TANKING up on alcohol could soon take on a whole new meaning. A compact reactor that makes hydrogen from alcohol could allow electric cars to run cleanly on hydrogen-powered fuel cells without needing high-pressure fuel tanks to carry the gas. Instead, they could use an ordinary fuel tank holding a mixture of ethanol and water.
The technology could also abolish the need for another problematic feature of the hydrogen economy 鈥� filling stations storing vast quantities of highly combustible hydrogen. This idea has already faced resistance. In Hornchurch, Essex in the UK, for instance, a trial fuel cell-powered bus service is being forced to bring in hydrogen by tanker after residents objected to plans for a hydrogen filling station.
The system developed by Lanny Schmidt and his colleagues at the University of Minnesota, Twin Cities, may change the way fuel cell vehicles are powered. Their prototype reactor 鈥� about 10 centimetres long and 2 cm in diameter 鈥� makes hydrogen for the car as it is needed. Industrial reactors that do this are much bulkier.
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The conversion of alcohol (ethanol) into hydrogen in the reactor is a two-stage process. First, a mixture of ethanol, water and air is injected into a reaction chamber and heated to 140 掳C to vaporise both components (Science, vol 303, p 993). The gases pass over a rhodium and cerium oxide catalyst that breaks up the ethanol to produce hydrogen, carbon monoxide and carbon dioxide. This also liberates heat, increasing the temperature to 700 掳C and speeding up the reaction. Some of the excess heat can also be used to heat incoming gases.
The mixture then passes along the reactor to a chamber where it is cooled to 400 掳C and passes over a platinum and cerium oxide catalyst. There the carbon monoxide reacts with the hot water vapour to produce carbon dioxide and hydrogen. 鈥淎bout 50 per cent of the gas emerging from the reactor is hydrogen,鈥� says Schmidt.
鈥淭hey have made a breakthrough in cutting the volume of the reactor,鈥� says Heather Haydock of the renewable energy specialist Future Energy Solutions, part of AEA Technology in Harwell, Oxfordshire, UK.
Schmidt says that fermenting surplus crops such as maize or potatoes could provide ethanol for the new reactor. Schmidt calculates that the cost of producing hydrogen this way would be similar to the cost of producing petrol, and the raw materials would all be renewable. But Haydock warns that relying on farm surpluses will make the price of hydrogen vary with harvests.
Liquid methanol is another option for powering fuel cells in cars, but as it is mainly made from the methane in natural gas it is not a renewable resource.
Although cars are an obvious target for the technology, generating electricity in places that do not have a mains supply could be an important market for it, too. Indeed, Schmidt thinks the first commercial product to use his technology could easily be fuel cells generating electricity. 鈥淐hina and India have lots of cheap agricultural produce. It鈥檚 so easy to build a fermentation plant,鈥� he says.
