A catalyst that boasts four to five times higher activity than pure platinum promises to significantly improve the performance of hydrogen fuel cells, say its developers at the University of Houston, Houston. The nanoparticle catalyst, which features a nearly pure platinum shell over a core made up of an alloy of cobalt, copper and platinum, speeds the reduction of oxygen, notes Peter Strasser, assistant professor of chemical and biomolecular engineering at the school. The increased activity versus pure platinum likely occurs because platinum in the new catalyst has a different geometric structure because of the base metal core, he explains.
The catalyst is made by first depositing pure platinum on a porous carbon support. This then is alloyed with copper and cobalt and thermally annealed at 400°C. The resultant nanoparticles, which consist of 60% cobalt, 20% copper and 20% platinum, are applied to the fuel cell membrane and then subjected for a few minutes to a cyclic voltage that causes dealloying, creating the nearly pure platinum shell, as cobalt and copper selectively dissolve into the liquid.
So far, the catalyst has been tested in a membrane assembly replicating a fuel cell.
Long-term stability is the key, stresses Strasser — both of platinum size and activity. Regular platinum catalyst does change size over time as a fuel cell operates. Tests now are taking place within the fuel cell industry, he notes, and should last about another year and a half.
If the tests go well, Strasser expects the catalyst to be used first in fuel cells for battery replacement in portable electronics, perhaps in as soon as three years. Such applications command premium prices and aren’t as demanding in operating times and conditions as automotive fuel cells, he notes. However, ultimately, Strasser foresees a role in fuel cells for automobiles.
The dealloying approach provides a new way to improve surface catalytic activity of noble metals in general, he says, adding that preliminary results already have been obtained for palladium. The technique is suitable for catalysts used in services taking place at 200°C or less. The chlorine industry may be one beneficiary, Strasser notes.
