Dominant Role of Coexisting Ruthenium Nanoclusters Over Single Atoms to Enhance Alkaline Hydrogen Evolution Reaction

Abstract Developing efficient and cost‐effective electrocatalysts to replace expensive carbon‐supported platinum nanoparticles for the alkaline hydrogen evolution reaction remains an important challenge. Recently, an innovative catalyst, composed of ruthenium single atoms (Ru 1 ) integrated with small Ru nanoclusters (Ru NC ), has attracted considerable attention from the scientific community. However, because of its complexity, this catalyst remains a topic of some debate. Here, a method is reported of precisely controlling the ratios of Ru 1 to Ru NC on a nitrogenated carbon (NC)‐based porous organic framework to produce Ru/NC catalysts, by using different amounts (0, 5, 10 wt.%) of reducing agent. The Ru/NC–10 catalyst, formed with 10 wt.% reducing agent, delivered the best performance under alkaline conditions, indicating that Ru NC played a significant role in actual alkaline hydrogen evolution reaction (HER). An anion exchange membrane water electrolyzer (AEMWE) system using the Ru/NC–10 catalyst required a significantly lower operating voltage (1.72 V) than the commercial Pt/C catalyst (1.95 V) to achieve 500 mA cm −2 . Moreover, the system can be operated at 100 mA cm −2 without notable performance decay for over 180 h. Theoretical calculations supported these experimental findings that Ru 1 contributed to the water dissociation process, while Ru NC is more actively associated with the hydrogen recombination process.