Preparation And Thermoelectric Properties Of Doped Polyaniline-nanocarbon Composites

Thermoelectric (TE) materials can achieve directly heat conversion intoelectricity, which has potential applications in the field of thermoelectric powergeneration and refrigeration technology. Compared with inorganic semiconductormaterials, conducting polymers with delocalized π-electron conjugated possessunique features for application as TE materials because of their wealth structure ofelectronic band, low density, low cost, easy synthesis, and facile processing intoversatile form. Furthermore, polymers inherently possess a low thermal conductivity,which offers them a significant advantage over conventional inorganicthermoelectric materials. However, poor electrical transport properties of polymers,including low electrical conductivity and low Seebeck coefficient, which haveexcluded them as feasible candidates for thermoelectric materials in the past. So it isurgent to find an effective way to improve the electrical transport properties ofconducting polymers.This thesis focused on the preparation and thermoelectricproperties of doped polyaniline and nanocarbon-polyaniline nanocomposites. Theirmechanisms of electrical and thermal transport were also discussed.The structures of polyaniline doped with organic-inorganic hybrid acid werecharacterized and their thermoelectric properties were investigated. XRD analysisshowed that polyaniline doped with appropriate ratio of mixed acid had highercrystallinity than eigenstates polyaniline. SEM also showed that the mixed acid withappropriate ratio could improve the regularity of the molecular chain. The ZT valueof polyaniline doped with SSA-HCl and SSA-H2SO4increases with increasingtemperature and more stable than that of doped with a single acid at highertemperature.The PANi/GNs composites prepared through an in situ polymerization werecharacterized and their thermoelectric performances were evaluated. Theconductivity of PANi/GNs composites decreased but the Seebeck coefficientincreased with increasing temperature. The conductivity and Seebeck coefficient ofPANi/GNs first increased and then decreased with the increasing the percentage ofGNs, while the ZT value increased with the increasing the percentage of GNs. Thepolyaniline grew along the surface of GNs due to π-π interactions between PANi andGNs forming a more extended chain structure during the polymerization process.The electrical conductivity and Seebeck coefficient of PANi/GNs nanocompositeswere higher than that of pure PANi, which could be attributed to the enhancedcarrier mobility in the ordered chain structures of the PANi. The thermal conductivities of the composites, even with high CNTs content, do not change muchand still keep very low values, which is attributed to the phonon scattering effect ofnanointerfaces produced by the PANi/GNs nanostructure.The PANi/GNs composites prepared through mechanical milling werecharacterized and their thermoelectric performances were evaluated. Theconductivity of PANi/GNs composites were almost no change with temperature, butsignificantly increased with the increasing content GNs. Seebeck coefficientincreases with increasing temperature, and no significant effect of GNs content onthe Seebeck coefficient PANi/GNs. Thermal conductivity decreases with increasingtemperature. When adding a small amount of La(NO3)3in PANi/GNs composite, thethermoelectric properties of the PANi/GNs can be further improved.Being network structure CNTs can also be connected to polyaniline chains andenhanced electrical transport.The PANi/GNs/CNTs composites prepared by in situpolymerization were characterized and their thermoelectric performances wereevaluated. The polyaniline grew along the surface of GNs due to π-π interactionsamong PANi, CNTs and GNs forming a more extended chain structure during thepolymerization process. The electrical conductivity and Seebeck coefficient ofPANi/GNs/CNTs nanocomposites were higher than those of pure PANi, which couldbe attributed to the enhanced carrier mobility in the ordered chain structures of thePANi. With the same mass10wt%, ZT value of the composite with the appropriateproportion of CNTs and GNs is larger than that of adding single CNTs. This isbecause GNs can significantly improve electrical conductivity, and more conductivenetwork structures are formed by the addition of CNTs in the composite. Thethermal conductivity of the composites can be further reduced by the scatteringeffect. The incorporation of CNTs can effectively increase the Seebeck coefficientand decrease thermal conductivity by adjusting the ratio of CNTs and GNs when theadded mass up to30wt%. The PANi/GNs/CNTs composites prepared throughmechanical milling were characterized and their thermoelectric performances wereevaluated. The thermoelectric performance of PANi/GNs composites can beimproved by adding an appropriate amount of CNTs. The conductivities of thecomposites can be improved, while their thermal conductivities can be reduced byadjusting the amount of CNTs, which is attributed to the increased phonon scatteringproduced by adding an appropriate amount of CNTs. Therefore, the thermoelectricproperties of iPANi/GNs composite materials can be further improved by exploitingsynergies effect of CNTs and GNs.