Thermoelectric material is world's best at converting heat waste to electricity

Sep 19, 2012

Northwestern University scientists have developed a thermoelectric material that is the best in the world at converting waste heat to electricity. This is very good news once you realize nearly two-thirds of energy input is lost as waste heat.

The material could signify a . The inefficiency of current thermoelectric has limited their commercial use. Now, with a very environmentally stable material that is expected to convert 15 to 20 percent of to useful electricity, thermoelectrics could see more widespread adoption by industry.

Possible areas of application include the (much of gasoline's goes out a vehicle's tailpipe), heavy manufacturing industries (such as glass and brick making, refineries, coal- and gas-fired ) and places were large operate continuously (such as in large ships and tankers).

Waste heat temperatures in these areas can range from 400 to 600 degrees Celsius (750 to 1,100 degrees Fahrenheit), the sweet spot for thermoelectrics use.

The new material, based on the common semiconductor lead telluride, is the most efficient thermoelectric material known. It exhibits a thermoelectric figure of merit (so-called "ZT") of 2.2, the highest reported to date. Chemists, physicists, material scientists and mechanical engineers at Northwestern and Michigan State University collaborated to develop the material.

The study will be published Sept. 20 by the journal Nature.

"Our system is the top-performing thermoelectric system at any temperature," said Mercouri G. Kanatzidis, who led the research and is a senior author of the paper. "The material can convert heat to electricity at the highest possible efficiency. At this level, there are realistic prospects for recovering high-temperature waste heat and turning it into useful energy."

Kanatzidis is Charles E. and Emma H. Morrison Professor of Chemistry in Northwestern's Weinberg College of Arts and Sciences. He also holds a joint appointment at Argonne National Laboratory.

"People often ask, what is the energy solution?" said Vinayak P. Dravid, one of Kanatzidis' close collaborators. "But there is no unique solution—it's going to be a distributed solution. Thermoelectrics is not the answer to all our energy problems, but it is an important part of the equation."

Dravid is the Abraham Harris Professor of Materials Science and Engineering at the McCormick School of Engineering and Applied Science and a senior author of the paper.

Other members of the team and authors of the Nature paper include Kanishka Biswas, a postdoctoral fellow in Kanatzidis' group; Jiaqing He, a postdoctoral member in Dravid's group; David N. Seidman, Walter P. Murphy Professor of Materials Science and Engineering at Northwestern; and Timothy P. Hogan, professor of electrical and computer engineering, at Michigan State University.

Even before the Northwestern record-setting material, thermoelectric materials were starting to get better and being tested in more applications. The Mars rover Curiosity is powered by lead telluride thermoelectrics (although it's system has a ZT of only 1, making it half as efficient as Northwestern's system), and BMW is testing thermoelectrics in its cars by harvesting heat from the exhaust system.

"Now, having a material with a ZT greater than two, we are allowed to really think big, to think outside the box," Dravid said. "This is an intellectual breakthrough."

"Improving the ZT never stops—the higher the ZT, the better," Kanatzidis said. "We would like to design even better materials and reach 2.5 or 3. We continue to have new ideas and are working to better understand the material we have."

The efficiency of waste heat conversion in thermoelectrics is governed by its figure of merit, or ZT. This number represents a ratio of electrical conductivity and thermoelectric power in the numerator (which need to be high) and thermal conductivity in the denominator (which needs to be low).

"It is hard to increase one without compromising the other," Dravid said. These contradictory requirements stalled the progress towards a higher ZT for many years, where it was stagnant at a nominal value of 1.

Kanatzidis and Dravid have pushed the ZT higher and higher in recent years by introducing nanostructures in bulk thermoelectrics. In January 2011, they published a report in Nature Chemistry of a thermoelectric material with a ZT of 1.7 at 800 degrees Kelvin. This was the first example of using nanostructures (nanocrystals of rock-salt structured strontium telluride) in lead telluride to reduce electron scattering and increase the energy conversion efficiency of the material.

The performance of the new material reported now in Nature is nearly 30 percent more efficient than its predecessor. The researchers achieved this by scattering a wider spectrum of phonons, across all wavelengths, which is important in reducing thermal conductivity.

"Every time a phonon is scattered the thermal conductivity gets lower, which is what we want for increased efficiency," Kanatzidis said.

A phonon is a quantum of vibrational energy, and each has a different wavelength. When heat flows through a material, a spectrum of phonons needs to be scattered at different wavelengths (short, intermediate and long).

In this work, the researchers show that all length scales can be optimized for maximum phonon scattering with minor change in electrical conductivity. "We combined three techniques to scatter short, medium and long wavelengths all together in one material, and they all work simultaneously," Kanatzidis said. "We are the first to scatter all three at once and at the widest spectrum known. We call this a panoscopic approach that goes beyond nanostructuring."

"It's a very elegant design," Dravid said.

In particular, the researchers improved the long-wavelength scattering of phonons by controlling and tailoring the mesoscale architecture of the nanostructured thermoelectric materials. This resulted in the world record of a ZT of 2.2.

The successful approach of integrated all-length-scale scattering of phonons is applicable to all bulk , the researchers said.

Explore further: Mapping the optimal route between two quantum states

More information: The paper is titled "High-Performance Bulk Thermoelectrics With Hierarchical Architecture."

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sstritt
1.7 / 5 (12) Sep 19, 2012
Pair this up with the e-cat (if real)
ValeriaT
1 / 5 (23) Sep 19, 2012
But there is no unique solution—it's going to be a distributed solution
This is paradigm of social parasites, who just want to ignore the cold fusion for the sake of their neverending research jobs and positions (the more of such "solutions", the more parasites we will need for their research). But the thermoelectric material is not even source of energy, it's only converter of it. If we would follow the paradigms of these modern alchemists, then we will end with world full of thermoelectric and piezoelectric materials, hydrogen storage materials and batteries - but we still wouldn't have any reliable source of energy to power them. Because these guys are just doing nothing but fooling layman publics, which gets nervous from nearing energetic crisis - so it's willing to sponsor another and another research, which cannot bring any substantial improvement. The first step in solving of this situation is to realize it clearly.
ValeriaT
1 / 5 (21) Sep 19, 2012
The people must realize, the rules driving the scientific research doesn't differ from principles, which are driving the expansion of every group of people, who are payed from mandatory fees (politicians and governmental officers, medicare doctors, patent office lawyers, etc.). Each such a group of people has a tendency to adjust rules of its existence in such a way, it will grow for ever, until the money are going. These people aren't stupid or lazy, they often work frenetically, but at the global level they just consume resources while contributing very slightly to actual progress. The fact, we cannot avoid these people completely just makes this situation worse. The publics should handle their requirements with caution and it should introduce a public control over their activities. The prioritization of research is absolutely unnecessary - or we'll end with nuclear war for the rest of resources with pile of theories about strings, Higgs bosons and similar useless stuffs.
packrat
1.8 / 5 (5) Sep 19, 2012
Now a question is can it be produced commercially at a reasonable price any time in the near future. If so, somebody(s) is going to make a good profit on it. This stuff will be very useful for a lot of things.
ValeriaT
1.1 / 5 (8) Sep 19, 2012
This material is based on lead telluride by doping PbTe with PbS and Na. It utilizes endotaxially arranged SrTe nanocrystals incorporated in the PbTe matrix, which inhibits the heat flow in the system, it does not affect the hole mobility, thus allowing a large power factor to be achieved concurrently with a very low thermal conductivity. This decoupling of phonon and electron transport allows the system to reach ZT =1.7 at 800K.

This is indeed nice and all, but the tellurium is still one of the rarest elements, impossible to use at the industrial scale. After all, the efficiency of Stirling engine is still nearly one order of magnitude higher, than the thermoelectric conversion with using of these materials.
fmfbrestel
4.8 / 5 (8) Sep 19, 2012
If we would follow the paradigms of these modern alchemists


Pot, meet kettle.
eric96
1 / 5 (4) Sep 19, 2012
Hmmm, interesting, might even be sufficient for low TDP CPUs, think tablets that last 20% longer; not too shabby though at least 5-6 years away; as low as 2 years for the auto industry, just under a year for Nasa and the Milatary. Current thermo-electrics are cheap, this would at least be double in price eventually (as prices drop), but then again 2X more efficient. In fact, at that price, heatsink manufacturers could sandwich into their heatsinks (the big ones without fans). You would it wouldn't operate at 15-20% efficiency, probaby closer to 13%. The reason is PC users hate noise, anything that helps solidstate cooling is more than welcome especially on a video card.
sennekuyl
3.7 / 5 (3) Sep 19, 2012
Eric, maybe the temperature difference isn't high enough? TC work best in a 673K - 873K range it says in the articles. Do cpu's have parts that go much higher than 348K?

(I only used K because I don't know the convention for writing degrees in the comments.)
VendicarD
5 / 5 (8) Sep 19, 2012
ValeriaT is growing increasingly testy and bitter as it realize that Cold Fusion is a fraud.

It is sad to see the inevitable pattern develop again and again in those who place their faith in scam artists.

Parsec
5 / 5 (3) Sep 20, 2012
This material is based on lead telluride by doping PbTe with PbS and Na. It utilizes endotaxially arranged SrTe nanocrystals incorporated in the PbTe matrix, which inhibits the heat flow in the system, it does not affect the hole mobility, thus allowing a large power factor to be achieved concurrently with a very low thermal conductivity. This decoupling of phonon and electron transport allows the system to reach ZT =1.7 at 800K.

This is indeed nice and all, but the tellurium is still http://www.metal-...-rising, impossible to use at the industrial scale. After all, the efficiency of Stirling engine is still nearly one order of magnitude higher, than the thermoelectric conversion with using of these materials.

Commercial price for 99.5% Tellurium in 2011 was about 300 dollars a kilogram. That price is certainly reasonable to allow commercial applications.
PinkElephant
3 / 5 (2) Sep 20, 2012
@eric96,

Using this type of material (that strives for low thermal conductivity) in a heatsink (which strives for highest possible thermal conductivity) -- or interposing this, what is effectively a thermal insulator, between the chip and the heat sink -- will serve only to drastically curtail the effectiveness of the heat sink, and will probably cause the CPU or GPU to self-destruct due to overheating. In other words, not a very good plan...
LordOfRuin
not rated yet Sep 20, 2012
Sorry for some newby questions. How much power does this represent please? If I had a 5cm square of this material, and affixed it to a surface with a temperature of 500degC, how much can I reclaim? Does it require a temperature gradiant? If so how much?
PinkElephant
5 / 5 (1) Sep 20, 2012
@LordOfRuin,

I can't answer specifics because they aren't available, however general-principle questions can be addressed:
Does it require a temperature gradiant?
Yes. All thermoelectrics require a temperature gradient; it is the temperature gradient that causes charge separation in the thermoelectric material, creating a voltage across the attached electrical terminals.
If so how much?
As much as possible. Efficiency of any thermoelectric only goes up with increasing thermal gradient (and conversely, goes down with a decreasing gradient.) The maximum gradient is limited only by what the material itself can tolerate before it undergoes chemical change or disintegrates due to structural stress.
antialias_physorg
5 / 5 (3) Sep 20, 2012
How much power does this represent please? If I had a 5cm square of this material, and affixed it to a surface with a temperature of 500degC

None at all

Does it require a temperature gradiant?

Yes (preferrably a steep one). Otherwise you'd be violating some pretty fundamental laws of thermodynamics. Remember that power is dW/dt (amount of work done per unit of time) and that to do work you require an energy potential - i.e. a difference in energy levels.
If everything is at a uniform energy level (same temperature or same elevation above ground or whatever...) you cannot extract work .

Squirrel
2.6 / 5 (5) Sep 20, 2012
No mention of China in Wikipedia "The principal source of tellurium is from anode sludges produced during the electrolytic refining of blister copper. It is a component of dusts from blast furnace refining of lead. Treatment of 500 tons of copper ore typically yields one pound (0.45 kg) of tellurium. Tellurium is produced mainly in the United States, Peru, Japan and Canada.[14] For the year 2009 the British Geological Survey gives the following numbers: United States 50 t, Peru 7 t, Japan 40 t and Canada 16 t.[15]"
antialias_physorg
not rated yet Sep 20, 2012
My realistic guess is

Huh? What is a 'realistic guess'? Is it based on anything (which wouldn't make it a guess) or do you usually make 'unrealistic guesses'?

From a more detailed article here:
http://www.mccorm...d-record

They report a ZT of 1.7 - 2.2 at 800K, so the ZT figure seems to be somewhat dependent on the temperature the material operates at (which limits its use. But 800K is in the ragen of car exhausts, so that's OK). Z is a function of electrical and thermal conductivity as well as the Seebeck coefficient squared. The Seebeck coefficient of a material is itself a function of temperture.
nathj72
5 / 5 (1) Sep 20, 2012
This technology has two modes of operation. One mode is given a heat differential it can convert thermal energy to electrical energy at an efficiency dictated by the Carnot efficiency and the figure of merit for the material. The other mode is cooling. In this mode, charge carriers carry heat from one side of the material to the other. The efficiency at which this can be done is dictated by temperature differential and thermoelectric figure of merit. Maturity of this type of technology will allow for efficient refrigeration without need of compressors or any moving parts. Electronics can be cooled down to cryogenic temperatures and lower allowing for quantum effects to be readily utilized (see the single electron transistor as an example). Given an increased capability to work with this class of material we will be able to make clothing with a dynamic thermal conductivity, thus allowing us to always be warm/cold enough. This technology provides so many possibilities.
antialias_physorg
not rated yet Sep 20, 2012
Maturity of this type of technology will allow for efficient refrigeration

At uni I screwed around with making a small refrigerated box using Peltier elements (which use the Peltier-Seebeck effects just like the thermoelectric elements described in the article) because it seemed like an 'elegant' way to cool stuff - no moving parts.

But power requirements for that was WAY beyond anything a conventional refrigerator used. While this was some time ago I'm not sure themoelectrics will overtake efficient conventional refrigerators (and the even more efficient magnetic cooling on the market).
antialias_physorg
not rated yet Sep 20, 2012
OK. So let's take a look at that Guesstimate

First of all: Heat flux is measured in Watt (not Watt/h).

And the article states quite plainly in the first paragraph that they expect 15-20% efficiency. So you dont need guess at all.

ValeriaT
1 / 5 (7) Sep 20, 2012
ValeriaT is growing increasingly testy and bitter as it realize that Cold Fusion is a fraud.
I'm just getting increasingly nervous with every day of delay of cold fusion research, because with continuing energetic crisis the sources of potential global nuclear conflict are emerging every day. You people have zero self-preservation instincts foresightedness the less - and the mainstream science just demonstrated colossal incompetence and failure in this matter.
Lurker2358
1 / 5 (3) Sep 23, 2012
The carnot limit at 800k with a 300k/27C/80.6f environment is 62.5%.

The 15% to 20% efficiency at 800k heat source and 300k (presumed) sink is not impressive at all.

I've played around with this before in the past, and in order for such a device to pay for itself on an automobile, it would need to be INCREDIBLY cheap. Metals that cost $300/kg doesn't sound cheap, by the time you build the device and an inverter to tie back into a battery or the car's electrical system, or a hybrid electric motor, it will cost more than that.

We all know how electrical auto parts end up costing insanely high prices, so you sould expect to get screwed on this.

I figure the real part will probably cost at least a few hundred dollars, and will take 3 or 4 years to pay for itself in energy savings under optimal conditions, primarily by removing the conventional belt driven alternator/generator on existing engines.
Quarky1
1 / 5 (1) Sep 26, 2012
Would it be feasible to imbed this material into roadbeds and other heat-retentive features in urban areas, and tie them into the power grid? If so maybe we could turn heat pollution to our advantage?
Quarky1
1 / 5 (3) Sep 26, 2012
ValeriaT is growing increasingly testy and bitter as it realize that Cold Fusion is a fraud.

It is sad to see the inevitable pattern develop again and again in those who place their faith in scam artists.

I agree that there are many who live to feed off others' false hope, but I don't see that as a reason to write the whole concept of cold fusion off as a scam... scientists thought that long distance AC power transmission was a pipe dream back in the late 1800's... we just need to have another Tesla come into the world.


bdh_hall
not rated yet Sep 26, 2012
Would it be feasible to imbed this material into roadbeds and other heat-retentive features in urban areas, and tie them into the power grid? If so maybe we could turn heat pollution to our advantage?


Sadly this particular material wouldn't help due to the temperature gradient required being too low at human-survivable temperatures. Roads can seem awful hot, but hot mix melted asphalt is generally applied around 300F - some parts of Arizona desert do heat the road enough to 'melt' the asphalt enough to make it squishy, but it would be truly hellish to get it over 400F.

This material, on the other hand, works best at a far higher temperature - 800k is over 900F. That's hot enough to melt tin, but just under the temperature required for a nice liquid silver.
SteveL
1 / 5 (1) Sep 26, 2012
scientists thought that long distance AC power transmission was a pipe dream back in the late 1800's... we just need to have another Tesla come into the world.
Well, it depends on what you consider "long distance". If it's a few hundred of miles, well AC is not a problem. If it's several hundred or even thousands of miles, you have a problem with AC. Happily in the 1930s HVDC was developed for long distance power transmission.

Reference: http://en.wikiped..._current

Another Tesla, while not needed for this particular issue, is more than welcome. Humanity needs all the brains it get to help solve our important energy issues.
antialias_physorg
not rated yet Sep 27, 2012
ValeriaT is growing increasingly testy and bitter as it realize that Cold Fusion is a fraud.

Well, since cold fusion proponents generate a lot of hot air...if we hook up a generator to that we could say that cold fusion is 'working'.
SteveL
not rated yet Sep 27, 2012
Humanity needs all the brains it get to help solve our important energy issues.
Or rather to stop to ignore the cold fusion research. Of course, the second option doesn't play well with employment of the "best brains" of humanity in research of alternative methods of energy production, conversion transport and storage - so it's ignored.
I haven't given up on an energy to matter converter that can pop out a hot pepperoni pizza or whatever else I'm wanting at the price of a KW or two, but I'm not going to go on and on about it even though it and cold fusion could be a reality at about the same time.