Stabilized High‐Valent Indium for Promoted Formate Production from Electrochemical CO₂ Reduction

Abstract Electrocatalysts based on high‐valent indium are promising for formate production via CO₂ electroreduction. However, reconstruction often occurs during the reaction progress, resulting in a decline in catalytic performance. Here, a composite of In₂O₃/In₂S₃ is developed, and its catalytic performance exceeds that of either individual phase, particularly in stability. Analysis of morphology, valence state, and in situ Raman spectroscopy reveals that In₂O₃ is well preserved during the reaction. Theoretical calculations suggest that the desorption energy of lattice oxygen on In₂O₃ can be strengthened due to In₂O₃‐In₂S₃ bonding within the composite. This reinforcement facilitates the formation of more active sites and promotes CO₂ adsorption, further decreasing the energy barrier of formate production to only 0.12 eV. As a result, the composite exhibits a formate selectivity over 95.05% at –1.13 V vs reversible hydrogen electrode accompanied by a partial current density of 434.4 mA cm^–2. Notably, the selectivity of formate maintains over 95% even after 50 h at an industrial‐level current density of 200 mA cm^–2, 17 times longer than the individual phase. Furthermore, 18.33% solar‐to‐formate and 19.49% solar‐to‐fuel are obtained when coupled with III‐V solar cells, demonstrating its feasibility.