How to Dope the Basal Plane of 2H-MoS2 to Boost the Hydrogen Evolution Reaction?

Molybdenum disulfide (MoS2) is considered one of the most likely materials that could be turned into low-cost hydrogen evolution reaction (HER) catalysts to replace noble metals in acidic medium. However, several challenges prevent MoS2 from being truly applicable, including limited number of active sites (typically only the edges are active) and poor conductivity. In this work, we perform an extensive density func- tional theory (DFT) screening of substitutional doping as a possibility to activate the otherwise inert basal surface. We assess 17 Earth abundant elements for molybdenum doping and 5 elements (N, O, P, Se and Te) for sulfur substitution. Systematically de- termining the preference of the metallic dopants to be located on the edges rather than in the basal plane, we reveal that most dopants are much more likely to be incorpo- rated at the edges, suggesting that advanced synthesis methods are required to obtain basal-plane doped catalysts. The latter may, however, feature many more active sites per MoS2 formula unit, motivating our study on the properties of such substitutionally doped surfaces. For the first time for such a screening study, we explore not only the adsorption of H, but also of OH and H2O to explore the solvent effect since the reac- tion takes place in an aqueous medium. Two additional phenomena that could hinder the hydrogen production at these sites are investigated, namely H2S release and the (local) segregation/dispersion tendency of the dopants in the basal surface. Moreover, to assess the electrocatalytic activity, we take the electrochemical potential explicitly into account via grand canonical DFT in combinations. Compared with pristine MoS2 nanosheets, our results show that most doping elements significantly enhanced the elec- trocatalytic activity. Considering all assessed factors, we identify the most promising systems: Dimers of Ti, Zr and Hf and the substitution of S by P are predicted to lead to stable active sites on the basal plane with overpotentials of about 0.2 V.