Sun-Free Photovoltaics Powered by Heat

Sun-Free Photovoltaics Powered by Heat

  6:24:00 PM    Science Lover

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A new photovoltaic energy-conversion system developed at MIT can be powered solely by heat, generating electricity with no sunlight at all. While the principle involved is not new, a novel way of engineering the surface of a material to convert heat into precisely tuned wavelengths of light -- selected to match the wavelengths that photovoltaic cells can best convert to electricity -- makes the new system much more efficient than previous versions.

A variety of silicon chip micro-reactors developed by the MIT team. Each of these contains photonic crystals on both flat faces, with external tubes for injecting fuel and air and ejecting waste products. Inside the chip, the fuel and air react to heat up the photonic crystals. In use, these reactors would have a photovoltaic cell mounted against each face, with a tiny gap between, to convert the emitted wavelengths of light to electricity. (Credit: Photo by Justin Knight)

The key to this fine-tuned light emission, described in the journal Physical Review A, lies in a material with billions of nanoscale pits etched on its surface. When the material absorbs heat -- whether from the sun, a hydrocarbon fuel, a decaying radioisotope or any other source -- the pitted surface radiates energy primarily at these carefully chosen wavelengths.

Based on that technology, MIT researchers have made a button-sized power generator fueled by butane that can run three times longer than a lithium-ion battery of the same weight; the device can then be recharged instantly, just by snapping in a tiny cartridge of fresh fuel. Another device, powered by a radioisotope that steadily produces heat from radioactive decay, could generate electricity for 30 years without refueling or servicing -- an ideal source of electricity for spacecraft headed on long missions away from the sun.

According to the U.S. Energy Information Administration, 92 percent of all the energy we use involves converting heat into mechanical energy, and then often into electricity -- such as using fuel to boil water to turn a turbine, which is attached to a generator. But today's mechanical systems have relatively low efficiency, and can't be scaled down to the small sizes needed for devices such as sensors, smartphones or medical monitors.

"Being able to convert heat from various sources into electricity without moving parts would bring huge benefits," says Ivan Celanovic ScD '06, research engineer in MIT's Institute for Soldier Nanotechnologies (ISN), "especially if we could do it efficiently, relatively inexpensively and on a small scale."

It has long been known that photovoltaic (PV) cells needn't always run on sunlight. Half a century ago, researchers developed thermophotovoltaics (TPV), which couple a PV cell with any source of heat: A burning hydrocarbon, for example, heats up a material called the thermal emitter, which radiates heat and light onto the PV diode, generating electricity. The thermal emitter's radiation includes far more infrared wavelengths than occur in the solar spectrum, and "low band-gap" PV materials invented less than a decade ago can absorb more of that infrared radiation than standard silicon PVs can. But much of the heat is still wasted, so efficiencies remain relatively low.

An ideal match

The solution, Celanovic says, is to design a thermal emitter that radiates only the wavelengths that the PV diode can absorb and convert into electricity, while suppressing other wavelengths. "But how do we find a material that has this magical property of emitting only at the wavelengths that we want?" asks Marin Soljačić, professor of physics and ISN researcher. The answer: Make a photonic crystal by taking a sample of material and create some nanoscale features on its surface -- say, a regularly repeating pattern of holes or ridges -- so light propagates through the sample in a dramatically different way.



"By choosing how we design the nanostructure, we can create materials that have novel optical properties," Soljačić says. "This gives us the ability to control and manipulate the behavior of light."

The team -- which also includes Peter Bermel, research scientist in the Research Laboratory for Electronics (RLE); Peter Fisher, professor of physics; and Michael Ghebrebrhan, a postdoc in RLE -- used a slab of tungsten, engineering billions of tiny pits on its surface. When the slab heats up, it generates bright light with an altered emission spectrum because each pit acts as a resonator, capable of giving off radiation at only certain wavelengths.

This powerful approach -- co-developed by John D. Joannopoulos, the Francis Wright Davis Professor of Physics and ISN director, and others -- has been widely used to improve lasers, light-emitting diodes and even optical fibers. The MIT team, supported in part by a seed grant from the MIT Energy Initiative, is now working with collaborators at MIT and elsewhere to use it to create several novel electricity-generating devices.

Mike Waits, an electronics engineer at the Army Research Laboratory in Adelphi, Md., who was not involved in this work, says this approach to producing miniature power supplies could lead to lighter portable electronics, which is "critical for the soldier to lighten his load. It not only reduces his burden, but also reduces the logistics chain" to deliver those devices to the field. "There are a lot of lives at stake," he says, "so if you can make the power sources more efficient, it could be a great benefit."

The button-like device that uses hydrocarbon fuels such as butane or propane as its heat source -- known as a micro-TPV power generator -- has at its heart a "micro-reactor" designed by Klavs Jensen, the Warren K. Lewis Professor of Chemical Engineering, and fabricated in the Microsystems Technology Laboratories. While the device achieves a fuel-to-electricity conversion efficiency three times greater than that of a lithium-ion battery of the same size and weight, Celanovic is confident that with further work his team can triple the current energy density. "At that point, our TPV generator could power your smartphone for a whole week without being recharged," he says.

Celanovic and Soljačić stress that building practical systems requires integrating many technologies and fields of expertise. "It's a really multidisciplinary effort," Celanovic says. "And it's a neat example of how fundamental research in materials can result in new performance that enables a whole spectrum of applications for efficient energy conversion."

Note: The full version of the MITEI story is available at: http://web.mit.edu/mitei/research/spotlights/making-electricity-with-photovoltaics.html

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Carbon Sequestration: Steam Process Could Remove Carbon Dioxide to Regenerate Amine Capture Materials

Carbon Sequestration: Steam Process Could Remove Carbon Dioxide to Regenerate Amine Capture Materials

  12:55:00 AM    Science Lover

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Because they can remove carbon dioxide from the flue gases of coal-burning facilities such as power plants, solid materials containing amines are being extensively studied as part of potential CO2 sequestration programs designed to reduce the impact of the greenhouse gas.

A relatively simple regeneration technique that could utilize waste steam to remove carbon dioxide from solid amine materials used to capture the greenhouse gas from the flue gases of coal-burning facilities. (Credit: iStockphoto/Andy Olsen)

But although these adsorbent materials do a good job of trapping the carbon dioxide, commonly-used techniques for separating the CO2 from the amine materials -- thereby regenerating them for re-use -- seem unlikely to be suitable for high-volume industrial applications.

Now, researchers have demonstrated a relatively simple regeneration technique that could utilize waste steam generated by many facilities that burn fossil fuels. This steam-stripping technique could produce concentrated carbon dioxide ready for sequestration in the ocean or deep-earth locations -- while readying the amine materials for further use.

"We have demonstrated an approach to developing a practical adsorption process for capturing carbon dioxide and then releasing it in a form suitable for sequestration," said Christopher Jones, a professor in the School of Chemical & Biomolecular Engineering at the Georgia Institute of Technology.

The research was reported online June 23, 2010 in the early view version of the journal ChemSusChem. The work was supported by New York-based Global Thermostat, LLC., a company that is developing and commercializing technology for the direct capture of carbon dioxide from the air.

Amine sorbents are often regenerated through a process that involves a change in temperature to supply the energy required to break the amine-carbon dioxide chemical bonds.

For convenience, researchers commonly remove the CO2 by heating the amine material in the presence of a flowing gas such as nitrogen or helium. That removes the carbon dioxide, but mixes it with the flowing gas -- regenerating the material, but leaving the CO2 mixed with nitrogen or helium.

Another approach is to heat the material in a carbon dioxide stream, but that is less efficient and can lead to fouling of the amine.

Jones and his team from Georgia Tech, SRI International and Global Thermostat took a different approach, heating the sorbent amine in steam at a temperature of approximately 105 degrees Celsius, causing the carbon dioxide to separate from the material. The steam can then be compressed, condensing the water and leaving a concentrated flow of carbon dioxide suitable for sequestration or other use -- such as a nutrient for algae growth.

Because most coal-burning facilities generate steam, some of that might be bled off to achieve the separation and regeneration without a significant energy penalty. "In many facilities, steam at this temperature would have no other application, so using it for this purpose would not have a significant cost to the plant," Jones noted.

The researchers studied three common formulations of the amine material: Class 1 adsorbents based on porous supports impregnated with monomeric or polymeric amines, Class 2 adsorbents that are covalently linked to a solid support, and Class 3 adsorbents based on porous supports upon which aminopolymers are polymerized in-situ, starting from an amine-containing monomer.

The adsorbents were studied through three cycles of carbon dioxide adsorption and steam-stripping. The researchers found differences in how each material was affected by the steam-stripping; performance of the most stable material actually improved, while the least stable material suffered a 13 percent efficiency decline.

"Steam-stripping is widely used in other separation processes, but has never been reported for use with supported amine materials, perhaps due to concerns about sorbent stability," Jones said. "We reported three uses of the materials in the paper and have only tested them through five or six uses, but we expect the materials could be used many more times. To be practical, the amine-containing materials need to be useful through thousands of cycles."

Pilot-scale carbon dioxide separation facilities are already in operation using amines dissolved in water. Because of the energy required to regenerate the liquid solutions, many researchers have been examining solid amines -- but the work so far has focused mostly on improving the efficiency of the materials, he added.

Though much remains to be done before solid amine materials can be used in large-scale applications, Jones believes the study demonstrates that improved materials can be developed with properties tailored for the steam regeneration process.

"We believe there is potential for development of materials that will be stable for long-term use during regeneration using this technique," he said. "This study lays the groundwork for an array of future studies that will lead to an understanding of the structural changes induced by steam-stripping."

In addition to Jones, the research team included Wen Li, Sunho Choi and Jeffery Drese from Georgia Tech, Marc Hornbostel and Gopala Krishnan from SRI International, and Peter M. Eisenberger of Global Thermostat, LLC.

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Renewable Energy: Inexpensive Metal Catalyst Can Effectively Generate Hydrogen from Water

Renewable Energy: Inexpensive Metal Catalyst Can Effectively Generate Hydrogen from Water

  11:55:00 PM    Science Lover

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Hydrogen would command a key role in future renewable energy technologies, experts agree, if a relatively cheap, efficient and carbon-neutral means of producing it can be developed. An important step towards this elusive goal has been taken by a team of researchers with the U.S. Department of Energy's (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California, Berkeley. The team has discovered an inexpensive metal catalyst that can effectively generate hydrogen gas from water.

From left, Jeffrey Long, Christopher Chang and 
Hemamala Karunadasa have discovered an inexpensive 
metal that can generate hydrogen from neutral water, 
even if it is dirty, and can operate in sea water. 
(Credit: Photo by Roy Kaltschmidt, Berkeley Lab Public Affairs)

"Our new proton reduction catalyst is based on a molybdenum-oxo metal complex that is about 70 times cheaper than platinum, today's most widely used metal catalyst for splitting the water molecule," said Hemamala Karunadasa, one of the co-discoverers of this complex. "In addition, our catalyst does not require organic additives, and can operate in neutral water, even if it is dirty, and can operate in sea water, the most abundant source of hydrogen on earth and a natural electrolyte. These qualities make our catalyst ideal for renewable energy and sustainable chemistry."

Karunadasa holds joint appointments with Berkeley Lab's Chemical Sciences Division and UC Berkeley's Chemistry Department. She is the lead author of a paper describing this work that appears in the April 29, 2010 issue of the journal Nature, titled "A molecular molybdenum-oxo catalyst for generating hydrogen from water." Co-authors of this paper were Christopher Chang and Jeffrey Long, who also hold joint appointments with Berkeley Lab and UC Berkeley. Chang, in addition, is also an investigator with the Howard Hughes Medical Institute (HHMI).

Hydrogen gas, whether combusted or used in fuel cells to generate electricity, emits only water vapor as an exhaust product, which is why this nation would already be rolling towards a hydrogen economy if only there were hydrogen wells to tap. However, hydrogen gas does not occur naturally and has to be produced. Most of the hydrogen gas in the United States today comes from natural gas, a fossil fuel. While inexpensive, this technique adds huge volumes of carbon emissions to the atmosphere. Hydrogen can also be produced through the electrolysis of water -- using electricity to split molecules of water into molecules of hydrogen and oxygen. This is an environmentally clean and sustainable method of production -- especially if the electricity is generated via a renewable technology such as solar or wind -- but requires a water-splitting catalyst.

Nature has developed extremely efficient water-splitting enzymes -- called hydrogenases -- for use by plants during photosynthesis, however, these enzymes are highly unstable and easily deactivated when removed from their native environment. Human activities demand a stable metal catalyst that can operate under non-biological settings.

Metal catalysts are commercially available, but they are low valence precious metals whose high costs make their widespread use prohibitive. For example, platinum, the best of them, costs some $2,000 an ounce.

"The basic scientific challenge has been to create earth-abundant molecular systems that produce hydrogen from water with high catalytic activity and stability," Chang says. "We believe our discovery of a molecular molybdenum-oxo catalyst for generating hydrogen from water without the use of additional acids or organic co-solvents establishes a new chemical paradigm for creating reduction catalysts that are highly active and robust in aqueous media."

The molybdenum-oxo complex that Karunadasa, Chang and Long discovered is a high valence metal with the chemical name of (PY5Me2)Mo-oxo. In their studies, the research team found that this complex catalyzes the generation of hydrogen from neutral buffered water or even sea water with a turnover frequency of 2.4 moles of hydrogen per mole of catalyst per second.

Long says, "This metal-oxo complex represents a distinct molecular motif for reduction catalysis that has high activity and stability in water. We are now focused on modifying the PY5Me ligand portion of the complex and investigating other metal complexes based on similar ligand platforms to further facilitate electrical charge-driven as well as light-driven catalytic processes. Our particular emphasis is on chemistry relevant to sustainable energy cycles."

This research was supported in part by the DOE Office of Science through Berkeley Lab's Helios Solar Energy Research Center, and in part by a grant from the National science Foundation.

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Scientists Create a Solar Energy Device from a Plant Protein Structure

Scientists Create a Solar Energy Device from a Plant Protein Structure

  9:46:00 PM    Science Lover

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If harnessing the unlimited solar power of the sun were easy, we wouldn't still have the greenhouse gas problem that results from the use of fossil fuel. And while solar energy systems work moderately well in hot desert climates, they are still inefficient and contribute only a small percentage of the general energy demand. A new solution may be coming from an unexpected source -- a source that may be on your dinner plate tonight.

New research suggests that minute crystals from peas can be illuminated and used as small battery chargers or form the core of more efficient artificial solar cells. (Credit: iStockphoto/Andrea Skjold)

"Looking at the most complicated membrane structure found in a plant, we deciphered a complex membrane protein structure which is the core of our new proposed model for developing 'green' energy," says structural biologist Prof. Nathan Nelson of Tel Aviv University's Department of Biochemistry. Isolating the minute crystals of the PSI super complex from the pea plant, Prof. Nelson suggests these crystals can be illuminated and used as small battery chargers or form the core of more efficient artificial solar cells.

Nanoscience is the science of small particles of materials and is one of the most important research frontiers in modern technology. In nature, positioning of molecules with sub-nanometer precision is routine, and crucial to the operation of biological complexes such as photosynthetic complexes. Prof. Nelson's research concentrates on this aspect.

The mighty PSI

To generate useful energy, plants have evolved very sophisticated "nano-machinery" which operates with light as its energy source and gives a perfect quantum yield of 100%. Called the Photosystem I (PSI) complex, this complex was isolated from pea leaves, crystalized and its crystal structure determined by Prof. Nelson to high resolution, which enabled him to describe in detail its intricate structure.

"My research aims to come close to achieving the energy production that plants can obtain when converting sun to sugars in their green leaves," explains Prof. Nelson.

Described in 1905 by Albert Einstein, quantum physics and photons explained the basic principles of how light energy works. Once light is absorbed in plant leaves, it energizes an electron which is subsequently used to support a biochemical reaction, like sugar production.

"If we could come even close to how plants are manufacturing their sugar energy, we'd have a breakthrough. It's therefore important to solve the structure of this nano-machine to understand its function," says Prof. Nelson, whose lab is laying the foundations for this possibility.

Since the PSI reaction center is a pigment-protein complex responsible for the photosynthetic conversion of light energy to another form of energy like chemical energy, these reaction centers, thousands of which are precisely packed in the crystals, may be used to convert light energy to electricity and serve as electronic components in a variety of different devices.

"One can imagine our amazement and joy when, upon illumination of those crystals placed on gold covered plates, we were able to generate a voltage of 10 volts. This won't solve our world's energy problem, but this could be assembled in power switches for low-power solar needs, for example," he concludes.

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Bacteria Engineered to Turn Carbon Dioxide Into Liquid Fuel

Bacteria Engineered to Turn Carbon Dioxide Into Liquid Fuel

  10:18:00 AM    Science Lover

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Global climate change has prompted efforts to drastically reduce emissions of carbon dioxide, a greenhouse gas produced by burning fossil fuels.

Genetically engineered strains of the cyanobacterium Synechococcus elongatus in a Petri dish. (Credit: Image courtesy of University of California - Los Angeles)

In a new approach, researchers from the UCLA Henry Samueli School of Engineering and Applied Science have genetically modified a cyanobacterium to consume carbon dioxide and produce the liquid fuel isobutanol, which holds great potential as a gasoline alternative. The reaction is powered directly by energy from sunlight, through photosynthesis.

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Bioengineers Succeed in Producing Plastics Without the Use of Fossil Fuels

Bioengineers Succeed in Producing Plastics Without the Use of Fossil Fuels

  12:34:00 AM    Science Lover

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A team of pioneering South Korean scientists have succeeded in producing the polymers used for everyday plastics through bioengineering, rather than through the use of fossil fuel based chemicals. This groundbreaking research, which may now allow for the production of environmentally conscious plastics, is published in two papers in the journal Biotechnology and Bioengineering.

Computer rendering of E. coli bacteria. A newly developed E. coli strain is capable of efficiently producing unnatural polymers, through a one-step fermentation process. (Credit: iStockphoto/Sebastian Kaulitzki)

 
Polymers are molecules found in everyday life in the form of plastics and rubbers. The team, from the KAIST University and the Korean chemical company LG Chem, led by Professor Sang Yup Lee focused their research on polylactic acid (PLA), a bio-based polymer which holds the key to producing plastics through natural and renewable resources.

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'Ice That Burns' May Yield Clean, Sustainable Bridge To Global Energy Future

'Ice That Burns' May Yield Clean, Sustainable Bridge To Global Energy Future

  9:46:00 AM    Science Lover

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Gas hydrates, known as "ice that burns," may provide a clean,
sustainable fuel source in the future.
(Credit: J. Pinkston and L. Stern/US Geological Survey)

In the future, natural gas derived from chunks of ice that workers collect from beneath the ocean floor and beneath the arctic permafrost may fuel cars, heat homes, and power factories. Government researchers are reporting that these so-called "gas hydrates," a frozen form of natural gas that bursts into flames at the touch of a match, show increasing promise as an abundant, untapped source of clean, sustainable energy.

The icy chunks could supplement traditional energy sources that are in short supply and which produce large amounts of carbon dioxide linked to global warming, the scientists say.*

"These gas hydrates could serve as a bridge to our energy future until cleaner fuel sources, such as hydrogen and solar energy, are more fully realized," says study co-leader Tim Collett, Ph.D., a research geologist with the U.S. Geological Survey (USGS) in Denver, Colo. Gas hydrates, known as "ice that burns," hold special promise for helping to combat global warming by leaving a smaller carbon dioxide footprint than other fossil fuels, Collett and colleagues note.

Last November, a team of USGS researchers that included Collett announced a giant step toward that bridge to the future. In a landmark study, the USGS scientists estimated that 85.4 trillion cubic feet of natural gas could potentially be extracted from gas hydrates in Alaska's North Slope region, enough to heat more than 100 million average homes for more than a decade.

"It's definitely a vast storehouse of energy," Collett says. "But it is still unknown how much of this volume can actually be produced on an industrial scale." That volume, he says, depends on the ability of scientists to extract useful methane, the main ingredient in natural gas, from gas hydrate formations in an efficient and cost-effective manner. Scientists worldwide are now doing research on gas hydrates in order to understand how this strange material forms and how it might be used to supplement coal, oil, and traditional natural gas.

Although scientists have known about gas hydrates for decades, they've only recently begun to try to use them as an alternative energy source. Gas hydrates, also known as "clathrates," form when methane gas from the decomposition of organic material comes into contact with water at low temperatures and high pressures. Those cold, high-pressure conditions exist deep below the oceans and underground on land in certain parts of the world, including the ocean floor and permafrost areas of the Arctic.

Today, researchers are finding tremendous stores of gas hydrates throughout the world, including United States, India, and Japan. In addition to Alaska, the United States has vast gas hydrate deposits in the Gulf of Mexico and off its eastern coast. Interest in and support of hydrate research is now growing worldwide. Japan and India currently have among the largest, most well-funded hydrate research programs in the world.

"Once we have learned better how to find the most promising gas hydrate deposits, we will need to know how to produce it in a safe and commercially-viable way," says study co-author Ray Boswell, Ph.D. He manages the National Methane Hydrate R&D Program of the U.S. Department of Energy's National Energy Technology Laboratory in Morgantown, W. Va. "Chemistry will be a big part of understanding just how the hydrates will respond to various production methods."

One of the more promising techniques for extracting methane from hydrates involves simply depressurizing the deposits, Boswell says. Another method involves exchanging the methane molecules in the "clathrate" structure with carbon dioxide. Workers can, in theory, collect the gas using the same drilling technology used for conventional oil and gas drilling.

Under the Methane Hydrate Research and Development Act of 2000, the U.S. government has already spent several million dollars, in collaboration with universities and private companies, to investigate gas hydrates as an alternative energy source. Scientists are particularly optimistic about the vast stores of gas hydrates located in Alaska and in the Gulf of Mexico. Research is also accelerating under the U.S. Department of Energy and USGS to better understand gas hydrate's role in the natural environment and in climate change.

"Gas hydrates are totally doable," Collett says. "But when and where we will see them depends on need, motivation, and our supply of other energy resources. In the next five to ten years, the research potential of gas hydrates will be more fully realized."

* They will present research on gas hydrates in Salt Lake City, Utah on March 23, 2009 at the American Chemical Society's 237th National Meeting. It is among two dozen papers on the topic scheduled for a two-day symposium, "Gas Hydrates and Clathrates," March 23-24.

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