Electrode Enhancements: New materials may boost fuel cell performance

Two teams have independently discovered ways to dramatically improve the materials used in the electrodes of fuel cells. Those developments could make the electricity-generating equipment more efficient, cheaper, and longer lasting, the researchers propose.

Fuel cells, like batteries, produce electric power via chemical reactions that occur on the surfaces of internal electrodes. Two problems that stand in the way of the widespread use of fuel cells are the high costs and short lifetimes of the electrodes, says Radoslav R. Adzic, a chemist at Brookhaven National Laboratory in Upton, N.Y.

The precious metal platinum, a reaction-boosting catalyst that’s often used to make or coat fuel cell electrodes, today costs about $36,000 per kilogram. Furthermore, “the platinum oxide layer that quickly forms on an electrode’s surface dramatically slows down the chemical reactions there,” says Adzic. Worse, the oxide layer tends to dissolve into the chemicals that bathe it, so that the electrode eventually fails, he notes.

Now, Adzic and his colleagues have developed a way to prevent that oxide layer from forming. They spray the platinum electrode with a smattering of gold nanoparticles. An inert element, gold doesn’t contribute to the chemical reactions, and it had been expected to reduce electrode performance by blocking access to some of the active platinum. However, Adzic suspected that because gold prevents an oxide layer from forming, it might keep the platinum from dissolving and thereby boost efficiency.

In the team’s lab tests of 30,000 power-generating cycles, a standard electrode in one fuel cell lost more than half its platinum, while an electrode dotted with gold nanoparticles lost almost none of its platinum. The researchers report their findings in the Jan. 12 Science.

Fuel cell designers’ goal is to prevent an electrode from dissolving during use but to avoid deactivating its surface, says Sanjeev Mukerjee, a materials scientist at Northeastern University in Boston. “This [team’s] material seems to strike a happy medium,” he comments.

Another team, led by physical chemist Vojislav R. Stamenkovic of Argonne (Ill.) National Laboratory, also announced this week an electrode material that might boost fuel cell performance.

That group tested an alloy consisting of three parts platinum and one part nickel, but with all the atoms on its crystal surfaces being platinum, says Stamenkovic. The electron sharing that takes place between the surface platinum and buried nickel atoms inhibits the formation of an oxide layer, he notes.

In lab tests, electrodes made of the platinum-nickel alloy are about 10 times as active chemically as ones made of pure platinum and about 90 times as active as the platinum-carbon electrodes now used in state-of-the-art fuel cells, the researchers report online and in the Jan. 26 issue of Science.

With the new material, engineers might design fuel cells with smaller electrodes that contain only one-twentieth as much platinum as those in use now—reducing cost and boosting efficiency of the devices at the same time, the team predicts.

The electrode materials developed by the Adzic and Stamenkovic teams are “really promising developments,” says Andrew A. Gewirth, a chemist at the University of Illinois at Urbana-Champaign. “This will give fuel cell designers new ideas about how to go forward,” he notes.

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