Bi2Te3-그래핀 복합체의 열전특성에 대한 연구

Abstract

Thermoelectric energy conversion has attracted immense attention for its wide applications from energy harvesting to electronic cooling. The efficiency of thermoelectric devices depends on the performances of thermoelectric materials, which is expressed as ZT (, where S is the Seebeck coefficient, is the electrical conductivity, T is the absolute temperature, and is the thermal conductivity). Among numerous materials, Bi2Te3-based compounds have been the most commercialized thermoelectric materials at near-room-temperature since the birth of modern thermoelectrics by Goldsmidin 1954. There have been numerous approaches for enhancing ZTs of the Bi2Te3-based compounds, and they can be briefly categorized in to two groups. One is the enhancement of power factor() by alloying and/or doping of other elements, and the other is the reduction of lattice thermal conductivity by introducing phonon scattering centers such as point defects, nanoinclusions, grain boundaries, dislocation arrays, and so on. Significant advances of ZT have been achieved in Bi2Te3-based compounds through these approaches and the highest ZT of 1.87 has been successfully realized in nanostructured p-type bismuth antimony telluride (BST) compounds prepared by melt-spinning. For n-type compounds, the highest ZT of 1.23 has been achieved in solvothermally synthesized bismuth telluride selenide (BTS) nanocomposites. Meanwhile, a hybrid strategy of graphene and thermoelectric materials has recently been proposed for enhancing ZT. Graphene-hybrid materials have been adapted in various fields of energy applications, such as super capacitor, Li-ion battery, photocatalyst, and so on, however, it is still at an early stage in thermoelectric research despite its huge potential. In literature, there have been numerous reports on the enhancement of electrical conductivity in graphene-hybrid materials through the percolated graphene network. Furthermore, we observed that the hybrid composite could exhibit single-crystalline electrical conductivity through the alleviation of grain boundary scattering even in nanocomposites if the matrix material had a proper band alignment with graphene. In addition, this graphene-hybrid strategy has a beneficial effect on thermoelectric materials in terms of thermal conductivity. Remarkable reduction in lattice thermal conductivity caused by the incorporation of graphene has been demonstrated in diverse material systems, such as oxides, chalcogenides, and skutterudites, even though graphene has an extremely high intrinsic thermal conductivity. Herein, we report the thermoelectric transport properties of p-type BST-reduced graphene oxide (rGO) and n-type BTS-rGO composites. The interface-controlled composites were prepared by the consolidation of BST-rGO and BTS-rGO hybrid powders using spark plasma sintering (SPS), which could result in the in situ reduction of GO into rGO (Fig. 1). In the both hybrid composites, the mobility was suppressed by the improper band alignment between the matrix and rGO and it led to the decrease in the power factor. However, this disadvantage could be compensated by significantly reduced lattice thermal conductivity due to the rGO network formed at the grain boundaries. Although we could not achieve the enhancement of ZT in the hybrid composites, these findings on the effects of interface control using rGO will be useful for developing thermoelectric materials with high ZTs based on the proposed hybrid strategy.