Effect of Mg substitution on hydrogen absorption–desorption behavior and crystal structure of Gd2−xMgxNi7. (12th January 2016)

• Record Type: Journal Article
• Authors: Iwase, Kenji; Terashita, Naoyoshi; Mori, Kazuhiro; Tashiro, Suguru; Yokota, Hitoshi; Suzuki, Tetsuya
• Is Part Of: International journal of hydrogen energy. Volume 41:Number 2(2016)
• Page Start: 1074
• Page End: 1079
• Publication Date: 2016-01-12
• Subjects: Crystal structure -- Superlattice structure -- XRD -- Pressure–composition isotherm -- Rietveld refinement; Hydrogen as fuel -- Periodicals; Hydrogène (Combustible) -- Périodiques; Hydrogen as fuel; Periodicals; 665.81
• DOI: 10.1016/j.ijhydene.2015.11.052
• Languages: English
• ISSNs: 0360-3199

Abstract

Abstract: The hydrogen absorption–desorption behavior and the crystal structure of Gd2− x Mg x Ni7 were investigated by pressure–composition (P–C) isotherm measurements and X-ray diffraction (XRD). Gd1.5 Mg0.5 Ni7 consists of two phases: 75% Gd2 Co7 -type structure and 25% PuNi3 -type structure. Mg atoms substitute at the Gd site of the MgZn2 -type cell in both Gd2 Co7 -type and PuNi3 -type phases. In the hydrogen-free alloy after the P–C isotherm measurement, the volumes of the (Gd/Mg)Ni2 and GdNi5 cells of the Gd2 Co7 -type phase do not change appreciably, while those of the PuNi3 -type phase experience shrinkage and expansion, respectively. A plateau region of Gd1.5 Mg0.5 Ni7 is observed between 0.06 H/M and 0.82 H/M. The reversible hydrogen content in the absorption–desorption cycle is approximately 1.0 H/M. The enthalpy of hydride formation is evaluated as −24 kJ/mol H2 from the Van't Hoff plot. The absorption–desorption behavior is excellent even at low temperatures below 243 K. The hydrogen storage property of Gd1.5 Mg0.5 Ni7 is markedly improved by Mg substitution. Highlights: The reversible hydrogen capacity of Gd1.5 Mg0.5 Ni7 reached 1.0 H/M. Gd1.5 Mg0.5 Ni7 consists of two phases: 75% Gd2 Co7 -type structure and 25% PuNi3 -type structure. The enthalpy of hydride formation is evaluated as −24 kJ/mol H2 from the Van't Hoff plot.