pH-Dependent Behavior of Ru-Based Hydrogen-Oxidation Electrocatalysis by a Reconstructed Hydrogen-Bond Network

Hydrogen oxidation reaction (HOR) exhibits a pH dependent behavior that the kinetics in acidic media are two to three orders of magnitude compared to that in alkaline media. Herein, to address the kinetic limitation on alkaline HOR, a series of Ru-based catalysts are constructed via introducing rare-earth oxides. The constructed Ru-SmO_x/C catalyst exhibits reversed pH-dependent HOR behavior, achieving superior performance in alkaline media compared to acidic media. Notably, the introduction of strongly oxophilic SmO_x can substantially increase the active sites for adsorbing OH species, alleviating the competitive behaviors and ensuring the synergistic interaction among diverse intermediates. Furthermore, the abundant strongly bonded surface OH species interact intensely with K⁺, releasing more free water molecules into the gap region and restructuring interfacial hydrogen-bond network, as confirmed by in situ surface-enhanced infrared absorption spectroscopy. Consequently, these synergistic effects promote proton-coupled electron transfer (PCET) at the electrode-electrolyte interface, thereby markedly accelerating the alkaline HOR kinetics and even resulting in the reversed pH effect. This work elucidates the pivotal roles of oxophilic promoters in synergistically modulating intermediate behavior and interfacial microenvironment, especially, in restructuring the hydrogen-bond network, which provides strategies for designing high-performance Ru-based HOR electrocatalysts and fundamental insights into pH-dependent electrocatalytic reactions.