Effects of CNTs on the hydrogen storage properties of MgH_2 and MgH_2-BCC composite

摘要

MgH_2 with 10 wt.% Ti_(0.4)Mn_(0.22)Cr_(0.1)V_(0.28) alloy (termed the BCC alloy for its body centred cubic structure) and 5 wt.% carbon nanotubes (CNTs) were prepared by planetary ball milling, and its hydrogen storage properties were compared with those of the pure MgH_2 and the binary mixture of MgH_2 and the BCC alloy. The sample with CNTs showed considerable improvement in hydrogen sorption properties. Its temperature of desorption was 125 ℃ lower than for the pure sample and 59 ℃ lower than for the binary mixture. In addition, the gravimetric capacity of the ternary sample was 6 wt.% at 300 ℃ and 5.6 wt.% at 250 ℃, and it absorbed 90% of this amount at 150 s and 516 s at 300 ℃ and 250 ℃, respectively. It can be hypothesised from the results that the BCC alloy assists the dissociation of hydrogen molecules into hydrogen atoms and also promotes hydrogen pumping into the Mg/BCC interfaces, while the CNTs facilitate access of H-atoms into the interior of Mg grains.