Thermoelectric Cu–S-Based Materials Synthesized via a Scalable Mechanochemical Process

In this work, Cu-based sulfides (chalcopyrite CuFeS2, mohite Cu2SnS3, tetrahedrite Cu12Sb4S13, mawsonite Cu6Fe2SnS8, and kesterite Cu2ZnSnS4) were synthesized by industrial milling in an eccentric vibratory mill to demonstrate the scalability of their synthesis. For a comparison, laboratory-scale milling in a planetary mill was performed. The properties of the obtained samples were characterized by X-ray diffraction and, in some cases, also by Mössbauer spectroscopy. For the densification of powders, the method of spark plasma sintering was applied to prepare suitable samples for thermoelectric (TE) characterization which created the core of this paper. A comparison of the figure-of-merit ZT, representative of the efficiency of thermoelectric performance, shows that the scaling process of mechanochemical synthesis leads to similar values as compared to using laboratory methods. This makes the cost-effective production of Cu-based sulfides as prospective energy materials for converting heat to electricity feasible. Several new concepts that have been developed involving combinations of natural and synthetic species (tetrahedrite) and nanocomposite formation (tetrahedrite/digenite, mawsonite/stannite) offer sustainable approaches in solid-state chemistry. Mechanochemical synthesis is selected as a simple, one-pot, and facile solid-state synthesis of thermoelectric materials with the capability to reduce, or even eliminate, solvents, toxic gases, and high temperatures with controllable enhanced yields. The synthesis is environmentally friendly and essentially waste-free. The obtained results illustrate the possibility of large-scale deployment of energy-related materials.