Phase structure and hydrogen storage properties of REMg8.35Ni2.18Al0.21 (RE=La, Ce, Pr, and Nd) hydrogen storage alloys

Abstract REMg 8.35 Ni 2.18 Al 0.21 (RE=La, Ce, Pr, and Nd) alloys were prepared by induction melting and following annealing. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that the alloys were composed of Mg 2 Ni, (La, Pr, Nd)Mg 2 Ni, (La, Ce) 2 Mg 17 , (Ce, Pr, Nd)Mg 12 and Ce 2 Ni 7 phases. The above phases were disproportioned into Mg 2 NiH 4 , MgH 2 and REH x ( x =2.51 or 3) phases in hydriding. CeH 2.51 phase transformed into CeH 2.29 phase in dehydriding, whereas LaH 3 , PrH 3 and NdH 3 phases remained unchanged. The PrMg 8.41 Ni 2.14 Al 0.20 alloy had the fastest hydriding kinetics and the highest dehydriding plateau pressure while the CeMg 8.35 Ni 2.18 Al 0.21 alloy presented the best hydriding/dehydriding reversibility. The onset hydrogen desorption temperature of the CeMg 8.35 Ni 2.18 Al 0.21 hydride decreased remarkably owing to the phase transformation between the CeH 2.51 and the CeH 2.29 .