More Powerful Electric Cars: Mechanism Behind Capacitor's High-Speed Energy Storage Discovered

More Powerful Electric Cars: Mechanism Behind Capacitor's High-Speed Energy Storage Discovered

  2:33:00 AM    Science Lover

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Researchers at North Carolina State University have discovered the means by which a polymer known as PVDF enables capacitors to store and release large mounts of energy quickly. Their findings could lead to much more powerful and efficient electric cars.

Researchers have discovered the means by which a polymer
known as PVDF enables capacitors to store and release large
amounts of energy quickly. Their findings could lead to
much more powerful and efficient electric cars.
(Credit: iStockphoto)

Capacitors are like batteries in that they store and release energy. However, capacitors use separated electrical charges, rather than chemical reactions, to store energy. The charged particles enable energy to be stored and released very quickly. Imagine an electric vehicle that can accelerate from zero to 60 miles per hour at the same rate as a gasoline-powered sports car. There are no batteries that can power that type of acceleration because they release their energy too slowly. Capacitors, however, could be up to the job -- if they contained the right materials.

NC State physicist Dr. Vivek Ranjan had previously found that capacitors which contained the polymer polyvinylidene fluoride, or PVDF, in combination with another polymer called CTFE, were able to store up to seven times more energy than those currently in use.

"We knew that this material makes an efficient capacitor, but wanted to understand the mechanism behind its storage capabilities," Ranjan says.

In research published in Physical Review Letters, Ranjan, fellow NC State physicist Dr. Jerzy Bernholc and Dr. Marco Buongiorno-Nardelli from the University of North Texas, did computer simulations to see how the atomic structure within the polymer changed when an electric field was applied. Applying an electric field to the polymer causes atoms within it to polarize, which enables the capacitor to store and release energy quickly. They found that when an electrical field was applied to the PVDF mixture, the atoms performed a synchronized dance, flipping from a non-polar to a polar state simultaneously, and requiring a very small electrical charge to do so.

"Usually when materials change from a polar to non-polar state it's a chain reaction -- starting in one place and then moving outward," Ranjan explains. "In terms of creating an efficient capacitor, this type of movement doesn't work well -- it requires a large amount of energy to get the atoms to switch phases, and you don't get out much more energy than you put into the system.

"In the case of the PVDF mixture, the atoms change their state all at once, which means that you get a large amount of energy out of the system at very little cost in terms of what you need to put into it. Hopefully these findings will bring us even closer to developing capacitors that will give electric vehicles the same acceleration capabilities as gasoline engines."

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Electricity from the nose: Engineers make power from human respiration

Electricity from the nose: Engineers make power from human respiration

  8:59:00 AM    Science Lover

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The same piezoelectric effect that ignites your gas grill with the push of a button could one day power sensors in your body via the respiration in your nose.

Graduate Student Jian Shi and Materials Science and
Engineering Assistant Professor Xudong Wang
demonstrate a material that could be used to
capture energy from respiration.

Writing in the September issue of the journal Energy and Environmental Science, Materials Science and Engineering Assistant Professor Xudong Wang, postdoctoral Researcher Chengliang Sun and graduate student Jian Shi report creating a plastic microbelt that vibrates when passed by low-speed airflow such as human respiration.

In certain materials, such as the polyvinylidene fluoride (PVDF) used by Wang’s team, an electric charge accumulates in response to applied mechanical stress. This is known as the piezoelectric effect. The researchers engineered PVDF to generate sufficient electrical energy from respiration to operate small electronic devices.



“Basically, we are harvesting mechanical energy from biological systems. The airflow of normal human respiration is typically below about two meters per second,” says Wang. “We calculated that if we could make this material thin enough, small vibrations could produce a microwatt of electrical energy that could be useful for sensors or other devices implanted in the face.”

Researchers are taking advantage of advances in nanotechnology and miniaturized electronics to develop a host of biomedical devices that could monitor blood glucose for diabetics or keep a pacemaker battery charged so that it would not need replacing. What’s needed to run these tiny devices is a miniscule power supply. Waste energy in the form or blood flow, motion, heat, or in this case respiration, offers a consistent source of power.

Wang’s team used an ion-etching process to carefully thin material while preserving its piezoelectric properties. With improvements, he believes the thickness can be controlled down to the submicron level. Because PVDF is biocompatible, he says the development represents a significant advance toward creating a practical micro-scale device for harvesting energy from respiration.

Provided by University of Wisconsin-Madison

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