We developed a method to determine the activation energy for hydride decomposition using a Sieverts-type apparatus and the Kissinger equation, not using thermal analysis methods. The quantity of hydrogen released from the sample and the temperature of the reactor were first measured as a function of time at different heating rates (Φ) in a Sieverts-type apparatus. The dehydriding rates were calculated according to time and the temperature T_m (at which the dehydriding rate was the highest). Φ and T_m were then applied to the Kissinger equation. The dehydriding rate of Mg-5Ni samples obeyed a first-order law, and the Kissinger equation could thus be used to determine the activation energy. On a heating rate of 3 K/min, the decomposition rate of hydride was the highest at 590.0 K. From a plot of ln (Φ/T_m²) versus 1/T_m, the obtained activation energy for hydride decomposition was 174 kJ/mole.

In order to increase hydrogen release rate of MgH₂ which had dehydriding rate of 0 at 573 K and 1.0 bar H₂, Ni was added to MgH₂. Samples with compositions of 94 wt.% MgH₂ + 6 wt.% Ni, 88 wt.% MgH₂ + 12 wt.% Ni, 85 wt.% MgH₂ + 15 wt.% Ni, and 82 wt.% MgH₂ + 18 wt% Ni [named MgH₂-xNi (x = 6, 12, 15, and 18), respectively] were prepared by grinding in a hydrogen atmosphere. Variations in hydrogen absorption and release properties at 573 K at the third hydrogen absorption-release cycle (n = 3) with Ni content were then investigated. These samples had smaller hydrogenstorage capacities than the as-ground MgH2. However, they showed much higher hydrogen release rates. MgH₂–12Ni had the highest initial hydrogen absorption and release rates. MgH₂–12Ni had the largest quantity of hydrogen released for 60 minutes, followed by MgH₂–18Ni, MgH₂–15Ni, and MgH₂–6Ni in descending order. After grinding in a hydrogen atmosphere, MgH₂–12Ni had the smallest average particle size. The hydrogen release rate of Mg was increased by the effects of grinding in H₂ (the decrease in the average particle size and the creation of defects) and the effect of Mg₂Ni phase that was formed during hydrogen absorption-release cycling.