Thermoelectric Behavior Of ZnO Based MWNTs/PVDF Composite Materials

Recently, CNTs/polymer composite thermoelectric materials have got more and moreattentions for their cheap manufacturing cost, non-toxic, good mechanics and thermometricperformances. Up to now, its figure of merit is still limited in0.02which impedes the widelycommercial use. To solve the problems, the researchers have used the way of combininglayers of n-type MWMTs with p-type MWNTs to construct new type compositethermoelectric material. And the composite thermoelectric material had taken benefits fromCNTs’ good quantum and interface effect, broadening the gaps of energy bands, changing thethermal conductivity efficient and then improving the thermal behavior. But there is still aproblem in practically utilizing. It is difficult to separate n-type MWNTs from p-typeMWNTs Thus, by using of n-type ZnO nanowire arrays replaces the n-type MWNTs, andPVDF is as insulation layer and NMP is decorating agent, we combine the MWNTs/PVDFcomposites with ZnO NW arrays to prepare a new ZnO base MWNTs/PVDF’s thermoelectricmaterial. In this thesis, the main experimental results are as below:(1) By using of hydrothermal method, aligned ZnO NW arrays were synthesized underdifferent ratios of demonized water and aqueous ammonia solution. The as-prepared sampleswere characterized by XRD, SEM and TEM, respectively. The results showed that the ZnONWs sample, which was prepared with15%ammonia solution concentration, had uniformdensity, good orientation of ZnO nanowire. It was chosen for substrate material to combinethe modified MWNTs to prepare a new ZnO base MWNTs/PVDF’s thermoelectric material.(2) This work studied MWNTs/PVDF samples which contain the percentages ofMWNTs are15,25,40and50, respectively. The micro-structure and morphology of thesamples were analyzed. Under the different temperature gradients, the short-circuit currentand open circuit voltage of the composite thermoelectric materials were studied. And thethermal electromotive force of different ZnO base MWNTs/PVDF thermoelectric material isanalyzed.(3) At a certain temperature gradient condition, p-type MWNTs provides with holes andn-ZnO brings electrons. When samples are provided with temperature differences, chargecarriers would migrate from the high temperature side to the low temperature side. As theMWNTs content increases in the composite thermoelectric material, the thermalelectromotive force and short circuit current also increases linearly. As the temperature difference is50degrees Celsius, the linked external load is200, the maximum outputpower of composite material, which contained MWNTs content is75%proportion, is125μW.This test value is larger than the reported data of MWNTs composite thermoelectric materialsin the literature. Our study also found that the output thermoelectric power will reach themaximum value as the thermal electromotive force is gradually close to the open-circuitcondition in the load is constant. And then, the output thermoelectric power will graduallydecrease.