The Origin of MoS Significantly Influences Its Performance for the Hydrogen Evolution Reaction due to Differences in Phase Purity.

Molybdenum disulfide (MoS ) is at the forefront of materials research. It shows great promise for electrochemical applications, especially for hydrogen evolution reaction (HER) catalysis. There is a significant discrepancy in the literature on the reported catalytic activity for HER catalysis on MoS . Here we test the electrochemical performance of MoS obtained from seven sources and we show that these sources provide MoS of various phase purity (2H and 3R, and their mixtures) and composition, which is responsible for their different electrochemical properties. The overpotentials for HER at -10 mA cm for MoS from seven different sources range from -0.59 V to -0.78 V vs. reversible hydrogen electrode (RHE). This is of very high importance as with much interest in 2D-MoS , the use of the top-down approach would usually involve the application of commercially available MoS . These commercially available MoS are rarely characterized for composition and phase purity. These key parameters are responsible for large variance of reported catalytic properties of MoS .