Supported Ruthenium Single‐Atom and Clustered Catalysts Outperform Benchmark Pt for Alkaline Hydrogen Evolution

Abstract Guaranteeing satisfactory catalytic behavior while ensuring high metal utilization has become the problem that needs to be addressed when designing noble‐metal‐based catalysts for electrochemical reactions. Here, well‐dispersed ruthenium (Ru) based clusters with adjacent Ru single atoms (SAs) on layered sodium cobalt oxide (Ru/NC) are demonstrated as a superb electrocatalyst for alkaline HER. The Ru/NC catalyst demonstrates an activity increase by a factor of two relative to the commercial Pt/C. Operando characterizations in conjunction with density functional theory (DFT) simulations uncover the origin of the superior activity and establish a structure–performance relationship, that is, under HER condition, the real active species are Ru SAs and metallic Ru clusters supported on the NC substrate. The excellent alkaline HER activity of the Ru/NC catalyst can be understood by a spatially decoupled water dissociation and hydrogen desorption mechanism, where the NC substrate accelerates the water dissociation rate, and the generated H intermediates would then migrate to the Ru SAs or clusters and recombine to have H 2 evolution. More importantly, comparing the two forms of Ru sites, it is the Ru cluster that dominates the HER activity.