Preparation And Mechanism Of Bismuth Telluride/Cellulose Fiber Composite Paper-based Thermoelectric Materials

With the increasing consumption of non-renewable fossil energy,the energy and environmental problems caused by it have become increasingly serious.Thermoelectric materials are a class of functional materials that directly convert thermal energy into electrical energy through carrier transport,providing a unique solution for sustainable power supply.Great progress has been made in the research of traditional inorganic thermoelectric materials,but its rigidity and brittleness make it difficult to achieve ideal contact with the heat source of complex shape,which limits its large-scale application.In recent years,nanocomposites provide a new direction for the further development of traditional thermoelectric materials.In this paper,bacterial nanocellulose was used as a surfactant to disperse Bi₂Te₃ to prepare a uniform and stable Bi₂Te₃/bacterial nanocellulose composite thermoelectric material,and its thermoelectric properties were studied.The flexible thermoelectric devices were constructed by the combination of Bi₂Te₃/bacterial nanocellulose composite thermoelectric material and paper substrate by Z-direction infiltration and surface coating,respectively.The output properties were studied,and the mechanism of Bi₂Te₃/bacterial nanocellulose binding and its infiltration mechanism in paper substrates were clarified.The main results are as follows:?1?A high-performance Bi₂Te₃/bacterial nanocellulose composite thermoelectric ink was prepared by using TEMPO oxidation-treated bacterial nanocellulose and high Seebeck coefficient Bi₂Te₃ powder.Bacterial nanocellulose contributes to the uniform and stable dispersion of Bi₂Te₃ particles.Bi₂Te₃/bacterial nanocellulose composite ink has excellent thermoelectric properties.When the bacterial nanocellulose content was 1 wt.%,its electrical conductivity was 90.91 S/cm and thermal conductivity was 0.3 W/m K.The Seebeck coefficients of P-and N-type composite materials were 63.3 ?V/K and-33.8 ?V/K.?2?The base paper substrate with different tightnesses was fabricated by using softwood pulp fiber.The paper-based flexible thermoelectric device was constructed by Z-penetration and surface coating methods with Bi₂Te₃/bacterial nanocellulose thermoelectric ink.Among them,the open circuit voltage and the maximum output power of the transparent paper-based thermoelectric generator with five thermoelectric units were 22.34 m V and 174.62 n W respectively at temperature difference of 60 K;the Bi₂Te₃/bacterial nanocellulose-coated flat paper-based thermoelectric device has an open circuit voltage of 34.65 m V and a maximum output power of 561.34 n W.Paper-based thermoelectric devices have excellent flexibility and mechanical stability.After a bending radius of 20 mm and a bending cycle of 1,000 times,the internal resistance of both thermoelectric devices changes less than 10%.?3?The surface morphology and element distribution of Bi₂Te₃/bacterial nanocellulose paper-based thermoelectric materials were observed by SEM,micro-CT and X-ray photoelectron spectroscopy.For Bi₂Te₃/bacterial nanocellulose,bacterial nanocellulose forms a thin film-like three-dimensional network structure during the drying process.These cellulose networks are distributed in the Bi₂Te₃ particles and are closely combined to form a good conductive interconnection between thermoelectric particles.For Bi₂Te₃/bacterial nanocellulose paper-based thermoelectric materials,pulp fibers are intertwined to form a threedimensional network skeleton,and Bi₂Te₃ particles are uniformly distributed in the fiber skeleton.The mechanical retention of the fiber network and the hydrogen bonding of cellulose produce a synergistic effect that allows Bi₂Te₃ particles to be uniformly distributed in the fiber network.Bi₂Te₃/bacterial nanocellulose thermoelectric ink forms an effective thermoelectric connection inside the paper through capillary action.