Carnegie Institution for Science researchers are reporting pressure improves the ability of thermoelectric materials to turn heat into electricity. The new information could potentially be used to create clean electricity generation.

The report comes from a team that includes Carnegie’s Alexander Goncharov and Viktor Struzhkin with the paper published in Nature Materials.

An artist’s conception of how applying pressure in the diamond anvil cell changes the electronic structure of lead selenide. Image Credit: Xiao-Jia Chen, Carnegie Institution for Science. Click image for the largest view.

Compounds with thermoelectric capabilities can convert thermal energy’s innate, physical need to spread from a hot place into a cold place into energy by harvesting electricity from the temperature differential. In theory, generators built from these materials could be used to recover electricity from “wasted” heat given off by other processes, making major contributions to the nation’s energy budget.

However, engineers have been unable to improve the worthwhile room-temperature performance of any thermoelectric materials in 60 years, meaning that devices built to take advantage of this capability are only practical for some very specific applications, including remote gas pipelines and spacecraft.

Goncharov said, “Our measurement of the efficiency of room-temperature thermoelectricity has not budged in more than half a century. Thermoelectric compounds have demonstrated improved performance at high temperatures, but we really need them to work well at room temperature to make the most of their potential for green energy.”

This is precisely the kind of problem that material science is suited to address.

The research team – led by Liu-Cheng Chen of the Center for High Pressure Science and Technology Advanced Research – found that they could improve the thermoelectric capability of lead selenide by applying pressure and mixing in charged particles of chromium.

By squeezing the material in the diamond anvil cell – which acted as a sort of “chemical pressure” – and adding the chromium, the lead selenide was encouraged to undertake a structural rearrangement at the atomic level, enabling the most-efficient demonstration of room-temperature thermoelectric generation ever recorded.

Under 30,000 times normal atmospheric pressure, the chromium-doped lead selenide was able to produce electricity with the same efficiency that the top-performing thermoelectric materials do at 27° Celsius (80° Fahrenheit).

“Our work presents a new way to use compression techniques to improve the thermoelectric performance, bringing us closer to practical applications that could help fight climate change,” concluded Xiao-Jia Chen of the Center for High Pressure Science and Technology Advanced Research (formerly of Carnegie).

To keep some clarity here, note that lead selenide is not a typical thermoelectric material. What is known is that lead selenide will hit the ZT (the measure of efficiency) below 1.0 and that at 700° K (800° F). After the pressure application the lead selenide can yield a ZT of 1.7 at room temperature (70° F or 294° K). That is almost a doubling and a very worthwhile reduction in temperature.

What makes this worth noting is knowing the pressure application has a value, in at least one material. Which begs the question how might the application affect other thermoelectric materials?

This may not be a breakthrough in and of itself, but there is a now foundation stone that may make breakthroughs possible. One hopes so. Let the experimentation proceed.


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