Effect of ball-milling duration and dehydrogenation on the morphology, microstructure and catalyst dispersion in Ni-catalyzed MgH2 hydrogen storage materials

The effects of high-energy ball-milling on catalyst morphology and dispersion as a function of milling duration and on hydrogen desorption were investigated. Samples of MgH2 doped with 0.05 Ni catalyst were examined after 1, 5 and 10 h of milling. Longer milling durations produced finer catalyst particle sizes and more uniform dispersions, but yielded higher hydrogen desorption temperatures. This behavior is attributed to the formation of Mg2NiH4 with increased milling times. Electron tomography was used to show that the Ni particles reside both inside and outside the MgH2 particles. On dehydrogenation there was a redistribution of catalyst and continued formation of Mg2Ni. The formation of this phase is proposed to explain the reported degradation of hydrogen capacity and the change in kinetics of this system with cycling.