Solar power ‘splits’ CO2

University of California researchers have devised a method to use solar power to split carbon dioxide into oxygen and carbon monoxide, which could be used in synthetic fuels

A device that uses solar energy to ‘split’ carbon dioxide into carbon monoxide and water could prove to be an unlikely contributor to efforts to reduce global warming. Developed at the University of California, San Diego, the device could be used to supply carbon monoxide as a feedstock for petrochemical production or for synthetic diesel fuels.

 

Carbon monoxide is probably best known for its toxicity, but it’s an important industrial gas. Currently derived from natural gas or by gasifying carbon-bearing solids, it can be converted into liquid fuels. ‘The technology to convert carbon monoxide into liquid fuel has been around a long time; it was invented in Germany in the 1920s,’ commented Clifford Kubiak, a professor of chemistry and biochemistry and director of the research. ‘When the energy crisis ended people lost interest. Now things have come full circle because rising fuel prices make it economically viable to convert CO into fuel.’

 

Kubiak and his graduate student, Aaron Sathrum, have developed a semiconductor-based device which works like a solar cell, but uses the electrical current to break carbon-oxygen bonds. The sunlight hits a layer of semiconducting gallium phosphide, which is an efficient absorber of solar energy. The energy pushes electrons in the semiconductor into high energy states, which creates an electric current when they fall back into their ground state. This current flows into catalyst coating on both sides of the semiconductor, which splits the carbon dioxide; CO is produced on one side of the semiconductor, and oxygen on the other. The catalyst, which was also developed by Kubiak’s laboratory, is a large organic molecule containing three nickel atoms.

 

Kubiak believes that more attention should be paid to the chemical conversion of CO2. ‘For every mention of CO2 splitting, there are more than a hundred articles on splitting water to produce hydrogen, yet CO2 splitting uses up more of what you want to put a dent into,’ he said. However, it’s quite a challenge, as Sathrum explained: ‘This project brings together many scientific puzzle pieces.’