A Thermoelectric Generator Based on Oxides

(De Gruyter) – Thermoelectric energy generation coverts changes in temperature to electrical energy and can be analyzed in terms of changes of entropy and charge, which the power factor of the device is directly related to. Zinc Aluminum based oxides and Calcium Cobalt based oxides individually have a low-cost and display good thermal and electrical stability. When stacked together these oxide layers produce an thermoelectric generator as one layer generates electrons while the other layer holes.

The n-type Zinc Aluminum oxide and the p-type Calcium Cobalt oxide-derived materials formed a thermoelectric generator for high-temperature application. The thermoelectric materials showed different temperature slopes of the power factor with the p-type material reaching 1.8 mW cm−1 K−2 at 1,000 K and the n-type reaching 1.6 mW cm−1 K−2 at 1,050 K. For a 10-leg thermoelectric generator, a figure of merit of zT = 0.10 was estimated at maximum electrical power output when the hot side was at 1,023 K, and a temperature difference of 200 K was applied.

The authors evaluated the microstructure of each  material and sub-micrometer precipitates of ZnAl2O4 spinel were observed. The p-type Ca3Co4O9-derived ceramic turned out to be a multi-component composite. Optimized sintering will preserve a higher amount of the misfit-layered cobaltite starting phase in the final ceramic product.

The authors suggest that a higher electrical generation capacity is expected by improvemening the n-type Zn0.98Al0.02O, which, in the temperature range of interest, showed a distinctly smaller power factor than the p-type material. The electronic conductivity limits the power factor of n-type Zn0.98Al0.02O. Doping the Zn-Al oxide material to increase the charge carrier concentration should be done. With increasing electrical conductivity of the n-type material, the resistance of the module will be decreased. This  would create a greater electrical current coupling.

While the authors succesfully demonstrate the production of a thermoelectric Generators for use at high temperatures there is still much room for improvement by modifying their microstructure.

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Edited for Content and Length by Dr. Matthew A. Hood.

The  full article can be found at De Gruyter in the journal of Energy Harvesting and Systems.

DOI: 10.1515/ehs-2014-0003

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