Mechanistic Insights into the Unique Role of Copper in CO2 Electroreduction Reactions.

Cu demonstrates a unique capability towards CO2 electroreduction that can close the anthropogenic carbon cycle; however, its reaction mechanism remains elusive, owing to the obscurity of the solid-liquid interface on Cu surfaces where electrochemical reactions occur. Using a genetic algorithm method in addition to density functional theory, we explicitly identify the configuration of a water bilayer on Cu(2 1 1) and build electrochemical models. These enable us to reveal a mechanistic picture for CO2 electroreduction, finding the key intermediates CCO* for the C2 H4 pathway and CH* for the CH4 pathway, which rationalize a series of experimental observations. Furthermore, we find that the interplay between the Cu surfaces, carbon monomers, and water network (but not the binding of CO*) essentially determine the unique capability of Cu towards CO2 electroreduction, proposing a new and effective descriptor for exploiting optimal catalysts.