Hydrogen, after all, is a gas at room temperature, and is also flammable. Some experts argue that physical storage, as a compressed gas or in liquefied form, is the best solution. Others advocate chemical storage of hydrogen, in such fuels as methanol or cleaner petrol. Both approaches would require expensive investments in fuel infrastructure. A growing number of scientists now believe that carbon structures, called nanotubes and nanofibres, could provide a clean and efficient way to store hydrogen.
Nobody really knows why carbon nanomaterials are good at storing hydrogen.
Michael Heben of America's National Renewable Energy Laboratory, a pioneer in the field, believes that it is something to do with the structure of the nanomaterials' surfaces. Molecules of the gas seem to fit into pores in these surfaces, though exactly why they prefer some pores over others is unclear. Her results met with widespread scepticism, for she has refused to reveal exactly how she synthesised the material. She and Terry Baker, her husband and collaborator at Northeastern University, insist that they need to keep the process secret for commercial reasons. Other experts, many of whom turned up to the MRS conference last week, have been openly critical of the Northeastern researchers, who stayed away.