Solar cell captures CO2 and sunlight

Researchers at the University of Illinois at Chicago (UIC) have engineered a potentially game-changing solar cell that cheaply and efficiently converts atmospheric carbon dioxide directly into usable hydrocarbon fuel, using only sunlight for energy.

Unlike conventional solar cells, which convert sunlight into electricity that must be stored in heavy batteries, the new device essentially does the work of plants, converting atmospheric carbon dioxide into fuel and thus solving two problems at once. A solar farm of such ‘artificial leaves’ could remove significant amounts of carbon from the atmosphere and produce energy-dense fuel efficiently.

“The new solar cell is not photovoltaic — it’s photosynthetic,” said Amin Salehi-Khojin, assistant professor of mechanical and industrial engineering at UIC and senior author on the study.

“Instead of producing energy in an unsustainable, one-way route from fossil fuels to greenhouse gas, we can now reverse the process and recycle atmospheric carbon into fuel using sunlight,” he said.

While plants produce fuel in the form of sugar, the artificial leaf delivers syngas, or synthesis gas — a mixture of hydrogen gas and carbon monoxide. Syngas can be burned directly or converted into diesel or other hydrocarbon fuels.

The ability to turn CO₂ into fuel at a cost comparable to petrol could render fossil fuels obsolete.

Chemical reactions that convert CO₂ into burnable forms of carbon are called reduction reactions, the opposite of oxidation or combustion. Engineers have been exploring different catalysts to drive CO₂ reduction, but so far such reactions have been inefficient and rely on expensive precious metals such as silver, Salehi-Khojin said.

“What we needed was a new family of chemicals with extraordinary properties,” he said.

The UIC artificial leaf consists of two silicon triple-junction photovoltaic cells of 18 cm² to harvest light: the tungsten diselenide and ionic liquid co-catalyst system on the cathode side and cobalt oxide in potassium phosphate electrolyte on the anode side.

The technology should be adaptable not only to large-scale use, like solar farms, but also to small-scale applications, Salehi-Khojin said.

The finding is reported in the journal Science and was funded by the National Science Foundation and the US Department of Energy. A provisional patent application has been filed.