Thermoelectric study of hydrogen storage in carbon nanotubes

Abstract

In situ resistivity $(\ensuremath{\rho})$ 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 $77 \mathrm{K}<T<500 \mathrm{K}.$ Isothermal plots of S vs $\ensuremath{\Delta}\ensuremath{\rho}/{\ensuremath{\rho}}_{0}$ are found to exhibit linear behavior as a function of gas coverage, consistent with a physisorption process. Studies of S, $\ensuremath{\rho}$ at $T=500 \mathrm{K}$ as a function of pressure exhibit a plateau at a pressure $P\ensuremath{\sim}40$ 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.