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

Main Research Collaborators Research Students (1994-present)   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  

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  

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.

Introduction to Thermoelectrics Heat in Current out + - Thermoelectric Couple Thermoelectric elements (legs) Th Tc N P   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.

Thermoelectrics Nomenclature Thermoelectric Device (Module) + -

Thermoelectrics Nomenclature Thermoelectric System/Application

Commercial Bulk TE Modules

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

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

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

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

Thermoelectric Efficient Figure of Merit ZT ZT= α is 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)).

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.

Coefficient of Performance for Thermoelectric Cooling as Function of ZT   

Figure of Merit – Bulk  

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

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.

Solid state refrigerators may replace traditional compressor refrigerators in the future  

Progress in Thermoelectric Efficiency ZT  

Thermoelectrics Materials: Bulk and Nano-Scale Less than 5% conversion efficiency Bulk More than 40 years Niche applications Well established product Nano-Scale Predicted with 30% conversion efficiency Less than 10 years Potential for a wide variety of applications Still being incubated at small companies, universities and national labs Just like thermocouples, where are a pair of dissimilar metals connected together at a junction is exposed to a temperature difference is

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

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. 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. These materials also have tunable properties that makes them valuable for many different real world applications.

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

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

Properties of Nanoscale Materials: CdSe Quantum Dots

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

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

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

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 Program Goals Research Goals: By 2012, achieve at least 21% efficiency in cost effective thermoelectric devices for waste heat recovery in transportation applications. This is the goal from the DOE OFCVT 5-year plan for waste heat rejection in cars and trucks Is this too conservative for our program?

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  

Science-based Approach for TE material Discovery  

Materials Technology Flow for Solid State Waste Heat Energy Recovery  

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.  

Potential Location for TE Generator  

Caterpillar’s 550 HP Heavy Truck Equipped with TEG

 

TE Generator for Light Vehicles  

TE Materials for Applications in Energy and Environment Thank you!