Economical and Facile Route to Produce Gram-Scale and Phase-Selective Copper Sulfides for Thermoelectric Applications

Producing thermoelectric materials without energy-intensive processes is essential to reduce the production costs and for wide-scale applications. Copper sulfides have recently been identified as new and promising environmentally friendly thermoelectric materials. Here, an economical synthetic route for the gram-scale preparation of copper sulfide is developed that enables selective control of the copper oxidation state, in turn allowing the stoichiometry to be tuned to optimize the thermoelectric characteristics of the product. Through this facile and scalable protocol, CuS, Cu1.75S, Cu1.80S, and Cu2S powders have been synthesized in conjunction with X-ray diffraction, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy to verify the stoichiometry of each material. The as-prepared compounds were further characterized by thermoelectric measurements and the performance of a test generator module containing ten p-type Cu2S legs was subsequently investigated. Upon heating one side of the module to 70 °C, the device produced an output voltage of 30.9 mV and a corresponding power output of 3.4 μW, which is comparable to the power outputs of many of devices fabricated with expensive and toxic thermoelectric elements. This work presents a novel pathway for the development of low-cost thermoelectric devices by introducing a facile, tunable, and high-yield CuxS synthesis procedure that may be readily adapted to other metal sulfides