Effect of pH on the growth of MoS2 (002) plane and electrocatalytic activity for HER

MoS2 with different (002) intensity have been synthesized for hydrogen evolution reaction (HER) through a facile hydrothermal method at different pH value. MoS2 obtained at pH = 2–3 exhibits the smallest intensity ratio between (002) and (100) peaks (I (002)/(100)) and the largest BET surface area, which implying the restrained growth of (002) plane and the decreasing of stacking layers of MoS2 at low pH. Because (002) plane is inert plane for HER, low pH (pH = 2–3) is more suitable for increasing the active sites of MoS2 than high pH. The results of the electrocatalytic HER confirm that MoS2 synthesized at pH = 2–3 has the smaller Tafel slope and the lower resistance than pH = 7–8 or pH = 12–13. The corresponding capacitive properties show similar results that MoS2 obtained at pH = 2–3 has the highest specific capacitance among the different pH, which identified the best dispersion and largest BET surface area of MoS2 at low pH. Therefore, pH has made important impact on the controlling growth of (002) plane and the improved active sites of MoS2.