Microstructures and hydrogen storage properties of LaMg8.40Ni2.34−xAlx alloys

Herein, we prepared a new type of magnesium and transition metal-based alloys with the formula of LaMg8.40Ni2.34−xAlx (x = 0 and 0.20). Their phase structures, morphologies and hydrogen storage properties were studied by different methods. The XRD patterns show that LaMg8.40Ni2.34−xAlx alloys are made of La2Mg17, LaMg2Ni and Mg2Ni phases. The SEM images indicate that the phase distributions in LaMg8.40Ni2.14Al0.20 alloy are more uniform compared with LaMg8.40Ni2.34 alloy. In addition, the reversible hydrogen storage capacity of LaMg8.40Ni2.14Al0.20 alloy is 3.22 wt.% at 558 K, which is higher than that of LaMg8.40Ni2.34 alloy. The partial substitution of Al for Ni effectively improves the hydrogen storage capacity, as well as the hydriding/dehydriding kinetics of the alloys, with the evidence that 89% hydrogen in the saturated state in LaMg8.40Ni2.14Al0.20 alloy was released in 1500 s at 573 K, while only 74% hydrogen in the saturated state in LaMg8.40Ni2.34 alloy was released at the same conditions. Consequently, we believe that the alloying of aluminum in the magnesium-rare earth-transition metal-based alloys can effectively improve their hydrogen storage performance.

► LaMg8.40Ni2.34 and LaMg8.40Ni2.14Al0.20 alloys consist of La2Mg17, LaMg2Ni and Mg2Ni phases.
► The distribution of initial phases in LaMg8.40Ni2.14Al0.20 alloy is more uniform.
► Reversible capacity of LaMg8.40Ni2.14Al0.20 alloy is higher than that of LaMg8.40Ni2.34 alloy.
► Mg hydride in LaMg8.40Ni2.14Al0.20 alloy is less stable, the stability of Mg2Ni hydride is similar.
► The better kinetics is due to the more uniform distribution of initial phases.