Elucidating the Facet-Dependent Selectivity for CO2 Electroreduction to Ethanol of Cu–Ag Tandem Catalysts

Abstract

Despite being desirable high-value products of the electrochemical CO 2 reduction reaction (CO 2 RR), alcohols are still obtained with lower selectivity compared to hydrocarbons and the reaction pathways leading to their formation are still under debate. In this joint experimental–computational work, we exploit structural sensitivity effects to elucidate the ethanol-producing active sites on Cu–Ag CO 2 RR tandem catalysts. Specifically, methane-selective Cu nano-octahedra (Cu oh ), enclosed by (111) facets, and ethylene-selective Cu nanocubes (Cu cub ), enclosed by (100) facets, are mixed with CO-selective Ag nanospheres (Ag sph ) to form Cu oh –Ag and Cu cub –Ag bimetallic catalysts. Ethanol is selectively enhanced via the *CH x –*CO coupling pathway at the terraces of Cu oh –Ag in the CO-enriched environment generated by the Ag sph . Conversely, on Cu cub –Ag, ethanol is selectively produced via the same pathway at the edges and corners of Cu cub, while ethylene continues to be produced at the terraces. The terraces being the predominant surfaces on the catalysts, such facet dependence explains the higher ethanol-to-ethylene ratio on the Cu oh –Ag. These findings illustrate how tandem catalysis and structure-sensitive effects can be combined to obtain notable changes in the selectivity of electrochemical reactions.