Another articleANAHEIM, March 27, 2011 — Scientists today claimed one of the milestones in the drive for sustainable energy — development of the first practical artificial leaf. Speaking here at the 241st National Meeting of the American Chemical Society, they described an advanced solar cell the size of a poker card that mimics the process, called photosynthesis, that green plants use to convert sunlight and water into energy.
“A practical artificial leaf has been one of the Holy Grails of science for decades,” said Daniel Nocera, Ph.D., who led the research team. “We believe we have done it. The artificial leaf shows particular promise as an inexpensive source of electricity for homes of the poor in developing countries. Our goal is to make each home its own power station,” he said. “One can envision villages in India and Africa not long from now purchasing an affordable basic power system based on this technology.”
The device bears no resemblance to Mother Nature’s counterparts on oaks, maples and other green plants, which scientists have used as the model for their efforts to develop this new genre of solar cells. About the shape of a poker card but thinner, the device is fashioned from silicon, electronics and catalysts, substances that accelerate chemical reactions that otherwise would not occur, or would run slowly. Placed in a single gallon of water in a bright sunlight, the device could produce enough electricity to supply a house in a developing country with electricity for a day, Nocera said. It does so by splitting water into its two components, hydrogen and oxygen.
The hydrogen and oxygen gases would be stored in a fuel cell, which uses those two materials to produce electricity, located either on top of the house or beside it.
Nocera, who is with the Massachusetts Institute of Technology, points out that the “artificial leaf” is not a new concept. The first artificial leaf was developed more than a decade ago by John Turner of the U.S. National Renewable Energy Laboratory in Boulder, Colorado. Although highly efficient at carrying out photosynthesis, Turner’s device was impractical for wider use, as it was composed of rare, expensive metals and was highly unstable — with a lifespan of barely one day.
Nocera’s new leaf overcomes these problems. It is made of inexpensive materials that are widely available, works under simple conditions and is highly stable. In laboratory studies, he showed that an artificial leaf prototype could operate continuously for at least 45 hours without a drop in activity.
The key to this breakthrough is Nocera’s recent discovery of several powerful new, inexpensive catalysts, made of nickel and cobalt, that are capable of efficiently splitting water into its two components, hydrogen and oxygen, under simple conditions. Right now, Nocera’s leaf is about 10 times more efficient at carrying out photosynthesis than a natural leaf. However, he is optimistic that he can boost the efficiency of the artificial leaf much higher in the future.
“Nature is powered by photosynthesis, and I think that the future world will be powered by photosynthesis as well in the form of this artificial leaf,” said Nocera, a chemist at Massachusetts Institute of Technology in Cambridge, Mass.
Nocera acknowledges funding from The National Science Foundation and Chesonis Family Foundation.
Truly badass stuff is coming out of that 241st National Meeting of the American Chemical Society.The leaf's ability to convert sunlight and water into storable fuel makes it the ultimate in solar energy. Now researchers say they have found a way to mimic this seemingly simple feat.
The technology developed by Dan Nocera of the Massachusetts Institute of Technology and colleagues could eventually power a house and bring electricity to the developing world with little more than a chip sunk into a bucket of water. The device could even store the energy for when the sun isn't shining.
The new technology copies the process of photosynthesis in which the sun's energy liberates electrons in a leaf, which then split water to form hydrogen and oxygen, providing stored energy for the plant.
"Whether you realize it or not, leaves are buzzing with electricity," Nocera said. "They just don't have any wires in them."
The leaves need two catalysts to make this reaction work, and similarly, so do the solar cells. Nocera's breakthrough is in finding two affordable catalysts that can do the reaction.
The sunlight is captured with the same silicon material that makes up a typical solar panel, but instead of connecting it to wires that can charge a battery, the coated silicon with catalysts is submerged in water.
"I can take the chip and put it in this bottle of water and just go and hold it up to the sun and you would start to see hydrogen and oxygen bubbles coming out," Nocera said.
The hydrogen and oxygen could later be used in a fuel cell to generate electricity as they recombine to form water.
The discovery is significant not because it's the first time researchers have made such a cell, but because it's the first to use materials cheap enough to make the device practical, Nocera said at a meeting of the American Chemical Society in Anaheim, Calif.
The device could match the efficiency of today's solar panels, he added, meaning that an array of panels on a household roof would be enough to power the house.
But a key target for the team's research is to provide energy to people in developing countries, especially India and rural China, he said. A key feature of his system in achieving this goal is that the device runs with whatever water is available; it need not be ultra-pure.
"The fact that you can just go over there and if there's a puddle, begin using it -- that's something that's very powerful for us," he said.
This could also be useful for military applications where it would be cumbersome to lug around ultra-pure water.
A remaining engineering challenge to take this from the lab to the rooftop is to figure out how to capture the oxygen and hydrogen and store them for later use. "That's going to be some tricky engineering," he said. It remains to be seen how expensive this aspect will be.
Today's photovoltaic panels can store solar power in a battery, but "a lot of the cost of a solar panel is in the wiring, the packaging," Nocera said. These expensive parts are eliminated with the artificial leaf. "In principle, that could be much cheaper."
The company Sun Catalytix of Cambridge, Mass. is commercializing this technology.
