Tiny battery is also a nanomotor

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(Top left) A scanning electron microscope image of a copper-platinum nanobattery-based nanomotor. (Top right) A scanning electron microscope image of an asymmetric copper nanorod. (Bottom) Motion diagrams for each device in bromine solution.

Measuring just 3.6 micrometers long, one of the smallest batteries ever made won’t be powering our electronic devices anytime soon, but it does serve as a self-powered nanomotor that is surprisingly fast and efficient. Ultimately, the nanobattery-based motor could be used as a nanomachine and to transport cargo for biomedical applications.
The researchers, Dr. Ran Liu and Prof. Ayusman Sen from the Department of Chemistry at The Pennsylvania State University, have published their study on the nanobattery-based motor in a recent issue of the Journal of the American Chemical Society ASAP.
The nanobattery consists of a single nanowire with a 3-micrometer-long copper end and a 600-nanometer-long platinum end. When the nanobattery is placed in a diluted solution of oxidant (such as bromine or iodine), the copper end serves as the anode and is oxidized while the platinum end functions as the cathode. As the nanobattery discharges itself in the solution, the electrophoresis phenomenon kicks in, so that the electric field generated by the battery’s redox reactions causes the battery to move.
Copper-platinum nanomotors move in an iodine solution (magnified 100x). The copper end of each nanomotor leads, while the brighter platinum end follows. Movement continues until the copper segments are completely converted to copper iodide by the iodine.

The scientific core of this finding is that a short-circuited nanobattery (e.g., copper-platinum segmented nanorod) can be moved by self-electrophoresis resulting from oxidation and reduction occurring, respectively, at the two metals,” Liu told “The generated current can be directly converted to mechanical force.”
This self-electrophoresis phenomenon propels the device to speeds of more than 10 microns (three times its length) per second. That’s the rough equivalent of a 5-meter (16-foot) motorboat moving at 54 kilometers per hour (33.5 miles per hour) through water.
“In this case, the direction of the nanomotor’s movement is random at long time scales,” Liu said. “It can be potentially controlled. For example, if we incorporate a magnetic metal segment in the nanobattery, we can control its moving direction by magnetic field.”
The nanomotor operates continuously until the copper segment is completely oxidized by the bromine or converted to copper iodide by the iodine. Its lifetime, therefore, depends on both the length of the copper segment and the concentration of the oxidant. In their experiments, the researchers observed nanobattery lifetimes of between 40 seconds and 1 minute by changing these variables. (The length of the copper segment can be controlled by its electrodeposition time during fabrication.) The researchers found that the nanomotor’s velocity also depends on the length of the copper segment, where a shorter copper segment gives a higher speed but decreased lifetime…….
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Written by physicsgg

October 19, 2011 at 1:39 pm


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