Interplay of Mass Transfer and Local pH Effects in CO2 Reduction Electrocatalysis

Abstract

Here we report on the study of mass transfer and local pH effects on CO2 reduction by using Cu nanowires as the electrocatalysts. Highly dense Cu nanowires were synthesized by first thermal oxidation of Cu mesh in air, and then reduction by applying a cathodic electrochemical potential or thermal annealing in a reducing atmosphere (see the Methods). Our previous report has shown that the electrochemically reduced (ECR) Cu nanowires are highly active for CO2 reduction, with favorable production of CO and formate at potentials more positive than ‒0.5 V (versus reversible hydrogen electrode; the same potential scale is used in the following discussion) and C2 species (ethanol, ethylene, and ethane) at more negative potentials. In this work, we performed more systematic studies in the high-overpotential region, i.e., potentials more negative than ‒0.5 V, where the mass transport of CO2 and high local pH near the electrode surface are believed to play a significant role in determining the electrocatalytic performance. We aimed to examine the interplay between the mass transfer and local pH effects in the electrocatalysis for CO2 reduction and elucidate their roles in the structure-performance relationships of the high-surface-area nanowire catalysts. The ultimate goal is to explore the optimal electrochemical conditions for CO2 reduction to produce valuable C2 products.