Hydrogenation of Carbon Nanotubes

Owens and Iqbal [146] succeeded in an electrochemical hydrogenation of open-ended SWCNTs synthesized by CVD. Sheets of SWCNT bucky paper were used as the negative electrode in an electrochemical cell containing aqueous KOH solution as electrolyte. The authors claimed to have incorporated up to 6 wt. % of hydrogen into the tubes, determined by laser Raman IR spectroscopy and hydrogen release by thermolysis at 135 °C under TGA conditions [146], However, the stability of exohydrogenated carbon nanotubes and the low temperature of hydrogen release at 135 °C [146] is contradictory with the 400-500 °C reported elsewhere [79a, 145], 

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S. Pekker et al., Hydrogenation of carbon nanotubes and graphite in liquid ammonia. J. Phys. Chem. B 105, 7938 (2001)... 

Figure 3.69 Hydrogenation of carbon nanotubes. The theoreticai structure of a compieteiy hydrogenated nanotube is shown in the lower right corner.

Case - Use of Carbon Nanotube-Based Catalysts in Hydrogen Production... 

It should he mentioned that carbon nanotubes do not store more than 0.5 wt. % H2 at room temperature, although it was claimed earlier that much higher capacities can be obtained. The initial results of carbon nanotubes with 30-60 wt.% of stored hydrogen are now considered to have been an experimental error. 

Another technology being pursued in the search for high-capacity hydrogen storage media is that of carbon nanotubes. Since their discovery in 1991 by Sumio... 

The addition of carbon nanotubes that were either reactively milled under hydrogen mixed with Mg powder [142] or simply mixed with MgH and subsequently milled [143, 144] was investigated. In vacuum, desorption at 200°C gave 3.6 wt.% within 1,800 s [142]. Another reference reports 5 wt.%Hj desorbed at 300°C within... 

Q. Wang, J.K. Johnson, Optimization of carbon nanotube arrays for hydrogen adsorption. J. Phys. Chem. B, 103 (1999) 4809-4813. 

The main difference between carbon nanotubes and high surface area graphite is the curvature of the graphene sheets and the cavity inside the tube. In microporous solids with capillaries which have a width not exceeding a few molecular diameters, the potential fields from opposite walls will overlap so that the attractive force which acts upon adsorbate molecules will be increased in comparison with that on a flat carbon surface [16]. This phenomenon is the main motivation for the investigation of the interaction of hydrogen with carbon nanotubes (Figure 5.14). 

So far, direct evidence of C60 hydrogenation inside of nanotubes from HRTEM imaging is absent. It is required as a decisive demonstration of possibility for hydrogen to penetrate inside of peapods but could possibly be challenging experimentally. Chemical reaction within nanospace of carbon nanotubes is possibly only first example of interesting nanoscale chemistry and fullerene hydrogenation in other exotic environments will possibly be successfully demonstrated in future. It is quite likely that hydrogenation in confined space results in formation of fulleranes with different molecular structures. 

B.N. Khare et al., Functionalization of carbon nanotubes using atomic hydrogen from a glow discharge. Nano Lett. 2, 73 (2002)... 

In other similar structures, such as IRMOF-6 and IRMOF-8, the specific hydrogen uptake is approximately doubled and quadrupled, respectively, compared to MOF-5 at room temperature and 2.0MPa pressure [244], The hydrogen absorption capacity of these structures at room temperature is comparable to that of carbon nanotubes at cryogenic temperatures and can be fine-tuned by modifying the porosity of the structure with suitable linkers [244],... 

Gao, X.P., Qin, X., and Wu, F. (2000) Synthesis of carbon nanotubes by catalytic decomposition of methane using LaNi5 hydrogen storage alloy as a catalyst, Chem. Phys. Lett., 327, 271-276. 

Tibbets, G.G., Meisner, G.P. and Oik, Ch.H. (2001) Hydrogen storage capacity of carbon nanotubes, filamenta, and vapor-grown libers, Carbon 39, 2291-2301. 

Besides the traditional markets for carbon, some novel applications for the carbon produced via methane decomposition are discussed in the literature. Kvaemer has initiated R D program to investigate the potential of novel grades of carbon black as a storage medium for hydrogen, and as a feedstock for the production of solar grade silicone.35 The production of carbon nanotubes and nanofibers via solar thermal decomposition of methane over supported Co and Ni catalysts, respectively, was also reported.36... 

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