Segmented Thermoelectric Oxide‐Based Module for High‐Temperature Waste Heat Harvesting

Abstract

We report a high‐performance thermoelectric (TE) oxide‐based module using the segmentation of half‐Heusler Ti0.3Zr0.35Hf0.35CoSb0.8Sn0.2 and misfit‐layered cobaltite Ca3Co4O9+δ as the p‐leg and 2 % Al‐doped ZnO as the n‐leg. The maximum output power of a 4‐couple segmented module at ΔT=700 K attains a value of approximately 6.5 kW m−2, which is three times higher than that of the best reported non‐segmented oxide module. The TE properties of individual legs, as well as the interfacial contact resistances, were characterized as a function of temperature. Numerical modeling was used to predict the efficiency and to evaluate the influence of the electrical and thermal losses on the performance of TE modules. Initial long‐term stability tests of the module at the hot and the cold side temperatures of 1073 K and 444 K, respectively, showed a promising result with 4 % degradation for 48 h operating in air.

Segmentation of low‐cost high efficiency oxide‐based thermoelectric materials

“…As mentioned above, all efficiencies of segmented single legs and unicouples were calculated under the assuming a perfect thermal and electrical contact between two adjusted materials. The contact resistance, is known as one of the main sources that detriment the performance of a TEG, especially for a segmented module which includes multiple number of interfaces, i.e., contact resistance . In the current calculations, we have included a parameter called “resistance ratio,” δ = R c / R leg , which is defined as the total contact resistance ( R c ) divided by the total electrical resistance ( R leg ) for a TE leg.…”

“…that the conversion efficiencies of segmented unicouple are linearly decreased with increasing the value of contact resistance. In practice, the contact resistance of metal–metal is in the range of 2 to 50 μΩcm 2 and for oxide with metal electrode, e.g., Ca 3 Co 4 O 9 and ZnO with Ag it is about 100 μΩcm 2 at about 1000 K . As a result, the major contribution to the δ magnitude is usually attributed to the oxide‐metal conjunctions.…”

“…In order to evaluate the efficiency of non‐segmented and segmented TE elements, a 1D model of thermoelectrics is used and detailed of the model can be found in . In this calculation, the efficiency of segmented and non‐segmented TE elements was calculated under the ideal conditions, i.e., neglecting all the heat losses, thermal and electrical contact resistances, but including all the thermoelectric effects.…”

In Operando Study of High‐Performance Thermoelectric Materials for Power Generation: A Case Study of β‐Zn4sb3

“…The thermocouple at the hot side was also used for setting up the PID of the heater controller. The detail of the experimental set up may be seen elsewhere [32,44] .…”

An Analytical Model for the Influence of Contact Resistance on Thermoelectric Efficiency

“…Experimentally, the manufacture of an electrical contact for thermoelectrics with a low electrical contact resistance has been especially studied in order to improve the device efficiency. [3][4][5][6][7] This is important as, e.g., adding electrodes to a single Mg 2 Si leg increased the total leg resistance by a factor of 2-3. 8 So far, metal contacts, 9 titanium disilicide (TiSi 2 ), 10 transitionmetal silicides, 8 silver-based alloys, 11 antimony (Sb), 12 Ti foil 13 and Ag and Cu 14 contacts have been tried out.…”