April 23, 2024

The thermoelectric performance of purified tin-selenide is extraordinarily high.

The device converts heat from plutonium radioactive decay to 4-5% on Mars. This is enough to run Perseverance but not for Earth-based applications.

Scientists from Northwestern University in the US and Seoul National University, Korea, have now demonstrated a thermoelectric material that is high-performing in a form that could be used for device development. The thermoelectric material, purified tin-selenide in a polycrystalline structure, converts heat into electricity more efficiently than the single-crystal version. It is the most efficient system ever. Researchers achieved a high conversion rate after removing a problem with oxidation that had affected performance in previous studies.

It could be used in thermoelectric devices for solid-state applications in many industries. This would result in substantial energy savings. One of the critical applications is to convert industrial waste heat into electricity. This includes waste heat from power plants, automobile factories, and glass and brick factories. Over 65% of the energy generated from fossil fuels worldwide is lost in waste heat.

Thermoelectrics are used but in niche applications. For example, the Mars rover said Northwestern’s Mercouri K. Kanatzidis. He is a chemist whose specialty is the design of novel materials. These devices are less popular than solar cells, and the challenges of making them are great. We are developing a low-cost, high-performance material to propel thermoelectric devices more widely into application.

Kanatzidis is the Charles E. and Emma H. Morrison Professor of Chemistry at the Weinberg College of Arts and Sciences. He is also a corresponding author of this study. He holds a joint appointment at Argonne National Lab.

Chung, from Seoul National University, is the other co-corresponding writer. Vinayak Dravid is the Abraham Harris professor of Materials Science and Engineering at Northwestern’s McCormick School of Engineering. He is also one of the senior authors of the paper. Dravid has been a collaborator with Kanatzidis for many years.

Kanatzidis says that the thermoelectric device is well-defined, but it’s the material used to make them work. The device has a hot side and a cold side. The material that is thermoelectric lies in the middle. The material is heated, and some heat is converted into electricity. This then leaves the device through wires.

To be effective at waste heat conversion, the material must have very low thermal conductivity and good electrical conductivity. The material must be stable in high temperatures, as the heat source can be 400-500 degrees Celsius. Due to these and other challenges, the production of thermoelectric devices is more challenging than that of solar cells.

“Something diabolical happened.”

Kanatzidis’ team reported 2014 that they had discovered a material that was best at converting waste heat into valuable electricity. The crystal form of tin-selenide, a chemical compound. The single-crystal version is not practical for mass production due to its fragility.

Researchers studied the material’s polycrystalline form because it is more robust, can be cut, and can be shaped to suit the application. The researchers were surprised to find that the material’s thermal conduction was higher than they had expected.

Kanatzidis: “We realized that something was diabolical happening.” “It was expected that polycrystalline tin-selenide would not have a high thermal conductivity. But it did.” “We had a problem.”

The researchers found a thin layer of oxidized metal on the material. The conductive surface increased the thermal conductivity of the device, which is not desirable in a thermoelectric device.

A solution is found, opening doors.

The Korean team discovered that oxygen significantly contributed to oxidation in both the process and the materials used. They then found a method to remove it. Researchers were able to produce tin-selenide pellets without oxygen. They then tested them.

As expected, the actual thermal conductivity for polycrystalline was found to be lower than initially thought. The performance of this thermoelectric device in converting heat into electricity was superior to that of the single-crystal form. It is the most efficient thermoelectric device ever.

ZT is the “figure-of-merit” that reflects the efficiency of waste heat in thermoelectrics. The higher the ZT, the better the conversion rate. The ZT for single-crystal selenide was previously between 2.2 and 2.6 Kelvin. Researchers found that the ZT for the polycrystalline form of purified tin-selenide was approximately 3.1 Kelvin. The thermal conductivity of the polycrystalline tin selenide was extremely low, much lower than that of single crystals.

Kanatzidis stated that the new device could be made from polycrystalline tin-selenide pellets, and its applications were investigated.

Northwestern is the owner of the intellectual property rights for tin-selenide material. The thermoelectric material could be used in the automotive industry (a large amount of the potential energy of gasoline is lost through the tailpipe of vehicles), heavy manufacturing (such as glass and brick production, refineries, and coal and gas-fired power plants), and areas where combustion engines are continuously running (such large ships or tankers).

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