Published on February 21st, 2014 | by James Ayre2
Thermoelectrics Get Big Boost From Nanoscale Pillars — Creating Electricty From Heat
February 21st, 2014 by James Ayre
Thermoelectric materials can see their performance radically improved via the utilization of an array of ‘nanoscale pillars,’ according to new research from the University of Colorado Boulder. These tiny pillars, built directly onto the thermoelectric material, represent an entirely new approach to a problem that has limited thermoelectrics since the birth of the field.
The researchers think that the new approach may lead to great improvements to a number of different technologies — from solar panels, to cooling equipment, to conventional fossil fuel power plants.
To explain the new work, here’s a bit of background — the thermoelectric effect was first discovered back in the 1800s, but the exploitation of this effect on a large scale has been somewhat limited by a couple of important obstacles. The thermoelectric effect, is, essentially, just the ability to generate an electric current by harnessing the temperature difference between two sides of the same material. Alternately, the application of an electric voltage to a thermoelectric material “can cause one side of the material to heat up while the other stays cool, or, one side to cool down while the other stays hot.” These materials have been used for both purposes — creating electricity from a heat source, and cooling precision instruments by consuming electricity.
There’s a fundamental problem with all of this, though — materials that allow electricity to flow through them also allow heat to flow through them. What that means is that, “at the same time a temperature difference creates an electric potential, the temperature difference itself begins to dissipate, weakening the current it created.”
The old solution to this problem was to use materials that allow electricity to flow through them relatively more easily than heat. The new approach tries something completely different.
“Until 20 years ago, people were looking at the chemistry of the materials,” explained researcher Mahmoud Hussein, an assistant professor of aerospace engineering sciences who pioneered the discovery. “And then nanotechnology came into the picture and allowed researchers to engineer the materials for the properties they wanted.”
The University of Colorado at Boulder provides more:
Using nanotechnology, material physicists began creating barriers in thermoelectric materials — such as holes or particles — that impeded the flow of heat more than the flow of electricity. But even under the best scenario, the flow of electrons — which carry electric energy — also was slowed.
In a new study, Hussein and doctoral student Bruce Davis demonstrate that nanotechnology could be used in an entirely different way to slow the heat transfer without affecting the motion of electrons.
The new concept involves building an array of nanoscale pillars on top of a sheet of a thermoelectric material, such as silicon, to form what the authors call a “nanophononic metamaterial.” Heat is carried through the material as a series of vibrations, known as phonons. The atoms making up the miniature pillars also vibrate at a variety of frequencies. Davis and Hussein used a computer model to show that the vibrations of the pillars would interact with the vibrations of the phonons, slowing down the flow of heat. The pillar vibrations are not expected to affect the electric current.
The researchers estimate that the new nanoscale pillars will reduce the heat flow through a material by at least half — noting though that the reduction could be considerably stronger, as the calculations used were quite conservative.
“If we can improve thermoelectric energy conversion significantly, there will be all kinds of important practical applications,” stated Hussein. “These include recapturing the waste heat emitted by different types of equipment — from laptops to cars to power plants — and turning that heat into electricity. Better thermoelectrics also could vastly improve the efficiency of solar panels and refrigeration devices.”
The researchers are currently working to fabricate the pillars in the lab and start real-world testing.
The new research was just published in the journal Physical Review Letters.
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