Tiny, highly porous carbon nanohorns could be the answer to the tricky problem of storing gaseous fuels for any future hydrogen economy.
Carbon nanotubes have previously been suggested as an answer to the headache of storing hydrogen in fuel cells in cars or aeroplanes. Nanotubes are light and highly porous making them good candidates for storage but have a major drawback in that the interaction between the nanotube and the hydrogen is very weak. This means that the hydrogen must be stored at very low temperatures to keep it liquid.
A group of French, Spanish and UK researchers compared carbon nanohorns’ capacity for holding hydrogen with that of nanotubes. Nanohorns are similar in structure to carbon nanotubes but flare like a trumpet making the structure more open at one end. The group found that the carbon nanohorns interacted far more strongly with hydrogen than nanotubes (Physical Review Letters 2007, 98, 215503).
Researcher Marie-Louise Saboungi said that there is much greater interaction between the hydrogen and carbon atoms in the nanohorn as the tips of these structures are quite narrow. Quantum effects also add to the stabilising effect. Saboungi said: ‘Realistic storage temperatures are two to three times higher for nanohorns versus nanotubes,’ but that further studies are needed to confirm this. This increase in temperature would make storage more economically viable as it substantially reduces the need for cooling.
Hydrogen has an excellent energy density by weight making it a good replacement for fossil fuels with the added bonus that burning it produces only water as a by-product. However, a number of challenges remain, including establishing an environmentally-friendly, economical method of obtaining hydrogen and creating a hydrogen infrastructure so that motorists can buy hydrogen for their cars.
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