Many research groups are in the race to make fuel cells that use little or no platinum–substituting platinum with a low-cost metal is the most common approach. Iron-based catalysts and platinum-palladium mixtures have both been tested, and MacFarlane has made porous electrodes coated with polymers. Others, such as Japan’s Daihatsu and researchers at Wuhan University in China, are making alkaline fuel cells that have membranes that conduct alkaline ions as opposed to acid ones. These designs work well with cheap catalysts like nickel and don’t require precious-metal catalysts. But all of these platinum alternatives have drawbacks: typically they give low current densities or their performance degrades after a few hundred hours.
ACAL Energy’s catalyst is based on a low-cost mix of molybdenum and vanadium, and the fuel cell’s polymer membrane is in direct contact with this liquid cathode. Around 80 percent of the platinum used in a conventional cell is found in the cathode, all of which is eliminated in the new design.
Creeth says the new catalyst is stable and can withstand the acidic conditions in the fuel cell. In company tests, the fuel cells performed well for more than 1,500 hours. The design has other advantages that decrease cost, he says. While conventional fuel-cell stacks need to be cooled with flowing liquid or air, and they also need a system to humidify the membrane, the liquid catalyst eliminates the need for both of these. “We believe ours is the best-performing platinum-free system,” Creeth says.