Small signal response of the BiCuVOx/noble metal/oxygen electrode system

The electrode properties of the Bi2Cu0.1V0.9O5.35/noble metal/oxygen system have been studied by impedance spectroscopy and polarisation measurements in a three-electrode cell. Little difference was observed in the performance of Au, Pt and Ag electrode metals. Gold showed the lowest electrode resistance, silver the highest, but these differences are most likely due to differences in the microscopic electrode geometry. The impedance spectra indicate three distinct electrode processes. A fourth process, identified by a negative loop, must be ascribed to ‘cross talk’ between reference and working electrode. The main feature in the impedance is a Warburg like, PO2 and polarisation dependent diffusion element, in parallel with a charge transfer type resistance. The observed electrode behaviour is similar to what has been found previously for the rare earth stabilized bismuth oxide electrolytes. This indicates that the electrolyte surface exposed to the ambient is the active area for the oxygen and charge transfer. At moderate temperatures a competition exists between oxygen exchange and oxygen redistribution (reduction/oxidation in the electrode-interface regions of the bulk), which is due to a small electronic conductivity.