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Professor Mercouri Kanatzidis holds up his device that can harvest 14 percent of waste heat as usable electricity.  (Source: Northwestern University)
New lead-based compound could see a variety of scenarios -- including helping power the machines in the absence of sunlight

A new material from researchers at Northwestern University could offer a way to capture and recycle waste heat better than ever before [press release].  The material can convert a record 14 percent of the waste heat passing through it to usable electric energy.

When manmade devices perform work, be it a computer or a car, they produce heat.  That heat is ultimately lost, reducing the energy efficiency of our devices.  Some have cleverly exploited this fact, using waste heat to offer desirable comfort heating.  But ultimately, the only good solution is to try to somehow recapture that heat in a usable form.  To do that, the right material was necessary.

Semiconductors have long been considered a promising candidate, as they can produce electricity when heated.  Lead telluride (composed of lead and tellurium ions on a lattice) was considered one of the most promising candidates, as it was relatively efficient in accomplishing the heat to electricity transformation.  

But attempts to improve that efficiency via various techniques, such as nano-inclusions resulted in an undesirable side effect -- increased scattering of electrons, reducing overall conductivity.  Obviously, if you're converting heat to electricity, you have to funnel it out of the device, so this was unacceptable.

The NU team, lead by Chemistry professor Mercouri Kanatzidis discovered that by using a special type of nano-inclusion, the scattering could actually be reduced.  The trick was to use special crystals of rock salt (SrTe).  Professor Kanatzidis sums up, "It has been known for 100 years that semiconductors have this property that can harness electricity. To make this an efficient process, all you need is the right material, and we have found a recipe or system to make this material."

Materials Science professor Vinayak Dravid also assisted in the study.  He describes the results, stating, "We can put this material inside of an inexpensive device with a few electrical wires and attach it to something like a light bulb. The device can make the light bulb more efficient by taking the heat it generates and converting part of the heat, 10 to 15 percent, into a more useful energy like electricity."

The study on the promising material earned a place [abstract] in the prestigious peer-reviewed journal Nature Chemistry.

So the material seems great, but what about its commercialization prospects?

Well, lead telluride is relatively rare , but occurs naturally in mountain deposits as the mineral Altaite.  Significant deposits have been found in the Altai mountains of northeast Asia;  Zyrianovsk, Kazakhstan; the Ritchie Creek Deposit in Price County, Wisconsin; the Koch-Bulak gold deposit in Kazakhstan; Moctezuma, Mexico; and Coquimbo, Chile.

Given that air or liquid bearing waste heat can be channeled through a relatively small area, a little telluride (say in a heatpipe on a computer component) could go a long ways, recycling almost a sixth of the wasted energy.

Strontium is very abundant, so coming up with sufficient quantities of the nano-inclusion material shouldn't be as big an issue.

Aside from making existing devices more efficient, the material could be used to make new low voltage electronic devices, powered by waste heat from the human body.

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RE: Use it on vehicles
By ddopson on 1/20/2011 12:13:21 AM , Rating: 5
heh, sadly engineering isn't that simple.

One challenge with recovering heat from an auto is that the heat is so diffuse. The engine has a lot of odd shaped parts and a huge ammount of surface area. Imagine trying to cover the entire surface of an engine with this stuff. Also, a car engine produces lots of heat and needs to stay reasonably cool to not break down. For this reason, we tend to actually expend energy pumping air and water and oil around to ensure the heat escapes quickly enough.

I highly suspect that this device was measured under some sort of ideal circumstance. 14% of the energy flowing across a large tempature gradient and as only measure over the surface area of the device (ie, ignoring heat lost to the non-harvested surface area of the heat source. Capturing heat from real world sources is much more difficult.

No doubt there will be useful applications, but this material is not going to be a panacea that returns 14% of the energy lost across a very complex system.

RE: Use it on vehicles
By semiconshawn on 1/20/11, Rating: 0
RE: Use it on vehicles
By gvaley on 1/20/2011 2:28:51 AM , Rating: 1
No, you are thinking in the right direction. This is exactly where past efforts have been directed at. Exhaust is the hottest part of the car and the surface area is relatively small. And it does not need cooling so stacking two or three layers of the energy recovery material would seem possible.

RE: Use it on vehicles
By Fritzr on 1/20/2011 10:41:28 AM , Rating: 1
A secondary radiator would be another good application. Run the hot water through the power unit to extract power from the water jacket, then into the normal radiator to provide the water cooling the engine needs.

The engineering problem is finding a place to put this extra radiator.

RE: Use it on vehicles
By Souka on 1/20/2011 11:32:07 AM , Rating: 2
In front of the engine, next to the radi... oh nevermind, there's already a radiator there!

I like the idea of a radiator in terms of delivering a very controlled temperature, but unless you go really high-pressure I suspect there is a correlation between temperature and energy produced (higher temp = more electricty).

Exaust manifold or nearby will probably be best location.

RE: Use it on vehicles
By lagomorpha on 1/20/2011 1:33:10 PM , Rating: 2
Lead compounds aren't exactly known for their high melting temperatures. And do you have any idea how hot exhaust manifolds get? I don't, my infrared thermometer wouldn't read that high.

RE: Use it on vehicles
By Bubbacub on 1/20/2011 3:47:22 AM , Rating: 2
i think bmw have started doing this to the exhaust system as part of their 'efficient dynamics'.

RE: Use it on vehicles
By superPC on 1/20/2011 5:58:16 AM , Rating: 2
you're right. BMW will use this tech in their car by 2013 ( ). ddopson is also right. there's only a limited places in cars that this tech can be applied to. since car produce a lot of heat but for longevity the engine itself has to be cool so it needs to remove all heat from it. this material is a thermal isolator so it would prevent heat from escaping thereby the engine would overheat and stall if someone cover an engine with this material. if thermoelectric generator do someday become efficient enough (40% or more) than there may be a reason to make a system that transfer as much heat out of the engine and move it to the thermoelectric generator to produce electricity. it must be difficult to keep a balance of sufficient thermal movement and extracting energy so this thermoelectric generator can generate enough energy while the engine can stay cool.

RE: Use it on vehicles
By FITCamaro on 1/20/2011 10:53:22 AM , Rating: 2
The best place for this would be on the exhaust system.

You want the exhaust to stay hot so it moves through the system. So any insulating effect the material has on the exhaust is a non-issue.

You're definitely not going to coat the engine with the stuff though. But what you might be able to do with it on the exhaust system is decrease the load on the motor that the alternator has. If heat can create electricity, then you could channel it back to the battery to keep the engine charged and then the alternator is not needed as much.

RE: Use it on vehicles
By FITCamaro on 1/20/2011 10:56:27 AM , Rating: 2
Sorry the battery charged.

Now for hybrids or electric cars, if this could be put into brake rotors, then the heat from braking could produce electricity to charge the battery.

RE: Use it on vehicles
By mmcdonalataocdotgov on 1/20/2011 11:55:43 AM , Rating: 2
I like that idea, but why stop there? Clutch-drive all the services that run off engine rotation so they can be disengaged. Run them instead with auxiliary electric motors powered by batteries (that are charged by exhaust heat), but only clutch them back to the engine when there is not enough juice to run the electric motors. That would reduce all the service load on the engine when it was up to temp.

RE: Use it on vehicles
By bobsmith1492 on 1/20/2011 12:11:46 PM , Rating: 2
This is happening more and more often:

- Electric power steering
- Electric coolant pump
- Electric radiator fan

We've been developing one of these here at my work, and it does have a clutch to engage the engine belt when the load is greater than the motor can produce.

Perhaps electric brakes may happen soon...

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