Thermodynamic properties and cyclic hydriding-dehydriding stability of LaNi5 thin films

Pressure-composition isotherms (P-C-T relations) for thin films LaNi5-H systems were measured volumetrically. The film samples were prepared by flash evaporation of LaNi5 powder. The deposited film had a very fine grain or amorphous-like structure and exhibited almost no temperature dependence of the isotherms whereas recrystallization of the film by annealing increased the maximum hydrogen storage capacity and the thermodynamic stability of the hydrided film. The first 10-20 hydriding-dehydriding reactions markedly increased the residual electrical resistance of the film sample and reduced the maximum hydrogen storage capacity by 60%. The reduction in hydrogen storage capacity during cycling may be attributed to the generation and accumulation of a high density of defects in the film caused by cyclic hydriding and dehydriding reactions.