Preparation of MoS2 spheres from Mo plate and elemental sulfur and the effect of sphericalization on electrochemical hydrogen evolution catalysis

The growth of MoS2 catalysts with a controlled morphology has been actively pursued to improve the electrocatalytic activity for hydrogen evolution reaction (HER) by modifying the shape of catalysts. However, it is questionable whether changes in morphological structure affect its intrinsic activity. Here we present a facile hydrothermal synthesis of amorphous MoSx spheres on Mo plates at 180 °C using elemental sulfur. Hydrolysis of elemental sulfur during the hydrothermal synthesis produces H2S and H2SO4 in hot water. Consequently, the surface of the Mo plate is sulfurized by H2S and dissolved by H2SO4 to form amorphous MoSx spheres with diameters in the range of 0.4–0.8 μm on the Mo plate. To investigate the effect of the sphericalization of crystalline MoS2 on its intrinsic activity for the HER, the amorphous MoSx spheres were annealed to form crystalline MoS2 spheres. The Tafel slopes of the amorphous MoSx (∼45 mV/dec) and crystalline MoS2 (∼103 mV/dec) spheres were similar to those of amorphous MoSx and crystalline MoS2 thin films, regardless of whether the shape of the catalyst was sphericalized or not. This reveals that the sphericalization cannot change the intrinsic activity and the HER mechanism on molybdenum sulfide.