Newly Developed Solar Cells Capable of Converting Atmospheric Carbon Dioxide into Burnable Fuel

Researchers from the University of Illinois in Chicago have developed new solar cells capable of utilizing energy from sunlight to convert atmospheric carbon dioxide into usable hydrocarbon fuel. The new solar cells works like plants, converting carbon dioxide from the atmosphere into fuel.

The new solar cell, described in the journal Nature, consist of of two silicon triple-junction photovoltaic cells of 18 square centimeters 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. When the cell is energized by the sunlight hydrogen and carbon monoxide gas bubble up from the cathode, while free oxygen and hydrogen ions are produced at the anode.

"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 of the study, in a statement. "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."

Instead of producing fuel in a form of sugar like plants, the new solar cells produce in a form of synthesis gas or syngas. Syngas is a mixture of hydrogen gas and carbon monoxide that can be burned directly or converted into diesel or other hydrocarbon fuels.

In order to convert carbon dioxide to burnable forms of carbon, it must first undergo reduction reactions, which is the opposite of oxidation or combustion. However, such reactions rely on expensive precious metals like silver as catalyst.

For the new solar cells, the researchers used the nano-structured compounds called transition metal dichalcogenides (TMDC) as catalyst for the reduction reaction. They paired the TMDC with an unconventional ionic liquid made from a 50-50 combination of water and ethyl-methyl-imidazolium tetrafluoroborate as the electrolyte inside a two-compartment, three-electrode electrochemical cell.

Upon trying several TMDC, the researchers noted that nanoflake tungsten diselenide is the best to be used as catalyst. More importantly, the new catalyst is 1,000 faster and about 20 times cheaper compared to the noble-metal catalysts.