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

In this work, we studied a sulfur-rich molybdenum sulfide (MoS 6 ) hydrogen evolution reaction (HER) catalyst prepared by chemical oxidation of thiodimolybdate (Mo 2 S 12 2– ). 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 (Mo 3 -like) clusters with the additional sulfur existing as bridging or terminal disulfide moieties. Used as a HER catalyst, MoS 6 has an HER overpotential of 130 mV at 10 mA/cm 2, compared to 178 mV for MoS 4 samples made from tetrathiomolybdate (MoS 4 2– ). Electrochemical surface area measurements show that the improved performance of MoS 6 over MoS 4 was not due to the sulfur-rich material having a higher surface area. Instead, we ascribe the performance of the sulfur-rich MoS 6 catalyst to the presence of additional disulfide active sites compared to other amorphous MoS x catalysts. This study highlights the possibility of using different thiomolybdate precursors to synthesize novel MoS x HER catalysts.