September 13, 2006

High power density fuel cells coming

New fuel cells could get an energy density up to about 2200 watt-hours per litre Gervasio says, compared to 200 watt-hours per litre for a lithium polymer battery. Chemist Don Gervasio and colleague Sonja Tasic, both at Arizona State University in the US, set out to develop a fuel cell that would generate more electricity for its weight than the best batteries, and would also work at room temperature.

Gervasio's solution was to use the alkaline compound borohydride. A 30% solution of borohydride in water actually contains one-third more hydrogen than the same volume of liquid hydrogen.

Gervasio's early systems ran into trouble when the hydrogen-generating cells became clogged with insoluble boron oxide. His team looked for something that would dissolve boron oxide, and found it in a widely-used material: ethylene glycol, otherwise known as antifreeze. The ethylene glycol also had no effect on hydrogen generation.

The researchers can now run the hydrogen generator on a 15% solution of borohydride, half-way to their goal of a truly power-packed 30% solution.

Magbeam can use 3,000 tons of batteries (400-600 Wh/kg) @ 4000 ISP to accelerate 10 tons of payload to 20 km/s or 72000 km/s The new fuel cell could bring the weight down to 700 tons.