enhancing kinetic properties of magnesium hydride for hydrogen storage applications
Résumé
Magnesium hydride MgH2 is a non-naturally occurring compound that can be synthesized through direct hydrogenation of Mg metal which is abundant in nature, inexpensive, and non- toxic.
In the present work, we are trying to lower the hydrogen adsorption/desorption (A/D) temperature of MgH2 to a reasonable level to allow its widespread use as a viable hydrogen storage medium, while still keeping its advantages over other forms of storage, namely safety and economics. Nanosizing and catalysis are the parameters used to improve the kinetic properties of hydrogen (A/D) processes of MgH2.
Ball-milling process is applied in this study for MgH2 nanostructuring. The main goal of such approach is to raise the value of the specific area, which in turn may lead to a decrease in the energy needed to start desorbing the hydrogen content since the molecules which are at or close to the surface react more readily than those which are trapped deep inside particle agglomerates.
The analytical method used to follow the hydrogen desorption kinetics of the processed MgH2 samples is Temperature Programmed Desorption (TPD) via a Thermo-Fischer TPDRO 1100 apparatus. The fresh and ball-milled powders are characterized by using techniques such as XRD, XPS, SEM.
The results obtained show that freshly milled MgH2 sample presents improved properties with a H2 desorbing peak centered at 406°C against 417°C for the commercial powder. Interestingly the milled sample stored during two or three weeks desorb H2 at even lower temperatures but with multiple peaks which may indicate that during the storage of the ball-milled powder, small agglomerates begun to form thus impacting the particle size and distribution.