Waste heat is a very promising source of energy conservation and reuse through the conversion of this heat into electricity – a process called thermoelectric conversion. Commercially available thermoelectric conversion devices are synthesized using rare metals. Although quite effective, they are expensive and in most cases use toxic materials. Both of these factors have led to limited use of these converters. One alternative is oxide-based thermoelectric materials, but the primary drawback these materials suffer from is the lack of evidence of their stability at high temperatures.
A team led by Professor Hiromichi Ohta of Hokkaido University’s Research Institute for Electronic Science has synthesized a barium-cobalt oxide-based thermoelectric converter that is reproducibly stable and efficient at temperatures up to 600°C. Their findings were published in the journal ACS Applied Materials & Interfaces.
Thermoelectric conversion is controlled by the Seebeck effect: when there is a temperature difference between a conducting material, an electric current is produced. However, the efficiency of the thermoelectric conversion is dependent on a value called the thermoelectric value ZT. Historically, oxide-based converters have had low ZTs, but recent research has revealed many candidates that have high ZTs, but their stability at high temperatures has not been well documented.
Hiromichi Ohta’s group has been working on cobalt oxide layered films for over two decades. In this study, the team sought to investigate the thermal and chemical stability of these films, as well as measure their ZT values ​​at high temperatures. They tested cobalt oxide films layered with sodium, calcium, strontium or barium, and analyzed their structure, resistivity and thermal conductivity.
They found that of the four variants, the cobalt barium oxide layer retained its stability in terms of structural integrity and electrical resistance at temperatures up to 600°C. In comparison, films of sodium oxide and calcium cobalt were only stable up to 350 °C, and a film of strontium oxide and cobalt was stable up to 450 °C. The ZT of the barium cobalt oxide film increased with temperature, reaching ∼0.55 at 600 °C, comparable to some commercially available thermoelectric converters. “Our study showed that barium oxide and cobalt oxide films would be excellent candidates for high-temperature thermoelectric conversion devices,” said Hiromichi Ohta. “In addition, they are environmentally friendly and provide the potential for widespread deployment.”
Source Reference: Xi Zhang, Yuqiao Zhang, Liao Wu, Akihiro Tsuruta, Masashi Mikami, Hai Jun Cho, Hiromichi Ohta. Ba1/3CoO2: A Thermoelectric Oxide Showing a Reliable ZT of ∼0.55 at 600 °C in Air. ACS Applied Materials & Interfaces, 2022; DOI: 10.1021/acsami.2c08555
