Thermoelectric study of hydrogen storage in carbon nanotubes

In situ resistivity $\left(\rho \right)$ and thermoelectric power (S) have been used to study the nature of the adsorption of hydrogen in bundles of single-walled carbon nanotubes for ${\mathrm{H}}_2$ pressure $P<~1$ atm and temperatures $77\hspace{0.5em}\mathrm{K}<T<\mathrm{}500\mathrm{}\hspace{0.5em}\mathrm{K}.$ Isothermal plots of S vs $\Delta \rho /{\rho }_0$ are found to exhibit linear behavior as a function of gas coverage, consistent with a physisorption process. Studies of S, $\rho$ at $T=500\mathrm{}\hspace{0.5em}\mathrm{K}$ as a function of pressure exhibit a plateau at a pressure $P\sim 40$ Torr, the same pressure where the H wt. % measurements suggest the highest binding energy sites are being saturated. The effects of ${\mathrm{H}}_2$ exposure at 500 K on the thermoelectric transport properties are fully reversible.