Hydrogen absorption/desorption cycling performance of Mg-based alloys with in-situ formed Mg2Ni and LaH (x = 2, 3) nanocrystallines

Aiming to elucidate the hydrogen absorption/desorption cycling properties of Mg-based alloys with in-situ formed Mg2Ni and LaHx (x = 2, 3) nanocrystallines, the hydrogen storage cycle stability, hydriding/dehydriding cycling kinetics and thermodynamic stability of the experimental alloys have been investigated in detail. The results show that the Mg–Ni–La alloys exhibit improved hydrogen storage cycling properties and can remain storage hydrogen above 5.5 wt% after 200 cycles. With the increase of cycling numbers, the dehydrogenation rates of the experimental samples increase firstly and then gradually decrease, and eventually maintain relative stable state. Microstructure observation reveals that powders sintering and hydrogen decrepitation both exist during hydrogen absorption/desorption cycles due to repeated volume expansion and contraction. Meanwhile, the in-situ formed LaHx (x = 2, 3) and Mg2Ni nanocrystallines stabilize the microstructures of the particles and hinder the powders sintering. After 200 cycles, the average particle size of the experimental samples decreases and the specific surface area apparently increases, which leads to the decomposition temperatures of MgH2 and Mg2NiH4 slightly shift to lower temperatures. Moreover, Mg2Ni and LaHx (x = 2, 3) have been proven to be stable catalysts during long-term cycling, which can still uniformly distribute within the powders after 200 cycles.