Effects of absorption/desorption cycles on hydrogen storage properties of V and V0.9Cr0.1 alloy

Through mechanical alloying treatment for V and V0.9Cr0.1 alloy with small amount of LaNi5, the activation properties of the both materials were improved. After more than 100 absorption/desorption cycles followed by thorough desorption, both V and V0.9Cr0.1 still maintained the single bcc structure. During the cycling the absorption plateau pressures of V increased, the absorption capacities decreased under the same hydrogen pressure and the absorption kinetics declined, which could be attributed to the relaxation of the internal strain introduced by ball milling and the contraction of the cell volumes. SEM observation revealed that with increasing cycle, a large amount of deep cracks formed on the surface and in the inner of the samples, which are beneficial to the enhancement of the hydrogen desorption plateau pressures and the improvement of the desorption kinetics. V showed greater degradation rate of effective hydrogen desorption capacity than V0.9Cr0.1 because of more decreases of the lattice strain and bcc cell volumes of V than those of V0.9Cr0.1, which induced more sever decrease of absorption capacity of V after absorption/desorption cycle.