Scientists have devised a scheme that could liberate hydrogen on demand from water to power a car.
The scheme was developed by Tareq Abu-Hamed, now at the University of Minnesota, together with his colleagues at the Weizmann Institute of Science in Rehovot, Israel, according to the latest issue of New Scientist.
By reacting water with the element boron, the system produces hydrogen that can be burnt in an internal combustion engine or fed to a fuel cell to generate electricity, the scientists said.
"The aim is to produce hydrogen on-board at a rate matching the demand of the car engine," Abu-Hamed was quoted as saying.
The hydrogen-on-demand approach is based on simple high-school chemistry, according to the scientists who said elements like sodium and potassium are well-known for their violent reactions with water, tearing hydrogen from its stable union with oxygen. Boron does the same, but at a more manageable pace as it requires no special containment because when all the boron is used up, the only by-product, boron oxide, can be removed from the car, turned back into boron, and used again.
To kick-start the reaction, the scientists said, the water has to be supplied as vapor heated to several hundred degrees, so the car will still require some start-up power, possibly from a battery. Once the engine is running, the heat generated by the highly exothermic oxidation reaction between boron and water could be used to warm the incoming water.
Alternatively, small amounts of hydrogen could be diverted from the engine and stored for use as the start-up fuel. Water produced when the hydrogen is burnt in an internal combustion engine or reacted in a fuel cell could be captured and cycled back to the vehicle's tank, making the whole on-board system truly zero-emission.
The team calculates that a car would have to carry just 18 kg of boron and 45 liters of water to produce 5 kg of hydrogen, which has the same energy content as a 40-liter tank of conventional fuel.
An Israeli company has begun designing a prototype engine which works in the same way, the science magazine reported.