Symposium EN13—Climate Change Mitigation Technologies

Direct air capture of CO2, or DAC, is gaining increasing attention as an important technology with significant potential as a climate change mitigation approach. DAC is a feasible technology, whose primary barrier to deployment in support of the climate is cost. Since 2010, Global Thermostat (GT) has been developing a technology platform for DAC addressing the primary cost drivers of the process. In this contribution, we discuss the primary elements of the GT DAC technology platform and their relation to reducing the cost of DAC.

The core challenges that GT has identified as critical to enabling low-cost DAC are i) efficient air processing, ii) selective and stable CO2 binding, iii) energy efficient sorbent regeneration, iv) efficient use of plant capital, and v) design for continuous improvement. Innovations in materials design and engineering spanning several decades of length scale are key to addressing these challenges. GT’s technology platform is based on structured honeycomb monolith air contactors, similar to those used in automobile catalytic converters or stationary deNOx emissions abatement cartridges. Porosity is engineered into these high surface area, low pressure-drop contactors through existing industrial manufacturing techniques. Quasi-solid amine-based CO2 sorbents are utilized in targeted porosity domains of the monolith contactors. These materials are employed in a rapid temperature swing process employing direct contact phase change heat transfer with saturated steam condensing on the monolith channel surface to regenerate the bound CO2 within the pore structure. Process performance is strongly linked to fundamental material-process phenomena such as adsorption rates, desorption rates, degradative mechanisms and the condensation / evaporation of steam.

The unique properties of these materials, and their interactions with the various environments imposed by the DAC process, present both opportunities and challenges in their successful deployment. In this talk we will discuss progress in both of these areas as well as an outlook on their potential.

Current industrial polymer particle production processes often use water as the main solvent, generally resulting in contamination of that water through the use of volatile organic compounds and chlorofluorocarbons¹. This results in contaminated wastewater streams, with negative consequences for the environment, oceans, and availability of drinking water. Additionally, water must be removed from the final product in costly and energy intensive drying processes, further increasing the negative environmental impact². As environmental impact becomes a more pressing concern, there is an increasing interest in sustainable solvents that have the potential to alleviate water contamination issues, reduce energy costs and reduce the impact on the environment³. Supercritical carbon dioxide (scCO₂) is a promising alternative solvent, combining considerable environmental advantages⁴ with desirable solvation and diffusivity properties of SCFs². It is a cheap, non-flammable and environmentally friendly solvent⁴, with an easily attainable critical point (T_c = 31.1 °C and P_c = 73.8 bar)². When returning to atmospheric conditions, CO₂ reverts to the gas phase providing a solvent free polymer product, without the need for energy and cost intensive drying processes and allowing the solvent to be reused.
A large hurdle in the development and wider adoption of scCO₂ as a polymerization medium is the lack of a reliable and accessible monitoring method. While the tracking of an ongoing polymerization reaction in traditional solvents can be achieved with a wide range of techniques⁵, reactions in scCO₂ are more complicated to monitor due to the elevated pressure contained in a sealed system.
Our recent publication⁶ shows a versatile and reliable on-line sampling system for polymerization reactions in supercritical fluids, unlocking the potential of this sustainable solvent. By withdrawing a small volume of a high-pressure reaction mixture and expanding it in a controlled volume before capturing it in a suitable solvent, reliable kinetic data were obtained for a range of polymerizations and reactions in scCO₂. The facile applicability of this monitoring method resulted in additional insights into the unique conditions found in scCO₂ and their effect on polymerization systems. It was discovered that the tunable density of scCO₂ could be exploited to control the particle size of dispersion polymerizations, further expanding on the usefulness of this green solvent.
The kinetic information gained from this research, was exploited for precise dosing control during multistage polymerizations allowing for controlled tapering between successive polymer feeds and predictable layering of core-shell polymer particles.
The combination of kinetic monitoring, solubility control, and sequential monomer addition has finally unlocked the potential to synthesize commercially desirable polymer particles in this green and sustainable solvent for a wide array of applications such as 3D printing, plastic additives, metal oxide templating and medical devices.

1. Lovell, P. A.; El-Aasser, M. S., Emulsion Polymerization and Emulsion Polymers. Wiley: 1997
2. Kendall, J., et al., Polymerizations in supercritical carbon dioxide. In Chem. Rev., 1999; Vol. 99, pp 543-563
3. Millner, A.; Ollivier, H., Beliefs, Politics, and Environmental Policy. Review of Environmental Economics and Policy 2016, 10 (2), 226-244
4. Krishna Mohan, S., Green solvents for polymerization of methyl methacrylate to poly(methyl methacrylate). In Green Solvents I: Properties and Applications in Chemistry, 2012; pp 251-298
5. Haven, J. J.; Junkers, T., Online Monitoring of Polymerizations: Current Status. European Journal of Organic Chemistry, 2017, 6474-6482
6. Kortsen, K., et al., On-line polymerisation monitoring in scCO2: a reliable and inexpensive sampling method in high pressure applications. The Journal of Supercritical Fluids, 2020, 105047

The Alkalinity Concentration Swing (ACS) is a new process for direct air capture of carbon dioxide, driven by concentrating an alkaline solution that has been exposed to the atmosphere and loaded with dissolved inorganic carbon (DIC). We theoretically and experimentally evaluate driving the ACS through capacitive deionization (CDI), a method of removing anions and cations from solution by applying a voltage across two electrodes. When voltage is applied, anions electrosorb to the positive electrode and cations to the negative electrode. When the voltage is switched off or reversed, ions are released, driving the ACS through concentration of ions in solution. Upon concentration, the DIC per unit alkalinity decreases and the partial pressure of CO₂ increases, allowing for extraction and compression. We find that higher concentration factors result in proportionally higher outgassing pressure, and higher initial alkalinity concentrations at the same concentration factor outgas a higher concentration of CO₂.

CDI has been deployed industrially in municipal wastewater treatment and brackish water desalination facilities. CDI operates best in brackish water conditions, enabling high concentration factors and access to higher efficiency ACS regimes, without the need for high pressure systems. CDI also enables selectivity of bicarbonate ions, through use of ion exchange membranes and enhanced porous carbon electrode ion selectivity, allowing for an increase in ACS efficiency.

Today, we capture less than 1% of all emitted carbon dioxide, but in 2018, the Intergovernmental Panel on Climate Change (IPCC) reported that limiting atmospheric warming to less than 2 degrees Celsius will require both capture of carbon emissions from point sources such as power and industrial plants as well as the removal of existing atmospheric carbon dioxide. Amine solvents have gained the most traction in large-scale CCUS implementation, but limitations include high energy penalties associated with regeneration, cost, toxic degradation products, and corrosiveness. Improvements in stability, binding capacity, kinetics, and vapor-liquid equilibria have been achieved by blending different primary, secondary, and tertiary amines, but accelerating their discovery with machine learning and AI has seen limited exploration.

We have built a parallelized assay platform for rapid testing and measurement of capacity, kinetics, and thermodynamics of CO₂ binding to binary and tertiary blends of standard primary, secondary, and tertiary amines. Our platform replicates gas sparging of CO₂ through liquid solvents and leverages NDIR sensors to measure CO₂ absorption from complex mixtures of simulated flue gas. We also measure other physical parameters such as pKa, viscosity, and stability. With these data sets, we leverage machine learning to capture properties of novel blends and rank performance of these mixtures. New blends are tested and validated, and these data are delivered back to the model to improve its predictive capabilities with the end goal of generating new materials and solvent blends with improved performance for carbon capture.

Rising atmospheric levels of the greenhouse gases carbon dioxide, nitrous oxide, and hydrofluorocarbons are contributing to global climate change. Therefore, new strategies for capturing greenhouse gas for subsequent sequestration or conversion into value-added products are needed to minimize global climate change over the next century. A promising strategy is to develop new reactivity-based separations of greenhouse gases, which will enable higher selectivities than traditional separations. Herein, we will discuss new separation strategies for greenhouse gas capture using metal-organic frameworks, which are crystalline well-defined porous materials with highly tunable pore environments. We will discuss carbon dioxide capture in frameworks bearing extra-framework and metal-bound hydroxide sites, which reversibly react with carbon dioxide to yield (bi)carbonates. In addition, we will discuss the interaction of nitrous oxide with redox-active metal centers in frameworks. Last, we will explore how hydrogen- and halogen-bonding interactions can be leveraged to capture fluorinated gases such as fluoroform and sulfur hexafluoride.

In 2018, the IPCC reported that limiting atmospheric warming to less than 2 °C will require both capture and storage of anthropomorphic carbon dioxide (CO₂) emissions. Despite estimates that we will need to capture upwards of 10 GtCO₂ per year by 2050, today we capture less than 1% of all emitted CO₂. Dramatic reductions in the cost of carbon capture processes are needed to drive adoption at scale. IBM Research is building AI-driven tools to accelerate the discovery of materials with improved performance for carbon capture, utilization, and storage including solvents, solid sorbents, and membranes. We have also developed automated synthesis platforms for production of carbon capture materials and novel catalysts for carbon dioxide conversion. Finally, we have created a digital rock platform coupled with high-precision microfluidics to accurately simulate CO₂ fluid flow at pore scales relevant for geological storage.

This talk provides the overview of Oak Ridge National Laboratory’s (ORNL) transformational science and technologies towards the clean and decarbonized energy future with capabilities spanning the entire spectrum from clean energy generation to distribution, at-scale storage, and end-use. Being the largest DOE Office of Science Laboratory, ORNL is well-recognized for its energy efficiency research portfolio with the most comprehensive user facilities and capabilities in fundamental science and applied energy space among all the DOE national laboratories. We are accelerating decarbonization in the US with a three-pronged approach on integrated energy systems: 1.) Achieve deeper energy savings through enhanced energy efficiency efforts across all spectrums of the energy service sectors, i.e., buildings, industry, and transportation; 2.) Accelerate net-carbon neutrality by capturing and converting CO₂ into valuable materials, fuels, and feedstocks for downstream utilizations; and 3.) Enable bi-directional electron flows between the grid and end users with at-scale energy storage and transactive controls to enable a sustainable, resilient, and secure energy infrastructure. Exemplary ORNL RD&D advancements in all the areas above will be presented and future opportunities and challenges in the integrated energy systems approach will be discussed.

The Alkalinity Concentration Swing (ACS) is a new process for direct air capture of carbon dioxide, driven by concentrating an alkaline solution that has been exposed to the atmosphere and loaded with dissolved inorganic carbon. We theoretically and experimentally evaluate driving the ACS through reverse osmosis (RO), a membrane-based separation process in which pressure is applied against a solvent-filled solution to create a concentrated and a dilute stream. RO is the most widely used desalination approach - producing approximately 100 million cubic meters of purified water per day - allowing for technological advances to be leveraged for ACS deployment. Upon concentration, the partial pressure of CO₂ increases, allowing for extraction and compression of gaseous CO₂. We find that higher concentration factors result in proportionally higher outgassing pressure, and higher initial alkalinity concentrations at the same concentration factor outgas a higher concentration of CO₂. Theoretical projections suggest the ACS poses certain challenges, such as high water and land requirements, but it also confers advantages over incumbent technologies, especially in terms of simplicity of material requirements and possibility of reaching low energy costs through tuning operation parameters.

While a wide range of carbon-capture efforts are being developed around the world to help mitigate the adverse effects of global climate change, advances in membrane technologies that combine greatly improved CO₂ separation efficacy with low cost, facile fabrication, upscaling and implementation, and mechanical robustness are still needed. In this study, we introduce an integrated membrane strategy wherein a high-permeability thin film is chemically functionalized with a highly CO₂-philic open, brush-like surface layer. This nanofabrication scheme is based on a low-diffusivity, high-solubility mechanism that relies on enrichment of CO₂ in the surface layer naturally hydrated by the water vapor present in all targeted gas streams, followed by fast CO₂ transport through a supported thin film of a highly permeable polymer. Since this design employs commercial polymer thin films that are already available for gas separations, these new membranes can immediately be produced, upscaled and put into field operation after surface functionalization, achieved by controllably growing short, controlled amine-modified chains from the polymer surface. Spectroscopic methods confirm the existence of the amine surface layer, which also serves to enhance surface roughness and, thus, separation area. Integrated multilayer membranes prepared in this fashion are not diffusion-limited and, in some cases, are able to retain much of their inherently high CO₂ permeability while their CO₂ selectivity is increased in some cases by over ~150x, far exceeding the Robeson upper bound that traditionally reflects the trade-off between gas permeability and selectivity.

The reduction in emission of greenhouse gases (GHGs) is an important step towards mitigating the human impact on the climate change. Technically capturing CO₂, for example, is addressed by different emerging and established technologies. To effectively monitor the actual result of such a removal of this or other greenhouse gases, especifically adapted gas measuring systems are required.
At present, to monitor the environment, each National surveillance agency uses highly sensitive, selective, complex, bulky and expensive systems, which can only be used as reference measuring units installed in few specific, mostly fixed, key locations. For a more detailed monitoring and for the development of climate change models, a more distributed control of the GHGs emission is required and can be achieved through large numbers of deployed and connected gas sensing systems, thanks to the advent of Internet of Things (IoT). The required devices need to be sensitive, selective and low energy consuming, usually with a lower level of accuracy and precision than the reference instruments. Current commercial sensors do not fulfill all the requirements together and novel improved functional nanomaterials and sensors are needed.
The goal of this work is to show the actual stage of development of advanced miniaturised gas sensing devices for their use in monitoring of GHGs emissions. These devices are based on metal-organic framework (MOF) materials, that present a high degree of porosity and a reasonable conductivity, which allows their resistance to be measured.
The synthesis of the MOFs uses triphenylene-derived ligands, namely hexahydroxytriphenylene (HHTP) or hexaiminotriphenylene (HITP), and different metal centers. The synthesis route is described in detail elsewhere [1] for Cu and Ni metals. In this work, we have extended the synthesis to Mg, Zn and Co. In this way, 2D arrangements of metal-ligand, giving rise to hexagonal structures with a center pore, are formed. Vertical arrangement of such 2D structures occur through p-p stacking, giving rise to nanostructures whose dimensions vary between 100 and 300 nm in any direction. X-ray diffraction spectra prove the crystalline nature of such nanostructures.
The MOFs have been dispersed in ultrapure water, sonicated for 10 minutes, and one drop (0.5 ml) of the solution has been dispersed on a glass chip with interdigitated Ti/Au electrodes (IDE). Next, the chips have been dry heated in a furnace at 80°C for 10 minutes. The remaining material contacted the IDE and allowed current to flow between the IDE. The sample was then mounted and bonded to a TO8 holder and this was introduced in a gas measuring system, whose volume was only 8.6 ml. Through Mass-flow controllers, different gases and their mixtures were allowed to flow into the chamber at a rate of 50 sccm while the resistance of the MOF material was simultaneously measured.
Due to the porous nature of these samples and to the charge transfer between the flowing background synthetic dry air gas and the MOF, the resistance changes over time as a result of the continuous adsorption of components of the gas. Strategies for reversing this situation and bringing back the sample to its initial resistance value consist in either controlled heating or vacuum treating the sample. By adding 500 ppm of CO₂ to the synthetic air, a sizeable increase in the resistance was observed, while after removal of the CO₂ from the atmosphere, an incomplete recovery of to its baseline was attained. This response to CO₂ has been observed for different metal core and ligands, proving that these materials are potential candidates for innovative CO₂ gas sensors.
In this work a systematic study of the effect of the metal cores, of the ligands and of the measuring history and recovery methods will be presented with the aim of bringing forward these innovative and low power consuming gas sensor devices for greenhouse gas detection.

[1] M.G. Campbell et al, JACS 137, 13780 (2015)

Complementing the rapid decarbonization of energy technology, CO₂ removal will be necessary to offset some continued emissions and avoid the most harmful climate outcomes. Direct air capture (DAC), separating atmospheric CO₂ for subsequent storage with physical or chemical methods, is one CO₂ removal approach. Many DAC technologies use a solid or solvent-based sorbent to reversibly bind CO₂, and CO₂ release is driven by heating. New electrochemical methods offer opportunities because they interface readily with sources of inexpensive carbon-free electricity and may operate at very high efficiency. A central challenge for these methods is minimizing the voltage required by the electrochemical process, which is determined by ohmic resistance of the reactor components and the voltage required for electrochemical reactions.

We propose a new DAC cycle utilizing a redox-mediated bipolar membrane electrodialysis (RM-BPMED) reactor that dramatically decreases the energy required compared to other reactors of this type. RM-BPMED is used for electrochemical salt splitting (e.g., NaCl) to create a strong base (e.g., NaOH) and a strong acid (e.g., HCl). The base is used to absorb CO₂ from ambient air; the acid is then used to extract the CO₂ by recombining with the base, essentially reversing the salt splitting process. The research presented here demonstrates the RM-BPMED reactor, which is the centerpiece of our DAC approach.

The iron (II/III) hexacyanide redox couple affords facile redox kinetics on carbon electrodes, replacing the hydrogen and oxygen evolution reactions at the anode and cathode of traditional BPMED processes to decrease the required cell voltage. In addition to the redox mediators, RM-BPMED relies on ion exchange membranes that direct the ion transport for salt splitting. The ion exchange membranes must minimize leakage of species via unwanted crossover mechanisms while enabling high ionic conductivity. Some particular advantages of this method for DAC are that the acid and base products need not be pure and the salt splitting need not reach complete desalination. This allows additional supporting salt in all electrolytes flowing through the reactor, including the product streams. We present a design process informed by a fundamental understanding of membrane phenomena: the water content of ion exchange membranes determines the available transport pathways. The effects of electrolyte composition and membrane chemistry on water content and conductivity are elucidated to design a membrane-electrolyte system for RM-BPMED. A model of this strategy of electrochemical reactor engineering predicts RM-BPMED energy use below 100 kJ/mol CO₂ removed, as well as salt splitting at up to 100 mA/cm² current density. We will report on experiments that are under way to test the model.

Porous carbon (PC) has been widely regarded as one of the most promising absorbents for methane storage. Studies show that its uptake capacity and selectivity highly depend on textural structures. Although much effort has been made, unveiling their detailed structure-performance relationship remains a challenge. Here, we propose an innovative study where, with the assistance of machine learning, the hidden relationship of the textural structures of PC with the methane uptake and separation can be derived from existing data in material literature. Machine learning models were trained by the data, including specific surface area, micropore volume, mesopore volume, temperature, and pressure as the input variables and methane uptake as the output variable for prediction. Among the tested models, the multilayer perceptron (MLP) shows the highest accuracy in predicting the methane uptake. In addition, the model enables to automatically construct a uptake performance map in terms of micropore volume and mesopore volume. The obtained MLP model was also extended to explore the CO₂/CH₄ selectivity by retraining it with the data collected from literature of PC for the CO₂ uptake. The constructed 2D selectivity map shows that the high selectivity can be achieved in the low CH₄ uptake region.

Dry reforming of methane (DRM) reaction (CH₄+CO₂↔2CO+2H₂) produces synthesis gas (CO/H₂) which can be used for the production of high value-added chemicals and fuels via Fischer-Tropsch (FT) process. Despite the benefits and significance of DRM, this process has not been industrialized yet due to the absence of a stable and coke resistance catalyst. Ni-based catalysts are economically feasible, yet they suffer mainly from coke deposition and deactivation through CH₄ decomposition and CO disproportionation routes. On the other hand, supports, especially ceria-based ones, play an important role in tackling the coking challenge. In supported catalysts, both active metal and support can be engineered to inhibit carbon formation. The approach followed in this particular work is (a) tuning the support’s basicity and lattice oxygen mobility via ceria doping with rare-earth metals (La³⁺, Sm³⁺, and Pr³⁺) and (b) inducing in situ alloying of the Ni active metal with Cu species (originated from the support).

This work’s originality and significance to the field is reflected in presenting the role of trivalent M= La³⁺ and Sm³⁺ used in the ternary type of reducible support Ce-M-Cu-O composition as a carrier of Ni nanoparticles on the carbon paths in the DRM reaction. In addition, transient kinetics and isotopic experiments were designed to investigate the crucial coking factors for the DRM reaction over La vs. Sm co-dopants. The experiments studied (a) the carbon formation and their relative contribution of CH₄ decomposition and CO disproportionation reaction in the coking network, (b) the amount of inactive carbon accumulation on the catalyst surface after DRM, and (c) the extent of participation of support’s labile oxygen in the removal of carbon from the catalyst surface via oxidation to CO.

Due to the complexity of the catalyst composition, many analytical techniques were employed to get an insight into the catalysts’ intrinsic properties and structure and relate these to catalytic performance. Powder XRD, HAADF-STEM, SAED, EELS, elemental mapping, Raman, CO₂-TPD, H₂-TPR, and H₂-TPD were employed. The La³⁺- and Sm³⁺-doped ceria supported Ni catalysts presented tuned intrinsic properties, such as redox behavior and oxygen vacant sites concentration, and surface basicity. Also, La³⁺- doped support composition favored the formation of NiCu alloy nanoparticles and enhanced lattice oxygen mobility, which in turn appears to favor reduction in carbon deposition and enhanced carbon removal rates under DRM via mainly the participation of lattice oxygen.

A systematic transient kinetic study of CH₄ and CO decomposition reactions (main carbon deposition routes in DRM) by measuring initial rates of carbon deposition and the following dynamics of it, over the La³⁺- and Sm³⁺-doped ceria-supported Ni catalysts, along with advanced experimentation in measuring both the rates of carbon oxidation by lattice oxygen of support and by oxygen from the CO₂ activation route under DRM were conducted. Ni nanoparticles (23 nm) supported on the La³⁺-doped ceria exhibited ~ 3 times higher rates of carbon oxidation to CO by lattice oxygen and ~13 times lower rates of carbon accumulation than Ni (18 nm) supported on Sm³⁺-doped ceria. The oxygen vacant sites and surface basic sites were found to correlate with carbon deposition.

We strongly believe that this type of transient and isotopic work paves the way to fundamentally understand the role of dopants introduced in the ceria lattice and used as a carrier of Ni (or other metal) nanoparticles towards an efficient design of carbon-resistant doped ceria-supported Ni catalysts.

Climate action scenarios that limit changes in global temperature to less than 4^oC require methane controls in addition to carbon dioxide mitigation, yet few methane abatement technologies exist. Importantly, restoration of atmospheric methane from current levels 1.85 ppmv to pre-industrial concentrations of 0.76 ppmv would save 16% of global climate forcing within decades. Here, we describe the use of a biomimetic copper zeolite capable of converting atmospheric and low-level methane at relatively low temperatures (e.g., 200-300^oC) in simulated air. Depending on the duty cycle, 40%, over 60%, or complete conversion could be achieved (a two-step process at 450oC activation and 200^oC reaction, or a short and long-activation at isothermal 310oC conditions, respectively). Conversion rate increased over a range of methane concentrations (0.0002 to 2% methane), indicating promise of this technology to abate methane from any sub-flamable stream. Finally, uncompromised catalyst turnover over 300 hours (12 days) in simulated air was demonstrated under isothermal reaction conditions (310^oC). Taken together, this work illustrates the promise of using low-cost, Earth-abundant materials innovations to mitigate methane at the diffuse and dilute sources that drive growth of this important greenhouse gas, and ultimately slow the pace of climate change.

Carbon dioxide mitigation is a great challenge for the twenty-first century. The increasing atmospheric CO2 concentration peaked near 420 ppm on May 2021 at NOAA’s Mauna Loa Atmospheric Baseline Observatory. Controlling CO₂ emissions can be achieved by capturing and converting it into value-added chemicals via dual function materials (DFM) for in-situ methanation. In this study, different Ni-based catalysts with composite supports i.e., Ni/nCeO₂/mAl₂O₃ (n = different wt.%, m = different porosities) were synthesized. A set of state-of-the-art techniques were utilized to unveil the physicochemical properties of the catalysts such as Raman, temperature programmed reduction/desorption techniques, XPS, and high-resolution imaging using HRTEM-EELS and HAADF. A key to the rational design of highly efficient catalyst is understanding the reaction mechanism of CO₂ hydrogenation via Operando SSITKA-DRIFTS technique. The current results show three types of CO-s correspond to linear type CO-s adsorbed on top surface defects, top hollow and 3-fold hollow nickel sites. Moreover, the catalytic results indicate that the CO₂ methanation in the 200–500°C temperature region has an optimum performance at 20 wt.% CeO₂ loading and medium alumina porosity at 300°C. However, when 450°C < T < 300°C CO production takes over, implying the predominance of RWGS side reaction. Finally, the synthetic methods towards formation of adjacent [Ni]–[Ce] sites or highly dispersed active metal entities was found to boost the catalytic activity.

Negative emissions technologies target the removal of CO₂ from the atmosphere as a way of combating global warming. Enhanced rock weathering (ERW) is a vital negative emissions technology that, applied globally, could remove gigatonnes of CO₂ per year from the atmosphere. In ERW, silicate minerals exposed to the atmosphere trap CO₂ via mineral carbonation as thermodynamically stable carbonates. The present challenge is that the most reactive naturally-occurring silicates are not abundant. In order to design novel materials for ERW, a fundamental understanding of their structure and reactivity is necessitated at the nanoscale. To this end, we have employed density functional theory to predict the atomic scale structure of (100), (010), and (001) surfaces of wollastonite (CaSiO₃) and study the thermodynamics of their interaction with CO₂. Based on surface energy calculations, (001) and (010) surfaces of wollastonite exhibit similar stabilities, whereas (100) surface is found to be least stable. Utilizing stable surface models, molecular and dissociative adsorption of CO₂ at various surface sites has been explored. A common trend emerges, wherein the CO₂ molecule demonstrates proclivity to bond with surface layer calcium atoms. We will shed light on the electronic charge transfer between the adsorbate and the substrate and discuss the fundamental aspects of these interactions. Results from this work will be exploited to study the reaction kinetics of CO₂ adsorption and dissociation on silicates using ab initio molecular dynamics. Overall, we will elucidate the fundamental mechanisms that govern the interaction between CO₂ and wollastonite. Such fundamental understanding will be imperative to guide large-scale synthesis of novel silicates for ERW.

Doped ceria-based oxides are widely used as supports and stand-alone catalysts in reactions where CO₂ is involved. Thus, it is important to understand how to tailor their CO₂ adsorptive behavior. In this work, steering the CO₂ activation behavior of Ce-La-Cu-O ternary oxide surfaces through the combined effect of chemical and mechanical strain was thoroughly examined using both experimental and ab initio modeling approaches. Chemical strain is originated from the doping of CeO₂ with aliovalent metal cations (La³⁺ or La³⁺/Cu²⁺), whereas mechanical strain is originated from post synthetic ball milling able to impose mechanical forces on the oxide. Ce-La-O (111), Ce-Cu-O (111) and CeO₂ (111) surfaces were used as reference surfaces due to the complexity of the solid composition under investigation. Experimentally, microwave-reflux prepared Ce-La-Cu-O ternary oxide was imposed into mechanical forces to tune the structure, defects and CO₂ surface adsorptive properties. The purpose was to decouple the combined effect of the chemical strain (ε_C), and mechanical strain (ε_M), on the modification of the Ce-La-Cu-O surface reactivity towards CO₂ activation. During the ab initio calculations, the stability (energy of formation, E^f_Ov) of different configurations of oxygen vacant sites (O_v) was assessed under biaxial tensile (ε>0) and compressive (ε<0) strain, whereas the CO₂-philicity of the surface was assessed at different levels of imposed mechanical strain. E^f_Ov values were found to decrease with increasing tensile strain. Ce-La-Cu-O (111) surface exhibited the lowest E^fO_v values for the single subsurface sites, implying that O_v may occur spontaneously upon Cu addition. The structural, textural, redox and basic properties of the surface were used as descriptors to unveil the mechanical strain impact. The mobility of the surface and bulk oxygen ions in the lattice contributing to the O_v population was measured using ¹⁶O/¹⁸O transient isothermal isotopic exchange (TIIE) experiments; the maximum rate in ¹⁶O¹⁸O formation, R_max (¹⁶O¹⁸O) was 13.1 and 8.5 μmol g^-1s^-1 for the pristine (chemically strained) and dry ball-milled (chemically and mechanically strained) oxide, respectively. The CO₂ activation pathway (redox vs. associative) was experimentally probed using in situ DRIFTS. It was demonstrated that mechanical strain increases up to 6 times the CO₂ adsorption sites, though reduces their thermal stability. This result supports a mechanical actuation of the ‘carbonate’ bound species; the latter is in agreement with the DFT calculated C-O bond lengths and O-C-O angles. Ab initio studies shed light on the CO₂ adsorption energy (E_ads) suggesting a covalent bonding which is enhanced in the presence of doping and under tensile strain. Bader charge analysis probed the adsorbate/surface charge distribution and illustrated that CO₂ interacts with dual sites (acidic and basic ones) on the surface leading to the formation of bidentate carbonate species. Density of States (DOS) studies gave an insight on the electronic structure of the Ce-La-Cu-O (111) surface, and revealed the band gap (E_g) engineering which takes place in the clean and reduced surface, with a significant E_g drop in the presence of double O_v and compressive strain; a finding with design implications in covalent type of interactions. This study opens new possibilities to manipulate the CO₂ activation for a portfolio of heterogeneous reactions.

Perhaps the greatest obstacle to commercialization of the Direct Air Capture (DAC) of CO₂ is the DAC cost. Aiming to reduce the cost of DAC, a novel honeycomb contactor has been developed, designed, tested and demonstrated, showing its strong potentials to markedly lower the DAC cost through reducing the amount of needed sorbent, the largest contributor to the total DAC cost [National Academy of Science, 2019*].
Utilizing a novel approach to configure the channel internal flow in the sorbent-coated contactor, the channels develop a strong and stable secondary flow in the form of one or more pairs of Dean vortices, accelerating transport of CO₂ to the channel walls coated with a solid sorbent (Polyethylenimine/ PEI). In essence, the diffusion-dominated CO₂ transport to the sorbent, dominant in standard, mainstream honeycomb contactors, is practically replaced with the far-stronger convective transport, increasing the net CO₂ transport per unit surface area per unit time.
Both modeling investigation and experiments were utilized in this study. The high fidelity model and extensive experiments focused on examining the impact of novel flow patterns on CO₂ adsorption to the sorbent-coated walls and its desorption from the sorbent. Model contactors coated with PEI adsorbent were subjected to CO₂ adsorption and desorption tests and compared with a standard (baseline) DAC contactor, so to evaluate the impact of novel channel configuration on CO₂ transport to/from the adsorbent.
Good agreement was observed between the modeling prediction and the test data. The novel contactor well outperforms the standard contactors, displaying Sherwood number as high as 7.5, i.e., 2.5 times higher than that in standard ones, accelerating the rate of CO₂ adsorption/ desorption per channel unit surface area, enabling more efficient use of the contactor volume and its sorbent for CO₂ capture. Results indicate that the novel DAC contactor
(i) Enables reducing the sorbent use by 37%. Considering that sorbent CapEx forms more than 80% of the total DAC cost [National Academy of Science, 2019 * ], it reduces the total DAC cost by about 30%.
(ii) Enables reducing the overall volume (downsizing) of DAC contactors by up to about 40%.

Acknowledgment: This R&D project was funded by the US Department of Energy.

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* National Academy of Science, Engineering and Medicine. “Negative Emissions Technologies and Reliable Sequestration: A Research Agenda.” National Academies Press. (2019).

CO₂ is usually considered as an environmental burden. Here, we reimagine CO₂ as a resource for the production of a concrete-like construction material, that is, a value-added product. We present a new carbon immobilization process based on a 3D-printable portlandite-based cementitious binder that permits CO₂ uptake by mineralization. This carbonation process is fast, inexpensive, and robust. Carbonation leads to an increase in the strength of the binder and, hence, increases its value. This process could facilitate the beneficial use of CO₂ as a key ingredient for durable construction materials, thereby resolving the apparent opposition between the needs for new infrastructure and enhanced sustainability.

Concrete is the second most consumed material in the world only behind water, comprising a majority of construction materials.[1] As a result, global cement production is responsible for about 8 percent of the world's carbon emissions. Biomass from algae offers serious advantages such as carbon and nitrogen capture as well as a superior growth per area than other conventional plant crops. [2] Algae production may play an important role in CO2 mitigation through the integration in existing technologies. In this work, we use algae to reduce the use of cement or replace it as a component in concrete. Samples were prepared similarly to concrete and characterized using a wide range of mechanical, chemical and spectroscopic techniques. Through this study, we evaluate the use of algae in construction materials to mitigate the CO2 emissions, reduce concrete use, lower construction costs, and utilize biomass.

1. Gagg, C.R., Cement and concrete as an engineering material: An historic appraisal and case study analysis. Engineering Failure Analysis, 2014. 40: p. 114-140.
2. Moreira, D. and J.C. Pires, Atmospheric CO2 capture by algae: negative carbon dioxide emission path. Bioresource technology, 2016. 215: p. 371-379.

The growing demand for environmental control for a variety of chemical molecules has led to considerable interest in the research devoted to the development of new materials for sensor devices. Since humidity is a very common component in our environment, measurements and/or control of humidity are important not only for human comfort but also for a broad spectrum of industries and technologies. The constructive design of a good humidity sensor is a rather complicated topic, because high performance humidity sensors claim many requirements, including linear response, high sensitivity, fast response time, chemical and physical stability, wide operating humidity range, and low cost.
Zeolites and zeo-type materials are known for their well-defined porous structure, moisture holding capacity, and ionic conduction properties. Therefore, a study is done to investigate humidity sensing Titano/Vanadosilicate thin films. Two different zeo-type materials with different types of quantum wires in their structures (i.e.,–Ti-O-Ti-O-Ti- and –V-O-V-O-V- in the structures of ETS-10 and AM-6, respectively) were prepared and the humidity sensors by using these types of films were fabricated for the first time.
Microporous Titano/Vanadosilicate Films were prepared by two different methods. Humidity sensing properties of these films prepared by the secondary growth method were shown to be tailored according to the desired range of humidity for sensing applications. The impedance modulus change is more than four orders of magnitude in the range from 8% to 97% at 100 Hz. High stability and low hysteresis were also observed. Complex impedance spectra, the corresponding equivalent circuit under different relative humidity was analyzed to explore the humidity sensing mechanism of these films.
The project leading to these results has received funding from the Scientific and Technological Research Council of Turkey (TÜBITAK), under grant agreement 118M631.

Anthropogenic hypereutrophication, namely the release of excess nutrients into natural bodies of water from human activity, introduces a variety of economic, ecological, and public health problems around the globe. As with other environmental problems, this challenge is projected to grow in coming years, as it is inextricably linked to climate change and rising temperatures due to increased levels of CO₂.

To bridge the gap between the laboratory-scale nature of promising nanostructure solutions and the practical benchmarks for deploying an environmental remediation tool, we have developed a nanocomposite membrane. Here, an economical, readily available, porous substrate is dip coated using scalable, water-based processes with a slurry of nanostructures with affinity for specific adsorption of pollutants. Our Phosphate Elimination and Recovery Lightweight (PEARL) membrane can selectively sequester up to 99% of phosphate ions from polluted waters at environmentally relevant concentrations. [1] Moreover, mild tuning of pH promotes at will adsorption and desorption of nutrients, leading to phosphate recovery and reuse of the PEARL membrane.

This work builds on our prior report of the OHM sponge, made with the same platform approach, which is a nanocomposite material that can be used to repeatedly remove oil from water. [2] These two distinct examples suggest that the tailored nanostructure membrane approach is potentially a versatile platform that can be tuned to remediate other contaminants with the same core principles. In this presentation, we discuss the PEARL membrane’s effective and selective performance. Moreover, we use correlative microscopy and spectroscopy techniques to interrogate the complex microstructure of the PEARL membrane and its binding efficacy, further suggesting how this approach can be applied to other pollutants.

[1] S. Ribet, et al. PNAS. 118, 23 (2021).
[2] V. Nandwana, S. Ribet, et al. Ind. Eng. Chem. Res. 59, 10945-10954 (2020).

Decarbonization of the energy industry is an environment driven requirement. A sustained expansion and deployment of large-scale carbon capture, utilization and storage (CCUS), is needed to address this challenge, at least partly. Effectiveness of CCUS is contingent upon developing miscibility through partitioning into water or hydrocarbon. Our work is motivated by the need to reliably monitor dissolved CO₂ under conditions of high temperature and pressure. We propose a new Raman spectroscopy-based sensor system for translating molecular interactions into molar concentrations. We propose the utility and feasibility of field deployment of our sensing system in aquifer and hydrocarbon reservoir CO₂ injection projects.

Traditionally, industrial thermocatalytic processes for reducing carbon dioxide (CO₂) require high temperatures (>300 ^oC), high pressures (>150 bar), and several recycling steps that consume up to 2% of the world’s energy supply annually. Solar-driven processes under moderate pressures (<5 bar) present a sustainable alternative to synthesis of fuels, chemicals and materials while also alleviating rising atmospheric concentrations of CO₂. Normally, heat loss from thermal radiation would prevent a solar-heated thermochemical system from reaching the operating temperatures required for industrially relevant reactions such as the Fischer-Tropsch, Sabatier, and Haber-Bosch reactions under illumination of unconcentrated solar irradiation (1 kW m^-2). To reach temperatures >90 ^oC under ambient sunlight, the spectral absorptivity and emissivity profiles of the reactor components must be redesigned such that absorption of the active catalyst region is high within the solar wavelength regime (0.3 – 2 µm) and reflectivity is high in the infrared blackbody regime (4 – 25 µm). Here, we report the design of a planar solar thermocatalytic reactor that incorporates a selective light absorber and allows for both flexibility and scalability of the desired reaction. The proposed solar thermocatalytic reactor has 4 layers from bottom-to-top: a broadband reflector, a solar thermocatalytic reaction chamber, a selective absorber layer, and a thermally insulating layer. We will discuss options for selective absorber layers using semiconductor layers for high absorption in the solar wavelength regime and optically transparent conductors for high reflectivity in the infrared blackbody wavelength regime. Thermocatalysis results will be reported for a model reaction converting ethylene into higher olefins via solar activated homogeneous catalysts.

Hierarchical nanoporous carbons (HNC) have been proven to be an effective adsorbent for the adsorption of volatile organic compounds (VOCs) and CO₂, although questions remain regarding the hierarchical structure regulation, the adsorption mechanisms of adsorbate uptake, and interactions within the HNC. We synthesize HNC from wood, using a microwave-induced heating method incorporating K₂CO₃ activation. HNC exhibit Murray’s Law multi-scale structures, prompting a molecular scale study of adsorbate adsorption via nuclear magnetic resonance (NMR). NMR chemical shifts are consistent with ring current effects from the adsorbent. Our NMR technique provides a convenient way to quantitate the adsorption of adsorbate in HNC. VOCs vapor adsorption results show NMR chemical shift changes with time, suggesting initial adsorption into mesopores, followed by diffusion into micropores. Schroeder’s Paradox is demonstrated by differences in observed shifts for adsorbed liquid vis-à-vis vapor phase in these HNC. These HNC show high CO₂ adsorption capacity, portending applications to carbon capture.

Climate change caused by emissions of greenhouse gases into the atmosphere is a most important issue for our society. The anthropogenic nature of climate change necessitates the development of novel technological solutions in order to reverse the current CO₂ trajectory. Direct capture of the carbon dioxide (CO₂) from the air (direct air capture, DAC) is one among a variety of negative emission technologies that are expected to keep global warming below 1.5 °C, as recommended by the Intergovernmental Panel for Climate Change (IPCC).
Current DAC technologies are mainly based on sorbent-based systems where CO₂ is trapped in the solution or on the surface of the porous solids covered with compounds with high CO₂ affinity. These processes are currently rather expensive, although the cost is expected to go down as the technologies are developed and deployed at scale.
CO₂ capture by permselective membranes is advantageous because of its smaller and simpler set-up. Unfortunately, its efficiency is less than satisfactory for the practical operation of the DAC. Among polymeric membrane materials, rubbery poly(dimethylsiloxane) (PDMS) is known to display high CO₂ permeance and ultimate thinning of PDMS membranes is a promising and straightforward way to prepare high CO₂ flux membranes.
We developed defect-free, free-standing nanomembranes of PDMS and discussed the membrane thickness's effect on the gas permeance by using precisely defined nanometer-thick PDMS membranes systematically. Throughout the efforts on ultimate thinning of PDMS membranes, our achieved CO₂ permeance reaches almost 40,000 GPU (the highest one ever reported) and reasonable CO₂/N₂ selectivity at the thickness of 34 nm without a gas leak from pinholes. This value is much higher than those reported by other groups in the past (less than several thousand). Furthermore, the separation is achieved even at a CO₂ concentration of 1,000 ppm in N₂, which has never been investigated under such ultra-diluted concentration conditions in past reports. The advantages of extremely efficient separation of CO₂ found in our result demonstrate the feasibility of direct air capture by a membrane, which has never been considered before.

Carbon capture and storage (CCS) plays a fundamental role in achieving the goals of the Paris agreement to limit global warming to 1.5-2°C, with estimated 115 GtCO₂ needed to be captured and safely stored by 2060 [1]. Most ongoing CCS projects inject pure CO₂ into sedimentary basins, such as saline aquifers or depleted oil or gas reservoirs where an impermeable cap rock prevents it from migrating to the surface.
Carbfix has since 2007 developed a safe and low-cost alternative in collaboration between industry and academia: By injecting dissolved CO₂ into reactive rock formations, such as mafic or ultra-mafic rocks, carbon mineralisation is promoted for CO₂ mineral storage [2]. The acidic CO₂-charged fluid releases metals from the bedrock which combine with the injected CO₂ and rapidly form stable carbonate minerals [3]. By mineralising the injected CO₂, it is permanently fixed and there is a negligible risk of it returning to the atmosphere.
Carbfix has since 2014 captured and injected over 70,000 tonnes of CO₂ at its flagship operation at Hellisheidi geothermal plant in SW-Iceland and is preparing for scale-up to maximise its potential impact. Emphasis is currently being placed on making this technology more cost effective and exploring its limits in terms of potential sites and injection methods, including injection of CO₂ captured directly from the atmosphere, and injection of seawater dissolved CO₂. Furthermore, Carbfix is working on its largest project currently under development aiming on transporting CO₂ captured from European industries to Iceland, where up to 3 Mt/CO₂ will be injected annually for permanent storage.
Mineral CO₂ storage offers a vast storage potential and unlocks large regions in the world where CCS has until now not been considered possible: The storage capacity of the Columbia River Basalts in USA alone has been estimated to be on the order of 10-100 GtCO₂ [4]. The largest potential lies offshore within the sub-marine basaltic crust, but suitable formations are also widespread onshore, and are found in every continent [5].

[1] IEA (2020). Special Report on Carbon Capture Utilisation and Storage. Energy Technology Perspectives, 169.
[2] Snæbjörnsdóttir et al. (2020). Carbon dioxide storage through mineral carbonation, Nature Reviews Earth & Environment.
[3] Matter, J.M., Stute, M., Snæbjörnsdóttir, S.Ó., Oelkers, E.H., Gíslason, S.R., Aradóttir, E.S., et al. (2016). Rapid carbon mineralization for permanent disposal of anthropogenic carbon dioxide emissions. Science, 352, 1312-1314.
[4] Blondes, M.S., Merrill, M.D., Anderson, S.T., and DeVera, C.A., 2019, Carbon dioxide mineralization feasibility in the United States: U.S. Geological Survey Scientific Investigations Report 2018–5079, 29 p., https://doi.org/10.3133/sir20185079.
[5] https://www.carbfix.com/atlas

The National Academies have done more than 1000 consensus studies and more than 1000 workshops related to climate change, the first being done in 1936. All of these reports are downloadable at the National Academies Press website (https://www.nap.edu/). A multitude of areas has been explored from urban sustainability to adaptation to sea level rise to decarbonization of the grid and transportation to geoengineering. Approximately 10% of the studies and workshops have specific relevance to technologies for mitigating the effects of climate change. This presentation will focus on the approximately 150 consensus reports and 110 workshops with proceedings that have been done on climate change over the past 5 years. Approximately half of the studies and workshops are relevant to climate change mitigation technologies. Specific recent reports will be reviewed with a focus on mitigation technologies for decarbonizing the grid, decarbonizing transportation including light to heavy ground vehicles and air vehicles, carbon capture and storage, mitigation of sea level rise and management of flooding, and the controversial topic of geoengineering.

In recent years, Direct Air Capture (DAC) has established itself as a promising approach to atmospheric Carbon Dioxide Removal (CDR), also referred to as Negative Emissions. In fact, DAC is seen today as critical to the 1.5°C target of the Paris Climate Agreement. Numerous studies have shown negative emissions to be necessary in order to stabilize atmospheric CO2 at the required levels towards the middle of the century. Although DAC has higher specific cost per tonne of CO2 than nature-based solutions - such as afforestation or soil carbon - it can scale faster and can guarantee permanence of the CO2 removed. Due to the huge amounts of excess CO2 in the atmosphere, CDR technologies will have to reach annual capacities at the gigaton scale over the next two to three decades in order to become climate relevant.

The presentation will give an overview of DAC and, in particular, the modular low-temperature technology developed by Climeworks.
In Climeworks' systems, ambient air is ingested by a so-called collector container during a cyclic ad-/desorption process. In the adsorption step, the CO2 molecules are bound to a special sorbent material inside the collector. Subsequently, the sorbent material is regenerated by thermal energy. The concentrated CO2 collected during this desorption step can then be used in different ways. For carbon removal, it is typically sent underground, where it is permanently stored in aquifers, rock formations, or depleted oil and gas reservoirs. Captured CO2 can also be used as feedstock e.g. for the food and beverage industry or for agricultural use. Another upcoming use case is ‘Power-to-X’, in which hydrocarbons are produced from atmospheric CO2, water, and renewable energy. Currently, Climeworks has 14 DAC plants of different size in operation across Europe, collecting tens of thousands of hours of real-life operational experience every year. Climeworks anticipates strongly increasing demand for carbon-removal services in the future and expects further significant cost reductions as industrial mass production of components for DAC systems gears up.

Potential co-benefits of DAC in relation to the Sustainable Development Goals (SDGs) of the UN are also briefly touched upon in the talk, which concludes with suggestions for policy approaches needed to ensure climate-relevant scale is reached in time.

President Biden has laid out a bold and ambitious goal of achieving net-zero carbon emissions in the U.S. by 2050. The pathway to that target includes cutting total greenhouse gas emissions in half by 2030 and eliminating them entirely from the Nation’s electricity sector by 2035. Research, development, demonstration, and deployment (RDD&D) will be required to achieve the president’s objectives, including investments in both point source carbon capture and carbon dioxide removal approaches that target the accumulated pool of carbon in the atmosphere. Both will be required to achieve net-zero carbon emissions in time and they will require increased deployment on an accelerated timeline in order to move down the cost curve. These efforts, combined with effective policy, will improve the economic viability of the implementation of these critical approaches.
Deployment of these technologies at the scale required will necessitate the use of resources including land, water, and low-carbon energy, while ensuring the secure and reliable storage of carbon dioxide (CO₂) on a timescale that impacts climate. Therefore, CCS and CDR deployment must be implemented strategically in terms of regional goals and requirements.
The Office of Fossil Energy and Carbon Management and the National Energy Technology Laboratory will play an important role in the transition to net-zero carbon emissions by reducing the environmental impacts of fossil energy production and use. This includes helping decarbonize other hard-to abate industrial sectors through investments in approaches like CCS, direct air capture, and technologies to produce low-carbon products and fuel - including hydrogen.

This is an unprecedented opportunity to address climate change in the United States. Moving to net-zero greenhouse gas emissions by 2050 requires greatly scaling up decarbonization technologies that do not emit carbon dioxide and the continued development, demonstration, and deployment of technologies that remove carbon dioxide directly from the atmosphere. It also requires eliminating or greatly reducing emissions of other greenhouse gases, including methane, nitrous oxide, and fluorinated gases. Eliminating energy sector carbon dioxide emissions, the most important greenhouse gas within the largest emissions sector, is required for approaching net-zero emissions. Optimistically, the United States’ large renewable resource base coupled with decreasing costs for electrification technologies can catalyze rapid progress over the first decade of this energy system transition. The United States also has an extremely rich base of scientists, engineers, social scientists, policy makers, and support within civic society to make progress on the other technological solutions. However, the country also faces rapidly emerging impacts from climate change that will not abate without decades of effort. In order to be successful, deep decarbonization cannot occur without broad support within society and therefore must be done in a way that not only accomplishes the net-zero emissions goal but does so in a manner that meets wider societal goals and aspirations.

This talk addresses technology, societal, and policy issues for scaling deep decarbonization technologies. It is based on two recent activities at the National Academy of Sciences, Engineering, and Medicine (NASEM), a 2018 workshop that resulted in the proceedings Deployment of Deep Decarbonization Technologies and a consensus study that produced Accelerating Decarbonization of the U.S. Energy System in 2021. There is widespread consensus on the implementation of no-regrets, deployment-ready technologies aimed at decarbonizing electricity and electrifying end uses that make significant progress towards achieving mid-century decarbonization while preserving optionality. However, to accomplish these elements of decarbonization, existing solar and wind electricity generation technologies must be deployed by greater than four times their current highest annual rates. Electrification of vehicle sales and other end uses will require similar increases in technology deployment rates as renewable electricity. The increased challenge for decarbonization technologies involves addressing hard-to-decarbonize sectors such as heavy industry and air, rail, and shipping. This involves expanding the innovation toolkit. Examples include research, development, and demonstration for clean-firm electricity resources, long-duration energy storage, net-zero carbon fuels, electrolysis to make fuels from renewable power, low-carbon process heat solutions, and more efficient carbon dioxide capture technologies. It also involves development and deployment of negative emissions technologies that will compete as mitigation options. All of these strategies not only face the question of whether they can provide effective decarbonization options, they also face similar scaling issues as with decarbonizing electricity and electrifying end uses.

Reaching net-zero emissions is a transformation of society that will occur over decades, not years. Consideration of the societal aspects of decarbonization involves developing a social compact around the need to decarbonize and benefits that will accrue from it. Policy elements encompass the roles of federal, sub-national, economic, and regulatory approaches. Because political fortunes and societal opinions will change over this timeframe, consensus-building scientific institutions including the National Academies to facilitate the independent technical and policy advice needed.

The U.S. Department of Energy’s Fossil Energy and Carbon Management (DOE-FECM) R&D Program is supporting the development of transformational cost-effective carbon dioxide (CO₂) capture technologies throughout the power-generation and industrial sectors as well as carbon dioxide reduction (CDR) technologies. Since 2001, DOE-FECM’s Carbon Capture Program has been identifying and advancing technologies with the goal of decreasing the cost and improving the efficiency of carbon capture. Technologies developed to date have primarily focused on the capture of CO₂ directly from large point sources, such as industrial sources and fossil fuel power plant flue gas streams. The Carbon Capture Program is leveraging this past research in materials, equipment and process development for both current and transformational CDR technologies, such as direct air capture (DAC) and bioenergy with carbon capture and storage (BECCS), while evaluating the opportunities in direct ocean capture and enhanced weathering. More research is needed to develop efficient processes and components utilizing the transformational materials to lower the cost of these systems. At the same time, DOE-FECM aims to better understand system costs, performance, as well as business case options for the existing technologies, to better focus its research and development program. Accelerating the development and deployment of these climate-critical technologies will support the U.S. goal to achieve a carbon pollution-free electricity sector by 2035 and zero-carbon economy by 2050.

Energy generated from fossil fuels dominate the global use portfolio which now has reached an all-time high emission of approximately 40 GtCO₂. Undoubtedly this has had consequential impacts on our climate and environment, and sadly emissions are expected to rise. This has brought the urgent need to remove carbon from the atmosphere to reverse the rising atmospheric CO₂ concentrations with effective carbon negative technologies. However, many strategies to capture or convert carbon dioxide have been met with challenges with standalone materials. Hence, we have developed hybrid materials that employ a polymer with intrinsic microporosity (PIM) which has superior CO₂ selectivity with tunable functional and structural characteristics to enhance its effectiveness for both capture and conversion pathways. Here we show the development of hybrid PIM materials for both (1) direct air capture (DAC) and (2) utilization processes. Our first example is of a hybrid fiber mat composed of a silica bound polyethyleneimine (PEI) nanoparticle core (NOHM) encapsulated with a PIM sheath for DAC applications. NOHMs have demonstrated CO₂ sorbent qualities such as low volatility and high selectivity, however their viscosity and water retention have impeded their effectiveness for DAC. PIM encapsulation of NOHMs allows for selective rejection water and other air pollutants to reduce the parasitic energy consumption effects of significant mass transport limitations, yet maintain high gas permeability and selectivity. Secondly, we will present our catalytic PIM for the simultaneous capture and conversion of CO₂ to chemicals. Initial experiments show that this hybrid catalyst can overcome high temperature and pressure conditions normally needed for catalytic CO₂ reduction. From these initial findings of hybrid PIM materials, we learn key material properties such as stability, capacity, and recyclability that will help to provide insight into the technical feasibility of large scale applications needed for DAC and CO₂ conversion.

The increase if the world population and qualify of life over the next few decades is anticipated to increase the demand for food, water and energy by nearly 50%, Supplying these necessary life resources will become even more challenging with the increases in drought and temperatures brought on with climate change, as we have seen this year with the devistation of agricultural communities in the western United States. However, the same agricultural lands that are being detroyed by drought can also be part of the solution if they can be utilized more effectively. For example, covering less than 10% of the worlds agricultural lands with power-generating greenhouses would, in theory, be able to meet the increased global demands for fresh water, healthy food and clean renewable electricity due to the a potential for an order of magnitude reduction of water consumption and increase in crop yields that carefully designed greenhouses can provide. This promise has spawned the new field of agrivoltaics, namely the co-location of PV with agriculture, as a climate change mitigation technology.

In this talk, I will give an overview of agrivoltaic technologies and critical economic, technology, and social challenges that exist for their wide-scale deployment. I will then discuss the basic science behind the agrivoltaics created by our laboratory at UCSC, in collaboration with Soliculture, consisting of luminescent photovoltaic (PV) panels that enhance the wavelenths of light that plants need while utlizing the wavelengths that plants do not need for renewable power generation, all while providing wavelength selective shading to reduce water consumption and overheating without negatively impacting crop yields. I will discuss the technology advances in moving this technology from small prototypes in the laboratory to full 1 meter by 2 meter agrivoltaic panels that can fit into standard greenhouse frames, including the challenges of demonstrating 20 years lifetimes and maintaining a competitive price with standard ground-mounted Si PV technology. In addition, I'll share our stories and results over the last 5 years of installing these greenhouses over acres of agricultural lands in Canada and California and working with farmers to measure the impact of the panels on crop yields. Having shown the promise, I'll end with potential ptifalls that agrivoltaics will still need to address to become widely deployed solutions for climate change mitigation.

Cement fulfils many important roles within society today. However, its production is highly CO2 intensive. We will consider a number of potential methods to incorporate the combination of biogenic material (including Municipal Solid Waste, but also considering waste woods, etc) within a cement plant which includes Carbon Capture and Storage. This will include the integration of a novel direct separation reactor within the cement production process. We will show that it is possible to produce significant net negative emissions from the production of cement, not including the subsequent uptake of CO₂ by the cement as it remains in place. We will consider the impact of different methods to cure the cement, including technologies such as those proposed by CarbonCure, and how these overall can add up with CCS, fuel selection and clinker substitution, to produce traceable net negative emissions from an industry that currently emits around 7 % of global CO₂.

Since the dawn of the industrial era, anthropogenic factors have contributed to an acceleration of climate change that is well documented in the literature. The human-induced factors presently overwhelm natural fluctuations and, global efforts to combat the effects of the same are underway. To this extent, several climate change mitigation technologies have been proposed on a global scale and reports published by the National Academies of Sciences, Engineering and Medicine (NASEM). Apart from the global efforts, it is also clear that regional efforts have to be undertaken to limit the adverse effects. Fellows and Senior Members of the National Academy of Inventors (NAI) have been at the forefront of developing and commercializing several related technologies. This relates to the overall mission of NAI in promoting innovation and technology commercialization for the benefit of humankind. This invited talk will summarize some of the technologies that are presently being considered for combating climate mitigation challenges in various parts of the world.

The continuously rising concentrations of CO₂ in the atmosphere have led to significant negative impacts on the environment, which has propelled research efforts to replace fossil fuel-based energy with clean energy sources. Chemical looping combustion (CLC) has emerged in recent years as a promising technology for CO₂ capture in power plants and other CO₂ intensive industries. One of the main components of CLC is the oxygen carrier (OC) that is circulated between air and fuel reactors. The evolution of effective OCs with the desired properties for CLC application is deemed to be very significant for the commercialization of CLC. The research in this field is rapidly growing to tackle the major materials and operational challenges to advance the knowledge toward an industrial scale CLC application. This study provides a review of the advancements accomplished over the past five years in the progress of synthetic single oxide-based OCs. A summary of key performance indicators used to evaluate OCs is presented in this study to enable a systematic assessment of the OCs properties and performance. A focused and critical literature review over the last 5 years (2016-2021) on the OCs development was summarized. Moreover, the role of supports, synthesis protocols, promoters and other aspects affecting the OCs performance in CLC were outlined. This talk summarizes the main challenges, research needs and opportunities for future progress to highlight the potential pathways to develop synthetic single oxide OCs in an environmentally friendly, and cost-effective manner.

With the increasing crises of the global warming phenomenon, greenhouse gas mitigation technologies are essential to maintain the world’s sustainability. Carbon dioxide (CO₂) sequestration is an inevitable component during this development. It aims to capture and store the CO₂ gases in the atmosphere to mitigate or reverse global warming. However, the selection of places to store the CO₂ gases is always a challenging process. The CO₂ storage in soil and ocean leads the sites to become acidic and threatens human life. To avoid potential problems like these, gas hydrates are potential material for CO₂ sequestration due to their excellent storage capacity.

Gas hydrates are guest-host crystalline materials formed by water cages and host gases such as methane and carbon dioxide. Regarding this structural feature, 1 m³ gas hydrate can contain approximately 160 m³ gases.

The CO₂ sequestration process is based on SI methane gas hydrates; methane is replaced by carbon dioxide. During this process, the pressures and temperatures surrounding the gas hydrates change, making the hydrate structure unstable. Jendi et al. reported that material properties of gas hydrates associated with structural stabilities change along with pressures and temperatures. Jia, J. et al. demonstrated the role of the guest molecules (methane and carbon dioxide) on the gas hydrates’ stability. However, although the performance of the gas hydrates under different pressures and temperatures was demonstrated, little attention has been paid to the description and characterization of their stability limits.

This contribution will present the pressure stability limits of monocrystal defect-free methane gas hydrates, using accurate density functional theory (DFT) to simulate the hydrate’s performance under varying pressure. The effects of pressure on the geometric and atomic bonding feature of this guest-host crystal are presented and analyzed using various atomic angle and bond length distribution functions. Important gaps or forbidden zones are identified and related to potential stability mechanisms as pressure increases. Locations of concentrated distortions in the crystal lattice are identified. Comprehensive characterization of the elastic properties with pressure is presented and related to the crystal geometry changes. Validation and accuracy are determined using available simulations, theory, and experiments. Taken together, these results contribute to understand the methane gas hydrate stability under a great range of pressures and provide a comprehensive prediction on the hydrate’s performance during CO₂ sequestration.

Negative emission technologies, including direct air capture (DAC) of carbon dioxide, are now considered essential for mitigating climate change, but existing DAC processes tend to have excessively high energy requirements, mostly associated with solvent/sorbent regeneration. Recently, we have developed a promising approach to DAC that combines atmospheric CO₂ absorption by aqueous amino acids or peptide (e.g., glycine, glycylglycine) with (bi)carbonate crystallization by simple guanidine compounds. In this phase-changing system, the amino acid/peptide and the guanidine compounds work in synergy, and the cyclic CO₂ capacity can be maximized by matching the basicity of the two components. The resulting DAC process has a significantly lower regeneration energy compared to state-of-the-art solvent-based DAC technologies.

This research was sponsored by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division.

The membrane-based gas separation proved to be energy efficient in industrial processes and is also studied for the post- and pre-combustion CO₂ separation from N₂ and H₂ respectively. Meanwhile, direct capture of CO₂ from air represents a tougher challenge for the membrane approach due to the significantly lower concentration and very low driving force needed for gas transport. Advances in the membranes design, membrane processes, combination with CO₂ conversion are important to enable the energy competitive CO₂ extraction from low concentrated environmental mixes.

Metal-organic frameworks (MOFs) are novel microporous and tunable materials that suggested for separation processes, due to ability to precisely design the internal pores’ size or chemical affinity via reticular chemistry. NbOFFiVE-1-Ni is among the recently discovered MOFs that demonstrated a peculiar CO₂ sorption property. Namely, in addition to its relevant sorption capacity of ~2.2 mmol CO₂ per gram of MOF, the sorption to full capacity undergoes at very low partial pressures. This causes the material to be filled with CO₂ when exposed to concentrations as low as 400 ppm. This property of NbOFFiVE-1-Ni and several other similar ultramicroporous materials suggested their use as solid sorbents in DAC application. However, the complexity of solid adsorption-based capture, tough requirements for the material regeneration (ultra-low vacuum), and even cost and scale make this approach impractical. To utilize the unique properties of NbOFFiVE-1-Ni we speculate that instead of solid adsorption it is possible to design the membranes and use the material in form of nanofillers in the mixed matrix architecture. It is known that fillers can improve membrane performance by increasing selectivity, permeability, or even both properties.

Here we report the fabrication, structure, and gas transport properties of mixed matrix membranes (MMM) composed of the fluorinated MOF (NbOFFIVE-1-Ni) and CO₂ selective polyether-polyamide block copolymer (Pebax-1657). The performance of MMM with different amounts of fillers (10-40 wt%) for CO₂, N₂, O_2, and H₂ gas permeation was studied with particular focus on the mixed CO₂/N₂ formulations (with concentrations as low as 1000 ppm CO₂). For better performance, MMMs should have well-dispersed fillers in matrix polymer without interfacial gaps or blocking interfaces between them. As such, the hypothesis of this study was that if NbOFFiVE-1-Ni material is optimally incorporated in the polymer it could provide better CO₂ separation from the matrices with low concentration.

It was found that the particles of as-synthesized NbOFFIVE-1-Ni MOFs have very large sizes, not suitable for uniform membranes fabrication. Therefore, planetary ball milling was used to reduce particle sizes reaching well below the sub-100 nm size range. The presence of ultramicroporous fillers of smaller size in Pebax-1567 made a significant impact on gas transport. In particular, the increased CO₂/N₂ selectivity (from ~60 in polymer to >100 in MMMs) was observed with the increase of filler loading. These results suggest the manifestation of the ultra-CO₂-selective nature of the NbOFFIVE-1-Ni. The highest CO₂/N₂ selectivity and CO₂ permeability of MMMs was observed when a 1000 ppm CO₂ mixture was used as a feed gas. The performance of MMMs at higher temperatures (40-60 °C) allowed us to achieve even better separation results matching the sorption performance of MOF in similar conditions and significantly overcoming the performance of pure polymer used as a matrix.

While the improvement in selectivity is important for the efficient membrane-based CO₂ capture processes, especially for the post-combustion and direct air capture, further efforts on the particle size reduction and mixed matrix membrane thinning for effective utilization of the excellent molecular sieving properties of NbOFFIVE-1-Ni are necessary. These experiments are underway, and results will be also reported.

Great many tons of waste glass and plastics end up in landfills without proper recycling, which aggravates the burden of waste disposal. Plastic pollution is especially harmful to the Earth’s ecosystem, and impacts the quality of life all around. Plastics and glass are used on a massive scale in various sectors of industry, including the automobile, textile, and packaging industries. The conversion from waste glass or plastics to favorable materials is of great significance for sustainable strategies. In this talk, I will describe recent advancements in upcycling polyethylene terephthalate (PET) waste and glass waste bottles into active electrode materials of nanocarbon fibers and nanostructured silicon particles, respectively. Compared to other quartz sources obtained via pre-leaching processes that apply toxic acids and require high energy-consuming annealing, an interconnected silicon network is directly derived from waste glass bottles via magnesiothermic reduction. In the case of PET waste plastic, materials are first dissolved in a mixture of trifluoroacetic acid and dichloromethane, followed by carbonization under an argon/hydrogen atmosphere. Nanocarbon electrodes derived from waste PET have been successfully employed in electric double layer supercapacitors. Glass bottles are directly utilized for magnesiothermic reduction without pre-leaching and annealing, which offers a more environmentally-benign, energy-saving and efficient route to prepare silica source materials. Their abundance in silica without any loss due to the non-etching process result in high silicon yield towards fabricating Li-ion battery anodes with excellent electrochemical performance with a capacity of over 1400 mAh/g at C/2 after 400 cycles. Both conversion processes for waste glass and plastics are highly scalable with environmental and economic advantages, and our methodologies could provide the means for achieving a circular economy involving the upcycling of sustainable waste materials integrated to manufacturing of scalable energy storage technologies.

Climate change is one of the central challenges facing the world today. One of the basic ways to reduce risks from climate change is to reduce emissions of the greenhouse gases that are causing our planet to warm. In climate change jargon, efforts to reduce emissions have come to be known as “climate change mitigation”.
The three main ways to reduce greenhouse gas emissions are to: (1) reduce consumption; (2) reduce amount of energy used per unit consumption (efficiency); and (3) reduce the amount of net greenhouse gas emissions per unit energy used (carbon-emission-free energy).
Most national governments are working hard to increase abilities of populations to consume, so most mitigation efforts center on improving efficiency and powering systems with carbon-emission-free energy.
Efficiency can be improved through a change in systems (e.g., a shift from manufacturing to service sector) or through a change in devices (e.g., a more efficient engine).
There are only a small number of possible energy carriers and a finite number of technologies that could in principle convert energy from one carrier to another at scale without releasing greenhouse gases into the atmosphere. These include wind, solar, hydropower, nuclear and perhaps power from the oceans. Fossil fuels and bioenergy could perhaps be made carbon neutral through some combination of flue gas and direct air carbon capture and storage.
While some non-emitting technologies are cost competitive with fossil-fuel alternatives in some settings, at today’s costs, near-zero emission energy systems have higher direct costs today than would a CO2-emitting system with similar characteristics. Therefore, substantial effort is being invested in lowering the “Green Premium” that must be paid to avoid greenhouse gas emissions.
This talk will present a taxonomy of mitigation technologies and approaches, with attention given to areas in which materials science might hopefully contribute to addressing important societal needs.

Polymer membranes are potent materials for exhaust gas separation in energy production and transportation. Separating off carbon dioxide (CO2) from flue gases could help to mitigate climate change which is mainly driven by greenhouse gas emissions. Due to the trade-off between a membrane’s CO2 permeability and its selectivity with regards to CO2 and nitrogen (N2), and because of the harsh operation conditions, only very few polymers are actually used at industrial scale. In this study, consider the complexity of the process conditions and complicated interaction when flue gases permeate the membrane, we develop a simplified end-to-end framework and target to homopolymer type membranes first. Powered by the less data hungry artificial intelligence algorithms and physical validation, a similar trend compared to the literature values is observed. The results and challenges which include small number of the dataset, molecule generation efficiency, and validation with molecular dynamics (MD) are discussed.

The dataset is mostly acquired from the review article [1] and then converted to their corresponding SMILES. The target is to find membrane materials perform superior to Robeson's 2008 upper bound. Within the selected 150 samples none of them perform over the boundary. With the small data size, we tested the performance of three linear models (Lasso, Ridge and elastic net) and three non-linear models (random forest, kernel ridge and support vector machine). By performing grid search the best hyperparameter sets are configured automatically. For the linear models, we selected important features based on the Lasso penalty available in the scikit-learn library. For the non-linear models, we performed a combination of greedy search with local search that attempts to bypass the local optimum of the R^2 score. This benefits to the final CV scores improve at least 0.1 and finally random forest is used for doing structure generation. In the generation step, our strategy is to involve prescribed sub-structures embed in those samples close to the boundary rather than decided by exhaustive generation algorithm. The newly generated SMILES are clustered by Murcko scaffolds first and those predicted over the boundary are selected for MD validation.

The newly generated structures lack of clear identification for the atom charge and bond type information. The purpose of the MD validation is to efficiently observe the trend rather than to reproduce the literature values. An automation process is developed to convert generated SMILES to polymer slabs with MD input format. Since most experimental observations are performed at constant temperature and pressure, we realize the permeability calculation with a isothermal-isobaric (NPT) based methodology in which constant pressure difference is kept during the gas injection. According to the benchmark results under available options, polymer slabs with 800 heavy atoms per chain, 6 nm in thickness, and DREDING force field are selected. The benchmark results shows that the CO2 permeability is in the same order between predicted and calculated values. Instead, the selectivity is less comparable to the original values which is because that N2 permeability usually 10 to 40-fold smaller and a long enough simulation time (ex: 100 ns) is necessary.

The overall fitting results we have obtained are encouraging, considering the limitations of the training dataset and the membrane formation method. The automated process allows to put innovation on structure generation and MD methodology. Based on the results obtained, we are now analyzing the newly generated structures with highest predicted CO2 permeability. The inclusion of additional physical parameters such as adsorption energy, free volume, and gyration radius in the optimization could help further improve our material discovery results for polymer separation membranes.

[1] M. Songolzadeh, et. al, The Scientific World Journal, Vol. 2014, Article ID 828131

Co-assembly of a structure-directing block copolymer and aluminium tri-sec-butoxide derived sols enables formation of highly ordered mesoporous alumina structures that are appealing for various applications such as carbon capture, separation and catalyst supports. We found that the addition of trimethylbenzene further induced an order-disorder-order mesophase transition in the F127-Al₂O₃ system. Thermal annealing resulted in the formation of micro-and mesoporous alumina structures with enhanced carbon dioxide adsorption capacity.

Millions of crystalline nanoporous materials have been identified for carbon capture, making the task of measuring the adsorption performance of each individual nanopore using computer simulations wholly unfeasible. Furthermore, experimentally synthesising and calculating the adsorption properties of each sample is even more impractical. A screening framework is thus required to identify a smaller number of promising candidates for further investigation. In this presentation, we introduce our work which deploys several distinct mathematical techniques to efficiently characterize nanopore structures, leading to a rapid high throughput nanopore screening mechanism.

Our automated cloud-based materials screening tool is composed of two distinct parts. Firstly, several computational geometric and topological descriptors are determined for each individual nanopore, allowing us to immediately discount samples with unfavourable structural properties. Next, Grand Canonical Monte Carlo (GCMC) simulations are deployed to calculate the target adsorption figures of merit. The computed results can be ingested into machine learning algorithms to produce a surrogate model to the original simulations, thus accelerating the estimation of desired adsorption properties of the candidate nanoporous materials.

Climate change is mainly due to CO2 emissions occurring in energy production and transportation. A set of technologies are being developed to separate and sequester CO2 from point sources. Among these are liquid and solid adsorbents as well as membranes and hydrates. Polymer membranes show certain advantages with regards to their storage and disposal properties, they allow for passive operation, have high tolerance to SOx and NOx content and can be integrated within an existing power plant steam cycle (post combustion application).

Candidate materials for application in polymer separation membranes must fulfill two key requirements: high CO2 permeability and high CO2/N2 selectivity. Many candidate materials exist today or can be computationally designed; however, the time and cost of experimental lab validation is the principal limitation in materials discovery applications. In this contribution, we investigate the potential of Classical Molecular Dynamics (CMD) simulations as a time- and cost-efficient validation option for suited polymer candidates.

CMD simulations have been employed successfully for calculating permeation in glassy polymers [1], however, significant uncertainties with this approach remain. We have reviewed a set of available CMD methodologies and analyzed their strengths and weaknesses in application to the polymer membrane use case. Specifically, we have investigated effects related to number of atoms, membrane thickness and area, size of polymeric chain and membrane composition, respectively, on both CO2 permeability and selectivity. We show quantitative results for representative polymers that lead to the conclusion that Constant Pressure Difference Molecular Dynamics (CPDMD) [2,3] is the most appropriate methodology.

References:
[1] H. Frentrup et al. In Silico Determination of Gas Permeabilities by Non-Equilibrium Molecular Dynamics: CO2 and He through PIM-1, Membranes 5, 99-119 (2015).
[2] X. Kong and J. Liu, An Atomistic Simulation Study on POC/PIM Mixed-Matrix Membranes for Gas Separation, J. Phys. Chem. C 123, 15113-15121 (2019).
[3] J. LKiu and J. Jiang, Molecular Design of Microporous Polymer Membranes for the Upgrading pf Natural Gas, J. Phys.Chem. C 123, 6607-6615 (2019).

Carbon dioxide capture and storage technologies will be required to reduce emissions into the atmosphere and limit global warming in the coming decades. Geo-sequestration involving the injection of CO2 directly into the pore space in sedimentary rocks, saline formations or abandoned oil fields may present a permanent storage solution. More scientific research is needed to understand and optimize CO2 injection process and long-term storage at the pore scale of these underground geological formations.
In our research, we model the rock pore space as a network of capillaries with spatially varying radii and the flow rate in each capillary is modelled as laminar flow. The capillary network representation is extracted from high-resolution X-ray microtomography images of suitable rocks [1]. This fined-grained capillary network representation allows for both single- and two-phase flow simulations with a high level of geometric accuracy at microscale.
The two-phase flow simulations employ a time-dependent interface tracking approach for simulating displacement experiments that results in a system of differential-algebraic equations. Solving these time-dependent equations on the high-resolution three-dimensional geometrical representation of the rock sample obtained from the X-ray microtomography remains very time and computationally intensive. Alternatively, analysis is carried out on the aggregate results of multiple two-phase flow simulations, each applied to a different simplified capillary network model of the rock sample. These simplified network models are generated algorithmically and allow for a higher level of control on the number of capillaries and their properties. The resulting networks are optimized to match the physical properties of permeability and porosity of the original sample at a significantly lower computational cost.
In this work we present results from the accuracy benchmark of the single-phase flow simulations against other known network methods from the literature and with respect to measurements of permeability performed at lab scale in the same rock samples. We then apply the methodology described to simulate two-phase flow on capillary network representations of porous sandstone rock samples extracted from the geometric boundaries of the connected pore space from x-ray microscale computer tomography data. In order to understand the physics of carbon dioxide trapping at the pore scale, we simulate two-phase fluid flow scenarios under varying conditions of temperature, pressure and fluid properties, and present our findings in optimizing parameters that maximize fluid saturation of the rock.
[1] Neumann, R.F., Barsi-Andreeta, M., Lucas-Oliveira, E. et al. High accuracy capillary network representation in digital rock reveals permeability scaling functions. Sci Rep 11, 11370 (2021). https://doi.org/10.1038/s41598-021-90090-0

The large column inventory enforced by the long regeneration times prevented the use of thermal swing adsorption for gas separation. But with shorter regeneration times the technology would have a good potential due to the low operation cost enabled by the use of low grade waste heat. The key to shorter regeneration times is a rapid thermal swing adsorption (RTSA) process. This process has been developed in adsorption heat pumps that offer a clean technology for cooling or heating utilizing waste or renewable heat as driving energy. RTSA constitutes a similar step improvement as the rapid pressure swing process that reduced the investment cost for many gas purification and separation processes including oxygen separators used in treating COVID patients. A crucial component to reduce cycling times is the use of hierarchically structured sorbents. As part of the development of better adsorption heat pumps we have devised an inexpensive and scalable magnetic alignment route for the fabrication of adsorptive coatings with vertically open channels and thermal bridges improves mass transport more than threefold [1]. This combined with methods to improve thermal transport accelerate the thermal swing process strongly reducing column inventory and cost.
A novel controlled fast temperature jump setup (TJS) accurately measures temperatures and sorption processes based on chamber pressure as function of time following temperature steps. The sorption material is mounted as beads or layers onto aluminum carries that are temperature controlled with high performance microchannel heat exchangers. The TJS allows fast acquisition of cycled mass, thermal resistance and mass transport resistance to screen and optimize material and process libraries. Measurements were carried out as function of wide choice of sorbent materials, gas type (CO2, N2, H2O) including mixtures, gas pressure, cycling time, temperature gradient, layer thickness, and layer structuring. A selection parameter was defined that contains exchanged mass per cycle, adsorption and desorption speed as well as layer thickness: Parameters that maximize the performance of an RTSA gas separation process.
The maximum achievable specific exchanged mass per cycle could be determined by gravimetric method through Dynamic Vapor Sorption experiments. All adsorbents were tested in both mono and multicomponent gases showing that maximum CO2 adsorption capacity alone does not sufficiently represent the potential of a material, as residuals of adsorbed water in the pore can significantly decrease the cycling capacity. The same methods, as well as full adsorption isotherms, were applied to the adsorber coating materials (including binders, surfactants and thermally conductive materials) to provide a benchmark for the evaluation of the enhanced coatings tested with different cycle times.
According to the results obtained with the TJS experiments, the initial coating formulation and process was improved aiming to increase the active mass use and the CO2 cycled per unit area, and to decrease the adsorption and regeneration times. As a result, a protocol ensuring good adsorbent adhesion, good thermal contact and fast kinetics was obtained.
It was demonstrated that a proper integration strategy of pore formation by magnetically aligned emulsions is as significant as the choice of the adsorbent material itself, leading improvement factors between 2 and 10. The material screening and integration tailoring methods proposed proved to quickly highlight the most promising direction on which to build on scale-up and further research activities. We thus can quickly select best materials and structuring processes to establish RTSA as a viable alternative to other carbon capture processes.

[1] J. Ammann, P. Ruch, B. Michel, and A. R. Studart, High-Power Adsorption Heat Pumps Using Magnetically Aligned Zeolite Structures, ACS Appl. Mater. Interfaces 2019, 11, 27, 24037–24046.

Natural gas is composed primarily of methane, a potent greenhouse gas, and is a quickly-growing non-renewable energy source worldwide. To mitigate pipeline emissions, transport has moved towards using pressure vessels with liquefied (LNG) or compressed (CNG) natural gas. Gas hydrates are crystalline compounds formed when a gas is enclosed in and stabilizes a lattice of hydrogen-bonded water molecules. They require less severe conditions for formation: lower pressures than CNG and higher temperatures than LNG. Also, 1 L of methane hydrate is estimated to store 160 L of gas. Due to the high storage capacities and reduced transportation costs, gas hydrate technologies are now being developed for natural gas transport and storage applications. Methane hydrate technologies could also be used for direct air capture of methane from pipeline leaks and could equally extend to removing atmospheric carbon dioxide using CO₂ hydrates, which have the same structure as their methane counterparts.
The study of materials that assist in the formation of hydrate structures has focused on kinetic promoters that induce the nucleation of stable gas hydrate crystals and enhance hydrate growth rates as well as gas storage capacities through higher cage occupancy. Improved gas dissolution in water at the liquid-vapor-hydrate equilibrium point has also been examined. Recently, this class of promoters has expanded to include graphene nanoflakes (GNFs) which have already been shown to increase the yields of many hydrate compounds. They are made through a plasma decomposition process wherein critical carbon clusters form homogeneously from carbon vapors. GNFs are hydrophobic as they consist of sheets of carbon atoms, so they agglomerate in and settle out of aqueous solutions. Stability improvement methods have included the addition of surfactants, though this reduces the system purity, and chemical additions on the graphene surface. Recent advancements have allowed for the GNF surface to be functionalized with oxygen-containing groups. Here, the CH₄/N₂ feed used initially to form hydrophobic GNFs is changed to air, and the oxygen forms an active species and interacts with the GNF surface. Through covalent bonding with these oxygenated functionalities (such as carboxyl, hydroxyl, and ether oxide groups), a stable nanofluid of aqueous GNFs was achieved. These hydrophilic GNFs, called O-GNFs, have in-plane dimensions of roughly 100 x 100 nm² and are between 5 and 20 atomic layers thick. The atomic composition of their surface is approximately 14.2% oxygen.
The growth rates of methane hydrates were measured in the presence of plasma-functionalized GNFs at 2 °C and 4646 kPa, a 1500 kPa driving force. Improving growth rates furthers the efficacy of hydrate technologies by increasing gas capture rates. Enhancement occurred due to improved mass transfer resulting from high GNF specific surface area and additional gas-liquid interfacial area. Enhancement by O-GNFs rose linearly and rapidly at low concentrations, peaking at 1 ppm at nearly quadruple the growth rate (288% enhancement): the most significant enhancement of a hydrate system currently demonstrated. At 5 ppm, enhancement dropped to 215% due to limitations on the mean free path of the nanoparticles. At 10 ppm, enhancement rose again to 247% due to further increases in surface area.
The dissolution rates of methane in hydrophilic GNF nanofluids at 2 °C and 3146 kPa (three-phase equilibrium) were also measured. These rates improved with loading and were at most 44% faster at concentrations of 5 ppm. Mean free path limitations may have restricted further dissolution rate enhancements beyond this point. The maximum dissolution rate for the specific system may also have been achieved. The amount of methane dissolved in the solution did not change with any GNF loading. This finding indicates that GNFs do not affect system thermodynamics: these additives may not affect how much gas can be stored in the hydrate.

Given that there will be some residual greenhouse gas emissions in 2050, to achieve net zero, we will need some options that remove greenhouse gases from the atmosphere. There are some engineering solutions for greenhouse gas removal, as well and some nature-based solutions, and some that include components for both. Since Nature-based Solutions (NbS) should be implemented with the full engagement and consent of Indigenous Peoples and local communities in a way that respects their cultural and ecological rights, and should be explicitly designed to provide measurable benefits for biodiversity, not all land-based greenhouse gas removal options constitute NbS. Most land-based greenhouse gas removal options can deliver benefits to the delivery of ecosystem services and to the UN Sustainable Development Goals (SDGs), if implemented appropriately, but if implemented poorly, many land-based greenhouse gas removal options could harm biodiversity, ecosystem services and impede delivery of the UN SDGs. The way in which land-based greenhouse gas removal options are implemented is critical to whether or not they can be considered as NbS. Large-scale afforestation (strongly depending on forest type and location), and the feedstock required for biochar production or BECCS potentially increase competition for land, but even these potential impacts are context and scale specific. Land-based greenhouse gas removal options that can be implemented in a way that is consistent with NbS should be prioritised, as they deliver multiple co-benefits. Not all NbS are land based – ocean-based approaches are comparatively under-researched.

Current carbon dioxide membranes suffer from limited flux and selectivity while conventional absorption-based CO₂ sequestration are associated with high temperatures and high costs, calling for alternative CO₂ separation approaches. Here, we describe an ultra-thin and robust liquid membrane that enables both high flux and high selectivity for CO₂ separation and capture at ambient temperatures and low costs. The membrane comprises 18-nm thick arrays of 8 nm diameter hydrophilic pores that stabilize water by capillary condensation and precisely accommodate the metalloenzyme carbonic anhydrase (CA). CA catalyzes the rapid interconversion of CO₂ and water into carbonic acid, promoting uptake and release of CO₂. By minimizing diffusional constraints, stabilizing and concentrating CA within the nanopore array to a concentration 10× greater than achievable in solution, our thin, liquid membrane separates CO₂ at the highest combined flux and selectivity yet reported for ambient condition operation.

Negative emissions technologies (NETs) are often viewed as a ‘risky backstop’ technology for climate change mitigation. This view stems from IAM-based assessments of NETs which require very large-scale deployment of NETs in the second half of the century, to compensate for a mid-century emissions overshoot. In this presentation, we challenge this limited view of NETs. Taking Princeton’s recent report, Net-zero America as a case study, we show the crucial role that negative emissions technologies plays in the economy-wide transitions to net-zero emissions by 2050 for the United States. The second part of the presentation proposes a fresh take on the value of NETs, and explores NETs via a bottom-up analysis. A decision-making framework is offered to determine the circumstances under which NETs could provide value as a mitigation option at jurisdictional scales. This framework is then applied to localized case studies to highlight how NETs could overcome socio-technical obstacles and/or unlock a variety of environmental and social co-benefits as part of the technology portfolio for achieving time-bound mitigation goals. Overall, the presentation aims to cut through what we see as a noisy discourse on NETs, which is wrapped-up in concerns that are dependent on scenario modeling, and offer a plain evaluation of NETs as a potential climate change mitigation option.

The continuous use of fossil fuels, along with other urban human activities, are behind an excessive emission of greenhouse gases. The intergovernmental panel on climate change (IPCC) stated that global greenhouse gas emissions must be reduced by 50-80 per cent by 2050 to mitigate climate change¹. From the list of greenhouse gases, carbon dioxide (CO₂) has been considered a key contributor to the current state-of-affairs². Therefore, there is a pressing demand for carbon capture and storage (CCS) technologies that allow for the capture and storage of CO₂ produced from fossil fuels. Solid porous adsorbent materials are the most competitive and promising candidates for CCS technologies, offering a high uptake capacity and tailored selectivity towards specific gases^3-5. Among these materials, biomass and microporous carbons have come into prominence due to a set of desirable characteristics such as high availability of source precursors, ease of preparation, low-cost production, highly developed porous structure, moderate adsorption heat and the possibility to induce an abundance of functional groups.
In this communication, we report a porous carbon-carbon powdered mixture designed to perform CO₂ capture. The hybrid powder is constituted by KOH activated hydrothermally carbonised palm date seeds (HTC-PDS) and reduced graphene oxide (rGO). Previous work with the KOH activated HTC-PDS component showed interesting results for CO₂ uptake⁶. In the present case, we mixed HTC-PDS with rGO in different ratios before activating the powder with alkaline KOH. The oxygen functional groups (remainders in the rGO) could assist in optimising the CO₂ heat of adsorption in the hybrid material, enhancing the selectivity compared to the activated biochar. The approach was also designed to test if, beyond the porous development, the structure of the graphite building units in the two carbon components could be controlled and influence the adsorption of the greenhouse gas. The structural analysis, by Raman and X-ray diffraction, confirms the development of a more ordered structure. The optimised activated mixture had a specific surface area of 845 m²/g, with 92% of the total surface area being microporous. The CO₂ adsorption capacity (at 1 bar, 273 K) was 3.40 mmol/g.

References
1. Nakicenovic, N. et al., Cambridge University Press, 2000
2. Raza, A. et al., Petroleum, 2019, 5(4), 335-340
3. Olivares-Marín, M. et al., Greenhouse Gases: Science and Technology, 2012, 2(1), 20-35.
4. Espinal, L. et al., Environmental Science & Technology, 2013, 47(21), 11960-11975
5. Pardakhti, M. et al., ACS Applied Materials & Interfaces, 2019, 11(38), 34533-34559
6. Alazmi, A. et al., Activated carbon from palm date seeds for CO2 capture, submitted