Performance of a skutterudite-based segmented unicouple with a metallic coating near hot junction

Skutterudite‐based thermoelectric unicouples are currently being considered for use in next generation Radioisotope Power Systems (RPSs) to reduce the amount of 238PuO2 fuel and the mission’s cost and increase the system specific power. In these unicouples, typically operateing at a hot junction temperature of 973K, the loss of the volatile antimony from the n‐ and p‐legs near the hot junction, if not suppressed, could gradually degrade their performance. Recently, it has been shown that such a loss of antimony could be effectively suppressed by applying a thin metallic coating on the legs near the hot junction. However, to minimize the impact on the conversion efficiency, the thickness and the length of the coating need to be optimized. An analytical model for coated skutterudite‐based segmented unicouples is developed and used to optimize the length and thickness of the coating and quantity its effect on the conversion efficiency and load electrical power. Several coating materials are investigated: Tantalum (Ta), Titanium (Ti), Molybdenum (Mo), and Vanadium (V). The required coating length for maintaining the antimony vapor pressure off the exposed portions of the legs ⩽ 10−3 Pa depends on its thickness, which varied from 1.0 to 9 μm. Results indicated that increasing the coating thickness decreases the conversion efficiency, but increases the load electrical power. The smallest decrease in the conversion efficiency occurs when using Ti or V coating, while using Ta or Mo coating results in a large decrease in the conversion efficiency.