Effect of Scandium on the Structure and Electrochemical Properties of La1-xScxNi3.5 Alloy Electrodes

Abstract

La-Sc-Ni based A 2 B 7 -type hydrogen storage alloys La 1-x Sc x Ni 3.5 (x = 0.0~1.0) is prepared by an arc furnace method and maintained for a week in a sealed stainless steel tube at 1173 K. XRD and SEM-EDS results show that the alloys are mainly consisted of LaNi 5 , La 2 Ni 7 and minor LaNi phases. Under appropriate amount of Sc addition (x = 0.3~0.5), the (La, Sc) 2 Ni 7 phase increases whereas the LaNi 5 and LaNi phases decreases. Moreover, the further increase of Sc content results in appearance of Sc 2 Ni 7 phase. The thermodynamic analyses show that the enthalpy change of La 0.7 Sc 0.3 Ni 3.5 -H 2 is more close to -7.5 kcal mol -1 for the La-Mg-Ni-H 2 system while the equilibrium absorption/desorption hydrogen pressure plateau of that is still higher than La-Mg-Ni systems, which indicate that the phase rule of Sc-containing alloy is different from Mg-containing alloy. Compared to pure La 2 Ni 7 alloy, the maximum discharge capacity increases and the cycle stability improves by adding the right amount of Sc content (x = 0.3~0.5). Especially when x = 0.5, the cycle stability (S 100 ) is up to 92.6% which is obviously superior to A 2 B 7 -type and AB 5 type hydrogen storage alloys. We hope that our experimental results can develop the novel La-Sc-Ni-based hydrogen storage alloys by tuning their superlattice structures.