Engineering High‐Density Grain Boundaries in Ru_0.8Ir_0.2O_x Solid‐Solution Nanosheets for Efficient and Durable OER Electrocatalysis

Abstract The oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers (PEMWE) has long stood as a formidable challenge for green hydrogen sustainable production, hindered by sluggish kinetics, high overpotentials, and poor durability. Here, these barriers are transcended through a novel material design: strategic engineering of high‐density grain boundaries within solid‐solution Ru_0.8Ir_0.2O_x ultrathin nanosheets. These carefully tailored grain boundaries and synergistic Ir─Ru interactions, reduce the coordination of Ru atoms and optimize the distribution of charge, thereby enhancing both the catalytic activity and stability of the nanosheets, as verified by merely requiring an overpotential of 189 mV to achieve 10 mA cm⁻² in acidic electrolyte. In situ electrochemical techniques, complemented by theoretical calculations, reveal that the OER follows an adsorption evolution mechanism, demonstrating the pivotal role of grain boundary engineering and electronic modulation in accelerating reaction kinetics. Most notably, the Ru_0.8Ir_0.2O_x exhibits outstanding industrial‐scale performance in PEMWE, reaching 4.0 A cm⁻² at 2 V and maintaining stability for >1000 h at 500 mA cm⁻². This efficiency reduces hydrogen production costs to $0.88 kg⁻¹. This work marks a transformative step forward in designing efficient, durable OER catalysts, offering a promising pathway toward hydrogen production technologies and advancing the global transition to sustainable energy.