Effect of hydrogen cycling on the hydrogen storage properties of MmNi4.2Al0.8

The effect of cycling on the hydrogen storage properties (storage capacity, plateau pressures, hysteresis and desorption kinetics) of MmNi4.2Al0.8 was investigated. The pressure-composition (PC) isotherms for hydriding/dehydriding and desorption kinetics were measured at 288, 298 and 308 K, both after initial activation and 1000 absorption–desorption cycles. The storage capacity, plateau pressures and desorption kinetics remained almost unchanged over 1000 cycles, whereas a minor increase was observed in hysteresis loss at 298 and 308 K after 1000 cycles. Cycling resulted in disintegration of the bulk sample. The particle size distribution after 1000 cycles was broader (0.5–90 μm) compared to that after initial activation (5–90 μm). The relative stability of MmNi4.2Al0.8 over 1000 cycles has been explained by considering the absence of impurities, disintegration of sample and crystal structure.