Development of Electro Supercapacitors

Abstract : Nonfluorinated proton conducting superionic molecular tunnel electrolytes (PSMTE) exhibiting high proton conductivity (approximately 10 exp-2 S/cm) have been synthesized. The highly hygroscopic nature of these polymers yielding deliquescent films has precluded their use in supercapacitors. Fluorinated analogs of these PSMTE's were synthesized to provide higher conductivity and greater hydrophobicity. Fluorinated PSMTE's exhibit higher conductivity than Nafion (1.3 x 10 exp-2 vs. 2.1 x 10 exp-4 S/cm) under identical conditions of relative humidity and temperature. Fluorinated PSMTE's show good film forming properties suitable for fabrication of supercapacitors. However, these materials have not yet been utilized in supercapacitors. Polymer films of aniline and its various derivatives having electron donating (-OCH3) and electron withdrawing groups (-SO3H, -NO2) were formed electrochemically using platinum and nickel substrates. These films were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electron withdrawing groups (-SO3H, -NO2) increased the voltage at which the redox reaction occurs for aniline. The electron donating groups (-OCH3) moved the redox potential in the negative direction. The monomers were also deposited on Nafion coated Pt. These films gave multiple oxidation-reductions peaks and better discharge characteristics as compared to films on bare Pt. They also exhibited electrochromic behavior. To demonstrate 'proof of concept,' different combinations of the polymers and Pt black were used as electrodes with a thin (0.001 in.) Nafion membrane to form a capacitor/battery. The capacity and the energy density were determined for the cells. The cells were able to pulse charge-discharge for times as low as 0.1 ms.