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Ding H.-L.,Yanshan University | Hao J.-S.,Yanshan University | Hao J.-S.,Inner Mongolia Rare Earth Ovonic Hydrogen Storage Alloys Corporation Ltd | Zhu X.-L.,Yanshan University | And 4 more authors.
Wuji Cailiao Xuebao/Journal of Inorganic Materials | Year: 2010

In order to improve cycling stability and overall electrochemical properties of La-Mg-Ni-based hydrogen storage alloys, an electroplating treatment was applied on La0.88Mg0.12Ni2.95Mn0.10Co0.55Al0.10 alloy powders. The effect of cobalt-nickel coating on the morphological and electrochemical properties was studied. FESEM results show that spherical nickel-cobalt alloy particles are deposited on the surface of the alloys. Electrochemical tests indicate that the maximum discharge capacity, the cycling stability and the high rate dischargeability (HRD) are remarkably improved. After 200 charge/discharge cycles, the capacity retention rate increases from 60% (uncoated) to 80% (nickel-cobalt coated). The HRD at 1080mA/g rises by 23% for the nickel-cobalt coated alloy electrodes. Linear polarization and Electrochemical Impedance Spectroscope (EIS) results reveal that the surface of alloy electrodes with cobalt-nickel coatings is more catalytic for the electrochemical charge transfer reactions.

Shang G.Y.,Yanshan University | Han S.M.,Yanshan University | Hao J.S.,Yanshan University | Hao J.S.,Inner Mongolia Rare Earth Ovonic Hydrogen Storage Alloys Corporation Ltd | And 5 more authors.
Journal of Alloys and Compounds | Year: 2010

Nd0.88Mg0.12Ni3.10+xAl0.20 (x = 0.00, 0.10, 0.20, 0.30) alloys were prepared by inductive melting. The factors leading to reversible and irreversible loss of capacity were evaluated by structural characterization, pressure-composition-temperature (P-C-T) measurements, and electrochemical tests. X-ray diffraction (XRD) analysis showed that the alloys had a multiphase structure, consisting mainly of Nd2Ni7 phase, NdNi5 phase and some minor impurity NdNi2 phase. The FESEM observed that some white and acicular substances were formed on surface of the alloy particles after 28 d storage under an open-circuit condition. XRD and EDS results revealed that the substances were Mg(OH)2 and Nd(OH)3. The oxidation of alloys led to irreversible capacity loss, the corrosion rate characterized by Icorr first decreased and then increased with increasing Ni content, and reached its lowest value at x = 0.20. P-C-T measurements indicated that with increasing Ni content the stability of the hydride first increased and then decreased, which resulted in the lowest self-discharge rate at x = 0.20. The 24-h charge retention rate (CRT) of alloy electrodes increased first from 22.5% (x = 0.00) to 82.1% (x = 0.20), and then decreased to 33.2% (x = 0.30) at 318 K. © 2009 Elsevier B.V. All rights reserved.

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