High-Efficiency Skutterudite Modules at a Low Temperature Gradient

Abstract

Thermoelectric skutterudite materials have been widely investigated for their potential application in mid-temperature waste heat recovery that has not been efficiently utilized A large amount of research has focused on developing materials with a high thermoelectric figure of merit (<i>zT</i>). However, the translation of material properties to device performance has limited success. Here, we demonstrate single-filling n-type Yb_0.25Fe_0.25Co_3.75Sb₁₂ and multi-filling La_0.7Ti_0.1Ga_0.1Fe_2.7Co_1.3Sb₁₂ skutterudites with a maximum <i>zT</i> of ~1.3 at 740 K and ~0.97 at 760 K. The peak <i>zT</i> of skutterudites usually occurs above 800 K, but, as shown here, the shift in peak <i>zT</i> to lower temperatures is beneficial for enhancing conversion efficiency at a lower hot-side temperature. In this work, we have demonstrated that the Fe-substitution significantly reduces the thermal conductivity of n-type skutterudite, closer to p-type skutterudite thermal conductivity, resulting in a module that is more compatible to operate at elevated temperatures. A uni-couple skutterudite module was fabricated using a molybdenum electrode and Ga&ndash;Sn liquid metal as the thermal interface material. A conversion efficiency of 7.27% at a low temperature gradient of 366 K was achieved, which is among the highest efficiencies reported in the literature at this temperature gradient. These results highlight that peak <i>zT</i> shift and optimized module design can improve conversion efficiency of thermoelectric modules at a low temperature gradient.