Sun converts carbon dioxide into fuel

We all know that the increasing concentration of carbon dioxide in the atmosphere has a major impact on the Earth climate. But now, chemists at the University of California at San Diego (UCSD) have developed "a device that can capture energy from the sun, convert it to electrical energy and split carbon dioxide into carbon monoxide and oxygen." As carbon monoxide can easily be converted to liquid fuel, this prototype device kills two birds with one stone: it helps saving fuel while reducing the concentration of a greenhouse gas.

We all know that the increasing concentration of carbon dioxide in the atmosphere has a major impact on the Earth climate. But now, chemists at the University of California at San Diego (UCSD) have developed "a device that can capture energy from the sun, convert it to electrical energy and split carbon dioxide into carbon monoxide and oxygen." As carbon monoxide can easily be converted to liquid fuel, this prototype device kills two birds with one stone: it helps saving fuel while reducing the concentration of a greenhouse gas. Still, this device needs some improvements before an industrial deployment.

This prototype has been developed at UCSD by a team composed of Clifford Kubiak, professor of chemistry and biochemistry, and his graduate student Aaron Sathrum, a member of Kubiak research group. Below is a picture of the "CO2 splitting semiconductor/catalyst device under construction (gallium phosphide wafer with metal contacts)" (Credit: Aaron Sathrum, UCSD). Here is a link to a larger version.

CO2 splitting device

Here is how this device works.

The device designed by Kubiak and Sathrum to split carbon dioxide utilizes a semiconductor and two thin layers of catalysts. It splits carbon dioxide to generate carbon monoxide and oxygen in a three-step process. The first step is the capture of solar energy photons by the semiconductor. The second step is the conversion of optical energy into electrical energy by the semiconductor. The third step is the deployment of electrical energy to the catalysts. The catalysts convert carbon dioxide to carbon monoxide on one side of the device and to oxygen on the other side.

This looks easier than it really is. You need a special catalyst to convert electrical energy to chemical energy. And you need to use the right semiconductor to make carbon dioxide splitting practical.

Kubiak and Sathrum initially used a silicon semiconductor to test the merits of their device because silicon is well-studied. However, silicon absorbs in the infrared range and the researchers say it is "too wimpy" to supply enough energy. The conversion of sunlight by silicon supplied about half of the energy needed to split carbon dioxide, and the reaction worked if the researchers supplied the other half of the energy needed.

They have now moved to a gallium-phosphide semiconductor and they think "it will absorb the optimal amount of energy from the sun to drive the catalytic splitting of carbon dioxide."

This research work has been presented on March 27, 2007 at the 233rd National Meeting & Exposition of the American Chemical Society (March 25-29, 2007, Chicago, IL) in one of the sessions focused on Catalysis Relevant to Energy and Sustainability. The title of the presentation was "Photochemical splitting of carbon dioxide" and here is a link to the abstract.

Sources: Sherry Seethaler, University of California at San Diego, April 17, 2007; and various websites

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