Lanthanide-regulating Ru-O covalency optimizes acidic oxygen evolution electrocatalysis.

Precisely modulating the Ru-O covalency in RuO x for enhanced stability in proton exchange membrane water electrolysis is highly desired. However, transition metals with d-valence electrons, which were doped into or alloyed with RuO x , are inherently susceptible to the influence of coordination environment, making it challenging to modulate the Ru-O covalency in a precise and continuous manner. Here, we first deduce that the introduction of lanthanide with gradually changing electronic configurations can continuously modulate the Ru-O covalency owing to the shielding effect of 5s/5p orbitals. Theoretical calculations confirm that the durability of Ln-RuO x following a volcanic trend as a function of Ru-O covalency. Among various Ln-RuO x , Er-RuO x is identified as the optimal catalyst and possesses a stability 35.5 times higher than that of RuO 2 . Particularly, the Er-RuO x -based device requires only 1.837 V to reach 3 A cm -2 and shows a long-term stability at 500 mA cm -2 for 100 h with a degradation rate of mere 37 μV h -1 .