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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Proton-Coupled Electron Transfer Mechanisms for CO 2 Reduction to Methanol Catalyzed by Surface-Immobilized Cobalt Phthalocyanine

Immobilized cobalt phthalocyanine (CoPc) is a highly promising architecture for the six-proton, six-electron reduction of CO 2 to methanol. This electroreduction process relies on proton-coupled electron transfer (PCET) reactions that can occur by sequential or concerted mechanisms. Immobilization on a conductive support such as carbon nanotubes or graphitic flakes can fundamentally alter the PCET mechanisms. We use density functional theory (DFT) calculations of CoPc adsorbed on an explicit graphitic surface model to investigate intermediates in the electroreduction of CO 2 to methanol. Our calculations show that the alignment of the CoPc and graphitic electronic states influences the reductive chemistry. These calculations also distinguish between charging the graphitic surface and reducing the CoPc and adsorbed intermediates as electrons are added to the system. This analysis allows us to identify the chemical transformations that are likely to be concerted PCET, defined for these systems as the mechanism in which protonation of a CO 2 reduction intermediate is accompanied by electron abstraction from the graphitic surface to the adsorbate without thermodynamically stable intermediates. Furthermore, this work establishes a mechanistic pathway for methanol production that is consistent with experimental observations and provides fundamental insight into how immobilization of the CoPc impacts its CO 2 reduction chemistry.

Adsorption↗
DOE OSTI2024

A Tandem Electrolysis Process for Multi-Carbon Chemical Production from Carbon Dioxide (Final Technical Report)

a two-step CO 2 electroreduction process for selective production of acetate and ethylene was successfully developed at the kW-scale. The CO 2 and CO electrolyzers were first investigated individually on the Watt-scale to achieve high current densities and more durable operation by using a reinforced GDL. High CO 2 conversion was obtained in the first CO 2 electrolyzer to produce a CO-dominant gas stream with minimal CO 2 , and highly pure acetate stream was produced in the second CO electrolyzer by using NiFe anode, which promoted alcohol oxidation to carboxylates. The two-step process operated stably for 200 h with acetate and ethylene as the major C 2+ products. Degradation mechanism study revealed that the flooding and the salt formation in the GDL is likely the biggest contributor to the performance degradation for both CO 2 and CO electrolyzers. A 1,000 cm 2 CO electrolyzer stack was then designed, fabricated, and operated up to a total current of 300 A along with a 500 cm 2 CO 2 electrolyzer stack which was operated up to a total current of 100 A. The CO electrolyzer stack demonstrated good stability at 300 A for at least 125 h at a carbon selectivity >96%. The impact of CO 2 , O 2 , N 2 , SO x , and NO x gas impurities on the CO electrolyzer stack was studied and a relatively high resistance to these contaminants was demonstrated. Electroreduction of CO 2 into acetic acid was also demonstrated to be environmentally favorable when compared to the traditional production of acetic acid when powered by renewable electricity. Additionally, electricity cost was identified as the primary source of cost sensitivity indicating substantial economic improvements could be achieved by continuing to drive down the cost of renewable electricity. Overall, the presented approach demonstrates the feasibility of the two-step electrochemical CO 2 reduction process for the effective production of C 2+ products at the kW-scale which should inspire future scaling efforts accelerating commercialization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Gold-in-copper at low *CO coverage enables efficient electromethanation of CO 2

The renewable-electricity-powered CO 2 electroreduction reaction provides a promising means to store intermittent renewable energy in the form of valuable chemicals and dispatchable fuels. Renewable methane produced using CO 2 electroreduction attracts interest due to the established global distribution network; however, present-day efficiencies and activities remain below those required for practical application. Here we exploit the fact that the suppression of *CO dimerization and hydrogen evolution promotes methane selectivity: we reason that the introduction of Au in Cu favors *CO protonation vs. C-C coupling under low *CO coverage and weakens the *H adsorption energy of the surface, leading to a reduction in hydrogen evolution. We construct experimentally a suite of Au-Cu catalysts and control *CO availability by regulating CO 2 concentration and reaction rate. This strategy leads to a 1.6× improvement in the methane:H 2 selectivity ratio compared to the best prior reports operating above 100 mA cm -2 . We as a result achieve a CO 2 -to-methane Faradaic efficiency (FE) of (56 ± 2)% at a production rate of (112 ± 4) mA cm -2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Enhanced multi-carbon alcohol electroproduction from CO via modulated hydrogen adsorption

Multi-carbon alcohols such as ethanol are valued as fuels in view of their high energy density and ready transport. Unfortunately, the selectivity toward alcohols in CO 2 /CO electroreduction is diminished by ethylene production, especially when operating at high current densities (>100 mA cm –2 ). Here we report a metal doping approach to tune the adsorption of hydrogen at the copper surface and thereby promote alcohol production. Using density functional theory calculations, we screen a suite of transition metal dopants and find that incorporating Pd in Cu moderates hydrogen adsorption and assists the hydrogenation of C 2 intermediates, providing a means to favour alcohol production and suppress ethylene. We synthesize a Pd-doped Cu catalyst that achieves a Faradaic efficiency of 40% toward alcohols and a partial current density of 277 mA cm –2 from CO electroreduction. The activity exceeds that of prior reports by a factor of 2.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

Pulsed Electrolysis Promotes Catalyst Activity in Dilute CO 2 Streams

Industrial CO 2 streams vary widely in composition, from pure to as low as 3%, posing challenges for purification or direct conversion. Electrochemical reduction offers a route for converting dilute CO 2 streams but faces severe mass transport limitations. This study demonstrates that pulsed electrolysis effectively overcomes these limitations, enhancing CO 2 electroreduction across variable feed compositions and current densities, particularly at low CO 2 concentrations and high current densities. At 25% CO 2 and 400 mA cm −2 , pulsing improved selectivity from 25.6 to 78.6%, production rate from 13.7 to 21.0 mol m −2 h −1 , and energy productivity from 0.77 to 2.59 mol kWh −1 . A dynamic, multiphysics continuum model confirms a 64% increase in CO 2 concentration within the catalyst layer during pulsing, resolving the transient chemical microenvironment. These findings establish pulsed electrolysis as a viable strategy for converting dilute industrial CO 2 streams into valuable feedstocks, bypassing costly pre-separation.

Orfali, Dania Muhieddine [New York University (NYU↗
DOE OSTI2020

A Robust, Scalable Platform for the Electrochemical Conversion of CO 2 to Formate: Identifying Pathways to Higher Energy Efficiencies

This work demonstrated a robust, scalable cell architecture for electroreduction of CO 2 (CO 2 R). An up to 90% faradaic efficiency for the conversion of CO 2 R to formate at 500 mA/cm 2 was realized at a 25 cm2 gas diffusion electrode (GDE) with a carbon-supported SnO 2 electrocatalyst. Furthermore, a 1.27 mm thick catholyte was used between the bipolar membrane and cathode GDE, which could be further reduced to tens of micrometers upon refinement. The deconvolution of the potential drop from each individual component/process guides the pathways to higher energy efficiencies of CO 2 R at this platform. Significant changes in the agglomerate size and aspect ratio on the electrode before and after an 11 h test were revealed by nano-CT, suggesting reduced CO 2 accessibility from electrode degradation. The versatility of this CO 2 R testing platform enables the ability to assess materials, components, and interactions at scales more in line with future devices.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2025

Integration of hydrophobic gas diffusion layers for zero-gap electrolyzers to enable highly energy-efficient CO 2 electrolysis to C 2 products

Electrochemical CO 2 reduction (eCO2R) is an attractive route for mitigating global CO 2 emissions while producing value-added chemicals. Ethylene is one product of eCO2R and is an essential industrial precursor with a global market of $230 billion. The large-scale implementation of C 2 H 4 -selective CO 2 electrolyzers remains challenging because of low energy efficiencies. In this work, we develop the design principles necessary for incorporating an expanded polytetrafluoroethylene (ePTFE) electrode into a zero-gap electrolyzer while simultaneously developing an integrated electrical front contact that reduces the ohmic resistances inherent to electrically insulating gas diffusion layers. By co-designing the catalyst layer, gas diffusion medium, and operating conditions for a zero-gap ePTFE gas diffusion electrode (GDE), we achieved a full-cell voltage of 2.5 V at 200 mA cm −2 at 25 cm 2 geometric area cell with Faradaic efficiencies of 48% for ethylene and 40% for ethanol. This work highlights strategies for developing a scalable, stable, and highly energy-efficient eCO2R for C 2 products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

2D High‐Entropy Transition Metal Dichalcogenides for Carbon Dioxide Electrocatalysis

Abstract High‐entropy alloys combine multiple principal elements at a near equal fraction to form vast compositional spaces to achieve outstanding functionalities that are absent in alloys with one or two principal elements. Here, the prediction, synthesis, and multiscale characterization of 2D high‐entropy transition metal dichalcogenide (TMDC) alloys with four/five transition metals is reported. Of these, the electrochemical performance of a five‐component alloy with the highest configurational entropy, (MoWVNbTa)S 2 , is investigated for CO 2 conversion to CO, revealing an excellent current density of 0.51 A cm −2 and a turnover frequency of 58.3 s −1 at ≈ −0.8 V versus reversible hydrogen electrode. First‐principles calculations show that the superior CO 2 electroreduction is due to a multi‐site catalysis wherein the atomic‐scale disorder optimizes the rate‐limiting step of CO desorption by facilitating isolated transition metal edge sites with weak CO binding. 2D high‐entropy TMDC alloys provide a materials platform to design superior catalysts for many electrochemical systems.

Cavin, John↗
DOE OSTI2023

Cationic Copper Species Stabilized by Zinc during the Electrocatalytic Reduction of CO 2 Revealed by In Situ X‐Ray Spectroscopy

Abstract Advanced in situ X‐ray absorption spectroscopy characterization of electrochemically co‐electrodeposited bi‐element copper alloy electrodes shows that zinc yields the formation of a stable cationic Cu species during the electroreduction of CO 2 at high cathodic polarization. In contrast, the formation/stabilization of cationic Cu species in copper oxides, or doping Cu with another element, like Ni, is not possible. It is found that the pure and mixed Cu:Zn electrodes behave similarly in term of electrocatalytic selectivity to multi‐carbon products. At higher Zn concentrations the electrode behaves like the pure Zn catalyst, which indicates that the Cu cationic species do not have a significant influence on the selectivity to multi‐carbon products. It is found that in the non‐monotonically distribution of products is dominated in term of surface energy in which copper prefers the surface. Otherwise, this work highlights the importance of in situ characterization to uncover the mechanisms mediating the catalytic reactions in contrast to ex situ or post mortem analysis, which can be a source of misinterpretation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Electrochemical Reduction of Flue Gas Carbon Dioxide to Commercially Viable C2-C4 Products (Final Report)

This is the final scientific/technical report for a DOE project focused on the electrochemical conversion of CO 2 in non-aqueous solvents to novel products. Electrochemical reduction of CO 2 provides an attractive route to produce valuable fuels and chemicals that can simultaneously lower greenhouse gas emissions when powered by renewable electricity. While recent technological advances have shown the feasibility of industrial CO 2 electroreduction, many challenges remain to improve this technology and expand the list of economically viable products. The vast majority of electrochemical CO 2 reduction research has been conducted in aqueous media under neutral to alkaline conditions, leading to commonly reported products including carbon monoxide, formic acid, methane, methanol, ethylene, acetic acid, and ethanol. In comparison, non-aqueous media for CO 2 reduction has been underexplored but represents a possible avenue to yield new products and improved operating conditions. The aim of the project was to convert waste CO 2 in the form of flue gas to a multicarbon C2 - C4 chemical product in a reactor designed to achieve economically competitive values of current density and selectivity. The project strived to advance the technology readiness of an electrochemical CO 2 reduction process in alcohol solvents from the proof-of-concept stage to a device capable of meeting performance metrics for commercial viability. In the initial plan, the University of Louisville researchers were to focus on investigating the electrochemical process and improving the faradaic efficiency for novel C2 – C4 species, while also working on a parallel effort to build a practical electrolysis reactor to markedly increase the CO 2 reduction current density. The reactor development effort also aimed to engineer a dual-electrolyte feed strategy with non-aqueous catholyte and aqueous anolyte to promote water oxidation as the coupling anodic half-reaction to enable a sustainable and economical overall process. At the outset, the University of North Dakota was to investigate the feasibility of operating directly from coal-derived flue gas without separate capture and purification. The research team sought to determine impurity effects and test mitigation strategies, as well as engineer the gaseous feed system for high reactor tolerance to lower CO 2 concentration. In the last half year of the project, the focus was planned to shift to integrating the advances in the catalysis, electrochemical conditions, reactor design, and flue gas compatibility into a fully functional device and improve it for maximum current density and faradaic efficiency for C2 – C4 species. Knowledge of the full system components, constraints, and maximum performance was then to be used as the basis for a thorough technoeconomic analysis (TEA) and life cycle analysis (LCA) at the end of the project.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2024

Electrochemical Conversion of CO 2 to Methyl Formate in a Flow Electrolyzer with Mixed Propylene Carbonate/Methanol Catholyte

Despite the promise of electrochemical carbon dioxide reduction as a technology for the production of clean fuels and decarbonization of the chemical industry, research has mostly focused on aqueous systems with a relatively limited set of products that have been achieved via electrosynthesis. Increasingly, CO 2 electroreduction in nonaqueous solvents is being pursued to develop new avenues for expanding the suite of products that can be made with high selectivity. CO 2 reduction in alcohols coupled with in situ esterification to produce esters is one such route that utilizes nonaqueous electrolyte. To be practical, such electrochemical syntheses need to be translated to a high-performance reactor such as a flow electrolyzer. However, many organic solvents, such as alcohols, wet and flood porous electrodes, thus impeding reactor performance. In this work, methanol was mixed with propylene carbonate as a catholyte for a gas-fed CO 2 flow electrolyzer that avoided cathode flooding. Simultaneously, a dual aqueous anolyte was used for water oxidation as a scalable and sustainable anodic half-reaction. The performance effect of methanol concentration, catholyte acidity, CO 2 flow rate, and dilute water in the catholyte were investigated. With 10 vol % methanol in 90 vol % propylene carbonate, 63% faradaic efficiency for methyl formate ester product was sustained without cathode flooding. However, improvements are still needed to lower the cell resistance and further increase the operating current density.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Dynamic Bubbling Balanced Proactive CO 2 Capture and Reduction on a Triple-Phase Interface Nanoporous Electrocatalyst

The formation and preservation of the active phase of the catalysts at the triple-phase interface during CO 2 capture and reduction is essential for improving the conversion efficiency of CO 2 electroreduction toward value-added chemicals and fuels under operational conditions. Designing such ideal catalysts that can mitigate parasitic hydrogen generation and prevent active phase degradation during the CO 2 reduction reaction (CO 2 RR), however, remains a significant challenge. Herein, we developed an interfacial engineering strategy to build a new SnO x catalyst by invoking multiscale approaches. This catalyst features a hierarchically nanoporous structure coated with an organic F-monolayer that modifies the triple-phase interface in aqueous electrolytes, substantially reducing competing hydrogen generation (less than 5%) and enhancing CO 2 RR selectivity (~90%). This rationally designed triple-phase interface overcomes the issue of limited CO 2 solubility in aqueous electrolytes via proactive CO 2 capture and reduction. Concurrently, we utilized pulsed square-wave potentials to dynamically recover the active phase for the CO 2 RR to regulate the production of C1 products such as formate and carbon monoxide (CO). This protocol ensures profoundly enhanced CO 2 RR selectivity (~90%) compared with constant potential (~70%) applied at -0.8 V (V vs RHE). We further achieved a mechanistic understanding of the CO 2 capture and reduction processes under pulsed square-wave potentials via in situ Raman spectroscopy, thereby observing the potential-dependent intensity of Raman vibrational modes of the active phase and CO 2 RR intermediates. Finally, this work will inspire material design strategies by leveraging triple-phase interface engineering for emerging electrochemical processes, as technology moves toward electrification and decarbonization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Controlled Acidity Gradients Enable CO 2 Reduction to Formic Acid (Not Formate) by Molecular Electrocatalysts

Neutral or basic conditions are commonly required for the selective electrochemical reduction of CO 2 , leading to the accumulation of carbonate salts and the generation of formate rather than formic acid. A generalizable strategy for obtaining formic acid (not formate) in the electroreduction of CO 2 with molecular catalysts is introduced, based on controlling acidity gradients using a dual-electrolyte cell with a proton-exchange membrane. This approach uses anodic water oxidation as the source of protons and electrons for CO 2 reduction to formic acid, while mitigating H 2 evolution near the cathode and avoiding carbonate formation. Mechanistic studies, including systems modeling, provide insight into the origin of the formic acid selectivity and guide the broader implementation of this strategy in molecular electrocatalysis for CO 2 utilization.

Alcohols↗
DOE OSTI2022

Accessing and Photo-Accelerating Low-Overpotential Pathways for CO 2 Reduction: A Bis-Carbene Ruthenium Terpyridine Catalyst

A ruthenium catalyst bearing a bidentate bis(carbene) ligand is prepared and studied as a catalyst for CO 2 electroreduction. The catalyst [Ru(tpy)(bis-mim)(MeCN)][PF 6 ] 2 (tpy) is 2,2′,:6′,2″-terpyridine; bis-mim is (methylenebis(N-methylimidazol-2-ylidene)) mediates reduction of CO 2 into CO with a turnover frequency of 630 s –1 and Faradaic efficiency (FE) of 30% at an overpotential of 730 mV. The strongly donating bis(carbene) ligand also enables access to a pathway operating at a lower overpotential of ca. 310 mV. While low-overpotential catalysis is slow in the dark (TOF = 0.01 s –1 ), visible light illumination increases the rate 10-fold (TOF = 0.11 s –1 ). Here, a full mechanistic picture is developed using kinetic analysis from cyclic voltammetry, spectroelectrochemistry, and computational methods, with the bis-mim ligand facilitating rapid CO 2 activation at low overpotentials. Comparisons with other ruthenium catalysts yield insight into the ability to tune the rate of chemical steps (e.g., ligand dissociation and CO 2 nucleophilic attack) and the overpotential by tailoring the primary coordination sphere while retaining the “redox-active” tpy ligand.

CO2 reduction↗
DOE OSTI2022

Bridging knowledge gaps in liquid- and vapor-fed CO 2 electrolysis through active electrode area

Increased use of gas diffusion electrodes for CO 2 electroreduction widens the experimental phase space that was previously inaccessible using foil electrodes, raising fundamental questions over the impacts of key variables that translate between liquid- and vapor-fed CO 2 electrolysis systems. This work focuses on studying the interplay of current-potential profiles and electrochemically active surface area (ECSA) by implementing a Cu nanoflower catalyst morphology. The results show decreased overpotentials as much as 460 and 174 mV for foil and gas diffusion electrodes, respectively, while maintaining or improving multi-carbon product current density. Furthermore, these overpotential shifts and product activities normalized by ECSA lead to current-potential relationships akin to those of the Tafel description, which are found through a continuum model to be useful for describing the roughness dependence for both liquid- and vapor-fed systems. This analysis establishes a holistic approach for establishing catalyst design criteria to improve materials development for CO 2 .

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2023

Assessment of the Degradation Mechanisms of Cu Electrodes during the CO 2 Reduction Reaction

Catalyst degradation and product selectivity changes are two of the key challenges in the electrochemical reduction of CO 2 on copper electrodes. Yet, these aspects are often overlooked. Here, we combine in situ X-ray spectroscopy, in situ electron microscopy, and ex situ characterization techniques to follow the long-term evolution of the catalyst morphology, electronic structure, surface composition, activity, and product selectivity of Cu nanosized crystals during the CO 2 reduction reaction. We found no changes in the electronic structure of the electrode under cathodic potentiostatic control over time, nor was there any build-up of contaminants. In contrast, the electrode morphology is modified by prolonged CO 2 electroreduction, which transforms the initially faceted Cu particles into a rough/rounded structure. In conjunction with these morphological changes, the current increases and the selectivity changes from value-added hydrocarbons to less valuable side reaction products, i.e. , hydrogen and CO. Hence, our results suggest that the stabilization of a faceted Cu morphology is pivotal for ensuring optimal long-term performance in the selective reduction of CO 2 into hydrocarbons and oxygenated products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Highly Tunable Syngas Product Ratios Enabled by Novel Nanoscale Hybrid Electrolytes Designed for Combined CO 2 Capture and Electrochemical Conversion

Coupling renewable energy with the electrochemical conversion of CO 2 to chemicals and fuels has been proposed as a strategy to achieve a new circular carbon economy and help mitigate the effects of anthropogenic CO 2 emissions. Liquid-like Nanoparticle Organic Hybrid Materials (NOHMs) are composed of polymers tethered to nanoparticles and are previously explored as CO 2 capture materials and electrolyte additives. Here, in this study, two types of aqueous NOHM-based electrolytes are prepared to explore the effect of CO 2 binding energy (i.e., chemisorption versus physisorption) on CO 2 electroreduction over a silver nanoparticle catalyst for syngas production. Poly(ethylenimine) (PEI) and Jeffamine M2070 (HPE) are ionically tethered to SiO 2 nanoparticles to form the amine-containing NOHM-I-PEI and ether-containing NOHM-I-HPE, respectively. At less negative cathode potentials, PEI and NOHM-I-PEI-based electrolytes produce CO at higher rates than 0.1 molal. KHCO 3 due to favorable catalyst-electrolyte interactions. Whereas at more negative potentials, H 2 production is favored because of the carbamate electrochemical inactivity. Conversely, HPE and NOHM-I-HPE-based electrolytes display poor CO 2 reduction performance at less negative potentials. At more negative potentials, their performance approached that of 0.1 molal. KHCO 3 , highlighting how the polymer functional groups of NOHMs can be strategically selected to produce value-added products from CO 2 with highly tunable compositions.

36 MATERIALS SCIENCE↗