Introduction to Thermoelectric Effects And Their Applications in Energy and Environment

1. Introduction to Thermoelectric Effects And Their Applications in Energy and Environment Shang-Fen Ren Department of Physics, Illinois State University Normal, IL 61790-4560 ren@phy.ilstu.edu Research Supported by National Science Foundation, Research Corporation, and Caterpillar, Inc

2. Main Research Collaborators Wei Cheng (Beijing Normal University) Gang Chen (MIT) Walter Harrison (Stanford) Peter Yu and Sam Mao (UC-Berkeley) Andrew McGilvray, Bo Shi, and Mahmoud Taher (Caterpillar) Research Students (1994-present) David Rosenberg, Latanya Molone, Garnet Erdakos, Heather Dowd, Jason Stanford, Maria A. Alejandra, Chad Johnson, Kim Goodwin, Joel Heidman, Paul Peng, Josh Matsko, Brian Mavity, Rory Davis, Nathan Tovo, Victor Nkonga, Shelley Dexter, Scott Gay, Tim Hughes, Gabriel Altay, Louis Little, Victor Nkonka, Benjamin Thompson, Jonathan Andreason, Zoe Paukstys, Colin Connolly, Marcus Woo, Courtney Pinard, Danthu H.Vu, Valerie Hackstadt, Derek Wissmiller, Scott Whitney, Chris S. Kopec, Erika Roesler, Elizabeth Williams,Trina Karim, Mike Morrissey, Nick Jurasek, Nathan Bogue, Mid-hat Abdulrhman, Maggie Hansen, Jade Exley

3. Outline Thermoelectric Effect What is Thermoelectric Effect (TE) Potential Applications of TE TE and Nanotechnology TE Applications in Energy and Environment Research Collaboration on TE with Caterpillar

4. Thermoelectric Effects Discovered in 1821 by Thomas Johann Seebeck: observed a compass needle to move when placed in the vicinity of a closed loop of two dissimilar metal conductors joined together at the ends to make a circuit, when the junctions were maintained at different temperatures.

5. Thermoelectric Couple Thermoelectric elements (legs) Heat in Th N P Tc - + Current out Introduction to Thermoelectrics Two legs of a thermocouple. The magnitude of the thermoelectric voltage is proportional to the difference of two temperatures. Most materials with good thermoelectricity efficient are semiconductors. Two legs are made by N-type and P-type of semiconductors respectively.

6. Thermoelectrics Nomenclature Thermoelectric Device (Module) + -

7. Thermoelectrics Nomenclature Thermoelectric System/Application

8. Commercial Bulk TE Modules

9. Thermoelectrics Power Generation (Seebeck Effect) Thermal Power in Qh Th - - Electric Power out Po + + Tc Carnot Efficiency

10. Thermoelectrics Cooling (Peltier Effect) Th Electric Power in Pin Tc Thermal Power Out Qc - - + + Peltier Effects was discovered 13 years later.

11. Applications of Thermoelectrics (I) TE Power Generation (Seebeck) Power generation for special applications Space Military Waste heat to energy (green energy)

12. Applications of Thermoelectrics (II) TE Cooling (Peltier) High accuracy thermometer Environmentally-friendly refrigerator New air-conditioning Cooling for electronics Simple system, small volume, high accuracy, high sensitivity, highly reliable, long lifetime, environmentally friendly

13. Thermoelectric Efficient Figure of Merit ZT ZT= αis the Seebeck coefficient of the material (V/K) is the electrical resistivity of the material (Ωm) is the thermal conductivity of the material (W/mK) Most materials have a ZT much less than 1. Thermoelectric systems in automobiles requires a ZT of about 2. To substitute conventional refrigerators requires a ZT of about 4 The heart of the research is to look for materials that conduct electricity well but conduct heat poorly (phonon glass and electron crystal (PGEC)).

14. Performance of Thermoelectric Generator as Function of ZT For above temperatures, the Carnot efficiency is about 61 percent, making the TE generator to be about 24 to 30 percent efficient with TE materials with ZT between 2 and 3.

15. Coefficient of Performance for Thermoelectric Cooling as Function of ZT

16. Figure of Merit – Bulk

17. Bulk Module Markets Dehumidifier Portable Fridge Electronics Cooling Automobile Offshore power generation Chiller Radioisotope thermoelectric generator Night vision

18. Climate Control Seat (CCS) System Vehicle Application In high end cars (GM, Ford, Toyota, Nissan, Lexus, etc) . Huge market!!! Over 4 million units sold so far.

19. Solid state refrigerators may replace traditional compressor refrigerators in the future

20. Progress in Thermoelectric Efficiency ZT

21. Thermoelectrics Materials: Bulk and Nano-Scale Nano-Scale Bulk Less than 5% conversion efficiency Predicted with 30% conversion efficiency • More than 40 years • Niche applications • Well established product • Less than 10 years • Potential for a wide variety of applications • Still being incubated at small companies, universities and national labs

22. A World from Macro to Nanoscale 1 nm = 10-9 m

23. Introduction: Nanoscience and Nanotechnology What is a Nanostructure? The word “nano” means 10-9 . So a nanometer is one billionth of a meter. In general, nanostructures are objects in the size range from tens to hundreds of nanometers. These materials also have tunable properties that makes them valuable for many different real world applications. Nanoscience concerns the study of objects in this size range, and nanotechnology is to fabricate and work on objects in this size range. Why nano? The nanoworld provides scientists with a rich set of materials that can be useful of probing the fundamental nature of matter.

24. Examples of Nanostructures 48 Fe atoms on Cu (111) surface, Quantum Corral, by D. Eigler,IBM Self-assembled Ge pyramid 10nm (www.nano.gov) Chemical Etching of Porous Silicon by Thomas Research Group Carbon Nanotubes (Ren, et al., Stanford Science, 1998) C60 discovered by Kroto in 1985

25. Properties of Nanostructures: Electron Density of States as a Function of Dimensionality Quantum well (QW) 2-D Quantum wires(QWR) 1-D Quantum Dots (QD) 0-D

26. Properties of Nanoscale Materials: CdSe Quantum Dots

27. Properties of Nanoscale Materials: Size and Band Gap Electrons: Blue shift of the electronic band gap Uncertainty Principle

28. US Energy Flow Trend (2002) Unit: quads, (1quads =1 quadrillion BTU, 1 BTU=1055J)

29. Opportunities for Recovery of Waste Heat in Transportation Distribution of Fuel Energy in Passenger Vehicles

31. Goal for TE in Transportation, a Research Roadmap By 2012, achieve at least 25% efficiency in advanced thermoelectric devices for waste heat recovery to potentially increase passenger and commercial vehicle fuel economy by 10%. DOE Initiative for a Science-Based Approach to Development of Thermoelectric Materials for Transportation Applications, ORNL, Nov. 2007

32. Technical Barriers • Unusual combination of properties • Matching n- and p- type materials • Performance often dependent on doping • Difficult metrology and lack of standards • Scale up of synthesis and processing of thin-film materials from lab scale • Cost effective thermoelectric materials and devices • System issues critical to operation of thermoelectric devices

33. Science-based Approach for TE material Discovery

34. Materials Technology Flow for Solid State Waste Heat Energy Recovery

35. Collaboration with Caterpillar We have developed a physics-based model that simulates the structure of multilayered nanostructures. Our modeling tool is used to predict the TE property of various multilayered structures with different structural configurations and doping concentrations. Our calculations have helped with the understating of the TE property of nanostructure affected by various conditions, and the results are used to guide the experimental research in developing nanostructured thin-film based materials for high-efficiency TE applications.

36. Potential Location for TE Generator

37. Caterpillar’s 550 HP Heavy Truck Equipped with TEG

39. TE Generator for Light Vehicles

40. TE Materials for Applications in Energy and Environment Thank you!