The effect of thermal cycling of $LaNi_5$ and $LaNi_{4.7}Al_{0.3}$ system on intrinsic degradation were investigated.
The change of pressure-composition-isotherm of $LaNi_5$ by thermal cycling was investigated to study the degradation process. The hydrogen storage capacity was decreased about 62% after 3500 cycles, the slope of plateau was increased, the hysteresis was enlarged to the whole composition range with the number of increasing cycles and plateau split in desorption stage was found for the thermal cycles, from 303 to 458K.
The effect of annealing conditions on the recovery of $LaNi_5$ was found that the degree of recovery was dependent on annealing temperature at 1 atm hydrogen pressure and for 3 hours.
The degradation rate by thermal cycling was increased after the heat treatment.
With the results of these experiments, the degradation phenomena was interpreted in view of surface segregation, particle size and structure reordering.
