Unveiling structural forms of Ru in WO _x -template catalysts for efficient acidic PEM water electrolysis

In acidic systems, elucidating the structural forms and mechanisms of Ru that achieve high activity and stability upon combination with oxides offers valuable insights for designing efficient and durable PEM water electrolysis catalysts. In this study, different Ru forms, including single atoms, sub-nanometric clusters, and heterostructures, were strategically introduced into a WO _x template to systematically investigate their effects on OER performance. In situ characterization techniques (ATR-SEIRAS, DEMS, and in situ Raman) combined with theoretical calculations reveal that the d-π interactions within the continuously coupled orbitals introduced by subnanometer Ru clusters accelerate electronic delocalization, thereby optimizing the interfacial water structure and hydrogen-bond network and enhancing *OH adsorption. Meanwhile, this interaction facilitates the deprotonation of intermediates, maintains a high surface coverage of *O species, and modulates the post-adsorption electronic structure, which collectively promote *O-*O coupling and the Oxide Path Mechanism (OPM) pathway, endowing the catalyst with superior activity and stability. The resulting Ru_SNCs-WO _x exhibits outstanding acidic OER performance, achieving 10 mA cm^-2 at only 171 mV overpotential and retaining excellent stability over 1000 hours. In PEM electrolyzer tests, it outperforms conventional RuO₂, sustaining 1 A cm^-2 operation for over 1000 hours.