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."
John Turner of the National Renewable Energy Laboratory, who first demonstrated an efficient "artificial leaf" in 1998, but using materials too expensive and unstable for commercialization, said about the advance, "We may have a path forward towards sustainable low-cost, carbon-free hydrogen production and a hydrogen economy."
He added, "The key will be taking this laboratory device and turning it into a manufacturable prototype."
The company Sun Catalytix of Cambridge, Mass., is commercializing this technology.