(67g) Understanding the Effects of Catalyst Surface Area on Electrochemical CO2 Reduction in Aqueous and Vapor-Fed Systems

Several advancements in materials discovery, component analysis and configuration, and system design have propelled electrochemical CO₂ reduction (CO₂R) as a promising renewable technology. And now with vapor-fed reactors, the use of gas diffusion electrodes (GDEs) has provided increased mass transport of CO₂ to the catalyst interface, allowing for high current densities to be reached. Nonetheless, catalyst development has driven the bulk of research in electrochemical CO₂R. In this work, we investigate the effects of catalytic surface area on the performance of both aqueous- and vapor-fed systems. By utilizing a Cu nanostructured flower catalyst (NF), we demonstrate both significant overpotential shifts (~460 mV at ~1 mA cm^-2 CO₂R) and increased formation of multi-carbon products from CO₂ (> 95% of CO₂R products are C₂₊) compared to polycrystalline Cu. Normalizing the data by the electrochemically active surface area (ECSA) allows us to deduce information about the reaction microenvironments and unchanging rate-limiting steps for multi-carbon products. We then translate this morphology in a GDE architecture for implementation in vapor-fed reactors. Analysis of these vapor-fed devices demonstrate a similar overpotential shift (~190 mV at <214 mA cm^-2), revealing that this shift is proportional to the difference in ECSAs of the electrodes akin to Tafel kinetics. By comparing the current-density trends for all systems, we highlight both similar and contrasting phenomena, speaking to the difference in microenvironments and enhancements observed in certain operating regimes. This work demonstrates that catalyst surface area is of key influence on the performance of these systems and can support electrode engineering efforts from a better understanding of the local catalytic environment.

Prepared by LLNL under Contract DE-AC52-07NA27344.