The effects and mechanisms of two-dimensional V2C and V2CT2 (T = O, F, and OH) on hydrogen adsorption and dissociation properties of MgH2: First-principles calculations

Abstract

Two-dimensional vanadium carbide (V2C) MXene has been confirmed the excellent catalytic activity on hydrogen storage of magnesium hydride (MgH2) in experimental. In present work, adsorption energy, density of states (DOS), charge density difference, dissociation barrier and dehydrogenation energy of the small MgH2 clusters on V2C and V2CT2 (T = O, F, and OH) were investigated by using density functional theory (DFT). The results revealed that the (MgH2)1 cluster adsorbed on the V2C has the best adsorption energy with −0.91eV and the lengths of Mg–H bonds were increased from 1.71 Å to 1.77 Å. The electronic structure results displayed that the H s states hybridized with the V d states, and the charge transferred from H atoms to V atoms. In addition, the (MgH2)1 cluster could be spontaneously dissociated on the V2C, and the dissociation barriers of (MgH2)2 and (MgH2)4 clusters on the V2C reduced by 1.33 and 1.25 eV than that of pristine (MgH2)2 and (MgH2)4 clusters, respectively. Compared with the pristine (MgH2)4 cluster, the dehydrogenation energies of (MgH2)4 cluster were dramatically promoted by adding V2C. The thermodynamic performance of MgH2 were noticeably improved.