Skutterudites Boost Thermoelectric Output

Researchers at the University of Michigan are taking a step towards more efficient recycling of waste heat into energy by using skutterudites in their new thermoelectric device experiments.

The UM press release explains with an offering from Massoud Kaviany, professor in the Department of Mechanical Engineering, “Today’s state-of-the-art thermoelectric materials are only five percent efficient. Skutterudites, and the new knowledge about how best to arrange their atoms, could help improve their performance to 15 to 20 percent, at which point they become useful in many practical applications.”

The UM researchers studied skutterudites, a class of mechanically strong thermoelectric materials that, when combined with certain elements such as the metal barium, has the right mix of properties to effectively make the projected energy conversion: The material conducts electricity well, and conducts heat poorly. The researchers identified certain configurations of the atoms in the compound that drastically increase the materials’ efficiency.

That suggests a properly designed material wrapped around your car’s exhaust system could one day scavenge heat that would otherwise be wasted, turning it into energy to warm the cabin or recharge the battery.  The UM engineers and have taken a major step toward improving the efficiency of a promising candidate for recapturing a huge energy resource.

The research paper has been published in the current edition of Physical Review Letters titled “Structural Order-Disorder Transitions and Phonon Conductivity of Partially Filled Skutterudites.”

Ctirad Uher, professor in the Department of Physics at UM explains the main point of the paper, “We knew that skutterudites are promising materials. But we did not know what features we could manipulate to maximize the conversion of heat into electricity. In this paper, we propose that certain configurations of the filler element barium will be very effective in lowering the materials’ thermal conductivity and thus increasing their conversion efficiency. This is an important advancement in the sense that it provides guidance for the experimentalists to focus as they try to synthesize highly efficient thermoelectric materials.”

Kaviany adds, “We explained the physics of these materials for the first time. This will help to advance the development of these materials. If you are designing them based on fundamental physics and materials and not just by trial and error, then you need to know how they work so you can avoid haphazard experimentation.”  For lots of researchers as well as developers this is important, time saving and cost reducing work.

The UM press release quoting Uher also points out automobile manufacturers are extremely interested in this technology. The ideal environments for these materials are locations where large differences in temperatures exist. One such place is the exhaust pipe system of a car between the motor and the catalytic converter.  “That’s a big source of heat that you paid for already,” Uher said.

Not quoted yet contributing to the research is Anton van der Ven, an assistant professor in the Department of Materials Science and Engineering.

The funding for the research making the information available for everyone came from the University of Michigan’s Center for Solar and Thermal Energy Conversion, which is funded by the U.S. Department of Energy’s Office of Basic Energy Sciences.  Not every tax dollar is wasted it seems.

It very hard to get a handle on the amount of energy just lost as heat. On a cold day looking out over a electrical generation plant, especially one using combustion fuel one can see the great cloud of condensed water vapor radiating energy into the atmosphere and out into space.  It’s enough to make a physicist cringe.  The losses go on continuously, world wide, at great loss.

Gaining back even 20% seems delightful.  Even combined heat and power plants should be able to recover more for higher efficiencies.  Perhaps heat cycling can double up the 20% to 40%.  So much is lost that the bait is entrancing.  This is work worth doing, and doing quickly.  And maybe the 20% estimate can be made to be higher with further work.

Read more at New Energy And Fuel