Cobalt−Iron Oxide Nanosheets for High‐Efficiency Solar‐Driven CO2−H2O Coupling Electrocatalytic Reactions

Solar‐driven electrochemical overall CO2 splitting (OCO2S) offers a promising route to store sustainable energy; however, its extensive implementation is hindered by the sluggish kinetics of two key reactions (i.e., CO2 reduction reaction and oxygen evolution reaction (CO2RR and OER, respectively)). Here, as dual‐functional catalysts, Co2FeO4 nanosheet arrays having high electrocatalytic activities toward CO2RR and OER are developed. When the catalyst is applied to a complete OCO2S system driven by a triple junction GaInP2/GaAs/Ge photovoltaic cell, it shows a high photocurrent density of ≈13.1 mA cm−2, corresponding to a remarkably high solar‐to‐CO efficiency of 15.5%. Density functional theory studies suggest that the Co sites in Co2FeO4 are favorable to the formation of *COOH and *O intermediates and thus account for its efficient bifunctional activities. The results will facilitate future studies for designing highly effective electrocatalysts and devices for OCO2S. Cobalt−iron oxide nanosheet arrays are demonstrated as efficient dual‐functional electrocatalysts toward CO2 reduction and oxygen evolution reactions. Using a triple‐junction GaInP2/GaAs/Ge photovoltaic cell as the power source, an overall CO2 splitting system is constructed with two cobalt−iron oxide electrodes, which exhibits a remarkably high solar‐to‐CO efficiency of 15.5%.