Mass transport plays an important role in the CO₂ reduction electrocatalysis. Albeit being more pronounced on nanostructured electrodes, the studies of mass transport for CO₂ reduction have yet been limited to planar electrodes. We report here the development of a mass transport model for the electroreduction of CO₂ on Cu nanowire electrodes. Fed with the experimental data from electrocatalytic studies, the local concentrations of CO₂, HCO₃^-, CO₃^2- and OH^- on the nanostructured electrodes are calculated by solving the diffusion equations with spatially distributed electrochemical reaction terms incorporated. The mass transport effects on the catalytic activity and selectivity of the Cu nanowire electrocatalysts are thus discussed by using the local pH as the descriptor. The established correlations between the electrocatalytic performance and the local pH shows that, the latter does not only determine the acid-base reaction equilibrium, but also regulates the mass transport and reaction kinetics. Based on these findings, the optimal range of local pH for the CO₂ reduction is discussed in terms of a fine balance of the suppression of hydrogen evolution, improvement of C₂ product selectivity and limitation of CO₂ supply. Our work highlights the importance of understanding the mass transport effects in interpretation of the CO₂ reduction electrocatalysis on high-surface-area catalysts.

The local pH on electrode surfaces is known to play an important role in the electrochemical reduction of CO 2 , 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 CO 2 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 CO 2 molecules at large current densities. An optimal range of local pH is determined for the electroreduction of CO 2 , which is insightful for improving the design of electrodes for more efficient energy conversion and chemical transformations.

Mass transfer effects play an important role in CO2 electroreduction, giving rise to diffusion-limited activity and selectivity on Cu nanowire electrocatalysts.

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