▎ 摘　　要

Since hydrogen is a clean and renewable energy source, the design of efficient and new catalysts for hydrogen evolution reaction (HER) has attracted significant attention. Ultrafine (similar to 2 nm) monodispersed Ru nanocrystals on N-doped graphene (Ru@NG) show Pt-like catalytic activity towards HER in both alkaline and acidic media with zero onset potential and better current density as compared to Pt/C. The HER performance strongly depends on the nanosize effect of Ru nanocrystals and their dispersion on NG. Transfer of electrons from Ru to carbon results in an electron-deficient metal centre and greatly enhances the HER activity. This new 4-d transition metal electrocatalyst has the potential to serve as an alternative to the Pt benchmark catalyst, which is more costly than Ru.