ABSTRACT
Energy conversion materials and systems are designed to extract various types of energy from the environment to provide sustainable power for sensors, actuators, electronics, heaters, etc., thus lowering the need for batteries or power generating devices. Examples of ambient energy sources are temperature gradients and fluctuations and mechanical motions, such as impacts and vibrations, which are otherwise wasted or harmful. Thermoelectric energy conversion mechanisms are based on the Seebeck effect, that is as electrons move from the high-temperature end to the low-temperature end of a conductor, a current is formed and thus electric power can be generated. Recently, studies have been carried out on nanostructured energy conversion materials. This chapter deals with the mechanism of thermoelectric energy conversion. The physical principles behind thermoelectricity will be discussed. 1.1 Thermoelectricity
1.1.1 Seebeck Effect and Thermoelectric PowerThermoelectric (TE) energy conversion is based on the Seebeck effect, which was discovered in 1821 by the Estonian German
physicist Thomas Johann Seebeck. In this effect, a temperature difference across the TE materials, preferably a p-type and an n-type semiconductor, as shown in Fig. 1.1, generates electricity, that is ΔT => I, where T stands for temperature and I represents electric current. The reverse effect is that electricity causes active cooling. Thermoelectricity may be simply demonstrated by using the installation shown in Fig. 1.2. In this demonstration, bismuth telluride alloy (Bi-Te) TE modules are installed between two aluminum legs. One leg is immersed in hot water, while the other is inserted into cold water. Due to the temperature difference, the Bi-Te unit generates electricity and drives the small electric fan to rotate.
