Effect of Co substitution for Ni on the microstructure and electrochemical properties of La-R-Mg-Ni-based hydrogen storage alloys

• Published in: Journal of solid state electrochemistry 2013-03, Vol.17 (3), p.727-735
• Main Authors: Gao, Zhi-Jie, Luo, Yong-Chun, Lin, Zhen, Li, Rong-Feng, Wang, Jian-Yi, Kang, Long
• Format: Article
• Language: English
• Subjects: Analytical Chemistry; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Condensed Matter Physics; Electrochemistry; Energy Storage; Original Paper; Physical Chemistry
• ISSN: 1432-8488; 1433-0768
• DOI: 10.1007/s10008-012-1878-1

Hydrogen storage alloys La 0.63 Gd 0.2  Mg 0.17 Ni 3.35− x Co x Al 0.15 ( x  = 0, 0.1, 0.3, 0.5, 1.0, 1.5, 2.0) were prepared by induction melting followed by annealing treatment in argon atmosphere. The electrochemical properties of La 0.63 Gd 0.2  Mg 0.17 Ni 3.35− x Co x Al 0.15 ( x  = 0, 0.1, 0.3, 0.5, 1.0, 1.5, 2.0) alloy electrodes depended on the alloy structure type. XRD patterns and EPMA showed that the alloys consisted of Ce 2 Ni 7 -type (Gd 2 Co 7 -type), CaCu 5 -type, Pr 5 Co 19 -type, and PuNi 3 -type phase structure. Pr 5 Co 19 -type and Ce 2 Ni 7 -type phase increased with the increase of Co content x . However, CaCu 5 -type phase firstly decreased then increased as Co content increased. Rietveld analysis showed that the c -axis lattice parameters and cell volumes of the component phases increased with increasing Co content. The electrochemical measurements showed that as the Co content increased, the maximum discharge capacity and the cyclic stability of the annealed alloys both first increased and then decreased. The La 0.63 Gd 0.2  Mg 0.17 Ni 3.05 Co 0.3 Al 0.15 alloy electrode exhibited the maximum discharge capacity (392.92 mAh/g), and La 0.63 Gd 0.2  Mg 0.17 Ni 1.85 Co 1.5 Al 0.15 alloy electrode showed the best cyclic stability (S 100  = 96.1 %). The electrochemical kinetics studies indicate that La 0.63 Gd 0.2  Mg 0.17 Ni 1.85 Co 1.5 Al 0.15 exhibited a higher rate dischargeability (HRD 900  = 86.3 %). Electrochemical analyses showed that the control process of alloy electrode reaction is charge-transfer rate in surface film of alloy.