Insight into the superior activity of bridging sulfur-rich amorphous molybdenum sulfide for electrochemical hydrogen evolution reaction

Hydrogen evolution reaction (HER) activity of the molybdenum sulfide-based electrocatalysts originates from diverse types of active sulfur (S) sites, different S configurations, the ratio of molybdenum to S, and the crystallinity. The bridging S-2(2-) has been considered as the major active site for HER. However, to realize more efficient electrocatalysts, newer architectures based on molybdenum sulfide are required to allow more active S sites beyond the endemic structural limits. Hence, the facile aging approach is used to maximize the bridging S-2(2-) in amorphous molybdenum sulfide by adding (NH4)(2)S-x, leading to the highest proportion of bridging S-2(2-) (up to 67%). Additionally, the effect of S configuration on HER activity in molybdenum sulfide is systematically studied by controlling of the amount of bridging S-2(2-). The bridging S-rich electrocatalysts exhibits an excellent HER activity with low onset potential of -96 mV and Tafel slope of 46 mV dec(-1), and stability for 1000 cycles.