Hydroxylation Strategy Enables Ru–Mn Oxide for Stable Proton Exchange Membrane Water Electrolysis under 1 A cm–2

Ruthenium (Ru)-based catalysts have demonstrated promising utilization potentiality to replace the much expensive iridium (Ir)-based ones for proton exchange membrane water electrolysis (PEMWE) due to their high electrochemical activity and low cost. However, the susceptibility of RuO2-based materials to easily be oxidized to high-valent and soluble Ru species during the oxygen evolution reaction (OER) in acid media hinders the practical application, especially under current density above 500 mA cm–2. Here, a manganese-doped RuO2 catalyst with the hydroxylated metal sites (i.e., H–Mn0.1Ru0.9O2) is synthesized for acidic OER assisted by hydrogen peroxide, where the hydroxylation results in the valence state of the Ru sites below +4. The H–Mn0.1Ru0.9O2 catalyst demonstrates an overpotential of 169 mV at 10 mA cm–2 and promising stability for an OER over 1000 h in an acidic electrolyte. A PEMWE device fabricated with the H–Mn0.1Ru0.9O2 catalyst as the anode shows a current density of 1 A cm–2 at ∼1.65 V, along with a low degradation over continuous tens of hours. Differential electrochemical mass spectrometry (DEMS) results and theoretical calculations confirm that H–Mn0.1Ru0.9O2 performs the OER through the adsorbate evolution mechanism (AEM) pathway, where the synergistic effect of hydroxylation and Mn doping in RuO2 can effectively enhance the stability of Ru sites and lattice oxygen atoms.