The activation and hydrogen storage characteristics of the cup-stacked carbon nanotubes

In this study, the cup-stacked carbon nanotubes (CSCNTs) are chemically modified and used for the hydrogen storage for the first time. The SEM and TEM analyses indicate that because they are formed by the stacking of the truncated conical graphene layers the inner- and outer-edges of which are completely exposed, during KOH activation the catalyst particles at the tips of them can be removed completely. The graphene layers of them are exfoliated seriously to form plenty of microcavities. Moreover, many nanosized straight caves and through-holes are formed in the walls of them. As a result, the micropore volume of them increases twelve times and the maximum hydrogen adsorption capacity of them reaches over ten times that of the pristine CSCNTs. These increases exceed the reported data for the conventional coaxial CNTs activated by the same method. Our findings indicate that due to the special graphene layer stacking mode, the micropore structure of CSCNTs can be improved more significantly than the conventional CNTs during KOH activation. They may be a kind of promising carbon nanotube for hydrogen storage.