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 (S₂^2- and S^2-) 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 S₂^2- and S^2- 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 on 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. (Graph Presented).