The behavior of the electrode systems M, O-2/O2-, where M = porous Pd, Pt, Au, and dense Ln(2)O(3); O2- = ZrO2-based single-crystal solid electrolyte, was studied by means of impedance measurements. The examination of the Pt, O-2/O2-electrode system showed that the constant phase element (CPE) can be attributed to a nonuniform distribution of current on the electrode surface. It was inferred that the CPE parameters n and B in the expression Y-CPE = B(j omega)(n), may be related one to the other by B = (C-dl)(n) (R-Omega)(n-1),where C-dl is the double layer capacitance and R-Omega the resistance of the electrolyte in the cell. Then C-dl of the electrode-electrolyte interface can be determined. The specific C-dl of the oxidized noble metals and india electrodes is nearly one order of magnitude lower than C-dl of the electrodes in the metallic state. The C-dl value of all the electrodes studied depends little or is independent of temperature and oxygen pressure. It was concluded that the Helmholtz model of a double-layer structure does not contradict the C-dl behavior.