SCIENTISTS are one step closer to battery-free wireless devices and cheap, efficient, durable fuel cells.
University of Washington (UW), United States, engineers have created a new wireless communication system that allows devices to interact with each other without relying on batteries or wires for power.
The researchers published their results at the Association for Computing Machinery’s Special Interest Group on Data Communication 2013 conference in Hong Kong, which began August 13. They have received the conference’s best-paper award for their research.
The new communication technique, which the researchers call “ambient backscatter,” takes advantage of the TV and cellular transmissions that already surround us around the clock. Two devices communicate with each other by reflecting the existing signals to exchange information. The researchers built small, battery-free devices with antennas that can detect, harness and reflect a TV signal, which then is picked up by other similar devices.
The technology could enable a network of devices and sensors to communicate with no power source or human attention needed.
Previous study published in March promised that wireless charging will soon be available for more and more mobile phones. VTT Technical Research Centre of Finland is working with the industry’s leading technological companies and standardisation bodies to expand the scope of application of wireless charging technology to other, smaller portable devices, such as mobile phone accessories, wrist devices, wireless mice and sensors. This can be done by combining wireless power transmission with NFC connectivity technology, which enables cost-effective and compact design.
Consumer need to recharge the batteries of various kinds of portable devices, whenever and wherever, continues to grow. Over the next five years, wireless charging will be available for more and more mobile devices. The first mobile phones with wireless charging capability are already on the market. Examples include recent smartphone releases by leading mobile phone manufacturers, many of which have wireless charging either built in or available through a special cover accessory charging case.
Meanwhile, a new cost-effective polymer membrane can decrease the cost of alkaline batteries and fuel cells by allowing the replacement of expensive platinum catalysts without sacrificing important aspects of performance, according to Penn State, United States, researchers.
The researchers report their findings in a recent issue of the Journal of the American Chemical Society.
“We have tried to break this paradigm of tradeoffs in materials (by improving) both the stability and the conductivity of this membrane at the same time, and that is what we were able to do with this unique polymeric materials design,” said Michael Hickner, associate professor of materials science and engineering.
In solid-state alkaline fuel cells, anion exchange membranes conduct negative charges between the device’s cathode and anode – the negative and positive connections of the cell – to create useable electric power. Most fuel cells currently use membranes that require platinum-based catalysts that are effective but expensive.
Also, research team of Ulsan National Institute of Science and Technology (UNIST), Georgia Institute of Technology, and Dong-Eui University developed a novel cathode material, which has outstanding performance and robust reliability even at the intermediate temperature range.
The research titled “Highly Efficient and robust cathode materials for low-temperature solid fuel cells: PrBa0.5Sr0.5Co2-xFexO5+?” was published in Scientific Reports on August 13.
As high power density devices, fuel cells can convert chemical energy directly into electric power very efficiently and environmentally friendly. Solid oxide fuel cells (SOFCs), based on an oxide ion conducting electrolyte, have several advantages over other types of fuel cells, including relatively inexpensive material costs, low sensitivity to impurities in the fuel, and high overall efficiency.
To make SOFC technology more affordable, the operating temperature must be further reduced so that substantially less expensive materials may be used for the cell components. Also there will be more choices of materials for other components with lower operating temperature.
However, at the low operating temperature, the problem is that the efficiency drop by the cathode is especially dramatic than the one due to the anode and/or electrolyte. It means that the cathode, as a key component of SOFC, contributes the most to the polarisation loss during intermediate temperature operation. As a result, the development of feasible low temperature SOFCs requires the generation of highly efficient cathode materials.
A UNIST research team tried to co-dope Sr and Fe and succeeded in yielding remarkable out-performance to present materials at lower operating temperature. The optimised composition has facilitated excellent oxygen reduction reaction and the novel structure has created pore channels that dramatically enhance oxygen ion diffusion and surface oxygen exchange while maintaining excellent compatibility and stability under operating conditions.
Lead researcher and UW assistant professor of computer science and engineering, Shyam Gollakota, said: “We can repurpose wireless signals that are already around us into both a source of power and a communication medium. It’s hopefully going to have applications in a number of areas including wearable computing, smart homes and self-sustaining sensor networks.”
Smart sensors could be built and placed permanently inside nearly any structure, then set to communicate with each other. For example, sensors placed in a bridge could monitor the health of the concrete and steel, then send an alert if one of the sensors picks up a hairline crack. The technology can also be used for communication – text messages and emails, for example – in wearable devices, without requiring battery consumption.
The researchers tested the ambient backscatter technique with credit card-sized prototype devices placed within several feet of each other. For each device the researchers built antennas into ordinary circuit boards that flash an LED light when receiving a communication signal from another device.
Groups of the devices were tested in a variety of settings in the Seattle area, including inside an apartment building, on a street corner and on the top level of a parking garage. These locations ranged from less than half a mile away from a TV tower to about 6.5 miles away.
They found that the devices were able to communicate with each other, even the ones farthest from a TV tower. The receiving devices picked up a signal from their transmitting counterparts at a rate of 1 kilobit per second when up to 2.5 feet apart outdoors and 1.5 feet apart indoors. This is enough to send information such as a sensor reading, text messages and contact information.
It’s also feasible to build this technology into devices that do rely on batteries, such as smartphones. It could be configured so that when the battery dies, the phone could still send text messages by leveraging power from an ambient TV signal. The applications are endless, the researchers say, and they plan to continue advancing the capacity and range of the ambient backscatter communication network.
Hickner and his research team are conducting tests on membrane electrode assembly fuel cells in their Reber Building laboratory on Penn State’s University Park campus.
Hickner’s new polymer is a unique anion exchange membrane – a new type of fuel cell and battery membrane – that allows the use of much more cost-efficient non-precious metal catalysts and does not compromise either durability or efficiency like previous anion exchange membranes
“What we’re really doing here is providing alternatives, possible choices, new technology so that people who want to commercialise fuel cells can now choose between the old paradigm and new possibilities with anion exchange membranes,” Hickner said.
Creating this alternative took some intuition and good fortune. In work spearheaded by Nanwen Li, a postdoctoral researcher in materials science and engineering, Hickner’s team created several variations of the membrane, each with slightly different chemical compositions. They then ran each variation under simulated conditions to predict which would be optimal in an actual fuel cell. The researchers report their findings in a recent issue of the Journal of the American Chemical Society.
Based on these initial tests, the group predicted that the membranes with long 16-carbon structures in their chemical makeup would provide the best efficiency and durability, as measured respectively by conductivity and long-term stability.
Chao-Yang Wang, William E. Diefenderfer Chair of Mechanical Engineering, and his team then tested each possibility in an operating fuel cell device. Yongjun Leng, a research associate in mechanical and nuclear engineering, measured the fuel cell’s output and lifetime for each material variation.
Despite predictions, the membranes containing shorter 6-carbon structures proved to be much more durable and efficient after 60 hours of continuous operation.
“We were somewhat surprised…that what we thought was the best material in our lab testing wasn’t necessarily the best material in the cell when it was evaluated over time,” said Hickner, who added that researchers are still trying to understand why the six-carbon variation has better long-term durability than the 16-carbon sample in the fuel cell by studying the operating conditions of the cell in detail.
Because the successful membrane was so much more effective than the initial lab studies predicted, researchers are now interested in accounting for the interactions that the membranes experienced while inside the cell.
“We have the fuel cell output -so we have the fuel cell efficiency, the fuel cell life time – but we don’t have the molecular scale information in the fuel cell,” Hickner said. “That’s the next step, trying to figure out how these polymers are working in the fuel cell on a detailed level.”
The new material developed by the UNIST research team led by Prof. Guntae Kim, could be used at significantly low temperature SOFC with higher efficiency and solid reliability than the previously reported materials.
This new novel cathode material enables the fuel cell designers have more flexible choices on the materials of fuel cell components, which leads to the lower fuel cell cost and, finally, to the step closer to the highly efficient and reliable fuel cells.
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