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

Abstract

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-Mn_0.1Ru_0.9O₂) 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-Mn_0.1Ru_0.9O₂ 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-Mn_0.1Ru_0.9O₂ 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-Mn_0.1Ru_0.9O₂ 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.