Gallium-Regulated Cu+/Cu0 Mixed Valence and Oxygen-Deficient Sites in Core-Shell Cu2O for Selective CO2-to-C2+ Electrosynthesis

Abstract

Electrochemical CO₂ reduction to multicarbon C₂₊ products requires efficient C─C coupling while maintaining catalytically favorable Cu states under strongly reducing conditions. Herein, Ga-modified core–shell Cu₂O catalysts are constructed by a wet-chemical reduction method to couple Cu-valence regulation with oxygen-defect generation within a phase-preserved Cu₂O framework. Ga incorporation retains the ca. 200 nm core–shell morphology but perturbs the local Cu─O environment, increases the Cu⁺/Cu⁰ ratio from 2.54 to 3.45, and raises the defect-associated O 1s contribution from 75.13% to 82.94%. In a flow cell containing 1.0 M KOH, the optimized Ga/Cu₂O-II catalyst delivers a C₂₊ Faradaic efficiency of 73.5%, a C₂₊ partial current density of 251 mA cm⁻², and an FE_C2+/FE_C1 ratio of 6.8 at −1.26 V versus RHE; the ethanol Faradaic efficiency reaches 37.9%. After 12 h electrolysis, the Cu⁺/Cu⁰ ratio remains 2.94 and FE_C2+ remains above 60%. The combined structural, electrochemical, and post-reaction results support a dual-regulation picture in which a Cu⁺-rich Cu⁺/Cu⁰ surface favors carbon-intermediate retention and C─C coupling, while oxygen-deficient sites increase the population of accessible adsorption environments and facilitate conversion of oxygen-containing intermediates. This work demonstrates a simple strategy for stabilizing a catalytically productive mixed-valence/defect state of Cu₂O for high-rate C₂₊ electrosynthesis.