Washington, July 25 : Scientists have invented a new material that will make cars even more efficient, by converting heat wasted through engine exhaust into electricity.
Such materials are called as thermoelectric materials by scientists, and they rate the materials' efficiency based on how much heat they can convert into electricity at a given temperature.
Previously, the most efficient material used commercially in thermoelectric power generators was an alloy called sodium-doped lead telluride, which had a rating of 0.71.
The new material, thallium-doped lead telluride, has a rating of 1.5 - more than twice that of the previous leader.
"The same technology could work in power generators and heat pumps," said project leader Joseph Heremans, Ohio Eminent Scholar in Nanotechnology at Ohio State University.
Some experts argue that only about 25 percent of the energy produced by a typical gasoline engine is used to move a car or power its accessories, and nearly 60 percent is lost through waste heat - much of which escapes in engine exhaust.
According to Heremans, a thermoelectric (TE) device can capture some of that waste heat. It would also make a practical addition to an automobile, because it has no moving parts to wear out or break down.
"The material does all the work. It produces electrical power just like conventional heat engines - steam engines, gas or diesel engines - that are coupled to electrical generators, but it uses electrons as the working fluids instead of water or gases, and makes electricity directly," he said.
"Thermoelectrics are also very small. I like to say that TE converters compare to other heat engines like the transistor compares to the vacuum tube," he added.
The new material is most effective between 450 and 950 degrees Fahrenheit - a typical temperature range for power systems such as automobile engines.
Researchers at the California Institute of Technology - G. Jeffrey Snyder, Eric S. Toberer, and Ali Saramat - tested the material at high temperatures.
Heremans and Vladimir Jovovic tested it at low temperatures and provided experimental proof that the physical mechanism they postulated was indeed at work.
The team found that near 450 degrees Fahrenheit, the material converted heat to electricity with an efficiency rating of about 0.75 - close to that of sodium doped telluride. ut as the temperature rose, so did the efficiency of the new material. It peaked at 950 degrees Fahrenheit, with a rating of 1.5.
"I think it should be quite possible to apply other lessons learned from thermoelectric nanotechnology to boost the rating by another factor of two - that's what we're shooting for now," said Heremans.