Dry and hydrated defective molybdenum Disulfide/Graphene bilayer heterojunction under strain for hydrogen evolution from water Splitting: A First-principle study

Abstract

In search of exploiting cost-effective, highly stable, efficient, and greatly active electrocatalysts for hydrogen evolution reaction (HER), molybdenum disulfide-graphene heterostructures (MoS2/graphene) are promising, in contrast to noble metals. We used density functional theory (DFT) to examine the changes in the electronic structure of MoS2/graphene under compressive strain for structural defects in the MoS2 and graphene layers, as well as from hydration of the MoS2 layer. In the pristine MoS2/graphene heterostructure, a small bandgap (minigap) is opened at the graphene Dirac point, which is located above the Fermi energy, for dry and hydrated configurations. The presence of sulfur and carbon vacancies in the MoS2/graphene upshifts the Dirac point and widens the minigap. However, additional sulfur vacancies further widen or shrink the minigap depending on the location of the MoS2 conduction band bottom and the presence of defect bands at the Dirac point. The minigap tunability in the MoS2/graphene heterostructure could be engineered for producing efficient HER electrocatalysts and beyond. The Quantum Theory of Atoms in Molecules (QTAIM) reveals SC bond critical points, which correspond to van der Waals forces interactions in agreement with the Non-covalent Interaction (NCI) analysis. A correlation is drawn between the minigap and the electron density at the SC bond critical points.