US scientists have developed an "artificial leaf" that converts sunlight into a chemical fuel that could be stored and used later, according to a study published Friday. When placed in a container of water, the silicon solar cell -- with catalytic materials on each side -- generates oxygen bubbles on one side and hydrogen bubbles on the other, which can be separated and collected. The gases could then be fed into a fuel cell that recombines them into water while producing an electric current, according to lead researcher Daniel Nocera, of the Massachusetts Institute of Technology (MIT). The device is the subject of a paper in the journal Science co-authored by six researchers from Sun Catalytix, a solar-energy firm founded by Nocera. Nocera says the "leaf" is made entirely of abundant, inexpensive materials. The sheet of semiconducting silicon is coated on one side with a cobalt-based catalyst, which releases the oxygen, and on the other with a nickel-molybdenum-zinc alloy, which separates the hydrogen. "I think there?s going to be real opportunities for this idea" Nocera said in a statement accompanying the article. "You can?t get more portable, you don?t need wires, it?s lightweight, and it doesn?t require much in the way of additional equipment, other than a way of catching and storing the gases that bubble off." The device will not be ready for commercial production, however, until systems are developed that can collect, store and use the gases, he said. "It's a step," Nocera said. "It's heading in the right direction."