INTRINSIC DEGRADATION OF LANI5 BY THE TEMPERATURE INDUCED HYDROGEN ABSORPTION-DESORPTION CYCLING

The temperature induced hydrogen absorption-desorption cycling of LaNi5 intermetallic compound was performed to study the intrinsic degradation mechanism. The degradation and annealing behavior of LaNi5 were investigated using the following: (i) the change in the P-C-isotherm curves, (ii) X-ray diffraction, (iii) DSC (Differential Scanning Calorimeter) and (iv) the hydrogen desorption analysis using GC (Gas Chromatography). The hydrogen storage capacity was reduced by 87% of the activated sample after 3150 cycles and the plateau region disappeared. Most of the degraded properties were considerably recovered by annealing treatment. It is found that most of the fully degraded LaNi5 phase is decomposed into Ni cluster and La-Ni hydrides. As a result of annealing, LaNiH3.6 and the Ni cluster recombined to form LaNi5. Thus the intrinsic degradation due to thermal cyclings might be caused by the formation of stable hydrides.