Long term stability testing of oxide unicouple thermoelectric modules

Thermoelectric devices based on oxides are good candidates for energy harvesting technologies for use in aggressive conditions where the materials should withstand high temperatures and corrosive environments over prolonged time. This leads to a natural concern for the stability of the electrical contacts, especially on the hot side of the module. In this work, we have assembled several prototype unicouple thermoelectric modules made by pyrolyzed and spark plasma sintered n-type CaMnO3 and p-type Ca3Co4O9 and then tested under different conditions mimicking end-user applications. For baseline experiments we have chosen to use nickel as the contact material in order to show the effect of its oxidation on performance. In later work we will utilize more oxidation resistant contact materials. A maximum specific power output of 56 mW/cm2 with a temperature difference of 760°C was obtained. Cycling test between 400 to 800°C during a period of 1 week showed a reduction in power output of more than 50% mainly due to crack-formation and oxidation near the nickel/oxide interfac