| Thermoelectric (TE) materials, as a novel energy material, has become a focus ofattention in the domain of science due to the badly need of energy. Bi2Te3basedthermoelectric material has become the superior one at room temperature because itshighest ZT can arrive at1due to its high Seebeck coeffiency and low thermalconductivity. Graphene, a flat monolayer of sp2-bonded two-dimensional (2D) carbonatoms, has received a great attention since its first exploratory reports. Someresearchers even speculate that the presence of graphene could improve the electricconductivity of the graphene-related composites by introducing extra electronictransmission channels. Based on this speculation, it is highly possible to combinedgraphene with thermoelectric materials to improve the electrical conductivity.However, up to now, there are only a few reports on utilizing graphene inthermoelectric materials as a composite additive. Currently, some researchers hasdone research on Bi2Te3/graphene through physic methods of which the ZT is only0.3.To prove its weakness, we suppose to fabricate Bi2Te3/graphene composite throughchemical methods.In this research, the high Seebeck coeffiency Bi2Te3compounds were selected toform composites in nano-scale range with high carrier mobility graphene, aiming tocombine both the two desirable features to boost the TE power factor, and also todecrease thermal conductivity by nanostructuring. We have explored the possibilityand process parameters of synthesizing Bi2Te3/graphene nanocomposites by utilizinga facile and novel one-pot low temperature wet chemical method. The detailedformation mechanism of such Bi2Te3/graphene nanocomposites is described here. Wehave also explored the densification process of the composites and afterwardsprovided a systematic evaluation of their phase composition, microstructure and TEtransport properties. The main conclusions are listed as below:Using the commercial graphene oxide nanosheets as the precursor, theBi2Te3/graphene composite was synthesized by a one-pot chemical method. FESEMand TEM measurements indicate that Bi2Te3nanoplates with thick of10~30nm are uniformly anchored on the surface of graphene. Graphene oxide is both thedispersants and the two-dimensional adsorption templates of cationic in the synthesisprocess. When the Bi3+ions are added into the graphene oxide solutions in advance,they react with the graphene oxide, and form a kind of Bi2O3compound. Thiscompound enables the Bi3+ions to be placed uniformly on the graphene oxide.Following the addition of N2H3·H2O, Bi2TeO5was formed immediately, and thenreacted into Bi2Te3slowly, when GO is also reduced to graphene, finally graphenesheets loaded with Bi2Te3self-assemble into layered Bi2Te3/graphene hybridnanostructure by confining Bi2Te3nanoparticles in between the reduced graphenesheets due to the hydrophobic nature of graphene. By adjusting the reaction processconditions, we could modify the Bi2Te3particles and the quality of graphene.Followed by the reduction of heat treatment and PAS sintering technique, we can gethighly condensed bulk materials.The microstructure and thermoelectric performance of n-type Bi2Te2.75Se0.15/G-ycomposite were studied systematically: the microstructure analysis showed that afterthe compositing, the Bi2Te3grain growth is greatly restrained. With the increase of y,the carrier mobility increased largerly and the thermal conductivity decreased largelydue to the high interfacial area concentration and inhibition effect to Bi2Te3particalgrowth because of the existence of graphene, which contribute to the largeimprovement of ite thermoelectric properties. For y=1%, the maximum ZT value of0.73is obtained, which is1.4times that of the bare sample. |
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