Composite of Few-Layered MoS2 Grown on Carbon Black: Tuning the Ratio of Terminal to Total Sulfur in MoS2 for Hydrogen Evolution Reaction

The terminal disulfide and sulfide (S-2(2-) and S2-) groups at the edge of layered MoS2 are believed to be highly active toward electrochemical hydrogen evolution reaction (HER). In this work, we prepared a composite of few-layered MoS2 grown on the surface of carbon black (CB). We demonstrated that the ratio of terminal S-2(2-) and S2- groups in the obtained MoS2/CB composite depended significantly on the content of CB, which suggests that the activity of the composite toward HER can be tuned by controlling the CB content. The current density on the MoS2/CB catalyst for HER was closely related to the average number of MoS2 layers and the ratio of terminal to total sulfur in the composite, with the former, dominating the conductivity of the MoS2 layers and the latter determining the density of active sites for HER. The highest activity and excellent stability were obtained on a MoS2/CB composite with an average of five MoS2 layers and a ratio of terminal to total sulfur of ca. 6.5%. This composite exhibited a current density of 80 mA.cm(-2) at -0.225 V vs RHE with a loading of 1.0 mg.cm(-2), which is as high as the value reported cm the highly active MoS2/graphene catalysts at the same loading. Considering the low cost of commercially available CB and the ease of preparation of the MoS2/CB composite, our MoS2/CB catalyst is highly competitive compared to other MoS2-based catalysts.