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Improved technique converts CO2 to green fuel

Photo courtesy of Phil De Luna

The world needs more fuel and less atmospheric carbon dioxide – and new research by Edward Sargent and his team at the University of Toronto might serve as a stepping stone toward achieving both goals.

At the heart of their project is a simple, well-known chemical reaction: You start with carbon dioxide, apply an electric voltage, and end up with carbon monoxide (an essential ingredient is synthetic fuels such as ethanol and methanol), and water. The biggest catch is that the reaction usually proceeds at a snail’s pace.

But Sargent, director of CIFAR’s Bio-inspired Solar Energy program, together with his colleagues in U of T’s Department of Electrical and Computer Engineering, has found a way to speed it up. It turns out that electrodes with certain microscopic structures on their surfaces can help boost the strength of the electric field, which attracts more carbon dioxide to the metal, speeding up the reaction.

In a paper in Nano Letters published this fall, as well as a paper in Nature published on-line in August, Sargent and his colleagues describe the use of needle-shaped gold “nanostructures” as catalysts. Phil De Luna, a PhD student in the Sargent lab and a co-author on the Nature paper, compares it to the way the CN Tower attracts lightning during a thunderstorm.

“You can think of it like a lightning bolt, that concentrates the reagents – in this case CO2 – so that the reaction can happen quicker,” De Luna says.

The whole set-up looks deceptively simple; at first glance, all you see are two small, sealed beakers of water (one serving as a cathode, the other as an anode); they’re connected by a variety of tubes and wires, and surrounded by computer equipment. The electrode itself is nothing more than a thin strip of metal inserted into one of the two water jars. If you peer closely at the apparatus, you can see little bubbles of oxygen rising up from the metal. The nanostructures, being 10,000 times thinner than a human hair, are of course invisible.

In spite of the small size of these experiments, De Luna says that there is in principle nothing to stop the technique from being scaled up.

“Conceptually, and theoretically, this is absolutely scalable,” says De Luna. “On a practical level, though, there are a lot of engineering challenges that we still have to face.”

The process, known as “field-induced reagent concentration,” has another potential payoff: It can help convert energy from renewable sources such as wind and solar into a more readily storable liquid form, such as ethanol and methanol.

“We’re taking carbon dioxide – a ‘dirty’ greenhouse gas – and we’re using renewable energy to turn that into a fuel,” says De Luna.

The lab is also a semi-finalist for the Carbon XPrize, a $20-million (U.S.) prize being offered by a consortium of private energy companies for the best approach to converting carbon dioxide emissions from the burning of fossil fuels into a useful product.

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