Cu-Induced Interfacial Water Engineering of SnO2 for Durable and Highly Selective CO2 Electroreduction

The behavior of interfacial water is a crucial factor in influencing the selectivity of CO2 reduction. However, modulating the behavior of interfacial water is challenging, and the investigation of its mechanism is still insufficient. In this regard, we present a Cu doping strategy to engineer the interfacial water of the SnO2 electrode. Amorphous SnO2 catalysts with uniformly doped Cu are prepared by using a coprecipitation method. Our results indicate that the introduction of Cu lowers the oxidation state of Sn and stabilizes surface Sn–O species by enhanced covalency of Sn–O bonds, which suppresses competitive water adsorption and promotes activation of CO2. Additionally, in situ spectroscopy reveals a blue shift of the H2O peak and easier *OCHO formation, indicating that the incorporation of Cu promotes the dissociation of interfacial water and *CO2 hydrogenation process. The optimized Cu–SnO2 catalyst exhibits a high formate Faradaic efficiency (>90%) in a wide current range (100–1000 mA cm–2). This study provides insights into the behavior of interfacial water and sheds light on the design of efficient CO2 electroreduction catalysts.