Title: Architecture of copper sulfide compound boosting thermoelectric performance

Abstract

Based on the development of high-performance necessity and urgency of the thermoelectric conversion material, copper sulfide has been regarded as a promising thermoelectric material with relatively high thermoelectric performance and abundant resources. The low intrinsic thermal conductivity and high electrical transport of these materials are born out of the “phonon liquid electron-crystal” structure between the copper and chalcogens. However, three thermoelectric parameters, Seebeck coefficient, electrical conductivity, thermal conductivity, are interrelated with each other. To further improve the thermoelectric properties of copper sulfides must be decoupled these parameters. We discuss the strategies for designed architecture to improve the thermoelectric performance of copper sulfides based on reducing lattice thermal conductivity of single-component material and tuning compositions for optimizing thermoelectric properties. Copper sulfide compound, including the compound structure of multiscale architecture engineered Cu2-xS at different mass ratios and carbon-encapsulated Cu2-xS, synthesized by a room-temperature wet chemical method. The observed electrical conductivity in the multiscale architecture-engineered Cu2-xS is four times as much as that of the Cu2-xS sample at 800 K, which is attributed to the potential energy filtering effect at the new grain boundaries. Moreover, the multiscale architecture in the sintered Cu2- xS increases phonon scattering and results in a reduced lattice thermal conductivity of 0.2 W•m 1•K-1 and figure of merit (zT) of 1.0 at 800 K. The electrical conductivity of Cu2−xS@C compound increases by approximately 50% compared to that of the pure Cu2−xS sample, and can be attributed to an increase in carrier concentration. Phonon scattering interface formation and superionic phase of Cu2−xS@C results in very low lattice thermal conductivity of 0.22 W•m−1•K−1 and maximum thermoelectric zT of 1.04 at 773 K. The results confirmed that these two strategies are effective for the enhancement of thermoelectric performance.