Cr dopant mediates hydroxyl spillover on RuO₂ for high-efficiency proton exchange membrane electrolysis

Simultaneously improving the activity and stability of catalysts for anodic oxygen evolution reaction (OER) in proton exchange membrane water electrolysis (PEMWE) remains a notable challenge. Here, we report a chromium-doped ruthenium dioxide with oxygen vacancies, termed Cr_0.2Ru_0.8O_2-x, that drives OER with an overpotential of 170 mV at 10 mA cm^-2 and operates stably over 2000 h in acidic media. Experimental and theoretical studies show that the synergy of Cr dopant and oxygen vacancy induces an unconventional dopant-mediated hydroxyl spillover mechanism. Such dynamic hydroxyl spillover from Cr dopant to Ru active site changes the rate-determining step from OOH* formation to O₂ formation and thus greatly improves the OER performance. Moreover, the Cr dopant and oxygen vacancy also play a crucial role in stabilizing surface Ru and lattice oxygen in the Ru-O-Cr structural motif. When assembled into the anode of a practical PEMWE device, Cr_0.2Ru_0.8O_2-x enables long-term durability of over 200 h at an ampere-level current density and 60 degrees centigrade.