Understanding the C1 Selectivity Descriptors in Electrochemical CO2 Reduction for Production of Solar Fuels

Generating solar fuels from carbon dioxide (CO2) and water offers an intriguing opportunity for a carbon-neutral, sustainable, and scalable source of energy. Electrochemical reduction of CO2 is a key reaction for the production of liquid fuels, but it follows a complex reaction network. Even for products with a single carbon atom (C1 products), two bifurcated pathways exist. In this study, we combine evidence from the experiments with a theoretical analysis of energetics to rationalize that not all steps in the reduction of CO2 are electrochemical. This insight enables us to create a selectivity map for two-electron products (carbon monoxide (CO) and formate) on elemental metal surfaces using only two energy descriptors. In the further reduction of CO*, we also find bifurcated pathway one for CHO* and one for COH*. We find Cu to be the only elemental metal capable of reducing CO2 to products beyond 2e− via the proposed COH pathway. Our analysis also rationalizes experimentally observed differences in products between the thermal and electrochemical reduction of CO2 on Cu.