Characterization of hydrogen storage properties of Mg-Fe-CNT composites prepared by ball milling, hot-extrusion and severe plastic deformation methods

A systematic investigation was performed on the hydrogen storage properties of mechanically prepared 2MgFe/carbon nanotube (CNT) composites. The powders were transformed into bulk form by three processing routes (hot-extrusion, cold-rolling and extrusion followed by cold-rolling). The samples were kept in air to test their resistance to oxidation. Hydrogen absorption capacity and hydriding kinetics of the composites were dependent on the quantity of added CNTs. A 5 wt% addition of CNTs is optimum to facilitate the hydrogen absorption and desorption. Single cold-rolling (CR) was found to be the best route. Compared with powder composites, samples prepared by CR presented improved kinetics, the same hydrogen capacity and a decrease in the incubation time for activation. The cold-rolled composite 2MgFe/5 wt% CNTs achieved 73% of the theoretical capacity of Mg2FeH6, and desorbs almost the same quantity. Moreover, these absorption and desorption processes occur faster than in the powders.