Investigations on the electrochemical behaviour of the phase boundary counter electrode/electrolyte of amperometric solid electrolyte gas sensors based on Ag β-alumina

Abstract

Amperometric gas sensors based on solid silver ion conductors, e.g. chlorine gas sensors, usually contain silver electrodes as counter electrodes or common counter/reference electrodes. The electrochemical kinetic behaviour of the system Ag electrode/Ag β-alumina solid electrolyte has been investigated in the temperature range between 275 and 375°C. The measurements have been carried out using different types of solid-state electrochemical cells. By appropriately combining the results of quasi-stationary galvanostatic and impedance measurements received from the different cells, the resistance behaviour of the electrode reaction occurring at the phase boundary Ag/Ag β-alumina has been evaluated. This behaviour is described in good approximation by an ohmic resistance R* referred to the geometrical area of the phase boundary, the value of which is given by an equation as a function of the temperature. Typical values are R*=264 Ω cm2 (quasi-stationary) and R*=143 Ω cm2 (100 kHz) at 275°C, and R*=97 Ω cm2 (quasi-stationary) and R*=71 Ω cm2 (100 kHz) at 375°C.