Researchers at the University of Illinois in Chicago have engineered a solar cell that converts atmospheric carbon dioxide into usable fuel so efficiently that it uses nothing but sunlight to make the energy conversion. The finding, funded by the National Science Foundation and the U.S. Department of Energy is under a provisional patent.

Mimicking the work of plants, the cell uses natural or artificial sunlight to convert carbon dioxide (CO₂) in the air directly into synthetic gas fuel. The researchers foresee a solar farm of artificial leaves that could remove carbon from the atmosphere and produce energy-dense fuel.

Simulated light powers a solar cell that converts carbon dioxide directly into syngas. Image credit: University of Illinois at ChicagoUnlike a photovoltaic, the cell is a photosynthetic. And rather than producing energy, the cells produce a mixture of hydrogen gas and carbon monoxide. This synthetic gas, or syngas, can be burned, converted into diesel or made into other hydrocarbon fuels.

The research team took a different approach to create the chemical reduction reaction. Most such reactions depend on precious metals, like silver, but are relatively inefficient. The researchers looked for a new catalyst to create the reaction and focused on nano-structured compounds called transition metal dichalcogenides, or TMDCs. They found nanoflake tungsten diselenide to be more active and better able to break the chemical bond of carbon dioxide.

The catalyst is about 20 times cheaper and 1,000 times faster than its noble-metal counterparts, the researchers say. But TMDCs can become oxidized and poisoned, and unable to survive the reaction. Using a co-catalyst, an ionic fluid called ethyl-methyl-imidazolium tetrafluoroborate, mixed 50-50 with water, the TMDC’s active sites were preserved during the reduction reaction, allowing for the conversion to take place.

The technique could be adapted to large-scale use for solar farms, but can also work in smaller applications, the researchers say.