Computational Study On The Hydrogen Storage Properties Of The Magnesium And Its Alloy

In the present paper, density functional theory (DFT) calculations were performed on adsorption, dissociation and diffusion, permeation behavior of hydrogen on clean and magnesium-based alloy.This paper includes the following two parts:1. Theoretical study of adsorption and desorption properties of hydrogen on Mg(0001) and M (Sc-Zn)-doped Mg(0001) surfacesThe adsorption and desorption properties of hydrogen on clean and M (Sc-Zn) doped Mg(0001) surfaces are investigated systematically by density functional theoretical method. The calculated results show that H? physically adsorb on Mg(0001), Fe-, Co-, Cu- and Zn-doped Mg surfaces; whereas H2 can adsorb both physically and chemically on Sc-, Ti-, V-, Cr-, Mn- and Ni-doped Mg surfaces. The energy barrier for hydrogen dissociation on the pure Mg(0001) surface is the highest comparing with those on M-doped surfaces. The dissociated hydrogen atoms are easily chemically adsorbed in the following three kinds of neighboring follow sites:fcc-hcp1 sites of Fe-doped Mg, hcp-hcp sites of Ni-doped Mg, fcc-fcc sites of the other M-doped Mg. The results display that Ti, V, Cr, Mn, and Ni are all the appropriate candidate doping metals for improving the adsorption and dissociation properties of H2.2. Theoretical study of adsorption, diffusion and permeation behavior of hydrogen on Mg and transition metal doped Mg surfaces and bulkThe adsorption, diffusion and permeation behavior of hydrogen on Mg and transition metal doped Mg surfaces and bulk are investigated by using density functional theory. The calculated results show that it is thermodynamically favorable for transition metal to dope into Mg and there is a significant charge transfer between doped metal and Mg. Hydrogen atoms tend to be adsorbed on the fcc and hcp sites of the Mg surface and the M-doped Mg surface. It is easily for hydrogen atoms to diffuse between the fcc site and the hcp site of the pure Mg or the vicinity of doped atoms, but it is much more difficult for hydrogen atom to diffuse between these sites involved in different metal atoms. The permeation pathway of hydrogen atom is depended on the position of doped atom. In a word, Ti and Ni are both appropriate candidate metals for improving the hydrogen storage properties, while Cu is not effective. The theoretical findings are consistent with the experimental observations and can provide valuable guide for the selection of doping metals.