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Results for “high Faradaic efficiency”

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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Local microenvironment tuning induces switching between electrochemical CO 2 reduction pathways

Gas diffusion layers (GDL) have become a critical component in electrochemical CO 2 reduction (CO 2 R) systems because they can enable high current densities needed for industrially relevant productivity. Besides this function, it is often assumed that the choice of catalyst and electrolyte play much more important roles than the GDL in influencing the observed product selectivity. Here, we show that tuning of the GDL pore size can be used to control the local microenvironment of the catalyst and hence, effect significant changes in catalytic outcomes. This concept is demonstrated using sputtered Ag films on hydrophobic PTFE substrates with 6 different pore sizes. Although Ag is known to be a predominantly CO generating catalyst, we find that smaller pore sizes favor the generation of formate up to a faradaic efficiency of 43%. Combined experimental and simulation results show that this is due to the influence of the pore size on CO 2 mass transport, which alters the local pH at the electrode, resulting in reaction pathway switching between CO and formate. Importantly, our results highlight the importance of the local microenvironment as an experimental knob that can be rationally tuned for controlling product selectivity: a key consideration in the design of CO 2 R systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Redesigning protonic ceramic electrochemical cells to lower the operating temperature

Protonic ceramic electrochemical cells (PCECs) can operate at intermediate temperatures (450° to 600°C) for power generation and hydrogen production. However, the operating temperature is still too high to revolutionize ceramic electrochemical cell technology. Lowering the operating temperature to <450°C will enable a wider material choice and reduce system costs. We present approaches to redesigning PCECs via readily fabricated single-grain–thick, chemically homogeneous, and robust electrolytes and a nano-micro positive electrode. At 450°C, the PCECs achieve a peak power density of 1.6 watt per square centimeter on H 2 fuel, 0.5 watt per square centimeter on NH 3 fuel, and 0.3 watt per square centimeter on CH 4 fuel in fuel cell mode. In steam electrolysis mode, a current density of >0.6 ampere per square centimeter with a Faradaic efficiency of >90% is achievable at 1.4 volt and 400°C. In addition, exceptional durability (>2000 hours) has been demonstrated, with a degradation rate of <0.01 millivolt per 100 hours in fuel cell mode at 400°C.

Science & Technology - Other Topics↗
DOE OSTI2025

Electron Inversion and Tunneling at Silicon Thermal Oxide Interfaces for Solar-Driven Molecular Catalysis to Syngas

Semiconductor photoelectrodes are regularly coupled to solid-state heterogeneous catalysts to perform solar-driven reduction of CO 2 . Less frequently, molecular catalysts are employed to better control the reactivity toward desired products, yet the development of robust semiconductor/molecule interfaces has proven challenging. Here, we demonstrate that a 2–3 nm thermal oxide layer on Si exhibits stability in aqueous solution, high photovoltage, and a photocurrent density of ∼10 mA/cm 2 for the solar-driven photoelectrochemical reduction of a homogeneous molecular catalyst, producing syngas with an ∼2:1 H 2 to CO ratio. Because of a low defect density, the oxide interface forms an electron inversion layer with metal-like electron density at cathodic potentials. This inversion layer facilitates electron transfer to redox-active molecules via tunneling even if the molecule’s reduction potential is beyond the semiconductor’s conduction band edge. Using an electrolyte solution composed of a homogeneous cobalt bis(terpyridine) catalyst in a water/organic solvent mixture, stable photoelectrochemistry was observed under 1-sun illumination, exhibiting an ∼30% Faradaic efficiency for CO that was similar to a glassy carbon electrode under comparable conditions. Furthermore, the results demonstrate that an ultrathin thermal oxide interface is a robust platform for development of aqueous-stable, molecule-driven photoelectrocatalysis.

Catalysts↗
DOE OSTI2020

Temperature-induced changes in the synthesis gas composition in a high-temperature H 2 O and CO 2 co-electrolysis system

Solid oxide electrolysis cell (SOEC) is an attractive renewable technology capable of producing synthesis gas (H 2 + CO) from H 2 O and CO 2 . An SOEC consists of a solid oxide electrolyte and two ceramic or metal-ceramic electrodes. H 2 O and CO 2 are electrolyzed at the cathode producing H 2 and CO, releasing O 2- ions, which travel through the electrolyte to the anode side and recombine to produce pure oxygen gas as the byproduct. In the present study, a La 0.7 Sr 0.2 Ni 0.2 Fe 0.8 O 3 cathode was used to co-electrolyze H 2 O and CO 2 at three different operating temperatures- 700 °C, 750 °C and 800 °C. Synthesis gas was produced at all three operating temperatures with 100% Faradaic efficiency. The composition of the syngas, however, was found to be a function of the operating temperature. In general, the H 2 /CO ratio in the syngas decreased with increased temperature. This was partially due to CO 2 electrolysis becoming more favorable compared to H 2 O electrolysis at higher temperatures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Assessment of lignite upgrade and hydrogen evolution via electrolysis

Lignite, considered as the lowest-rank coal, accounts for 45% of the total coal resources worldwide, and its low carbon and high ash contents limit its large-scale application. In order to upgrade lignite effectively, a modified coal electrolytic cell (MCEC) was designed, built, and then evaluated for lignite upgrade and hydrogen production through electrolysis, and the operating conditions were optimized. The results show that the performance of the MCEC outperformed the previous coal electrolytic cell (CEC). The operating temperature and iron concentration significantly impact the average current density per milligram of catalyst (ACDMC). The content of dry fixed carbon and heating value increased by 20.9% (wt%) and 8.15%, respectively, in electrolyzed lignite compared with raw lignite. Besides, 71.5% ash and 39.6% mercury were removed from raw lignite after electrolysis, which is the first report. The Faradaic efficiency (FE) for hydrogen evolution reached 99% using MCEC. In addition, the analysis of spectroscopy methods (SEM, EDX, FTIR, and XRD) revealed that the lignite particles were cracked; the oxygen-containing functional groups increased; the minerals of quartz and hematite formed on the surface of lignite particles after electrolysis. Furthermore, the facts indicate that electrolysis of lignite is a competitive approach for lignite upgrade and hydrogen production.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Highly dense atomic Fe–Ni dual metal sites for efficient CO 2 to CO electrolyzers at industrial current densities

Carbon-supported, atomically dispersed, nitrogen-coordinated metal sites (e.g., Fe and Ni) are arguably the most promising catalysts for the electrochemical reduction of CO 2 to CO due to their unique catalytic properties and the use of earth-abundant elements. However, conventional single metal sites are constrained by their structural simplicity, causing either too weak or too strong absorption/desorption of multiple critical intermediates (e.g., *COOH and *CO). Current catalysts also suffer from ultra-low loadings (<1.0 wt%) of atomic metal active sites in catalysts, leading to inadequate performance for CO 2 -to-CO conversion. Here, we develop dual Ni/Fe metal site catalysts with significantly increased atomically dispersed metal loadings (up to 4.8 wt%). A gas-phase chemical vapor deposition (CVD) approach to introducing single Ni sites was integrated with Fe 2 O 3 /ZIF-8 precursors, followed by an optimal thermal activation. The optimized CVD-Ni/Fe–N–C catalyst exhibited remarkable electrocatalytic performance for the CO 2 reduction to CO in a continuous membrane-electrode-assembly electrolyzer, achieving a maximum CO faradaic efficiency (FE CO ) of 96% at a current density of 700 mA cm −2 in a near-neutral electrolyte. Furthermore, a desirable but challenging acidic flow-cell electrolyzer was designed using this dual metal site catalyst to improve CO 2 utilization, accomplishing a FE CO of up to 95% at a CO partial current density close to 600 mA cm −2 . Density functional theory (DFT) calculations suggest a synergetic effect between Fe–Ni pairs facilitating *COOH intermediate formation and *CO desorption simultaneously during CO 2 to CO conversion. This is key to breaking the linear scaling relationship of conventional single-metal site catalysts during the CO 2 reduction reaction.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Anolyte Buffering and CO Coverage Effects in the Electrochemical Reduction of CO at Cu Electrocatalysts

Electrolytic CO reduction was investigated at copper electrocatalysts in zero-gap membrane electrode assemblies as a function of buffering agents and cofeeding with CO 2 or Ar. Results show an acetate Faradaic efficiency (FE) of 90% at 300 mA cm −2 using pure CO feeds and phosphate-buffered anolyte near pH 8. When using CO feeds with more alkaline anolytes, the hydrogen evolution reaction becomes the dominant reduction reaction, independent of the buffer. Product distributions of cofeeding experiments with CO and CO 2 show that increasing CO 2 cofeeding results in increased selectivity toward ethylene (42% FE) in near-neutral KHCO 3 anolytes or ethanol (40% FE) in alkaline KOH anolytes. Evaluation of several commercial anion exchange membranes shows similar selectivity trends, suggesting product selectivity is dominated by the local pH and surface coverage of CO. Based on these results, we propose pH buffering and CO coverage behaviors that facilitate high selectivities to acetate.

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

Continuous Flow Photoelectrochemical Reactor with Gas Permeable Photocathode: Enhanced Photocurrent and Partial Current Density for CO 2 Reduction

Photoelectrochemical (PEC) CO 2 reduction using a photocathode is an attractive method for making valuable chemical products due to its simplicity and lower overpotential requirements. However, previous PEC processes have often been diffusion-limited leading to low production rates of the CO 2 reduction reaction, due to inefficient gas diffusion through the liquid electrolyte to the catalyst surface, particularly at high current densities. In this study, a gas-permeable photocathode in a continuous flow PEC reactor is incorporated, which facilitates the direct supply of CO 2 gas to the photocathode-electrolyte interface, unlike dark reaction-based flow reactors. This concept is demonstrated using Ag-TiO 2 on carbon paper, illuminated through a quartz window and flowing liquid electrolyte. CO 2 supply is managed via pressure and flow control on the non-illuminated side of the carbon paper. The photocurrent density is significantly influenced by the flow rates and pressure of CO 2 gas, and the electrolyte flow rates. Compared to the traditional H-cell, the continuous PEC flow reactor achieves ≈10-fold increase in CO faradaic efficiency, 30-fold increase in production rate and 16-fold increase in stability without catalyst modifications. This work provides essential insights into the design and application of continuous gas-liquid flow PEC reactor systems, highlighting their potential for other PEC reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Self‐Standing Carbon Nanofibers@Carbon Felt Electrodes to Boost Electrolyzer Productivity: Application to the Electro‐Manufacturing of trans ‐3‐Hexenedioic Acid and Adipic Acid

The industrial implementation of electrosynthesis for chemical manufacturing remains constrained by the limited surface area of conventional electrodes. Herein, this challenge is addressed by designing a carbon nanofiber@carbon felt (CNF@CF) electrode platform that combines the high conductivity, flexibility, and ease of handling of commercial carbon felts (CF) with the large surface area and tunable surface chemistry of carbon nanofibers (CNFs). CNFs are deliberately grown onto the CF scaffold to form a sword-in-sheath structure, where entangled nanofibers wrap the felt macrofibers to provide excellent mechanical stability and electrical conductivity without binders. CNF@CF is evaluated both as an electrode and as a catalyst support for the electrochemical hydrogenation of cis,cis-muconic acid (ccMA), a biobased platform molecule key to the production of performance polyamides and renewable Nylon 6,6. As a noncatalytic electrode for the partial hydrogenation to trans-3-hexenedioic acid, CNF@CF achieves a threefold increase in both cumulative productivity and Faradaic efficiency (FE) compared to bare CF. A similar boost in catalytic activity and energy efficiency is observed using Pd/CNF@CF for the hydrogenation of ccMA to adipic acid. These results highlight the opportunities of the CNF@CF platform for electro-organic synthesis and sustainable chemical manufacturing.

electrochemical hydrogenation↗
DOE OSTI2020

Optimal conditions for efficient flow-electrode capacitive deionization

One of the current barriers to achieving fast and stable performance for flow-electrode capacitive deionization (FCDI) is determining optimal operating parameters. To date, however, no consensus has been reached for universal conditions for FCDI. Through experimental and modeling approaches in this study, we systematically evaluated the influence of applied potential (V = 1.2–2.4 V) and electrolyte concentration (C0 = 0.05–0.5 M) on the FCDI and electrodialysis (ED) desalination processes. Evaluation indicators include the concentration decrease in the desalinated solution, salt removal rates, pH fluctuations, charge efficiency, and energy consumption. Results demonstrated that the dynamic curves of concentration decrease at 2.0 V nearly overlapped with the response at 1.6 V at certain electrolyte concentrations, while the salt removal rates at 0.2 M salt concentration were the best among all concentrations tested at a range of applied potential. Therefore, it was thus concluded that the optimum conditions for FCDI operation are 1.6 V applied potential and 0.2 M initial salt concentration, under which faradaic reactions are not being triggered, and concentration polarization does not significantly affect ion transfer. Furthermore, a comparative study between FCDI and ED indicated that ED has a different dependence on the electrolyte concentration and applied potential, in which the desalination can be linearly enhanced with increasing potential but greatly limited at high concentrations. Due to the presence of carbon particles in FCDI, the enhanced charge/ion transfer is probably the main reason for the different desalination performance of FCDI and ED. Overall, the optimal operating parameters obtained in this work could be used as basic test conditions for further development of new carbon-based materials for FCDI.

42 ENGINEERING↗
DOE OSTI2024

Structure Activity Relationships for Second‐Coordination Sphere Functional Group Dependent CO 2 Reduction by Manganese Bipyridyl Electrocatalysts

Abstract A series of twelve second coordination sphere (SCS) functionalized manganese tricarbonyl bipyridyl complexes are investigated for their electrocatalytic CO 2 reduction properties in acetonitrile. A qualitative and quantitative assessment of the SCS functional groups is discussed with respect to the catalysts’ thermodynamic and kinetic efficiencies, and their product selectivities. In probing a broad scope of functional groups, it is clear that only the aprotic ortho‐arylester SCS is capable of promoting the highly desired low‐overpotential proton‐transfer electron‐transfer (PT‐ET) pathway for selective CO production. The ortho‐phenolic analogues cause an increase in overpotential with a product selectivity favoring H 2 evolution, consistent with a high‐overpotential pathway via the anionic [Mn−H] − intermediate. Alternative aprotic Lewis base functional groups such as trifluoromethyl, morpholine and acetamide are shown to also be capable of intermediate manganese hydride generation. The tertiary amine substituent, 2‐morpholinophenyl, exhibits a desirable product distribution characteristic of syn‐gas (CO : H 2 =30 : 48) with an impressive turnover frequency, while the secondary amine group, 2‐acetamidophenyl, induces a notable shift in selectivity with a faradaic yield of 55 % for the formate (HCO 2 − ) product. In addition to their catalytic properties, cyclic voltammetry and infrared spectroelectrochemistry (IR‐SEC) studies are presented to probe pre‐catalyst electronic properties and the two‐electron reduction activation pathway.

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

Covalent Functionalization of Silicon with Plasma-Grown “Fuzzy” Graphene: Robust Aqueous Photoelectrodes for CO 2 Reduction by Molecular Catalysts

Carbon electrodes are ideal for electrochemistry with molecular catalysts, exhibiting facile charge transfer and good stability. Yet for solar-driven catalysis with semiconductor light absorbers, stable semiconductor/carbon interfaces can be difficult to achieve, and carbon’s high optical extinction means it can only be used in ultrathin layers. Here, we demonstrate a plasma-enhanced chemical vapor deposition process that achieves well-controlled deposition of out-of-plane “fuzzy” graphene (FG) on thermally oxidized Si substrates. The resulting Si|FG interfaces possess a silicon oxycarbide (SiOC) interfacial layer, implying covalent bonding between Si and the FG film that is consistent with the mechanical robustness observed from the films. The FG layer is uniform and tunable in thickness and optical transparency by deposition time. Using p-type Si|FG substrates, noncovalent immobilization of cobalt phthalocyanine (CoPc) molecular catalysts was employed for the photoelectrochemical reduction of CO 2 in aqueous solution. The Si|FG|CoPc photocathodes exhibited good catalytic activity, yielding a current density of ∼1 mA/cm 2 , Faradaic efficiency for CO of ∼70% (balance H 2 ), and stable photocurrent for at least 30 h at −1.5 V vs Ag/AgCl under 1-sun illumination. Furthermore, the results suggest that plasma-deposited FG is a robust carbon electrode for molecular catalysts and suitable for further development of aqueous-stable Si photocathodes for CO 2 reduction.

CO2 reduction↗
DOE OSTI2019

Electrocatalytic cleavage of lignin model dimers using ruthenium supported on activated carbon cloth

Biomass lignin is the largest natural source of renewable aromatic compounds, creating an opportunity for its use as a feedstock provided that deconstruction and upgrading methods become available. Valorization of lignin is challenging because its complex structure is naturally recalcitrant to biological degradation. Deconstruction of this amorphous cross-linked polymer requires cleavage of aryl ether bonds, which account for more than half of the linkages between lignin's phenylpropanoid building blocks. High temperature cracking of lignin is possible via pyrolysis, but linkages such as 4-O-5 bonds are resistant to thermal degradation. Electrocatalytic hydrogenation offers a mild alternative; operated at low temperature and atmospheric pressure, it cleaves ether bonds while saturating aromatic rings with in situ generated hydrogen. To investigate the use of catalytic ruthenium supported on activated carbon cloth to cleave 4-O-5 bonds, model compounds that exhibit this linkage were selected, including 3-phenoxyphenol, 4-phenoxyphenol, 3-phenoxyanisole, and 3-phenoxytoluene. The two phenols, 3-phenoxyphenol and 4-phenoxyphenol, were cleaved and hydrogenated to form cyclohexanol. 3-Phenoxyanisole and 3-phenoxytoluene were also cleaved but with lower conversion rates and cyclohexanol yields. Alkaline electrolyte solutions showed the highest cyclohexanol yields for both substrates. Increasing substrate concentrations from 10 mM to 40 mM increased faradaic efficiency to 25%, while decreasing current density from 100 mA (33.33 mA cm -2 ) to 20 mA (6.67 mA cm -2 ) greatly improved the faradaic efficiency to 96%.

09 BIOMASS FUELS↗
DOE OSTI2025

A Rhenium Bis -tetramethylphenanthroline Catalyst for CO 2 Reduction to Formate

Catalytic CO 2 reduction reactions featuring high selectivity toward formate are relatively rare. In some homogeneous molecular CO 2 -reducing electrocatalysis, using triethylamine (TEA) and isopropanol (IPA) as additives improves catalytic performance in producing formate. In this paper, we investigate whether the rhenium(I) bis-diimine dicarbonyl complexes, cis-[Re(N^N) 2 (CO) 2 ] + , where N^N is 2,2’-bipyridine ([1] + ) or 3,4,7,8-tetramethyl-1,10-phenanthroline ([2] + ), are capable of electrocatalytically reducing CO 2 to formate in acetonitrile containing TEA and IPA. Catalyst [1] + was ineffective at CO 2 reduction, yielding formate quantities comparable to those produced in experiments without the catalyst. Catalyst [2] + , however, is a promising electrocatalyst for the CO 2 reduction reaction in the presence of TEA and IPA, with formate being produced in millimolar concentrations (10.5 mM), as detected by 1 H NMR spectroscopy after 6 h electrolysis (formate Faradaic efficiency = 11%, with the major balance going to H 2 ). Upon more detailed examination, [2] + exhibited a turnover frequency (TOF) of 12 s –1 for formate, comparable to other leading molecular catalysts that competently execute this reduction. Combinations of spectroscopy, electrochemistry, and theory were used to better understand the mechanism of CO 2 reduction by [2] + . Fourier transform infrared spectroelectrochemical (FTIR-SEC) data provided no evidence for CO ligand dissociation or substitution upon one- and two-electron reduction of [2] + , suggesting that a mechanism distinct from one that is metal-hydride-based is operative in catalysis. Computational studies guide mechanistic investigations toward the proposed formation of a hydrophenanthroline-based intermediate responsible for hydride transfer to CO 2 and electrocatalytic formate production from [2] + .

Beverages↗
DOE OSTI2020

Molybdenum Carbide Electrocatalysts for Electrochemical Synthesis of Ammonia from Nitrogen: Activity and Stability

Ammonia production has increased from few thousand tons in 1908 to above 200 million tons per year today, revolutionizing the fertilizer industry thanks to the Haber-Bosch (HB) process. However, the HB process is highly energy intensive consuming about 1.4% of fossil energy generated worldwide and releasing 1.87 tons of CO 2 per ton of ammonia produced. This further reduces ammonia’s scope as a carrier fuel for the hydrogen economy. Hence, finding alternative energy efficient ways to synthesize ammonia is important from more than one perspective. Ammonia synthesis from its constituent nitrogen and hydrogen gases is mainly hampered by the nitrogen reduction reaction (NRR) due to the strong N≡N bond (945 kJ mol −1 ). Electrochemical synthesis (ES) routes in this regard offer a milder approach. However, ES of ammonia under different temperatures, utilizing different electrolytes and catalysts has not yet reliably produced ammonia at viable rates and efficiencies. We report an origami-like Mo 2 C cathode catalyst for NRR that achieved a maximum synthesis rate of 2.16 × 10 −11 mol cm −2 s −1 and a faradaic efficiency of 1.8% at 30 °C using Nafion-212 as electrolyte. Origami-like morphology containing numerous kinks appears to improve electrocatalytic activity and show a promising route for fabricating NRR catalysts with higher catalytic activity.

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

Oxidation‐Driven Enhancement of Intrinsic Properties in MXene Electrodes for High‐Performance Flexible Energy Storage

Abstract MXenes, a novel class of 2D materials, exhibit great potential for energy storage due to their unique layered structure and excellent electrical conductivity. However, improving the intrinsic electrochemical storage capacity of MXenes remains a significant challenge, often requiring the incorporation of other Faradaic materials. Oxidation, in particular, poses a key issue that impacts the capacity of MXene devices. In this study, controlled oxidation is employed to create nanoscale holes within MXene, transforming them into holey MXene (H‐MXene) nanosheets. These porous structures shorten ion transport distances and increase ion transport pathways, thereby significantly enhancing the electrochemical storage capacity of MXenes. The resulting H‐MXene micro‐supercapacitors (MSCs) demonstrate exceptional performance, achieving an aerial capacitance 2.5 times that of unmodified MXene electrodes, along with excellent cycling stability, retaining 91.7% of their capacitance after 10 000 cycles. Additionally, a flexible integrated system combining energy storage and sensing functionalities is developed, showcasing its scalability in self‐powered sensing applications. The incorporation of self‐healing polyurethane (PU) enables the device to retain 90% of its storage capacity after undergoing self‐healing. This study presents a novel approach for developing high‐performance MXene‐based energy storage devices and provides valuable insights into efficient ion transport and storage in 2D materials.

Cheng, Yongfa [Department of Materials Science and↗
DOE OSTI2022

Membrane‐electrode assembly design parameters for optimal CO 2 reduction

Commercial-scale generation of carbon-containing chemicals and fuels by means of electrochemical CO 2 reduction (CO 2 R) requires electrolyzers operating at high current densities and product selectivities. Membrane-electrode assemblies (MEAs) have been shown to be suitable for this purpose. In such devices, the cathode catalyst layer controls both the rate of CO 2 R and the distribution of products. In this study, we investigate how the ionomer-to-catalyst ratio (I:Cat), catalyst loading, and catalyst-layer thickness influence the performance of a cathode catalyst layer containing Ag nanoparticles supported on carbon. In this paper, we explore how these parameters affect the cell performance and establish the role of the exchange solution (water vs. CsHCO 3 ) behind the anode catalyst layer in cell performance. We show that a high total current density is best achieved using an I:Cat ratio of 3 at a Ag loading of 0.01–0.1 mg Ag /cm 2 and with a 1.0 M solution of CsHCO 3 circulated behind the anode catalyst layer. For these conditions, the optimal CO partial current density depends on the voltage applied to the MEA. The work also reveals that the performance of the cathode catalyst layer is limited by a combination of the electrochemically active surface area and the degree to which mass transfer of CO 2 to the surface of the Ag nanoparticles and the transport of OH – anions away from it limit the overall catalyst activity. Hydration of the ionomer in the cathode catalyst layer is found not to be an issue when using an exchange solution. The insights gained allowed for a Ag CO 2 R MEA that operates between 200 mA/cm 2 and 1 A/cm 2 with CO faradaic efficiencies of 78–91%, and the findings and understanding gained herein should be applicable to a broad range of CO 2 R MEA-based devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗