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

To increase the hydrogen de-/absorption rate and reduce the stability of MgH ₂ , element indium (In) is introduced into the hypereutectic Mg ₈₅Ni ₁₅ alloy. The results show that solid solution phases of Mg(In) and Mg ₂ Ni(In) are formed simultaneously, and the lattice parameters of Mg crystals decrease while that of Mg ₂Ni crystals increase. The hydrogen storage capacity of Mg ₈₅Ni _14.5In _0.5 alloy reaches 3.5 wt% at 125 ℃ with the hydrogenation rates accelerated significantly, which is higher than the 2.4 wt% of Mg ₈₅Ni ₁₅ alloy. For dehydrogenation, Mg ₈₅Ni ₁₄In _1.0 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 Mg ₈₅Ni _13.5In _1.5 hydride from 246.1 ℃ of Mg ₈₅Ni ₁₅ hydride and decomposition enthalpy (ΔH) of Mg ₈₅Ni _13.5In _1.5 hydride is decreased to 60.9 kJ/mol. The rapid hydrogenation rate is owing to the dissolved In atoms in Mg ₂Ni lattice causing lattice expansion, which acts as fast diffusion path for hydrogen atoms. In Mg(In)H ₂ phase, the strong interaction between Mg and In weakens the affinity of Mg and H, which accounts for the reduced ΔH of Mg(In)H ₂ . The weakened strength of Ni-H bond in Mg ₂Ni(In)H ₄ also results in the decreased stability of hydride.