Nanostructuring and metal−support interactions have been explored as effective methods to improve the electrocatalytic activity in heterogeneous catalysis. In this study, we have fabricated ultrasmall Ru nanoparticles (NPs) dispersed on S-doped graphene (denoted as Ru/S-rGO) by a facile "one-pot" procedure. The experimental results indicated that both the S doping and moderate degree of oxidization of GO can induce the formation and high dispersion of the ultrasmall Ru NPs with larger electrochemically active surface areas for exposing more active sites. Metal−support interaction between S-doped graphene and Ru NPs was observed from the X-ray photoelectron spectroscopy and electronic charge-difference studies. It resulted in the decrease in the electron density of Ru, which facilitated electron release from H 2 O and H−OH bond breakage. The results of density functional theory calculation confirmed that the S-dopants could reduce the energy barrier for breaking the H−OH bond to accelerate water dissociation during the alkaline hydrogen evolution reaction (HER). At a current density 20 mA cm −2 , the lowest overpotential of 14 mV, superior to that of Pt/C in alkaline solution, was observed for Ru/S-rGO-24. The observed lowest value of overpotential was because of the ultrasmall size, high dispersion, and metal−support interaction. This work provides a simple and effective method in designing advanced electrocatalysts for the HER in an alkaline electrolyte.

Engineering nanocomposites with interfaces was already found to be an efficient method for designing water-splitting catalysts. In this study, a rationally designed 3D Ru/RuO 2 @N-rGO hierarchical porous heterocatalyst containing abundant interfaces was obtained via a hydrothermal-calcining strategy for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). In the synthesis process, polypyrrole helped the self-assembled GO to form a hybrid aerogel network, in situ reducing the Ru salt as reductant and doping graphene as N precursor. CO 2 , which was in situ produced via the reaction between Na 2 SO 4 and C, could partially or totally oxidize metal Ru to regulate the composition of Ru/RuO 2 nanoparticles. Benefiting from the large surface area and a high number of bifunctional active sites coupled interfaces, the as-obtained Ru/RuO 2 @N-rGO heterostructure catalyst revealed high HER/ OER activities in 1.0 M KOH and 0.5 M H 2 SO 4 solutions, respectively. The present work could provide a way to engineer Ru/RuO 2 nanoparticles in 3D electrocatalysts to boost HER/OER performances.