One way to reign in climate change is to capture carbon dioxide and convert it into liquid fuels. To do that, the gas has to first be split into carbon monoxide by stripping off one oxygen atom. Current techniques for doing that require a lot of energy and expensive catalysts.

Now Swiss researchers have found a way to break down carbon dioxide using sunlight and a catalyst made of copper and tin. The method, described in Nature Energy, could lead to a low-cost way to convert carbon dioxide emissions into fuel.

Carbon dioxide is a stable molecule. Chemists have to put in energy to break its bonds and produce carbon monoxide, which can then be combined with hydrogen to make fuels such as gasoline and kerosene.

A promising method for this breakdown involves passing electric current through an aqueous solution containing added carbon dioxide. The problem is that the catalysts needed to speed up the process are made of precious metals such as gold and platinum. Plus, carbon dioxide can react with water and generate many unwanted byproducts.

Michael Grätzel, Jingshan Luo, and their colleagues at EPFL Lausanne made a catalyst of “Earth-abundant” materials that predominantly converts carbon dioxide to carbon monoxide. They made it by first creating copper oxide nanowires on a copper film, then coating the nanowires with an atom-thick layer of tin oxide.

The films serve two functions: they act as both electrodes and catalyst. The researchers set up a basic electrolysis system by immersing two electrodes in a solution containing carbon dioxide.

Electric current passed through the liquid breaks down carbon dioxide into its components. A membrane separates the two electrodes and keeps the carbon monoxide and oxygen apart. The electricity comes from a solar cell, and the system converts carbon dioxide into carbon monoxide with an efficiency of 13.4 percent.

This solar-to-CO efficiency is double that from the researchers’ previous report of 6.5 percent, they write in the paper. “The work sets a new benchmark for solar-driven CO 2 reduction,” Luo said in a press release.

Source: M Shreier et al. Solar conversion of CO 2 to CO using Earth-abundant electrocatalysts prepared by atomic layer modification of CuO. Nature Energy. 2017.

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