Tubular ring thermoelectric module for exhaust pipes: From Skutterudite nanopowders to the final device

Abstract

There is an important number of thermoelectric applications in the range of medium temperatures (between 200 and 600 °C), such as heat recovery in automotive applications, where these temperatures are easily reached in the exhaust or the motor. Among the various materials which exhibit good thermoelectric properties in this range, Skutterudites (with the general formula CoSb3) stand out as some of the most used. In recent years, different improvements have been done to decrease their thermal conductivity, from using rattler atoms inside their structure to nanostructuring by sintering nanoparticles and increasing the number of grain boundaries. In this work, we present the subsequent development of the nanopowder ball-milling fabrication method, to obtain a scalable production of n-type and p-type nanostructured Skutterudites. The sintering of these powders into nano-composites was done by different pressing and annealing treatments, which not only could substitute other sintering processes such as Spark Plasma Sintering, giving competitive values of the thermoelectric properties of the final nanostructured material, but can also be used to directly obtain different geometries to be used in certain implementations. This procedure has been tested by fabricating thermoelectric legs of the thermoelectric nanostructured material in the shape of rings, in contrast with the more generally available thermoelectric modules, which have a planar architecture. The ring-shaped architecture was obtained by pressing the nano-powders between copper rings, and from them, cylindrical thermoelectric generators were implemented, which present several of advantages for their use in automotive waste heat recovery from the exhaust, for instance. The optimal parameters, as far as geometry and the materials used in the final device, can be extracted from simulations based on the actual measurements obtained in the fabricated thermoelectric rings. Taking all these into account, in this work we present a route to fabricate low-cost nano-structured Skutterudite in an easily scalable way, suitable for the implementation of different architectures of thermoelectric generators for mid-range temperature applications.