Pure and stable metallic phase molybdenum disulfide nanosheets for hydrogen evolution reaction

Metallic-phase MoS(2) (M-MoS(2)) is metastable and does not exist in nature. Pure and stable M-MoS(2) has not been previously prepared by chemical synthesis, to the best of our knowledge. Here we report a hydrothermal process for synthesizing stable two-dimensional M-MoS(2) nanosheets in water. The metal–metal Raman stretching mode at 146 cm(−1) in the M-MoS(2) structure, as predicted by theoretical calculations, is experimentally observed. The stability of the M-MoS(2) is associated with the adsorption of a monolayer of water molecules on both sides of the nanosheets, which reduce restacking and prevent aggregation in water. The obtained M-MoS(2) exhibits excellent stability in water and superior activity for the hydrogen evolution reaction, with a current density of 10 mA cm(−2) at a low potential of −175 mV and a Tafel slope of 41 mV per decade.