Calculations of hydrogen coverage on single-walled carbon nanotubes: Dependence on nanotube size, temperature, and pressure

We have investigated the stability of various hydrogenated single-walled carbon nanotubes. We find that the storage capacity of hydrogen depends significantly on the diameters of carbon nanotubes. Full hydrogen coverage can be reached for nanotubes with small size, while for nanotubes with large size, the saturation coverage is lower than 1. We have calculated the variation of the hydrogen coverage with the change of temperature and pressure. In particular, we find that nanotubes with diameters of about $1\mathrm{nm}$ can achieve a coverage of 80% at ambient temperature and low pressure, which is in agreement with the experimental results.

Figure 1

The sites for the adsorption of hydrogen atoms on the walls of carbon nanotubes.

Figure 2

(a) The intercalation energies of various structures of the hydrogenated (8,0) tube. (b) The intercalation energies of the stable structures of the hydrogenated carbon nanotubes with different diameters and chiralities.

Figure 3

The phase diagram of coverage vs chemical potential. Different symbols in the curves are used to distinguish the tubes.

Figure 4

The phase diagram of coverage vs temperature at the pressure of $1\times {10}^{-9}\text{Torr}$. Different symbols in the curves are used to distinguish the tubes.

Figure 5

The phase diagram of coverage vs the logarithm of pressure at the temperature of $300\mathrm{K}$. The unit of pressure is pascal. Different symbols in the curves are used to distinguish the tubes.