Cluster-Scale MoOx-IrO2 Heterointerfaces Steer Dual-Site Coupling and Interfacial Water Dynamics for Fast and Durable Oxygen Evolution.

Proton exchange membrane water electrolyzers (PEMWEs) are central to renewable-powered green hydrogen production. As the benchmark electrocatalyst for the oxygen evolution reaction (OER), conventional single-phase IrO2 is constrained by linear scaling relations among oxygenated intermediates, compounded by severe mass-transport limitations and poorly regulated interfacial water structures. Here, we design a Turing-type MoOx-IrO2 heterostructure with strongly coupled cluster-scale interfaces, which enables dual-function Ir-Mo synergy that breaks fundamental kinetic limitations and optimizes interfacial water structures. At the reaction pathway level, Brønsted-acidic MoOx clusters promote water dissociation to generate reactive Mo─OH* intermediates, triggering radical coupling with adjacent Ir─O* species to form OOH* and thus circumventing the linear scaling relation. At the interfacial microenvironment level, MoOx reorganizes the rigid hydrogen-bonding networks and increases the population of free H2O species, effectively alleviating concentration overpotentials under high-current-density operation. When integrated into a practical 25 cm2 membrane electrode assembly, this catalyst delivers a PEMWE cell voltage of 1.71 V at 3 A cm-2 and an ultralow degradation rate of ∼9.5 µV h-1 over 1000 h, with a total platinum-group-metal loading of merely 0.5 mg cm-2 across both electrodes. Our dual-modulation strategy establishes a transformative paradigm for developing low-iridium and durable OER electrocatalysts toward practical green hydrogen production.