Dual quartz crystal microbalance for hydrogen storage in carbon nanotubes

Hydrogen storage in single-walled carbon nanotubes (SWCNTs) was investigated by using a dual quartz-crystal microbalance (QCM). The chamber pressure can be adjusted from 10^{- 9} torr up to 1 MPa. The dual QCM decreases the frequency fluctuations that originate from environmental variables such as temperature and pressure. Our moisture-free chamber enables us to measure accurately the hydrogen storage capacity in carbon nanotubes. Highly purified SWCNTs store about 0.2 wt% of hydrogen at room temperature under 0.5 MPa through physical adsorption. Our SWCNTs without baking adsorb up to 1 wt% of water, often obscuring the hydrogen storage capacity. Our results suggest that the hydrogen storage capacity relies strongly on the functional groups remaining on the SWCNTs which may enhance the storage capacity.