Double Layer Capacitance and Charging Rate of Ultramicroporous Carbon Electrodes

Abstract

Adsorption of ions from aqueous solutions into pores, as narrow as 3.7Å was observed, using linear sweep cyclic voltametry. The conductivity of the solution in pores of less than 7Å diameter is several orders of magnitude lower than that of a free solution in contact with the carbon electrode. It seems negligibly slow in pores of less than 3.7Å diameter, which are still completely filled with water. Highly oxidized ultramicroporous carbons show much lower double layer capacitance at positive potentials than nonporous carbon surfaces. This is interpreted as repulsive ion‐dipole interaction of the anion with the dipole of the chemisorbed oxygen. Ions can penetrate the tiny pores after depletion of the hydration sheath. The double layer charging rate is therefore much slower if is replaced by . A brief discussion is presented in order to confirm that the electroactive surface groups can be treated in terms of (capacitative) double layer charging.