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A3: High temperature materials
Thermoelectric energy harvesting can be easily understood as the reloading of energy from an entropy current to a charge current. Depending on the sign of the Seebeck coefficient α of a thermoelectric material, charge current and entropy current run in the same or in opposite direction. Electrical series and thermal parallel connection of n-type (α < 0) and p-type (α > 0) semiconductors allow constructing thermoelectric modules which can extract electrical power from an entropy current running from “hot” to “cold”. Over recent years, our group has investigated new mixed ionic and electronic conducting (MIEC) oxide ceramics with the aim to use them as oxygen-transporting membranes in gas separation and purification at elevated temperature even under harsh conditions [1-4]. Total electronic conductivity is governed by semiconducting electronic transport which is provided by polaronic hopping and turns into quasi-metallic behavior at high temperature due to presence of itinerant electrons. These MIEC ceramic materials exhibit thermoelectric properties by principle, which however have not been quantified so far. Here, we report on measurements of Seebeck coefficient and electrical conductivity which allow estimate the power factor as an indicator of material’s suitability for the thermoelectric application. Materials in focus are oxygen deficient perovskites [1, 2, 5], Ruddlesden-Popper phases [3] or spinel/fluorite composites [4]. The findings on materials developed initially in other context are discussed to elucidate their applicability for thermoelectric energy harvesting under high-temperature (high-T) conditions [6].
[1] J. Martynczuk, F. Liang, M. Arnold, V. Šepelák, and A. Feldhoff, Chem. Mater. 21, 1586 (2009).
[2] K. Efimov, T. Halfer, A. Kuhn, P. Heitjans, J. Caro, and A. Feldhoff, Chem. Mater. 22, 1540 (2010).
[3] H. Luo, K. Efimov, H. Jiang, A. Feldhoff, H. Wang, and J. Caro, Angew. Chem. Int. Ed. 50, 759 (2011).
[4] T. Klande, K. Efimov, S. Cusenza, K.-D. Becker, and A. Feldhoff, J. Solid State Chem. 184, 3310 (2011).
[5] W. Zhou, J. Sunarso, M. Zhao, F. Liang, T. Klande, and A. Feldhoff, Angew. Chem. Int. Ed. 52, 14036 (2013).
[6] A. Feldhoff and B. Geppert, Energy Harvest. Systems (submitted).