FEASIBILITY OF A POTENTIOMETRIC CO2 SENSOR-BASED ON NA-BETA-ALUMINA IN THE LIGHT OF THE ELECTRONIC CONDUCTIVITY OF THE ELECTROLYTE

The sodium activities occurring at the measuring electrode of a CO2 sensor with an Na2CO3 sensitive layer are compared with the data known so far on the electronic conductivity of the Na-beta-alumina electrolyte. This comparison indicates that the sodium potential of the measuring electrode is far away from the electrolytic domain of the electrolyte by several orders of magnitude. Therefore, the measurement of both very high contents and minute traces of CO2 in air should be impossible by means of such a sensor. Since this is in contradiction to general practical experience, the conclusion must be drawn that the so-far published data on the p-conductivity of Na-beta-alumina are probably erroneous. However, it has to be assumed that the behaviour of a CO2 sensor will be affected, possibly considerably, by electronic transference in the electrolyte. This throws new light upon the feasibility of a CO2 sensor and the understanding of its behaviour.