Engineering of Thermoelectric Composites Based on Silver Selenide in Aqueous Solution and Ambient Temperature

The direct, solid state, and reversible conversion between heat and electricity using thermoelectric devices finds numerous potential uses, especially around room temperature. However, the relatively high material processing cost limits their real applications. Silver selenide (Ag₂Se) is one of the very few n-type thermoelectric (TE) materials for room-temperature applications. Herein, we report a room temperature, fast, and aqueous-phase synthesis approach to produce Ag₂Se, which can be extended to other metal chalcogenides. These materials reach TE figures of merit (zT) of up to 0.76 at 380 K. To improve these values, bismuth sulfide (Bi₂S₃) particles also prepared in an aqueous solution are incorporated into the Ag₂Se matrix. In this way, a series of Ag₂Se/Bi₂S₃ composites with Bi₂S₃ wt % of 0.5, 1.0, and 1.5 are prepared by solution blending and hot-press sintering. The presence of Bi₂S₃ significantly improves the Seebeck coefficient and power factor while at the same time decreasing the thermal conductivity with no apparent drop in electrical conductivity. Thus, a maximum zT value of 0.96 is achieved in the composites with 1.0 wt % Bi₂S₃ at 370 K. Furthermore, a high average zT value (zT_ave) of 0.93 in the 300-390 K range is demonstrated.