Electrical double-layer capacitance of the M, O2/O2− interfaces (M=Pt, Au, Pd, In2O3; O2−=zirconia-based electrolyte)

The behavior of the electrode systems M, O2/O2−, where M=porous Pd, Pt, Au, and dense In2O3; O2−=ZrO2-based single-crystal solid electrolyte, was studied by means of impedance measurements. The examination of the Pt, O2/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 YCPE=B(jω)n, may be related one to the other by B=(Cdl)n (RΩ)n−1,where Cdl is the double layer capacitance and RΩ the resistance of the electrolyte in the cell. Then Cdl of the electrode–electrolyte interface can be determined. The specific Cdl of the oxidized noble metals and india electrodes is nearly one order of magnitude lower than Cdl of the electrodes in the metallic state. The Cdl 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 Cdl behavior.