• The 'artificial leaf,' a device that can harness sunlight to split water into hydrogen and oxygen without needing any external connections, is seen with some real leaves, which also convert the energy of sunlight directly into storable chemical form.

    Photo: Dominick Reuter

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  • Daniel Nocera, the Henry Dreyfus Professor of Energy and Professor of Chemistry at MIT.

    Photo: Dominick Reuter

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‘Artificial leaf’ makes fuel from sunlight

Solar cell bonded to recently developed catalyst can harness the sun, splitting water into hydrogen and oxygen.


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Researchers led by MIT professor Daniel Nocera have produced something they’re calling an “artificial leaf”: Like living leaves, the device can turn the energy of sunlight directly into a chemical fuel that can be stored and used later as an energy source.

The artificial leaf — a silicon solar cell with different catalytic materials bonded onto its two sides — needs no external wires or control circuits to operate. Simply placed in a container of water and exposed to sunlight, it quickly begins to generate streams of bubbles: oxygen bubbles from one side and hydrogen bubbles from the other. If placed in a container that has a barrier to separate the two sides, the two streams of bubbles can be collected and stored, and used later to deliver power: for example, by feeding them into a fuel cell that combines them once again into water while delivering an electric current.

The creation of the device is described in a paper published Sept. 30 in the journal Science. Nocera, the Henry Dreyfus Professor of Energy and professor of chemistry at MIT, is the senior author; the paper was co-authored by his former student Steven Reece PhD ’07 (who now works at Sun Catalytix, a company started by Nocera to commercialize his solar-energy inventions), along with five other researchers from Sun Catalytix and MIT.

The device, Nocera explains, is made entirely of earth-abundant, inexpensive materials — mostly silicon, cobalt and nickel — 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.

The artificial leaf is a thin sheet of semiconducting silicon — the material most solar cells are made of — which turns the energy of sunlight into a flow of wireless electricity within the sheet. Bound onto the silicon is a layer of a cobalt-based catalyst, which releases oxygen, a material whose potential for generating fuel from sunlight was discovered by Nocera and his co-authors in 2008. The other side of the silicon sheet is coated with a layer of a nickel-molybdenum-zinc alloy, which releases hydrogen from the water molecules.


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



“I think there’s going to be real opportunities for this idea,” Nocera says. “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. “You just drop it in a glass of water, and it starts splitting it,” he says.

Now that the “leaf” has been demonstrated, Nocera suggests one possible further development: tiny particles made of these materials that can split water molecules when placed in sunlight — making them more like photosynthetic algae than leaves. The advantage of that, he says, is that the small particles would have much more surface area exposed to sunlight and the 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.)

The new device is not yet ready for commercial production, since systems to collect, store and use the gases remain to be developed. “It’s a step,” Nocera says. “It’s heading in the right direction.”

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. Such systems, Nocera hopes, could be made simple and inexpensive enough so that they could be widely adopted throughout the world, including many areas that do not presently have access to reliable sources of electricity.

Professor James Barber, a biochemist from Imperial College London who was not involved in this research, says Nocera’s 2008 finding of the cobalt-based catalyst was a “major discovery,” and these latest findings “are equally as important, since now the water-splitting reaction is powered entirely by visible light using tightly coupled systems comparable with that used in natural photosynthesis. This is a major achievement, which is one more step toward developing cheap and robust technology to harvest solar energy as chemical fuel.”

Barber cautions that “there will be much work required to optimize the system, particularly in relation to the basic problem of efficiently using protons generated from the water-splitting reaction for hydrogen production.” But, he says, “there is no doubt that their achievement is a major breakthrough which will have a significant impact on the work of others dedicated to constructing light-driven catalytic systems to produce hydrogen and other solar fuels from water. This technology will advance side by side with new initiatives to improve and lower the cost of photovoltaics.”

Nocera’s ongoing research with the artificial leaf is directed toward “driving costs lower and lower,” he says, and looking at ways of improving the system’s efficiency. At present, the leaf can redirect about 2.5 percent of the energy of sunlight into hydrogen production in its wireless form; a variation using wires to connect the catalysts to the solar cell rather than bonding them together has attained 4.7 percent efficiency. (Typical commercial solar cells today have efficiencies of more than 10 percent). One question Nocera and his colleagues will be addressing is which of these configurations will be more efficient and cost-effective in the long run.

Another line of research is to explore the use of photovoltaic (solar cell) materials other than silicon — such as iron oxide, which might be even cheaper to produce. “It’s all about providing options for how you go about this,” Nocera says.


Topics: Chemistry and chemical engineering, Energy, Energy storage, Innovation and Entrepreneurship (I&E), Research, Solar, Solar race, Artificial leaf, Photosynthesis, Photovoltaics

Comments

What about the use of this to produce clean water in areas where such water is scarce? Large containers separating the elements out to then be burned to produce the clean water? Since the main drawback to using electrolysis to separate out the H20 is the power this would definitely be a means of doing so without the need for generating that electricity with other fuels. Since the gasses are intended to be burned simple to produce water is there really a need to separate them?
That's a great idea!
In my opnion, this is a very helpful invention with a alot of research. Nevertheless, I consider this to be inefficent. The Sterling Engline - An external combustion engine, will replace the Solar Cell and The Hydrogen Fuel cell, due to the fact it produces more energy in less area, thus it is also cheaper. I will prefer that over the Fuel Cell, with respect to efficency.
"Typical commercial solar cells today have efficiencies of more than 10 percent." Efficiency should always be evaluated through the complete energy cycle rather than exclusively on a specific point of the process - though each step needs to be optimized. i.e. solar cells maybe at 10 percent, but this is then greatly reduced by the conversion for stocking electricity in polluting and technologically complex batteries , then even more complex electrical engines etc. The "leaf" is rather easy tech, sun and water mostly free, stocking H2 and 02 can be low tech and even if used in thermal combustion engines to generate power (with an awful ! efficiency conversion level) all the rather low tech and easy feasibility are making the technology very cheap and widely deployable worldwide... This tech is really opening a boulevard for a cleaner response to local or mobile energy production.
Its great ! Kudos !!
It probably would not be required to split them, no... just do not try and store them mixed. a coffee mug filled with such a mixture, when ignited, would explode so violently that it could take your hand with it. So your large containers would have the potential of taking out the hole house, and resounding houses. keep the mixed volume as small as possible, thin tubing from where they get split to where they are being burned should do the trick. This being said, a fuel-sell does actually produce distilled water when making electricity, so not only would you have the electricity, but pure water too.... of coarse you would probably channel that back to the container where the splitting takes place, and in so doing keep the cycle as clean as possible.
I've asked this before when this project was written about here, but... why does the catalyzed electrolytic reaction have to occur right together with the solar collection/electical conversion, again? It mentions "wireless" and "wired" versions... does this refer to solar cells directly coated with the catalytic materials (wireless) versus those remotely connected to the catalyst materials (wired)? I guess I'm just not getting the reasoning behind the "wireless" version at all, esp. considering its much lower efficiency. The real value here is the catalyzed electrolitic reaction, right. Where it gets its electricity from is a side issue - it could come from solar, but other "green" sources just as easily. There's no reason that I can see to have the catalysts deposited right on a solar cell other than being able to claim the very catchy and PC title of "artificial leaf", which I'm sure brings in many an eager, environmentally-conscious (-guilty?) investor. Or am I missing something?
Electrical engine is several times more efficient than combustion engine. So solar panels are more efficient. Besides, you rarely need a combustion engine for stationary applications, usually you need electricity instead. So, solar panels are more efficient most of the time.
This being said, a fuel-sell does actually produce distilled water when making electricity, so not only would you have the electricity, but pure water too.... of coarse you would probably channel that back to the container where the splitting takes place, and in so doing keep the cycle as clean as possible.
good evening. We are thristy. Our soils are going dryer every day. This summer i could not stay out in the sun, because it was so hot. My mum has skin cancer cellules in her. There´s war everywhere because of gas and fuel. there´s famine. There´s pollution... WHAT are U WaiTING FOR? Best regards Nina
Just because an electrical engine is more efficient than a combustion engine doesn't mean that solar panels are more efficient than this device. The efficiency of these devices is determined by the usable energy output divided by the total energy input. In addition, I believe spagano was suggesting that the hydrogen COULD be used in a combustion engine, BUT could also by used in a fuel cell to produce electricity. On the other hand, the hydrogen would have to be compressed which would reduce the efficiency somewhat.
A very similar device was reported 8 years ago with the same reported "wireless" efficiency: Y Yamada, N Matsuki, T Ohmori, H Mametsuka, M Kondo, A Matsuda, E Suzuki, One chip photovoltaic water electrolysis device, International Journal of Hydrogen Energy, Volume 28, Issue 11, November 2003, Pages 1167-1169 Not much new here from what I can tell.
Thanks for providing that reference, Druey. One thing that's new here is that Nocera's reaction takes place in a neutral solution. The device by Yamada required "the KOH electrolyte at pH 13" which is extremely basic. I've also read that previous catalysts (including, presumably, Yamada's) are either very expensive/rare, or not durable, while Nocera's is inexpensive and self-repairing. Showing that this catalyst can be used in a Yamada type device is new.
I am an mechanical enginiering student in India inventing gravity engine(engine that runs on Gravity),also inventing nuclear battery engine,(eco friendly )The Artificial leaf is an excellent invention.We could have vehicles carrying a water tank which supplies water to this device which then converts water into H2 and O2 which can power a compact fuel cell for vehicle power train. I think this device is one of the most promising device.It is even better than having an electric car with expensive batteries such as tesla model S having a range of 480 Kms per charge.
I imagine that the water must be absolutely pure because certain impurities will likely inactivate the catalysts over time. Have they tested what impact water impurities have on the lifespan?
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