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Flawed Graphene Structure Actually Improves Fuel Cells

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Purposefully introducing flaws into graphene used in fuel cells can improve the cells and make them more efficient, researchers are reporting.

While the honeycomb structure found in pristine atom-thick graphene is beautiful, allowing it to have a number of tiny holes results in a proton-selective membrane paving the way for improved fuel cells, they say.

Separating protons from hydrogen efficiently is a major challenge for fuel cell technology, and Northwestern University scientists collaborating with researchers from five other institutions have discovered that graphene that is slightly imperfect can shuttle protons from one side of a graphene membrane to the other in just seconds.

The selectivity and speed of the imperfect version are much improved over conventional membranes, giving engineers a possible new and simpler model of fuel cell design, the researchers report in the journal Nature Communications.

"We found if you just dial the graphene back a little on perfection, you will get the membrane you want," says Franz J. Geiger, a Northwestern chemistry professor. "Everyone always strives to make really pristine graphene, but our data show if you want to get protons through, you need less perfect graphene."

At the atomic scale, protons are fairly big, which makes them difficult to be driven through a single layer of structurally perfect graphene at room temperature, the researchers explain.

In graphene immersed in water, protons were observed moving through it, and the researchers used computer simulations, imaging techniques and lasers in an effort to understand what was going on.

Naturally occurring defects in the graphene - tiny pinholes where a single carbon atom is absent - triggers a chemical conveyor belt that shuttles protons from the water on one side of the membrane to the other in a few seconds, they found.

In conventional membranes, which can be hundreds of nanometers thick, the desired proton selection takes minutes, compared to the quick transfer in a one-atom-thick layer of graphene, they say.

Although more research is needed, Geiger says, it offers a way for engineers to create a quicker and more efficient proton separation membrane than previously thought possible.

The advantages could be significant, he adds.

"Imagine an electric car that charges in the same time it takes to fill a car with gas," says Geiger. "And better yet - imagine an electric car that uses hydrogen as fuel, not fossil fuels or ethanol, and not electricity from the power grid, to charge a battery.

"Our surprising discovery provides an electrochemical mechanism that could make these things possible one day."

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