Abstract

The effect of extended H₂ sorption cycles on the structure and on the hydrogen storage performances of MgH₂ powders with 5 wt% of Fe particle catalyst is reported. MgH₂ powders with and without Fe have been ball milled under Argon, the doped MgH₂ nanocomposite has been cycled under hydrogen pressure up to a maximum of 47 desorption and absorption cycles at 300 °C. After acceleration during the first 10 cycles, the kinetics behavior of doped MgH₂ is constant after extended cycling, in terms of maximum storage capacity and rate of sorption. The major effect of cycling on particle morphology is the progressive extraction of Mg from the MgO shell surrounding the powder particles. The Mg extraction from the MgO shell leaves the catalyst particles inside the hydride particles. Many empty MgO shells are observed in the pure ball milled MgH₂ upon cycling at higher temperature, suggesting that this enhancement of the extraction efficiency is related to the higher operating temperature which favors Mg diffusivity with respect to the H ion one. View Full-Text