New materials turn heat into electricity

Researchers have invented a new type of heat that can make cars more useful by turning waste heat through engine smoke into electricity.

On the issue of Science, researchers say the new material is twice as effective as any material currently on the market.

Similar technology can be used in energy generators or heat pumps, according to project leader Joseph Heremans and Ohio Eminent scholars at the nanotechnology department of Ohio State University. Scientists call these materials thermoelectric materials , they evaluate the effectiveness of materials based on the amount of heat they can convert into electricity at the given temperature.

Previously, the most efficient materials used for commercial purposes in thermoelectric generators were alloys called sodium-doped lead telluride (telluride) with a ratio of 0.71. The new material - tali- containing lead telluride , has a ratio of 1.5 - nearly double that of the previous material. More important for Heremans is the most effective new material at temperatures between 450 and 950 degrees F. This is a typical temperature range for energy systems such as car engines.

Some experts argue that only about 25% of the energy produced from a gasoline engine is normally used to run a car or power its parts, and nearly 60% of energy is lost through heat. discharged. Most of the heat is lost through engine smoke.

Thermoelectric equipment (TE) can retain some of the waste heat. It can also be attached to a car because it has no moving parts to be worn or damaged.

'New materials do all the necessary work. It generates electricity like a conventional heat engine - steam, gas or diesel engine - while still working in conjunction with the generator. But it uses electrons to act as a fluid instead of water or gas while generating direct electricity. '

Engineers have adopted a unique comb to design this new material.

New materials can make cars more useful by turning waste heat through engine smoke into electricity.

To maximize the amount of electricity produced by TE materials, engineers often have to limit the amount of heat that can pass through the material without being trapped and converted into electricity. So the specific strategy for creating thermoelectric materials is to effectively lower its thermal conductivity.

In Heremans' lab, he often seeks to lower the thermal conductivity by building nanometer-sized structures such as nanowires in materials. One nanometer is one-billionth of a meter. Nanostructured materials are not very durable, and are difficult to produce in large quantities. They are also difficult to connect to conventional circuits and external heat sources. With new materials, Heremans and colleagues applied another strategy: they did not use nanostructures, instead focusing on how to transform as well as the maximum amount of heat retained inside the material itself. Of course.

To do this, they took advantage of the idea of ​​quantum mechanics. Heremans aimed for a 2006 paper published by several other scientists in Physical Review Letters. The paper suggests that elements such as thallium and tellurium can interact at the quantum mechanical level to create a resonance between thallium and electron electrons in the thermoelectric telluride material depending on the link between atoms.

He said: 'The electron in a thallium atom has unusual activity when it has a telecom neighbor on its side. We had to study for 10 years to get this activity using different nanostructured materials but only with limited success. Then I read the article, at which time I knew we could do the same thing when trying to do with nanostructures, but with alternative semiconductors. '

Heremans designed the new material with Vladimir Jovovic, who did the research in his doctoral thesis in Mechanical Engineering, Ohio. Osaka University researchers - including Ken Kurosaki, Anek Charoenphakdee, and Shinsuke Yamanaka - have created materials to test. Then scientists from the California Institute of Technology - including G. Jeffrey Snyder, Eric S. Toberer, and Ali Saramat - experiment with new materials at high temperatures. Heremans and Jovovic tested materials at low temperatures while providing empirical evidence that the natural mechanism they assumed was indeed happening.

The team found that at temperatures close to 450 degrees Fahrenheit, the material converts heat into electricity at a rate of 0.75 - close to the ratio of the telluride-lead sodium additive. But as the temperature rises, the efficiency of new materials also increases. It peaks at 950 degrees F with a ratio of 1.5.

Heremans' group is continuing to research on patented technology. He said: 'We hope to go further. I think it is possible to apply other lessons from thermoelectric technology to improve the ratio of another factor. That's what we're aiming for. '

The research was funded by BSST, the Center for the development of vontaic photovoltaic and commercialization at Ohio State University, Beckman Institute, Swedish Bengt Lundqvist Minne Foundation, and NASA's Jet Motion Laboratory.