Size-selected molybdenum sulfide (MoSx) nanoclusters obtained by magnetron sputtering and gas condensation on glassy carbon substrates are typically sulfur-deficient (x = 1.6 ± 0.1), which limits their crystallinity and electrocatalytic properties. Here we demonstrate that a sulfur-enriching method, comprising sulfur evaporation and cluster annealing under vacuum conditions, significantly enhances their activity towards the hydrogen evolution reaction (HER). The S-richness (x = 4.9 ± 0.1) and extended crystalline order obtained in the sulfur-treated MoSx nanoclusters lead to consistent 200 mV shifts to lower HER onset potentials, along with two-fold and more-than 30-fold increases in turnover frequency and exchange current density values respectively. The high mass activities (~111 mA mg-1 @ 400 mV) obtained at ultra-low loadings (~100 ng cm-2, 5 % surface coverage) are comparable to the best reported MoS2 catalysts in the literature.
Bibliographical noteCreative Commons Attribution 4.0 International (CC BY 4.0)
Funding: EPSRC for support through funding for the Centre for Doctoral Training in Fuel Cells and their fuels (D.E.L., N.V.R., EP/G037116/1) and a fellowship grant (R.E.P., EP/L015749/1 and EP/K006061/2) and the European Commission for the Marie-Curie ITN project “Catsense” (Y.N.)
- molybdenum disulfide
- hydrogen evolution
- magnetron sputtering deposition