Surprise Discovery Could Revolutionize Solar Energy

This is the experimental setup used to generate femtosecond laser pulses which serve as an ultrafast “flash ” for the camera so that very rapid phenomenon can be filmed. Credit: Simon Gelinas

In a newly published study, researchers from Cambridge’s Cavendish Laboratory detail the surprise discovery that could revolutionize solar energy.

Researchers have been able to tune ‘coherence’ in organic nanostructures due to the surprise discovery of wavelike electrons in organic materials, revealing the key to generating “long-lived charges” in organic solar cells – material that could revolutionize solar energy.

By using an ultrafast camera, scientists say they have observed the very first instants following the absorption of light into artificial yet organic nanostructures and found that charges not only formed rapidly but also separated very quickly over long distances – phenomena that occur due to the wavelike nature of electrons which are governed by fundamental laws of quantum mechanics.

This result surprised scientists as such phenomena were believed to be limited to “perfect” – and expensive – inorganic structures; rather than the soft, flexible organic material believed by many to be the key to cheap, ‘roll-to-roll’ solar cells that could be printed at room temperatures – a very different world from the traditional but costly processing of current silicon technologies.

The study,sheds new light on the mystery mechanism that allows positive and negative charges to be separated efficiently – a critical question that continues to puzzle scientists – and takes researchers a step closer to effectively mimicking the highly efficient ability to harvest sunlight and convert into energy, namely photosynthesis, which the natural world evolved over the course of millennia.

“This is a very surprising result. Such quantum phenomena are usually confined to perfect crystals of inorganic semiconductors, and one does not expect to see such effects in organic molecules – which are very disordered and tend to resemble a plate of cooked spaghetti rather than a crystal,” said Dr Simon Gélinas, from Cambridge’s Cavendish Laboratory, who led the research with colleagues from Cambridge as well as the University of California in Santa Barbara.

During the first few femtoseconds (one millionth of one billionth of a second) each charge spreads itself over multiple molecules rather than being localized to a single one. This phenomenon, known as spatial coherence, allows a charge to travel very quickly over several nanometers and escape from its oppositely charged partner – an initial step which seems to be the key to generating long-lived charges, say the researchers. This can then be used to generate electricity or for chemical reactions.

By carefully engineering the way molecules pack together, the team found that it was possible to tune the spatial coherence and to amplify – or reduce – this long-range separation. “Perhaps most importantly the results suggest that because the process is so fast it is also energy efficient, which could result in more energy out of the solar cell,” said Dr Akshay Rao, a co-author on the study from the Cavendish Laboratory.

Dr Alex Chin, who led the theoretical part of the project, added that, if you look beyond the implications of the study for organic solar cells, this is a clear demonstration of “how fundamental quantum-mechanical processes, such as coherence, play a crucial role in disordered organic and biological systems and can be harnessed in new quantum technologies”.

The work at Cambridge forms part of a broader initiative to harness high tech knowledge in the physics sciences to tackle global challenges such as climate change and renewable energy. This initiative is backed by both the UK Engineering and Physical Sciences Research Council (EPSRC) and the Cambridge Winton Program for the Physics of Sustainability. The work at the University of California in Santa Barbara was supported by the Center for Energy Efficient Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award #DC0001009.

Publication: Simon Gélinas, et al., “Ultrafast Long-Range Charge Separation in Organic Semiconductor Photovoltaic Diodes,” Science, 2013; DOI: 10.1126/science.1246249

Source: University of Cambridge

Image: Simon Gelinas

New System Converts Sun’s Energy into Hydrogen Fuel

Tom Meyer at the Energy Frontier Research Center at the University of North Carolina at Chapel Hill built a device that converts the sun’s energy not into electricity but hydrogen fuel and stores it for later use. The device, a dye-sensitized photoelectrosynthesis cell generates hydrogen fuel by using the sun’s energy to split water into its component parts. After the split, hydrogen is sequestered and stored, while the byproduct, oxygen, is released into the air.

A new system designed by researchers at UNC and NC State converts the sun’s energy into hydrogen fuel and stores it for later use.

Solar energy has long been used as a clean alternative to fossil fuels such as coal and oil, but it could only be harnessed during the day when the sun’s rays were strongest. Now researchers led by Tom Meyer at the Energy Frontier Research Center at the University of North Carolina at Chapel Hill have built a system that converts the sun’s energy not into electricity but hydrogen fuel and stores it for later use, allowing us to power our devices long after the sun goes down.

“So called ‘solar fuels’ like hydrogen offer a solution to how to store energy for nighttime use by taking a cue from natural photosynthesis,” said Meyer, Arey Distinguished Professor of Chemistry at UNC’s College of Arts and Sciences. “Our new findings may provide a last major piece of a puzzle for a new way to store the sun’s energy – it could be a tipping point for a solar energy future.”

In one hour, the sun puts out enough energy to power every vehicle, factory and device on the planet for an entire year. Solar panels can harness that energy to generate electricity during the day. But the problem with the sun is that it goes down at night—and with it the ability to power our homes and cars. If solar energy is going to have a shot at being a clean source for powering the planet, scientists had to figure out how to store it for night-time use.

The new system designed by Meyer and colleagues at UNC and with Greg Parsons’ group at North Carolina State University does exactly that. It is known as a dye-sensitized photoelectrosynthesis cell, or DSPEC, and it generates hydrogen fuel by using the sun’s energy to split water into its component parts. After the split, hydrogen is sequestered and stored, while the byproduct, oxygen, is released into the air.

“But splitting water is extremely difficult to do,” said Meyer. “You need to take four electrons away from two water molecules, transfer them somewhere else, and make hydrogen, and, once you have done that, keep the hydrogen and oxygen separated. How to design molecules capable of doing that is a really big challenge that we’ve begun to overcome.”

Meyer had been investigating DSPECs for years at the Energy Frontier Research Center at UNC and before. His design has two basic components: a molecule and a nanoparticle. The molecule, called a chromophore-catalyst assembly, absorbs sunlight and then kick starts the catalyst to rip electrons away from water. The nanoparticle, to which thousands of chromophore-catalyst assemblies are tethered, is part of a film of nanoparticles that shuttles the electrons away to make the hydrogen fuel.

However, even with the best of attempts, the system always crashed because either the chromophore-catalyst assembly kept breaking away from the nanoparticles or because the electrons couldn’t be shuttled away quickly enough to make hydrogen.

To solve both of these problems, Meyer turned to the Parsons group to use a technique that coated the nanoparticle, atom by atom, with a thin layer of a material called titanium dioxide. By using ultra-thin layers, the researchers found that the nanoparticle could carry away electrons far more rapidly than before, with the freed electrons available to make hydrogen. They also figured out how to build a protective coating that keeps the chromophore-catalyst assembly tethered firmly to the nanoparticle, ensuring that the assembly stayed on the surface.

With electrons flowing freely through the nanoparticle and the tether stabilized, Meyer’s new system can turn the sun’s energy into fuel while needing almost no external power to operate and releasing no greenhouse gases. What’s more, the infrastructure to install these sunlight-to-fuel converters is in sight based on existing technology. A next target is to use the same approach to reduce carbon dioxide, a greenhouse gas, to a carbon-based fuel such as formate or methanol.

“When you talk about powering a planet with energy stored in batteries, it’s just not practical,” said Meyer. “It turns out that the most energy dense way to store energy is in the chemical bonds of molecules. And that’s what we did – we found an answer through chemistry.”

Related Studies:

• Leila Alibabaeia, et al., “Solar water splitting in a molecular photoelectrochemical cell,” PNAS, vol. 110 no. 50, 20008–20013; doi: 10.1073/pnas.1319628110
• Hanlin Luo, et al., “A Sensitized Nb2O5 Photoanode for Hydrogen Production in a Dye-Sensitized Photoelectrosynthesis Cell,” Chem. Mater., 2013, 25 (2), pp 122–131; DOI: 10.1021/cm3027972

Source: University of North Carolina at Chapel Hill

Image: Yan Liang

Engineers Convert Yeast Cells into Biofuel

Left: Starting cells with around 15 percent lipid content. Right: Engineered cells with nearly 90 percent lipid content.

Using genetically engineered yeast cells and ordinary table sugar, engineers from the Cockrell School of Engineering developed a new biofuel.

Austin, Texas — Researchers at The University of Texas at Austin’s Cockrell School of Engineering have developed a new source of renewable energy, a biofuel, from genetically engineered yeast cells and ordinary table sugar. This yeast produces oils and fats, known as lipids, that can be used in place of petroleum-derived products.

Assistant professor Hal Alper, in the Cockrell School’s McKetta Department of Chemical Engineering, along with his team of students, created the new cell-based platform. Given that the yeast cells grow on sugars, Alper calls the biofuel produced by this process “a renewable version of sweet crude.”

The researchers’ platform produces the highest concentration of oils and fats reported through fermentation, the process of culturing cells to convert sugar into products such as alcohol, gases or acids.

The UT Austin research team was able to rewire yeast cells to enable up to 90 percent of the cell mass to become lipids, which can then be used to produce biodiesel.

“To put this in perspective, this lipid value is approaching the concentration seen in many industrial biochemical processes,” Alper said. “You can take the lipids formed and theoretically use it to power a car.”

Since fatty materials are building blocks for many household products, this process could be used to produce a variety of items made with petroleum or oils — from nylon to nutrition supplements to fuels. Biofuels and chemicals produced from living organisms represent a promising portion of the renewable energy market. Overall, the global biofuels market is expected to double during the next several years, going from $82.7 billion in 2011 to $185.3 billion in 2021.

“We took a starting yeast strain of Yarrowia lipolytica, and we’ve been able to convert it into a factory for oil directly from sugar,” Alper said. “This work opens up a new platform for a renewable energy and chemical source.”

The biofuel the researchers formulated is similar in composition to biodiesel made from soybean oil. The advantages of using the yeast cells to produce commercial-grade biodiesel are that yeast cells can be grown anywhere, do not compete with land resources and are easier to genetically alter than other sources of biofuel.

“By genetically rewiring Yarrowia lipolytica, Dr. Alper and his research group have created a near-commercial biocatalyst that produces high levels of bio-oils during carbohydrate fermentation,” said Lonnie O. Ingram, director of the Florida Center for Renewable Chemicals and Fuels at the University of Florida. “This is a remarkable demonstration of the power of metabolic engineering.”

So far, high-level production of biofuels and renewable oils has been an elusive goal, but the researchers believe that industry-scale production is possible with their platform.

In a large-scale engineering effort spanning over four years, the researchers genetically modified Yarrowia lipolytica by both removing and overexpressing specific genes that influence lipid production. In addition, the team identified optimum culturing conditions that differ from standard conditions. Traditional methods rely on nitrogen starvation to trick yeast cells into storing fat and materials. Alper’s research provides a mechanism for growing lipids without nitrogen starvation. The research has resulted in a technology for which UT Austin has applied for a patent.

“Our cells do not require that starvation,” Alper said. “That makes it extremely attractive from an industry production standpoint.”

The team increased lipid levels by nearly 60-fold from the starting point.

At 90 percent lipid levels, the platform produces the highest levels of lipid content created so far using a genetically engineered yeast cell. To compare, other yeast-based platforms yield lipid content in the 50 to 80 percent range. However, these alternative platforms do not always produce lipids directly from sugar as the UT Austin technology does.

Alper and his team are continuing to find ways to further enhance the lipid production levels and develop new products using this engineered yeast.

This research was funded by the Office of Naval Research Young Investigator Program, the DuPont Young Professor Grant and the Welch Foundation under grant F-1753.

Publication: John Blazeck, et al., “Harnessing Yarrowia lipolytica lipogenesis to create a platform for lipid and biofuel production,” Nature Communications 5, Article number: 3131; doi:10.1038/ncomms4131

Source: University of Texas at Austin’s Cockrell School of Engineering

Image: University of Texas at Austin’s Cockrell School of Engineering