Manganese dioxide/exfoliated graphite composite as materials for electrochemical capacitor was synthesized using a redox reaction. The synthesized product was characterized using thermogravimetric analysis, nitrogen adsorption-desorption (BET) method, and X-ray diffraction. Electrochemical characterization was performed by cyclic voltammetry using a three-electrode setup and also by constant current charge-discharge method. Aqueous Na₂SO₄, NaCl, KCl and KNO₃ solutions were used as electrolytes. The results showed that the structure of manganese dioxide in composite was amorphous and the exfoliated graphite (EG) functioned to give good conductivity. The capacitances of the manganese dioxide increased with increasing amount of EG, while the BET surface area of the composites decreased. The electrochemical behavior of the MnO₂/EG composite electrode in different electrolytes suggested that cation species mainly affect the electrochemical performance. The charge from the accessible total sites (Q_T) and the apparent charge in Na^＋-containing electrolyte are larger than those in K^＋-containing electrolytes while a good current response could be found in K^＋-containing electrolytes due to their different hydration number, hydrated radius and ion conductivity. The optimized sample, MnO₂/EG24, exhibited a specific capacitance of around 220 F/g in 1 mol/L Na₂SO₄ solution at 2 mV/s scan rate with a good cycleability.

Key words: manganese dioxide, exfoliated graphite, composite, electrochemical capacitor