In Situ Construction of IrOx Nanofilm on TiOx for Boosting Low-Ir Catalysis in Practical PEM Electrolyze

Exploring low-iridium (Ir) electrocatalysts for oxygen evolution reaction (OER) is exigent to promote the commercialization of proton electrolyte membrane water electrolyzers (PEMWEs). Herein, the study presents a scalable and facile strategy to in situ construct an IrO_x nanofilm continuously coated on TiO_x support as efficient and durable OER catalyst through one-step annealing of Ir-salt-adsorbed titanium-based metal–organic frameworks (MOFs) precursor. The unique nanofilm structure forms a continuous p-n junction interface, endowing a strong interfacial electron transfer from TiO_x to IrO_x and also ensuring a well-connected conductive network in the anodic catalytic layer due to the continuous dispersion of IrO_x. The optimal catalyst requires a low overpotential of 233 mV at 10 mA cm⁻² with a 40-fold of com. IrO₂ in mass activity. The assembled PEMWE shows a cell voltage of 1.762 V at 1 A cm⁻² with ≈220 h durable operation under start/shut-down operation. Operando characterizations and theoretical calculation reveal that the p-n junction not only reduces the energy barrier of water dissociation and deprotonation step of *OOH boosting OER kinetics but also prevents oxidation of Ir sites to form soluble Ir species that improves durability. This work offers a new avenue to rationally design and synthesize efficient low-Ir OER catalyst for PEMWE application.