Engineers from Ulsan National Institute of Science and Technology (UNIST), in South Korea, have developed a technique to turn industrial waste heat into electricity for vehicles and other applications.

The team, led by Jae Sung Son, professor of materials science and engineering, has devised new types of high-performance thermoelectric (TE) materials that possess liquid-like properties. The materials are both shape engineerable and geometrically compatible, in that they can be brush painted directly on almost any surface.

Existing liquid-like TE materials are limited in their effectiveness by the flat or angular shape of the generator modules used. Image credit: UNIST. The "thermoelectric effect" involves the direct conversion of temperature differences to electric voltage, and vice versa. It can be used either for heating or for cooling, such as in automotive cooling systems and waste heat recovery systems on ships.

According to the research team, existing liquid-like TE materials are limited in their effectiveness by the flat or angular shape of the generator modules used. The modules that the team has devised are instead configured as rectangular parallelepipeds.

Recognizing that the surfaces of most heat sources where these planar devices are attached are curved, the researchers developed a shape-engineerable TE painting technique, in which they directly brush TE paints onto the surface of heat sources to produce electricity. Using this method, electricity can be generated via the application of TE paints on the exterior surfaces of buildings, roofs, cars and other curved or irregular surfaces.

To show the feasibility of the technology, they fabricated TE generators by painting TE paints on flat, curved and large-sized hemispherical substrates, demonstrating heat energy collection with an output power density of 4.0 mW cm⁻².

“By developing integral thermoelectric modules through the painting process, we have overcome limitations of flat thermoelectric modules and are able to collect heat energy more efficiently,” says Son. “Our thermoelectric material can be applied to any heat source regardless of its shape, type and size.”