Engineered Tantalum–Iridium Oxide Nanoparticles via High‐Temperature Calcination for Oxygen Evolution Catalysis

ABSTRACT Sustainable hydrogen production via low‐temperature water electrolysis is key to advancing the hydrogen economy, with polymer electrolyte membrane water electrolysis (PEM‐WE) as a central technology. However, sluggish oxygen evolution reaction (OER) kinetics at the anode limit PEM‐WE efficiency. Iridium‐based catalysts remain the benchmark due to their balance of activity and stability under harsh conditions, though iridium scarcity necessitates designs with reduced Ir content. Here, we report a highly active and stable OER catalyst based on TaO x –IrO 2 nanoparticles synthesized via a reverse microemulsion method and calcined at 800°C. Encapsulation in silica nanoreactors enabled precise control over particle size and crystallinity during thermal treatment. The TaO x –IrO 2 catalyst achieves a mass activity of 619 ± 93 mA mg Ir − 1 at 1.55 V RHE , outperforming commercial IrO 2 by a factor of 2.5 and bare IrO 2 synthesized under identical conditions. While TaO x is electrochemically inactive, it shows exceptional dissolution resistance. The intrinsic stability of TaO x –IrO 2 , expressed via the S‐number, exceeds that of commercial IrO 2 and matches bare IrO 2 calcined at 600°C. These results highlight TaO x –IrO 2 as a promising OER catalyst, combining enhanced activity with notable stability, and support the development of durable, efficient catalysts for PEM‐WE.