ported by Dillon et al. [208]. These workers measured the hydrogen adsorption
capacity of the as-prepared SWNT bundles (0.1–0.2 wt.%) containing unidentified
carbonaceous materials as well as large fractions of cobalt catalyst particles (20
wt.%). Composition (H/C) versus pressure isotherms at 80 K (À197
C) of asprepared SWNTs, sonicated SWNTs and a high surface area carbon (Saran) are
reported by Ye et al. [207]. These workers find the hydrogen storage capacity in arcderived SWNTs to be 8.25 wt.% at 80 K and @4 MPa. A hydrogen storage capacity
of 4.2 wt.% for SWNTs was reported by Liu et al. [209] at 27
C and 10.1 MPa. The
SWNTs used in this study had a large mean diameter of 1.85 nm. Moreover, 78.3%
of the adsorbed hydrogen (3.3 wt.%) could be released under ambient pressure at
room temperature, while the release of the residual hydrogen (0.9%) required
heating of the sample. A comparative study of high-pressure hydrogen adsorption
experiments along with electrochemical hydrogen storage has been carried out by
Gundiah et al. on various carbon nanotube samples [210]. The carbon samples
that they used for hydrogen storage studies are as follows: SWNTs synthesized
by the arc-discharge method (as-synthesized), I; SWNTs synthesized by the arcdischarge method (treated with conc. HNO 3 ), II; MWNTs synthesized by the pyrolysis of acetylene (as-synthesized), III; MWNTs synthesized by the pyrolysis of
acetylene (treated with conc. HNO 3 ), IV; MWNTs synthesized by the arc-discharge
method, V; aligned MWNT bundles synthesized by the pyrolysis of ferrocene (assynthesized), VI; aligned MWNT bundles synthesized by the pyrolysis of ferrocene
(treated with acid), VII; aligned MWNT bundles synthesized by the pyrolysis of
ferrocene and acetylene (as-synthesized), VIII; and aligned MWNT bundles synthesized by the pyrolysis of ferrocene and acetylene (treated with acid), IX. Figure
8.18(a), shows the plots of hydrogen adsorption versus time for the various carbon nanostructured samples studied by them. By eliminating most of the common errors encountered in these experiments, they achieved a maximum storage
capacity of 3.75 wt.% (143 bar, 27
C) in the case of densely aligned nanotubes,
prepared by the pyrolysis of ferrocene–hydrocarbon mixtures. SWNTs and MWNTs
(arc-generated) showed a high-pressure hydrogen storage capacity, which is much
less than 3 wt.%. In Figure 8.18(b) we show the plots of electrochemical charging capacity of various types of carbon nanotubes. Electrodes made out of
aligned MWNTs, clearly demonstrate higher electrochemical charging capacities
up to 1100 mA h g
À1 which correspond to a hydrogen storage capacity of 3.75
wt.%. SWNTs and MWNTs (arc-generated), however, show capacity in the range
2–3 wt.%.
8.3
Inorganic Nanotubes
8.3.1
Preliminaries
Several layered inorganic compounds possess structures comparable to the structure of graphite, the metal dichalcogenides (sulfides, selenides, and tellurides),
8.3 Inorganic Nanotubes 239
capacity of the as-prepared SWNT bundles (0.1–0.2 wt.%) containing unidentified
carbonaceous materials as well as large fractions of cobalt catalyst particles (20
wt.%). Composition (H/C) versus pressure isotherms at 80 K (À197
C) of asprepared SWNTs, sonicated SWNTs and a high surface area carbon (Saran) are
reported by Ye et al. [207]. These workers find the hydrogen storage capacity in arcderived SWNTs to be 8.25 wt.% at 80 K and @4 MPa. A hydrogen storage capacity
of 4.2 wt.% for SWNTs was reported by Liu et al. [209] at 27
C and 10.1 MPa. The
SWNTs used in this study had a large mean diameter of 1.85 nm. Moreover, 78.3%
of the adsorbed hydrogen (3.3 wt.%) could be released under ambient pressure at
room temperature, while the release of the residual hydrogen (0.9%) required
heating of the sample. A comparative study of high-pressure hydrogen adsorption
experiments along with electrochemical hydrogen storage has been carried out by
Gundiah et al. on various carbon nanotube samples [210]. The carbon samples
that they used for hydrogen storage studies are as follows: SWNTs synthesized
by the arc-discharge method (as-synthesized), I; SWNTs synthesized by the arcdischarge method (treated with conc. HNO 3 ), II; MWNTs synthesized by the pyrolysis of acetylene (as-synthesized), III; MWNTs synthesized by the pyrolysis of
acetylene (treated with conc. HNO 3 ), IV; MWNTs synthesized by the arc-discharge
method, V; aligned MWNT bundles synthesized by the pyrolysis of ferrocene (assynthesized), VI; aligned MWNT bundles synthesized by the pyrolysis of ferrocene
(treated with acid), VII; aligned MWNT bundles synthesized by the pyrolysis of
ferrocene and acetylene (as-synthesized), VIII; and aligned MWNT bundles synthesized by the pyrolysis of ferrocene and acetylene (treated with acid), IX. Figure
8.18(a), shows the plots of hydrogen adsorption versus time for the various carbon nanostructured samples studied by them. By eliminating most of the common errors encountered in these experiments, they achieved a maximum storage
capacity of 3.75 wt.% (143 bar, 27
C) in the case of densely aligned nanotubes,
prepared by the pyrolysis of ferrocene–hydrocarbon mixtures. SWNTs and MWNTs
(arc-generated) showed a high-pressure hydrogen storage capacity, which is much
less than 3 wt.%. In Figure 8.18(b) we show the plots of electrochemical charging capacity of various types of carbon nanotubes. Electrodes made out of
aligned MWNTs, clearly demonstrate higher electrochemical charging capacities
up to 1100 mA h g
À1 which correspond to a hydrogen storage capacity of 3.75
wt.%. SWNTs and MWNTs (arc-generated), however, show capacity in the range
2–3 wt.%.
8.3
Inorganic Nanotubes
8.3.1
Preliminaries
Several layered inorganic compounds possess structures comparable to the structure of graphite, the metal dichalcogenides (sulfides, selenides, and tellurides),
8.3 Inorganic Nanotubes 239