Microwave solvothermal synthesis and HTHP sintering of CoSb3/rGO composites: In-situ synthesis and enhanced thermoelectric properties

The utilization of CoSb ₃ -based thermoelectric materials is currently confined to aviation applications, primarily attributed to their elevated thermal conductivity (κ) values. The incorporation of a nanostructuring approach, coupled with the introduction of a secondary phase, has demonstrated efficacy in diminishing the thermal conductivity ( κ) values of CoSb ₃ materials. Here, the CoSb ₃/reduced graphene oxide (CoSb ₃/rGO) composites are obtained by sintering the as-synthesized powders, which ultra-fast synthesized in situ via microwave solvothermal method, under the High-temperature and High-Pressure (HTHP) conditions. The influence of reduced graphene oxide (rGO) on the structural and thermoelectric characteristics of CoSb ₃ composites has been systematically explored. In this study, CoSb ₃ nanoparticles with an average size of ∼33 nm exhibit uniform distribution, being effectively anchored onto the 2D sheets of rGO. In this work, the lattice thermal conductivity of CoSb ₃/rGO composites decreased with the addition of rGO. Based on the Debye-Callaway model, we attribute this to the effective scattering of phonons by the interface formed between the CoSb ₃ nanocrystals and the lamellar rGO. As a result, the CoSb ₃/rGO composite, containing 2 wt% graphene, exhibits a significantly enhanced maximum thermoelectric figure of merit ( ZT) value, reaching ∼0.325 at 700 K. This represents an impressive improvement of approximately 300 % compared to the ZT value of the graphene-free CoSb ₃ bulk counterpart, which is ∼0.106. This study demonstrates the microwave solvothermal synthesis and HTHP sintering are in favor for an efficient, economical, and controllable synthesis of CoSb ₃/rGO composites, which provides a novel strategy for securing better thermoelectric performance.