Tag Archives: energy harvesting

Maxwell’s demon at Simon Fraser University (Vancouver, Canada)

James Clerk Maxwell (1831 – 1879), a Scottish physicist, is famous for many scientific breakthroughs (see Maxwell’s Wikipedia entry) and also for a thought experiment known as Maxwell’s demon. This graphical abstract illustrates a paper from three Simon Fraser University (SFU) physicists that advances the ‘demon’s’ possibiliteis,

Graphical Abstract: Energy flows in conventional and information engines used to displace a bead. Credit: Advances in Physics: X (2024). DOI: 10.1080/23746149.2024.2352112

A June 6, 2024 news item on phys.org describes Maxwell’s thought experiment and announces a possible breakthrough, Note: Links have been removed,

The molecules that make up the matter around us are in constant motion. What if we could harness that energy and put it to use?

Over 150 years ago, Maxwell theorized that if molecules’ motion could be measured accurately, this information could be used to power an engine. Until recently this was a thought experiment, but technological breakthroughs have made it possible to build working information engines in the lab.

SFU Physics professors John Bechhoefer and David Sivak teamed up to build an information engine and test its limits. Their work has greatly advanced our understanding of how these engines function, and a paper led by postdoctoral fellow Johan du Buisson and published recently in Advances in Physics: X summarizes the findings made during their collaboration.

A June 5, 2024 SFU news release (also on EurekAlert but published June 6, 2024) by Erin Brown-John, which originated the news item, describes the breakthrough in more detail,

“We live in a world full of extra unused energy that potentially could be used,” says Bechhoefer. Understanding how information engines function can not only help us put that energy to work, it can also suggest ways that existing engines could be redesigned to use energy more efficiently, and help us learn how biological motors work in organisms and the human body.

The team’s information engine consists of a tiny bead in a water bath that is held in place with an optical trap. When fluctuations in the water cause the bead to move in the desired direction, the trap can be adjusted to prevent the bead from returning to the place where it was before. By taking accurate measurements of the bead’s location and using that information to adjust the trap, the engine is able to convert the heat energy of the water into work.

To understand how fast and efficient the engine could be, the team tested multiple variables such as the mass of the bead and sampling frequency, and developed algorithms to reduce the uncertainty of their measurements.

“Stripped down to its simplest essence, we can systematically understand how things like temperature and the size of the system changes the things we can take advantage of,” Sivak says. “What are the strategies that work best? How do they change with all those different properties?”

The team was able to achieve the fastest speed recorded to date for an information engine, approximately ten times faster than the speed of E. coli, and comparable to the speed of motile bacteria found in marine environments.

Next, the team wanted to learn if an information engine could harvest more energy than it costs to run. “In equilibrium, that’s always a losing game,” Bechhoefer says. “The costs of gathering the information and processing it will always exceed what you’re getting out of it, but when you have an environment that has extra energy, [molecules doing] extra jiggling around, then that can change the balance if it’s strong enough.”

They found that in a non-equilibrium environment, where the engine was in a heat bath with a higher temperature than the measuring apparatus, it could output significantly more power than it cost to run.

All energy on Earth comes from the sun, and it eventually radiates out into space. That directional flow of energy manifests itself in many different ways, such as wind or ocean currents that can be harvested. Understanding the principles behind information engines can help us make better use of that energy.

“We’re coming at [energy harvesting] from a very different point of view, and we hope that this different perspective can lead to some different insights about how to be more efficient,” Bechhoefer says.

The pair is looking forward to working together on other projects in the future. “We were lucky to get a joint grant together. That really helped with the collaboration,” says Bechhoefer.

Sivak, a theorist, and Bechhoefer, an experimentalist, bring complementary approaches to their work, and they have been able to attract trainees who want to work with both. “We have different styles in terms of how we go about mentoring and leading a group,” says Sivak. “Our students and post-docs can benefit from both approaches.”

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

Performance limits of information engines by Johan du Buisson, David A. Sivak, & John Bechhoefer. Advances in Physics: X Volume 9, 2024 – Issue 1 Article: 2352112 DOI: https://doi.org/10.1080/23746149.2024.2352112 Published online: 21 May 2024

This paper is open access.

Tracks of my tears could power smartphone?

So far the researchers aren’t trying to power anything with tears but they have discovered that tears could be used to generate electricity (from an Oct. 2, 2017 news item on phys.org),

A team of Irish scientists has discovered that applying pressure to a protein found in egg whites and tears can generate electricity. The researchers from the Bernal Institute, University of Limerick (UL), Ireland, observed that crystals of lysozyme, a model protein that is abundant in egg whites of birds as well as in the tears, saliva and milk of mammals can generate electricity when pressed. Their report is published today (October 2) in the journal, Applied Physics Letters.

An Oct. 2, 2017 University of Limerick press release (also on EurekAlert), which originated the news item, offers additional detail,

The ability to generate electricity by applying pressure, known as direct piezoelectricity, is a property of materials such as quartz that can convert mechanical energy into electrical energy and vice versa. Such materials are used in a variety of applications ranging from resonators and vibrators in mobile phones to deep ocean sonars and ultrasound imaging. Bone, tendon and wood are long known to possess piezoelectricity.

“While piezoelectricity is used all around us, the capacity to generate electricity from this particular protein had not been explored. The extent of the piezoelectricity in lysozyme crystals is significant. It is of the same order of magnitude found in quartz. However, because it is a biological material, it is non toxic so it could have many innovative applications such as electroactive anti-microbial coatings for medical implants,” explained Aimee Stapleton, the lead author and an Irish Research Council EMBARK Postgraduate Fellow in the Department of Physics and Bernal Institute of UL.

Crystals of lysozyme are easy to make from natural sources. “The high precision structure of lysozyme crystals has been known since 1965,” said structural biologist at UL and co-author Professor Tewfik Soulimane.
“In fact, it is the second protein structure and the first enzyme structure that was ever solved,” he added, “but we are the first to use these crystals to show the evidence of piezoelectricity”.

According to team leader Professor Tofail Syed of UL’s Department of Physics, “Crystals are the gold-standard for measuring piezoelectricity in non-biological materials. Our team has shown that the same approach can be taken in understanding this effect in biology. This is a new approach as scientists so far have tried to understand piezoelectricity in biology using complex hierarchical structures such as tissues, cells or polypeptides rather than investigating simpler fundamental building blocks”.

The discovery may have wide reaching applications and could lead to further research in the area of energy harvesting and flexible electronics for biomedical devices. Future applications of the discovery may include controlling the release of drugs in the body by using lysozyme as a physiologically mediated pump that scavenges energy from its surroundings. Being naturally biocompatible and piezoelectric, lysozyme may present an alternative to conventional piezoelectric energy harvesters, many of which contain toxic elements such as lead.

Professor Luuk van der Wielen, Director of Bernal Institute and Bernal Professor of Biosystems Engineering and Design expressed his delight at this breakthrough by UL scientists.

“The €109-million Bernal Institute has the ambition to impact the world on the basis of top science in an increasingly international context. The impact of this discovery in the field of biological piezoelectricity will be huge and Bernal scientists are leading from the front the progress in this field,” he said.

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

The direct piezoelectric effect in the globular protein lysozyme featured by A. Stapleton, M. R. Noor, J. Sweeney, V. Casey, A. L. Kholkin, C. Silien, A. A. Gandhi, T. Soulimane, and S. A. M. Tofail. Appl. Phys. Lett. 111, 142902 (2017); doi: http://dx.doi.org/10.1063/1.4997446

This paper is open access.

As for Tracks of My Tears,

Vampire nanogenerators: 2017

Researchers have been working on ways to harvest energy from bloodstreams. I last wrote about this type of research in an April 3, 2009 posting about ‘vampire batteries ‘(for use in pacemakers). The latest work according to a Sept. 8, 2017 news item on Nanowerk comes from China,

Men build dams and huge turbines to turn the energy of waterfalls and tides into electricity. To produce hydropower on a much smaller scale, Chinese scientists have now developed a lightweight power generator based on carbon nanotube fibers suitable to convert even the energy of flowing blood in blood vessels into electricity. They describe their innovation in the journal Angewandte Chemie (“A One-Dimensional Fluidic Nanogenerator with a High Power Conversion Efficiency”)

A Sept. 8, 2017 Wiley Publishing news release (also on EurekAlert), which originated the news item, expands on the theme,

For thousands of years, people have used the energy of flowing or falling water for their purposes, first to power mechanical engines such as watermills, then to generate electricity by exploiting height differences in the landscape or sea tides. Using naturally flowing water as a sustainable power source has the advantage that there are (almost) no dependencies on weather or daylight. Even flexible, minute power generators that make use of the flow of biological fluids are conceivable. How such a system could work is explained by a research team from Fudan University in Shanghai, China. Huisheng Peng and his co-workers have developed a fiber with a thickness of less than a millimeter that generates electrical power when surrounded by flowing saline solution—in a thin tube or even in a blood vessel.

The construction principle of the fiber is quite simple. An ordered array of carbon nanotubes was continuously wrapped around a polymeric core. Carbon nanotubes are well known to be electroactive and mechanically stable; they can be spun and aligned in sheets. In the as-prepared electroactive threads, the carbon nanotube sheets coated the fiber core with a thickness of less than half a micron. For power generation, the thread or “fiber-shaped fluidic nanogenerator” (FFNG), as the authors call it, was connected to electrodes and immersed into flowing water or simply repeatedly dipped into a saline solution. “The electricity was derived from the relative movement between the FFNG and the solution,” the scientists explained. According to the theory, an electrical double layer is created around the fiber, and then the flowing solution distorts the symmetrical charge distribution, generating an electricity gradient along the long axis.

The power output efficiency of this system was high. Compared with other types of miniature energy-harvesting devices, the FFNG was reported to show a superior power conversion efficiency of more than 20%. Other advantages are elasticity, tunability, lightweight, and one-dimensionality, thus offering prospects of exciting technological applications. The FFNG can be made stretchable just by spinning the sheets around an elastic fiber substrate. If woven into fabrics, wearable electronics become thus a very interesting option for FFNG application. Another exciting application is the harvesting of electrical energy from the bloodstream for medical applications. First tests with frog nerves proved to be successful.

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

A One-Dimensional Fluidic Nanogenerator with a High Power Conversion Efficiency by Yifan Xu, Dr. Peining Chen, Jing Zhang, Songlin Xie, Dr. Fang Wan, Jue Deng, Dr. Xunliang Cheng, Yajie Hu, Meng Liao, Dr. Bingjie Wang, Dr. Xuemei Sun, and Prof. Dr. Huisheng Peng. Angewandte Chemie International Edition DOI: 10.1002/anie.201706620 Version of Record online: 7 SEP 2017

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

Scientists claim off-the-shelf, power-generating clothes almost here

PEDOT-coated yarns act as “normal” wires to transmit electricity from a wall outlet to an incandescent lightbulb. Materials scientist Trisha Andrew at UMass Amherst and colleagues outline in a new paper how they have invented a way to apply breathable, pliable, metal-free electrodes to fabric and off-the-shelf clothing so it feels good to the touch and also transports electricity to power small electronics. Harvesting body motion energy generates the power. Courtesy: UMass Amherst

I’m not quite as optimistic (it’s a long way from the lab to the marketplace) as the scientists do eventually note but this does seem promising (from a May 23, 2017 news item on Nanowerk),

A lightweight, comfortable jacket that can generate the power to light up a jogger at night may sound futuristic, but materials scientist Trisha Andrew at the University of Massachusetts Amherst could make one today.

In a new paper this month, she and colleagues outline how they have invented a way to apply breathable, pliable, metal-free electrodes to fabric and off-the-shelf clothing so it feels good to the touch and also transports enough electricity to power small electronics.

A May 23, 2017 University of Massachusetts Amherst news release (also on EurekAlert), which originated the news item,

She says, “Our lab works on textile electronics. We aim to build up the materials science so you can give us any garment you want, any fabric, any weave type, and turn it into a conductor. Such conducting textiles can then be built up into sophisticated electronics. One such application is to harvest body motion energy and convert it into electricity in such a way that every time you move, it generates power.” Powering advanced fabrics that can monitor health data remotely are important to the military and increasingly valued by the health care industry, she notes.

Generating small electric currents through relative movement of layers is called triboelectric charging, explains Andrew, who trained as a polymer chemist and electrical engineer. Materials can become electrically charged as they create friction by moving against a different material, like rubbing a comb on a sweater. “By sandwiching layers of differently materials between two conducting electrodes, a few microwatts of power can be generated when we move,” she adds.

In the current early online edition of Advanced Functional Materials, she and postdoctoral researcher Lu Shuai Zhang in her lab describe the vapor deposition method they use to coat fabrics with a conducting polymer, poly(3,4-ethylenedioxytiophene) also known as PEDOT, to make plain-woven, conducting fabrics that are resistant to stretching and wear and remain stable after washing and ironing. The thickest coating they put down is about 500 nanometers, or about 1/10 the diameter of a human hair, which retains a fabric’s hand feel.

The authors report results of testing electrical conductivity, fabric stability, chemical and mechanical stability of PEDOT films and textile parameter effects on conductivity for 14 fabrics, including five cottons with different weaves, linen and silk from a craft store.

“Our article describes the materials science needed to make these robust conductors,” Andrew says. “We show them to be stable to washing, rubbing, human sweat and a lot of wear and tear.” PEDOT coating did not change the feel of any fabric as determined by touch with bare hands before and after coating. Coating did not increase fabric weight by more than 2 percent. The work was supported by the Air Force Office of Scientific Research.

Until recently, she and Zhang point out, textile scientists have tended not to use vapor deposition because of technical difficulties and high cost of scaling up from the laboratory. But over the last 10 years, industries such as carpet manufacturers and mechanical component makers have shown that the technology can be scaled up and remain cost-effective. The researchers say their invention also overcomes the obstacle of power-generating electronics mounted on plastic or cladded, veneer-like fibers that make garments heavier and/or less flexible than off-the-shelf clothing “no matter how thin or flexible these device arrays are.”

“There is strong motivation to use something that is already familiar, such as cotton/silk thread, fabrics and clothes, and imperceptibly adapting it to a new technological application.” Andrew adds, “This is a huge leap for consumer products, if you don’t have to convince people to wear something different than what they are already wearing.”

Test results were sometimes a surprise, Andrew notes. “You’d be amazed how much stress your clothes go through until you try to make a coating that will survive a shirt being pulled over the head. The stress can be huge, up to a thousand newtons of force. For comparison, one footstep is equal to about 10 newtons, so it’s yanking hard. If your coating is not stable, a single pull like that will flake it all off. That’s why we had to show that we could bend it, rub it and torture it. That is a very powerful requirement to move forward.”

Andrew is director of wearable electronics at the Center for Personalized Health Monitoring in UMass Amherst’s Institute of Applied Life Sciences (IALS). Since the basic work reported this month was completed, her lab has also made a wearable heart rate monitor with an off-the-shelf fitness bra to which they added eight monitoring electrodes. They will soon test it with volunteers on a treadmill at the IALS human movement facility.

She explains that a hospital heart rate monitor has 12 electrodes, while the wrist-worn fitness devices popular today have one, which makes them prone to false positives. They will be testing a bra with eight electrodes, alone and worn with leggings that add four more, against a control to see if sensors can match the accuracy and sensitivity of what a hospital can do. As the authors note in their paper, flexible, body-worn electronics represent a frontier of human interface devices that make advanced physiological and performance monitoring possible.

For the future, Andrew says, “We’re working on taking any garment you give us and turning it into a solar cell so that as you are walking around the sunlight that hits your clothes can be stored in a battery or be plugged in to power a small electronic device.”

Zhang and Andrew believe their vapor coating is able to stick to fabrics by a process called surface grafting, which takes advantage of free bonds dangling on the surface chemically bonding to one end of the polymer coating, but they have yet to investigate this fully.

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

Rugged Textile Electrodes for Wearable Devices Obtained by Vapor Coating Off-the-Shelf, Plain-Woven Fabrics by Lushuai Zhang, Marianne Fairbanks, and Trisha L. Andrew. Advanced Functional Materials DOI: 10.1002/adfm.201700415 Version of Record online: 2 MAY 2017

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

Offering privacy and light control via smart windows

There have been quite a few ‘smart’ window stories here on this blog but this one is the first to feature a privacy option. From a Nov. 17, 2016 news item on Nanowerk,

Smart windows get darker to filter out the sun’s rays on bright days, and turn clear on cloudy days to let more light in. This feature can help control indoor temperatures and offers some privacy without resorting to aids such as mini-blinds.

Now scientists report a new development in this growing niche: solar smart windows that can turn opaque on demand and even power other devices. …

A Nov. 17, 2016 American Chemical Society (ACS) news release, which originated the news item, goes on to explain the work,

Most existing solar-powered smart windows are designed to respond automatically to changing conditions, such as light or heat. But this means that on cool or cloudy days, consumers can’t flip a switch and tint the windows for privacy. Also, these devices often operate on a mere fraction of the light energy they are exposed to while the rest gets absorbed by the windows. This heats them up, which can add warmth to a room that the windows are supposed to help keep cool. Jeremy Munday and colleagues wanted to address these limitations.

The researchers created a new smart window by sandwiching a polymer matrix containing microdroplets of liquid crystal materials, and an amorphous silicon layer — the type often used in solar cells — between two glass panes. When the window is “off,” the liquid crystals scatter light, making the glass opaque. The silicon layer absorbs the light and provides the low power needed to align the crystals so light can pass through and make the window transparent when the window is turned “on” by the user. The extra energy that doesn’t go toward operating the window is harvested and could be redirected to power other devices, such as lights, TVs or smartphones, the researchers say.

For anyone who finds reading text a bit onerous, there’s this video,

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

Electrically Controllable Light Trapping for Self-Powered Switchable Solar Windows by Joseph Murray, Dakang Ma, and Jeremy N. Munday. ACS Photonics, Article ASAP DOI: 10.1021/acsphotonics.6b00518 Publication Date (Web): October 26, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

Cellulose-based nanogenerators to power biomedical implants?

This cellulose nanogenerator research comes from India. A Jan. 27, 2016 American Chemical Society (ACS) news release makes the announcement,

Implantable electronics that can deliver drugs, monitor vital signs and perform other health-related roles are on the horizon. But finding a way to power them remains a challenge. Now scientists have built a flexible nanogenerator out of cellulose, an abundant natural material, that could potentially harvest energy from the body — its heartbeats, blood flow and other almost imperceptible but constant movements. …

Efforts to convert the energy of motion — from footsteps, ocean waves, wind and other movement sources — are well underway. Many of these developing technologies are designed with the goal of powering everyday gadgets and even buildings. As such, they don’t need to bend and are often made with stiff materials. But to power biomedical devices inside the body, a flexible generator could provide more versatility. So Md. Mehebub Alam and Dipankar Mandal at Jadavpur University in India set out to design one.

The researchers turned to cellulose, the most abundant biopolymer on earth, and mixed it in a simple process with a kind of silicone called polydimethylsiloxane — the stuff of breast implants — and carbon nanotubes. Repeated pressing on the resulting nanogenerator lit up about two dozen LEDs instantly. It also charged capacitors that powered a portable LCD, a calculator and a wrist watch. And because cellulose is non-toxic, the researchers say the device could potentially be implanted in the body and harvest its internal stretches, vibrations and other movements [also known as, harvesting biomechanical motion].

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

Native Cellulose Microfiber-Based Hybrid Piezoelectric Generator for Mechanical Energy Harvesting Utility by
Md. Mehebub Alam and Dipankar Mandal. ACS Appl. Mater. Interfaces, 2016, 8 (3), pp 1555–1558 DOI: 10.1021/acsami.5b08168 Publication Date (Web): January 11, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

I did take a peek at the paper to see if I could determine whether or not they had used wood-derived cellulose and whether cellulose nanocrystals had been used. Based on the references cited for the paper, I think the answer to both questions is yes.

My latest piece on harvesting biomechanical motion is a June 24, 2014 post where I highlight a research project in Korea and another one in the UK and give links to previous posts on the topic.

Hyper stretchable nanogenerator

There’s a lot of talk about flexibility, stretchability and bendability in electronics and the latest is coming from Korea. An April 13, 2015 Korea Advanced Institute for Science and Technology (KAIST) news release on EurekAlert describes the situation and the Korean scientists’ most recent research into stretchable electronics,

A research team led by Professor Keon Jae Lee of the Department of Materials Science and Engineering at the Korea Advanced Institute of Science and Technology (KAIST) has developed a hyper-stretchable elastic-composite energy harvesting device called a nanogenerator.

Flexible electronics have come into the market and are enabling new technologies like flexible displays in mobile phone, wearable electronics, and the Internet of Things (IoTs). However, is the degree of flexibility enough for most applications? For many flexible devices, elasticity is a very important issue. For example, wearable/biomedical devices and electronic skins (e-skins) should stretch to conform to arbitrarily curved surfaces and moving body parts such as joints, diaphragms, and tendons. They must be able to withstand the repeated and prolonged mechanical stresses of stretching. In particular, the development of elastic energy devices is regarded as critical to establish power supplies in stretchable applications. Although several researchers have explored diverse stretchable electronics, due to the absence of the appropriate device structures and correspondingly electrodes, researchers have not developed ultra-stretchable and fully-reversible energy conversion devices properly.

Recently, researchers from KAIST and Seoul National University (SNU) have collaborated and demonstrated a facile methodology to obtain a high-performance and hyper-stretchable elastic-composite generator (SEG) using very long silver nanowire-based stretchable electrodes. Their stretchable piezoelectric generator can harvest mechanical energy to produce high power output (~4 V) with large elasticity (~250%) and excellent durability (over 104 cycles). These noteworthy results were achieved by the non-destructive stress- relaxation ability of the unique electrodes as well as the good piezoelectricity of the device components. The new SEG can be applied to a wide-variety of wearable energy-harvesters to transduce biomechanical-stretching energy from the body (or machines) to electrical energy.

Professor Lee said, “This exciting approach introduces an ultra-stretchable piezoelectric generator. It can open avenues for power supplies in universal wearable and biomedical applications as well as self-powered ultra-stretchable electronics.”

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

A Hyper-Stretchable Elastic-Composite Energy Harvester by Chang Kyu Jeong, Jinhwan Lee, Seungyong Han, Jungho Ryu, Geon-Tae Hwang, Dae Yong Park, Jung Hwan Park, Seung Seob Lee, Mynghwan Byun, Seung Hwan Ko, and Keon Jae Lee. Advanced Materials DOI: 10.1002/adma.201500367 30 March 2015Full

This paper is behind a paywall.

The researchers have prepared a short video (22 secs. and silent),

Bendable, stretchable, light-weight, and transparent: a new competitor in the competition for ‘thinnest electric generator’

An Oct. 15, 2014 Columbia University (New York, US) press release (also on EurekAlert), describes another contender for the title of the world’s thinnest electric generator,

Researchers from Columbia Engineering and the Georgia Institute of Technology [US] report today [Oct. 15, 2014] that they have made the first experimental observation of piezoelectricity and the piezotronic effect in an atomically thin material, molybdenum disulfide (MoS2), resulting in a unique electric generator and mechanosensation devices that are optically transparent, extremely light, and very bendable and stretchable.

In a paper published online October 15, 2014, in Nature, research groups from the two institutions demonstrate the mechanical generation of electricity from the two-dimensional (2D) MoS2 material. The piezoelectric effect in this material had previously been predicted theoretically.

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

Piezoelectricity of single-atomic-layer MoS2 for energy conversion and piezotronics by Wenzhuo Wu, Lei Wang, Yilei Li, Fan Zhang, Long Lin, Simiao Niu, Daniel Chenet, Xian Zhang, Yufeng Hao, Tony F. Heinz, James Hone, & Zhong Lin Wang. Nature (2014) doi:10.1038/nature13792 Published online 15 October 2014

This paper is behind a paywall. There is a free preview available with ReadCube Access.

Getting back to the Columbia University press release, it offers a general description of piezoelectricity and some insight into this new research on molybdenum disulfide,

Piezoelectricity is a well-known effect in which stretching or compressing a material causes it to generate an electrical voltage (or the reverse, in which an applied voltage causes it to expand or contract). But for materials of only a few atomic thicknesses, no experimental observation of piezoelectricity has been made, until now. The observation reported today provides a new property for two-dimensional materials such as molybdenum disulfide, opening the potential for new types of mechanically controlled electronic devices.

“This material—just a single layer of atoms—could be made as a wearable device, perhaps integrated into clothing, to convert energy from your body movement to electricity and power wearable sensors or medical devices, or perhaps supply enough energy to charge your cell phone in your pocket,” says James Hone, professor of mechanical engineering at Columbia and co-leader of the research.

“Proof of the piezoelectric effect and piezotronic effect adds new functionalities to these two-dimensional materials,” says Zhong Lin Wang, Regents’ Professor in Georgia Tech’s School of Materials Science and Engineering and a co-leader of the research. “The materials community is excited about molybdenum disulfide, and demonstrating the piezoelectric effect in it adds a new facet to the material.”

Hone and his research group demonstrated in 2008 that graphene, a 2D form of carbon, is the strongest material. He and Lei Wang, a postdoctoral fellow in Hone’s group, have been actively exploring the novel properties of 2D materials like graphene and MoS2 as they are stretched and compressed.

Zhong Lin Wang and his research group pioneered the field of piezoelectric nanogenerators for converting mechanical energy into electricity. He and postdoctoral fellow Wenzhuo Wu are also developing piezotronic devices, which use piezoelectric charges to control the flow of current through the material just as gate voltages do in conventional three-terminal transistors.

There are two keys to using molybdenum disulfide for generating current: using an odd number of layers and flexing it in the proper direction. The material is highly polar, but, Zhong Lin Wang notes, so an even number of layers cancels out the piezoelectric effect. The material’s crystalline structure also is piezoelectric in only certain crystalline orientations.

For the Nature study, Hone’s team placed thin flakes of MoS2 on flexible plastic substrates and determined how their crystal lattices were oriented using optical techniques. They then patterned metal electrodes onto the flakes. In research done at Georgia Tech, Wang’s group installed measurement electrodes on samples provided by Hone’s group, then measured current flows as the samples were mechanically deformed. They monitored the conversion of mechanical to electrical energy, and observed voltage and current outputs.

The researchers also noted that the output voltage reversed sign when they changed the direction of applied strain, and that it disappeared in samples with an even number of atomic layers, confirming theoretical predictions published last year. The presence of piezotronic effect in odd layer MoS2 was also observed for the first time.

“What’s really interesting is we’ve now found that a material like MoS2, which is not piezoelectric in bulk form, can become piezoelectric when it is thinned down to a single atomic layer,” says Lei Wang.

To be piezoelectric, a material must break central symmetry. A single atomic layer of MoS2 has such a structure, and should be piezoelectric. However, in bulk MoS2, successive layers are oriented in opposite directions, and generate positive and negative voltages that cancel each other out and give zero net piezoelectric effect.

“This adds another member to the family of piezoelectric materials for functional devices,” says Wenzhuo Wu.

In fact, MoS2 is just one of a group of 2D semiconducting materials known as transition metal dichalcogenides, all of which are predicted to have similar piezoelectric properties. These are part of an even larger family of 2D materials whose piezoelectric materials remain unexplored. Importantly, as has been shown by Hone and his colleagues, 2D materials can be stretched much farther than conventional materials, particularly traditional ceramic piezoelectrics, which are quite brittle.

The research could open the door to development of new applications for the material and its unique properties.

“This is the first experimental work in this area and is an elegant example of how the world becomes different when the size of material shrinks to the scale of a single atom,” Hone adds. “With what we’re learning, we’re eager to build useful devices for all kinds of applications.”

Ultimately, Zhong Lin Wang notes, the research could lead to complete atomic-thick nanosystems that are self-powered by harvesting mechanical energy from the environment. This study also reveals the piezotronic effect in two-dimensional materials for the first time, which greatly expands the application of layered materials for human-machine interfacing, robotics, MEMS, and active flexible electronics.

I see there’s a reference in that last paragraph to “harvesting mechanical energy from  the environment.” I’m not sure what they mean by that but I have written a few times about harvesting biomechanical energy. One of my earliest pieces is a July 12, 2010 post which features work by Zhong Lin Wang on harvesting energy from heart beats, blood flow, muscle stretching, or even irregular vibrations. One of my latest pieces is a Sept. 17, 2014 post about some work in Canada on harvesting energy from the jaw as you chew.

A final note, Dexter Johnson discusses this work in an Oct. 16, 2014 post on the Nanoclast blog (on the IEEE [Institute of Electrical and Electronics Engineers] website).

It takes more than research to change energy sources and use

Much of the talk about reducing or eliminating dependency on fossil fuels is focused on research to accomplish these goals or policies to support and promote new patterns of energy use as opposed to the details needed to implement a change in the infrastructures. For example, one frequently sees news about various energy research efforts such as this one at the University of Texas at Dallas featured in a Feb. 14, 2013 news item on Azonano,

University of Texas at Dallas researchers and their colleagues at other institutions are investigating ways to harvest energy from such diverse sources as mechanical vibrations, wasted heat, radio waves, light and even movements of the human body.

The goal is to develop ways to convert this unused energy into a form that can self-power the next generation of electronics, eliminating or reducing the need for bulky, limited-life batteries.

Beyond the more familiar wind and solar power, energy harvesting has a wide range of potential applications. These include: powering wireless sensor networks placed in “intelligent” buildings, or in hard-to-reach or dangerous areas; monitoring the structural health of aircraft; and biomedical implants that might transmit health data to your doctor or treat a chronic condition.

The Feb. 14, 2013 University of Texas at Dallas news release, which originated the news item, describes a recent energy research event and highlights some of the work being performed by the Center for Energy Harvesting Materials and Systems (CEHMS) consortium (Note: A link has been removed),

At a recent scientific conference held at UT Dallas, experts from academia, industry and government labs gathered to share their latest research on energy harvesting. Energy Summit 2013 focused on research initiatives at UT Dallas, Virginia Tech and Leibniz University in Germany, which form a consortium called the Center for Energy Harvesting Materials and Systems (CEHMS).

Founded in 2010, CEHMS is an Industry/University Cooperative Research Center funded in part by the National Science Foundation. It includes not only academic institutions, but also corporate members who collaborate on research projects and also provide funding for the center.  Roger Nessen, manager of sales and marketing at Exelis Inc. is chairman of the CEHMS advisory board.

Here are some examples of the research,

For example, Dr. Mario Rotea, the Erik Jonsson Chair and head of the Department of Mechanical Engineering at UT Dallas, discussed some of his work aimed at advancing the development of wind energy systems. He represents UT Dallas in a proposed new consortium of universities and companies called WindSTAR that would collaborate with CEHMS on wind energy science and technology issues.

On the chemistry front, Smith’s [Dennis Smith, co-director of CEHMS and the Robert A. Welch Distinguished Chair in Chemistry at UT Dallas] synthetic chemistry lab is working with advanced materials that use piezoelectrics. If a piezoelectric material is deformed by a mechanical stress – such as stepping on it or subjecting it to vibrations – it produces an electric current. Smith’s lab is investigating whether the addition of nanoparticles to certain piezoelectric materials can boost this so-called piezoelectric effect.

CEHMS co-director Dr. Shashank Priya, professor of mechanical engineering and the James and Elizabeth Turner Fellow of Engineering at Virginia Tech, collaborates with Smith on piezoelectric research. Among many projects, researchers at Virginia Tech are incorporating piezoelectrics into “smart” tiles that produce electricity when stepped upon, as well as into materials that might be applied like wallpaper to gather light and vibrational energy from walls.

Other university and industry projects include:

  • Investigating how to redesign systems to require less power.
  • An intelligent tire system that harvests energy from the vibrations in a rotating tire, powering embedded sensors that gather and report data on tire pressure, tire conditions and road conditions.
  • A new class of magnetoelectric materials that can simultaneously convert magnetic fields and vibrations into energy.
  • A textile-type material that converts wasted thermal energy into electricity, which could be wrapped around hot pipes or auto exhaust pipes to generate power.
  • Flexible solar cells that could be integrated into textiles, and worn by hikers or soldiers to power portable electronic devices far away from an electric socket.

It’s exciting to talk about research, startups, and policies but at some point one needs to develop an infrastructure to support these efforts as Kyle Vanhemert points out (in an elliptical fashion) in his Feb.14, 2013 article, A Deeply Thought-Out Plan for EV [electric vehicle] Charging Stations, on the Fast Company website,

Currently, the best estimates suggest that upwards of 80% of electric vehicle charging happens at home. … If we want to see wider adoption of EVs, however, one thing is obvious: We need to make it possible for drivers to charge in places other than their garage. It’s a more complex problem than it might seem, but a series of reports by the New York-based architecture and design studio WXY will at least give urban planners and prospective charging station entrepreneurs a place to start.

The studies, sponsored by the U.S. Department of Energy and the New York State Energy Research and Development Authority, address a major obstacle standing in the way of more ubiquitous charging–namely, that no one knows exactly what ubiquitous charging looks like. And in fairness, that’s because it doesn’t look like any one thing.  …

The WXY design studio has developed guidelines for these hypothetical EV charging stations,

The study identifies 22 design elements in all, divided into three categories: installation, access, and operation. The first looks at the infrastructural nuts and bolts of the site, including factors like physical dimensions of the station and its proximity to the power grid. Access deals with the factors that shape the basic user experience, things like proximity to traffic and building entrances, lighting, and signage. …

Vanhemert’s article includes some design diagrams, more details about these charging stations, and links to the design studio’s report and other reports that have been commissioned for the US Northeast Electric Vehicle Network.

Thank you to Kyle Vanhemert for a thought-provoking article, which raises questions about what kinds of changes will need to be made to infrastructure and everyday gadgets as we transition to new energy sources.