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The growing interest in the thermoelectrics industry has resulted in an expectation that the market value will reach a staggering worth of over $750 million USD by the year 2022. Recent advancements in thermoelectric materials (particularly thermoelectric ceramics) are expected to significantly expand the current applications of thermoelectric technology beyond consumer uses, vehicle waste heat recovery, and industrial purposes.
What are Thermoelectric Materials?
The continuously advancing field of sensor technologies demands increasingly powerful and dynamic energy harvesting tools capable of powering these sensors, without requiring continuous battery replacement. Some of the most relevant technologies that are used for this purpose include thermoelectrics, piezoelectrics, magnetoelectrics, mechanical vibrations, and electromagnetic waves.
Thermoelectric (TE) materials generate electricity by converting thermal energy, or heat, as it is imposed upon the surface of a TE element. An ideal TE material is one that possesses a large Seebeck coefficient (ZT), low resistivity, and low thermal conductivity; all the while maintaining an appropriate temperature gradient. Additionally, TE materials should exhibit a lower toxicity index as compared to intermetallic alloys that often decompose when exposed to higher temperatures. Some intermetallic alloys that are associated with this inherent limitation include CoSb3, Bi2Te3, and PBTe.
As a result of these properties, many facilities have become increasingly interested in TE technologies for their capacity to improve the energy productivity and efficiency of day to day operations.
Some of the most widely studied TE material classifications include:
- Polymer thermoelectrics
- Organic-inorganic hybrid thermoelectrics
- Thermoelectric inorganic films
- Thin films
Insufficient Energy Recovery in Vehicles
Traditional TE materials have often been limited in their ability to operate at temperatures greater than 300° C, as temperatures above 300° C have been found to incapacitate the material or the system. As a result of this inherent limitation, many TE technologies have not been applicable for waste heat recovery from diesel or gasoline engine exhaust, such as that which is generated by military and commercial vehicles, jet-based aircraft, and industrial power plants.
To overcome the fact that approximately 75% of the energy produced by vehicles during peak combustion is lost in the exhaust, numerous automotive companies including Volkswagen, Volvo, Ford, and BMW have begun developing thermoelectric waste heat recovery systems that are capable of improving the fuel economy of their vehicles by up to 5%. As research in this area continues to progress, researchers anticipate that the development of combustion-engine-based transport, which will function by converting waste that is produced by motors directly into electricity that can be utilized by the vehicles, will subsequently emerge.
Ceramic Thermoelectrics for Energy Recovery
Some of the proposed technical approaches that researchers are taking to achieve these goals involve the doping oxide ceramic thermoelectric compounds in an effort to increase their electrical conductivity while simultaneously decreasing their thermal conductivity. To this end, researchers created multiple structured layers within ceramic oxide thermoelectric materials that exhibit both dense and porous properties. By improving the porosity of these ceramics, researchers are hopeful that their thermoelectric properties will also improve.
Additional research endeavors in this field will promote the development of high-temperature p-type and n-type ceramic oxide thermoelectric materials. Recent work in this area has successfully utilized ceramic thermoelectrics as a substrate material in oxygen transport membrane applications that will eventually allow for efficient sequestration of carbon dioxide (CO2).
Sources and Further Reading
- Noudem, J. G., Lemonnier, S., Prevel, M., Reddy, E. S., Guilmeu, E. & Goupil, C. (2008). Thermoelectric ceramics for generators. Journal of the European Ceramic Society 28(1); 41-48. DOI:10.1016/j.jeurceramsoc.2007.05.012.
- Ponamma, D., Ogunleye, G. J., Sharma, P. & AlMaadeed, M. A. (2017). Piezo- and Thermoelectric Materials from Biopolymer Composites. Biopolymer Composites in Electronics; 333-352. DOI: 10.1016/B978-0-12-809261-3.00012-7.