Reactivity and Stability of Reduced Ir-Weight TiO₂-Supported Oxygen Evolution Catalysts for Proton Exchange Membrane (PEM) Water Electrolyzer Anodes

Reducing the iridium demand in Proton Exchange Membrane Water Electrolyzers (PEM WE) is a critical priority for the green hydrogen industry. This study reports the discovery of a TiO₂-supported Ir@IrO(OH)_<i>x</i> core-shell nanoparticle catalyst with reduced Ir content, which exhibits superior catalytic performance for the electrochemical oxygen evolution reaction (OER) compared to a commercial reference. The TiO₂-supported Ir@IrO(OH)_<i>x</i> core-shell nanoparticle configuration significantly enhances the OER Ir mass activity from 8 to approximately 150 A g_Ir^-1 at 1.53 V_RHE while reducing the iridium packing density from 1.6 to below 0.77 g_Ir cm^-3. These advancements allow for viable anode layer thicknesses with lower Ir loading, reducing iridium utilization at 70% LHV from 0.42 to 0.075 g_Ir kW^-1 compared to commercial IrO₂/TiO₂. The identification of the Ir@IrO(OH)_<i>x</i>/TiO₂ OER catalyst resulted from extensive HAADF-EDX microscopic analysis, operando XAS, and online ICP-MS analysis of 30-80 wt % Ir/TiO₂ materials. These analyses established correlations among Ir weight loading, electrode electrical conductivity, electrochemical stability, and Ir mass-based OER activity. The activated Ir@IrO(OH)_<i>x</i>/TiO₂ catalyst-support system demonstrated an exceptionally stable morphology of supported core-shell particles, suggesting strong catalyst-support interactions (CSIs) between nanoparticles and crystalline oxide facets. Operando XAS analysis revealed the reversible evolution of significantly contracted Ir-O bond motifs with enhanced covalent character, conducive to the formation of catalytically active electrophilic O^I- ligand species. These findings indicate that atomic Ir surface dissolution generates Ir lattice vacancies, facilitating the emergence of electrophilic O^I- species under OER conditions, while CSIs promote the reversible contraction of Ir-O distances, reforming electrophilic O^I- and enhancing both catalytic activity and stability.