Influence of aluminum location on hydrogen sorption kinetics of magnesium-based materials

Abstract

Hydrogen storage materials from Mg – Al alloy and Mg + Al mixture were prepared by reactive milling under H 2 atmosphere with carbonized anthracite as milling aid. The crystal structure of the materials and influence of Al location on hydrogen absorption/desorption kinetics were investigated. Results show that Mg partly got hydrided into β- MgH 2 and γ- MgH 2 during reactive milling. The average crystallite sizes of β- MgH 2 in the as-milled Mg – Al alloy and Mg + Al mixture were calculated by Scherrer equation to be 10 nm and 17 nm, respectively. In the process of hydrogen desorption, the catalytic ability of Al in Mg crystal lattice was not as effective as that on particle surface. The apparent activation energies for hydrogen desorption of the two materials were estimated by Kissinger equation to be 112.2 kJ/mol and 63.7 kJ/mol, respectively. Mg 17 Al 12 reacted with H 2 to convert into MgH 2 and elemental Al during static hydrogenation at 300°C. For the hydrogenated Mg + Al mixture, the obvious increase of crystallite size resulted in a low rate of hydrogen absorption and a high temperature for hydrogen desorption.