Revealing the Effect of Bond Length of Amorphous Iridium Oxide via Redox Control for Oxygen Evolution Reaction Electrocatalysis

Achieving a carbon-free energy system requires efficient hydrogen production, and the oxygen evolution reaction (OER) remains a critical bottleneck. Reducing the overpotential is essential for improving OER performance, and noble metal oxides such as IrO 2 and RuO 2 are widely employed owing to their favorable activity. Recent studies revealed that amorphous structures outperform their crystalline counterparts. In this study, we focused on IrO 2 and investigated its amorphous phase in detail. Although differences in short- and long-range disorder and variations in the oxidation state have been proposed to explain activity trends, a comprehensive understanding remains elusive. Therefore, we synthesized amorphous iridium oxides under different conditions and, through a combination of machine learning and advanced structural characterization, identified the Ir−O bond length as a key factor governing both the overpotential and stability. Our findings provide a diverse perspective for analyzing amorphous catalysts, highlighting the central role of local Ir−O bonding environments in determining OER performance.