First principles study towards the influence of interstitial nitrogen on the hydrogen storage properties of the Mg2Ni (0 1 0) surface

Abstract

Doping light elements into Mg-based alloy has been viewed as an effective method for improving the hydrogen storage properties without remarkably reducing hydrogen capacity. The influences of interstitial nitrogen doping on the crystal structure, thermal stability, hydrogen adsorption energy and electronic properties of Mg2Ni (0 1 0) surface were investigated by first principles calculations. The calculation results showed that the addition of interstitial N results in an anisotropic expansion in the crystal structure and a better improvement effect on lowering thermal stability of the Mg2Ni surface than the commonly used transition metal. Three stable sites including the NiNi bridge site, the top sites of Mg and Ni atoms, were determined to take in hydrogen in the pure surface. When the nonmetal N is doped into the pure surface, the number of the stable adsorption sites is increased and the adsorption energy of H in the NiNi bridge site is also increased from −0.9614 eV for the pure to −0.5441 eV for the N-doped counterpart. The increases in both the stable adsorption sites and the energy caused by the addition of N indicate that more hydrogen could be adsorbed in the weaker NiH bonds of the N-doped Mg2Ni alloy, thereby improving the hydrogen storage behaviors of Mg-based alloy.