Phase Transformation and Hydrogen Storage Properties of an La7.0Mg75.5Ni17.5 Hydrogen Storage Alloy

X-ray diffraction showed that an La7.0Mg75.5Ni17.5 alloy prepared via inductive melting was composed of an La2Mg17 phase, an LaMg2Ni phase, and an Mg2Ni phase. After the first hydrogen absorption/desorption process, the phases of the alloy turned into an La-H phase, an Mg phase, and an Mg2Ni phase. The enthalpy and entropy derived from the van't Hoff equation for hydriding were -42.30 kJ<bold>mol</bold>-1 and -69.76 J<bold>K</bold>-1<bold>mol</bold>-1, respectively. The hydride formed in the absorption step was less stable than MgH2 (-74.50 kJ<bold>mol</bold>-1 and -132.3 J<bold>K</bold>-1<bold>mol</bold>-1) and Mg2NiH4 (-64.50 kJ<bold>mol</bold>-1 and -123.1 J<bold>K</bold>-1<bold>mol</bold>-1). Differential thermal analysis showed that the initial hydrogen desorption temperature of its hydride was 531 K. Compared to Mg and Mg2Ni, La7.0Mg75.5Ni17.5 is a promising hydrogen storage material that demonstrates fast adsorption/desorption kinetics as a result of the formation of an La-H compound and the synergetic effect of multiphase.