Capacitance enhancement of carbon fabric electrodes in electrochemical capacitors through electrodeposition with copper

Electrodeposition of copper on activated carbon fabric was conducted in an attempt to promote the capacitance of the carbon fabric employed as electrodes in electrochemical capacitors using KOH solutions as the electrolyte. The deposition was conducted in CuSO4 for different lengths of time at a current density of 0.25 mA cm(-2), and this was followed by thermal oxidation that was found to be essential for capacitance enhancement. The capacitance was shown to increase with the degree of deposition and passed through a maximum at a deposition time of 4 h, at which a Cu content of ca. 6 wt % with a capacitance enhancement of ca. 40%, e. g., from 114 to 163 F g(-1), was achieved. The capacitance enhancement may partially result from the reversible redox transitions of Cu in the presence of OH- ions. The Cu-deposited fabrics exhibited an increase in capacitance at the early stage of charge-discharge cycling. Cyclic voltammetric measurements suggest that the capacitance increase may result from the formation of surface complexes that serve as centers for reversible redox reactions. The deposition with Cu resulted in the reduction of electrode resistance, while the leakage current was found to increase upon deposition. The results of the present study have provided a simple and economical means that can substantially enhance the capacitance of carbonaceous electrodes. (C) 2002 The Electrochemical Society.