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Forschungszentrum Jülich - Research in Jülich 2_2012

Research in Jülich 2|201220 Materials with More Thermopower In cars and numerous industrial production processes, a great deal of energy is lost in the form of heat. With thermoelectric materials, the waste heat could be utilized and therefore less energy squandered. Dr. Raphaël Hermann and his Helmholtz young investigators group conduct research on how these materials can be improved. R aphaël Hermann, who hails from Belgium, says with satisfaction, “We have just undergone evalua- tion – with excellent results. This means that I can continue my work at Jülich.” By “we” Hermann means the Helmholtz young investigators group he estab- lished in 2008 and which he also heads. With its young investigators group pro- gramme, the Helmholtz Association (HGF) supports early-career scientists in conducting research independently and “offers them secure career prospects”, as HGF puts it. This means first and fore- most a permanent contract – and noth- ing stands in the way of this for Hermann after the results of the latest evaluation. Hermann’s objects of research in- clude materials that can be used to build thermoelectric generators (TEGs). TEGs convert temperature differences into electrical energy. They could therefore help utilize the waste heat that is cur- rently lost in cars with petrol or diesel engines. Car manufacturers believe that in this way fuel consumption can be re- duced by at least five percent, which would curb carbon dioxide emissions as well. Excess heat is also released in many industrial processes and in com- bined heat and power plants. The reason why TEGs are not yet used, neither in these applications nor in cars, is that to date they only convert a small fraction of the excess heat into electrical power. Ex- perts consider their efficiency to be too low: it is usually less then ten percent, even if the temperature difference be- tween the hot and the cold side of the TEG is high. THE GOAL: HIGHER EFFICIENCY An increase in efficiency requires materials that conduct electric current effectively but have a low thermal con- ductivity. Unfortunately, high electrical conductivity usually goes hand in hand with a high thermal conductivity, be- Dr. Raphaël Hermann (left) and his Helmholtz young investigators group at Jülich. Vacuum suction cup with a sample for lattice vibra- tion measurements.

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