In Situ Construction of IrO _x Nanofilm on TiO _x for Boosting Low‐Ir Catalysis in Practical PEM Electrolyze

Abstract 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. IrO 2 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.