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

Abstract 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 5 s /5 p 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 .