Formation of Core‐Shell Ir@TiO₂ Nanoparticles through Hydrogen Treatment as Acidic Oxygen Evolution Reaction Catalysts

Abstract The transition to a sustainable energy economy requires the availability of renewably produced hydrogen through proton exchange membrane water electrolysis. The techno‐economic viability of this technology requires addressing materials challenges regarding the lack of active and stable catalysts for the electrochemical oxygen evolution reaction (OER) in acidic conditions. Herein, core‐shell iridium/titanium dioxide (Core‐shell Ir@TiO₂) catalysts for acidic OER are synthesized through a polyol method to create TiO₂ nanoparticles, followed by urea reduction with Ir, and subsequent annealing in hydrogen. The formation process of the core‐shell structure is observed through in situ environmental transmission electron microscopy under annealing conditions. Ir segregation occurred from an initially blended mixed metal oxide structure to a core‐shell configuration at 500 °C. Core‐shell Ir@TiO₂ showed a three‐fold higher stability number (i.e., S‐number) than commercial IrO_x (3.34 × 10⁶ versus 1.02 × 10⁶). Furthermore, an Ir‐mass normalized activity of 1,880 A g_Ir⁻¹ at 1.7 V versus RHE is measured for Core‐shell Ir@TiO₂, compared to 624 A g_Ir⁻¹ for commercial IrO_x. The developed synthetic route to prepare a composite structure with a TiO₂ core and Ir‐based shell has enabled an Ir content reduction without a compromise in activity and stability, thus offering a promising avenue for developing next‐generation catalysts tailored for acidic water electrolysis.