A Nanoparticle Heart

It’s easy for ethanol to combust in an engine at high temperatures, but fuel cells operate at room temperature. That’s where nanoparticles like this heart-shaped one, which is an alloy of three metals—platinum, iridium, and tin—come in. Grouped together, they act as a catalyst in fuel cells, driving the production of energy from ethanol without the need for extra heat.

“This is a very special type of catalyst, which we use to oxidize ethanol into water and carbon dioxide,” says Xiaowei Teng, an assistant professor of chemical engineering at the University of New Hampshire, who spearheads work on the material. The process releases electrons that can be used to power cars, cell phones, and other devices that require electricity.

In the image above, which has been artificially colored red, each dot is an atom of one of the three elements. Dong Su, a scientist at Brookhaven National Laboratory on Long Island, used electron microscopy to reveal the nanoparticle’s structure. The unusual heart shape wasn’t intentional, Teng says, but “it might expose more active sites for catalytic reactions.”

Platinum has long been used as a catalyst for many chemical reactions, but because it’s very expensive, reducing the amount used in fuel cells is an active area of research. Teng says that combining other metals with platinum reduces the amount of the pricey material needed and improves how well the fuel cell works. Tin, for example, can make the reaction go 10-30 times faster. Iridium, meanwhile, can help convert the ethanol completely into carbon dioxide instead of acetic acid, which is less efficient at producing energy.

Teng sees ethanol fuel cells as more practical than the traditional idea of using hydrogen for energy. For one, hydrogen is extremely flammable, and transportation of the gas is dangerous. “To a certain degree, it’s a moving bomb,” says Teng. By comparison, ethanol is relatively benign—Teng’s group oxidizes solutions that are in the range of 5-40 percent ethanol, which is essentially like working with beer or whiskey. Plus, gas stations mix ethanol—a biofuel made from corn and other plant materials—in their pumps, so the infrastructure is already there.

Work on the fuel cell is still in the early stages. The efficiency is low—Teng’s team is able to convert 10-15 percent of ethanol into carbon dioxide at most, and the rest ends up as acetic acid. But by continuing to tweak the alloy, and by learning more about how its structure affects its function, he hopes to maximize the amount of energy he can get out of the 2-3 nanometer-sized particles. Regardless, he’s putting his heart into it.