Ligand-Capped Ru Nanoparticles as Efficient Electrocatalyst for the Hydrogen Evolution Reaction

Multielectron reductions such as the hydrogen evolution reaction (HER) play an important role in the development of nowadays energy economy. Herein, the application of the organometallic approach as synthetic method allows obtaining very small, ligand-capped but also highly active ruthenium nanoparticles (RuNPs) for the HER in both acidic and basic media. When deposited onto glassy carbon, the catalytic activity of this nanomaterial in 1 M H2SO4 solution is highly dependent on the oxidation state of the NPs surface, with metallic Ru sites being clearly more active than RuO2 ones. In sharp contrast, in 1 M NaOH as electrolyte, the original Ru/RuO2 mixture is maintained even under reductive conditions. Estimation of surface active sites and electrochemically active surface area (ECSA) allowed benchmarking this catalytic system, confirming its leading performance among HER electrocatalysts reported at both acidic and basic pH. Thus, in 1 M NaOH condition, it displays lower overpotentials (η0 ≈ 0 mV, η10 = 25 mV) than those of commercial Pt/C and Ruthenium black (Rub), and also fairly outperforms them in short- and long-term stability tests. In 1 M H2SO4 solution, it clearly outdoes commercial Rub and is competitive or even superior to commercial Pt/C, working at very low overpotentials (η0 ≈ 0 mV, η10 = 20 mV) with a Tafel slope of 29 mV·dec–1, achieving TOFs as high as 17 s–1 at η = 100 mV and reaching a current density of |j| = 10 mA·cm–2 for at least 12 h without any sign of deactivation.