U of Washington: Fast, Cheap method to make supercapacitor electrodes for EV’s and High-Powered Lasers


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Supercapacitors are an aptly named type of device that can store and deliver energy faster than conventional batteries. They are in high demand for applications including electric cars, wireless telecommunications and high-powered lasers.

But to realize these applications, supercapacitors need better electrodes, which connect the supercapacitor to the devices that depend on their energy. These electrodes need to be both quicker and cheaper to make on a large scale and also able to charge and discharge their electrical load faster. A team of engineers at the University of Washington thinks they’ve come up with a process for manufacturing supercapacitor electrode materials that will meet these stringent industrial and usage demands.
The researchers, led by UW assistant professor of materials science and engineering Peter Pauzauskie, published a paper on July 17 in the journal Nature Microsystems and Nanoengineering (“Rapid synthesis of transition metal dichalcogenide–carbon aerogel composites for supercapacitor electrodes”) describing their supercapacitor electrode and the fast, inexpensive way they made it.
Their novel method starts with carbon-rich materials that have been dried into a low-density matrix called an aerogel. This aerogel on its own can act as a crude electrode, but Pauzauskie’s team more than doubled its capacitance, which is its ability to store electric charge.
These inexpensive starting materials, coupled with a streamlined synthesis process, minimize two common barriers to industrial application: cost and speed.
“In industrial applications, time is money,” said Pauzauskie. “We can make the starting materials for these electrodes in hours, rather than weeks. And that can significantly drive down the synthesis cost for making high-performance supercapacitor electrodes.”
A coin-cell battery
Full x-ray reconstruction of a coin cell supercapacitor.
Effective supercapacitor electrodes are synthesized from carbon-rich materials that also have a high surface area. The latter requirement is critical because of the unique way supercapacitors store electric charge. While a conventional battery stores electric charges via the chemical reactions occurring within it, a supercapacitor instead stores and separates positive and negative charges directly on its surface.
“Supercapacitors can act much faster than batteries because they are not limited by the speed of the reaction or byproducts that can form,” said co-lead author Matthew Lim, a UW doctoral student in the Department of Materials Science & Engineering. “Supercapacitors can charge and discharge very quickly, which is why they’re great at delivering these ‘pulses’ of power.”
“They have great applications in settings where a battery on its own is too slow,” said fellow lead author Matthew Crane, a doctoral student in the UW Department of Chemical Engineering. “In moments where a battery is too slow to meet energy demands, a supercapacitor with a high surface area electrode could ‘kick’ in quickly and make up for the energy deficit.”
To get the high surface area for an efficient electrode, the team used aerogels. These are wet, gel-like substances that have gone through a special treatment of drying and heating to replace their liquid components with air or another gas. These methods preserve the gel’s 3-D structure, giving it a high surface area and extremely low density. It’s like removing all the water out of Jell-O with no shrinking.
“One gram of aerogel contains about as much surface area as one football field,” said Pauzauskie.
Crane made aerogels from a gel-like polymer, a material with repeating structural units, created from formaldehyde and other carbon-based molecules. This ensured that their device, like today’s supercapacitor electrodes, would consist of carbon-rich materials.
Previously, Lim demonstrated that adding graphene — which is a sheet of carbon just one atom thick — to the gel imbued the resulting aerogel with supercapacitor properties. But, Lim and Crane needed to improve the aerogel’s performance, and make the synthesis process cheaper and easier.
In Lim’s previous experiments, adding graphene hadn’t improved the aerogel’s capacitance. So they instead loaded aerogels with thin sheets of either molybdenum disulfide or tungsten disulfide. Both chemicals are used widely today in industrial lubricants.
The researchers treated both materials with high-frequency sound waves to break them up into thin sheets and incorporated them into the carbon-rich gel matrix. They could synthesize a fully-loaded wet gel in less than two hours, while other methods would take many days. After obtaining the dried, low-density aerogel, they combined it with adhesives and another carbon-rich material to create an industrial “dough,” which Lim could simply roll out to sheets just a few thousandths of an inch thick. They cut half-inch discs from the dough and assembled them into simple coin cell battery casings to test the material’s effectiveness as a supercapacitor electrode.
A coin-cell battery
Slice from x-ray computed tomography image of a supercapacitor coin cell assembled with the electrode materials. The thin layers — just below the coin cell lid — are layers of electrode materials and a separator. (Image: William Kuykendall)
Not only were their electrodes fast, simple and easy to synthesize, but they also sported a capacitance at least 127 percent greater than the carbon-rich aerogel alone.
Lim and Crane expect that aerogels loaded with even thinner sheets of molybdenum disulfide or tungsten disulfide — theirs were about 10 to 100 atoms thick — would show an even better performance. But first, they wanted to show that loaded aerogels would be faster and cheaper to synthesize, a necessary step for industrial production. The fine-tuning comes next.
The team believes that these efforts can help advance science even outside the realm of supercapacitor electrodes. Their aerogel-suspended molybdenum disulfide might remain sufficiently stable to catalyze hydrogen production. And their method to trap materials quickly in aerogels could be applied to high capacitance batteries or catalysis.
Source: By James Urton, University of Washington

 

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In one-two punch, researchers load ‘nanocarriers’ to deliver cancer-fighting drugs and imaging molecules to tumors


nano-carriers-161129161516_1_540x360Zhang’s group created this nanocarrier using a “load during assembly” approach, shown along the top. Images b, c and d are microscopic views of the nanocarriers at each major step of the assembly and loading process. Credit: Miqin Zhang

In one-two punch, researchers load ‘nanocarriers’ to deliver cancer-fighting drugs and imaging molecules to tumors

A conundrum of cancer is the tumor’s ability to use our bodies as human shields to deflect treatment. Tumors grow among normal tissues and organs, often giving doctors few options but to damage, poison or remove healthy parts of our body in attempts to beat back the cancer with surgery, chemotherapy or radiation.

But in a paper published Sept. 27 in the journal Small, scientists at the University of Washington describe a new system to encase chemotherapy drugs within tiny, synthetic “nanocarrier” packages, which could be injected into patients and disassembled at the tumor site to release their toxic cargo.

The group, led by UW professor of materials science and engineering Miqin Zhang, is not the first to work on nanocarriers. But the nanocarrier package developed by Zhang’s team is a hybrid of synthetic materials, which gives the nanocarrier the unique ability to ferry not just drugs, but also tiny fluorescent or magnetic particles to stain the tumor and make it visible to surgeons.

“Our nanocarrier system is really a hybrid addressing two needs — drug delivery and tumor imaging,” said Zhang, who is senior author on the paper. “First, this nanocarrier can deliver chemotherapy drugs and release them in the tumor area, which spares healthy tissue from toxic side effects. Second, we load the nanocarrier with materials to help doctors visualize the tumor, either using a microscope or by MRI scan.”

Their hybrid nanocarrier builds on years of research into the types of synthetic materials that could package drugs for delivery into a specific part of a patient’s body. In previous attempts, scientists would often first try make an empty nanocarrier out of a synthetic material. Once assembled, they would load the nanocarrier with a therapeutic drug. But this approach was inefficient, and carried a high risk of damaging the fragile drugs and rendering them ineffective.

“Most chemotherapy drugs have complex structures — essentially, they’re very fragile — and they do no good if they are broken by the time they reach the tumor,” said Zhang.

Nano Body II 43a262816377a448922f9811e069be13Zhang’s team worked around this problem by designing a nanocarrier that could be assembled and loaded simultaneously. Their approach is akin to laying cargo within a shipping container even as the container’s walls, floor and roof are being assembled and bolted together.

This “load during assembly” technique also let Zhang’s team incorporate multiple chemical components into the nanocarrier’s structure, which could help hold cargo in place and make the tumor easy to image in clinical settings.

Their nanocarrier sports a core of iron oxide, which provides structure but can also be used as an imaging agent in MRI scans. A shell of silica surrounds the core, and was designed to efficiently stack the chemotherapy drug paclitaxel. They also included space in the nanocarrier for carbon dots, tiny particles that can “stain” tissue and make it easier to see under a microscope, helping doctors resolve the boundaries between cancerous and healthy tissue for further treatment or surgery. The intensity of many imaging agents fades over time, but Zhang said this nanocarrier can provide sustained imaging for months.

Yet despite holding so much cargo, the fully loaded nanocarriers are less than the thickness of a sheet of flimsy notebook paper.

The silica shell keeps the nanocarriers watertight. In addition, they do not interfere with healthy tissue, as Zhang’s team showed by injecting healthy mice with empty nanocarriers or nanocarriers loaded with drug cargo. Five days after injection, they checked vital organs in the mice for evidence of toxicity and found none.

“This would indicate that the nanocarriers themselves do not trigger an adverse reaction in the body, and that the loaded nanocarriers are keeping their toxic cargo shielded from the body,” said Zhang.

The UW team also designed the nanocarriers to be easily disassembled once they reached a desired location. Gentle heating from low-level infrared light was sufficient to make the nanocarriers break apart and disgorge their cargo, which is something doctors could apply to the tumor site during treatment.

As their final test of the nanocarrier effectiveness, Zhang’s team turned to mice with a form of transmissible cancer. Mice that they injected with empty nanocarriers showed no reduction in tumor size. But tumors shrank significantly in mice injected with nanocarriers that were loaded with paclitaxel. They saw a similar affect on human cancer cells cultured and tested in the lab.

“These results show that the nanocarriers can deliver their cargo intact to the tumor site,” said Zhang. “And while we designed this nanocarrier specifically to accommodate paclitaxel, it is possible to adjust this technique for other drugs.”

There are still mountains to climb before this technology is proven safe and effective for humans. But Zhang hopes her team’s approach and promising results will accelerate the ascent.


Story Source:

Materials provided by University of Washington. Original written by James Urton. Note: Content may be edited for style and length.


Journal Reference:

  1. Hui Wang, Kui Wang, Bowei Tian, Richard Revia, Qingxin Mu, Mike Jeon, Fei-Chien Chang, Miqin Zhang. Preloading of Hydrophobic Anticancer Drug into Multifunctional Nanocarrier for Multimodal Imaging, NIR-Responsive Drug Release, and Synergistic Therapy. Small, 2016; DOI: 10.1002/smll.201602263

University of Washington: Nanoscale Probe could produce big improvements in batteries and fuel cells


Nanowires 060116 micromachines-05-00171-g004-1024A new method helps scientists get an atom’s level understanding of electro-chemical properties

A team of American and Chinese researchers 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 to the needed improvements likely lies in the nanoscale, said Jiangyu Li, a professor of Mechanical Engineering at the University of Washington in Seattle. The nanoscale is a realm so tiny that the movement of a few atoms or molecules can shift the landscape. Li and his colleagues have built a new window into this world to help scientists better understand how batteries really work. They describe their nanoscale probe in the Journal of Applied Physics, from AIP Publishing.

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 ten to fifteen 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 materials 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.

Rice Nanoporus Battery 102315 untitledYou Might Also Want To Read About A New Technology for Next Generation “Nano-Batteries” Developed by Rice University: Dr. James Tour

 

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, respectively.

“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.”


Story Source:

The above post is reprinted from materials provided byAmerican Institute of Physics. Note: Materials may be edited for content and length.


Journal Reference:

  1. Ahmadreza Eshghinejad, Ehsan Nasr Esfahani, Peiqi Wang, Shuhong Xie, Timothy C. Geary, Stuart B. Adler, Jiangyu Li.Scanning thermo-ionic microscopy for probing local electrochemistry at the nanoscale. Journal of Applied Physics, 2016; 119 (20): 205110 DOI: 10.1063/1.4949473

 

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University of Washington: Nanocrystals for Luminescent Solar Concentrators


Abstract

Abstract Image

Luminescent solar concentrators (LSCs) harvest sunlight over large areas and concentrate this energy onto photovoltaics or for other uses by transporting photons through macroscopic waveguides. Although attractive for lowering solar energy costs, LSCs remain severely limited by luminophore reabsorption losses.

Here, we report a quantitative comparison of four types of nanocrystal (NC) phosphors recently proposed to minimize reabsorption in large-scale LSCs: two nanocrystal heterostructures and two doped nanocrystals. Experimental and numerical analyses both show that even the small core absorption of the leading NC heterostructures causes major reabsorption losses at relatively short transport lengths.

Doped NCs outperform the heterostructures substantially in this critical property. A new LSC phosphor is introduced, nanocrystalline Cd1–xCuxSe, that outperforms all other leading NCs by a significant margin in both small- and large-scale LSCs under full-spectrum conditions.

Read Publication Here: http://pubs.acs.org/doi/abs/10.1021/nl504510t?src=recsys&

Copyright © 2015 American Chemical Society

Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, United States
Mathematics Department, Western Washington University, 516 High Street, Bellingham, Washington 98225, United States