Graphene battery demonstrated to power an LED

Researchers led by Zihan Xu of the Department of Applied Physics and Materials Research Centre at the Hong Kong Polytechnic University, attached silver and gold electrodes to a graphene sheet, typically 7 mm x 7 mm in area, mounted on a silicon substrate. The assembly was then immersed in a saturated solution of copper chloride (CuCl2), and was found to produce an electrical voltage of 0.35 V. They also found that six assemblies arranged in series produced enough electricity to power a light-emitting diode (LED). The device continued to produce around the same voltage for 25 days, but after a month it dropped to about 40 mV.

Graphene is a material that consists of a layer of carbon only one atom thick, and it has been the subject of intense research in recent years because of its unusual properties. One of these properties is an exceptionally high electron mobility.

Xu and colleagues write in their paper that they think the voltage arises from the kinetic energy of the copper ions in the copper chloride solution, which they say is enough to knock electrons out of the graphene, and that these electrons then flow through the sheet. They noted that the voltage increases when the copper chloride solution is heated, and varies with its concentration.

Enlarge

Experimental setup of six graphene devices connected with a commercial LED before (a) and after (b) it was lighted up. Image: arXiv:1203.0161v2

The group also found the voltage increased when the assembly was exposed to pulses of ultrasound, and they say this lends weight to the idea that kinetic energy is the source of the voltage, since the ultrasound would increase the velocity of the copper ions. Small voltages were also produced with ionic solutions such as NaCl and CuSO4. The researchers also carried out control experiments to rule out the possibility that chemical reactions were responsible for the voltage generated.

Dr. Wanlin Guo, the graduate supervisor of one of Xu’s team (Guoan Tai), expressed skepticism at the proposed mechanism, and added that he had so far been unable to reproduce the findings in his own experiments, in which he used graphene sheets of varying sizes, mounted on varying substrates, and with different kinds of electrodes. He was unable to achieve voltages greater than around 0.1 mV.

In 2011, a research group led by Nikhil Koratkar of New York’s Rensselaer Polytechnic Institute also reported on experiments in which graphene was shown to generate a voltage when an ionic solution was made to flow over the sheets. Dr. Guo, of Nanjing University in China, also refuted these results and carried out experiments that showed the interaction of the ions in solution with the electrodes was responsible for the voltage, rather than any interaction with the graphene.

If Xu’s “graphene battery” is harnessing the thermal energy of motion of the ions to generate electricity, this source of energy is essentially unlimited. The researchers say their experimental results provide a “huge breakthrough” in the research into self-powered technology.

More information: Self-Charged Graphene Battery Harvests Electricity from Thermal Energy of the Environment, arXiv:1203.0161v2 [cond-mat.mes-hall] http://arxiv.org/abs/1203.0161

Abstract
The energy of ionic thermal motion presents universally, which is as high as 4 kJbullet kg-1bullet K-1 in aqueous solution, where thermal velocity of ions is in the order of hundreds of meters per second at room temperature1,2. Moreover, the thermal velocity of ions can be maintained by the external environment, which means it is unlimited. However, little study has been reported on converting the ionic thermal energy into electricity. Here we present a graphene device with asymmetric electrodes configuration to capture such ionic thermal energy and convert it into electricity. An output voltage around 0.35 V was generated when the device was dipped into saturated CuCl2 solution, in which this value lasted over twenty days. A positive correlation between the open-circuit voltage and the temperature, as well as the cation concentration, was observed. Furthermore, we demonstrated that this finding is of practical value by lighting a commercial light-emitting diode up with six of such graphene devices connected in series. This finding provides a new way to understand the behavior of graphene at molecular scale and represents a huge breakthrough for the research of self-powered technology. Moreover, the finding will benefit quite a few applications, such as artificial organs, clean renewable energy and portable electronics.

? 2011 PhysOrg.com

View the original article here

Silicon-carbon electrodes snap, swell, don't pop

Published online in the journal Nano Letters last week, the study includes videos of the electrodes being charged at nanometer-scale resolution. Watching them in use can help researchers understand the strengths and weaknesses of the material.

"The electrodes expand as they get charged, and that shortens the lifespan of the battery," said lead researcher Chongmin Wang at the Department of Energy's Pacific Northwest National Laboratory. "We want to learn how to improve their lifespan, because silicon-carbon nanofiber electrodes have great potential for rechargeable batteries."

Plus & Minus

Silicon has both advantages and disadvantages for use as a battery material. It has a high capacity for energy storage, so it can take on a hefty charge. Silicon's problem, though, is that it swells up when charged, expanding up to 3 times its discharged size. If silicon electrodes are packed tightly into a battery, this expansion can cause the batteries to burst. Some researchers are exploring nano-sized electrodes that perform better in such tight confines.

A multi-institution group led by PNNL's Wang decided to test nano-sized electrodes consisting of carbon nanofibers coated with silicon. The carbon's high conductivity, which lets electricity flow, nicely complements silicon's high capacity, which stores it.

Researchers at DOE's Oak Ridge National Laboratory in Oak Ridge, Tenn., Applied Sciences Inc. in Cedarville, Ohio, and General Motors Global R&D Center in Warren, Mich. created carbon nanofibers with a thin layer of silicon wrapped around. They provided the electrodes to the team at PNNL to probe their behavior while functioning.

First, Wang and colleagues tested how much lithium the electrodes could hold and how long they lasted by putting them in a small testing battery called a half-cell. After 100 charge-discharge cycles, the electrodes still maintained a very good capacity of about 1000 milliAmp-hours per gram of material, five to 10 times the capacity of conventional electrodes in lithium ion batteries.

This video is not supported by your browser at this time.

The silicon (light-colored edge) on this silicon-coated carbon nanofiber electrode (dark middle section) swells up as it is being charged with lithium ions under high magnification. A little more than 200 nanometers wide, the electrode's outer edge of silicon and lithium ions crystallize and appear wavy and shiny as the crystalline material changes the reflection of light. Credit: Chongmin Wang

Although they performed well, the team suspected that the expansion and contraction of the silicon could be a problem for the battery's longevity, since stretching tends to wear things out. To determine how well the electrodes weather the repeated stretching, Wang popped a specially designed, tiny battery into a transmission electron microscope, which can view objects nanometers wide, in DOE's EMSL, the Environmental Molecular Sciences Laboratory on the PNNL campus.

They zoomed in on the tiny battery's electrode using a new microscrope that was funded by the Recovery Act. This microscope allowed the team to study the electrode in use, and they took images and video while the tiny battery was being charged and discharged.

Not Crystal Glass

Previous work has shown that charging causes lithium ions to flow into the silicon. In this study, the lithium ions flowed into the silicon layer along the length of the carbon nanofiber at a rate of about 130 nanometers per second. This is about 60 times faster than silicon alone, suggesting that the underlying carbon improves silicon's charging speed.

As expected, the silicon layer swelled up about 300 percent as the lithium entered. However, the combination of the carbon support and the silicon's unstructured quality allowed it to swell evenly. This compares favorably to silicon alone, which swells unevenly, causing imperfections.

In addition to swelling, lithium is known to cause other changes to the silicon. The combination of lithium and silicon initially form an unstructured, glassy layer. Then, when the lithium to silicon ratio hits 15 to 4, the glassy layer quickly crystallizes, as previous work by other researchers has shown.

Wang and colleagues examined the crystallization process in the microscope to better understand it. In the microscope video, they could see the crystallization advance as the lithium filled in the silicon and reached the 15 to 4 ratio.

They found that this crystallization is different from the classic way that many substances crystallize, which builds from a starting point. Rather, the lithium and silicon layer snapped into a crystal all at once when the ratio hit precisely 15 to 4. Computational analyses of this crystallization verified its snappy nature, a type of crystallization known as congruent phase transition.

But the crystallization wasn't permanent. Upon discharging, the team found that the crystal layer became glassy again, as the concentration of lithium dropped on its way out of the silicon.

To determine if repeated use left its mark on the electrode, the team charged and discharged the tiny battery 4 times. Comparing the same region of the electrode between the first and fourth charging, the team saw the surface become rough, similar to a road with potholes.

The surface changes were likely due to lithium ions leaving a bit of damage in their wake upon discharging, said Wang. "We can see the electrode's surface go from smooth to rough as we charge and discharge it. We think as it cycles, small defects occur, and the defects accumulate."

But the fact that the silicon layer is very thin makes it more durable than thicker silicon. In thick silicon, the holes that lithium ions leave behind can come together to form large cavities. "In the current design, because the silicon is so thin, you don't get bigger cavities, just like little gas bubbles in shallow water come up to the surface. If the water is deep, the bubbles come together and form bigger bubbles."

In future work, researchers hope to explore the thickness of the silicon layer and how well it bonds with the underlying carbon to optimize the performance and lifetime of the electrodes.

More information: Chong-Min Wang, Xiaolin Li, Zhiguo Wang, Wu Xu, Jun Liu, Fei Gao, Libor Kovarik, Ji-Guang Zhang, Jane Howe, David J. Burton, Zhongyi Liu, Xingcheng Xiao, Suntharampillai Thevuthasan, and Donald R. Baer, 2012. In situ TEM investigation of congruent phase transition and structural evolution of nanostructured silicon/carbon anode for lithium ion batteries, Nano Letters, March 2, doi: 10.1021/nl204559u

Provided by Pacific Northwest National Laboratory (news : web)

View the original article here

'Tunable' metal nanostructures for fuel cells, batteries and solar energy

But Cornell chemists have now developed a way to make porous metal films with up to 1,000 times the electrical conductivity offered by previous methods. Their technique also opens the door to creating a wide variety of metal nanostructures for engineering and biomedical applications, the researchers said.

The results of several years of experimentation are described March 18 online edition of the journal Nature Materials.

"We have reached unprecedented levels of control on composition, nanostructure and functionality -- for example, conductivity -- of the resulting materials, all with a simple 'one-pot' mix-and-heat approach," said senior author Ulrich Wiesner, the Spencer T. Olin Professor of Engineering.

Enlarge

How it looks to a chemist: 3-isocyanatopropyltriethoxysilane (ICPTS), links to an amino acid which in turn grabs a metal ion ("M" represents whatever metal is chosen) from a metal acetate, leaving acetic acid behind. Having these structures in mind led to the Aha! moment for researcher Scott Warren.

The new method builds on the "sol-gel process," already familiar to chemists. Certain compounds of silicon mixed with solvents will self-assemble into a structure of silicon dioxide (i.e., glass) honeycombed with nanometer-scaled pores. The challenge facing the researchers was to add metal to create a porous structure that conducts electricity.

About 10 years ago, Wiesner's research group, collaborating with the Cornell Fuel Cell Institute, tried using the sol-gel process with the catalysts that pull protons off of fuel molecules to generate electricity. They needed materials that would pass high current, but adding more than a small amount of metal disrupted the sol-gel process, explained Scott Warren, first author of the Nature Materials paper.

Enlarge

Just about any metal in the entire periodic table (shown in red and blue) can be used in the new process. Those labeled in blue can be bought off the shelf from chemical supply houses in the appropriate form. Credit: Wiesner Lab

Warren, who was then a Ph.D. student in Wiesner's group and is now a researcher at Northwestern University, hit on the idea of using an amino acid to link metal atoms to silica molecules, because he had realized that one end of the amino acid molecule has an affinity for silica and the other end for metals.

"If there was a way to directly attach the metal to the silica sol-gel precursor then we would prevent this phase separation that was disrupting the self-assembly process," he explained.

The immediate result is a nanostructure of metal, silica and carbon, with much more metal than had been possible before, greatly increasing conductivity. The silica and carbon can be removed, leaving porous metal. But a silica-metal structure would hold its shape at the high temperatures found in some fuel cells, Warren noted, and removing just the silica to leave a carbon-metal complex offers other possibilities, including larger pores.

The researchers report a wide range of experiments showing that their process can be used to make "a library of materials with a high degree of control over composition and structure." They have built structures of almost every metal in the periodic table, and with additional chemistry can "tune" the dimensions of the pores in a range from 10 to 500 nanometers. They have also made metal-filled silica nanoparticles small enough to be ingested and secreted by humans, with possible biomedical applications. Wiesner's group is also known for creating "Cornell dots," which encapsulate dyes in silica nanoparticles, so a possible future application of the sol-gel process might be to build Graetzel solar cells, which contain light-sensitive dyes. Michael Graetzel of the École Polytechnique Fédérale de Lausanne and innovator of the Graetzel cell is a co-author of the new paper. The measurement of the record-setting electrical conductivity was performed in his laboratory.

The research has been supported by the Department of Energy and, through several channels, the National Science Foundation.

Provided by Cornell University (news : web)

View the original article here

What Does the Easter Bunny Have To Do With Easter?

There's no story in the Bible about a long-eared, cotton-tailed creature known as the Easter Bunny. Neither is there a passage about young children painting eggs or hunting for baskets overflowing with scrumptious Easter goodies.

And real rabbits certainly don't lay eggs.

BRIEF: How the Moon Affects the Date of Easter

Why are these traditions so ingrained in Easter Sunday? And what do they have to do with the resurrection of Jesus?

Well, nothing.

Bunnies, eggs, Easter gifts and fluffy, yellow chicks in gardening hats all stem from pagan roots. These tropes were incorporated into the celebration of Easter separately from the Christian tradition of honoring the day Jesus Christ rose from the dead.

According to the University of Florida's Center for Children's Literature and Culture, the origin of the celebration -- and the origin of the Easter Bunny -- can be traced back to 13th-century, pre-Christian Germany, when people worshiped several gods and goddesses. The Teutonic deity Eostra was the goddess of spring and fertility, and feasts were held in her honor on the Vernal Equinox. Her symbol was the rabbit because of the animal’s high reproduction rate.

NEWS: Was the Last Supper a Day Earlier?

Spring also symbolized new life and rebirth; eggs were an ancient symbol of fertility. According to History.com, Easter eggs represent Jesus' resurrection. However, this association came much later when Roman Catholicism became the dominant religion in Germany in the 15th century and merged with already ingrained pagan beliefs.

The first Easter Bunny legend was documented in the 1500s. By 1680, the first story about a rabbit laying eggs and hiding them in a garden was published. These legends were brought to the United States in the 1700s, when German immigrants settled in Pennsylvania Dutch country, according to the Center for Children's Literature and Culture.

The tradition of making nests for the rabbit to lay its eggs in soon followed. Eventually, nests became decorated baskets and colorful eggs were swapped for candy, treats and other small gifts.

DISCOVERY NEWS: All About Easter

So, while you're scarfing down chocolate bunnies (I hear chocolate is good for you!) and marshmallow chicks this Easter Sunday, think fondly of this holiday's origins and maybe even impress your friends at your local Easter egg hunt.

Happy Easter!

Credits: Ian O'Neill, Library of Congress, Corbis

View the original article here

James Webb Space Telescope to TiVo Universe's Birth

This week, the James Webb Space Telescope (JSWT) got its brain. Or at least the bit responsible for its memory. The first solid-state electronics unit that will store the telescope's data was delivered by contractor SEAKR Engineering to the telescope's manufacturer, Northrop Grumman.

It's a major milestone leading up the JWST's launch since without data there would be no mission. "All the digital data Webb gathers about our universe... is stored on the onboard solid state recorder until it is delivered to the world's scientists," said Scott Willoughby, vice president and Webb program manager at Northrop Grumman.

PHOTOS: The JWST's Mind-Blowing Science Potential

JWST isn't the first to use solid-state recorders. When Hubble launched in 1990, it stored its data on a pair or reel-to-reel tape recorders, but they didn't last long. One was replaced with a solid-state recorder during the telescope's second Space Shuttle servicing mission in 1997. The second was replaced during servicing mission 3A in 1999. The solid-state recorders were the same size as the reel-to-reel recorders but could hold up to ten times the amount of data.

The solid-state recorder acts just like a digital video recorder, storing the spacecraft's science data together and continuous engineering "state of health" telemetry 24 hours a day, seven days a week on 58.9 GB of available space.

When the telescope communicates with Earth every 12 hours, the data is downloaded to NASA's Deep Space Network, this is comprised of three strategically placed centers around the world for continuous radio contact.

PHOTOS: Hubble Logs Millionth Observation

The unit is specially designed to survive the harsh space environment, extreme cold and inevitable radiation. Chris Miller, senior vice president of Programs at SEAKR Engineering, says the company is completely confident in its hardware. It has had "a 100 percent on-orbit success rate," he said of previously flown systems, adding that "SEAKR is confident the Webb Telescope recorder will continue this tradition."

The telescope is designed to play its own part in protecting and preserving its memory. JWST will use a sunshield to block the light from the sun, the Earthshine, and the moonshine -- light that can affect its optical instruments and heat up its sensitive brain.

But for the shield to block all this cosmic light, the telescope needs to be at a point where all three bodies are in the same place.

NASA's solution is to put JWST in a Lagrange point 1.5 million kilometers (1 million miles) away from the Earth. That's far too far for any servicing missions -- by comparison, Hubble orbits just 563 kilometers (350 miles) away -- so we better hope its solid-state recorder is truly ready for the harsh space environment. SEAKR is so confident that there won't be a backup unit on board.

ANALYSIS: James Webb Space Telescope Saved?

From its distant vantage point, JWST will focus on infrared light, allowing it to capture matter that is moving away from the Earth. Looking far enough away, about 13.5 billion years ago, it will look into the early universe and the dusty regions where planets and stars form.

It might be easier to think of JWST as a cosmic TiVo -- video recorders use the same technology. Once it launches, the new telescope might manage to TiVo the birth of the universe for the world to see. Now that's one show no one wants to miss.

Image: An engineer inspects the JWST's primary mirror segments at NASA's Marshall Space Flight Center in Huntsville, Ala. Credit: Chris Gunn/NASA

View the original article here

Illicit Drug Use Rising For 50+ Crowd

Cocaine, heroin amphetamines and other drugs are, stereotypically, vices of teenagers and young adults who get caught up with the wrong crowd. But illicit drug use is becoming increasingly common among older generations, too, at least in England.

A new study that surveyed thousands of British found that, in less than a decade, there has been a 10-fold increase in the number of people, ages 50 to 64, who said they had recently used marijuana. For people 65 to 74, the number of recent pot-smokers was twice as high in 2007 as it was in 2000.

When the researchers looked at overall lifetime use, they also found a ten-fold increases for amphetamines, cocaine and LSD from 1993 to 2007 in 50- to 64-year olds.

Cannabis was by far the most commonly used drug among older people, with just under two percent of Brits in the 50-64 group and 0.4 percent of the 65-plus group saying they had used it in the last year. Rates were higher in inner London, where 9 percent of 50- to 64-year olds said they had used marijuana and related drugs in the previous year, and 42 percent said they had used it at some point in their lives.

NEWS: Magic Mushrooms Could Treat Depression

Total percentages were fairly low, but enough older people seem to be using drugs that, the researchers say, doctors should pay more attention to possible effects that illicit substances might be having on their patients’ health.

“Our data suggest at the very least that large numbers of people are entering older age groups with lifestyles about which we know little in terms of their effects on health and would benefit from further monitoring,” the team wrote in the journal Age and Ageing.

“The key message of this paper confirms something which has been long-suspected but which has not, to our knowledge, ever been formally investigated in the UK,” said one of the study’s authors, Robert Stewart, from King's College London, in a press release. “Illicit drug use will become a more common feature in older generations over the next one to two decades. One particular issue is that we really know very little about the effects of drugs like cannabis in older people but will need to work fast if research is to keep up with its wider use at these ages."

Photo: Corbis

View the original article here

Nine Exoplanets Discovered in Solar System's 'Twin'

In 2010, a star 127 light-years away stunned the world -- it had become the largest star system beyond our own, playing host to five, possibly seven, alien worlds. Now, the star (called HD 10180) is back in the headlines; it may actually have nine exoplanets orbiting it.

Interestingly, HD 10180 is a yellow dwarf star very much like the sun, so this discovery has drawn many parallels with our own Solar System. It is a multi-planetary system surrounding a sun-like star. But it is also a very alien place with an assortment of worlds spread over wildly different orbits.

It is believed that one of HD 10180's exoplanets is small -- although astronomers only know the planets' masses, not their physical size or composition. The smallest world weighs-in at 1.4 times the mass of Earth, making it a "super-Earth."

NEWS: New Solar System Discovered

When it was first revealed that HD 10180 was a multi-planetary system, astronomers of the European Southern Observatory (ESO) detected six exoplanets gravitationally "tugging" on their host star. Using the "radial velocity" exoplanet detection method, the astronomers watched the star's wobble to decipher up to seven worlds measuring between 1.4 to 65 times the mass of Earth.

Five exoplanets were found to be 12-to-25 times the mass of Earth -- "Neptune-like" masses -- while another was detected orbiting in the outermost reaches of the system with a mass of 65 Earth masses (a "Saturn-like" world), taking around 2,200 days to complete one orbit.

But now, in addition to verifying the signal of the small 1.4 Earth-mass world, there appears to be another two small alien worlds.

"In addition to these seven signals, we report two additional periodic signals that are, according to our model probabilities ... statistically significant and unlikely to be caused by noise or data sampling or poor phasecoverage of the observations," Mikko Tuomi, of the University of Hertfordshire, reports in a new research paper (PDF) accepted for publication in the journal Astronomy & Astrophysics.

SLIDE SHOW: Exquisite Exoplanetary Art

This basically means that Tuomi has reanalyzed the data from previous observations made by the HARPS spectrograph (attached to the ESO's 3.6-meter telescope at La Silla, Chile), confirmed signals relating to the seven exoplanets discovered in 2010 and uncovered two new worlds in the process.

What's more, these two new signals represent another two super-Earths, says Tuomi. One is 1.9 times more massive than Earth and the other is 5.1 Earth-masses.

Although these may be "super-Earths," the only similarity to Earth is their mass, so don't go getting excited that we may have spotted the much sought-after Earth analogs.

The 1.4 Earth-mass exoplanet has an orbital period of only 1.2 days. The two new super-Earths also have very tight orbits, where their "years" last only 10 and 68 days. Therefore, any question of life (as we know it) existing on these worlds is moot -- they will likely be hellishly hot, with no chance of liquid water existing on their surfaces. It's debatable whether these worlds could hold onto any kind of atmosphere as they would be constantly sandblasted by intense stellar winds.

ANALYSIS: Billions of Habitable Worlds in Our Galaxy?

As we continue hunting for exoplanets, it's only a matter of time until we make the groundbreaking discovery of an Earth-mass world orbiting its sun-like star within the habitable zone -- the distance from a star where water may exist in a liquid state. Unfortunately, even if planet-hunting projects -- like NASA's Kepler space telescope -- detect such an "Earth-like" world, we'd need an even more powerful means of detecting whether or not such a world even has an atmosphere, let alone whether it has a solid surface with oceans of liquid water.

And as for detecting any kind of life, we may actually have to physically go there. But in the case of HD 10180, 127 light-years is one long trek.

Source: "Evidence for 9 planets in the HD 10180 system," Tuomi, 2012. arXiv:1204.1254v1 [astro-ph.EP]

Image credit: ESO

View the original article here