Microstructure and hydrogen storage property of Mg/MWNTs composites

Abstract

The Mg-x wt.% multi-walled nanotubes (MWNTs) (x=5, 20) composites were made by catalytic reacting ball-milling under the hydrogen atmosphere. Their microstructures were characterized by using XRD and TEM-SAED techniques. The absorption/desorption kinetics for Mg/MWNTs were examined by taking the hydriding/dehydriding apparatus. It was found that under 2.0 MPa hydrogen pressure, the maximum hydrogen storage capacities of the composites were both very low and similar at 298 K; at 373, 473 and 553 K, the maximum hydrogen storage capacities of Mg-5 wt.% MWNTs were 5.34, 5.89 and 6.08 wt.%, respectively; but only 2.11, 2.68 and 2.75 wt.% for Mg-20 wt.% MWNTs. Compared with other hydrogen storage composite materials, the Mg-5 wt.% MWNTs not only keeps the maximum hydrogen storage capacities better but also has good hydrogen absorption/desorption rates. It absorbed 4.27, 4.86 wt.% (80% maximum hydrogen storage capacity) within 15 and 1 min at 373 and 553 K under 2.0 MPa, while it desorbed 3.62 wt.% within 30 min at 473 K in vacuum. The carbon component (the broken MWNTs) in the composite may play an important role in the hydrogen uptake and release. A favorable discussion was given in this paper.