Enhancing the hydrogen evolution activity of MoS basal planes and edges using tunable carbon-based supports.

The hydrogen adsorption free energy (ΔG) on the basal plane and edges of MoS is studied using periodic density functional theory, with the catalyst supported by a range of two-dimensional carbon-based materials. Understanding how ΔG can be tuned with support gives insight into MoS as a catalyst for the hydrogen evolution reaction. The supports studied here include graphene oxide materials, heteroatom doped (S, B, and N) graphene, and some insulator materials (hexagonal boron nitride and graphitic carbon nitride). For the basal plane of MoS, a wide range of values for ΔG are observed (between 1.4 and 2.2 eV) depending on the support material used. It is found that ΔG relates directly to the energy of occupied p-orbital states in the MoS catalyst, which is modified by the support material. On the Mo-edge of MoS, different supports induce smaller variations in ΔG, with values ranging between -0.27 and 0.09 eV. However, a graphene support doped with graphitic N atoms produces a ΔG value of exactly 0 eV, which is thermodynamically ideal for hydrogen evolution. Furthermore, ΔG is found to relate closely and linearly to the amount of charge transfer between MoS and support when they adhere together. The support-induced tuning of ΔG on MoS observed here provides a useful tool for improving current MoS catalysts, and the discovery of variables which mediate changes in ΔG contributes to the rational design of new hydrogen evolution catalysts.