Study of CO2 electrodes in open devices of potentiometric sensors

Potentiometric CO2 sensors in open devices with NASICON as solid electrolyte were tested in the temperature range 150–500 °C and at partial pressures between 10−6 and 0.1 atm in air. The sensors were built with sodium titanate and La1−xSrXMnO3±δ (LSM) mixtures as oxygen reference electrode and Na2CO3–BaCO3 or Na2CO3–SrCO3 mixed with gold as measuring electrodes. The CO2 electrode reaction is based on an electrochemical mechanism with a fast electron transfer and an adsorption–diffusion phenomenon. In sensor devices, the system with Na2CO3–BaCO3 deviates from Nernst law in all the pressure ranges whatever the device (pellet or coplanar devices) is. The system with Na2CO3–SrCO3 obeys a Nernst behaviour for the highest CO2 pressures. The observed responses are very fast. A discussion is engaged to explain the subnernstian behaviour from the thermodynamic stability of Na2CO3 and a mixed voltage phenomenon.