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Thermoelectric Milestone from UC Berkeley: Organic Thermoelectric Material
15 February 2007
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| A benzenedithiol molecule trapped between two gold surfaces. Click to enlarge. Credit: Ben Utley. |
Researchers at the University of California, Berkeley, have successfully generated electricity from heat by trapping organic molecules between metal nanoparticles to create an organic thermoelectric material. The new UC Berkeley study marks the first time the Seebeck effect has been measured in an organic molecule.
The discovery, described in a study published today in Science Express, could lead to the development of more cost-effective thermoelectric converters that could be applied to waste heat recovery—including in vehicles. (Earlier post.)
Utilizing wasted heat has been a major focus of research into thermoelectric converters, which rely upon the Seebeck effect, a phenomenon in which the application of heat to combinations of certain metals induces an electric current.
In 2005, the DOE selected BSST, a subsidiary of Amerigon, to lead the development of an efficient and practical thermoelectric system that will improve fuel economy by converting waste heat in automobile engine exhaust into electrical power. (Earlier post.)
Although the efficiency of thermoelectric materials has improved dramatically, it is still rather low and the materials are costly.
The goal is to make things out of materials that are more abundant and more easily processed. Organics are cheap and can be processed easily.
—Rachel Segalman, UC Berkeley professor of chemical engineering
The researchers coated two gold electrodes with molecules of benzenedithiol, dibezenedithiol or tribenzenedithiol, then heated one side to create a temperature differential. For each degree Celsius of difference, the researchers measured 8.7 microvolts of electricity for benzenedithiol, 12.9 microvolts for dibezenedithiol, and 14.2 microvolts for tribenzenedithiol. The maximum temperature differential tested was 30 degrees Celsius (54 degrees Fahrenheit).
The effect may seem quite small now, but this is a significant proof of concept, and the first step in organic molecular thermoelectricity. We are going down the road of cheap thermoelectric materials.
—Pramod Reddy, co-lead author
The next step for the researchers includes testing different organic molecules and metals, as well as fine tuning the assembly of the structure.
This research was supported by the US Department of Energy, the National Science Foundation and the Berkeley-ITRI Research Center. The Industrial Technology Research Institute, or ITRI, is a large research organization in Taiwan that is collaborating with UC Berkeley on nano-energy innovation.
Resources:
“Thermoelectricity in Molecular Junctions”; Pramod Reddy, Sung-Yeon Jang, Rachel Segalman, Arun Majumdar; Science DOI: 10.1126/science.1137149
February 15, 2007 in Thermoelectrics | Permalink | Comments (29) | TrackBack (0)
Comments
Posted by: Roger Pham | February 16, 2007 at 02:04 PM
For more interesting information about the 60% efficient system check this link:
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Posted by: Jorge | February 16, 2007 at 02:07 PM
sOver at Berkley's school of Nuclear Engineering they may be surprised about this new milestone since they they have been offering courses about making small amounts with thermoelectric devices in satellites and huge amounts of electricity with fission. Funny thing too, no one is too worried about efficiency. It is not that they do not know how, but when you are dealing with an unlimited energy source who cares.
Investors care. Improve efficiency 1% at coal or nuke plant and that might help the bottom line $50M. A million here, fifty million there, pretty soon you are talking real money. Improvements at nuke plants in the US the last 10 years is like building 25 new nukes. Generation IX, HTGRs should approach CCGT efficiency for making electricity. More importantly, efficiently produce hydrogen. Doug or Roger can explain that one.
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Neil,
Unless you live in areas with high-temp geothermal heat like Iceland, other areas in Western USA, with heat of several hundred degrees, the temperature different between ground and air in most areas won't be enough to be worth the money investment in machinery (ie. the thermal efficiency would be too low). Kalina cycle involving ammonia as working fluid, or Rankine cycle involving highly volatile organic substances can be used for heat engines with low temperature difference, or even Sterling engine will work with level of temperature gradient, though, again, as an academic experiment and not practical enough for energy recovery.
The ground's large themal storage capacity may be used to increase the efficiency of summer AC and winter heat pump, because the ground is relatively cool in comparison to summer air, and relatively warm in comparison to winter air, and so, the COP (coefficient of efficiency) will be much higher when heat is pumped between regions of low temperature difference. Heat pump is nothing but a heat engine in reverse, so will obey the second law of thermodynamic.
The potential for recovering exhaust heat energy from ICE is not high, and unless the exhaust heat recovering equipment is cheap and simple and light-weight, it usually is not worth the effort. Look at the BMW turbo steamer, with all the plumbing hook up and linkages, machinery and additional weight of 200 lbs, and the efficiency gain is ~14% and additional power gained is but 10%.