SANS/USANS investigations of nanocrystalline MgH2 for reversible storage of hydrogen

Nanocrystalline magnesium hydride is considered to be one of the most promising alternatives for the reversible storage of hydrogen. In this work structural changes of high-energy ball-milled MgH x and MgH2/Cr2O3 with varying hydrogen content were investigated with small and ultra small-angle neutron scattering (SANS/USANS) using different milling parameters, e.g., milling time, vial and ball material, to obtain information about hydrogen sorption and desorption mechanisms. In a first attempt size distributions of spheres with radii from 1 nm up to 20 μm were calculated in order to characterize the influence of cycling history on the microstructure. Apparent changes of crystallite and particle structures due to hydrogen loading and unloading were found. The use of Cr2O3 nanoparticle additives result in distinct differences of the obtained scattering curves, which indicate that Cr2O3 not only has a catalytic function for the hydrogen sorption properties of MgH2 but also serves as an agent to breakup particles during the milling process. The results demonstrate the potential of the combination of SANS and USANS for structural characterization of nanocrystalline light-metal hydrides over the large size range of 1 nm up to 20 μm