Effective decoupling of grain boundaries and secondary phase interfaces for enhanced thermoelectric performance of Cu1.8S/WS2 nanocomposites

Copper Sulfide (Cu1.8S) has influentially concerned the increasing attention in mid-temperature thermoelectric materials. The inherent low Seebeck coefficient and high thermal conductivity of Cu1.8S hinders the thermoelectric performance. The superionic conductivity exhibited by Cu1.8S phase possess characteristic phonon-liquid electron-crystal property eliminate transverse phonon vibrations. In this study, improved thermoelectric performance for the Cu1.8S material was obtained through the efficient strategy of compositing with WS2 nanoparticles. A minimum thermal conductivity of 1.4 W/mK at 753 K for the Cu1.8S/5 wt. % WS2 nanocomposite. Along with the increased Seebeck coefficient values, the thermal conductivity is suppressed by WS2 composite due to the formation of Cu2WS4 secondary phase which strengthens the phonon scattering. The evident reduction in the thermal conductivity, coupled with less affected Seebeck coefficient, led to increased figure of merit (zT) of 0.46 at 753 K, which is 95 % higher than that of pure Cu1.8S. This work provides a distinguished improvement in the performance of Cu1.8S thermoelectric material thereby enabling its employment in the application of waste heat harvesting.