A new catalyst based on iron works as well as platinum-based catalysts for accelerating the chemical reactions inside hydrogen fuel cells. The finding could help make fuel cells for electric cars cheaper and more practical.
Fuel cell researchers have been looking for cheaper, more abundant alternatives to platinum, which costs between $1,000 and $2,000 an ounce and is mined almost exclusively in just two countries: South Africa and Russia. One promising catalyst that uses far less expensive materials–iron, nitrogen, and carbon–has long been known to promote the necessary reactions, but at rates that are far too slow to be practical.
Now researchers at the Institut National de la Recherche Scientifique (INRS) in Quebec have dramatically increased the performance of this type of iron-based catalyst. Their material produces 99 amps per cubic centimeter at 0.8 volts, a key measurement of catalytic activity. That is 35 times better than the best nonprecious metal catalyst so far, and close to the Department of Energy’s goal for fuel-cell catalysts: 130 amps per cubic centimeter. It also matches the performance of typical platinum catalysts, says Jean-Pol Dodelet, a professor of energy, materials, and telecommunications at INRS who led the work.
The improvement, reported in the latest issue of the journal Science, is “quite surprising,” says Radoslav Adzic, a senior chemist at Brookhaven National Laboratory in Upton, NY, who also develops catalysts for fuel cells. The new material meets a benchmark for hydrogen fuel cells set five years ago that “we thought nobody would ever meet,” adds Hubert Gasteiger, a visiting professor of mechanical engineering at MIT. “For the very first time, a nonprecious metal catalyst makes sense.”
The INRS researchers’ key insight was finding a way to increase the number of active catalytic sites within the material–with more sites for chemical reactions, the overall rate of the reactions in the material increases. In previous work, the researchers had shown that heating carbon black (a powdery form of carbon similar to graphite) to high temperatures in the presence of ammonia and iron acetate created gaps in the carbon that are just a few atoms wide. Nitrogen atoms bind to opposite sides of these tiny gaps, and an iron ion bridges these atoms, forming an active site for catalysis.