Confinement-Engineered Ir-IrO2 Interfaces Activate Hydrogen-Bond-Mediated Oxide Pathway Mechanism for Durable Acidic Water Oxidation.

Achieving durable acidic oxygen evolution at low iridium loadings remains the bottleneck for proton exchange membrane water electrolysis (PEMWE). Conventional Ir catalysts are limited by adsorbate evolution mechanism scaling and lattice-oxygen-induced degradation, while the oxide pathway mechanism (OPM) has remained inaccessible due to the instability of sub-2.9 Å Ir─Ir dual sites under high anodic potentials. Here, we report a confinement-engineered strategy that localizes Ir precursors within the nanochannels and interlayer galleries of a layered covalent organic framework, yielding ultrathin twinned Ir-IrO2 interfaces with a contracted 2.68 Å Ir─Ir dual-site geometry. Operando spectroscopic analyses establish that these interfaces activate the oxide pathway during OER. Kinetic analysis reveals a hydrogen-bond-mediated OPM (HB-OPM), in which hydrogen bonding between surface intermediates (*OH···*OH/*O···HO*) and electric-field-induced reorganization of interfacial water cooperatively lowers the O─O coupling barrier and suppresses Ir over-oxidation. This catalyst achieves low‑iridium (0.28 mgIr  cm-2) PEMWE performance with high activity (2 A cm-2 at 1.71 V) and exceptional durability, operating for over 5500 h at 1 A cm-2 with a decay rate of 3.5 mV kh-1. These results demonstrate that confinement-engineered Ir-IrO2 interfaces provide an effective strategy for activating OPM and support HB-OPM as a key mechanism for designing durable, low-Ir acidic OER catalysts.