Preparation And Thermoelectric Properties Of Bi₂Te₃/Ti₃C₂T_x Nanocomposites

Thermoelectric materials are functional materials that can directly convert heat into electric energy.Thermoelectric conversion has become an indispensable part in distributed power generation and the utilization of various waste heat.Currently,Bi₂Te₃materials have the best performance at room temperature,but it is still necessary to further improve the thermoelectric performance of Bi₂Te₃.A large number of researches have proved that nanostructure contributes to the improvement of thermoelectric performance.There are still many deficiencies in the preparation of Bi₂Te₃ nanomaterials,the long preparation period,and pollution from strong reductants.In this paper,Bi₂Te₃ nanosheets were prepared by the solvothermal method.Ti₃C₂T_x was introduced into the Bi₂Te₃nanosheets matrix to form Bi₂Te₃/Ti₃C₂T_x nanocomposites.The thermoelectric properties of Bi₂Te₃/Ti₃C₂T_x nanocomposites have been studied.The main research contents are as follows:（1）The electronic structure of Bi₂Te₃/Ti₃C₂ nanocomposite interface was analyzed based on density functional theory.The energy state density and work function of Ti₃C₂and Bi₂Te₃ were calculated.The effect of Ti₃C₂ on the electrical conductivity and Seebeck coefficient of Bi₂Te₃ was analyzed.The simulation results showed that Ti₃C₂T_x had no effect on the energy band structure of Bi₂Te₃.However,an energy barrier was formed at the interface of Bi₂Te₃/Ti₃C₂T_x nanocomposites,which increased the scattering factor and improved the Seebeck coefficient.The difference in work functions of Bi₂Te₃ and Ti₃C₂T_xled to the increase of the carrier concentration of Bi₂Te₃ and the improvement of electrical conductivity.（2）Based on the solvothermal method,an efficient and environmentally friendly method for the synthesis of Bi₂Te₃ nanosheets was proposed.Single-crystal hexagonal Bi₂Te₃ nanosheets with regular morphology and good monodispersion were prepared by controlling the reaction temperature,the amount of sodium hydroxide and reacting precursor in the synthesis process with ethylene glycol as the solvent and weak reducing agent.The Bi₂Te₃/Ti₃C₂T_x nanocomposites were prepared by ultrasonic dispersion-flash freeze-freeze drying method.The Bi₂Te₃/Ti₃C₂T_x nanocomposites were successfully prepared by the sintering plasma sintering.TEM image showed that there was no agglomeration of Ti₃C₂T_x in the matrix of Bi₂Te₃.The SEM images showed that there were a lot of nanograin boundaries in the sintered samples,which increase phonon scattering and decrease thermal conductivity.（3）The thermoelectric properties of Bi₂Te₃/Ti₃C₂T_x nanocomposites were studied.The results showed that the Bi₂Te₃ nanosheets prepared in this paper have good thermoelectric properties,and the ZT value is 14%higher than that of commercial Bi₂Te₃.The power factor of Bi₂Te₃ was further improved and the thermal conductivity was reduced by introducing Ti₃C₂T_x into the nano-Bi₂Te₃ matrix.The carrier concentration of Bi₂Te₃ was increased,which led to the increase of electrical conductivity and decrease of Seebeck coefficient of nanocomposites.The energy barrier scattering of the nanocomposite interface avoids the significant decrease of Seebeck coefficient.Phonon scattering and interfacial thermal resistance were increased at the interface,which led to the decrease of thermal conductivity of nanocomposites.Compared with Bi₂Te₃nanomatrix,the ZT value of 1 vol%Bi₂Te₃/Ti₃C₂T_x nanocomposite was increased by 25%,indicating that Ti₃C₂T_x can improve the thermoelectric properties of Bi₂Te₃.In this paper,the influence of Ti₃C₂ on the electrical properties of Bi₂Te₃ was analyzed by the simulation of the electronic structure of Bi₂Te₃ and Ti₃C₂,which provides a theoretical basis for the experiment.An efficient and environmentally friendly synthesis method of Bi₂Te₃ nanosheets based on the solvothermal method is proposed.The introduction of Ti₃C₂T_x into Bi₂Te₃ nanosheets further optimizes the thermoelectric properties of Bi₂Te₃ materials,which is of great significance for improving the conversion efficiency of thermoelectric devices.