One approach for the energy harvesting from waste-heat is the use of thermoelectric materials. They can directly convert heat from different sources (for example geothermal, solar heat or waste heat) into electricity. The state of the art for the conversion efficiency of the so-called thermoelectric energy-recovery lies around seven percent. Different classes of materials (Oxides, Half-Heusler, Clathrates, Silicides, Antimonides, Tellurides, etc.) are currently investigated worldwide in order
to increase the thermoelectric performance. However, the high thermoelectric efficiency is not the unique criterion for applications at large scale and the requirements are very complex. For example, the thermoelectric materials should be constituted of low-price and non-toxic elements with large natural availability.
Furthermore, the electric contacts should be mechanically as well as thermally and chemically stable in the complete application temperature range. In addition, the oxidation plays an important role. Protective coatings or encapsulation of the thermoelectric generator are necessary to prevent corrosion during the operation at high temperature.
The final thermoelectric device should also possess good mechanical properties since it might be exposed to temperature oscillations that damage the mechanical stability.