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Figure 6. TGA profile of reversible H2 sorption-desorption cycle on Li-doped CNT. The sample was cooled to 300 K, and then heated again to 873 K. Reprinted with permission from [64], P. Chen et al., Science 285, 91 (1999). © 1999, American Association for the Advancement of Science.

Yang prepared alkali-doped carbon nanotubes according to the method prescribed in the work of Chen et al. [64]. Nevertheless, ultrahigh-purity hydrogen (99.999%, with moisture trap) was used to conduct the adsorption measurements on Li-doped SWNT (Fig. 7). The results of hydrogen adsorption with added water (2.3 vol%) was also obtained to compare with the results of dry hydrogen adsorption (Fig. 8). Furthermore, calibration runs were made under the same conditions to calibrate the weight gains/losses [65]. The similar qualitative features of the result of Chen et al. [64] were reproduced over Li/nanotubes; however, the total weight differential was only 2.5%, rather than 20% reported by Chen et al. The essential qualitative feature of the TGA profile was still maintained with moisture addition, and the total weight differential in wet H2 was substantially greater, at 12%, compared to 2.5% in dry H2. The weight gains reached 1.8 and 21% over K/nanotubes in dry or wet H2, respectively, compared to 14% reported by Chen et al.

Yang also reported the IR spectrum of LiOH (with one hydrate), and a striking similarity existed between this spectrum and that of Chen et al. This shows that the alkali hydroxide and additional hydrates may form. The weight gains by forming hydroxides (plus hydrates) agreed well with the total weight gains reported by Chen et al. Although Chen et al. did not find the emergence of water in the desorption product using TPD, the work of Yang showed that the TGA measurements strongly depended on the concentration and rate of supply of moisture.

Pinkerton et al. [66] made further investigations on doped CNTs. The results indicate that, on Li-doped CNTs, neither hydrogen nor carbon is required to generate the qualified

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