Huge amounts of energy are lost every day in the form of waste heat. Now, an interdisciplinary team at Chalmers University of Technology, in Sweden, has found that a class of materials known as high-entropy alloys could open the door to efficient heat recycling.

In an effort to boost energy efficiency, many research teams are working to develop thermoelectric materials that can convert waste heat into energy. But it is no easy task. To efficiently convert heat to electricity, the materials need to be good at conducting electricity but, at the same time, poor at conducting heat. For many materials, that’s a contradiction in terms.

“One particular challenge is creating thermoelectric materials that are so stable that they work well at high temperatures,” says Anders Palmqvist, professor of materials chemistry, who is conducting research on thermoelectric materials.

Together with Chalmers materials scientist Sheng Guo and Paul Erhart, of the university's Department of Physics, he investigated as a potential solution high-entropy alloys, which typically consist of at least five elements, usually metals, at fairly similar quantities. They are stable even at high temperatures, and the characteristics of the alloys can be manipulated by varying the components or the quantities of the components.

A high-entropy alloy imaged with a scanning electron microscope. Image credit: Sheng Guo.A high-entropy alloy imaged with a scanning electron microscope. Image credit: Sheng Guo.The team manufactured and studied high-entropy alloys consisting of aluminum, cobalt, chromium, iron and nickel. It turned out that the scientists were able to enhance the qualities that lead to good thermoelectric capabilities, and they concluded that high-entropy alloys have the potential to develop into very good thermoelectric materials.

The task now is to continue developing the materials to try to understand the ideal formulation of high-entropy alloys for optimal thermoelectric properties.

“It’s a slow process, because there are many variables to play around with and a whole periodic table of elements to investigate,” Erhart explains. “But with good theoretical understanding, we can try to predict which elements are the most interesting.”

“Currently, the automotive industry is showing the greatest interest in converting waste heat to electricity,” Palmqvist notes. “But if we create a really good thermoelectric material, the potential applications would expand. For example, we could produce electricity as a by-product at industries like steel mills.”

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