Study on self-discharge property of Nd_(0.88)Mg_(0.12)Ni_(3.1o+x)Al_(0.20) (x = 0.00,0.10, 0.20, 0.30) hydrogen storage alloys

摘要

Nd_(0.88)Mg_(0.12)Ni_(3.1o+x)Al_(0.20) (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 Nd_2Ni_7 phase, NdNi_5 phase and some minor impurity NdNi_2 phase. The FESEM observed that some white and acic-ular 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 I_(corr) 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.