The origin of oxygen dependence in a potentiometric CO2 sensor with Li-ion conducting electrolytes

When the electrochemical cell arrangement of type III, O2, CO2, Au, Li2CO3∣Li+ conductor∣O2, reference (aLi2O=constant) is used to measure the CO2 concentration in air, the emf should depend only on the logarithmic concentration of CO2. In reality, however, the sensor response is also affected by the oxygen present in the environment. The oxygen dependence of the CO2 sensing electrochemical cell originates from an influence of electronic conduction in the electrolyte. The theoretical change of emf with oxygen pressure, which is predicted from the modified emf-equation for the electrochemical cell with a mixed conducting electrolyte, agrees well with the measured emf change.