Harnessing Direct Oxo Coupling for Durable Water Oxidation via Atomic‐Level Strain Engineering

ABSTRACT Iridium oxides are the state‐of‐the‐art oxygen evolution reaction (OER) catalysts in proton exchange membrane water electrolysis (PEMWE). However, its activity is still hampered by the high thermodynamic barrier of *OOH intermediates in the conventional adsorbate evolution mechanism (AEM). To resolve this challenge, we present an atomic‐level compressive strain‐engineering strategy to modulate reaction pathways by incorporating erbium (Er ^{3 +} ) into the IrO ₂ (Er‐IrO _x ) framework. The large ionic radius of Er ^{3 +} shortens the Ir–Ir distance and optimizes the electronic structure of active sites. This strain‐induced reconfiguration shifts the OER pathway from AEM to the direct oxo coupling mechanism (OPM), where O─O formation occurs through radical coupling, bypassing the high‐energy *OOH intermediate. The resulting Er‐IrO _x catalyst reaches a small Tafel slope of 70.55 mV dec ^{− 1} and a remarkably low overpotential of 209 mV at 10 mA cm ⁻² . More importantly, when configured into a practical PEMWE, it delivers a high current density of 6 A cm ⁻² at a low voltage of 1.899 V and maintains durable operation for over 400 h. This work offers a generalized approach for breaking activity‐stability trade‐offs in Ir‐based catalysts, promoting the commercial implementation of green hydrogen production.