Boston College, MIT researchers achieve dramatic increase in thermoelectric efficiency with nanotechnology

Last week, I spoke at a Kingston Ontario Innovation conference, warning participants to expect big surprises in nanotechnology and energy conversion (heat to electricity or vibrations to electricity). To my great surprise, I found this breakthrough announcement on my laptop, when I got back to Toronto.

"Would you like to have a jacket that charges your cellphone using your own body heat?  How about your own in-home distributed mini-power plant that uses the heat from your apartment to light your lamps?  A car that would use tailpipe exhaust to recharge its battery?"

Such futuristic-sounding gadgets are theoretically possible, due to a scientific phenomenon called the thermoelectric effect: Some materials can transform heat into electricity and vice versa. 

(In a related note ...researchers this week also announced an exciting energy conversion proof-of-concept -the direct conversion of uranium radiation, as well as spent fuel radiation directly into electricity with the help of carbon nanotubes...a working prototype is likely still about 10 years away.)

But high costs and low efficiency have made thermoelectrics the forgotten stepchild of more mainstream clean energy sources like solar and wind - relegated to niche markets like temperature-controlled seats for luxury automobiles.

Researchers at Boston College and MIT in the USA have used nanotechnology to achieve a major increase in thermoelectric efficiency, a milestone that paves the way for a new generation of products — from semiconductors, air conditioners, heating and cooling systems to car exhaust systems and solar power technology — that run cleaner.

The team’s low-cost approach, details of which were published last week (March 20th) in the online version of the journal Science, involves building tiny alloy nanostructures that can serve as micro-coolers and power generators.  The researchers said that in addition to being inexpensive, their method will likely result in practical, near-term enhancements to make products consume less energy or capture energy that would otherwise be wasted.

The findings represent a key milestone in the quest to harness the thermoelectric effect, which has both enticed and frustrated scientists since its discovery in the early 19th century.  The effect refers to certain materials that can convert heat into electricity and vice versa.  But there has been a hitch in trying to exploit the effect: most materials that conduct electricity also conduct heat, so their temperature equalizes quickly. 

In order to improve efficiency, scientists have sought materials that will conduct electricity but not similarly conduct heat.

Using nanotechnology, the researchers at Boston College and MIT produced a big increase in the thermoelectric efficiency of bismuth antimony telluride — a semiconductor alloy that has been commonly used in commercial devices since the 1950s — in bulk form.  Specifically, the team realized a 40 percent increase in the alloy’s figure of merit, a term scientists use to measure a material’s relative performance.  The achievement marks the first such gain in a half-century using the cost-effective material that functions at room temperatures and up to 250 degrees Celsius.  The success using the relatively inexpensive and environmentally friendly alloy means the discovery can quickly be applied to a range of uses, leading to higher cooling and power generation efficiency.

“By using nanotechnology, we have found a way to improve an old material by breaking it up and then rebuilding it in a composite of nanostructures in bulk form,” said Boston College physicist Zhifeng Ren, one of the leaders of the project.  “This method is low cost and can be scaled for mass production.  This represents an exciting opportunity to improve the performance of thermoelectric materials in a cost-effective manner.”

Caption: A cross-section of nano-crystalline bismuth antimony telluride grains, as viewed through transmission electron microscope. Colors highlight the features of each grain of the semiconductor alloy in bulk form. A team of researchers from Boston College and MIT produced a major increase in thermoelectric efficiency after using nanotechnology to structure the material, which is commonly used in industry and research. Credit: Boston College, MIT and GMZ Inc.

See MIT Technology Review and  From heat to electricity and back again and original press release and original paper in Science

Update April 1.2008

One colleague in Ukraine writes:

"This effect was used during Great Patriotic War to feed partisan’s radiostations.  Developed in Leningrad, by A.Ioffe. The slang name of the device was the ‘partisan kettle’.

The usage of Bi-Sb-Te system for thermoelectricity started in mid-50 with the rise of general interest to semiconductors.  Some industrial devices were produced and marketed.

The authors of publication intentionally avoid to cite the efficiency if their devise and substitute it with arbitrary parameter – figure of merit (ZT).  They are well aware that increase from 2% to 2,5-3% can’t strike imagination of neither technical nor business community (see first sentence of last paragraph).

I strongly recommend to use well-known Kapitsa’s analysis as a ‘filter’ for estimation of such achievements and their value for venture business."