Oxygen electrodes of zirconia electrolytes: fundamentals and application to analysis of oxygen containing gases

The kinetics of the oxygen exchange reaction and the reduction of NO at La_0.8Sr_0.2CoO₃−, La_0.8Sr_0.2MnO₃− and Ag-electrodes on stabilized zirconia (8mol% Y₂0₃=YSZ) has been studied by means of electrochemical methods (impedance, I-U characteristics). For La_0.8Sr_0.2CoO₃ electrodes the oxygen exchange was found to proceed via the bulk of the electrode with a rate limiting oxygen exchange at the electrode surface. Electrodes based on La_0.8Sr_0.2MnO₃ change their electrode characteristics with the applied potential. At low cathodic polarization the electrode reaction is limited to the three-phase boundary electrode/YSZ/gas. At high cathodic potentials oxygen vacancies are created and consequently additional oxygen is exchanged via the electrode bulk. Furthermore, a significant NO reduction was observed which indicate a reaction with the oxygen vacancies at the electrode surface. For Ag a rate limiting transport of oxygen atoms through the bulk of the electrode was found. As a consequence the oxygen concentration at the electrode surface remains nearly constant. In this context, the observed inactivity for the NO reduction of Ag-electrodes may be explained. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995