Influence of Cr/Zr doping on the electronic structure and hydrogen storage properties of the Mg2Ni (0 1 0) surface: A first principles study

Abstract

The influences of Cr and Zr dopants on the electronic structure and the hydrogen adsorption of the Mg2Ni (010) surface have been studied by using the first-principles method. The calculated results show that Cr/Zr substitutions increase the activity of the Mg2Ni (010) surface, reduce the Ni–Mg and Ni–Ni interactions in Mg2Ni, and increase the hollow size between two atoms, which would aid hydrogen adsorption and further diffusion. As the hydrogen absorbs on clean Mg2Ni (010) surface, three stable hydrogen absorption sites are determined: the top sites of the Ni atom as well as the Ni–Ni and Mg–Ni bridge sites. Substituting the Ni atoms on the Mg2Ni (010) surface with Cr or Zr increase the number of stable hydrogen adsorption sites, decrease the hydrogen adsorption energy, and improve the hydrogen storage capacity of Mg2Ni. For both clean and Cr/Zr-doped Mg2Ni (010) surfaces, the most stable adsorption site is the Ni–M (M=Ni, Cr, or Zr) bridge site. Density of states calculations show that the adsorption on Ni–M bridge site occurs from the overlap of the H 1s and M outermost s states. All of the calculated results show Zr and Cr atoms, especial Zr atom, to be good candidates for improving the hydrogen storage capacity of Mg2Ni.