The limited durability of Ru-based electrocatalysts for the acidic oxygen evolution reaction (OER) remains a significant challenge for their application in water electrolyzers. This instability arises from a coupled failure mode in which lattice-oxygen participation promotes oxygen-vacancy formation, Ru over-oxidation, soluble ruthenate species, and structural collapse. Herein, we use high-valent 5d transition-metal dopants as a compact platform to tune Ru-O covalency and Ru redox stability, taking advantage of their spatially extended d orbitals, large ionic radii, and accessible high oxidation states. Comparative studies of Ta-, W-, Re-, and Os-doped RuO2 suggest that different 5d dopants emphasize different stabilization roles: Ta is associated with attenuated lattice-oxygen reactivity, W underscores suboptimal Ru−O covalency, Os highlights the importance of redox buffering, and Re provides the most balanced combination of lattice-oxygen stabilization and Ru-valence regulation in our material series. Operando differential electrochemical mass spectroscopy, X-ray spectroscopy, electrochemical analysis, and theoretical calculations show that Re expands the RuO2 lattice, weakens Ru-O covalency, suppresses latticeoxygen participation, and dynamically regulates Ru valence under OER conditions. Re-RuO2 consequently achieves an overpotential of 138 mV at 10 mA cm-2, stable operation for >700 h at 200 mA cm-2 with reduced Ru dissolution, and >300 h operation in a PEMWE device at 1 A cm-2 with a negligible degradation rate of 69 μV h-1. These results establish a 5d-dopant design principle for RuO2: durable acidic OER requires simultaneous control of lattice oxygen and Ru overoxidation.
