A team led by 91̽�� engineers has developed a new tool that could aid in the quest for better batteries and fuel cells.

Although battery technology has come a long way since Alessandro Volta first stacked metal discs in a “voltaic pile” to generate electricity, major improvements are still needed to meet the energy challenges of the future, such as powering electric cars and storing renewable energy cheaply and efficiently.

The key likely lies in the nanoscale, said , 91̽��professor of mechanical engineering. The nanoscale is a realm so tiny that the movement of a few atoms or molecules can shift the landscape. In a published May 31 in the , Li and his colleagues describe a nanoscale probe that offers a new window into this world to help scientists better understand how batteries really work.

Batteries, and their close kin fuel cells, produce electricity through chemical reactions. The rates at which these reactions occur determine how fast the battery can charge, how much power it can provide and how quickly it degrades.

Although the material in a battery electrode may look uniform to the human eye, to the atoms themselves, the environment is surprisingly diverse.

Near the surface and at the interfaces between materials, huge shifts in properties can occur — and the shifts can affect the reaction rates in complex and difficult-to-understand ways.

Research in the last 10 to 15 years has revealed just how much local variations in material properties can affect the performance of batteries and other electrochemical systems, Li said.

The complex nanoscale landscape makes it tricky to fully understand what’s going on, but “it may also create new opportunities to engineer material properties so as to achieve quantum leaps in performance,” he said.

To get a better understanding of how chemical reactions progress at the level of atoms and molecules, Li and his colleagues developed a nanoscale probe. The method is similar to atomic force microscopies: a tiny cantilever “feels” the material and builds a map of its properties with a resolution of nanometers or smaller.

In the case of the new electrochemical probe, the cantilever is heated with an electrical current, causing fluctuations in temperature and localized stress in the material beneath the probe.  As a result, atoms and ions within the material move around, causing it to expand and contract.  This expansion and contraction causes the cantilever to vibrate, which can be measured accurately using a laser beam shining on the top of the cantilever.

If a large concentration of ions or other charged particles exist in the vicinity of the probe tip, changes in their concentration will cause the material to deform further, similar to the way wood swells when it gets wet. The deformation is called Vegard strain.

Both Vegard strain and standard thermal expansion affect the vibration of the material, but in different ways. If the vibrations were like musical notes, the thermally induced Vegard strain is like a harmonic overtone, ringing one octave higher than the note being played, Li explained.

The device identifies the Vegard strain-induced vibrations and can extrapolate the concentration of ions and electronic defects near the probe tip. The approach has advantages over other types of atomic microscopy that use voltage perturbations to generate a response, since voltage can produce many different kinds of responses, and it is difficult to isolate the part of the response related to shifts in ionic and electronic defect concentration. Thermal responses are easier to identify, although one disadvantage of the new system is that it can only probe rates slower than the heat transfer processes in the vicinity of the tip.

Still, the team believes the new method will offer researchers a valuable tool for studying electrochemical material properties at the nanoscale. They tested it by measuring the concentration of charged species in Sm-doped ceria and LiFePO4, important materials in solid oxide fuel cells and lithium batteries.

“The concentration of ionic and electronic species are often tied to important rate properties of electrochemical materials — such as surface reactions, interfacial charge transfer, and bulk and surface diffusion — that govern the device performance,” Li said. “By measuring these properties locally on the nanoscale, we can build a much better understanding of how electrochemical systems really work, and thus how to develop new materials with much higher performance.”

Co-authors include 91̽��doctoral students , , and , 91̽��chemical engineering associate professor and Shuhong Xie of Xiangtan University.

For more information, contact Li at jjli@uw.edu.

This was adapted from an press release.

91̽�� researchers have shown that a favorable electrical property is present in a type of protein found in organs that repeatedly stretch and retract, such as the lungs, heart and arteries. These findings are the first that clearly track this phenomenon, called ferroelectricity, occurring at the molecular level in biological tissues.

The researchers online June 23 in the Proceedings of the National Academy of Sciences.

“We wanted to bring in different experimental techniques, evidence and theoretical understanding of ferroelectricity in biological functions,” said , a 91̽��professor of mechanical engineering and corresponding author of the paper. “We certainly have much more confidence now in the phenomenon itself.”

Ferroelectricity is a response to an electric field in which a molecule switches from having a positive to a negative charge. This switching process in synthetic materials serves as a way to power computer memory chips, display screens and sensors. This property only recently has been discovered in animal tissues and researchers think it may help build and support healthy connective tissues in mammals.

A research team led by Li ferroelectric properties in biological tissues in 2012, then in 2013 found that this property in the body’s connective tissues, wherever the protein elastin is present. But while ferroelectricity is a proven entity in synthetic materials and has long been thought to be important in biological functions, its actual existence in biology hasn’t been firmly established.

This study proves that ferroelectric switching happens in the biological protein elastin. When the researchers looked at the base structures within the protein, they saw similar behavior to the unit cells of solid-state materials, where ferroelectricity is well understood.

“When we looked at the smallest structural unit of the biological tissue and how it was organized into a larger protein fiber, we then were able to see similarities to the classic ferroelectric model found in solids,” Li said.

The researchers wanted to establish a more concrete, precise way of verifying ferroelectricity in biological tissues. They used small samples of elastin taken from a pig’s aorta and poled the tissues using an electric field at high temperatures. They then measured the current with the poling field removed and found that the current switched direction when the poling electric field was switched, a sign of ferroelectricity.

They did the same thing at room temperature using a laser as the heat source, and the current also switched directions.

Then, the researchers tested for this behavior on the smallest-possible unit of elastin, called tropoelastin, and again observed the phenomenon. They concluded that this switching property is “intrinsic” to the molecular make-up of elastin.

The next step is to understand the biological and physiological significance of this property, Li said. One hypothesis is that if ferroelectricity helps elastin stay flexible and functional in the body, a lack of it could directly affect the hardening of arteries.

“We may be able to use this as a very sensitive technique to detect the initiation of the hardening process at a very early stage when no other imaging technique will be able to see it,” Li said.

The team also is looking at whether this property plays a role in normal biological functions, perhaps in regulating the growth of tissue.

Co-authors are Pradeep Sharma at the University of Houston, Yanhang Zhang at Boston University, and collaborators at Nanjing University and the Chinese Academy of Sciences.

The research was funded by the National Science Foundation, National Institutes of Health, the National Natural Science Foundation of China and the UW.

###

For more information, contact Li at jjli@uw.edu or 206-543-6226.

Researchers at the 91̽�� and Boston University led by and have discovered that a certain type of protein found in organs that repeatedly stretch and retract – such as the heart and lungs – is the source for a favorable electrical property that could help build and support healthy connective tissues. But when exposed to sugar, some of the proteins no longer could perform their function, according to findings April 15 in the journal .

The property, called ferroelectricity, is a response to an electric field in which a molecule switches from having a positive to a negative charge. Only recently discovered in animal tissues, researchers have traced this property to elastin and found that when exposed to sugar, the elastin protein sometimes slows or stops its ferroelectric switching. This could lead to the hardening of those tissues and, ultimately, degrade an artery or ligament.

“This finding is important because it tells us the origin of the ferroelectric switching phenomenon and also suggests it’s not an isolated occurrence in one type of tissue as we thought,” said co-corresponding author Li, a 91̽��associate professor of mechanical engineering. “This could be associated with aging and diabetes, which I think gives more importance to the phenomenon.”

About a year ago, Li and collaborators ferroelectric switching in mammalian tissues, a surprising first for the field. Ferroelectricity is common in synthetic materials and is used for displays, memory storage and sensors. Li’s research team found that the wall of a pig’s aorta, the largest blood vessel carrying blood to the heart, exhibits ferroelectric switching properties.

Li said that discovery left researchers with a lot of questions, including whether this property is found in other soft tissues and the health implications of its presence. Observing differences in ferroelectric behavior at the protein level has helped to answer some of those questions.

The research team separated the aortic tissue into two types of proteins, collagen and elastin. Fibrous collagen is widespread in biological tissues, while elastin has only been found in animals with a backbone. Elastin, as its name suggests, is springy and helps the heart and lungs stretch and contract. Ferroelectric switching gives elastin the flexibility needed to perform repeated pulses as with an artery.

When researchers treated the elastin with sugar, they found that glucose suppressed ferroelectric switching by up to 50 percent. This interaction between sugar and protein mimics a natural process called glycation, in which sugar molecules attach to proteins, degrading their structure and function. Glycation happens naturally when we age and is associated with a number of diseases such as diabetes, high blood pressure and arteriosclerosis, a thickening and hardening of the arteries.

The research team has focused solely on the aortic tissues, but this finding likely applies to other biological tissues that have the protein elastin, such as the lungs and skin.

“I would expect the same phenomena will be observed in those tissues and organs as well,” Li said. “It will be more common than what we originally thought.”

Researchers next will drill down even more to look at the molecular mechanics of ferroelectric switching and further try to connect the process with disease onset.

Co-authors are Yuanming Liu, Nataly Q. Chen and Feiyue Ma at the UW, and Zhang, Yunjie Wang and Ming-Jay Chow at Boston University.

The research was funded by the National Science Foundation, the National Institutes of Health, the 91̽��and a NASA Space Technology Research Fellowship.

###

For more information, contact Li at 206-543-6226 or jjli@uw.edu.

A team led by the 91̽�� in Seattle and the Southeast University in China discovered a molecule that shows promise as an organic alternative to today’s silicon-based semiconductors. The findings, published this week in the journal , display properties that make it well suited to a wide range of applications in memory, sensing and low-cost energy storage.

“This molecule is quite remarkable, with some of the key properties that are comparable with the most popular inorganic crystals,” said co-corresponding author , a 91̽��associate professor of mechanical engineering.

The carbon-based material could offer even cheaper ways to store digital information; provide a flexible, nontoxic material for medical sensors that would be implanted in the body; and create a less costly, lighter material to harvest energy from natural vibrations.

The new molecule is a ferroelectric, meaning it is positively charged on one side and negatively charged on the other, where the direction can be flipped by applying an electrical field. Synthetic ferroelectrics are now used in some displays, sensors and memory chips.

In the study the authors pitted their molecule against , a long-known ferroelectric material that is a standard for performance. Barium titanate is a ceramic crystal and contains titanium; it has largely been replaced in industrial applications by better-performing but lead-containing alternatives.

The new molecule holds its own against the standard-bearer. It has a natural polarization, a measure of how strongly the molecules align to store information, of 23, compared to 26 for barium titanate. To Li’s knowledge this is the best organic ferroelectric discovered to date.

A recent study in announced an organic ferroelectric that works at room temperature. By contrast, this molecule retains its properties up to 153 degrees Celsius (307 degrees F), even higher than for barium titanate.

The new molecule also offers a full bag of electric tricks. Its dielectric constant – a measure of how well it can store energy – is more than 10 times higher than for other organic ferroelectrics. And it’s also a good piezoelectric, meaning it’s efficient at converting movement into electricity, which is useful in sensors.

The organic crystal is made from bromine, a natural element isolated from sea salt, mixed with carbon, hydrogen and nitrogen (its full name is diisopropylammonium bromide). Researchers dissolved the elements in water and evaporated the liquid to grow the crystal. Because the molecule contains carbon, it is organic, and pivoting chemical bonds allow it to flex.

The molecule would not replace current inorganic materials, Li said, but it could be used in applications where cost, ease of manufacturing, weight, flexibility and toxicity are important.

Li is working on a number of projects relating to ferroelectricity. Last year he and his graduate student found the first evidence for . He was co-author on a 2011 paper in Science that in ferroelectric films, showing how such molecules could be used to store digital information.

“Ferroelectrics are pretty remarkable materials,” Li said. “It allows you to manipulate mechanical energy, electrical energy, optics and electromagnetics, all in a single package.”

He is working to further characterize this new molecule and explore its combined electric and mechanical properties. He also plans to continue the search for more organic ferroelectrics.

The joint first authors of the new paper are Yuanming Liu, a 91̽��postdoctoral researcher in mechanical engineering, and Da-Wei Fu, a doctoral student working with co-corresponding author Ren-Gen Xiong at Southeast University. Other co-authors are Hong-Ling Cai, Qiong Ye, Wen Zhang and Yi Zhang at Southeast University; Xue-Yuan Chen at the Chinese Academy of Sciences; and Gianluca Giovannetti and Massimo Capone at the Italian National Simulation Centre.

The research was funded by the U.S. National Science Foundation, China’s National Natural Science Foundation and the European Research Council.

###

For more information, contact Li at 206-543-6226 or jjli@uw.edu.