chemistry

Affordable, stable fuel cells from platinum

CORNELL (US)—Researchers have discovered that platinum nanoparticles could be the catalyst that make fuel cells more stable, cost-effective, and more resistant to carbon monoxide poisoning.

Hydrogen fuel cells offer an appealing alternative to gasoline-burning cars, says Héctor Abruña, a professor of chemistry and chemical biology at Cornell University, because they have the potential to power vehicles for long
distances using hydrogen as fuel, mitigate carbon dioxide production, and emit only water vapor.

But they also require very pure hydrogen to work—meaning that conventional fuel must be stripped of its carbon monoxide (CO)—a process that is too expensive to make fuel cells commercially viable.

Fuel cells work by electrochemically decomposing fuel instead of burning it, converting energy directly into electricity.

In proton exchange membrane (PEM) fuel cells, an anode and cathode are separated by a membrane that blocks electrons but allows protons to pass through. At the anode, a catalyst oxidizes hydrogen, generating electrons and protons.

The protons pass through the membrane while the electrons create an electric current. At the cathode, electrons reunite with protons and oxygen from the air to form water.

Platinum and platinum/ruthenium alloys are often used as catalysts in PEM fuel cells, but both elements are rare, expensive, and easily rendered ineffective by exposure to even low levels of CO.

To create a catalyst that can tolerate more CO, researchers deposited platinum nanoparticles on a support material of titanium oxide (with added tungsten to increase its electrical conductivity).

Tests show that the new material works with fuel that contains as much as 2 percent CO, losing only 5 percent efficiency compared with a 30 percent drop in efficiency for conventional platinum catalysts. The material is also more stable and less expensive than pure platinum.

With the new catalyst, “you can use much less-clean hydrogen, and that’s more cost-effective because petroleum has a very high content of carbon monoxide,” Abruña says.

Otherwise, to reduce the CO content, “you need to scrape off the carbon monoxide, and it’s very expensive to do that.”

Details are published online in the Journal of the American Chemical Society.

The researchers are now preparing to put the catalyst to the test in real fuel cells. “So far, indications are very good,” Abruña says.

In preliminary experiments comparing the new material’s performance with pure platinum, he adds, the platinum cell was readily poisoned by CO and conked out early. “But ours was still running like a champ.”

The research was supported by the U.S. Department of Energy and by the Energy Materials Center at Cornell, an Energy Frontier Research Center funded by the Department of Energy.

More news from Cornell University: www.news.cornell.edu

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