Researchers at MIT have produced something they're calling an "artificial leaf," which converts sunlight directly into a chemical fuel that can be stored and used later as an energy source. The artificial leaf is a silicon solar cell with different catalytic materials made from cobalt and a nickel/molybdenum/zinc alloy bonded onto its two sides. When the cell is placed in a container of water and exposed to sunlight, electrolysis occurs, which generates oxygen bubbles on one side and hydrogen bubbles on the other.
By using a container that separates the two sides, the oxygen and hydrogen can be collected and stored to deliver power to a fuel cell that combines them once again into water to produce an electric current.
The device is described in a paper by professor Daniel Nocera and his coworkers at MIT and published in the journal Science. As Nocera explains, "The device is made entirely of earth-abundant, inexpensive materials and works in ordinary water. Other attempts to produce devices that could use sunlight to split water have relied on corrosive solutions or on relatively rare and expensive materials such as platinum."
He went on to say, "I think there are going to be real opportunities for this idea. 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. You just drop it in a glass of water, and it starts working." However, he doesn't think the new device is ready for commercial production, mainly because the infrastructure to collect, store and use such large amounts of the gases has not yet been developed.
He suggests one possible further refinement is to apply the technology to tiny particles, making them more like photosynthetic algae than an artificial leaf. The advantage of that, he says, is that the small particles would have much more surface area exposed to sunlight and water, allowing them to harness the sun's energy more efficiently. On the other hand, engineering a system to separate and collect the two gases would be more complicated in such a setup.
Ultimately, he sees a future in which individual homes could be equipped with solar-collection systems based on this principle. Panels on the roof could use sunlight to produce hydrogen and oxygen that would be stored in tanks and then fed to a fuel cell whenever electricity is needed.
"The potential for this could be enormous," Nocera explains. "It could be made simple and inexpensive enough so it could be widely adopted throughout the world, including [in] many third-world countries that do not presently have access to reliable sources of electricity."
An 'artificial leaf' made by Daniel Nocera and his team, using a silicon solar cell with novel catalyst materials bonded to its two sides, is shown in a container of water with light (simulating sunlight) shining on it. The light generates a flow of electricity that causes the water molecules, with the help of the catalysts, to split into oxygen and hydrogen, which bubble up from the two surfaces. Video courtesy of the Nocera Lab/Sun Catalytix
- MIT: Norcea Lab