Local pH Effect in the CO2 Reduction Reaction on High-Surface-Area Copper Electrocatalysts

The local pH on electrode surfaces is known to play an important role in the electrochemical reduction of CO2, which could alter the chemical kinetics and molecular transport under the reaction conditions. Here we report the study of local pH effect on the catalytic performance of high-surface-area Cu electrocatalysts. The electroreduction of CO2 was systematically investigated on three types of Cu nanowires with distinct surface roughness factors and nanostructures. The measured electrocatalytic activities and selectivities were further correlated to the simulated local pH on the electrode surface. It was revealed that the high local pH induced by the production of hydroxide from the reaction beneficially suppresses the evolution of hydrogen and enhances the selectivity toward multi-carbon products, but detrimentally limits the transport of CO2 molecules at large current densities. An optimal range of local pH is determined for the electroreduction of CO2, which is insightful for improving the design of electrodes for more efficient energy conversion and chemical transformations. (C) 2018 The Electrochemical Society.