Development of a high efficiency thermoelectric unicouple for power generation applications

To achieve high thermal-to-electric energy conversion efficiency, it is desirable to operate thermoelectric generator devices over large temperature gradients and also to maximize the performance of the thermoelectric materials used to build the devices. However, no single thermoelectric material is suitable for use over a very wide range of temperatures (/spl sim/300-1000 K). It is therefore necessary to use different materials in each temperature range where they possess optimum performance. This can be achieved in two ways: (1) multistage thermoelectric generators where each stage operates over a fixed temperature difference and is electrically insulated but thermally in contact with the other stages; and (2) segmented generators where the p- and n-legs are formed of different segments joined in series. The concept of integrating new thermoelectric materials into a segmented thermoelectric unicouple has been introduced in earlier publications. This new unicouple is expected to operate over a 300-973 K temperature difference and will use novel segmented legs based on a combination of state-of-the-art thermoelectric materials and novel p-type Zn/sub 4/Sb/sub 3/, p-type CeFeSb/sub 12/-based alloys and n-type CoSb/sub 3/-based alloys. A conversion efficiency of about 15% is predicted for this new unicouple. We present the latest experimental results from the fabrication of this unicouple, including bonding studies between the different segments of the p-legs, n-legs, and p-leg to n-leg interconnect. Thermal and electrical tests of the unicouple are in progress and are briefly described.