Sulfur‐Doped IrO2 Enable Pathway Switch to Lattice Oxygen Mechanism with Enhanced Stability for Low Iridium PEM Water Electrolysis

Abstract Achieving high activity and stability while minimizing Ir usage poses a significant challenge in the industrialization of proton exchange membrane water electrolysis (PEMWE). Herein we report a sulfur‐doping strategy that enables the OER pathway on IrO 2 nanoparticles (IrO 2 /S) to switch from conventional adsorption evolution mechanism (AEM) to lattice oxygen mechanism (LOM) while maintaining Ir─O bond stability, thus achieving a significant enhancement in both intrinsic activity and durability. Advanced spectroscopies and theoretical calculations reveal that the Ir─S coordination motif within the lattice increases the electron density of the Ir center and enhances Ir─O covalency, thus triggering the LOM pathway. Importantly, the lattice distortion and unsaturated Ir─O coordination within the IrO 2 /S generate the oxygen nonbonding state that acts as an electron sacrificial agent to preserve Ir─O bonds upon the LOM‐dominated OER process. As a result, PEMWE integrated with such IrO 2 /S electrocatalyst delivers a low cell voltage (1.769 V at 2.0 A cm −2 ) and long‐term stability (16.6 µV h⁻¹ over 1000 h@1.0 A cm⁻ 2 ) while dramatically reducing Ir usage from 1.0 to 0.3 mg cm −2 . This work establishes S doping as a viable strategy to trigger LOM and stabilize lattice oxygen redox in Ir‐based catalysts, opening a new avenue for low‐Ir PEMWEs.