NMR investigations of hydrogen in carbon nanotubes

We report on proton nuclear magnetic resonance ( 1 H-NMR) experiments on high-pressure hydrogen loaded single walled carbon nanotubes (SWNT). The temperature dependence of the spectral intensity reveals an adsorption process around 150 K with an activation energy of 5.6 kJ/mol. We discuss this behavior assuming various adsorption sites which can be attributed to the nanotubes and the catalyst used in the production process.