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

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 (Ru₁) 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 Ru₁ 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 Ru₁ contributed to the water dissociation process, while Ru_NC is more actively associated with the hydrogen recombination process.