The equivalent circuit for the electrical double layer

An aperiodic equivalent electrical circuit for the electrical double layer at the interface between an electrode and a dilute electrolyte solution is derived. After account has been taken of small changes in electrolyte concentration near the electrode surface when the potential is slightly varied, the circuit contains resistive as well as reactive components. The apparent differential capacity obtained by measuring the a.c. impedance of the interface may differ from the zero frequency value of the capacity if the electrolyte concentration is small. A method for the determination of surface excesses of ionic components is suggested.