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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>(</mml:mo><mml:msubsup><mml:mrow><mml:mi>CO</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>-</mml:mo></mml:mrow></mml:msubsup><mml:mo>)</mml:mo></mml:math> 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.