Electrochemical Characterization of Double Layer Capacitors Based on Nafion Electrolyte

The goal of present work is to verify the possibility that an ionomer solution of Nafion may be efficiently used in the preparation of polymer electrolyte membranes and carbon composite electrodes for all solid double layer capacitors (DLCs). The membranes were prepared by a casting procedure starting from the Nafion solution. The electrodes were obtained spreading a carbon-Nafion ink on a carbon paper substrate by a printing method. The Nafion solution used in carbon based electrode preparation, has a double function of binding and proton conducting material. Three different electrolyte separators were investigated in capacitor configuration: a commercial Nafion 115, a Nafion membrane prepared by a recasting method and a porous glass fiber matrix impregnated with a 1 M H2SO4 solution. The membrane and electrodes assemblies (MEA) had thicknesses of 0.6-0.8 mm and active geometric area of 4 cm2. The performances of the investigated DLCs were evaluated by cyclic voltammetry (CV), DC charge-discharge (CCD) measurements and electrochemical impedance spectroscopy (EIS). Proton conductivity values of 5.7?10-2 and 3.1?10-2 S?cm-1 were obtained at room temperature with Nafion 115 and recast Nafion membrane respectively. The related value recorded with the acid impregnated porous matrix was 2?10-1 S?cm-1. A specific capacitance of 13.2 F/g was obtained by the capacitor using the Nafion recast membrane and electrodes containing carbon with a specific surface area of 1500 m-2 g-1. This value is 70% of specific capacitance obtained with the capacitor using sulfuric acid and about 140% of that of Nafion 115. Further studies are in progress in the perspective of an optimisation of polymer electrolyte membranes, electrode preparation as well as in the build up of a DLC with enhanced performance.