First-principles calculations of the crystal structure, electronic structure, and thermodynamic stability of Si-doped Mg2Ni and Mg2NiH4

Mg2Ni is considered as one of the promising candidates of hydrogen storage materials because of its reasonable (de)hydrogenation kinetics and low costs. In view of the high operating temperature for hydrogen release due to the high thermodynamic stability of hydride, Mg2NiH4 is a serious obstacle to overcome for application usage. In this work, the crystal structure, electronic structure and thermodynamic stability of Si doped Mg2Ni and Mg2NiH4 are studied by first-principles calculations based on density functional theory. It is shown that the hydrogen desorption enthalpy can be reduced from 63.3 to 48.2 and 46.2 kJ/mol H2 with one in sixteen Mg and one in eight Ni atoms is replaced by Si, respectively. The crystal structure and electron properties of Si doped Mg2Ni and Mg2NiH4 are clarified. It is found that the weakened covalent interaction of H–Ni bonding contributes dominantly to the deteriorative thermodynamic stability of hydrides.