Strategic Facet Design of In2O3 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.