IrO ₂ /Ir Composite Nanoparticles (IrO ₂ @Ir) Supported on TiN _x O _y Coated TiN: Efficient and Robust Oxygen Evolution Reaction Catalyst for Water Electrolysis

Abstract It is crucial but challenging to reduce the required noble‐metal loading without compromising the catalytic performance of oxygen evolution reaction (OER) catalysts. This study presents a highly active OER catalyst composed of IrO 2 with Ir rich surface (IrO 2 @Ir) nanoparticles supported over nano TiN coated with TiO x N y (IrO 2 @Ir/TiN). The present approach demonstrates superior OER catalysts with high activity through small, uniformly dispersed IrO 2 @Ir nanoparticles, along with high durability owing to robust catalyst support and strong catalyst‐support interaction. The synthesized IrO 2 @Ir/TiN with an Ir loading of 40 wt % exhibits a mass‐normalized OER activity of 637 Ag Ir −1 , which is 2.4 times that of the unsupported commercial benchmark IrO 2 OER electrocatalyst. The fine nanoparticles and high activity enable significant (∼60 %) reduction in the Ir metal loading required to obtain equivalent OER performance. In addition, when evaluated through an accelerated stress test using potential cycling, the catalyst exhibits outstanding durability (79 % retention) compared to that of the commercial equivalent (66 % retention). The OER activity loss was attributed to the catalyst dissolution (30 % loss) and the catalyst particle growth (70 %), with no measurable loss due to the TiN support corrosion. The development of ultra‐fine IrO 2 @Ir nanoparticles and robust ceramic catalyst support significantly improved the Ir utilization and open a new perspective for supported OER catalyst.