Designing of Surface Engineering of Mesoporous Ru/RuO ₂ Heterostructure for Effective Water‐Splitting Reaction in Proton Exchange Membrane Water Electrolyzer

The development of effective proton exchange membrane water electrolyzer (PEMWE) electrocatalysts is critical for hydrogen production. Here, we synthesized a mesoporous Ru/RuO₂ heterostructure as a bifunctional electrocatalyst prepared by a surfactant-assisted approach, followed by annealing at three different temperatures. Among them, prepared catalyst treated at 600°C has the highest activity toward the bifunctional activity of overall water splitting in an acidic medium with a turnover frequency of 13.59 and 4.2 s⁻¹, and an overpotential of 230 and 88 mV, consistently operating at 10 mA cm⁻² for 280 and 120 h for OER and HER, which is considerably superior to commercial RuO₂. It is worth noting that the zero-gap PEMWE was fabricated using m-Ru/RuO₂-600 with fed water, delivering the overall current density of 0.6 A cm⁻² at 25°C and 1.0 A cm⁻² at 60°C. The integrated PEMWE was demonstrated for 300 h at 100 mA cm⁻². The enhanced performance of m-Ru/RuO₂-600 catalysts is due to the presence of both metallic Ru and RuO₂, which produce a synergistic effect, leading to a Ru⁺⁴-O-Ru⁰ interfacial structure that effectively alters the oxidation state of ruthenium, boosting kinetics, as confirmed by pre- and post-OER and HER characterizations. This study offers a unique opportunity for low-cost PEMWE.