ScienceDaily (Nov. 10, 2010) — Stop-and-go driving can wear on your nerves, but it really does a number on the precious platinum that drives reactions in automotive fuel cells. Before large fleets of fuel-cell-powered vehicles can hit the road, scientists will have to find a way to protect the platinum, the most expensive component of fuel-cell technology, and to reduce the amount needed to make catalytically active electrodes.
Now, scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory have developed a new electrocatalyst that uses a single layer of platinum and minimizes its wear and tear while maintaining high levels of reactivity during tests that mimic stop-and-go driving. The research -- described online in Angewandte Chemie, International Edition -- may greatly enhance the practicality of fuel-cell vehicles and may also be applicable for improving the performance of other metallic catalysts.
The newly designed catalysts are composed of a single layer of platinum over a palladium (or palladium-gold alloy) nanoparticle core. Their structural characterization was performed at Brookhaven's Center for Functional Nanomaterials and the National Synchrotron Light Source.
"Our studies of the structure and activity of this catalyst -- and comparisons with platinum-carbon catalysts currently in use -- illustrate that the palladium core 'protects' the fine layer of platinum surrounding the particles, enabling it to maintain reactivity for a much longer period of time," explained Brookhaven Lab chemist Radoslav Adzic, who leads the research team.
In conventional fuel-cell catalysts, the oxidation and reduction cycling -- triggered by changes in voltage that occur during stop-and-go driving -- damages the platinum. Over time, the platinum dissolves, causing irreversible damage to the fuel cell.
In the new catalyst, palladium from the core is more reactive than platinum in these oxidation and reduction reactions. Stability tests simulating fuel cell voltage cycling revealed that, after 100,000 potential cycles, a significant amount of palladium had been oxidized, dissolved, and migrated away from the cathode. In the membrane between the cathode and anode, the dissolved palladium ions were reduced by hydrogen diffusing from the anode to form a "band," or dots.
In contrast, platinum was almost unaffected, except for a small contraction of the platinum monolayer. "This contraction of the platinum lattice makes the catalyst more active and the stability of the particles increases," Adzic said.
Reactivity of the platinum monolayer/palladium core catalyst also remained extremely high. It was reduced by merely 37 percent after 100,000 cycles.
Building on earlier work that illustrated how small amounts of gold can enhance catalytic activity, the scientists also developed a form of the platinum monolayer catalyst with a palladium-gold alloy core. The addition of gold further increased the stability of the electrocatalyst, which retained nearly 70 percent of reactivity after 200,000 cycles of testing.
"This indicates the excellent durability of this electrocatalyst, especially when compared with simpler platinum-carbon catalysts, which lose nearly 70 percent of their reactivity after much shorter cycling times. This level of activity and stability indicates that this is a practical catalyst. It exceeds the goal set by DOE for 2010-2015 and it can be used for automotive applications," Adzic said.
He noted that fuel cells made using the new catalyst would require only about 10 grams of platinum per car -- and less than 20 grams of palladium. Currently, in catalytic convertors used to treat exhaust gases, 5 to 10 grams of platinum is used. Since fuel-cell-powered cars would emit no exhaust gases, there would be no need for such catalytic converters, and therefore no net increase in the amount of platinum used.
"In addition to developing electrocatalysts for automotive fuel cell applications, these findings indicate the broad applicability of platinum monolayer catalysts and the possibility of extending this concept to catalysts based on other noble metals," Adzic said.
The fundamental science leading to the development of the new electrocatalyst and early scale-up work was funded by the DOE Office of Science. Additional funding came from the Toyota Motor Corporation.
Showing posts with label Nanotechnology. Show all posts
Showing posts with label Nanotechnology. Show all posts
Thursday, November 11, 2010
Thursday, February 19, 2009
How Can Hamsters Create More Energy?
ScienceDaily (Feb. 14, 2009) — Could hamsters help solve the world's energy crisis? Probably not, but a hamster wearing a power-generating jacket is doing its own small part to provide a new and renewable source of electricity.
And using the same nanotechnology, Georgia Institute of Technology researchers have also generated electrical current from a tapping finger – moving the users of BlackBerry devices, cell phones and other handhelds one step closer to powering them with their own typing.
"Using nanotechnology, we have demonstrated ways to convert even irregular biomechanical energy into electricity," said Zhong Lin Wang, a Regent's professor in the Georgia Tech School of Materials Science and Engineering. "This technology can convert any mechanical disturbance into electrical energy."
The demonstrations of harnessing biomechanical energy to produce electricity were reported February 11 in the online version of the American Chemical Society journal Nano Letters.
The study demonstrates that nanogenerators – which Wang's team has been developing since 2005 – can be driven by irregular mechanical motion, such as the vibration of vocal cords, flapping of a flag in the breeze, tapping of fingers or hamsters running on exercise wheels. Scavenging such low-frequency energy from irregular motion is significant because much biomechanical energy is variable, unlike the regular mechanical motion used to generate most large-scale electricity today.
The nanogenerator power is produced by the piezoelectric effect, a phenomenon in which certain materials – such as zinc oxide wires – produce electrical charges when they are bent and then relaxed. The wires are between 100 and 800 nanometers in diameter, and between 100 and 500 microns in length.
To make their generators, Wang's research team encapsulated single zinc oxide wires in a flexible polymer substrate, the wires anchored at each end with an electrical contact, and with a Shottky Barrier at one end to control current flow. They then attached one of these single-wire generators to the joint area of an index finger, or combined four of the single-wire devices on a "yellow jacket" worn by the hamster.
The running and scratching of the hamster – and the tapping of the finger – flexed the substrate in which the nanowires were encapsulated, producing tiny amounts of alternating electrical current. Integrating four nanogenerators on the hamster's jacket generated up to up to 0.5 nanoamps; less current was produced by the single generator on the finger.
Wang estimates that powering a handheld device such as a Bluetooth headset would require at least thousands of these single-wire generators, which could be built up in three-dimensional modules.
Beyond the finger-tapping and hamster-running, Wang believe his modules could be implanted into the body to harvest energy from such sources as muscle movements or pulsating blood vessels. In the body, they could be used to power nanodevices to measure blood pressure or other vital signs.
Because the devices produce alternating current, synchronizing the four generators on the hamster's back was vital to maximizing current production. Without the synchronization, current flow from one generator could cancel out the flow from another.
The research team – which also included Rusen Yang, Yong Qin, Cheng Li and Guang Zhu – solved that problem by using a substrate that was flexible in only one direction, forcing the generators to flex together. Still, there was substantial variation in the output from each generator. The differences result from variations in the amount of flexing and from inconsistencies in the hand-built devices.
"The nanogenerators have to be synchronized, with the output of all of them coordinated so the current adds up constructively," Wang noted. "Through engineering, we would expect this can be resolved in the future through improved design and more consistent manufacturing."
To ensure that the current measured was actually produced by the generators, the researchers took several precautions. For instance, they substituted carbon fibers – which are not piezoelectric – for the zinc oxide nanowires and measured no output electrical signal.
The research team encountered a number of obstacles related to its four-legged subjects. Wang's team first tried to outfit a rat with the power-generating jacket, but found that the creature wasn't very interested in running.
At the suggestion of Wang's daughter, Melissa, the researchers found that hamsters are more active creatures – but only after 11 p.m. They had to experiment with a jacket configuration that was tight enough to stay on and to wrinkle the nanogenerator substrate – but not so tight as to make the hamster uncomfortable.
"We believe this is the first demonstration of using a live animal to produce current with nanogenerators," Wang added. "This study shows that we really can harness human or animal motion to generate current."
The research was supported by the Defense Advanced Research Projects Agency (DARPA), the U.S. Department of Energy, the U.S. Air Force, and the Emory-Georgia Tech Center for Cancer Nanotechnology Excellence.
And using the same nanotechnology, Georgia Institute of Technology researchers have also generated electrical current from a tapping finger – moving the users of BlackBerry devices, cell phones and other handhelds one step closer to powering them with their own typing.
"Using nanotechnology, we have demonstrated ways to convert even irregular biomechanical energy into electricity," said Zhong Lin Wang, a Regent's professor in the Georgia Tech School of Materials Science and Engineering. "This technology can convert any mechanical disturbance into electrical energy."
The demonstrations of harnessing biomechanical energy to produce electricity were reported February 11 in the online version of the American Chemical Society journal Nano Letters.
The study demonstrates that nanogenerators – which Wang's team has been developing since 2005 – can be driven by irregular mechanical motion, such as the vibration of vocal cords, flapping of a flag in the breeze, tapping of fingers or hamsters running on exercise wheels. Scavenging such low-frequency energy from irregular motion is significant because much biomechanical energy is variable, unlike the regular mechanical motion used to generate most large-scale electricity today.
The nanogenerator power is produced by the piezoelectric effect, a phenomenon in which certain materials – such as zinc oxide wires – produce electrical charges when they are bent and then relaxed. The wires are between 100 and 800 nanometers in diameter, and between 100 and 500 microns in length.
To make their generators, Wang's research team encapsulated single zinc oxide wires in a flexible polymer substrate, the wires anchored at each end with an electrical contact, and with a Shottky Barrier at one end to control current flow. They then attached one of these single-wire generators to the joint area of an index finger, or combined four of the single-wire devices on a "yellow jacket" worn by the hamster.
The running and scratching of the hamster – and the tapping of the finger – flexed the substrate in which the nanowires were encapsulated, producing tiny amounts of alternating electrical current. Integrating four nanogenerators on the hamster's jacket generated up to up to 0.5 nanoamps; less current was produced by the single generator on the finger.
Wang estimates that powering a handheld device such as a Bluetooth headset would require at least thousands of these single-wire generators, which could be built up in three-dimensional modules.
Beyond the finger-tapping and hamster-running, Wang believe his modules could be implanted into the body to harvest energy from such sources as muscle movements or pulsating blood vessels. In the body, they could be used to power nanodevices to measure blood pressure or other vital signs.
Because the devices produce alternating current, synchronizing the four generators on the hamster's back was vital to maximizing current production. Without the synchronization, current flow from one generator could cancel out the flow from another.
The research team – which also included Rusen Yang, Yong Qin, Cheng Li and Guang Zhu – solved that problem by using a substrate that was flexible in only one direction, forcing the generators to flex together. Still, there was substantial variation in the output from each generator. The differences result from variations in the amount of flexing and from inconsistencies in the hand-built devices.
"The nanogenerators have to be synchronized, with the output of all of them coordinated so the current adds up constructively," Wang noted. "Through engineering, we would expect this can be resolved in the future through improved design and more consistent manufacturing."
To ensure that the current measured was actually produced by the generators, the researchers took several precautions. For instance, they substituted carbon fibers – which are not piezoelectric – for the zinc oxide nanowires and measured no output electrical signal.
The research team encountered a number of obstacles related to its four-legged subjects. Wang's team first tried to outfit a rat with the power-generating jacket, but found that the creature wasn't very interested in running.
At the suggestion of Wang's daughter, Melissa, the researchers found that hamsters are more active creatures – but only after 11 p.m. They had to experiment with a jacket configuration that was tight enough to stay on and to wrinkle the nanogenerator substrate – but not so tight as to make the hamster uncomfortable.
"We believe this is the first demonstration of using a live animal to produce current with nanogenerators," Wang added. "This study shows that we really can harness human or animal motion to generate current."
The research was supported by the Defense Advanced Research Projects Agency (DARPA), the U.S. Department of Energy, the U.S. Air Force, and the Emory-Georgia Tech Center for Cancer Nanotechnology Excellence.
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