Ball milled MgH<inf>2</inf> + 5% wt. M (M=Fe and Fe<inf>F</inf>3) nanocomposites for improving hydrogen storage

Abstract

Magnesium hydride ball milled nanocomposites was prepared separately using vibratory and planetary ball milling devices under argon atmosphere, mixing with 5%wt. Fe and FeF3 to improve the kinetics of H-sorption without reducing the high hydrogen storage capacity. Morphology, structural and thermal characterization of the MgH2 composites was performed using XRD, SEM and simultaneous TG and DSC techniques. The X-ray diffraction patterns reveal the presence of mainly tetragonal beta-MgH2 , Fe, FeF3 and some peaks of meta-stable gamma-MgH2. The peaks intensity of the gamma-MgH2 phase increases and the peak intensities of Fe and FeF3 decrease when increasing milling time, indicates physical and chemical transformations of MgH2 and the catalysts during the milling process. The magnesium hydride milled with the catalyst release hydrogen in two stages, which occurs in different temperatures, depending on the catalysts, type of milling devices and duration of milling. MgH2 develops uniform distribution and similar microstructures when it mixes with the catalyst during the vibratory milling process. The catalyst powders are broken up to the fine particles during the planetary milling and are well distributed over the MgH2 matrix. Electrochemical study of hydrogen charge-discharge process in MgH2 provides distinct information on thermodynamic and kinetics of the MgH2-catalyst system. The potentials of the absorption and desorption were showed a good reversibility, indicating the product was significantly activated due to the catalytic effects.