Experimental probes of the molecular hydrogen–carbon nanotube interaction

Abstract

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 H 2 physisorption under the experimental conditions investigated (4 K< T<500 K; 0.1 atm< P<20 atm). The response of S, R to 1 atm 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, H 2 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.