Modification And Hydrogen Storage Properties Of Carbon Nanotubes

Carbon nanotubes, which is a new hydrogen storage material, has attracted great attention of the world. Previous work on hydrogen storage in carbon nanotubes (CNTs) has been comprehensively reviewed. On the basis of previous work, the hydrogen storage capabilities of CNTs have been investigated systemically. First, the hydrogen storage capacities of single-walled carbon nanotubes(SWNTs) and multi-walled carbon nanotubes(MWNTs) were tested. Second, on the purpose of improving the hydrogen storage capabilities of CNTs, we ball-milled CNTs under different conditions, including: (1) CNTs were ball-milled at different time in different atmosphere(air, Ar, cyclohexane), and then their hydrogen storage capacities were investigated; (2) CNTs doped with different zeolites ( NaA or SBA-15 )were ball-milled at different time in different atmosphere, and then their hydrogen storage capacities were tested to analyse the influencing factors of different zeolites, atmosphere and ball-milling time; (3) we ball-milled CNTs first, and then doped with K⁺ in CNTs to improve their hydrogen storage capacities. By SEM, TEM and XRD, the morphology, micro-structure and the surface information of CNTs had been investigated. The results showed that:(1) SWNTs had greater hydrogen storage capacity than MWNTs. At 77K, 1.94MPa, the hydrogen storage capacity of SWNTs was 2.34wt.%. The hydrogen storage capacity of MWNTs was reversely proportional to the diameter. The maximum hydrogen storage capacity of MWNTs was 2.20wt.% at 77K, 1.94MPa.(2) The hydrogen storage capacity of ball-milled MWNTs was improved. Modification by ball-milling made shorter and tip-opening CNTs so that hydrogen could access more easily. CNTs ball-milled in different atmosphere for the same time, the hydrogen storage capacities were different, at 77K, 1.9MPa, hydrogoen storage capacities of SWNTs ball-milled in air, Ar, cyclohexane for 2 hours were 2.6wt.%, 2.55wt.%, 2.48wt.% respectively, the optimal time of MWNTs (10-20nm) in Ar was 6 hours, but in cyclohexane it was 8 hours. CNTs ball-milled at different time in the same atmosphere, the hydrogen storage capacities were different also, at 77K, 2.0MPa, hydrogen storage capacities of MWNTs(10-20nm) ball-milled in Ar for 2 hours, 4 hours, 6 hours were 1.68wt.%, 1.70wt.%, 1.73wt.% respectively.(3) The hydrogen storage capacities of ball-milled MWNTs mixed with zeolites NaA and SBA-15 were improved. It was better for MWNTs' hydrogen storage capacity when doped with SBA-15 than that doped with NaA. If ball-milling time was less than 6 hour, it was better to choose Ar as ball-milling atmosphere. For example, at 77K, 2.0MPa, the hydrogen storage capacity of MWNTs in NaA+MWNTs ball-milled in Ar for 4 hours was 1.79wt.%, but the hydrogen storage capacity of MWNTs in NaA+MWNTs ball-milled in cyclohexane for 4 hours was 1.67wt.%. If ball-milling time was more than 6 hour, it was better to choose cyclohexane as ball-milling atmosphere. It benefited for the improvement of MWNTs' hydrogen storage capacity to increase ball-milling time properly. At 77K, 2.0MPa, the hydrogen storage capacity of MWNTs in NaA+MWNTs ball-milled in cyclohexane for 2 hours was 1.55wt.%. But if for 8 hours, it was 2.06wt.%.(4) Hydrogen storage capacity of MWNTs doped with K⁺ was improved. Hydrogen storage capacity of MWNTs which was ball-milled first and then doped with K⁺ was greater. At 77K, 2.09MPa, the hydrogen storage capacity of MWNTs modified directly by K⁺ was 1.52wt.%. The hydrogen storage capacity of MWNTs which was ball-milled first and then doped with K⁺(stirred for 4h) was 1.57wt.%. The longer the ball-milled MWNTs stirred in KNO₃ solution, the greater the hydrogen storage capacity of MWNTs. At 77K, 2.09MPa, the hydrogen storage capacities of MWNTs stirred in KNO₃ solution for 12 hours was 1.68wt.%.