Abstract
In this paper, a solvent vapor-induced phase separation (SVIPS) technique was used to create a porous structure in polyvinylidene fluoride/Multi-walled carbon nanotube (PVDF/MWNTs) composites with the aim of increasing the electrical conductivity through the incorporation of MWNTs while retaining a low thermal conductivity. By using the dimethylformamide/acetone mixture, porous networks could be generated in the PVDF/MWNTs composites upon the rapid volatilization of acetone. The electrical conductivity was gradually enhanced by the addition of MWNTs. At the same time, the thermal conductivity of the PVDF film could be retained at 0.1546 W·m−1·K−1 due to the porous structure being even by loaded with a high content of MWNTs (i.e., 15 wt.%). Thus, the Seebeck coefficient, power factor and figure of merit (ZT) were subsequently improved with maximum values of 324.45 μV/K, 1.679 μW·m−1·K−2, and 3.3 × 10−3, respectively. The microstructures, thermal properties, and thermoelectric properties of the porous PVDF/MWNTs composites were studied. It was found that the enhancement of thermoelectric properties would be attributed to the oxidation of MWNTs and the porous structure of the composites. The decrease of thermal conductivity and the increase of Seebeck coefficient were induced by the phonon scattering and energy-filtering effect. The proposed method was found to be facile and effective in creating a positive effect on the thermoelectric properties of composites.
Highlights
Converting waste heat to electricity via thermoelectric (TE) materials is an important means of developing green sustainable energy
The scanning electron microscopy (SEM) images clearly depict the distribution of MWNTs structure that showed particles of ca. 2 μm in diameter (Figure 1b)
Our results showed good the polyvinylidene fluoride (PVDF)/MWNTs composites an MWNT
Summary
Converting waste heat to electricity via thermoelectric (TE) materials is an important means of developing green sustainable energy. Chen et al reported that carbon nanotubes with porous structures possess superlow thermal conductivity and high Seebeck coefficient due to the porous boundary conducting energy-filtering [11]. This energy-filtering effect strongly increases the scattering effect of low-energy carriers, while the high-energy counterparts are unaffected [12]. N-type flexible thermoelectric fabrics based on Bi2 Se3 nanoplate/PVDF composites were prepared and the composites exhibited a high Seebeck coefficient (−80 μV/K), high electrical conductivity (5100 S/m), low thermal conductivity (0.42 W·m−1 ·K−1 ) and an estimated ZT value of 0.02 [28]. An improvement in the thermoelectric properties was successfully demonstrated in the porous PVDF/MWNTs composites
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