Researchers at the University of Illinois at Chicago have developed a 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, the new device essentially does the work of plants, converting atmospheric carbon dioxide into fuel.

Whereas plants produce fuel in the form of sugar, the solar cell delivers syngas, a mixture of hydrogen and carbon monoxide. Syngas can be burned directly, or converted into diesel or other hydrocarbon fuels.

A solar farm of such “artificial leaves” could remove significant amounts of carbon from the atmosphere while efficiently producing energy-dense fuel.

Engineers have long been exploring different catalysts to turn carbon dioxide into carbon-based fuels but, until now, such reactions have been inefficient and relied on expensive precious metals such as silver.

The University of Illinois researchers focused on a family of nano-structured compounds called transition metal dichalcogenides as catalysts, pairing them with an unconventional ionic liquid as the electrolyte inside a two-compartment, three-electrode electrochemical cell. The best of several catalysts they studied turned out to be nanoflake tungsten diselenide which proved to be 1,000 times faster than precious metal catalysts and about 5% of the cost.

Their “artificial leaf” consists of two silicon triple-junction photovoltaic cells to harvest light with 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 light energizes the cell, hydrogen and carbon monoxide gas bubble up from the cathode, while free oxygen and hydrogen ions are produced at the anode. The hydrogen ions diffuse through a membrane to the cathode side where they combine with the carbon monoxide in the syngas.

The researchers believe that their technology should be adaptable to both large-scale use, like solar farms, and to small-scale applications. They even think that, in the future, it may prove useful on Mars, whose atmosphere is mostly carbon dioxide.