First-principles Study of H₂ Adsorption Mechanism on Defective MoSe₂/Graphene Heterostructures

Transition metal di-chalcogenide monolayers (TMD-MLs), a novel class of the 2D materials, exhibit tremendous properties, such as their tuneable band gap, high surface to volume ratio, appropriate carrier mobility, large spin-orbit coupling and thermal stability, which make this class of 2D-materials a promising leading candidate for many applications. In the present work, the spin-polarised density-functional theory (DFT) is applied to investigate the adsorption of hydrogen-gas molecules on six different adsorbents: (1) MoSe₂ ML with single vacancy of Mo “MoSe₂:V_Mo ML”; (2) Mn-doped MoSe₂ ML at Mo/Se site “MoSe₂:Mn ML”; (3) MoSe₂:V_Mo/graphene hetero-structure; and (4) MoSe₂:Mn/graphene hetero-structures. The hydrogen molecule is found to interact in different ways depending on the adsorbents diverse band structures and magnetizations. The MoSe₂:V_Mo/graphene hetero-structure showed the highest adsorption energy of -0.41 eV, but the hydrogen molecule exhibits chemisorption associated with a dissociation which qualify it for gas sensing applications. Moreover, Mn substitutional doping at Se site stands prone as the best candidate for H₂ storage. The H₂ molecule can be spontaneously adsorbed on top of Mn site with E_ads = -0.28 eV. The desorption is shown to cost an energy of about 0.36 eV. Furthermore, the uptake capacity can further be enhanced by increasing the doping concentration of Mn (e.g., MoSe₂:2Mn@2Se was tested and found to reach 2.9% wt).