Electric double layer capacitor (EDLC) has gained much attention as a power source in electronic devices and hybrid electric vehicles, due to high power density, long cycle life, and long lifetime. Porous carbons have been extensively investigated as an electrode material for EDLC because of their high surface area wherein large amounts of electrolytes can be accumulated. Recently, an anomalous increase in the specific capacitance was observed for the carbon materials with pore diameters less than 1 nm. It was explained by the accumulation of desolvated electrolyte ions in the micropores. Furthermore, in an aqueous solution, it was reported that ultra-micropore of 0.5 nm was effective for high capacitance.

In this work, we investigated EDLC behavior of ultra-microporous carbon synthesized using ZSM-5 zeolite as a template. For the synthesis of the carbon, ZSM-5 zeolite was fully ion-exchanged with Ca²⁺ ion and acetylene was used as a carbon source. The embedded Ca²⁺ ions promoted the carbonization of acetylene at 500°C, leading to the pore-selective carbon deposition without external carbon layer. The resultant carbon reflected the morphology of the zeolite quite well. Furthermore, Ar sorption results showed that the carbon had ultra-micropores of 0.5 nm, corresponding to thickness of the zeolite pentasil layer. The electrochemical performances of the carbon were measured with a two-electrode cell in 6 M KOH. The cyclic voltammogram of the carbon had a quasi-rectangular shape, indicating capacitive behavior. In the galvanostatic charge/discharge experiment, the specific capacitance of the carbon was higher than that of commercial activated carbon, although the carbon has lower BET surface area. We attribute these results to the accumulation of desolvated electrolyte ions in the ultra-micro pores of 0.5 nm.