Tag Archives: artificial leaf

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Artificial leaf breakthrough makes solar fuels one step closer

A team at Caltech has devised a new film coating that facilitates catalysis and electron transfer in a solar powered system that splits water into hydrogen and oxygen, which can be used as fuels. Such a system is also called an artificial leaf or solar-fuel generator because in many ways it mimics the process which plants use to convert sunlight and CO2 into oxygen and fuel (sugars, carbohydrates). The researchers make note, however, that they’re still a long way from making it commercial viable, but these sort of updates are inspiring.

Inspired by nature, nurtured by technology

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Image: Techietonics

The artificial leaf developed at the Caltech Joint Center for Artificial Photosynthesis (JCAP) consists of three main components: two electrodes — a photoanode and a photocathode — and a membrane. At the photoanode side, water molecules are split into oxygen gas (O2), electrons and hydrogen protons through oxidation in the presence of sunlight and the thin film coating the team recently developed. The coating is a nickel oxide film that prevents rusts building-up on the semiconductor electrodes (silicon or gallium arsenide), while also acting as a highly reactive catalysis. The electrons travel through a circuit to the photocathode where they combine with the hydrogen protons to make hydrogen gas (H2). Like in a fuel cell, the membrane is not only essential to collecting the hydrogen, but also to keep the highly reactive oxygen and hydrogen from recombining. In some cases, this reaction can also lead to explosions. Essentially, the Caltech membrane for their artificial leaf only allows hydrogen protons to pass through, like an ion sieve, while hydrogen and oxygen gases are safely and separately expelled to use as fuels or oxidants.

Ke Sun's reflection onto a sample coating with the nickel oxide film his team developed. Image: Lance Hayashida, Caltech Marcomm

Ke Sun’s reflection onto a sample coating with the nickel oxide film his team developed. Image: Lance Hayashida, Caltech Marcomm

Of course, the system is nothing new – the coating represents the real breakthrough. The photoelectrodes, left by themselves, are very vulnerable to oxidation (rust) and in a short while this ruins the solar-fuel generator’s operation. Scientists had to find a film that is easy to apply, highly catalytic, doesn’t oxidize and cheap to make. It took a lot of hard work, but eventually the team led by Nate Lewis, the George L. Argyros Professor and professor of chemistry at Caltech, hit the jackpot.

“After watching the photoanodes run at record performance without any noticeable degradation for 24 hours, then 100 hours and then 500 hours, I knew we had done what scientists had failed to do before,” says Ke Sun for ZME Science, a postdoc in Lewis’s lab and the first author of the new study.

The film also had to work well with the membrane to make it safe. To make the nickel oxide coating, the researchers used  a technique which involves smashing atoms of argon into a pellet of nickel atoms at high speed.

“Without a membrane, the photoanode and photocathode are close enough to each other to conduct electricity, and if you also have bubbles of highly reactive hydrogen and oxygen gases being produced in the same place at the same time, that is a recipe for disaster,” Lewis says regarding his findings published in PNAS. “With our film, you can build a safe device that will not explode, and that lasts and is efficient, all at once.”

Next, Lewis and colleagues need to perfect the photocathode. Their system isn’t viable (too little hydrogen is made), but at least one key piece of the jigsaw puzzle that has eluded scientists for the past 50 years has been solved.

The prototype for the first practical "artificial leaf," which has been hyped in the media since its flashy debut at the American Chemical Society national meeting last year. Image: MIT

Artificial leaf and bacteria turn sunlight into liquid fuel

Using only energy from the sun, a pioneering artificial leaf system splits water to generate hydrogen – a highly energy dense fuel. When Daniel Nocera, then a professor at MIT, announced his device for the first time four years ago, people were really hyped about it but it soon became clear that making hydrogen was only part of the solution. “The problem with the artificial leaf,” Nocera says, is that “it makes hydrogen. You guys don’t have an infrastructure to use hydrogen.” Why aren’t we seeing more hydrogen cars on the streets? Because there aren’t any hydrogen fueling stations. Why aren’t any hydrogen pumps? Because hydrogen is one bad mother. It’s the smallest stable molecule and it naturally wants to escape into the atmosphere. To contain it you need to compress it to at least 10,000 PSI (more like 100,000 PSI to be sure) which makes it extremely expensive and prohibitive.

Sunlight to liquid fuel

The prototype for the first practical "artificial leaf," which has been hyped in the media since its flashy debut at the American Chemical Society national meeting last year. Image: MIT

The prototype for the first practical “artificial leaf,” which has been hyped in the media since its flashy debut at the American Chemical Society national meeting last year. Image: MIT

Conspiracies aside, diesel and gasoline are here to stay for a long while because they’re so convenient – they’re cheap, readily available and liquid at normal temperature and pressure. Also, while hydrogen  has more energy per unit mass than other fuels, it’s much less dense than other fuels. A gallon of gasoline has a mass of 6.0 pounds, the same gallon of liquid hydrogen only has a mass of 0.567 pounds or only 9.45% of the mass of gasoline.  Therefore one gallon of gasoline yields 125,400 BTUs of energy while a gallon of liquid hydrogen yields only 34,643 BTUs or 27.6% of the energy in a gallon of gasoline. What are we to do with an artificial leaf that makes hydrogen, then? Well, Nocera and his new colleagues at Harvard now report pairing their hydrogen-generating leaf with an engineered bacteria called Ralstonia eutropha to generate biomass and isopropyl alcohol, respectively – an alcohol fuel comparable to ethanol. This way, the extra step converts the hydrogen in a much more manageable fuel. Though, far from efficient right now, the system might become a viable means of storing energy from the sun – still a lifelong engineering problem.

Biofuels like ethanol are made from biomass. We call biomass any biological material derived from living, or recently living organisms – most often than not plants. In nature, plants use photosynthesis to capture CO2 and use it with water in the presence of energy from the sun to make organic compounds of carbons. These are stored and can then be used to generate energy. Sticking with ethanol, this can be broken down from starchy corn kernels. The Harvard system bypasses the biomass step and goes straight to liquid fuel thanks to their engineered bacterium.

The simple setup consists of a  triple-junction solar cell, connected with two catalysts: cobalt-borate for splitting the water molecule and a nickel-molybdenum-zinc alloy to form the hydrogen gas. The bacteria then absorbs the hydrogen, combines it with carbon dioxide, eventually producing the isopropyl alcohol. The resulting system would look like an algae farm, Nocera says, except that the bacteria wouldn’t need the continuous light or maintenance that algae require.

While it all sounds extremely appealing, there are still many challenges that the researchers need to overcome. One has already been met. In initial runs the bacteria kept dying. They eventually identified  reactive oxygen as being the culprit, but what was surprising was its source. Reactive oxygen species were coming out of the hydrogen side of the water splitting, not the oxygen side. “We were shocked,” Nocera said for National Geographic. “That confused us for a while.”

Next, they need to improve the system’s flow such that it might become efficient and make sense economically. Right now, there’s more energy going into growing the microbes and extracting the fuel than going out. Findings appeared in PNAS.

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First man-made biological leaf might actually be useless

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Credit: Julian Melchiorri

This past week, social media channels have been flooded with the story of the first functioning artificial leaf – a material that encases chloroplasts into silk proteins to generate oxygen from water and light. Websites like CNET and Gizmodo rushed to hail the invention as a viable means to generate oxygen inside spaceships or off-Earth colonies on Mars or the moon. If the leaf really works as the hype would have us believe, then it’s really a fantastic display of ingenuity. However, there’s no scientific paper, no data from tests that might tell us how efficient the leaf is at photosynthesis (if such tests even exist) and no solid scientific grounds that would suggest the leaf would actually work as intended. For the moment, it seems like this artificial leaf in question is more conceptual than it is practical.

Does it really work?

Its creator is Julian Melchiorri, a student at the Royal College of Art. He claims he has created the first man-made, biologically functional leaf that takes in carbon dioxide, water, and light and releases oxygen. Basically, the leaf consists of chloroplasts – organelles found in plant cells and eukaryotic algae that conduct photosynthesis – suspended in a body made of silk protein.

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Credit: Julian Melchiorri

“This material has an amazing property of stabilizing (the chloroplast) organelles,” Melchiorri says in a presentation video. “As an outcome I have the first photosynthetic material that is living and breathing as a leaf does.”

The leaf could be used in space exploration as an oxygen generator. Its advantage over regular plants would be that it doesn’t require soil or special nutrients and isn’t confined to any problems that plant growth might face in zero gravity. Here on Earth, the leaf could be used for both indoor and outdoor environments, literally providing a breath of fresh air.

The "Silk Leaf" uses light given off by your bulbs to fuel fresh oxygen generation in your living room. Image: Julian Melchiorri

The “Silk Leaf” uses light given off by your bulbs to fuel fresh oxygen generation in your living room. Image: Julian Melchiorri

It all sounds very exciting, but is it all just for show? Wrapping chloroplasts into silk proteins is a great idea, yet while the design may provide photosynthesis, it’s highly unlikely this can be sustained. Chloroplasts are membrane wrapped-organelles. As such, they depend on various cellular pathways that cycle membrane and proteins to keep healthy. So, once you put them out of their environment, they’ll stop working soon. Dr. Wim Vermaas of Arizona State University’s Center for Bioenergy and Photosynthesis puts it better than I ever will:

‘[…] while it may possibly be true that silk proteins stabilize chloroplast function somehow, proteins in a cell are in a constant state of turnover (some more than others) and eventually (on the scale of hours or perhaps days), the system will inactivate. In isolated chloropolasts spread out on silk, no new nuclear-encoded proteins can be accessed. And as most of the proteins in the chloroplast need to be important, the life of an isolated chloroplast is necessarily short-lived. So, it won’t be surviving long enough to be useful for a space mission, I’m afraid,’ said Dr. Vermaas speaking for Materia.

For now, the best means of generating oxygen in space remains electrolysis, a process which uses electricity to split water into hydrogen and oxygen. The electricity is sourced from solar panels strapped on the spaceship or space station. Melchiorri’s leaf has the added advantage of working without any external energy input. If it works in the first place. Again, we’ve only been offered a superficial view of its inner workings. Personally, I hope it will eventually work, but I’m not betting on it.

 

Laying a roadmap for future artificial leafs

MIT researchers have published a detailed analysis of all the factors that could limit the efficiency of such a system, basically laying a roadmap for a research program to improve the efficiency of so-called artificial leafs.

An artificial leaf has to produce a storable fuel, such as hydrogen, instead of electricity for immediate use; the fuel could then be used in another mechanism to generate electricity. This latest paper was published in PNAS by associate professor of mechanical engineering Tonio Buonassisi, former MIT professor Daniel Nocera (now at Harvard University), MIT postdoc Mark Winkler (now at IBM) and former MIT graduate student Casandra Cox (now at Harvard).

“We don’t always get it right,” Buonassisi says, but such an analysis “lays a roadmap for development and identifies a few ‘levers’ that can be worked on.”

Their work discusses two technologies: a standard silicon solar cell, which converts sunlight into electricity, and chemical catalysts applied to each side of the cell. The goal is to make something cost-effective that could be built from cheap materials but is also efficient – because after all, this is a technology that has to be applied large scale to work.

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“What’s significant is that this paper really describes all this technology that is known, and what to expect if we put it all together,” Cox says. “It points out all the challenges, and then you can experimentally address each challenge separately.”

“We were surprised, actually,” Winkler says: Conventional wisdom held that the characteristics of silicon solar cells would severely limit their effectiveness in splitting water, but that turned out not to be the case. “You’ve just got to question the conventional wisdom sometimes,” he says.

They key to obtaining high solar-to-fuel efficiencies is to combine the right solar cells with a catalyst – and the first thing you have to know in order to do this is what you shouldn’t do. You can then take the individual components that work effectively on their own, and see which ones would also work together. The voltage produced by a standard silicon solar cell, about 0.7 volts, is insufficient to power the water-splitting reaction – which requires at least 1.2 volts. A solution would be to pair multiple solar cells in series – while you would lose some energy between cells, this would be acceptable.

Another problem they have tried to solve is that of the water itself. In order to complete the electrical circuit, the current must pass through a significant distance in water, which has resistance to electrons.

“In our simulations, we have a framework to determine the limits of efficiency” that are possible with such a system, Buonassisi says. For a system based on conventional silicon solar cells, he says, that limit is about 16 percent; for gallium arsenide cells, a widely touted alternative, the limit rises to 18 percent.

The next step is to put all these models and theoretical improvements into practice:

“It is very important to construct a working system which has a large surface area and operates with solar energy under open field conditions for a long period of time, as is done with the testing of solar cells.” If this can be achieved, he says, “the construction of robust and efficient solar-driven modules which produce hydrogen from water on a large industrial scale would have considerable impact on human society.”, Barber concludes.

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Artificial leaf closer to reality after two new studies

If harnessed at a much greater potential than it is now, sunlight might not only become the primary source of energy on the planet, but the cheapest too. In one hour the sun sprays our planet with enough energy to power all the electrical needs of the word for an entire YEAR. Now that’s something to think about, and luckily scientists around the world have studied this prospect to find a solution, other than the current counter-efficient photo-voltaic cells that power solar panels. This past week alone, two independent studies published almost concomitently come up as breakthroughs for the ultimate development of cost-effective and productive sun harnessing technology.

You might remember  Daniel Nocera, an MIT professor of Chemistry, and his artificial leaf setup featured on ZME Science a few months back. Now, Nocera has officially presented his work to rest of the scientific community, after his paper was published in the journal Science. Basically, the chemist’s device splits water into molecular hydrogen (H2) and oxygen (O2), somewhat similar to the way plants carry out the first step in photosynthesis. These components can then be stored and used as fuels.

Other research in the past rendered similar results to that of professor Nocera, however the conditions and equipement required to produced the same effects were way more cost detriment. However, Nocera’s group managed to get artificial photosynthesis to work using benign conditions and cheap, abundant materials as catalysts. Specifically, the setup was comprised of a simple, commercially available triple-junction solar cell, connected with two catalysts: cobalt-borate for splitting the water molecule and a nickel-molybdenum-zinc alloy to form the hydrogen gas.

Artificial Leaf

The researchers say they haven’t fixed a release date or even size for the final product, which scientists claim will be capable of powering a small home without a problem. The artificial leaf system will also have wireless capabilities, which is actually the most enticing part of this particular research.

“Because there are no wires, we are not limited by the size that the light-absorbing material has to be,” says Steven Reece, a research scientist with Sun Catalytix (a company cofounded by Nocera) who worked on the discovery. “We can operate on the micro- or even nanoscale…so you can imagine micro- or nanoparticles, similar to the cells we’ve worked with here, dispersed in a solution.”

Researchers believe such devices could help provide power in poor areas that lack consistent sources of electricity.

“As the inputs are light and water, and the output is fuel, one can certainly see the applicability of something like that to the developing world,” says Thomas Jarvi, chief technology officer at Sun Catalytix.

The second study, published concomitently with the hydrogen fuel artificial leaf producer, involves a different take on harnessing photosynthesis, namely recycling CO2. In the natural world, the sun’s energy extracts electrons from a water molecule, which then reduce CO2 into fuel (in plants, the fuel takes the form of carbohydrates).

In the report, published by a team led by chemists Richard Masel of Dioxide Materials in Champaign, Illinois, and Paul Kenis of the University of Illinois Urbana-Champaign, the researchers show how they’ve managed to come up with a more energy efficent solution to turning CO2 into CO.  Converting CO2 to CO has always required applying large electrical voltages to CO2 to make the change. These large eletrical voltages actually translate into high loss of energy, which would’ve never compensate in carbohydrate fuel.

However, the researchers have managed to make the process extremely cost-effective, now, by using ionic liquid in their setup, a novel component to use as a solvent in junction with CO2 – one that is 10 times more energy efficient.

Remarkably, study leader Masel claims the photosinthetic setup might provide the necessary background for an upgrade capable of  turning CO2 into “syngas”—a mixture used in the petrochemical industry to make gasoline and other fuels.

The experiment “shows that one can make syngas efficiently from any source of electricity,” Masel says. However, large-scale versions of the device probably won’t be demonstrated until 2018. “Presently we have demonstrated the process on the 1-centimeter-squared scale. We need to go to the million cm2 to make significant amounts of gasoline.

‘Artificial leafs’ turn water and sunlight into electricity

The sun is the biggest source of energy on our planet, and it’s all natural. It’s enough to realize that in one hour the sun produces enough energy to power all the electrical needs of the word for an entire YEAR! Naturally, research has been underway for many years now for means of practically and efficiently exploiting this remarkable natural resource, however progress is slow and so far solar energy accounts for a negligible percentage (around 0.05%) of the total electricity generating resources.

Conventional photovoltaic solar panels are getting more popular and used, but rejoicing as it is, they’re highly inefficient and hard to deploy at a necessary mass scale. A very interesting alternative is the so called “artificial leaf” technology, which has been in the works for a decade now, but only recently it has come to a practical, efficient and cheap form out of MIT labs.

What artificial leafs do is harness the power of nature just like nature does it, in this case by artificial photosynthesis. Massachusetts Institute of Technology professor Daniel Nocera presented the results of his work and that of colleagues on the artificial leaf at this year’s National Meeting of the American Chemical Society. There, he showed how we can draw cheap and clean energy from water and the sun, by splitting water to get hydrogen fuel and oxygen.

Placed in a single gallon of water in bright sunlight, the device could produce enough electricity to supply a house in a developing country with electricity for a day, Nocera said.

“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,” Nocera said in a statement.

The breakthrough was made when the manufacturing of the indispensable catalysts was made possible using cheap materials like nickel and cobalt, instead of platinum.

“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, in a press release. “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. One can envision villages in India and Africa not long from now purchasing an affordable basic power system based on this technology.”

A prototype of the artificial leaf device was reported to have run for more than 45 hours continously without any degradation in performance whatsoever. Also, it’s artificial photosynthesis is 10 times more efficient than that of a plant, and researchers hope to improve it to a much greater extent.

This is the researchers’ second-generation product, an improvement on their earlier release called “electrolyzer that splits water into hydrogen and oxygen” under the Sun Catalytix company, a start-up founded by Nocera which received a $4,000,000 grant from the Advanced Research Projects Agency-Energy (ARPA-E). Reports say that Sun Catalytix has signed a deal with the Indian company Tata group that could try to bring the technology to market consumers all over the world.

To get a better idea on how the artificial leaf works, press play on the youtube video below where the concept and how it works is explained in detail.