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.
“The difference is that the borohydride is at room temperature, and it’s stable, non-toxic and cost-effective,” Gervasio says.
The borohydride solution releases its hydrogen as it flows over a catalyst made of ruthenium. The hydrogen passes through a membrane and combines with oxygen in the fuel cell, generating electricity and waste water.
Theoretically, this could achieve 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.
“For the same size and weight you can make a lot more electricity, so your laptop or camcorder will run a lot longer,” he says.
However, 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. “By using this additive, we’ve raised the hydrogen storage to about 600 usable watt-hours per litre, which is two to three times as good as any battery,” Gervasio says. “We’re half-way there.”
Gervasio recognises that there are still many steps between his prototype and a competitively priced, off-the-shelf, battery-sized fuel cell. Nevertheless, he believes they could appear in power-hungry devices such as laptops, camcorders, and radios within five years.
Gervasio revealed details of the prototype system at the 232nd American Chemical Society National Meeting, in San Francisco, US, on Tuesday.