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

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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.