Strategic Facet Design of In ₂ O ₃ Catalysts for Enhanced Kinetics and Hydrogen Suppression in Iron–Chromium Flow Batteries

Iron-chromium redox flow batteries (ICRFBs) show promise for large-scale energy storage, but their performance is hindered by the hydrogen evolution reaction (HER) and sluggish anode Cr³⁺/Cr²⁺ redox kinetics. Here, an octahedral In₂O₃ catalyst with exposed high-activity (222) crystal planes is reported, synthesized via high-temperature solution thermal decomposition and grown in situ on carbon cloth. The catalyst is grown in situ on carbon cloth to form a nanostructured indium-based electrode (In₂O₃-TCC). Grazing incidence wide-angle X-ray scattering confirms In₂O₃ phase formation, while XANES reveals abundant oxygen vacancies (Ov) serving as anode reaction active sites. In₂O₃-TCC exhibits enhanced electrochemical properties, including a tripled double-layer capacitance (8.92 mF cm^- ²), a reduced charge transfer resistance (1.042 Ω), and improved Cr³⁺/Cr²⁺ kinetics. Density functional theory (DFT) shows that anode HER suppression arises from favorable H⁺ adsorption energy and a high desorption barrier. Furthermore, an in situ differential electrochemical mass spectrometer (DEMS) confirms effective anode HER suppression. The electrode achieves an energy efficiency of 84.02% at 140 mA cm^- ² and stable performance over 500 cycles. This work offers a new pathway for designing high-efficiency, long-lifetime ICRFB electrodes.