MICROSTRUCTURE AND RESPONSE BEHAVIOR OF ELECTRODES FOR CO2 GAS SENSORS BASED ON SOLID ELECTROLYTES

The response behaviour of electrodes for solid-electrolyte Nernstian CO2 gas sensors is characterized using the pressure-modulation technique. Porous electrodes are formed on Na2CO3/BaCO3 discs. Response times and their dependence on temperature and O-2, CO2 partial pressures are found to differ widely for various electrode materials, For Ag electrodes, diffusion of silver ions into the carbonate bulk causes a slow response and blocking at both high CO2 and O-2 partial pressures. The response of Au electrodes becomes slower at low O-2 partial pressures due to a rate-determining reaction step. Pd and Pt electrodes generally show the fastest response, which is only slightly dependent on gas composition and is governed by diffusion.