Category Archives: energy

Vitamin-driven lithium-ion battery from the University of Toronto

It seems vitamins aren’t just good for health, they’re also good for batteries. My Aug. 2, 2016 post on vitamins and batteries focused on work from Harvard, this time the work is from the University of Toronto (Canada). From an Aug. 3, 2016 news item on ScienceDaily,

A team of University of Toronto chemists has created a battery that stores energy in a biologically derived unit, paving the way for cheaper consumer electronics that are easier on the environment.

The battery is similar to many commercially-available high-energy lithium-ion batteries with one important difference. It uses flavin from vitamin B2 as the cathode: the part that stores the electricity that is released when connected to a device.

“We’ve been looking to nature for a while to find complex molecules for use in a number of consumer electronics applications,” says Dwight Seferos, an associate professor in U of T’s Department of Chemistry and Canada Research Chair in Polymer Nanotechnology.

“When you take something made by nature that is already complex, you end up spending less time making new material,” says Seferos.

An Aug. 2, 2016 University of Toronto news release (also on EurekAlert) by Peter McMahon, which originated the news item, explains further,

To understand the discovery, it’s important to know that modern batteries contain three basic parts:

  • a positive terminal – the metal part that touches devices to power them – connected to a cathode inside the battery casing
  • a negative terminal connected to an anode inside the battery casing
  • an electrolyte solution, in which ions can travel between the cathode and anode electrodes

When a battery is connected to a phone, iPod, camera or other device that requires power, electrons flow from the anode – the negatively charged electrode of the device supplying current – out to the device, then into the cathode and ions migrate through the electrolyte solution to balance the charge. When connected to a charger, this process happens in reverse.

The reaction in the anode creates electrons and the reaction in the cathode absorbs them when discharging. The net product is electricity. The battery will continue to produce electricity until one or both of the electrodes run out of the substance necessary for the reactions to occur.

Organic chemistry is kind of like Lego

While bio-derived battery parts have been created previously, this is the first one that uses bio-derived polymers – long-chain molecules – for one of the electrodes, essentially allowing battery energy to be stored in a vitamin-created plastic, instead of costlier, harder to process, and more environmentally-harmful metals such as cobalt.

“Getting the right material evolved over time and definitely took some test reactions,” says paper co-author and doctoral student Tyler Schon. “In a lot of ways, it looked like this could have failed. It definitely took a lot of perseverance.”

Schon, Seferos and colleagues happened upon the material while testing a variety of long-chain polymers – specifically pendant group polymers: the molecules attached to a ‘backbone’ chain of a long molecule.

“Organic chemistry is kind of like Lego,” he says. “You put things together in a certain order, but some things that look like they’ll fit together on paper don’t in reality. We tried a few approaches and the fifth one worked,” says Seferos.

Building a better power pack

The team created the material from vitamin B2 that originates in genetically-modified fungi using a semi-synthetic process to prepare the polymer by linking two flavin units to a long-chain molecule backbone.

This allows for a green battery with high capacity and high voltage – something increasingly important as the ‘Internet of Things’ continues to link us together more and more through our battery-powered portable devices.

“It’s a pretty safe, natural compound,” Seferos adds. “If you wanted to, you could actually eat the source material it comes from.”

B2’s ability to be reduced and oxidized makes its well-suited for a lithium ion battery.

“B2 can accept up to two electrons at a time,” says Seferos. “This makes it easy to take multiple charges and have a high capacity compared to a lot of other available molecules.”

A step to greener electronics

“It’s been a lot of trial-and-error,” says Schon. “Now we’re looking to design new variants that can be recharged again and again.”

While the current prototype is on the scale of a hearing aid battery, the team hopes their breakthrough could lay the groundwork for powerful, thin, flexible, and even transparent metal-free batteries that could support the next wave of consumer electronics.

Here’s a link to and a citation for the paper,

Bio-Derived Polymers for Sustainable Lithium-Ion Batteries by Tyler B. Schon, Andrew J. Tilley, Colin R. Bridges, Mark B. Miltenburg, and Dwight S. Seferos. Advanced Functional Materials DOI: 10.1002/adfm.201602114 Version of Record online: 14 JUL 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

Could your photo be a solar cell?

Scientists at Aalto University (Finland) have found a way to print photographs that produce energy (like a solar cell does) according to a July 25, 2016 news item on Nanowerk,

Solar cells have been manufactured already for a long from inexpensive materials with different printing techniques. Especially organic solar cells and dye-sensitized solar cells are suitable for printing.

“We wanted to take the idea of printed solar cells even further, and see if their materials could be inkjet-printed as pictures and text like traditional printing inks,” tells University Lecturer Janne Halme.

A semi-transparent dye-sensitized solar cell with inkjet-printed photovoltaic portraits of the Aalto researchers (Ghufran Hashmi, Merve Özkan, Janne Halme) and a QR code that links to the original research paper. Courtesy: Aalto University

A semi-transparent dye-sensitized solar cell with inkjet-printed photovoltaic portraits of the Aalto researchers (Ghufran Hashmi, Merve Özkan, Janne Halme) and a QR code that links to the original research paper. Courtesy: Aalto University

A July 26, 2016 Aalto University press release, which originated the news item, describes the innovation in more detail,

When light is absorbed in an ordinary ink, it generates heat. A photovoltaic ink, however, coverts part of that energy to electricity. The darker the color, the more electricity is produced, because the human eye is most sensitive to that part of the solar radiation spectrum which has highest energy density. The most efficient solar cell is therefore pitch-black.

The idea of a colorful, patterned solar cell is to combine also other properties that take advantage of light on the same surface, such as visual information and graphics.

– For example, installed on a sufficiently low-power electrical device, this kind of solar cell could be part of its visual design, and at the same time produce energy for its needs, ponders Halme.

With inkjet printing, the photovoltaic dye could be printed to a shape determined by a selected image file, and the darkness and transparency of the different parts of the image could be adjusted accurately.

– The inkjet-dyed solar cells were as efficient and durable as the corresponding solar cells prepared in a traditional way. They endured more than one thousand hours of continuous light and heat stress without any signs of performance degradation, says Postdoctoral Researcher Ghufran Hashmi.

The dye and electrolyte that turned out to be best were obtained from the research group in the Swiss École Polytechnique Fédérale de Lausanne, where Dr. Hashmi worked as a visiting researcher.

– The most challenging thing was to find suitable solvent for the dye and the right jetting parameters that gave precise and uniform print quality, tells Doctoral Candidate Merve Özkan.

This puts solar cells (pun alert) in a whole new light.

Here’s a link to and a citation for the paper,

Dye-sensitized solar cells with inkjet-printed dyes by Syed Ghufran Hashmi, Merve Özkan, Janne Halme, Shaik Mohammed Zakeeruddin, Jouni Paltakari, Michael Grätzel, and Peter D. Lund. Energy Environ. Sci., 2016,9, 2453-2462 DOI: 10.1039/C6EE00826G First published online 09 Jun 2016

This paper is behind a paywall.

Generating clean fuel with individual gold atoms

A July 22, 2016 news item on Nanowerk highlights an international collaboration focused on producing clean fuel,

A combined experimental and theoretical study comprising researchers from the Chemistry Department and LCN [London Centre for Nanotechnology], along with groups in Argentina, China, Spain and Germany, has shed new light on the behaviour of individual gold atoms supported on defective thin cerium dioxide films – an important system for catalysis and the generation of clean hydrogen for fuel.

A July ??, 2016 LCN press release, which originated the news item, expands on the theme of catalysts, the research into individual gold atoms, and how all this could result in clean fuel,

Catalysis plays a vital role in our world; an estimated 80% of all chemical and materials are made via processes which involve catalysts, which are commonly a mixture of metals and oxides. The standard motif for these heterogeneous catalysts (where the catalysts are solid and the reactants are in the gas phase) is of a high surface area oxide support that is decorated with metal nanoparticles a few nanometres in diameter. Cerium dioxide (ceria, CeO2) is a widely used support material for many important industrial processes; metal nanoparticles supported on ceria have displayed high activities for applications including car catalytic converters, alcohol synthesis, and for hydrogen production. There are two key attributes of ceria which make it an excellent active support material: its oxygen storage and release ability, and its ability to stabilise small metal particles under reaction conditions. A recent system that has been the focus of much interest has been that of gold nanoparticles and single atoms with ceria, which has demonstrated high activity towards the water-gas-shift reaction, (CO + H2O —> CO2 + H2) a key stage in the generation of clean hydrogen for use in fuel cells.

The nature of the active sites of these catalysts and the role that defects play are still relatively poorly understood; in order to study them in a systematic fashion, the researchers prepared model systems which can be characterised on the atomic scale with a scanning tunnelling microscope.

Figure: STM images of CeO2-x(111) ultrathin films before and after the deposition of Au single atoms at 300 K. The bright lattice is from the oxygen atoms at the surface – vacancies appear as dark spots

These model systems comprised well-ordered, epitaxial ceria films less than 2 nm thick, prepared on a metal single crystal, upon which single atoms and small clusters of gold were evaporated onto under ultra-high-vacuum (essential to prevent contamination of the surfaces). Oxygen vacancy defects – missing oxygen atoms in the top layer of the ceria – are relatively common at the surface and appear as dark spots in the STM images. By mapping the surface before and after the deposition of gold, it is possible to analyse the binding of the metal atoms, in particular there does not appear to be any preference for binding in the vacancy sites at 300 K.

Publishing their results in Physical Review Letters, the researchers combined these experimental results with theoretical studies of the binding energies and diffusion rates across the surface. They showed that kinetic effects governed the behaviour of the gold atoms, prohibiting the expected occupation of the thermodynamically more stable oxygen vacancy sites. They also identified electron transfer between the gold atoms and the ceria, leading to a better understanding of the diffusion phenomena that occur at this scale, and demonstrated that the effect of individual surface defects may be more minor than is normally imagined.

Here’s a link to and a citation for the paper,

Diffusion Barriers Block Defect Occupation on Reduced CeO2(111) by P.G. Lustemberg, Y. Pan, B.-J. Shaw, D. Grinter, Chi Pang, G. Thornton, Rubén Pérez, M. V. Ganduglia-Pirovano, and N. Nilius. Phys. Rev. Lett. Vol. 116, Iss. 23 — 10 June 2016 2016DOI:http://dx.doi.org/10.1103/PhysRevLett.116.236101 Published 9 June 2016

This paper is behind a paywall.

Making perovskite solar cells more stable and more humidity tolerant

Living in what’s considered a humid environment the news of solar cells that are humidity-resistant caught my attention. From a July 18, 2016 news item on phys.org,

Widely known as one of the cleanest and most renewable energy sources, solar energy is a fast growing alternative to fossil fuels. Among the various types of solar materials, organometal halide perovskite in particular has attracted researchers’ attention thanks to its superior optical and electronic properties. With a dramatic increase in the power conversion efficiency (PCE) from 3% in 2009 to as high as over 22% today [according to my July 13, 2016 posting that efficiency could now be as high as 31%], perovskite solar cells are considered as a promising next-generation energy device; only except that perovskite is weak to water and quickly loses its stability and performance in a damp, humid environment.

A team of Korean researchers led by Taiho Park at Pohang University of Science and Technology (POSTECH), Korea, has found a new method to improve not only the efficiency, but stability and humidity tolerance of perovskite solar cells. Park and his students, Guan-Woo Kim and Gyeongho Kang, designed a hydrophobic conducting polymer that has high hole mobility without the need of additives, which tend to easily absorb moisture in the air. …

A July 18, 2016 Pohang University of Science and Technology (POSTECH) press release on EurekAlert, which originated the news item, provides more information about the work,

Perovskite solar cells in general consist of a transparent electrode, an electron transport layer, perovskite, a hole transport layer, and a metal electrode. The hole transport layer is important because it not only transports holes to the electrode but also prevents perovskite from being directly exposed to air. Spiro-MeOTAD, a conventionally used hole-transport material, needs additives due to its intrinsically low hole mobility. However, Bis(trifluoromethane)sulfonimide lithium salt (LiTFSI), one of the common additives, is prone to suck in moisture in the air. Moreover, Spiro-MeOTAD forms a slightly hydrophilic layer that easily dissolves in water, and thus it cannot work as a moisture barrier itself.

Park’s team focused on an idea of an additive-free (dopant-free) polymeric hole transport layer. They designed and synthesized a hydrophobic conducting polymer by combining benzodithiophene (BDT) and benzothiadiazole (BT). As the new polymer has a face-on orientation, which helps vertical charge transport of holes, the researchers were able to achieve high hole mobility without any additives.

Park and colleagues confirmed that the perovskite solar cells with the new polymer showed high efficiency of 17.3% and dramatically improved stability — the cells retained the high efficiency for over 1400 hours, almost two months, under 75 percent humidity.

“We believe that our findings will bring perovskite one step closer to use and accelerate the commercialization of perovskite solar cells,” commented Taiho Park, a professor with the Department of Chemical Engineering at POSTECH.

Here’s a link to and a citation for the paper,

Dopant-free polymeric hole transport materials for highly efficient and stable perovskite solar cells by Guan-Woo Kim, Gyeongho Kang, Jinseck Kim, Gang-Young Lee, Hong Il Kim, Limok Pyeon, Jaechol Lee, and Taiho Park. Energy Environ. Sci., 2016,9, 2326-2333 DOI: 10.1039/C6EE00709K First published online 28 Apr 2016

I wonder if the press release was originally written in April 2016? That would explain the difference in efficiency I noted earlier in the press release. Getting back to the paper, it is open access with three different means of accessing the material from the publisher, the Royal Society of Chemistry.

Vitamin-inspired batteries

Vitamin-inspired batteries from Harvard University? According to a July 18, 2016 news item on ScienceDaily that’s exactly the case,

Harvard researchers have identified a whole new class of high-performing organic molecules, inspired by vitamin B2, that can safely store electricity from intermittent energy sources like solar and wind power in large batteries.

The development builds on previous work in which the team developed a high-capacity flow battery that stored energy in organic molecules called quinones and a food additive called ferrocyanide. That advance was a game-changer, delivering the first high-performance, non-flammable, non-toxic, non-corrosive, and low-cost chemicals that could enable large-scale, inexpensive electricity storage.

While the versatile quinones show great promise for flow batteries, Harvard researchers continued to explore other organic molecules in pursuit of even better performance. But finding that same versatility in other organic systems has been challenging.

“Now, after considering about a million different quinones, we have developed a new class of battery electrolyte material that expands the possibilities of what we can do,” said Kaixiang Lin, a Ph.D. student at Harvard and first author of the paper. “Its simple synthesis means it should be manufacturable on a large scale at a very low cost, which is an important goal of this project.”

A July 18, 2016 Harvard University John A. Paulson School of Engineering and Applied Sciences press release (also on EurekAlert) by Leah Burrows, which originated the news item, expands on the theme,

Flow batteries store energy in solutions in external tanks — the bigger the tanks, the more energy they store. In 2014, Michael J. Aziz, the Gene and Tracy Sykes Professor of Materials and Energy Technologies at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), Roy Gordon, the Thomas Dudley Cabot Professor of Chemistry and Professor of Materials Science, Alán Aspuru-Guzik, Professor of Chemistry and their team at Harvard replaced metal ions used as conventional battery electrolyte materials in acidic electrolytes with quinones, molecules that store energy in plants and animals. In 2015, they developed a quinone that could work in alkaline solutions alongside a common food additive.

In this most recent research, the team found inspiration in vitamin B2, which helps to store energy from food in the body. The key difference between B2 and quinones is that nitrogen atoms, instead of oxygen atoms, are involved in picking up and giving off electrons.

“With only a couple of tweaks to the original B2 molecule, this new group of molecules becomes a good candidate for alkaline flow batteries,” said Aziz.

“They have high stability and solubility and provide high battery voltage and storage capacity. Because vitamins are remarkably easy to make, this molecule could be manufactured on a large scale at a very low cost.”

“We designed these molecules to suit the needs of our battery, but really it was nature that hinted at this way to store energy,” said Gordon, co-senior author of the paper. “Nature came up with similar molecules that are very important in storing energy in our bodies.”

The team will continue to explore quinones, as well as this new universe of molecules, in pursuit of a high-performing, long-lasting and inexpensive flow battery.

Here’s a link to and a citation for the paper,

A redox-flow battery with an alloxazine-based organic electrolyte by Kaixiang Lin, Rafael Gómez-Bombarelli, Eugene S. Beh, Liuchuan Tong, Qing Chen, Alvaro Valle, Alán Aspuru-Guzik, Michael J. Aziz, & Roy G. Gordon.  Nature Energy 1, Article number: 16102 (2016)  doi:10.1038/nenergy.2016.102 Published online: 18 July 2016

This paper is behind a paywall.

Using light to make gold crystal nanoparticles

Gold crystal nanoparticles? Courtesy: University of Florida

Gold crystal nanoparticles? Courtesy: University of Florida

A team from the University of Florida has used gold instead of silver in a process known as plasmon-driven synthesis. From a July 8, 2016 news item on phys.org,

A team of University of Florida researchers has figured out how gold can be used in crystals grown by light to create nanoparticles, a discovery that has major implications for industry and cancer treatment and could improve the function of pharmaceuticals, medical equipment and solar panels.

A July 6, 2016 University of Florida news release, which originated the news item, provides more detail,

Nanoparticles can be “grown” in crystal formations with special use of light, in a process called plasmon-driven synthesis. However, scientists have had limited control unless they used silver, but silver limits the uses for medical technology. The team is the first to successfully use gold, which works well within the human body, with this process.

“How does light actually play a role in the synthesis? [This knowledge] was not well developed,” said David Wei, an associate professor of chemistry who led the research team. “Gold was the model system to demonstrate this.”

Gold is highly desired for nanotechnology because it is malleable, does not react with oxygen and conducts heat well. Those properties make gold an ideal material for nanoparticles, especially those that will be placed in the body.

When polyvinylpyrrolidone, or PVP, a substance commonly found in pharmaceutical tablets, is used in the plasmon-driven synthesis, it enables scientists to better control the growth of crystals. In Wei’s research, PVP surprised the team by showing its potential to relay light-generated “hot” electrons to a gold surface to grow the crystals.

The research describes the first plasmonic synthesis strategy that can make high-yield gold nanoprisms. Even more exciting, the team has demonstrated that visible-range and low-power light can be used in the synthesis. Combined with nanoparticles being used in solar photovoltaic devices, this method can even harness solar energy for chemical synthesis, to make nanomaterials or for general applications in chemistry.

Wei has spent the last decade working in nanotechnology. He is intrigued by its applications in photochemistry and biomedicine, especially in targeted drug delivery and photothermal therapeutics, which is crucial to cancer treatment. His team includes collaborators from Pacific Northwest National Laboratory, where he has worked as a visiting scholar, and Brookhaven National Laboratory. In addition, the project has provided an educational opportunity for chemistry students: one high school student (through UF’s Student Science Training Program), two University scholars who also [sic] funded by the Howard Hughes Medical Institute, five graduate students and two postdocs.

Here’s a link to and a citation for the paper,

Polyvinylpyrrolidone-induced anisotropic growth of gold nanoprisms in plasmon-driven synthesis by Yueming Zhai, Joseph S. DuChene, Yi-Chung Wang, Jingjing Qiu, Aaron C. Johnston-Peck, Bo You, Wenxiao Guo, Benedetto DiCiaccio, Kun Qian, Evan W. Zhao, Frances Ooi, Dehong Hu, Dong Su, Eric A. Stach, Zihua Zhu, & Wei David Wei. Nature Materials (2016) doi:10.1038/nmat4683 Published online 04 July 2016

This paper is behind a paywall.

Pushing efficiency of perovskite-based solar cells to 31%

This atomic force microscopy image of the grainy surface of a perovskite solar cell reveals a new path to much greater efficiency. Individual grains are outlined in black, low-performing facets are red, and high-performing facets are green. A big jump in efficiency could possibly be obtained if the material can be grown so that more high-performing facets develop. (Credit: Berkeley Lab)

This atomic force microscopy image of the grainy surface of a perovskite solar cell reveals a new path to much greater efficiency. Individual grains are outlined in black, low-performing facets are red, and high-performing facets are green. A big jump in efficiency could possibly be obtained if the material can be grown so that more high-performing facets develop. (Credit: Berkeley Lab)

It’s always fascinating to observe a trend (or a craze) in science, an endeavour that outsiders (like me) tend to think of as impervious to such vagaries. Perovskite seems to be making its way past the trend/craze phase and moving into a more meaningful phase. From a July 4, 2016 news item on Nanowerk,

Scientists from the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have discovered a possible secret to dramatically boosting the efficiency of perovskite solar cells hidden in the nanoscale peaks and valleys of the crystalline material.

Solar cells made from compounds that have the crystal structure of the mineral perovskite have captured scientists’ imaginations. They’re inexpensive and easy to fabricate, like organic solar cells. Even more intriguing, the efficiency at which perovskite solar cells convert photons to electricity has increased more rapidly than any other material to date, starting at three percent in 2009 — when researchers first began exploring the material’s photovoltaic capabilities — to 22 percent today. This is in the ballpark of the efficiency of silicon solar cells.

Now, as reported online July 4, 2016 in the journal Nature Energy (“Facet-dependent photovoltaic efficiency variations in single grains of hybrid halide perovskite”), a team of scientists from the Molecular Foundry and the Joint Center for Artificial Photosynthesis, both at Berkeley Lab, found a surprising characteristic of a perovskite solar cell that could be exploited for even higher efficiencies, possibly up to 31 percent.

A July 4, 2016 Berkeley Lab news release (also on EurekAlert), which originated the news item, details the research,

Using photoconductive atomic force microscopy, the scientists mapped two properties on the active layer of the solar cell that relate to its photovoltaic efficiency. The maps revealed a bumpy surface composed of grains about 200 nanometers in length, and each grain has multi-angled facets like the faces of a gemstone.

Unexpectedly, the scientists discovered a huge difference in energy conversion efficiency between facets on individual grains. They found poorly performing facets adjacent to highly efficient facets, with some facets approaching the material’s theoretical energy conversion limit of 31 percent.

The scientists say these top-performing facets could hold the secret to highly efficient solar cells, although more research is needed.

“If the material can be synthesized so that only very efficient facets develop, then we could see a big jump in the efficiency of perovskite solar cells, possibly approaching 31 percent,” says Sibel Leblebici, a postdoctoral researcher at the Molecular Foundry.

Leblebici works in the lab of Alexander Weber-Bargioni, who is a corresponding author of the paper that describes this research. Ian Sharp, also a corresponding author, is a Berkeley Lab scientist at the Joint Center for Artificial Photosynthesis. Other Berkeley Lab scientists who contributed include Linn Leppert, Francesca Toma, and Jeff Neaton, the director of the Molecular Foundry.

A team effort

The research started when Leblebici was searching for a new project. “I thought perovskites are the most exciting thing in solar right now, and I really wanted to see how they work at the nanoscale, which has not been widely studied,” she says.

She didn’t have to go far to find the material. For the past two years, scientists at the nearby Joint Center for Artificial Photosynthesis have been making thin films of perovskite-based compounds, and studying their ability to convert sunlight and CO2 into useful chemicals such as fuel. Switching gears, they created pervoskite solar cells composed of methylammonium lead iodide. They also analyzed the cells’ performance at the macroscale.

The scientists also made a second set of half cells that didn’t have an electrode layer. They packed eight of these cells on a thin film measuring one square centimeter. These films were analyzed at the Molecular Foundry, where researchers mapped the cells’ surface topography at a resolution of ten nanometers. They also mapped two properties that relate to the cells’ photovoltaic efficiency: photocurrent generation and open circuit voltage.

This was performed using a state-of-the-art atomic force microscopy technique, developed in collaboration with Park Systems, which utilizes a conductive tip to scan the material’s surface. The method also eliminates friction between the tip and the sample. This is important because the material is so rough and soft that friction can damage the tip and sample, and cause artifacts in the photocurrent.

Surprise discovery could lead to better solar cells

The resulting maps revealed an order of magnitude difference in photocurrent generation, and a 0.6-volt difference in open circuit voltage, between facets on the same grain. In addition, facets with high photocurrent generation had high open circuit voltage, and facets with low photocurrent generation had low open circuit voltage.

“This was a big surprise. It shows, for the first time, that perovskite solar cells exhibit facet-dependent photovoltaic efficiency,” says Weber-Bargioni.

Adds Toma, “These results open the door to exploring new ways to control the development of the material’s facets to dramatically increase efficiency.”

In practice, the facets behave like billions of tiny solar cells, all connected in parallel. As the scientists discovered, some cells operate extremely well and others very poorly. In this scenario, the current flows towards the bad cells, lowering the overall performance of the material. But if the material can be optimized so that only highly efficient facets interface with the electrode, the losses incurred by the poor facets would be eliminated.

“This means, at the macroscale, the material could possibly approach its theoretical energy conversion limit of 31 percent,” says Sharp.

A theoretical model that describes the experimental results predicts these facets should also impact the emission of light when used as an LED. …

The Molecular Foundry is a DOE Office of Science User Facility located at Berkeley Lab. The Joint Center for Artificial Photosynthesis is a DOE Energy Innovation Hub led by the California Institute of Technology in partnership with Berkeley Lab.

Here’s a link to and a citation for the paper,

Facet-dependent photovoltaic efficiency variations in single grains of hybrid halide perovskite by Sibel Y. Leblebici, Linn Leppert, Yanbo Li, Sebastian E. Reyes-Lillo, Sebastian Wickenburg, Ed Wong, Jiye Lee, Mauro Melli, Dominik Ziegler, Daniel K. Angell, D. Frank Ogletree, Paul D. Ashby, Francesca M. Toma, Jeffrey B. Neaton, Ian D. Sharp, & Alexander Weber-Bargioni. Nature Energy 1, Article number: 16093 (2016  doi:10.1038/nenergy.2016.93 Published online: 04 July 2016

This paper is behind a paywall.

Dexter Johnson’s July 6, 2016 posting on his Nanoclast blog (on the IEEE [Institute of Electrical and Electronics Engineers] website} presents his take on the impact that this new finding may have,

The rise of the crystal perovskite as a potential replacement for silicon in photovoltaics has been impressive over the last decade, with its conversion efficiency improving from 3.8 to 22.1 percent over that time period. Nonetheless, there has been a vague sense that this rise is beginning to peter out of late, largely because when a solar cell made from perovskite gets larger than 1 square centimeter the best conversion efficiency had been around 15.6 percent. …

A 3D paper-based microbial fuel cell (MFC) from Iowa State University (US)

A July 1, 2016 news item on ScienceDaily proclaims the news about a paper-based microbial fuel cell (MFC),

A team of researchers from the Iowa State University in Ames, IA has demonstrated a proof-of-concept three-dimensional paper-based microbial fuel cell (MFC) that could take advantage of capillary action to guide the liquids through the MFC system and to eliminate the need for external power. …

A July 1, 2016 (?) World Scientific news release (also on EurekAlert), which originated the news item, describes the MFC in greater detail,

The paper-based MFC runs for five days and shows the production of current as a result of biofilm formation on anode. The system produces 1.3 µW of power and 52.25 µA of current yielding a power density of approximately 25 W/m3 for this experiment. These results show that the paper-based microbial fuel cells can create power in an environmentally friendly mode without the use of any outside power. “All power created in this device is useable because no electricity is needed to run the fluids through the device. This is crucial in the advancement of these devices and the expansion of their applications.” says Nastaran Hashemi, PhD, Assistant Professor of Mechanical Engineering and the senior author of the paper.

The biofilm formation on the carbon cloth during the test provides further evidence that the current measured was the result of the bio-chemical reaction taking place. This is important because the biofilm plays a vital role in current production of a microbial fuel cell. Increased biofilm size and thickness ultimately leads to increased current production. Individual bacterial cells metabolize electron-rich substances in a complex process involving many enzyme-catalyzed reactions. The electrons are then free to travel to the anode through one of many modes of electron transport. Electron transport is very complicated, and evidence suggests that it is unique to each type of bacteria. For Shewanella Oneidensis MR-1, the most predominantly known ways of shuttling electrons from the individual bacteria cells to the anode are through direct contact, excreted soluble redox molecules, and biological nanowires. Of these, it is widely believed that excreted soluble redox molecules serving as extracellular electron shuttles makes up for as much as 70% of electron transfer mechanisms from individual bacterial cells to the electrode. Moreover, it is shown that direct contact between individual S. Oneidensis MR-1 and the electrode has little impact on the current generation, supporting a mediated electron transfer mechanism. Biofilm helps with the adsorption of the redox molecules to the electrode, which makes it important to have in high power density microbial fuel cells. There are not many studies on power production from paper-based microbial fuel cells running for few days. Without enough time for biofilm to form, the reported current and power data would predominantly be associated with extracellular electron transfer, which represents does not fully represent electrical producing capabilities of microbial fuel cells. This device for the first time demonstrates the longer duration of use and ability to operate individually, a development that could help increase the number of situations where microbial fuel cells can be applied.

The Iowa State University team is currently exploring options to better control the voltage output and create constant current. Controlled environment tests will aid in the regulation of the systems output and yield more stable results. For optimal usability and decrease in cost, the team would also like to explore a device that would not need to use Nafion and Potassium Ferricyanide in its application. …

Here’s a link to and a citation for the paper,

A paper-based microbial fuel cell operating under continuous flow condition by Niloofar Hashemi, Joshua M. Lackore, Farrokh Sharifi, Payton J. Goodrich, Megan L. Winchell, Nastaran Hashemi. Technology 04, 98 (2016). DOI: http://dx.doi.org/10.1142/S2339547816400124

I believe this paper is behind a paywall.

Photovoltaics as rose petals

Where solar cells (photovoltaics) are concerned, mimimicking plants is a longstanding pursuit. The latest  plant material to be mimicked is the rose petal’s surface. From a June 24, 2016 news item on ScienceDaily,

With a surface resembling that of plants, solar cells improve light-harvesting and thus generate more power. Scientists of KIT (Karlsruhe Institute of Technology) reproduced the epidermal cells of rose petals that have particularly good antireflection properties and integrated the transparent replicas into an organic solar cell. This resulted in a relative efficiency gain of twelve percent. …

Caption: Biomimetics: the epidermis of a rose petal is replicated in a transparent layer which is then integrated into the front of a solar cell. Credit Illustration: Guillaume Gomard, KIT

Caption: Biomimetics: the epidermis of a rose petal is replicated in a transparent layer which is then integrated into the front of a solar cell.
Credit Illustration: Guillaume Gomard, KIT

A June 24, 2016 KIT press release on EurekAlert, which originated the news item, expands on the theme,

Photovoltaics works in a similar way as the photosynthesis of plants. Light energy is absorbed and converted into a different form of energy. In this process, it is important to use a possibly large portion of the sun’s light spectrum and to trap the light from various incidence angles as the angle changes with the sun’s position. Plants have this capability as a result of a long evolution process – reason enough for photovoltaics researchers to look closely at nature when developing solar cells with a broad absorption spectrum and a high incidence angle tolerance.

Scientists at the KIT and the ZSW (Center for Solar Energy and Hydrogen Research Baden-Württemberg) now suggest in their article published in the Advanced Optical Materials journal to replicate the outermost tissue of the petals of higher plants, the so-called epidermis, in a transparent layer and integrate that layer into the front of solar cells in order to increase their efficiency.

First, the researchers at the Light Technology Institute (LTI), the Institute of Microstructure Technology (IMT), the Institute of Applied Physics (APH), and the Zoological Institute (ZOO) of KIT as well as their colleagues from the ZSW investigated the optical properties, and above all, the antireflection effect of the epidermal cells of different plant species. These properties are particularly pronounced in rose petals where they provide stronger color contrasts and thus increase the chance of pollination. As the scientists found out under the electron microscope, the epidermis of rose petals consists of a disorganized arrangement of densely packed microstructures, with additional ribs formed by randomly positioned nanostructures.

In order to exactly replicate the structure of these epidermal cells over a larger area, the scientists transferred it to a mold made of polydimethylsiloxane, a silicon-based polymer, pressed the resulting negative structure into optical glue which was finally left to cure under UV light. “This easy and cost-effective method creates microstructures of a depth and density that are hardly achievable with artificial techniques,” says Dr. Guillaume Gomard, Group Leader “Nanopothonics” at KIT’s LTI.

The scientists then integrated the transparent replica of the rose petal epidermis into an organic solar cell. This resulted in power conversion efficiency gains of twelve percent for vertically incident light. At very shallow incidence angles, the efficiency gain was even higher. The scientists attribute this gain primarily to the excellent omnidirectional antireflection properties of the replicated epidermis that is able to reduce surface reflection to a value below five percent, even for a light incidence angle of nearly 80 degrees. In addition, as examinations using a confocal laser microscope showed, every single replicated epidermal cell works as a microlense. The microlense effect extends the optical path within the solar cell, enhances the light-matter-interaction, and increases the probability that the photons will be absorbed.

“Our method is applicable to both other plant species and other PV technologies,” Guillaume Gomard explains. “Since the surfaces of plants have multifunctional properties, it might be possible in the future to apply multiple of these properties in a single step.” The results of this research lead to another basic question: What is the role of disorganization in complex photonic structures? Further studies are now examining this issue with the perspective that the next generation of solar cells might benefit from their results.

Here’s a link to and a citation for the paper,

Flower Power: Exploiting Plants’ Epidermal Structures for Enhanced Light Harvesting in Thin-Film Solar Cells by Ruben Hünig, Adrian Mertens, Moritz Stephan, Alexander Schulz, Benjamin Richter, Michael Hetterich, Michael Powalla, Uli Lemmer, Alexander Colsmann, and Guillaume Gomard. Advanced Optical Materials  Version of Record online: 30 MAY 2016 DOI: 10.1002/adom.201600046

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.