Nanocrack Coating Enhances Performance of Membranes for Water Filtration, Fuel Cells

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A team of researchers with members from institutions in South Korea and Australia has developed a coating for membranes used in fuel cells and many other applications that allows it to continue to perform at a high level even as temperatures rise and humidity drops to levels that normally cause performance to suffer.

In their paper published in the journal Nature, the team describes their coating, how it works and the different materials that can be improved through its use. Jovan Kamcev and Benny Freeman with the University of Texas at Austin have published a News & Views article in the same journal issue describing the work done by the team and the many ways that the membrane coating has been successfully tested.

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A hydrophobic coating layer provides a self-controlled mechanism for water conservation using nanometre-sized cracks (nanocracks) tuned by membrane swelling behaviour in response to external humidity conditions, which act as nanovalves. …more

Membranes are a critical part of machines that rely on ionic or size separation—some well-known applications are water filtration efforts, energy generation in fuel cells and flow batteries and by reverse electrodialysis. Though useful, membranes also have a reputation of being rather fragile, resulting in expensive repairs, replacement or performance degradation.

One such example is that most membranes need to be kept moist to work properly, which can become problematic in certain environments. Water filtration in a hot Middle Eastern desert, for example, suffers when temperatures soar and humidity levels drop. In this new effort, the research team reports that they have developed a coating for membranes that works similarly to stomatal pores in a cactus plant—the pores open to allow for taking in carbon dioxide during times of higher humidity, such as at night and then close again as the humidity levels drop during the heat of the day.

The membrane coating is made by placing a thin layer of fluorine-related material that is water repellant over the membrane, in a low-humidity environment—under high humidity conditions, nanocracks appear in the material, allowing the water in the air to pass through to the membrane below. But, as temperatures rise and drop, the material tightens, closing the gaps where the cracks exist, preventing the water in the from evaporating. Kamcev and Benny Freeman report that the has been tested successfully on a wide variety of applications under various environmental conditions, and that thus far, it has proven able to protect delicate membranes in severe environments, allowing for their use in a much broader range to applications.

Explore further: Self-assembling, biomimetic membranes may aid water filtration

More information: Chi Hoon Park et al. Nanocrack-regulated self-humidifying membranes, Nature (2016). DOI: 10.1038/nature17634

The regulation of water content in polymeric membranes is important in a number of applications, such as reverse electrodialysis and proton-exchange fuel-cell membranes. External thermal and water management systems add both mass and size to systems, and so intrinsic mechanisms of retaining water and maintaining ionic transport1, 2, 3 in such membranes are particularly important for applications where small system size is important.

For example, in proton-exchange membrane fuel cells, where water retention in the membrane is crucial for efficient transport of hydrated ions1, 4, 5, 6, 7, by operating the cells at higher temperatures without external humidification, the membrane is self-humidified with water generated by electrochemical reactions5, 8. Here we report an alternative solution that does not rely on external regulation of water supply or high temperatures. Water content in hydrocarbon polymer membranes is regulated through nanometre-scale cracks (‘nanocracks’) in a hydrophobic surface coating.

These cracks work as nanoscale valves to retard water desorption and to maintain ion conductivity in the membrane on dehumidification. Hydrocarbon fuel-cell membranes with surface nanocrack coatings operated at intermediate temperatures show improved electrochemical performance, and coated reverse-electrodialysis membranes show enhanced ionic selectivity with low bulk resistance.


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Genesis Nanotechnology, Inc. ~ “Great Things from Small Things”

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Is Capacitive Deionization The Key To Desalination?

Deionization 042916 375_250-saltCapacitive deionization (CDI) is a process by which the ions are removed from water with the use of two electrodes. A positively charged electrode captures the water’s negatively charged anions while a negatively charged electrode captures the water’s positively charged cations.

“The technology can be best thought of as a tool which removes dissolved ionic species from a solvent using highly porous carbon electrodes charged to a small voltage,” explained Matthew Suss, assistant professor at the Israel Institute of Technology. “It works by a phenomenon known as electrosorption, where charging the porous carbon electrodes positively allows for dissolved ions of opposite charge to be brought to the pore surface and held there electrostatically. In this way, ions are removed from the water and held along the surface until the voltage is removed.”

This may seem like an abstract practice until you remember that salt is an ionic compound and that through CDI, it can be removed from water.

In the 2015 study “Water desalination via capacitive deionization: what it is and what you can expect” published by the Royal Society of Chemistry, Suss and a team of researchers take a long view at a field that has grown rapidly in the last few years, in large part because of its implications for the water industry.

“It is a highly scalable technique which does not require much energy for brackish water desalination,” he said. “To run it, you need mainly a low-voltage input, so no high-pressure pumps or heat sources are required.”

Probably the most popular desalination alternative to CDI is reverse osmosis (RO). That involves using high-pressure pumps to force water through semipermeable membranes which screen out the salt. These pumps need lots of energy to keep running and the process requires about 5 kWh to produce a cubic meter of freshwater, according to an online encyclopedia of desalination and water resources.

In contrast, a Chinese CDI operation featured in Suss’ study reported energy consumption around 1 kWh for every cubic meter of freshwater produced.

In their study, Suss and his research team put the water recovery ratio (the ratio of produced freshwater volume to feedwater volume) for a typical seawater reverse osmosis (SWRO) plant at 45 percent to 55 percent, while CDI systems have the potential to attain a ratio significantly higher than 55 percent.

However, as a relatively new technology there aren’t that many full-scale operations that utilize CDI. It’s hard to gauge how well it could perform if widely employed.

“It is a fast-emerging technology in the research world and so that is now translating to growth in the industry,” as Suss put it. “The main obstacle is the lack of demonstration plants and scaled-up systems at the moment. Most systems are lab-scale right now.”

With water scarcity propelling us to find creative solutions just so we have enough to drink, it won’t be long until CDI gets its time in the spotlight.

Image credit: “Salt,” © 2008 Kevin Dooley, used under an Attribution­ShareAlike 2.0 Generic license:­sa/2.0/


energyor-announces-new-h2quad-1000-fuel-cell-powered-uav.jpgEnergyOr Technologies Inc., a developer of advanced proton exchange membrane (PEM) fuel cell systems and integrated UAV platforms, has announced that it has launched the H2Quad 1000, a multirotor drone with 1 kg payload capacity and over 2 hours of flight endurance.

EnergyOr’s CEO, Michel Bitton, stated: “The H2Quad 1000 is an industry game-changer. It not only has the ability to carry 1 kg of payload for more than two hours, it can fly a distance of up to 80 km which provides unprecedented multirotor performance.” He continued by saying: “There is no other multirotor drone available with this capability. Even so, EnergyOr will continue to push the envelope and develop fuel cell powered multirotor platforms with even longer endurance and more payload capacity.”

The extended range of the H2Quad 1000 makes it ideal for mail, parcel or component delivery, whether for commercial, medical or military purposes. EnergyOr claims that it effectively triples the delivery radius that is currently possible with existing multirotor UAVs, and thus the potential delivery area is increased by a factor of 9 times.

The commercial market for multirotor drones used in civil applications is expected to increase dramatically in the coming years, with new uses being announced on a daily basis. Current applications include disaster response, hydro and rail line inspections, flare stack inspections, precision agriculture, search and rescue missions and film production, just to name a few. Battery powered multirotor UAVs have very limited flight times due to the relatively low specific energy (Watthours/kg) of existing rechargeable battery technologies.

EnergyOr will exhibit at the AUVSI Xponential Conference and Exposition in New Orleans as part of the Canadian Pavilion.

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Fuel Cell vs. Battery Power: And the Winner Is ????

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Fuel-cell supporters say the main impediment when it comes to the vehicles is the lack of places to fill up with hydrogen.There’s just one station in Ontario: Canada’s only others are in B.C. And this province’s lone pump, for now, serves a single converted Hyundai Tucson.

Interest in both options is accelerating as the battle between fuel cell and battery power continues.

Battery power or hydrogen fuel cell: Which will lead us to gasoline-free driving?

In sales and acceptance, battery power is now far ahead. A majority of the major manufacturers have EVs in showrooms or, like Chevrolet’s Bolt, close to market.

Tesla’s Model S is among the world’s most desired cars, and the company has enticed nearly 400,000 people to deposit $1,000 for a Model 3 that’s still under development.

But interest in fuel cells is accelerating. Toyota, Honda and Hyundai have models available for lease; others are working on the technology. The numbers are tiny and the companies lose a bundle on each deal. But the technology works well; the main impediment, fuel-cell supporters say, is the lack of places to fill up with hydrogen.


There’s just one station in Ontario: Canada’s only others are in B.C. And this province’s lone pump, for now, serves a single converted Hyundai Tucson. The number of U.S. hydrogen stations is actually falling; to 39 last year from 63 in 2009.

Which is more useful?


Battery range is improving, but it’s still limited: The current maximum, apart from a $130,000 Model S, is about 300 kilometres. It takes at least half an hour to recharge an EV, if a 480-volt fast-charger is available and the vehicle is equipped to handle it. Otherwise, it’s hours.

Fast-charging stations are still rare, although the number is growing quickly.

This isn’t a problem if your usual driving is within the car’s range. You simply plug in at home and recharge overnight. It’s far more convenient than visiting a gas station. For longer trips, though, you need a non-battery vehicle.


Fuel-cell vehicles operate like those propelled by internal combustion: They refuel in three minutes, with each fill lasting 500 km or more, which means one vehicle meets every driving need. Unlike batteries, fuel cells don’t lose capacity in cold weather.


Which is greener?


Both technologies avoid harmful tailpipe emissions, but that’s just part of the story.

Batteries, of course, are recharged with electricity, so their environmental impact depends mainly on how it’s generated. If the fuel is coal or oil, it’s dirty. Natural gas is marginally better. Nuclear power is dangerously expensive and creates a massive legacy of radioactive waste.


Waterpower is green, except when it’s from dams that flood vast tracts of land. Large-scale wind and solar power can be a nuisance, and building the equipment involves mining and energy.


Hydrogen for fuel cells can be extracted from water, in a process that consumes a lot of energy, and faces the same issues as batteries.

At present, though, 95 per cent is derived from natural gas, in a process that requires steam, and thus large amounts of energy, and emits carbon monoxide and carbon dioxide.

That’s on top of the energy and emissions involved in extracting and refining the gas.

Batteries require rare earth metals; fuel cells, platinum — although in decreasing quantities.


Fuel cells are twice as efficient as internal combustion, but still below batteries on that score.


Which wins? Both are — equally — greener than internal combustion but less green than their enthusiasts claim. Fuel cells let one vehicle cover all driving needs; a big advantage. But EVs might catch up in range by the time there are enough stations to make hydrogen useful.

MIT: Cleaning Water with Solar Energy … without “the grid”

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MIT researchers have developed a solar-powered desalination system that could significantly increase the groundwater available for drinking in Indian villages.

Amos Winter may be an assistant professor of mechanical engineering at MIT, but he describes one of the most important aspects of his job as “detective work.” That’s what he, MIT PhD candidate Natasha Wright, and their fellow researchers did for two years before coming up with a potential solution to issues of clean-water access in India.

It paid off. Their research team, sponsored by the MIT Tata Center for Technology and Design and its partner, the Indian firm Jain Irrigation Systems, won the United States Agency for International Development (USAID)’s Desal Prize earlier last year with their design of a solar-powered electrodialysis desalination system.

The detective work began when Jain Irrigation pointed out that small-scale farmers in India who use Jain’s irrigation systems often lack access to safe drinking water. Winter, Wright, and others on the Tata Center team spent two years meeting with farmers and village dwellers trying to understand the reason for drinking water shortages in rural Indian communities.

They expected the villagers’ primary concern to be contamination of water by bacteria. But in their meetings, the team identified another, generally overlooked contaminant in India’s water: salt. “What can happen frequently,” Winter says, “is that people who only have access to a salty drinking source won’t want to drink [the water] because it tastes bad. Instead, they’ll go drink from a surface source like a pond or a river that can have biological contaminants in it.” By removing salt from water sources, the team could more than double the groundwater available to villagers for drinking.

The announcement of the USAID Desal Prize competition hit shortly after the team published a paper on the importance of desalination to clean drinking water. Background research already in hand, the team connected a trailer containing their prototype system to a Tata Center-supplied truck and drove it to the competition in New Mexico. And in a pool that had close to 70 applicants, they won. In fact, they were the only entry to meet all of USAID’s specifications for flow rate and salinity.

The win was game-changing. According to Winter, the Desal Prize has seriously accelerated the typical development timeline for a project like this. Winning the prize has connected him and Wright with other major players in the clean water space, and international expertise provided by USAID has put more potential locations for the new desalination system on the team’s radar. One of them is Gaza. “It’s pretty exciting,” Winter says, “because the needs and requirements for off-grid desalination [in the Middle East] are very similar to those in India.”

First, though, the team has to work out a few kinks in the technology. Winter identifies two major “pain points”: the overall materials cost of the system and the energy needed to pump water through it. The only “real necessary power” for running the system is the power required by the electrodialysis technology to separate the ions of salt from the rest of the water, Winter says. Cutting down other energy consumption would both conserve power and bring down cost.

One way to cut cost could be to wean the system off battery usage. In fall 2015, the team began researching whether their system could run effectively on solar energy without using batteries as a buffer to store energy when the sun is down. The research involves conducting pilot tests in which farmers come to one of Jain Irrigation’s test farms in India and use the system in real time. Their experience will shed light on whether demand for water throughout the day aligns with the availability of solar energy.

Winter and Wright have also just signed a three-year contract with Tata Projects, an engineering subsidiary of the Tata Group currently focusing on village-scale water systems. Tata Projects already has a well-developed reverse-osmosis water-purifying operation, but it wants to expand to off-grid communities — places where solar-powered electrodialysis desalination would be a better option. Tata Projects is also looking into the possibility of using the technology in specific subsets of urban environments, such as apartment complexes. “There are a number of market opportunities for this technology beyond just small-scale villages,” Winter says.

The work, of course, is far from done. “The research that we’re doing now, and that the Tata Center in general does, involves tackling problems in emerging markets that require high-performance but relatively low-cost solutions,” Winter says. “We don’t just say, ‘OK, we’re going to make a technology [in our lab] and then see if we can commercialize it.’ We try to understand from the start the user-centered, real-life requirements for a technology so we can design to meet them.” Not elementary at all, but certainly the work of good detectives.

MIT: Solar cells as light as a soap bubble


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Ultrathin, flexible photovoltaic cells from MIT research could find many new uses

Imagine solar cells so thin, flexible, and lightweight that they could be placed on almost any material or surface, including your hat, shirt, or smartphone, or even on a sheet of paper or a helium balloon.

Researchers at MIT have now demonstrated just such a technology: the thinnest, lightest solar cells ever produced. Though it may take years to develop into a commercial product, the laboratory proof-of-concept shows a new approach to making solar cells that could help power the next generation of portable electronic devices.

The new process is described in a paper by MIT professor Vladimir Bulović, research scientist Annie Wang, and doctoral student Joel Jean, in the journal Organic Electronics.

Bulović, MIT’s associate dean for innovation and the Fariborz Maseeh (1990) Professor of Emerging Technology, says the key to the new approach is to make the solar cell, the substrate that supports it, and a protective overcoating to shield it from the environment, all in one process. The substrate is made in place and never needs to be handled, cleaned, or removed from the vacuum during fabrication, thus minimizing exposure to dust or other contaminants that could degrade the cell’s performance. Soap Bubble Solar Cells 042816 MIT-Ultrathin-Solar_0

(Right) The MIT team has achieved the thinnest and lightest complete solar cells ever made, they say. To demonstrate just how thin and lightweight the cells are, the researchers draped a working cell on top of a soap bubble, without popping the bubble.

Photo: Joel Jean and Anna Osherov

“The innovative step is the realization that you can grow the substrate at the same time as you grow the device,” Bulović says.

In this initial proof-of-concept experiment, the team used a common flexible polymer called parylene as both the substrate and the overcoating, and an organic material called DBP as the primary light-absorbing layer. Parylene is a commercially available plastic coating used widely to protect implanted biomedical devices and printed circuit boards from environmental damage. The entire process takes place in a vacuum chamber at room temperature and without the use of any solvents, unlike conventional solar-cell manufacturing, which requires high temperatures and harsh chemicals. In this case, both the substrate and the solar cell are “grown” using established vapor deposition techniques.

One process, many materials

The team emphasizes that these particular choices of materials were just examples, and that it is the in-line substrate manufacturing process that is the key innovation. Different materials could be used for the substrate and encapsulation layers, and different types of thin-film solar cell materials, including quantum dots or perovskites, could be substituted for the organic layers used in initial tests.

MITnano_ 042216 InfCorrTerraceView_label (1)But already, the team has achieved the thinnest and lightest complete solar cells ever made, they say. To demonstrate just how thin and lightweight the cells are, the researchers draped a working cell on top of a soap bubble, without popping the bubble. The researchers acknowledge that this cell may be too thin to be practical — “If you breathe too hard, you might blow it away,” says Jean — but parylene films of thicknesses of up to 80 microns can be deposited easily using commercial equipment, without losing the other benefits of in-line substrate formation.

A flexible parylene film, similar to kitchen cling-wrap but only one-tenth as thick, is first deposited on a sturdier carrier material – in this case, glass. Figuring out how to cleanly separate the thin material from the glass was a key challenge, explains Wang, who has spent many years working with parylene.

The researchers lift the entire parylene/solar cell/parylene stack off the carrier after the  fabrication process is complete, using a frame made of flexible film. The final ultra-thin, flexible solar cells, including substrate and overcoating, are just one-fiftieth of the thickness of a human hair and one-thousandth of the thickness of equivalent cells on glass substrates — about two micrometers thick — yet they convert sunlight into electricity just as efficiently as their glass-based counterparts.

No miracles needed

“We put our carrier in a vacuum system, then we deposit everything else on top of it, and then peel the whole thing off,” explains Wang. Bulović says that like most new inventions, it all sounds very simple — once it’s been done. But actually developing the techniques to make the process work required years of effort.

While they used a glass carrier for their solar cells, Jean says “it could be something else. You could use almost any material,” since the processing takes place under such benign conditions. The substrate and solar cell could be deposited directly on fabric or paper, for example.

While the solar cell in this demonstration device is not especially efficient, because of its low weight, its power-to-weight ratio is among the highest ever achieved. That’s important for applications where weight is important, such as on spacecraft or on high-altitude helium balloons used for research. Whereas a typical silicon-based solar module, whose weight is dominated by a glass cover, may produce about 15 watts of power per kilogram of weight, the new cells have already demonstrated an output of 6 watts per gram — about 400 times higher.

“It could be so light that you don’t even know it’s there, on your shirt or on your notebook,” Bulović says. “These cells could simply be an add-on to existing structures.”

Still, this is early, laboratory-scale work, and developing it into a manufacturable product will take time, the team says. Yet while commercial success in the short term may be uncertain, this work could open up new applications for solar power in the long term. “We have a proof-of-concept that works,” Bulović says. The next question is, “How many miracles does it take to make it scalable? We think it’s a lot of hard work ahead, but likely no miracles needed.”

“This demonstration by the MIT team is almost an order of magnitude thinner and lighter” than the previous record holder, says Max Shtein, an associate professor of materials science and engineering, chemical engineering, and applied physics, at the University of Michigan, who was not involved in this work. As a result, he says, it “has tremendous implications for maximizing power-to-weight (important for aerospace applications, for example), and for the ability to simply laminate photovoltaic cells onto existing structures.”

“This is very high quality work,” Shtein adds, with a “creative concept, careful experimental set-up, very well written paper, and lots of good contextual information.” And, he says, “The overall recipe is simple enough that I could see scale-up as possible.”

The work was supported by Eni S.p.A. via the Eni-MIT Solar Frontiers Center, and by the National Science Foundation.

Non-toxic and cheap thin-film solar cells for ‘zero-energy’ buildings

Non Toxic Solar Cells 042816 160428103023_1_540x360Dr Xiaojing Hao of UNSW’s Australian Centre for Advanced Photovoltaics holding the new CZTS solar cells.
Credit: Quentin Jones/UNSW

World’s highest efficiency rating achieved for CZTS thin-film solar cells

‘Zero-energy’ buildings — which generate as much power as they consume — are now much closer after a team at Australia’s University of New South Wales achieved the world’s highest efficiency using flexible solar cells that are non-toxic and cheap to make.

Until now, the promise of ‘zero-energy’ buildings been held back by two hurdles: the cost of the thin-film solar cells (used in façades, roofs and windows), and the fact they’re made from scarce, and highly toxic, materials.

That’s about to change: the UNSW team, led by Dr Xiaojing Hao of the Australian Centre for Advanced Photovoltaics at the UNSW School of Photovoltaic and Renewable Energy Engineering, have achieved the world’s highest efficiency rating for a full-sized thin-film solar cell using a competing thin-film technology, known as CZTS.

NREL, the USA’s National Renewable Energy Laboratory, confirmed this world leading 7.6% efficiency in a 1cm2 area CZTS cell this month.

Unlike its thin-film competitors, CZTS cells are made from abundant materials: copper, zinc, tin and sulphur.

And CZTS has none of the toxicity problems of its two thin-film rivals, known as CdTe (cadmium-telluride) and CIGS (copper-indium-gallium-selenide). Cadmium and selenium are toxic at even tiny doses, while tellurium and indium are extremely rare.

“This is the first step on CZTS’s road to beyond 20% efficiency, and marks a milestone in its journey from the lab to commercial product,” said Hao, named one of UNSW’s 20 rising stars last year. “There is still a lot of work needed to catch up with CdTe and CIGS, in both efficiency and cell size, but we are well on the way.”

“In addition to its elements being more commonplace and environmentally benign, we’re interested in these higher bandgap CZTS cells for two reasons,” said Professor Martin Green, a mentor of Dr Hao and a global pioneer of photovoltaic research stretching back 40 years.

“They can be deposited directly onto materials as thin layers that are 50 times thinner than a human hair, so there’s no need to manufacture silicon ‘wafer’ cells and interconnect them separately,” he added. “They also respond better than silicon to blue wavelengths of light, and can be stacked as a thin-film on top of silicon cells to ultimately improve the overall performance.”

By being able to deposit CZTS solar cells on various surfaces, Hao’s team believe this puts them firmly on the road to making thin-film photovoltaic cells that can be rigid or flexible, and durable and cheap enough to be widely integrated into buildings to generate electricity from the sunlight that strikes structures such as glazing, façades, roof tiles and windows.

However, because CZTS is cheaper — and easier to bring from lab to commercialisation than other thin-film solar cells, given already available commercialised manufacturing method — applications are likely even sooner. UNSW is collaborating with a number of large companies keen to develop applications well before it reaches 20% efficiency — probably, Hao says, within the next few years.

“I’m quietly confident we can overcome the technical challenges to further boosting the efficiency of CZTS cells, because there are a lot of tricks we’ve learned over the past 30 years in boosting CdTe and CIGS and even silicon cells, but which haven’t been applied to CZTS,” said Hao.

Currently, thin-film photovoltaic cells like CdTe are used mainly in large solar power farms, as the cadmium toxicity makes them unsuitable for residential systems, while CIGS cells is more commonly used in Japan on rooftops.

First Solar, a US$5 billion behemoth that specialises in large-scale photovoltaic systems, relies entirely on CdTe; while CIGS is the preferred technology of China’s Hanergy, the world’s largest thin-film solar power company.

Thin-film technologies such as CdTe and CIGS are also attractive because they are physically flexible, which increases the number of potential applications, such as curved surfaces, roofing membranes, or transparent and translucent structures like windows and skylights.

But their toxicity has made the construction industry — mindful of its history with asbestos — wary of using them. Scarcity of the elements also renders them unattractive, as price spikes are likely as demand rises. Despite this, the global market for so-called Building-Integrated Photovoltaics (BIPV) is already valued at US$1.6 billion.

Hao believes CZTS’s cheapness, benign environmental profile and abundant elements may be the trigger that finally brings architects and builders onboard to using thin-film solar panels more widely in buildings.

Until now, most architects have used conventional solar panels made from crystalline silicon. While these are even cheaper than CZTS cells, they don’t offer the same flexibility for curved surfaces and other awkward geometries needed to easily integrate into building designs.

Story Source:

The above post is reprinted from materials provided byUniversity of New South Wales. The original item was written by Wilson da Silva. Note: Materials may be edited for content and length.

A Chemical Switch-Flip Helps Perovskite Solar Cells Beat the Heat

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Thin films of crystalline materials called perovskites provide a promising new way of making inexpensive and efficient solar cells. Now, an international team of researchers has shown a way of flipping a chemical switch that converts one type of perovskite into another — a type that has better thermal stability and is a better light absorber.

The study, by researchers from Brown University, the National Renewable Energy Laboratory (NREL) and the Chinese Academy of Sciences’ Qingdao Institute of Bioenergy and Bioprocess Technology published in the Journal of the American Chemical Society, could be one more step toward bringing perovskite solar cells to the mass market.

“We’ve demonstrated a new procedure for making solar cells that can be more stable at moderate temperatures than the perovskite solar cells that most people are making currently,” said Nitin Padture, professor in Brown’s School of Engineering, director of Brown’s Institute for Molecular and Nanoscale Innovation, and the senior co-author of the new paper. “The technique is simple and has the potential to be scaled up, which overcomes a real bottleneck in perovskite research at the moment.”

Perovskites have emerged in recent years as a hot topic in the solar energy world. The efficiency with which they convert sunlight into electricity rivals that of traditional silicon solar cells, but perovskites are potentially much cheaper to produce. These new solar cells can also be made partially transparent for use in windows and skylights that can produce electricity, or to boost the efficiency of silicon solar cells by using the two in tandem.

Despite the promise, perovskite technology has several hurdles to clear — one of which deals with thermal stability. Most of the perovskite solar cells produced today are made with of a type of perovskite called methylammonium lead triiodide (MAPbI3). The problem is that MAPbI3 tends to degrade at moderate temperatures.

“Solar cells need to operate at temperatures up to 85 degrees Celsius,” said Yuanyuan Zhou, a graduate student at Brown who led the new research. “MAPbI3 degrades quite easily at those temperatures.”Flip Chem Switch 042716 solarenergy

That’s not ideal for solar panels that must last for many years. As a result, there’s a growing interest in solar cells that use a type of perovskite called formamidinium lead triiodide (FAPbI3) instead. Research suggests that solar cells based on FAPbI3 can be more efficient and more thermally stable than MAPbI3. However, thin films of FAPbI3 perovskites are harder to make than MAPbI3 even at laboratory scale, Padture says, let alone making them large enough for commercial applications.

(Right) Thin films of crystalline materials called perovskites provide a promising new way of making inexpensive and efficient solar cells. Now, an international team of researchers has shown a way of flipping a chemical switch that converts one type of perovskite into another — a type that has better thermal stability and is a better light absorber. Credit: Padture Lab / Brown University

Part of the problem is that formamidinium has a different molecular shape than methylammonium. So as FAPbI3 crystals grow, they often lose the perovskite structure that is critical to absorbing light efficiently.

This latest research shows a simple way around that problem. The team started by making high-quality MAPbI3 thin films using techniques they had developed previously. They then exposed those MAPbI3 thin films to formamidine gas at 150 degrees Celsius. The material instantly converted from MAPbI3 to FAPbI3 while preserving the all-important microstructure and morphology of the original thin film.

“It’s like flipping a switch,” Padture said. “The gas pulls out the methylammonium from the crystal structure and stuffs in the formamidinium, and it does so without changing the morphology. We’re taking advantage of a lot of experience in making excellent quality MAPbI3 thin films and simply converting them to FAPbI3 thin films while maintaining that excellent quality.”

This latest research builds on the work this international team of researchers has been doing over the past year using gas-based techniques to make perovskites. The gas-based methods have the potential of improving the quality of the solar cells when scaled up to commercial proportions. The ability to switch from MAPbI3 to FAPbI3 marks another potentially useful step toward commercialization, the researchers say.

“The simplicity and the potential scalability of this method was inspired by our previous work on gas-based processing of MAPbI3 thin films, and now we can make high-efficiency FAPbI3-based perovskite solar cells that can be thermally more stable,” Zhou said. “That’s important for bringing perovskite solar cells to the market.”

Laboratory scale perovskite solar cells made using this new method showed efficiency of around 18 percent — not far off the 20 to 25 percent achieved by silicon solar cells.

“We plan to continue to work with the method in order to further improve the efficiency of the cells,” said Kai Zhu, senior scientist at NREL and co-author of the new paper. “But this initial work demonstrates a promising new fabrication route.”

NREL Study finds Carbon Nanotube Semiconductors Well-Suited for PV Systems

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Researchers at the Energy Department’s National Renewable Energy Laboratory (NREL) discovered single-walled carbon nanotube semiconductors could be favorable for photovoltaic systems because they can potentially convert sunlight to electricity or fuels without losing much energy.

The research builds on the Nobel Prize-winning work of Rudolph Marcus, who developed a fundamental tenet of physical chemistry that explains the rate at which an electron can move from one chemical to another. The Marcus formulation, however, has rarely been used to study photoinduced electron transfer for emerging organic semiconductors such as (SWCNT) that can be used in organic PV devices.

In organic PV devices, after a photon is absorbed, charges (electrons and holes) generally need to be separated across an interface so that they can live long enough to be collected as electrical current. The electron transfer event that produces these separated charges comes with a potential loss as the molecules involved have to structurally reorganize their bonds. This loss is called reorganization energy, but NREL researchers found little energy was lost when pairing SWCNT semiconductors with fullerene molecules.

“What we find in our study is this particular system—nanotubes with fullerenes—have an exceptionally low reorganization energy and the nanotubes themselves probably have very, very low reorganization energy,” said Jeffrey Blackburn, a senior scientist at NREL and co-author of the paper “Tuning the driving force for exciton dissociation in single-walled carbon nanotube heterojunctions.”

The paper appears in the new issue of the journal Nature Chemistry. Its other co-authors are Rachelle Ihly, Kevin Mistry, Andrew Ferguson, Obadiah Reid, and Garry Rumbles from NREL, and Olga Boltalina, Tyler Clikeman, Bryon Larson, and Steven Strauss from Colorado State University.

Organic PV devices involve an interface between a donor and an acceptor. In this case, the SWCNT served as the donor, as it donated an electron to the acceptor (here, the fullerene). The NREL researchers strategically partnered with colleagues at Colorado State University to take advantage of expertise at each institution in producing donors and acceptors with well-defined and highly tunable energy levels: semiconducting SWCNT donors at NREL and fullerene acceptors at CSU. This partnership enabled NREL’s scientists to determine that the event didn’t come with a large energy loss associated with reorganization, meaning solar energy can be harvested more efficiently. For this reason, SWCNT semiconductors could be favorable for PV applications.

Explore further: Researchers achieve record 8.4 percent conversion efficiency in fullerene-free organic solar cells

More information: Rachelle Ihly et al, Tuning the driving force for exciton dissociation in single-walled carbon nanotube heterojunctions, Nature Chemistry (2016). DOI: 10.1038/nchem.2496

Journal reference:Nature Chemistrysearch and more infowebsite

Provided by: National Renewable Energy Laboratory


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MIT: Fuel Cells: Hybrid System could Cut Coal-Plant Emissions IN HALF !

Hybrid Fuel Cell Cuts Coal Emissions 042616 160404111312_1_540x360

Combining gasification with fuel-cell technology could boost efficiency of coal-powered plants

Most of the world’s nations have agreed to make substantial reductions in their greenhouse gas emissions, but achieving these goals is still a considerable technological, economic, and political challenge. The International Energy Agency has projected that, even with the new agreements in place, global coal-fired power generation will increase over the next few decades. Finding a cleaner way of using that coal could be a significant step toward achieving carbon-emissions reductions while meeting the needs of a growing and increasingly industrialized world population.

Now, researchers at MIT have come up with a plan that could contribute to that effort by making it possible to generate electricity from coal with much greater efficiency — possibly reaching as much as twice the fuel-to-electricity efficiency of today’s conventional coal plants. This would mean, all things being equal, a 50 percent reduction in carbon dioxide emissions for a given amount of power produced.

The concept, proposed by MIT doctoral student Katherine Ong and Ronald C. Crane (1972) Professor Ahmed Ghoniem, is described in their paper in the Journal of Power Sources. The key is combining into a single system two well-known technologies: coal gasification and fuel cells.

Coal gasification is a way of extracting burnable gaseous fuel from pulverized coal, rather than burning the coal itself. The technique is widely used in chemical processing plants as a way of producing hydrogen gas. Fuel cells produce electricity from a gaseous fuel by passing it through a battery-like system where the fuel reacts electrochemically with oxygen from the air.

The attraction of combining these two systems, Ong explains, is that both processes operate at similarly high temperatures of 800 degrees Celsius or more. Combining them in a single plant would thus allow the two components to exchange heat with minimal energy losses. In fact, the fuel cell would generate enough heat to sustain the gasification part of the process, she says, eliminating the need for a separate heating system, which is usually provided by burning a portion of the coal.

Hybrid Fuel Cell Cuts Coal Emissions 042616 160404111312_1_540x360

This illustration depicts a possible configuration for the combined system proposed by MIT researchers. At the bottom, steam (pink arrows) passes through pulverized coal, releasing gaseous fuel (red arrows) made up of hydrogen and carbon monoxide. This fuel goes into a solid oxide fuel cell (disks near top), where it reacts with oxygen from the air (blue arrows) to produce electricity (loop at right).
Credit: Jeffrey Hanna

Coal gasification, by itself, works at a lower temperature than combustion and “is more efficient than burning,” Ong says. First, the coal is pulverized to a powder, which is then heated in a flow of hot steam, somewhat like popcorn kernels heated in an air-popper. The heat leads to chemical reactions that release gases from the coal particles — mainly carbon monoxide and hydrogen, both of which can produce electricity in a solid oxide fuel cell.

In the combined system, these gases would then be piped from the gasifier to a separate fuel cell stack, or ultimately, the fuel cell system could be installed in the same chamber as the gasifier so that the hot gas flows straight into the cell. In the fuel cell, a membrane separates the carbon monoxide and hydrogen from the oxygen, promoting an electrochemical reaction that generates electricity without burning the fuel.

Because there is no burning involved, the system produces less ash and other air pollutants than would be generated by combustion. It does produce carbon dioxide, but this is in a pure, uncontaminated stream and not mixed with air as in a conventional coal-burning plant. That would make it much easier to carry out carbon capture and sequestration (CCS) — that is, capturing the output gas and burying it underground or disposing of it some other way — to eliminate or drastically reduce the greenhouse gas emissions. In conventional plants, nitrogen from the air must be removed from the stream of gas in order to carry out CCS.

One of the big questions answered by this new research, which used simulations rather than lab experiments, was whether the process would work more efficiently using steam or carbon dioxide to react with the particles of coal. Both methods have been widely used, but most previous attempts to study gasification in combination with fuel cells chose the carbon dioxide option. This new study demonstrates that the system produces two to three times as much power output when steam is used instead.

Conventional coal-burning power plants typically have very low efficiency; only 30 percent of the energy contained in the fuel is actually converted to electricity. In comparison, the proposed combined gasification and fuel cell system could achieve efficiencies as high as 55 to 60 percent, Ong says, according to the simulations.

The next step would be to build a small, pilot-scale plant to measure the performance of the hybrid system in real-world conditions, Ong says. Because the individual component technologies are all well developed, a full-scale operational system could plausibly be built within a few years, she says. “This system requires no new technologies” that need more time to develop, she says. “It’s just a matter of coupling these existing technologies together well.”

The system would be more expensive than existing plants, she says, but the initial capital investment could be paid off within several years due to the system’s state-of-the-art efficiency. And given the importance of reducing emissions, that initial capital expense may be easy to justify, especially if new fees are attached to the carbon dioxide emitted by fossil fuels.

“If we’re going to cut down on carbon dioxide emissions in the near term, the only way to realistically do that is to increase the efficiency of our fossil fuel plants,” she says.

Story Source:

The above post is reprinted from materials provided byMassachusetts Institute of Technology. The original item was written by David L. Chandler. Note: Materials may be edited for content and length.

Journal Reference:

  1. Katherine M. Ong, Ahmed F. Ghoniem. Modeling of indirect carbon fuel cell systems with steam and dry gasification.Journal of Power Sources, 2016; 313: 51 DOI:10.1016/j.jpowsour.2016.02.050