Van der Waals hetero-structures of 1H-MoS₂ and N-substituted graphene for catalysis of hydrogen evolution reaction

First-principles theoretical analysis of the catalytic activity of van der Waals hetero-structures of 1H-MoS₂ and graphene substituted with three chemical types of nitrogen species (i) Graphitic (G), (ii) Pyridinic (Pn) and (iii) Pyrrolic (Pr), for application in catalysis of hydrogen evolution reaction (HER) has been presented. Graphitic and pyrrolic N substituents result in n-type electronic structure, whereas substitution of pyridinic N imparts p-type electronic character to the hetero-structure. Work functions (φ) of the hetero-structures suggest that graphitic N-graphene:MoS₂ hetero-structure ($\phi =3.8eV$) is expected to be effective in catalysing the reduction of H⁺ to evolve H₂. 1H-MoS₂ monolayer in the hetero-structure contributes by enabling increased H₂O adsorption and offsetting the band edge energies optimal for the catalytic activity. Near optimum Gibbs free energy of H-adsorption ($\Delta G_H$) were obtained for graphitic ($\Delta G_H$ ∼ 0.29 eV) and pyrrolic ($\Delta G_H$ ∼ −0.2 eV) N-graphene:MoS₂ hetero-structures. Our work showcases how catalytic and electronic properties of the N-doped graphene:MoS₂ hetero-structure depends on the chemical identity of N-sites and uncovers a route to 2D hetero-structures with high catalytic activity. (paper)