Scientists have made the first renewable fuel cell that can store more energy than petrol.

Electric vehicles are potentially more environmentally friendly than petrol vehicles because they do not emit greenhouse gases, but the cells they use for power can't store as much energy as fossil fuels. Now, Stuart Licht and colleagues at the University of Massachusetts, Boston, US, have developed a vanadium boride-air fuel cell with a much larger energy capacity than current vehicle batteries. 'The cell has ten times the energy capacity of lithium ion batteries and three times the energy density of zinc-air batteries,' says Licht, 'although all these devices work in the same way.'

General Motors' electric car 'Volt' © General Motors

In its electric car 'Volt', launching in 2010, General Motors (GM) uses a lithium ion battery which can power the car for 40 miles before it needs to be recharged. To extend this range, GM added a standard combustion engine to recharge the battery when it runs low.

'Our renewable fuel cell opens the door to electric vehicles with viable driving ranges, without a separate combustion engine and frequent battery recharges,' says Licht. The vanadium boride-air fuel cell needs only air and fresh fuel to complete the recharge process. Using this system, a motorist would drive into a fuel station, receive fresh fuel and drive away.

Peter Bruce, an expert in new materials for energy storage devices at St Andrews University, UK, comments: 'Finding ways to store more energy than is possible at present is a key challenge and imaginative solutions are necessary. Replacing the zinc in a zinc-air primary battery with a vanadium boride anode is certainly interesting. However, it does raise a number of challenges for practical devices, such as recharging the batteries, and more scientific questions to be answered.'

Licht acknowledges that there is lots of work to do before the fuel cell can be commercialised. 'This is a first study demonstrating the very high capacity of the cell. Engineering details, systems optimisation and scale-up need to be developed,' he says.

Janet Crombie