Abstract The design of a low‐iridium‐loading anode catalyst layer with high activity and durability is a key challenge for a proton exchange membrane water electrolyzer (PEMWE). Here, the synthesis of a novel supported IrO 2 nanocatalyst with a tri‐layered structure, dubbed IrO 2 @TaO x @TaB that is composed of ultrasmall IrO 2 nanoparticles anchored on amorphous TaO x overlayer of TaB nanorods is reported. The composite electrocatalyst shows great activity and stability toward the oxygen evolution reaction (OER) in acid, thanks to its dual‐interface structural feature. The electronic interaction in IrO 2 /TaO x interface can regulate the coverage of surface hydroxyl groups, the Ir 3+ / Ir 4+ ratio, and the redox peak potential of IrO 2 for enhancing OER activity, while the dense TaO x overlayer can prevent further oxidation of TaB substrate and stabilize the IrO 2 catalytic layers for improving structural stability during OER. The IrO 2 @TaO x @TaB can be used to fabricate an anode catalyst layer of PEMWE with an iridium‐loading as low as 0.26 mg cm −2 . The low‐iridium‐loading PEMWE delivers high current densities at low cell voltages (e.g., 3.9 A cm −2 @2.0 V), and gives excellent activity retention for more than 1500 h at 2.0 A cm −2 current density.

Supported IrO2 Nanocatalyst with Multilayered Structure for Proton Exchange Membrane Water Electrolysis