The Origin of MoS₂ Significantly Influences Its Performance for the Hydrogen Evolution Reaction due to Differences in Phase Purity

Molybdenum disulfide (MoS₂) 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 MoS₂. Here we test the electrochemical performance of MoS₂ obtained from seven sources and we show that these sources provide MoS₂ of various phase purity (2H and 3R, and their mixtures) and composition, which is responsible for their different electrochemical properties. The overpoten-tials for HER at -10 mAcm(-2) for MoS₂ 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-MoS₂, the use of the top-down approach would usually involve the application of commercially available MoS₂. These commercially available MoS₂ are rarely characterized for composition and phase purity. These key parameters are responsible for large variance of reported catalytic properties of MoS₂.