Microstructure and electrochemical investigations of La_(0.76-x)Ce_xMg_(0.24)Ni_(3.15)Co_(0.245)Al_(0.105) (x = 0, 0.05, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys

摘要

The effects of substitution of Ce for La on the microstructure and electrochemical performance of La_(0.76-x)Ce_xMg_(0.24)Ni_(3.15)Co_(0.245)Al_(0.105) (x = 0, 0.05, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys were investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analyses showed that the main phases of the alloys consist of (La, Mg)Ni_3 phase (PuNi_3-type rhombohedral structure), LaNi_5 phase (CaCu_5-type hexagonal structure) and (La, Mg)_2Ni_7 phase (Ce_2Ni_7-type hexagonal structure). The cell volume of the (La, Mg)Ni_3 phase, (La, Mg)_2Ni_7 phase and LaNi_5 phase decreased monotonously with increasing Ce content. Electrochemical investigations showed a decrease in the discharge capacity, while high rate dischargeability (HRD) first increased and then decreased with increasing Ce content. The Ce substitution for La slightly enhanced the cyclic stability of the alloy electrodes. The pressure-composition (P-C) isotherms showed that the plateau region was broadened with Ce content increased in the alloys, meanwhile, two plateaus appeared and pressure of the hydrogen absorption and desorption increased accordingly.