Fabrication of Nb 2 O 5 @IrO 2 Core–Shell Catalysts for Enhanced Oxygen Evolution Reaction in Acidic Media

Iridium oxide (IrO 2 ) is the benchmark catalyst for the acidic oxygen evolution reaction (OER) in proton exchange membrane water electrolysis (PEMWE), but its cost and scarcity require improved Ir utilization. Herein, Nb 2 O 5 @IrO 2 core–shell catalysts were developed using ball‐milled Nb 2 O 5 supports with uniform IrO 2 shell formation. Ball‐milling at 300 rpm for 8 h produced a rounded and relatively uniform Nb 2 O 5 morphology with a high defect‐related oxygen contribution, providing favorable support characteristics for homogeneous IrO 2 deposition. Electron microscopy and elemental mapping supported an approximately 3 nm IrO 2 shell on the Nb 2 O 5 core. Among catalysts prepared from supports milled for different durations, BM‐8h‐Nb 2 O 5 @IrO 2 exhibited the best OER performance in 0.1 M HClO 4 , with an overpotential of 307 mV at 10 mA cm −2 and an IrO 2 mass activity of 304.17 A g IrO2 −1 , outperforming unsupported IrO 2 . Although the 18 h ball‐milled catalyst exhibited the largest electrochemically active surface area, its lower OER activity indicates that optimized support morphology and defect structure, rather than surface area alone, govern IrO 2 utilization. These results demonstrate that ball‐milled Nb 2 O 5 support provides an effective platform for Ir‐efficient acidic OER catalysts relevant to PEMWE anodes.