Paper Supercapacitor

By coating ordinary paper with layers of gold nanoparticles and other materials, researchers have fabricated flexible paper supercapacitors that exhibit the best performance of any textile-type supercapacitor to date. In particular, the paper supercapacitors address one of the biggest challenges in this area, which is to achieve a high energy density in addition to an already high power density, since both properties are essential for realizing high-performance energy-storage devices. In the future, flexible paper supercapacitors could be used in wearable electronics for biomedical, consumer, and military applications. The researchers, led by Seung Woo Lee at the Georgia Institute of Technology and Jinhan Cho at Korea University, have published a paper on the flexible paper supercapacitor electrodes in a recent issue of Nature Communications. As energy-storage devices, supercapacitors have several advantages over batteries, such as a higher power density, rapid charge/discharge rate, and longer lifetime, yet they lag behind batteries in energy density (the amount of energy that can be stored in a given amount of space). Although several methods have been attempted to improve the energy density of paper supercapacitors by coating them with various conductive materials, often these methods have the drawback of reducing the power density.

The paper electrodes based on layer-by-layer-assembled metal nanoparticles exhibit metal-like electric conductivity, paper-like mechanical properties, and a large surface area without any thermal treatment and/or mechanical pressing,” explains coauthor Yongmin Ko at Korea University. “The periodic insertion of metal nanoparticles within high-energy nanoparticle-based paper electrodes could resolve the critical tradeoff in which an increase in the loading amount of materials to enhance the energy density of supercapacitors decreases the power density.”
Tests  showed that the flexible paper supercapacitors had a maximum capacitance that is higher than any previously reported textile-based supercapacitor. In addition, the new devices exhibits an excellent capacity retention, demonstrated by a 90% capacity retention after 5,000 bending cycles.


Perovskite Solar Cells Conversion Efficiency Rises Up To 20%

A new low-temperature solution printing technique allows fabrication of high-efficiency perovskite solar cells with large crystals intended to minimize current-robbing grain boundaries. The meniscus-assisted solution printing (MASP) technique boosts power conversion efficiencies to nearly 20 percent by controlling crystal size and orientation.

The process, which uses parallel plates to create a meniscus of ink containing the metal halide perovskite precursors, could be scaled up to rapidly generate large areas of dense crystalline film on a variety of substrates, including flexible polymers. Operating parameters for the fabrication process were chosen by using a detailed kinetics study of perovskite crystals observed throughout their formation and growth cycle.

We used a meniscus-assisted solution printing technique at low temperature to craft high quality perovskite films with much improved optoelectronic performance,” said Zhiqun Lin, a professor in the School of Materials Science and Engineering at the Georgia Institute of Technology. “We began by developing a detailed understanding of crystal growth kinetics that allowed us to know how the preparative parameters should be tuned to optimize fabrication of the films.”

The new technique is reported in the journal Nature Communications.


Electric Car: Nanofiber Electrodes Boost Fuel Cells By 30 Percent

At the same time Honda and Toyota are introducing fuel cell cars to the U.S. market, a team of researchers from Vanderbilt University, Nissan North America and Georgia Institute of Technology have teamed up to create a new technology designed to give fuel cells more oomph. The project is part of a $13 million Department of Energy program to advance fuel cell performance and durability and hydrogen storage technologies announced last month.

hydrogen fuel cells

Fuel cells were invented back in 1839 but their first real world application wasn’t until the 1960’s when NASA used them to power the Apollo spacecraft. Fuel cells need fuel and air to run, like a gasoline engine, but they produce electricity, like a battery. In hydrogen/air fuel cells, hydrogen flows into one side of the device. Air is pumped into the other side. At the anode, the hydrogen is oxidized into protons. The protons flow to the cathode where the air is channeled, reducing the oxygen to form water. Special catalysts in the anode and cathode allow these reactions to occur spontaneously, producing electricity in the process. Fuel cells convert fuel to electricity with efficiencies ranging from 40 percent to 60 percent. They have no moving parts so they are very quiet. With the only waste product being water, they are environmentally friendly.The $2.5 million collaboration is based on a new nanofiber mat technology developed by Peter Pintauro, Professor of Chemical Engineering at Vanderbilt, that replaces the conventional electrodes used in fuel cells. The nanofiber electrodes boost the power output of fuel cells by 30 percent while being less expensive and more durable than conventional catalyst layers. The technology has been patented by Vanderbilt and licensed to Merck KGaA in Germany, which is working with major auto manufacturers in applying it to the next generation of automotive fuel cells.

Conventional fuel cells use thin sheets of catalyst particles mixed with a polymer binder for the electrodes. The catalyst is typically platinum on carbon powder. The Vanderbilt approach replaces these solid sheets with mats made from a tangle of polymer fibers that are each a fraction of the thickness of a human hair made by a process called electrospinning. Particles of catalyst are bonded to the fibers. The very small diameter of the fibers means that there is a larger surface area of catalyst available for hydrogen and oxygen gas reactions during fuel cell operation. The pores between fibers in the mat electrode also facilitate the removal of the waste water. The unique fiber electrode structure results in higher fuel cell power, with less expensive platinum.

Efficient Triboelectric Generator Embedded In A Shoe

A two-stage power management and storage system could dramatically improve the efficiency of triboelectric generators that harvest energy from irregular human motion such as walking, running or finger tapping. The system uses a small capacitor to capture alternating current generated by the biomechanical activity. When the first capacitor fills, a power management circuit then feeds the electricity into a battery or larger capacitor. This second storage device supplies DC current at voltages appropriate for powering wearable and mobile devices such as watches, heart monitors, calculators, thermometers – and even wireless remote entry devices for vehicles. By matching the impedance of the storage device to that of the triboelectric generators, the new system can boost energy efficiency from just one percent to as much as 60 percent.

Triboelectric shoes

llustration shows how a triboelectric generator embedded in a shoe would produce electricity as a person walked

With a high-output triboelectric generator and this power management circuit, we can power a range of applications from human motion,” said Simiao Niu, a graduate research assistant in the School of Materials Science and Engineering at the Georgia Institute of Technology. “The first stage of our system is matched to the triboelectric nanogenerator, and the second stage is matched to the application that it will be powering.

The research has been reported in the journal Nature Communications.


Super Smart Keyboard Replaces Passwords

By analyzing such parameters as the force applied by key presses and the time interval between them, a new self-powered non-mechanical intelligent keyboard could provide a stronger layer of security for computer users. Designed by the Professor Zhong Lin Wang and his team from Georgia Tech, the self-powered device generates electricity when a user’s fingertips contact the multi-layer plastic materials that make up the device.

By analyzing such parameters as the force applied by key presses and the time interval between them, a new self-powered non-mechanical intelligent keyboard could provide a stronger layer of security for computer users
“This intelligent keyboard changes the traditional way in which a keyboard is used for information input,” said Zhong Lin Wang, a Regents professor in the School of Materials Science and Engineering at the Georgia Institute of Technology. “Every punch of the keys produces a complex electrical signal that can be recorded and analyzed.

Conventional keyboards record when a keystroke makes a mechanical contact, indicating the press of a specific key. The intelligent keyboard records each letter touched, but also captures information about the amount of force applied to the key and the length of time between one keystroke and the next. Such typing style is unique to individuals, and so could provide a new biometric for securing computers from unauthorized use.


Computing Gloves Teach You Braille And Piano

Several years ago, Georgia Institute of Technology researchers created a technology-enhanced glove that can teach beginners how to play piano melodies in 45 minutes. Now they’ve advanced the same wearable computing technology to help people learn how to read and write Braille. The twist is that people wearing the glove don’t have to pay attention. They learn while doing something else.

The process is based on passive haptic learning (PHL),” said Thad Starner, a Georgia Tech professor and wearable computer pioneer. “We’ve learned that people can acquire motor skills through vibrations without devoting active attention to their hands.”
In their new study, Starner and Ph.D. student Caitlyn Seim examined how well these gloves work to teach Braille. Each study participant wore a pair of gloves with tiny vibrating motors stitched into the knuckles. The motors vibrated in a sequence that corresponded with the typing pattern of a pre-determined phrase in Braille. Audio cues let the users know the Braille letters produced by typing that sequence. Afterwards, everyone tried to type the phrase one time, without the cues or vibrations, on a keyboard.
Seim is currently in the middle of a second study that uses PHL to teach the full Braille alphabet during four sessions. Of the eight participants so far, 75 percent of those receiving PHL reached perfect typing performance.

The sequences were then repeated during a distraction task. Participants played a game for 30 minutes and were told to ignore the gloves. Half of the participants felt repeated vibrations and heard the cues; the others only heard the audio cues. When the game was over, participants tried to type the phrase without wearing the gloves.
Remarkably, we found that people could transfer knowledge learned from typing Braille to reading Braille,” said Seim. “After the typing test, passive learners were able to read and recognize more than 70 percent of the phrase’s letters.”

How To Build Nano-Machines Networks

Networks of nanometer-scale machines offer exciting potential applications in medicine, industry, environmental protection and defense, but until now there’s been one very small problem: the limited capability of nanoscale antennas fabricated from traditional metallic components. With antennas made from conventional materials like copper, communication between low-power nanomachines would be virtually impossible. But by taking advantage of the unique electronic properties of the material known as graphene, researchers now believe they’re on track to connect devices powered by small amounts of scavenged energy.
Based on a honeycomb network of carbon atoms, graphene could generate a type of electronic surface wave that would allow antennas just one micron long and 10 to 100 nanometers wide to do the work of much larger antennas. While operating graphene nano-antennas have yet to be demonstrated, the researchers say their modeling and simulations show that nano-networks using the new approach are feasible with the alternative material.
graphene-antenna-schematicSchematic shows how surface plasmon polariton (SPP) waves would be formed on the surface of tiny antennas fabricated from graphene. The antennas would be about one micron long and 10 to 100 nanometers wide

We are exploiting the peculiar propagation of electrons in graphene to make a very small antenna that can radiate at much lower frequencies than classical metallic antennas of the same size,” said Ian Akyildiz, a Ken Byers Chair professor in Telecommunications in the School of Electrical and Computer Engineering at the Georgia Institute of Technology. “We believe that this is just the beginning of a new networking and communications paradigm based on the use of graphene.”


Artificial Skin For Robots Like Human Skin

Researchers from the Georgia Institute of Technology have fabricated arrays of piezotronic transistors capable of converting mechanical motion directly into electronic controlling signals. The arrays could help give robots a more adaptive sense of touch. Mimicking the sense of touch electronically has been challenging, and is now done by measuring changes in resistance prompted by mechanical touch. The devices developed By Georgia Tech scientists rely on a different physical phenomenon – tiny polarization charges formed when piezoelectric materials such as zinc oxide are moved or placed under strain. In the piezotronic transistors, the piezoelectric charges control the flow of current through the wires just as gate voltages do in conventional three-terminal transistors.


Any mechanical motion, such as the movement of arms or the fingers of a robot, could be translated to control signals,” explained Zhong Lin Wang, a Regents’ professor and Hightower Chair in the School of Materials Science and Engineering at the Georgia Institute of Technology. “This could make artificial skin smarter and more like the human skin. It would allow the skin to feel activity on the surface.

Power Cell Converts and Stores Energy

Researchers have developed a self-charging power cell that directly converts mechanical energy to chemical energy, storing the power until it is released as electrical current. By eliminating the need to convert mechanical energy to electrical energy for charging a battery, the new hybrid generator-storage cell utilizes mechanical energy more efficiently than systems using separate generators and batteries. For instance by harnessing a compressive force, such as a shoe heel hitting the pavement from a person walking, the power cell generates enough current to power a small calculator. A hybrid power cell the size of a conventional coin battery can power small electronic devices – and could have military applications for soldiers who might one day recharge battery-powered equipment as they walked.

People are accustomed to considering electrical generation and storage as two separate operations done in two separate units,” said Zhong Lin Wang, a Regents professor in the School of Materials Science and Engineering at the Georgia Institute of Technology. “We have put them together in a single hybrid unit to create a self-charging power cell, demonstrating a new technique for charge conversion and storage in one integrated unit.”

The research was supported by the Defense Advanced Research Projects Agency (DARPA), the U.S. Air Force, the U.S. Department of Energy, the National Science Foundation, and the Knowledge Innovation Program of the Chinese Academy of Sciences.
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