Solid Electrolyte CO2 Sensor Fabricated with Li2CO3-La9.33Si6O26 as Sensing Electrode.

Recently NASICON (Na3Zr2Si2PO12) has been used as the solid electrolyte for EMF (electromotive force) CO2 sensors. However, it has been difficult to obtain a sufficiently high quality of this type of sensor. In general, when the EMF CO2 sensor is exposed to a high-humidity atmosphere, the EMF of the sensor decreases to less than two-thirds of its initial value. For the purpose of improving the humidity resistance of the sensor, the reason for the decrease of the EMF sensor after exposure to a high-humidity atmosphere is investigated, and an appropriate counterplan is devised. In this report, Li2CO3, Li2CO3-La2O3, and Li2CO3-La9.33Si6O26 are adopted as materials for the sensing electrodes. Li2CO3 reacts with NASICON and forms friable compounds when these materials are exposed to an atmosphere of 90% relative humidity at 60°C. In contrast, Li2CO3-La9.33Si6O26 is the material most resistant to humidity, because La9.33Si6O26 prevents the reaction between NASICON and Li2CO3.