In Situ Defect Engineering of Atomically Dispersed Iridium on Mesoporous Mixed Oxide Frameworks for Robust PEM Water Electrolysis

ABSTRACT Reconciling exceptional catalytic activity with operational durability at ultralow noble‐metal loadings remains a central challenge for proton exchange membrane water electrolysis. Herein, an in situ acid‐etching‐assisted defect engineering strategy is reported for constructing an ultrahigh‐loading electrocatalyst (Ir@CM4) that predominantly features atomically dispersed iridium anchored on hierarchical mesoporous CeMn oxides. Directional Mn dissolution generates a dense oxygen vacancy network that traps Ir species, inducing a profound strong metal‐support interaction to establish a highly electron‐deficient, rigid Ir‐O‐Ce covalent framework. Consequently, Ir@CM4 delivers an exceptional mass activity of 948.15 A g −1 at 1.53 V versus RHE (31‐fold higher than commercial Ir Black). In a PEMWE full cell with an ultralow loading of 0.28 mg Ir cm −2 , it sustains robust operation for 6350 h at an industrial‐relevant 1 A cm −2 . Multimodal in situ tracking confirms that this covalent rigidity thermodynamically locks lattice oxygen, bypassing degradation‐prone pathways to strictly enforce the highly stable adsorbate evolution mechanism. Density functional theory uncovers the quantum‐mechanical origin: strong metal‐support interaction‐induced charge transfer downshifts the Ir d‐band center to ‐3.93 eV, which circumvents traditional scaling relations by weakening antibonding orbital filling. This multiscale structural and electronic synergy effectively decouples the activity‐stability trade‐off, providing a translatable paradigm for industrial‐grade acidic water electrolysis.