Sulfur-Rich MoS6 as an Electrocatalyst for the Hydrogen Evolution Reaction

In this work, we studied a sulfur-rich molybdenum sulfide (MoS6) hydrogen evolution reaction (HER) catalyst prepared by chemical oxidation of thiodimolybdate (Mo2S122–). Using X-ray photoelectron spectroscopy, X-ray diffraction, and other techniques, we found that the material had an overall S:Mo ratio of 6:1 and is likely an amorphous coordination polymer of molybdenum–sulfur (Mo3-like) clusters with the additional sulfur existing as bridging or terminal disulfide moieties. Used as a HER catalyst, MoS6 has an HER overpotential of 130 mV at 10 mA/cm2, compared to 178 mV for MoS4 samples made from tetrathiomolybdate (MoS42–). Electrochemical surface area measurements show that the improved performance of MoS6 over MoS4 was not due to the sulfur-rich material having a higher surface area. Instead, we ascribe the performance of the sulfur-rich MoS6 catalyst to the presence of additional disulfide active sites compared to other amorphous MoSx catalysts. This study highlights the possibility of using different...