Effects of *CO Coverage on Selective Electrocatalytic Reduction of CO2 to Ethylene over Cu2O with Undercoordinated Cu Sites

Cu2O surface with the coordinatively unsaturated Cu sites reveals advantages in the electroreduction of CO2 toward C2H4 production. Understanding the role of *CO coverage and veritable active sites is of great significance for a good command of the catalytic mechanism. Herein, based on density functional theory, the effects of *CO coverage during the reduction of CO2 to C2H4 on various active sites of Cu2O(111) surface, in terms of the adsorption and structural changes of *CO and key intermediates; the energy profiles of the C-C coupling steps; and the subsequent reaction mechanisms were investigated. Results show that CuCUS on the Cu2O(111) surface is especially reactive toward the *CO adsorption and subsequent reactions, being the preferred site owing to the unsaturated Cu atoms. The *CO coverage obviously tunes the adsorption stability of *COH and *CHO intermediates by affecting the adsorbent-adsorbent interactions. Higher coverage of *CO within 0.13-0.25 promotes the C-C coupling by lowering the energy barrier of *CH2 dimerization, favoring the C2H4 production. Due to the more facile generation of *CHO than *COH, the rate-determining step is speculated to be the C-C coupling with the highest barrier energy occurring in the *CHO pathway. Results provide a fundamental understanding of the CO2 reduction mechanism on Cu-based surfaces, favoring novel catalysts, rational design, and chemical fuel production.