US researchers have developed what they called a "potentially game-changing" solar cell that cheaply and efficiently converts atmospheric carbon dioxide and sunlight directly into usable hydrocarbon fuel.

Conventional solar cells convert sunlight into electricity that must be stored in heavy batteries, but the new device essentially does the work of plants, converting carbon dioxide into a mixture of hydrogen gas and carbon monoxide, which 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 and produce energy-dense fuel efficiently, they reported this week in the US journal Science.

"The new solar cell is not photovoltaic -- it's photosynthetic," senior author Amin Salehi-Khojin, assistant professor of mechanical and industrial engineering at the University of Illinois at Chicago, said 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," he said.

There is much interest surrounding chemical reactions that convert carbon dioxide into burnable forms of carbon, but existing catalysts for this reaction are too inefficient and rely on expensive precious metals such as silver.

Salehi-Khojin and his coworkers focused on a family of nano-structured compounds called transition metal dichalcogenides -- or TMDCs -- 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 was not only more active and more able to break carbon dioxide's chemical bonds, but also 1,000 times faster than noble-metal catalysts and about 20 times cheaper.

The researchers also used an ionic fluid called ethyl-methyl-imidazolium tetrafluoroborate, mixed 50-50 with water.

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

In the future, he said, it may prove useful on Mars, whose atmosphere is mostly carbon dioxide, if the planet is also found to have water.