Effect of hydrogen cycling on the hydrogen storage properties of MmNi(4.2)Al(0.8)

The effect of cycling on the hydrogen storage properties (storage capacity, plateau pressures, hysteresis and desorption kinetics) of MmNi(4.2)Al(0.8) was investigated. The pressure-composition (PC) isotherms for hydriding/de hydriding and desorption kinetics were measured at 288, 298 and 308 K, both after initial activation and 1000 absorption-desorption cycles. The storag e capacity, plateau pressures and desorption kinetics remained almost uncha nged 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 b roader (0.5-90 mu m) compared to that after initial activation (5-90 mu m). The relative stability of MmNi(4.2)Al(0.8) over 1000 cycles has been expla ined by considering the absence of impurities, disintegration of sample and crystal structure. (C) 1999 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.