Experimental probes of the molecular hydrogen-carbon nanotube interaction

Electrical transport (resistance R and thermoelectric power S), Raman scattering, and hydrogen adsorption are used to study the interaction of hydrogen molecules with ropes of single-walled carbon nanotubes. The data are consistent with H₂ physisorption under the experimental conditions investigated (4 K < T < 500 K; 0.1 atm < P < 20 atm). The response of S, R to 1atm hydrogen at 500 K is consistent with the introduction of a new scattering channel for electrons/holes in the metallic tubes. Raman scattering from the Q-branch of hydrogen molecules adsorbed on the surface is found shifted only by 1-2 cm^-1 from their frequencies in the free molecule and indicates that two different adsorption sites can be detected. Finally, H₂ wt% storage in heavily processed ropes of SWNTs are found to exceed 6% at ∼1 atm and T = 77 K and the isosteric heat of adsorption is found to be 120 meV.