Revealing the CO Coverage-Driven C-C Coupling Mechanism for Electrochemical CO 2 Reduction on Cu 2 O Nanocubes via Operando Raman Spectroscopy

Electrochemical reduction of carbon dioxide (CO RR) is an attractive route to close the carbon cycle and potentially turn CO into valuable chemicals and fuels. However, the highly selective generation of multicarbon products remains a challenge, suffering from poor mechanistic understanding. Herein, we used Raman spectroscopy to track the potential-dependent reduction of Cu O nanocubes and the surface coverage of reaction intermediates. In particular, we discovered that the potential-dependent intensity ratio of the Cu-CO stretching band to the CO rotation band follows a volcano trend similar to the CO RR Faradaic efficiency for multicarbon products. By combining spectroscopic insights with Density Functional Theory, we proved that this ratio is determined by the CO coverage and that a direct correlation exists between the potential-dependent CO coverage, the preferred C-C coupling configuration, and the selectivity to C products. Thus, Raman spectroscopy can serve as an effective method to quantify the coverage of surface intermediates during an electrocatalytic reaction.