Today you can drive your car down Commonwealth Avenue as your vehicle emits tons of exhaust into the atmosphere, continuing humanity's onslaught on the earth's environment. In the future, due to recent efforts by a joint research team from Boston College and the Massachusetts Institute of Technology, that exhaust might be used to power your car's battery.
In more technical terms, these researchers have demonstrated a huge increase in thermoelectric efficiency - effectively introducing a new standard for the creation and use of heating, cooling, and power. Though the technology has been around for years, this specific advancement is important because it has paved the way for commercial application - ranging from refrigerators and air conditioners to solar technology to automobiles to semiconductors. The primary ramifications are that the products will be cleaner and will run more efficiently.
The team is composed of Zhifeng Ren, a BC physics professor and co-leader of the project, six researchers from Ren's lab, Gang Chen, a mechanical engineering professor from MIT and the project's other co-leader, Mildred S. Dresselhaus, an MIT physics professor, Bed Poudel of GMZ Energy, Inc., and Junming Liu, a physicist from Nanjing University in China and a visiting professor at BC. The research was funded by the Department of Energy and the National Science Foundation. The team's results were published on Thursday, March 20 in the online edition of Science, a world-renowned journal for scientific research. The team approached the project with a novel low-cost strategy, which consists of producing minute alloy nanostructures approximately one one-thousandth the width of human hair that can act as power generators or micro-coolers. Besides being economical, this technique can be adopted by many product manufactures so their products will either recapture energy that would otherwise be wasted or simply consume less energy.
The research is based on the thermoelectric effect, which is the conversion of temperature differences into electric voltage and electric voltage into temperature differences. There are several useful applications of the thermoelectric effect: measuring temperature, generating electricity, and the cooling or heating of objects. On one hand, a thermoelectric device can create a voltage when there is a temperature difference between its sides. On the other, when a voltage is applied to a thermoelectric device, the result is a temperature difference. Such devices make great temperature controllers because the direction of the heating or cooling is determined by the applied voltage's sign (positive or negative). The thermoelectric effect, however, is not the same as Joule heating - the heat that is produced when a voltage difference is used on a resistive material. The thermoelectric effect is reversible, while Joule heating is not. The team's achievement is important because it is a successful attempt to utilize the applications of the thermoelectric effect, which has stymied researchers since the 19th century after French physicist Jean Charles Athanase Peltier and Estonian-German physicist Thomas Johann Seebeck each independently discovered it. In the 1950s, scientists tried to improve thermoelectric efficiency using all kinds of materials such as silicon wires and expensive, complex lattices. The main problem is that many materials conduct both electricity and heat, which makes their temperatures equalize quickly. The team has used materials that conduct electricity without also conducting heat.
And so, using nanotechnology, the researchers demonstrated a dramatic increase in the thermoelectric efficiency of bismuth antimony telluride in bulk form. The material is a semiconductor alloy that has been widely used since the '50s in many commercial devices. More specifically, the researchers have demonstrated a 40 percent increase in the alloy's "figure of merit," which is a quantity that characterizes a material's performance relative to other materials of the same type, ultimately to gauge their utility for application. Since the alloy is both cost-friendly and environmentally friendly, the researchers are confident it will be swiftly adopted for a number of things - elevating us to completely new levels of efficiency for heating, cooling, and power generation.
The team has primarily focused on balancing efficiency and cost. Thermoelectric materials, again, have been in use for years. For instance, NASA has been harnessing them to generate power for ships involved in deep space exploration and some automobile seat makers have used them to produce cool seats for drivers in hot weather.
One of the most exciting applications of the team's research is using thermoelectric materials to convert the waste heat of a car's exhaust system into an electric current that would be recycled and, in turn, power the vehicle. This technique will be crucial in the fight against global warming, Ren said. Instead of hurting the environment, waste heat will be recycled. In an article for The Boston Globe titled "From heat to electricity and back again," Felicia Mello mentions two other intriguing applications: jackets that charge cell phones by using body heat and a mini-power plant that lights lamps by using the heat in an apartment.
Ren and Chen, along with Chief Executive Officer Mike Clary, have formed a company named GMZ Energy Inc., based in Newton, which will begin exploring the commercial opportunities engendered by the team's research, bringing low-cost and efficient thermoelectric technology to public consumers. It is quite possible that thermoelectric cooling devices - once their efficiency is further developed - will one day replace regular refrigerators and thermoelectric power will be used in all environmentally friendly homes.
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