Carbon nanofiber and PEDOT-PSS bilayer systems as electrodes for symmetric and asymmetric electrochemical capacitor cells

In this work, we describe the fabrication of electrodes based on carbon nanofibers (NFC), bilayer systems of NFC and a commercial polythiophene (PEDOT-PSS), and NFC/PEDOT-PSS composites, for symmetric and asymmetric electrochemical capacitor (EC) cells. The basic electrochemical characterization was carried out for each electrode material by cyclic voltammetry (CV) using a three-electrode cell and a non-aqueous electrolyte (1 M LiCIO4 in acetonitrile). We assembled two-electrode cells using Swagelok cells with filter paper as the electrode separator with only the best electrode materials (NFC, and bilayer electrodes), and they were electrochemically characterized by CV to determine the working voltage window, and galvanostatic cycling to evaluate the cycle-life of the symmetric (NFC--NFC, NFCP--NFCP) and asymmetric (NFC--NFCP) cell assemblies. Capacitance values were normalized by electrode area and calculated from galvanostatic cycling experiments. We discuss the influence of PEDOT-PSS as a dispersing agent for NFCs and as an electrical conductivity enhancer. Also, we found that the asymmetric cell configuration doubled the capacity in comparison to NFCs symmetric cells, and the cycle-life was compared to the symmetric cell assembled with bilayered electrodes. (C) 2006 Elsevier B.V. All rights reserved.