Stabilizing Highly Active Ru Sites by Electron Reservoir in Acidic Oxygen Evolution.

Proton exchange membrane water electrolysis is hindered by the sluggish kinetics of the anodic oxygen evolution reaction. RuO 2 is regarded as a promising alternative to IrO 2 for the anode catalyst of proton exchange membrane water electrolyzers due to its superior activity and relatively lower cost compared to IrO 2 . However, the dissolution of Ru induced by its overoxidation under acidic oxygen evolution reaction (OER) conditions greatly hinders its durability. Herein, we developed a strategy for stabilizing RuO 2 in acidic OER by the incorporation of high-valence metals with suitable ionic electronegativity. A molten salt method was employed to synthesize a series of high-valence metal-substituted RuO 2 with large specific surface areas. The experimental results revealed that a high content of surface Ru 4+ species promoted the OER intrinsic activity of high-valence doped RuO 2 . It was found that there was a linear relationship between the ratio of surface Ru 4+ /Ru 3+ species and the ionic electronegativity of the dopant metals. By regulating the ratio of surface Ru 4+ /Ru 3+ species, incorporating Re, with the highest ionic electronegativity, endowed Re 0.1 Ru 0.9 O 2 with exceptional OER activity, exhibiting a low overpotential of 199 mV to reach 10 mA cm -2 . More importantly, Re 0.1 Ru 0.9 O 2 demonstrated outstanding stability at both 10 mA cm -2 (over 300 h) and 100 mA cm -2 (over 25 h). The characterization of post-stability Re 0.1 Ru 0.9 O 2 revealed that Re promoted electron transfer to Ru, serving as an electron reservoir to mitigate excessive oxidation of Ru sites during the OER process and thus enhancing OER stability. We conclude that Re, with the highest ionic electronegativity, attracted a mass of electrons from Ru in the pre-catalyst and replenished electrons to Ru under the operating potential. This work spotlights an effective strategy for stabilizing cost-effective Ru-based catalysts for acidic OER.