Nature of the bound states of molecular hydrogen in carbon nanohorns

NH aggregates

Background: TEM image of NH aggregates. Graph: H2-NH neutron spectrum; its characteristic line shape provides direct access to the energetics (rotational barrier) and geometry (quantization axis) of the H2 adsorbate.
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Hydrogen has great potential as an energy source.

Unlike fossil fuels, it can be generated from renewable sources. It is also non-polluting and forms water as a harmless by-product. Yet it is so difficult to store in a safe and cost-effective manner that its use as a fuel has been very limited. Carbon nanotubes (NT) have been considered for this task but, so far, their feeble interaction with molecular hydrogen (H2) has kept storage temperatures below a chilling -196 °C. Carbon nanohorns (NH), however, appear to offer some hope. NHs have an average length of 2-3 nm and aggregate to form beautiful dahlia-like structures (see figure). As a result, they display huge surface areas, approaching 1500 m2g-1 (that is, roughly the area of a football field in just a handful of this material!). High-resolution neutron spectroscopy experiments on Iris have provided quantitative insight about the adsorption of H2 in this novel form of carbon. A high density of conical ‘nanotips’ leads to solid-fluid interaction energies at least four times stronger than those found in NTs. Our results therefore suggest that NHs and related nanostructures can offer significantly better prospects as lightweight media for hydrogen storage applications.

F Fernandez-Alonso (ISIS), FJ Bermejo, C Cabrillo (CSIC, Spain), RO Loutfy (MER Corporation, USA), V Leon, and ML Saboungi (CNRS, France) 

Research date: December 2007

Further Information

F Fernandez-Alonso et al., Phys.Rev. Lett. 98 (2007) 215503

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