Valence Oscillation of Ru Active Sites for Efficient and Robust Acidic Water Oxidation.

The continuous oxidation and leachability of active sites in Ru-based catalysts hinder practical application in proton-exchange membrane water electrolyzers (PEMWE). Herein, robust inter-doped tungsten-ruthenium oxide heterostructures [(Ru-W)Ox ] fabricated by sequential rapid oxidation and metal thermomigration processes are proposed to enhance the activity and stability of acidic oxygen evolution reaction (OER). The introduction of high-valent W species induces the valence oscillation of the Ru sites during OER, facilitating the cyclic transition of the active metal oxidation states and maintaining the continuous operation of the active sites. The preferential oxidation of W species and electronic gain of Ru sites in the inter-doped heterostructure significantly stabilize RuOx on WOx substrates beyond the Pourbaix stability limit of bare RuO2 . Furthermore, the asymmetric Ru-O-W active units are generated around the heterostructure interface to adsorb the oxygen intermediates synergistically, enhancing the intrinsic OER activity. Consequently, the inter-doped (Ru-W)Ox heterostructures not only demonstrate an overpotential of 170 mV at 10 mA cm-2 and excellent stability of 300 h in acidic electrolytes but also exhibit the potential for practical applications, as evidenced by the stable operation at 0.5 A cm-2 for 300 h in PEMWE.