Studying the O2, metal/O2- (solid electrolyte) electrode system with use of model electrodes: The exchange current density determination

Cells with model gold and platinum electrodes are studied by an impedance spectroscopy method. Distinguishing features of these electrodes are a large characteristic size of the metal/electrolyte contact (up to 100 μm) and such well definable geometrical parameters as the length of triple-phase boundary (TPB) and the contact area. E. Shouler discovered that the electrolyte resistance, measured in an electrochemical cell, varies with the oxygen activity. Modern view is that this is connected with the TPB expansion. The expansion parameters determined here depend on the electrolyte prehistory and reach a few tens of micrometers. Specific (referred to a unit TPB length) values of polarization conductivities of both electrodes are obtained. Depending on the electrode prehistory, they amount to (2–6.5) × 10–4 and (3–22)× 10–4 S cm–1 for Pt and Au, respectively, at 977°C in an oxygen atmosphere. The polarization conductivity, calculated per unit active area of electrolyte, is independent of the Pt electrode prehistory. Calculated exchange current densities are compared with radioisotope assay results.