From electricity to fuels: Descriptors for C1 selectivity in electrochemical CO2 reduction

Electrochemical reduction of carbon dioxide (CO2RR) over transition metals follows a complex reaction network. In this study, we combine observations from experimental literature with a theoretical analysis of energetics to rationalize that not all intermediates in the reduction of CO2 are formed through direct protonation steps. We derive a selectivity map for two-electron products (carbon monoxide (CO) and formate) on pure metal surfaces using only the CO and OH binding energies as descriptors. For the pure metals that are selective towards CO formation, the variation of the CO binding energy is sufficient to further subdivide the map into domains that predominantly form H2, CO, and more reduced products. Our analysis rationalizes experimentally observed product distributions in CO2RR across pure metal systems. Overall, we highlight the need for additional material screening descriptors for CO2R and the importance of considering competition from the elementary steps of the hydrogen evolution reaction.