| The research for this MSc thesis focuses on creating a supercapacitor using hybrid conducting polymer/polyoxometalate materials. The interest in supercapacitors comes from their possible use in devices that require transient and high power input such as electromagnetic projectiles, high intensity lasers, and denial and blinding apparatus in RF/electronic warfare. Current capacitors lack the high energy storage density needed to power such devices. A high power density device, a supercapacitor, coupled with a battery or fuel cell for high energy density could fill the necessary power supply role. At the electrode surface there are two contributions to the charge storage capability of the material, the Guoy-Chapmann and Stern-Geary electrochemical double layer (ECDL) and redox pseudocapacitance. The electrochemical double layer (ECDL) involves a diffuse layer of charge that surrounds the electrode due to electrostatic attraction. Pseudocapacitance relies on the reduction/oxidation of electroactive species on the surface of the electrode to build up charge and can store ten times as much charge as the double layer.;The energy stored in a capacitor is proportional to its potential window. Capacitors with asymmetric designs offer a wider potential window than symmetric devices. That is, in the asymmetric case, both electrodes are different material with different electrochemical stabilities that complement each other. For a negative electrode, poly(3,4-ethylenedioxythiophene) was polymerized electrochemically onto carbon paper using phosphotungstic acid as a dopant. With a PPy(PMA) on carbon paper as a positive electrode and Nafion soaked in sulfuric acid, a supercapacitor was assembled. From this configuration, a energy density, power density and capacitance of 4 Wh/kg, 103 W/kg, and 31 F/g, respectively, was obtained.;One option for improving the performance characteristics for a capacitor is to create an open, porous microstructure in the polymer films which increases the ionic conductivity over uniform films. Using pyrrole (Py) with phosphomolybdic acid (PMA), as the oxidizing agent and dopant, allowed for in situ polymerization of the monomer. Sodium sulphate was used as a porogen and was introduced to the solution prior to casting of the film. It was later leeched out in water and micrometer sized pores were observed in the film by scanning electron microscopy. Polypyrrole(PMA) films made with 2 mg/ml of Na2SO4 displayed high ionic conductivity of 121 muS/cm and could be cycled up to 20 V/s in 0.5 M H2SO4. |
