Turning waste heat into useful electricity
Thermoelectric (TE) devices are solid-state devices in which electricity flows through a solid semiconductor. They convert temperature differences directly into electricity and vice versa. The potential applications are numerous, especially for cooling and electric power generation. TE devices have no moving mechanical parts and so are very reliable and quiet in operation. They are also very small and environmentally friendly. Promising materials for TE generators are silicides. These are binary compounds of silicon, such as magnesium silicide, or their solid solutions, which are mixtures of two crystalline solids that co-exist as a new crystalline solid. The main disadvantage of TE materials relates to their efficiency of energy conversion which is still low and limits their widespread development and use. The objective EU-funded 'High-temperature stable nano-structured silicides for highly efficient thermogenerators and their contacting technology' (NANOSICON) project set out to increase their efficiency. Project partners studied the high temperature TE properties of magnesium silicide and its solid solutions and examined the influence of doping. The latter involves the addition of certain impurities to reduce the semiconductor's electrical resistance. They then characterised the resulting materials according to their electronic and thermal transport properties. Project efforts achieved remarkable improvements in the potential performance of these semiconductors in TE applications. This makes these materials excellent candidates for thermogenerator applications. One area of relevance is for automobiles where waste heat from a car's exhaust can be converted into electricity.
Keywords
Silicides, thermoelectric, thermogenerators, energy conversion, waste-heat recovery
