Researchers have developed a new type of solar cell that is capable of transforming carbon dioxide into usable hydrocarbon fuel using only sunlight as energy.

Compared with conventional solar cells that convert sunlight into electricity to be stored in batteries, the new solar cells cheaply and efficiently convert carbon dioxide in the atmosphere directly into usable fuel.

The new device works much like trees and plants that capture and convert carbon dioxide into sugars to store them into energy. Unlike plants that use catalysts to produce sugar, the researchers used nanoflake tungsten diselenide catalyst to convert carbon dioxide to carbon monoxide.

"In photosynthesis, trees need energy from light, water and carbon dioxide in order to make their fuel; in our experiment, the ingredients are the same, but the product is different," study co-author Larry Curtiss said.

The potentially game-changing system may solve crucial problems related to energy use. The new solar cells produce usable energy-dense fuel, which could help address challenges linked with the burning of other kinds of hydrocarbons such as oil, gasoline and coal.

A solar farm of these so-called artificial leaves can also remove significant amounts of the greenhouse gas carbon dioxide in the atmosphere known to significantly drive global warming.

In plants, the process of converting carbon dioxide into sugar involves the organic catalyst enzyme. Curtiss, a chemist from the Argonne National Laboratory of the U.S. Department of Energy, and colleagues, however, used a metal compound called tungsten diselenide as a catalyst that can convert carbon dioxide into usable fuel.

Carbon monoxide is also a planet-warming greenhouse gas but scientists have already found a way to convert it into usable fuel such as methanol. Converting carbon dioxide into something usable, on the other hand, is more challenging because of it being relatively chemically unreactive.

"The chemical inertness of CO2 renders many electrochemical and photochemical conversion processes inefficient," the researchers reported in their study, which was published in the journal Science on July 29.

"We report a transition metal dichalcogenide nanoarchitecture for catalytic electrochemical CO2 conversion to carbon monoxide (CO) in an ionic liquid."

The system involves a reaction very much similar to that found in nature. The artificial leaf converts photons, or packets of light, into pairs of negatively charged electrons and positively charged holes that separate from each other. When the holes react with water molecules, protons and oxygen molecules are created. Along with carbon dioxide, the protons and electrons then react together to produce carbon monoxide and water.

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