Liquid Exfoliation and Electrochemical Properties of WS₂ Nanosheets.

Commercial WS2 powders were exfoliated in sodium dodecyl sulfate solution with a combination of ball-milling and sonication. WS2 nanosheets can be uniformly dispersed in the solution. The layers and thicknesses of WS2 nanosheets could be tailored via changing the ball-milling speed. The effects of the ball-milling speed on crystallinity and morphology of the samples were analyzed. The results show that the layer structure of WS2 nanosheets is destroyed and the crystallinity is decreased with increase of the ball-milling rate. The monolayer WS2 nanosheets at 200 rpm are obtained, which are mesoporous with the specific surface area as 5.419 m2 g-1. The specific capacitance and charge/discharge efficiency of WS2 nanosheets at 200 rpm are better than those of other samples. Its specific capacitance under the scanning rate of 20 mV s-1 and the current density of 0.5 A g-1 are 13.46 F g-1 and 22.50 F g-1, respectively. The charge/discharge curve of WS2 nanosheets at 200 rpm is a symmetrical triangle, which shows rapid charge and slow discharge. It means that WS2 nanosheets at 200 rpm has good electrochemical reversibility. The load transfer resistance and the internal series resistance of this sample are 84.60 Ω and 4.18 Ω, respectively.