Asymmetric O₂–Ru–N₂ Active Sites via Coordination Engineering for Tuning Hydrogen Evolution across the Full pH Value

The asymmetric coordination engineering of single metal atom is a challenging task for single-atom catalysts (SACs) to further amplify the catalytic potential. Hence, a unique asymmetric O2–Ru–N2 active site is meticulously engineered through the pyrolysis of an organic complex with 1,10-phenanthroline-2,9-dicarboxylic acid and Ru metal ions. The coordination evolution of the Ru atom is examined as a function of annealing temperature, evolving from the asymmetric O2–Ru–N2 configuration to the asymmetric O2–Ru–Ru and finally to the Ru–Ru structure. The electrocatalytic hydrogen evolution performance makes it clear that the SACs with asymmetric O2–Ru–N2 active sites outperform intermediate O2–Ru–Ru, Ru nanosheets, and even commercial Pt/C catalysts across the full pH value. The optimal HER performance is attributed to the formation of asymmetric O2–Ru–N2 active sites, which exhibit the lowest ΔGH* owing to the unique structure of Ru coordinated with double heterononmetallic atoms, which is confirmed by X-ray absorption spectroscopy. This work underscores the pivotal role of coordination engineering in SACs, with particular emphasis on the significance of asymmetric single-atom catalytic centers and their potential in diverse catalytic applications.