First Principles Study on Hydrogen Desorption from a Metal (=Al, Ti, Mn, Ni) Doped MgH2 (110) Surface

First principles calculations on an Al, Ti, Mn, and Ni doped MgH2 (110) surface were carried out to study the influence of dopants on the dehydrogenation properties of MgH2. It was shown that Al prefers to substitute for an Mg atom, whereas Ti, Mn, and Ni prefer to occupy interstitial sites. The dopants used different mechanisms to improve the dehydrogenation properties of MgH2. Al weakens the interactions between the Mg and the H atoms in its vicinity and so slightly improved the dehydrogenation properties of the Al doped system. The H atoms near the dopants of the transition metal doped systems were dramatically distorted. Ti has a high potential to generate a TiH2 phase by attracting two H atoms, which frees one H atom from its host Mg atom. The dehydrogenation properties of the Mn doped system were improved by the formation of a Mn-H cluster with a similar structure to Mg3MnH7 but weaker interactions between its atoms. If the MgH2 (110) surface is doped with Ni, the Ni will attract four H atoms to form a regular tetrahedral NiH4 group almost identical in structure to that in Mg2NiH4. The improvement of the dehydrogenation properties of Ni-doped MgH, is expected as the bonding between the Mg and the H atoms is weakened, and there is a high possibility that the Mg2NiH4 phase will be formed, which is thermodynamically less stable than the MgH2 in this system.