Effect of hydride on the hydrogen storage performance of Mg₂Ni based alloys

Pure Mg₂Ni, Mg₂Ni with TiH₂ of 10% and Mg₂Ni with NbH of 10% hydrogen storage alloys were prepared by mechanical ball milling, respectively. The effects of additives (TiH₂, NbH) on the phase composition, microstructure and hydrogen storage properties of Mg₂Ni hydrogen storage alloys were studied. The results showed that the unit cell volume of the Mg₂NiH₄/Mg₂Ni phase of hydrogen storage alloys added with 10% TiH₂ or NbH, decreased to varying degrees, after sufficient hydrogen absorption/desorption, compared with pure Mg₂Ni hydrogen storage alloy. TiH₂ was uniformly distributed in the hydrogen storage alloys after mechanical ball milling, while NbH was agglomerated to a certain extent. The hydrogen absorption and desorption platforms of the hydrogen storage alloys with the addition of 10% TiH₂ or NbH were higher, and the enthalpy change and entropy change in the process of hydrogen evolution reaction were smaller than that of pure Mg₂Ni alloy. In the same amount of time, hydrogen evolution capacity of hydrogen storage alloys was listed in order from the largest to the smallest: Mg₂Ni + 10% TiH₂>Mg₂Ni + 10% NbH>pure Mg₂Ni alloy. When the temperature was 573 K, the time required for the hydrogen storage alloy to reach the maximum hydrogen release capacity in order from least to most was Mg₂Ni + 10% TiH₂ < Mg₂Ni + 10% NbH < pure Mg₂Ni alloy. Adding hydride TiH₂ or NbH will increase the reaction rate constant of hydrogen storage alloys, and TiH₂ improves hydrogen diffusion performance better than NbH.