Hydrogenation and structural properties of Gd2Ni7 with superlattice structure

The crystal structure and hydrogenation properties of Ce2Ni7-type Gd2Ni7 were investigated by X-ray diffraction (XRD) and the hydrogen pressure composition (P C) isotherm. Ce2Ni7-type Gd2Ni7 was obtained by annealing at 1523 K for 12 h and quenching in ice water. Two superlattice reflections (002 and 004) of the Ce2Ni7-type were dearly observed at 2 theta = 7.3 degrees and 14.6 degrees in the XRD profile. The refined lattice parameters were a = 0.49662(9) nm and c = 2.4255(3) nm, respectively. Two plateaus were clearly observed during the absorption-desorption process in the P C isotherm. The first and second plateaus were at 0.015 and 0.13 MPa, respectively, in the first desorption. The maximum hydrogen capacity reached was 1.13 HIM. The enthalpy and entropy were calculated as -20 kJ/mol H-2 and -80 J/mol H-2 K, respectively, from the van't Hoff plot. After the P-C isotherm, the GdNi5 cell expanded by 2.15%, but the Gd2Ni4 cell shrank by 2.83%. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.