Ge4+ Stabilizes Cu1+ Active Sites to Synergistically Regulate the Interfacial Microenvironment for Electrocatalytic CO2 Reduction to Ethanol

Electrocatalytic conversion of CO2 to high-energy-density multicarbon products (C2+) offers a sustainable route for renewable energy storage and carbon neutrality. Precisely modulating Cu-based catalysts to enhance C2+ selectivity remains challenging due to uncontrollable reduction of Cuδ+ active sites. Here, an efficient and stable Ge/Cu catalyst was developed for CO2 reduction to ethanol via Ge modification. A Cu2O/GeO2/Cu core–shell composite was constructed by controlling Ge doping. The structure–performance relationship was elucidated through in situ characterization and theoretical calculations. Ge4+ stabilized Cu1+ active sites and regulated the surface microenvironment via electronic effects. Ge modification simultaneously altered CO intermediate adsorption to promote asymmetric CO–CHO coupling, optimized water structure at the electrode/electrolyte interface, and inhibited over-reduction of Cuδ+. This multi-scale synergistic effect enabled a significant ethanol Faradaic efficiency enhancement (11–20%) over a wide potential range, demonstrating promising applicability for renewable energy conversion. This study provides a strategy for designing efficient ECR catalysts and offers mechanistic insights into interfacial engineering for C–C coupling in sustainable fuel production.