Besides the catalyst structures, the electrocatalysis for CO2 reduction is also dependent on the electrolyte and CO2 partial pressure, which can affect the catalytic activity and selectivity via mass transfer and/or local pH effects. While protons are readily available in aqueous solutions, the supply of reactants to the electrode surface is limited by the concentration and diffusivity of dissolved CO2 molecules, which places a hurdle on the current density and efficiency of CO2 reduction. The reduction of CO2, as well as the evolution of H2, produces hydroxide anions (OH–) and causes rise of the local pH on the electrode surface. 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. 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) and C2 species (ethanol, ethylene, and ethane) at more negative potentials. We have further 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. Simulations have been developed to understand the interplay between the mass transfer and local pH effects and elucidate their roles in the structure-performance relationships of the high-surface-area nanowire catalysts. Based on these results, discussions are provided for optimizing the electrochemical conditions for CO2 reduction to produce valuable C2 products.

Interplay of mass transfer and local pH effects in CO2 reduction electrocatalysis

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.