Low loading of lrO₂/TiO₂ enabled by Pd promoter in acidic water electrolysis

Reducing iridium (Ir) loading in proton exchange membrane water electrolyzers (PEMWEs) while maintaining high catalytic performance remains a critical challenge. Herein, we develop a palladium (Pd) doped IrO₂/TiO₂ catalyst with a high mass activity of 750.4 A·g_Ir⁻¹ at 1.53 V during acidic oxygen evolution reaction (OER). When integrated into a PEMWE as anode catalyst, it delivers a high current density of 3.6 A·cm⁻² at 1.9 V even with Ir loading as low as 0.35 mg_Ir·cm⁻², which surpasses the DOE 2025 target (3 A·cm⁻²@1.9 V). Systematic characterizations reveal that Pd doping induces a low Ir coordination environment, leading to the formation of abundant Ir(III) species and providing more active sites. It promotes the OER kinetics by weakening the adsorption behavior of *OH intermediate, which is further confirmed by the downshift of Ir d-band center through First-principles calculations. The reduced Ir–O bonds interaction facilitates the adsorbate evolution mechanism (AEM) pathway, with a much lower kinetics energy barrier compared to the undoped one, thereby balancing good activity and stability during the OER process. This work offers a strategy for designing low-Ir electrocatalysts for high-performance PEMWEs.