Hydrogen storage properties and phase structures of RMg2Ni (R=La, Ce, Pr, Nd) alloys

Abstract

Abstract RMg 2 Ni alloys were prepared by inductive melting where R is rare earth (R = La, Ce, Pr, Nd). X-ray diffraction (XRD) patterns revealed a single-phase composition of RMg 2 Ni phase when R was one of the three elements (La, Pr, Nd), and a double-phase composition of CeMg 2 Ni and CeMg 3 phases when R was Ce. In the hydriding process, RMg 2 Ni phases transformed to rare earth hydrides (R-H) and Mg 2 NiH 4 phase, and for CeMg 3 phase, it is decomposed to CeH 2.74 and MgH 2 phases. The enthalpy change of Mg 2 Ni phase in RMg 2 Ni alloys during the hydriding/dehydriding process was smaller compared with that of pristine Mg 2 Ni alloy, which could be attributed to the existence of R-H. The hydrogen storage properties of RMg 2 Ni alloys changed with different R compositions in R-H. At 573 K, the NdMg 2 Ni alloy had the highest hydrogen storage capacity and dehydriding plateau, and the descending order of hysteresis was PrMg 2 Ni 2 Ni 2 Ni 2 Ni, which suggested that the PrMg 2 Ni alloy exhibited a better cycling stability and reversibility than the other three alloys. At 523 K, the uptake time of RMg 2 Ni alloys to reach 90% of the maximum hydrogen storage capacity was 75 s, 34 s, 65 s and 52 s, respectively, compared with 110 s of pristine Mg 2 Ni alloy. Therefore, we believed the R-H in the alloys not only improved their thermodynamic properties but also accelerated their hydriding kinetics.