D1.3 - Characterization of Ageing of Solid Electrolyte Sen¬sors by Impedance Spectroscopy

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
D1 - High Temperature Sensors I
J. Zosel, F. Gerlach, K. Ahlborn, U. Guth - Meinsberg Kurt-Schwabe Research Institute, Ziegra-Knobelsdorf, A. Solbach, D. Tuchtenhagen - ACEOS GmbH, Fürth, C. Treu, H. Heelemann - Software & Technologie Glas GmbH, Cottbus (Germany)
527 - 531


Ageing processes as the most important limitations for long-term stability of electrochemical sensors depend on side conditions of application, sensor operation and construction as well as the sensor materials. Solid electrolyte sensors operating at temperatures above 500 °C show some characteristic ageing phenomena like electrolyte degradation, electrode delamination, diffusion of dust particles to the electrochemical active sites and changes of diffusion barriers. The interaction of these processes complicates their clarification and the proper assortment of counteractive measures. In this paper electrochemical impedance spectroscopy (EIS) was combined with different X-ray-techniques to investigate potentiometric oxygen sensors for combustion control over glass melts and miniaturized amperometric oxygen sensors for breath gas control. Side conditions in the measuring gas trigger some serious ageing processes, which were investigated by EIS combined with X-ray photo electron spectroscopy (XPS) and scanning electron microscopy (SEM).
Sensors of different states of ageing were investigated at various temperatures, oxygen partial pressures and polarization potentials by means of EIS. Equivalent circuits were developed and adapted to the experimental results. Additional investigations were carried out with SEM as well as XPS to correlate the results of impedance measurements with changes at microscopic scale.
The impedance plots of a newly fabricated potentiometric oxygen sensor in comparison to a sensor operated more than five years in combustion gases over a glass melt, enable to distinguish between electrolyte and polarization resistances and therefore to characterize the main ageing processes. The impedance results of an amperometric sensor at different temperatures were taken for the validation of a model for the separation of electrolyte and polarization parts of the impedance. Activation energies calculated from the Arrhenius plots of the electrolyte resistance as well as the cathode polarization range between 70 and 120 kJ/mol.
The results illustrate that this investigation strategy including impedance spectroscopy and different X-ray diagnostics can be successfully adapted to clarify ageing of solid electrolyte high temperature sensors and also to evaluate counteractive measures.