Effect of La2O3-CaO composite additive on the hydrogen storage properties of Mg2Ni alloy

La2O3-CaO composite additive is employed to accelerate the hydrogen absorption/desorption rate of the Mg2Ni alloy. The composite additive was ball milled with Mg2Ni hydride to produce Mg2Ni–5 wt.% La2O3–5 wt.% CaO composite. The composite additive significantly reduces the thermal stability of Mg2NiH4. The onset decomposition temperature of the hydrogenated composite is 470 K, 21 K lower than that of the pure Mg2NiH4. Meanwhile, the composite presents accelerated hydriding/dehydriding kinetic properties. It absorbs 1.61 wt.% H at 373 K in 2 h and releases 2.44 wt.% H at 573 K in 1200 s, while the absorbed and desorbed hydrogen by the Mg2NiH4 is only 0.78 wt.% H and 1.32 wt.% H, respectively. The improvement in the hydrogen storage properties of the Mg2Ni alloy by the adoption of La2O3-CaO additive is ascribed to the modified catalytic effects of La2O3 and CaO in the composite.