Enhancing the hydrogen evolution activity of MoS2 basal planes and edges using tunable carbon-based supports

Abstract

The hydrogen adsorption free energy (ΔG_Hads) on the basal plane and edges of MoS₂ is studied using periodic density functional theory, with the catalyst supported by a range of two-dimensional carbon-based materials. Understanding how ΔG_Hads can be tuned with support gives insight into MoS₂ 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 MoS₂, a wide range of values for ΔG_Hads are observed (between 1.4 and 2.2 eV) depending on the support material used. It is found that ΔG_Hads relates directly to the energy of occupied p-orbital states in the MoS₂ catalyst, which is modified by the support material. On the Mo-edge of MoS₂, different supports induce smaller variations in ΔG_Hads, with values ranging between −0.27 and 0.09 eV. However, a graphene support doped with graphitic N atoms produces a ΔG_Hads value of exactly 0 eV, which is thermodynamically ideal for hydrogen evolution. Furthermore, ΔG_Hads is found to relate closely and linearly to the amount of charge transfer between MoS₂ and support when they adhere together. The support-induced tuning of ΔG_Hads on MoS₂ observed here provides a useful tool for improving current MoS₂ catalysts, and the discovery of variables which mediate changes in ΔG_Hads contributes to the rational design of new hydrogen evolution catalysts.