Cations Responsible for Varied CO₂RR Product Selectivity at High Overpotentials over Cu₂O Nanocubes

This study investigates the role of cations in tuning the structure and chemical state of Cu2O nanocubes during CO2 reduction reactions (CO2RR) and how these changes impact product selectivity. Different cations (Li+, K+, Cs+) in carbonate (CO32-) electrolytes have a significant effect on the dissolution and reprecipitation of Cu species, which alters the surface chemistry of electrodes. Li+ promotes the dissolution of Cu, leading to a metallic surface that favors CH4 production, while K+ and Cs+ stabilize the Cu oxide and hydroxide species on the surface, resulting in higher faradaic efficiency for C2H4. A combination of ex situ and in situ techniques, including X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and electrochemical surface-enhanced Raman spectroscopy (EC-SERS), demonstrates cation-induced changes in the Cu oxidation state and surface structure directly affecting CO2RR product selectivity.