Bismuth telluride-based thermoelectric materials: Coatings as protection against thermal cycling effects

Thermoelectric (TE) devices, both TE generators (TEGs) and TE coolers (TECs), have short service lives as TE materials undergo degradation from sublimation, oxidation and reactions in corrosive environments at high temperatures. We have investigated four high-temperature polymers (HTPs) as candidates for TE element coatings and/or TE device fillers to minimize or prevent this degradation. Two of these HTPs have shown good thermal stability in the 400-500 degrees C temperature range. The coatings were initially applied to bismuth telluride (Bi2Te3)-based TE materials that are used for commercial power generation devices specified for operation up to 250 degrees C. The HTPs protect the Bi2Te3 from both weight loss and weight gain up to 500 degrees C. This is clearly outside the optimum TE operation range of Bi2Te3 materials, but demonstrates the ability of the HTP coatings to protect the Bi2Te3 materials at least up to 250 degrees C. The properties that HTP materials demonstrated during the examination of suitability of their use for TE element coatings and/or TE device fillers using Bi2Te3 are expected to hold good for higher operating temperature TE materials also.