A thermoelectric generator based on an n-type clathrate and a p-type skutterudite unicouple

The type I clathrates A8Ga16X30 (A=Sr, Ba, Eu; X=Si, Ge, Sn) and filled skutterudites Ay(Fe1-xMx)4Sb12 (A=rare-earth, M=Co, Ni,) are intermetallic compounds with good thermoelectric performance in the temperature range 400-800K. Here we report on the first mixed clathrate-skutterudite unicouple thermoelectric generator and address important technical issues such as upscaling, contacting, and electrode material selection. At 600K, the materials Eu8Ga16Ge30, Ba8Ga16Ge30, and Mm0.7Fe3.5Ni0.5Sb12 synthesized for this purpose have figures of merit ZT=0.32, 0.15, and 0.46, respectively. The clathrate and skutterudite legs were brazed to a hot side nickel electrode. An average contact resistivity of 16 mu cm2 was obtained with Pb-Ag (hot side) and In-Sn (cold side) brazings combined with and intermediate Ni layer. For a temperature difference T=250K (hot side temperature=573K), this generator produced an open circuit voltage Uopen=54mV and an electrical specific power P=178mWcm-2 as our best result with the couple Mm0.7Fe3.5Ni0.5Sb12 and Eu8Ga16Ge30