Characterization of half-Heusler unicouple for thermoelectric conversion

A thermoelectric unicouple is constructed with half-Heusler materials for characterizing power generation. The electric power and heat flow are measured simultaneously under various temperature differences, and the efficiencies are calculated. Phase structures and thermoelectric properties are characterized for the p- and n-type legs; the latter are used for finite-element simulations to calculate numerically the ideal electric power, heat flow and efficiency under the same temperature conditions. Seebeck voltage, internal resistance, electric power, heat flow, and efficiency are compared between the measurement and simulation. Thereby, the contact electrical resistance is estimated, and the extra thermal resistance is analyzed in terms of the compared open-circuit voltage and heat flow. The maximum efficiency of 4.0% is attained from the measurement with the hot side at 470-°C, in contrast to 5.7% from the simulation. The simulation permits an investigation on the one-dimensional heat flow through the p- and n-type legs that is coupled with Peltier, Thomson, and Joule heat.