Fabrication Of PEDOT Nanotube Arrays And Assembly Of High-rate Supercapacitors

Supercapacitors,also known as electrochemical capacitors,relies on fast ion adsorption(double layer mechanism)or rapid surface redox reaction(pseudo-capacitance mechanism)to store energy.Supercapacitor represents one of attractive energy storage devices in view of its high power density,good reversibility and long cycle life(>100000 times).As a highly conductive polymer,poly(3,4-ethylenedioxythiophene)(PEDOT)stores energy through fast ion adsorption at the electrode/electrolyte interfaces,but suffers from rather low specific capacitance.On the other hand,polyaniline exhibits very high specific capacitance.However,it is limited by the sluggish redox reactions.Thereby,integrating the highly conductive PANi with the highly conductive PEDOT to design a composite electrode having fast ion and electron transport capacity is of significance for developing flexible polymer-based supercapacitor.In the chapter III of this thesis,tubular PEDOT on textile carbon(TC)has been fabricated by constant voltage electrodeposition method to improve the contact area between electrode and electrolyte and shorten the transport path of ions and electrons.The ZnO nanowires grown on TCs serve as a sacrificial template.Electrochemical polymerization of 3,4-ethyl enedioxythiophene followed by template removal of ZnO nanowires yields a hybrid composed of PEDOT nanotubes which were vertically grown on TC(TC@PEDOT).When the deposition time is 10 min,the PEDOT loading is 2.9 mg cm-2.PEDOT nanotubes shows a coral structure on the TC substrate.The strong interfacial interaction between TC substrate and PEDOT nanotubes creats a three-dimensional conductive path,which remarkabley reduces the interface resistance between them and greatly improve the overall conductivity of the electrode(790 S m-1).More importantly,the tubular structure delivers a specific capacitance 184 F g-1 in 1.0 M H2SO4 electrolyte with 88%capacitance retention after 10000 cycles.A solid-state TC@PEDOT-based supercapacitor with PVA-H2SO4 as gel electrode exhibits a high-rate capability with a relaxation time constant(?0=0.96 s)very close to that in aqueous H2SO4 electrolyte(?0=0.87 s).Moreover,it can withstand various bending and twisting tests without notable performance loss.In order to further reduce the interface resistance and improve the rate performance and enhance the areal capacitance of PEDOT electrode,In chapter ?,the ZnO nanoroad grown on titanium foil(Ti)served as a sacrificial template.Electrochemical polymerization of 3,4-ethylenedioxythiophene followed by template removal of ZnO nanoroad yields a hybrid composed of PEDOT nanotubes vertically grown on Ti(Ti@PEDOT).Polyaniline(PANi)nanofibers were coated on the surface of Ti@PEDOT by electrochemical polymerization to obtain titanium foil/PEDOT-PANi composite electrode(Ti@PEDOT-PANi).The as-prepared Ti@PEDOT nanotube arrays offer a three-dimensionally conductive network.Such arrays have been successfully connected with each other through the uniform coating of PANi onto the surface,thus contributing a substantial pseudocapacitance.the Ti@PEDOT-PANi hybrid electrode delivers a nearly 9 times enhancement of areal capacitance(2876 mF cm-2 at 5 mA cm-2)together with a remarkable rate performance(85%capacitance retention at 100 mA cm-2).Moreover,a flexible supercapacitor assembled with the Ti@PEDOT-PANi electrode also exhibits a high-rate property with a relaxation time constant as small as 0.83 s(?0=0.83 s)and a volumetric energy density of 15.9 mWh cm-3 under the power density of 178.9 mW cm-3.The cycling stability of such a device is also remarkable,indicating the great advantages of the Ti@PEDOT-PANi electrode.More gratifying,such device can endure continuous bending at a maximum angle of 145° for 200 cycles.The above results show that the high-capacity and high-rate polymer-based energy storage device has a broad application prospect.