Three-electrode current-voltage measurements on erbia stabilized bismuth oxide with co-pressed gold gauze electrodes

The polarization behaviour of (Bi₂O₃)_0.75(Er₂O₃)_0.25(BE25) with a co-pressed gold gauze electrode was studied as a function of temperature and oxygen partial pressure in a three electrode cell. The anodic polarization is smaller than the cathodic polarization. The cathodic charge transfer coefficient, α_c, is about 0.5 while the anodic one, α_a, is about 1.5. The exchange current density shows a (PO₂)¹² dependence for partial pressures below 1 atm with an activation enthalpy of ∼126 kJ mol⁻¹. These values compare well with results obtained from ¹⁸O exchange experiments. Current densities for the co-pressed gold gauze electrodes are about a factor of 5 to 10 larger than found for the previously reported porous sputtered gold electrodes. Analysis of the electrode impedance shows strong influence of surface diffusion on the electrode reaction, which must take place at the surface of the electrolyte.