NMR spectroscopy of hydrogen adsorption on single-walled carbon nanotubes after exposure to high pressure.

Hydrogen storage properties of single-walled carbon nanotubes (CNTs) after exposure to a pressure of 14.3 MPa are studied by (1)H nuclear magnetic resonance spectroscopy. The nanotubes were carefully pre-characterized using inductively coupled plasma mass spectrometry (ICP-MS), transmission electron microscopy (TEM), and Raman spectroscopy. We have shown previously that at ambient temperature in the pressure range from 0 to 1.5 MPa, hydrogen adsorption is fast and reversible and must be described as physisorption. However, exposure to a much higher pressure (14.3 MPa) of hydrogen leads to slower desorption kinetics where longer exposure causes greater hydrogen uptake. Our data suggest that interstitial sites and the tube interior may be identified as these strong adsorption sites.