Hydrogen absorption/desorption properties of MmNi4.5Cr0.5−xZrx alloys

Hydrogen absorption/desorption properties of MmNi4.5Cr0.5−xZrx alloys (x = 0, 0.05, 0.1) were investigated in the present work. The Pressure-Composition (PC) isotherms and absorption kinetics were measured in the temperature range of 273 ≤ T ≤ 303 K by the volumetric method. XRD patterns showed that the as-annealed MmNi4.5Cr0.5−xZrx alloys had CaCu5 type hexagonal structure and could keep the same single phase after 16 cycles of absorption/desorption. It was found that with the increase of x in MmNi4.5Cr0.5−xZrx alloys, the dissociation plateau pressure increased, the hysteresis was diminished, the hydrogen uptake capacity was reduced and the absorption kinetics was improved. The absorption plateau pressure increased when x was increased to 0.05, but decreased when x increased to 0.1. It was also found that the dissociation plateau pressure increased linearly with increasing cell volume V and the lattice parameter a, and the hydrogen uptake capacity decreased linearly with increasing Zr content.