Activated carbon (AC) powder as an active electrode material and open-pore nickel foam as a current collector material were used for an electric double layer capacitor (EDLC) with an aqueous electrolyte of KOH mixture. The electrochemical characteristics of the EDLC being made of 3 cm by 3 cm electrode size were investigated by charge-discharge cycle tests, impedance analyzer and cyclic voltametry measurements. As a current collector, nickel foam with concave surface and many open-pore showed larger specific capacitance and lower impedance than that of nickel foil with a flat surface. As results from experiments, much improved specific capacitance of about 300 F/g at 40 mA/cm2 of discharge current density and fairly low specific ESR of 0.63 Ωcm2 at 1 kHz were obtained from the EDLC with the nickel foam current collector. The specific leakage current was measured as 0.18 mA/cm2 with respect to the apparent electrode area of the EDLC with nickel foam current collector.
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