Thermodynamic destabilization and kinetic optimization for the de-/hydrogenation of Mg85Ni15 alloy by tailoring Mg(In) and Mg2Ni(In) double solid solution

Abstract

To increase the hydrogen de-/absorption rate and reduce the stability of MgH2, element indium (In) is introduced into the hypereutectic Mg85Ni15 alloy. The results show that solid solution phases of Mg(In) and Mg2Ni(In) are formed simultaneously, and the lattice parameters of Mg crystals decrease while that of Mg2Ni crystals increase. The hydrogen storage capacity of Mg85Ni14.5In0.5 alloy reaches 3.5 wt% at 125 ℃ with the hydrogenation rates accelerated significantly, which is higher than the 2.4 wt% of Mg85Ni15 alloy. For dehydrogenation, Mg85Ni14In1.0 hydride can release 4.1 wt% hydrogen at 225 ℃ in 15 min. The main peak temperature in DSC test for dehydrogenation is decreased to 226.6 ℃ of Mg85Ni13.5In1.5 hydride from 246.1 ℃ of Mg85Ni15 hydride and decomposition enthalpy (ΔH) of Mg85Ni13.5In1.5 hydride is decreased to 60.9 kJ/mol. The rapid hydrogenation rate is owing to the dissolved In atoms in Mg2Ni lattice causing lattice expansion, which acts as fast diffusion path for hydrogen atoms. In Mg(In)H2 phase, the strong interaction between Mg and In weakens the affinity of Mg and H, which accounts for the reduced ΔH of Mg(In)H2. The weakened strength of Ni-H bond in Mg2Ni(In)H4 also results in the decreased stability of hydride.