Hydrogen diffusion by substitution of aluminum and cobalt for a part of nickel in LaNi5-H alloy

Hydrogen diffusion in LaNi5-H, LaNi5−xAlx-H (x = 0.05, 0.12, 0.25, 0.5, 1) and LaNi5−yCoy-H (y = 0.25, 2) alloys has been studied by the desorption method with the help of measurements of the thermal desorption spectrum (TDS). The diffusion of hydrogen in LaNi5-H alloy is delayed owing to the trapping by lattice defects induced by hydrogenation and it can be concluded that trapping sites are mainly vacancies and vacancies clusters. For LaNi5−xAlx-H alloys, the temperature dependence of the hydrogen diffusivities in the range of x = 0.12-1 is much different from those at x = 0 and 0.05. On the other hand, the substitution of cobalt for a part of nickel in LaNi5 enhances the hydrogen diffusivity. These variations of the hydrogen diffusivities by the substitution of aluminum or cobalt depend on the number of sites occupied by hydrogen, the densities of trapping sites and the binding energy between a hydrogen atom and a trapping site.