Hydrogen storage in carbon nanostructures

Carbon nanotubes have been known for more than 10 years. It is a challenge to fill their unique tubular structure with metals and gases. Especially, the absorption of hydrogen in single wall nanotubes has attracted many research groups worldwide. The values published for the quantity of hydrogen absorbed in nanostructured carbon materials varies between 0.4 and 67 mass%. With the assumption that the hydrogen condenses in the cavity of the nanotube or forms an adsorbed monolayer of hydrogen at the surface of the tube, the potential of nanotubes as a host material for hydrogen storage can be estimated. The hydrogen storage density due to condensed hydrogen in the cavity of the tube depends linearly on the tube diameter and starts at 1.5 mass% for a 0.671 nm single wall carbon nanotube. The surface adsorption of a monolayer of hydrogen leads to a maximum storage capacity of 3.3 mass%. We have investigated a large number of nanostructured carbon samples, i.e. high surface area graphite, single wall and multiwall nanotubes, by means of volumetric gas adsorption, galvanostatic charge/discharge experiments and temperature programmed desorption spectroscopy. The reversible hydrogen capacity of the carbon samples measured in an electrochemical half-cell at room temperature correlates with the specific surface area (BET) of the sample and is 1.5 mass%/1000 m2/g.