Indium Metal Oxide Tandem Ag Catalyst toward Highly Selective CO₂ Electroreduction to CO over a Wide Potential Window

We report In2O3 tandem Ag-based catalysts for an electrochemical CO2 reduction reaction (eCO2RR), which achieve remarkable selectivity toward CO and desirable Faradaic efficiencies (FEs) exceeding 90%, with a maximum value of 97.8%, achieved over 12.25%In2O3–Ag using the H-type cell within a wide potential window ranging from −0.48 to −0.88 V vs RHE. Moreover, a high current density of −102.6 mA cm–2 can be attained in the flow cell while maintaining an FE of CO above 90%. The theoretical calculations show a more negative Gibbs free energy for the formation of the key intermediate *CO2– on the In site, which demonstrates that In2O3 of the tandem catalyst exhibits a stronger adsorption and activation capacity for CO2. Additionally, DFT simulation reveals the thermodynamic feasibility of the surface transport of *CO2–, wherein the *CO2– intermediate migrates from the In site to the Ag site. The rapid electron transfer at the In2O3–Ag heterointerface influences the electronic environment of the Ag site, accelerating migration and reducing the energy barrier for *CO2– conversion to *COOH, ultimately facilitating the generation of CO.