Ultralow-Iridium Oxygen Evolution Catalyst with Dual-Site Oxide Pathway for Proton Exchange Membrane Water Electrolysis

Developing cost-effective low-iridium catalysts for the acidic oxygen evolution reaction (OER) is essential for the advancement of proton exchange membrane (PEM) water electrolyzers. Here, we report a cerium oxide-supported iridium cluster catalyst (Ir@CeO₂) that features ultrafine Ir clusters dispersed within a CeO₂ matrix, achieving low noble metal loading and favorable activity-stability balance. The Ir@CeO₂ exhibits a small overpotential of 197 mV at 10 mA cm^-2 and a large mass activity of 247 A g_Ir^-1 at 300 mV, surpassing commercial IrO₂ by more than 38 times. The enhanced OER kinetics is attributed to the dual-site oxide pathway mechanism enabled by increased Ir-O covalency and a shortened Ir-Ir distance at chelation interfaces within Ir@CeO₂. Utilizing the Ir@CeO₂ catalyst in an actual PEM electrolyzer with a minimal Ir loading of 0.3 mg cm^-1 demonstrated durable water electrolysis for over 1000 h at a current density of 1 A cm^-2 under a cell voltage of 1.68 V.