Crystal structure and hydrogen storage property of Nd2Ni7 superlattice alloy

This study investigates the crystal structure and Pressure–composition (P–C) isotherm of Nd2Ni7 prepared by annealing an arc-melted ingot at 1448 K for 10 h followed by ice-water quenching. The crystal structure was further refined by X-ray Rietveld analysis based on the Ce2Ni7-type structure. The lattice parameters were determined as a = 0.5001(1) nm and c = 2.4437(4) nm. A single plateau was observed during the first absorption–desorption cycle. In the first absorption cycle, the maximum hydrogen capacity reached 1.22 H/M (1.58 mass%) at 233 K. The absorption and desorption plateau pressures were approximately 1.0 and 0.002 MPa, respectively. In the first desorption process, 0.63 H/M of hydrogen remained in the sample. Further, a single sloping plateau was observed in the second absorption–desorption process. Heavy peak broadening was observed in the X-ray diffraction (XRD) profile after hydrogenation, with no detection of an amorphous phase.

► The maximum hydrogen capacity of Nd2Ni7 reached 1.22 H/M at 233 K. ► After initial P–C isotherm, heavy peak broadening was observed in the XRD profile. ► The structure of the hydrogenated phase was not amorphous.