Harmonizing Ruthenium Atom-Cluster Moieties for Stable Proton Exchange Membrane Water Electrolysis

Developing noniridium-based catalysts is highly desired yet challenging for the oxygen evolution reaction (OER) in proton exchange membrane electrolyzers and other devices. In this study, uncoordinated RuOx clusters with adjacent atomically dispersed Ru sites on the N-doped carbon support (RuSAC@RuOx/N–C) is reported for OER in acids, delivering an overpotential of 186 mV at 10 mA cmgeo–2 and steady operation for 519 h in 0.5 M H2SO4, significantly outperforming commercial RuO2 with an overpotential of 326 mV and stability less than 5 h. Physical characterizations, poison experiments, and theoretical results reveal that uncoordinated RuOx clusters act as the dominant active sites; the neighboring Ru sites effectively increase the Ru 4d–O 2p orbital hybridization in RuOx, which in turn increases the electron delocalization of the Ru sites and optimizes the binding strength with intermediates to enhance catalytic activity. Importantly, the Ru single sites efficiently suppress the thermal vibrations of the Ru–O bonds in RuOx clusters, reducing the tendency for Ru atom detachment and promoting stability performance. This work sheds light on the unique function of metal single sites as immobilizers for stabilizing metal oxides and opens pathways to design stable catalyst materials for reactions under harsh conditions.