Sulfur doping and oxygen vacancy in In2O3 nanotube co-regulate intermediates of CO2 electroreduction for efficient HCOOH production and rechargeable Zn-CO2 battery

By manipulating the distribution of surface electrons, defect engineering enables effective control over the adsorption energy between adsorbates and active sites in the CO₂ reduction reaction (CO₂RR). Herein, we report a hollow indium oxide nanotube containing both oxygen vacancy and sulfur doping (V_o-S_x-In₂O₃) for improved CO₂-to-HCOOH electroreduction and Zn-CO₂ battery. The componential synergy significantly reduces the *OCHO formation barrier to expedite protonation process and creates a favorable electronic micro-environment for *HCOOH desorption. As a result, the CO₂RR performance of V_o-S_x-In₂O₃ outperforms Pure-In₂O₃ and V_o-In₂O₃, where V_o-S₅₃-In₂O₃ exhibits a maximal HCOOH Faradaic efficiency of 92.4% at −1.2 V vs. reversible hydrogen electrode (RHE) in H-cell and above 92% over a wide window potential with high current density (119.1 mA cm⁻² at −1.1 V vs. RHE) in flow cell. Furthermore, the rechargeable Zn-CO₂ battery utilizing V_o-S₅₃-In₂O₃ as cathode shows a high power density of 2.29 mW cm⁻² and a long-term stability during charge–discharge cycles. This work provides a valuable perspective to elucidate co-defective catalysts in regulating the intermediates for efficient CO₂RR.