The influence of Cu(OH)2 addition on the low-temperature electrochemical performance of La0.75Mg0.25Ni3.5 hydrogen storage alloy

The influence of Cu(OH)(2) addition in 7 mol/L KOH alkaline electrolyte on the electrochemical properties of La0.75Mg0.25Ni3.5 hydrogen storage alloy electrode was investigated in the testing temperature range of from 25 degrees C to -40 degrees C in this paper. XRD Rietveld analyses shows that the La0.75Mg0.25Ni3.5 hydrogen storage alloy consists of LaNi5 phase, (La, Mg)(2)Ni-7 phase and (La, Mg)Ni-3 phase. The maximum discharge capacity and the high-rate dischargeability (HRD) of the La-0.75 Mg0.25Ni3.5 alloy electrode both decrease with decreasing testing temperature, which mainly due to the slower hydrogen transfer in the bulk of the alloy and the lower electrocatalytic activity at lower temperatures. The scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS) analyses indicate that, with the addition of Cu(OH)(2) to the KOH alkaline electrolyte, fine particles of metal Cu can be coated on the La0.75Mg0.25Ni3.5 alloy electrode surface during charging process by electrodeposition. The Cu powders deposited on the La0.75Mg0.25Ni3.5 alloy electrode can improve the alloy's low-temperature discharge properties by decreasing its charge-transfer resistance and increasing its exchange current density. The cyclic stability of the Cu-deposited La0.75Mg0.25Ni3.5 alloy electrode can be also improved to a certain extent by increasing its corrosive resistance in KOH alkaline electrolyte. (C) 2008 Elsevier Ltd. All rights reserved.