Preparation And Properties Of Conductive Polymer-Based Supercapacitor Electrode Materials

Supercapacitor has become an important electrochemical energy storage element due to its high power density and good safety.It’s vital to design the electrode materials for supercapacitors,which directly determines the overall performance of supercapacitors.Among many electrode materials,conductive polymers have become important research objects because of their unique advantages of good capacitance performance,low cost,and high mechanical flexibility.Heteropolyacid is a kind of metal-oxygen cluster compound with unique structure and rich physicochemical properties.It’s a good choice to modify conductive polymer,which has excellent redox properties.In this thesis,from the perspective for improving the pseudocapacitance of electrode materials,two typical heteropolyacid phosphomolybdic acid(PMo12)and phosphotungstic acid(PW12)are used as electroactive components,and a series of polypyrroles are prepared by chemical oxidation.In addition,from the perspective of improving the electrochemical performance of the electrode material,the metal organic framework(ZIF-67)/polyaniline(PANI)composite electrode was prepared by using ZIF-67 with large specific surface area,high porosity and strong structural adjustability.The main research contents and conclusions are as follows:PMo12/PPy and PMo12/TSA/PPy composite electrodes with spherical microstructure were prepared by simple chemical oxidation polymerization using PMo12 with unique redox activity as a multifunctional dopant and TSA as a co-dopant.The materials were characterized by scanning electron microscope(SEM),transmission electron microscope(TEM),electron spin resonance(ESR),Raman spectrometer(Raman)and other testing techniques.In lmol/L sulfuric acid(H2SO4)electrolyte,the electrochemical performance of PPy composite electrode materials were carried out by cyclic voltammetry(CV),constant current charge and discharge(GCD),alternating current impedance(EIS)and other electrochemical tests.The results exhibited that the introduction of PMo12 is good for obvious Faraday pseudocapacitive behavior and form a more regular nano-microsphere structure for the composites.The diameter of the composite can be controlled in the range of 100～120 nm.Compared with pure PPy,PMo12/PPy and PMo12/TSA/PPy composite electrode materials provided more excellent superelectric performance.When the molar ratio of TSA:pyrrole was 0.5:1,the specific capacitance of PPymicrospheres can reach 400 F g-1,which was more than 3 time of pure PPy.PMo12-xWx formed by PMo12 and PW12 was used as oxidant and redox dopant,through simple chemical oxidation method,the polymerization of pyrrole monomers were initiated,and PPy nanospheres were successfully assembled on the surface of MWNTs.The obtained PMo12-xWx/PPy/MWNTs(MPNs)composite exhibit a unique core-shell structure,high doping level and strong redox activity,which were very beneficial to the diffusion of electrolyte ions and the transfer of electrons.The results exhibited that the specific capacitance of MPNs(409～570 F g-1 at current density 1 A g-1)are significantly higher than that of pure PPy(145 F g-1).For MPNs composites,the specific capacitance of MPN10(the mass ratio of MWNTs to pyrrole monomer 10:90)could reach 570 F g-1,which are about 4 times than that of pure PPy.In addition,in a typical two-electrode symmetrical system with MPN10 as the symmetric electrode and PVA-H2SO4 gel as the solid electrolyte,the specific capacitance and areal capacitance of the supercapacitor device were 93.3 F g-1 and 466.3 mF cm-2,respectively.The capacitance retention rate can reach 90.2%after 2000 cycles,indicating good cyclic stability.MPNs electrode materials have shown great potential application in the field of supercapacitors.In order to further improve the specific surface area of the electrode,ZIF-67/PANI nanocomposites were prepared considering the excellent pore characteristics,high specific surface area and adjustable microstructure of ZIF-67.Hydrochloric acid(HCl)was used as dopant.The results revealed that the PANI chains evenly coat on the surface of ZIF-67,and the isolated ZIF-67 crystals are connected to each other.The ZIF-67/PANI composite exhibited a loose and porous structure.When the mass ratio of ZIF-67 to aniline monomer was 30%:70%,the 30%PZ showed good electrochemical performance.Then by changing the molar ratio of CoNO3·6H2O and 2-methylimidazole,the electrochemical performance of the composite material was further improved.When the molar ratio of CoNO3·6H2O to 2-methylimidazole was 1:8,the specific capacitance of the electrode material can reach 565 F g-1,which is much higher than PANI(289 F g-1 at current density 1 A g-1).