Polymer-based thermoelectric materials and modules
Thermoelectricity is the interdependence of temperature and electricity. If different temperatures are applied to the ends of an electrically conductive material, a potential difference occurs, which is defined as thermoelectric voltage. This effect was first described in 1823 by the German physicist THOMAS JOHANN SEEBECK. The combination of n- and p-conductive materials is necessary for the construction of a thermoelectric module.
The focus for thermoelectric investigations at the IPF is on electrically conductive thermoplastic polymer composites (CPC); intrinsically conductive polymers (ICP) are also investigated.
In this process, melt- or solvent-mixed composites of various thermoplastic polymers and different carbon nanotubes (single-walled, multi-walled, nitrogen-, boron-doped) are produced and various additives are added. The aim is to obtain both n- and p-conducting materials in order to be able to produce thermoelectric modules. In previous work, structure-property relationships for thermoelectric materials could be demonstrated. Thus, the incorporation of carbon nanotubes with n-type behaviour (e.g. nitrogen-doped MWCNTs) always leads to n-type composites. However, the combination of p-type SWCNTs with nitrogen-containing polymers in particular can lead to composites with n-type behaviour.
In addition to composites based on thermoplastic polymers, cellulose-based composites and aerogels based on them were also investigated as thermoelectric materials.
A measuring stand was developed at the IPF to determine the thermoelectric properties. In addition to the thermoelectric voltage at different temperature differences, the electrical resistance and current can also be measured on the samples. The measurements can be carried out between room temperature and 110°C on solid specimens as well as on powders or liquids.
In the EU project InComEss, thermoelectric materials are being developed to generate energy for energy-autonomous IoT applications like e.g. sonsors for structural health monitoring.