follows a power law in more complicated situations. The most obvious consequence of this is that the prefactor of the Arrhenius equation includes the true attempt frequency, v_oo , multiplied by a term which increases exponentially with ΔΕ, and may vary by 15 orders of magnitude for a range of ΔΕ on the order of 2 eV. This is known to physicists as the Meyer-Neldel rule (MNR), to chemists as the Isokinetic rule, and to biologists as the Compensation rule. MNR can provide information concerning microscope aspects of the kinetic process. For example, the constant of proportionality between ΔS_M and ΔΕ provides information concerning the source of the excitation fluctuation. In measurements of conductivity, we may be able to learn some of the physics of the process, by extracting a σ₀₀ from MNR. MNR has been observed in protonic conductivity in minerals and hydrogen storage in solids. We discuss what may be learned from such observations.

The evergrowing demand for developing environmentally friendly technologies has been driving efforts to utilize biomaterials in modern devices. The use of proteins for the fabrication of proton conducting materials seems to be particularly attractive, since they naturally contain acidic and basic groups that can promote proton conduction. However, only little is known about the contribution of these groups to the proton conductivity. In this talk I will present a bio-inspired approach, in which the tendency of short protein sequences (peptides) to self-assemble into fibers and nanotubes is used to design prepare and characterize proton conducting materials.
Using the design flexibility offered by peptides, I will show that the introduction of acidic or basic side chains significantly increases proton conduction. In particular the side chains are found to be much more effective in promoting proton conduction then the termini of the peptides. Furthermore, it will be shown that acidic side chains induce higher conductivity then basic side chains both due to higher efficiency of producing charge carriers and their higher mobility. Focusing on proton accepting groups, I will further demonstrate the intimate relationships between the nature of the side chain and the obtained conductivity.
Our studies highlight the delicate interplay between peptide sequence and functional behavior. The rational design of peptides based on the discovered design rules provides a promising route for fabrication of novel type of environmentally friendly, high performance proton conducting materials.

In biological systems, most of the communication between cells is mediated by membrane proteins and ion channels that passively allow or actively control the flow of ions and small molecules across the cell membrane. A bioelectronic device in which ion channels control ionic flow across a lipid bilayer with an applied voltage should therefore be ideal for interfacing with biological systems. Here, we demonstrate a biotic-abiotic bioprotonic device in which Pd contacts actively regulate proton (H⁺) flow across a supported lipid bilayer (SLB) incorporating the ion channel Gramicidin A (gA) and the voltage gated ion channel Alamethicin (ALM). This is the first time that H⁺ conducting channels have been integrated with Pd/PdHx H⁺-conducting contacts and that the H⁺ current flowing through these channels has been directly measured and controlled. This work opens the door to integrating more complex H⁺ channels such as bacteriorhodopsin at the Pd contact interface to produce responsive biotic-abiotic devices with increased functionality.

Biocompatible and biodegradable materials that store electrochemical energy are attractive candidates for applications in bioelectronics and electronics for everywhere. We report on the discovery of the energy storage properties of the pigment melanin in supercapacitors and flexible micro-supercapacitors. Biocompatibility and biodegradability make the pigment melanin, which is based on dihydroxyindole and dihydroxyindole carboxylic acid building blocks, an interesting candidate for applications in bioelectronics and sustainable electronics. In addition, the efficient and reversible charge storage properties of melanin in aqueous electrolytes permits to exploit it as an electrode in electrochemical energy storage/conversion devices, such as batteries and supercapacitors.
Here we report on the use of melanin as electrode material for supercapacitors and microsupercapacitors. The catechol-quinone moieties present in the melanin and the proton conducting properties of melanin are likely responsible for the reversible pseudocapacitive current observed. The main novelty of our work is the discovery of a new material for supercapacitor electrodes, in addition to well-established materials, such as activated carbons, carbon nanotubes, graphene, metal oxides and conducting polymers. The biocompatibility and biodegradability featured by melanin, together with its low cost, make it an extremely attractive material for environmentally and human friendly energy storage solutions.
We demonstrated supercapacitors and flexible micro-supercapacitors making use of electrodes based on the biocompatible and biodegradable pigment melanin, working in aqueous electrolyte. In slightly acidic media, a gravimetric specific capacitance as high as 167 F/g (specific capacity of 24 mAh/g) was observed for melanin-based electrodes on carbon paper. A maximum power density of up to 20 mW/cm² was deduced for the corresponding melanin supercapacitor.
Capitalizing on these results, we demonstrated a binder-free micro-supercapacitor fabricated on flexible polyethylene terephthalate (PET). The microfabrication was performed by unconventional lithography based on ParyleneC patterning. Our flexible micro-supercapacitors showed a power density of 5.24 mW/cm² at an energy density of 0.44 mJ/cm² and a specific capacitance of 10.8 F/g (about 4.3 mF/cm², i.e. 1.7 F/cm³). Micro-supercapacitors were operated at fast electrode potential scan rates (up to 10 V/s). These results suggest that melanin based bio-micro-supercapacitor may serve as biodegradable power source for implantable medical devices.

In 1804, Theodore von Grotthuss proposed a mechanism for proton (H+) transport between hydrogen bonded water molecules that involves the exchange of a covalent bond between H and O with a hydrogen bond. This mechanism also supports the transport of OH- as a proton hole and describes proton transport in intramembrane proton channels. Inspired by the Grotthuss mechanism and its similarity to electron and hole transport in semiconductors, we have developed semiconductor type devices that to control and monitor a current of H+ as well as OH- in hydrated biopolymers derived from shrimp and squid. Here, I will present our efforts in integrating these devices with ion channels. I will
also present recent data on jelly extracted from the Ampullae of Lorenzini in shark and skates and I will discuss how this data may contribute to the understanding of their electrosensing function.

Accelerated Computational Materials Design of Proton and Mixed Electronic Conductors

Qiang Bai, Yifei Mo

The design and discovery of new materials have been pursued through a trial-and-error manner based on human intuition and serendipity. This traditional materials design process is time consuming and labor intensive, which significantly impede the research and development for advanced materials critical to meet our societal needs. Computational techniques based on first principles are capable of predicting materials properties accurately with little experimental input. In this presentation, I will share our success stories of leveraging first principles computation techniques in accurately predicting various properties, ranging from ionic transport, chemical stability, phase stability, and electronic conductivity, for proton conductor materials. In particular, using SrCeO3 a promising materials for H2 membrane as an example, we will demonstrate how various dopants affect the defect equilibria and materials properties. Novel polaron mechanism will also be studied and demonstrated in this proton conductor using first principles computation. The design guidelines to enhance or inhibit electronic conductivity in proton conductors will be discussed.

Designing and developing solid oxide materials that can selectively transport protons will enable us to develop the next generation solid oxide fuel cells. Protons require less activation energy compared to oxygen ions which results in lower operating temperature, higher operating efficiency and better material reliability. In this work we focus obtaining fundamental insights on how properties of host material structure along with dopants, disorder and strain influences proton transport properties in solid oxides.

We initially focus on the perovskite family of compounds (such as doped BaZrO₃). We benchmark our calculations against a wide range of experimental measurements such as kelvin probe force microscopy (KPFM), inelastic neutron scattering (INS) and atom probe tomography (APT) (obtained on epitaxial thin films). To obtain better insights on why certain cubic perovskite/dopant combinations are better at conducting protons compared to others, we developed a high-throughput framework to perform ab initio calculations. The high-throughput framework can scale massively to tens of thousands of nodes to fully exploit the computational capability of Titan at OLCF supercomputing facility. We employ this approach to calculate proton transport properties in more than 120 cubic perovskite materials with different host atoms and dopants. The results obtained from these calculations enables us to obtain better insights on how material structure – such as atomic properties (electronegativity, ionic radius) and lattice properties (sub-lattice distortion) influences proton transport properties. The results obtained from this high-throughput analysis is being employed to develop a machine learning framework to predict structure-property correlations on a larger set of perovskites materials.

Finally, we explore the role of disorder on proton transport by studying lanthanum tungstate - a disordered fluorite material. The results obtained from ab-initio models validated with inelastic neutron scattering measurements indicate that the oxygen vacancies organize in a manner to maximize the octahedral coordination of the W atoms. Further, the results also indicate that it is more favorable for the protons to adsorb onto the oxygen atoms that have minimal W coordination. We are also working towards understanding the influence of acceptor dopants such as Nb and Re on defect (oxygen vacancy, proton interstitials) formation and defect migration energies.

Acceptor-doped barium zirconate (BaZrO₃) shows considerable potential as an electrolyte material for intermediate temperature solid oxide fuel cells due to its high bulk proton conductivity and chemical stability. However, in polycrystalline materials the grain boundaries (GBs) display high proton resistivity, severely limiting the overall proton transport in the material. The low GB conductivity has been thought to be due to an intrinsic mechanism, the space charge effect.

Using density functional theory (DFT) proton and oxygen vacancy segregation have been investigated for an extensive set of tilt GBs. Both defect species are found to segregate to the GB core, with typical segregation energies of -1.5 eV and -1.0 eV for oxygen vacancies and protons, respectively. A layer-by-layer space charge model (E. E. Helgee, A. Lindman, G. Wahnström, Fuel Cells, 13, 19 (2013)) is employed to determine the potential barrier and core charge resulting from defect segregation. Below 900 K and at wet conditions potential barrier heights around 0.6V are obtained, which is consistent with experimental results. We have also investigated dopant segregation and its effect on the potential barrier. We find that if low-energy sites in the core are saturated with positive defects, an increase in the dopant concentration does lower the potential barrier. However, if the low-energy sites are not saturated an increased dopant concentration in the core could also lead to an increase in the concentration of positive defects and the core concentration is instead limited by the electrostatic potential.

To conclude, segregation of oxygen vacancies and protons plays an important role in the formation of space charge potentials at the grain boundary interface. Additionally, our results show that protons may be the main source to the space-charge potentials under conditions relevant for fuel cell applications.

Electrolytes, at the center of various electrochemical devices, follow an incremental evolution together with breakthroughs. The finding of new electrolytes is rather challenging as it must fit certain constraints such as wide electrochemical windows, sufficient ionic conductivities, excellent thermal stability and sufficient mechanical properties. Many studies have converged towards the study of hybrid electrolytes consisting of organic and inorganic phases and to fulfill all these constraints. These electrolytes have recently experienced new advances by controlling their structure at various length scales from macro- to nano-scales. Two families of hybrid membranes for Proton Exchange Membranes for Fuel Cells, especially for temperatures up to 120 C, have recently been studied.

1) The first family of membranes consists of an original composite membrane composed of conducting polystyrenesulfonic acid-grafted silica particles into a PVdF-HFP matrix. Through extensive investigation by methods in the reciprocal and direct spaces, the structural variation of the various phases constituting the composite membranes, as a function of the amount of hybrid particles, were described. These results stress the possibility of a dichotomous interpretation leading to an overall quantitative and qualitative description of the nanostructure.

2) Another strategy has been to couple together the electrospinning and the sol-gel chemistry to obtain hybrid network for proton conduction. These hybrid membranes consist of fibers formed by cylindrical hybrid shells. By varying the nature of the various additives of the solutions and the parameters of the electrospinning, membranes with different nanostructures and nanosegregations between hydrophilic and hydrophobic domains have been obtained and described.

This complexity, both with the choice of components and with different process and chemistry options, shows the importance of the obtained multiscale structures to improve the performance of electrolytes. The control of these structures at different scales including the nanoscale seems to be a key to their evolution towards an application.

Regardless of whether they are used in the automotive industry for rear view mirrors and windows or as a part of smart fenestration systems in buildings, more and more applications of electrochromic devices are established as commercial products. This development is a result of intensive experimental and theoretical studies since the discovery of electrochromic properties of tungsten trioxide (WO₃) in 1969. A further increase of the number of electrochromic devices commercially available may be anticipated due to the increasing need for efficient energy management in the future. But despite existing electrochromic devices and widespread application, the fundamental processes of colouration in WO₃ thin films are not completely understood and the role of different oxidation states in the colouration mechanism is not clarified entirely. This lack of knowledge about the processes taking place and the influences of e.g. the film morphology or other experimental parameters arises from a lack of sufficient experimental data obtained on the same samples and therefore several theories describing only single aspects of experimental results have been proposed. We face this issue by applying a new experimental approach, based on in situ optical methods during electrochemical ion insertion into thin films of WO₃. By correlating results gathered from cyclic voltammetry, in situ transmission spectroscopy and ex situ XPS analysis, we already related the colouration in crystalline electrochromic thin films of WO₃ with the reduction of W⁵⁺ states to W⁴⁺ states^[1]. This correlation allows us to monitor the transport of ions in electrochromic films. With structured PMMA layers on top of WO₃ thin films, we can also investigate lateral diffusion of protons by in situ transmission spectroscopy. Here we present our results on proton diffusion in amorphous and crystalline WO₃ thin films. We discuss latest insights relating film morphology with transport and colouration processes in electrochromic WO₃ thin films.

^[1] S. Darmawi, S. Burkhardt et al., Phys. Chem. Chem. Phys., 2015, 17, p. 15903-15911.