Ensemble Effect of Ruthenium Single-Atom and Nanoparticle Catalysts for Efficient Hydrogen Evolution in Neutral Media.

Hydrogen evolution reaction (HER) plays a key role in electrochemical water splitting, which is a sustainable way for hydrogen production. The kinetics of HER is sluggish in neutral media that requires noble metal catalysts to alleviate energy consumption during the HER process. Here, we present a catalyst comprising a ruthenium single atom (Ru 1 ) and nanoparticle (Ru n ) loaded on the nitrogen-doped carbon substrate (Ru 1 -Ru n /CN), which exhibits excellent activity and superior durability for neutral HER. Benefiting from the synergistic effect between single atoms and nanoparticles in the Ru 1 -Ru n /CN, the catalyst exhibits a very low overpotential down to 32 mV at a current density of 10 mA cm -2 while maintaining excellent stability up to 700 h at a current density of 20 mA cm -2 during the long-term test. Computational calculations reveal that, in the Ru 1 -Ru n /CN catalyst, the existence of Ru nanoparticles affects the interactions between Ru single-atom sites and reactants and thus improves the catalytic activity of HER. This work highlights the ensemble effect of electrocatalysts for HER and could shed light on the rational design of efficient catalysts for other multistep electrochemical reactions.