Perchlorate Fusion–Hydrothermal Synthesis of Nano‐Crystalline IrO 2 : Leveraging Stability and Oxygen Evolution Activity

Abstract Iridium oxides are the state‐of‐the‐art oxygen evolution reaction (OER) electrocatalysts in proton‐exchange‐membrane water electrolyzers (PEMWEs), but their high cost and scarcity necessitate improved utilization. Crystalline rutile‐type iridium dioxide (IrO 2 ) offers superior stability under acidic OER conditions compared to amorphous iridium oxide (IrO x ). However, the higher synthesis temperatures required for crystalline phase formation result in lower OER activity due to the loss in active surface area. Herein, a novel perchlorate fusion–hydrothermal (PFHT) synthesis method to produce nano‐crystalline rutile‐type IrO 2 with enhanced OER performance is presented. This low‐temperature approach involves calcination at a mild temperature (300 °C) in the presence of a strong oxidizing agent, sodium perchlorate (NaClO 4 ), followed by hydrothermal treatment at 180 °C, yielding small (≈2 nm) rutile‐type IrO 2 nanoparticles with high mass‐specific OER activity, achieving 95 A g Ir −1 at 1.525 V RHE in ex situ glass‐cell testing. Most importantly, the catalyst displays superior stability under harsh accelerated stress test conditions compared to commercial iridium oxides. The exceptional activity of the catalyst is confirmed with in situ PEMWE single‐cell evaluations. This demonstrates that the PFHT synthesis method leverages the superior intrinsic properties of nano‐crystalline IrO 2 , effectively overcoming the typical trade‐offs between OER activity and catalyst stability.