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 $\left({\mathrm{CO}}_3^{2-}\right)$ 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.