Coupled Electrolysis for Energy Efficient CO2 Reduction to Formic Acid Enabled by Reconstruction of Indium-Based Catalysts

Abstract Electrochemical CO2 reduction to formate represents a promising avenue for closing the anthropogenic carbon cycle, yet the structural reconstruction of selective indium-based catalysts under operating conditions poses challenges for identifying active sites and elucidating reaction mechanisms. Here, we demonstrate that modulating the oxygen vacancies (OV) concentration in In2O3 enables precise control over the reconstruction pathway, yielding metallic In with tunable grain boundary (GB). An optimal OV concentration directs the formation of a GB-rich In catalyst (In-GB) that delivers a formate Faradaic efficiency of 96.3% at an industrial current density of −400 mA cm–2. Operando spectroscopy and density functional theory calculations reveal that the GB structure redistributes the surface electronic structure to stabilize the critical *OCHO intermediate and lower the energy barrier of the potential-determining step. To address the challenge of high energy consumption in traditional electrolysis systems, we further propose a coupled system of CO2 reduction and methanol oxidation. In the membrane electrode assembly (MEA) configuration at a current density of −300 mA cm–2, this coupled system reduces the overall energy consumption by 60% and increases the formate production rate by 51.2% compared with the conventional CO2RR//OER system. This work elucidates the mechanistic origins of reconstruction–driven activity in In-based catalysts and establishes a versatile framework for catalyst and system-level optimization in energy-efficient CO2 electroreduction.