Flexible N-Type Thermoelectric Composites Based on Non-Conductive Polymer with Innovative Bi2Se3-CNT Hybrid Nanostructured Filler

Abstract

This research is devoted to the fabrication of polyvinyl alcohol (PVOH) based n-type thermoelectric composites with innovative hybrid bismuth selenide-multiwalled carbon nanotube (Bi2Se3-MWCNT) fillers for application in flexible thermoelectric devices. Hybrid fillers were synthesized by direct deposition of Bi2Se3 on multiwalled carbon nanotubes using a physical vapor deposition method, thus ensuring direct electrical contact between the carbon nanotubes and Bi2Se3. The Seebeck coefficient of prepared PVOH/Bi2Se3-MWCNT composites was found to be comparable with that for the Bi2Se3 thin films, reaching −100 µV·K−1 for the composite with 30 wt.% filler, and fluctuations of the resistance of these composites did not exceed 1% during 100 repetitive bending cycles down to 10 mm radius, indicating the good mechanical durability of these composites and proving their high potential for application in flexible thermoelectrics. In addition, other properties of the fabricated composites that are important for the use of polymer-based materials such as thermal stability, storage modulus and linear coefficient of thermal expansion were found to be improved in comparison with the neat PVOH.

Highly Efficient Flexible n‐Type Thermoelectric Films Formed by Encapsulation of Bi2Se3‐MWCNT Hybrid Networks in Polyvinyl Alcohol

“…Rapid increase of the resistance of the encapsulated Bi 2 Se 3 -MWCNT hybrid network during the first 20 bending cycles, followed by its stabilization at constant level is similar to the bending behavior reported for the PVOH/Bi 2 Se 3 -MWCNT composites prepared by mechanical mixing, [17] and may be explained by the change of the orientation of PVOH macromolecules in the direction of tensile stress during the first 20 cycles. However, the relative resistance changes of the encapsulated Bi 2 Se 3 -MWCNT hybrid networks during the repetitive bending down to 3 mm is 50 times smaller in comparison with the mixed composites (0.5% vs 25% [17] ). Significant improvement of the electrical stability of the PVOH-Ag-Bi 2 Se 3 -MWCNT hybrid networks in comparison with the mixed PVOH/Bi 2 Se 3 -MWCNT composites may be explained by much lower density of the TE network in the mixed composites.…”

“…It was experimentally realized that due to the hydrophobic properties of the MWCNTs and freshly synthesized Bi 2 Se 3 , the best binders for successful encapsulation and lift-off of Bi 2 Se 3 -MWCNT hybrid structures are water-soluble polymers, such as PVOH. [15,17] For the encapsulation of as-grown at the glass substrate Bi 2 Se 3 -MWCNT hybrid network, the PVOH solution was uniformly applied over the network by drop-casting method (Figure 2). After drying, the encapsulated in the PVOH Bi 2 Se 3 -MWCNT hybrid network was easily lifted off the glass substrate using scalpel.…”

“…Figure 5b shows the Seebeck coefficients and resistances of the Bi 2 Se 3 -MWCNT hybrid structures varied from 1.5 to 6.5 wt% amount of MWCNTs at atmospheric conditions before (hollow circles and triangles) and after (filled circles and triangles) [17] and PVOH/Bi 2 Te 3 mixed composites [26] . Mixed PVOH/Bi 2 Se 3 -MWCNT (30 wt% filler) [17] −100 ± 4 4.8 ± 1.5 0.0025 ± 0.0011 194 ± 1 0.043 ± 0.03…”

“…The simplicity of fabrication and storage of such bismuth selenide-multiwalled carbon nanotubes (Bi 2 Se 3 -MWCNT) networks made them perspective for application in innovative n-type flexible TE composites, based on non-conductive environmentally friendly and stable polymers: application of Bi 2 Se 3 -MWCNT hybrid structures as filler for polyvinyl alcohol (PVOH) resulted in obtaining of flexible n-type TE films with S up to −100 μV K −1 , but relatively low PF (2.5 nW m −1 K −2 ) due to the low electrical conductivity. [17] In this study, to increase the TE efficiency of resulting n-type flexible thermoelectric films, the mixing approach is replaced with a novel technique of encapsulation of as-grown n-type Bi 2 Se 3 -MWCNT hybrid networks in PVOH polymer matrix without the destruction of the interconnects established in Bi 2 Se 3 -MWCNT hybrid network.…”

Nonlinear Thermopower Behaviour of N-Type Carbon Nanofibres and Their Melt Mixed Polypropylene Composites

“…Moreover, inorganic/organic hybrids, consisting of those electrically conductive polymers and inorganic TE materials, have also attracted great interest [8,9]. However, these type of compounds have not yet provided zTs higher than those obtained only with inorganic materials due to the random dispersion of the latter ones in the CPs, as well as the existing divergence of their Fermi energy levels (E F ) [10]. Moreover, the processing in the melt state is more environmentally friendly than in solution as it permits the production of large material volumes with existing equipment and prevents the need of using solvents [11].…”