Cluster‐Scale MoO x ‐IrO 2 Heterointerfaces Steer Dual‐Site Coupling and Interfacial Water Dynamics for Fast and Durable Oxygen Evolution

ABSTRACT 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 IrO 2 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 MoO x ‐IrO 2 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 MoO x 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, MoO x reorganizes the rigid hydrogen‐bonding networks and increases the population of free H 2 O species, effectively alleviating concentration overpotentials under high‐current‐density operation. When integrated into a practical 25 cm 2 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.