Effect Of The Partial Substitution Of Sm For La On The Structure And Electrochemical Properties Of La₁₅Fe₇₇B₈Type Hydrogen Storage Alloys

Fe77B8hydrogen storage alloys were prepared using a vacuum induction-quenching furnace. This paper studied the phase structure and the electrochemical performance of as-quenched and annealled La15-xSmxFe2Ni76Mn5B2(x=0,2,4,6) hydrogen storage alloy electrodes at room temperature (298K) and low temperature (233K) systematically.XRD and SEM analysis suggests that La15-xSmxFe2Ni76Mn5B2(x=0,2,4,6) alloys have multiphase structure including the main LaNi5phase, La3Ni13B2phase and (Fe, Ni) phase. After annealing treatment, the different amount of Sm in the alloy results in different phase composition. With the increasing substitution of Sm for La, the main phase structure of alloys has not change, while the unit cell volumes decreases, the cycle stability is improved and the maximum discharge capacity decreases. The maximum discharge capacity at low temperature is close to that at room temperature gradually with the increase of Sm/La ratio for alloy of the same substitution, which shows that the partial substitution of La by Sm is in favour of the low-temperature dischargeability (LTD) of La15Fe77B8hydrogen storage alloys. For the same substitution alloys, self-discharge characteristics and cycle stability at low temperature are better than that at room temperature. In addition, the maximum discharge capacity of the alloy electrodes increases significantly after annealing heat treatment. Furthermore, the high-rate dischargeability (HRD), the exchange current density I0and the limiting current density IL of the alloy electrodes first increase and then decrease with the increasing of Sm content, whereas the hydrogen diffusion coefficient D in alloy bulk decreases gradually, which indicate that appropriate substitution of Sm for La improves the electrochemical kinetics properties of the alloys. The HRD is mainly dominated by the charge-transfer rate on the alloy surface.