Carbon Dioxide Gas Sensor with Li₂TiSiO₅ Solid Electrolyte and NiO-Li₂CO₃ as Sensing Electrode

Abstract

Sodium ionic conductors such as NASICON (Na₃Zr₂Si₂PO₁₂) have been used as a solid electrolyte for electromotive force (EMF) CO₂ sensor. However, it has been difficult to obtain a sufficiently high quality for this type of sensor. In general, when the EMF CO₂ senser is left in an atmosphere having a high water concentration, such as a high-humidity atmosphere or condensation atmosphere, the EMF of the sensor greatly decreases. For the purpose of improving the humidity-resistance of the CO₂ sensor, Li₂TiSiO₅ is employed as a solid electrolyte. It is composed of the following electrochemical cell: CO₂-Air/Au-Li₂CO₃/Li₂TiSiO₅/Au/CO₂-Air. The electrochemical reaction is in good agreement with the Nernst equation, and reacted electron is calculated as 2.04. The sensor fabricated with Li₂TiSiO₅ shows good linearity when it is exposed to an atmosphere of 90% relative humidity at 60°C. However, the EMF of the sensor decreases slightly as compared to its initial value. In order to obtain a high humidity-resistance for the sensor, NiO-Li₂CO₃ is used as the sensing electrode. In this case, the reaction constant, 2.04, is preserved and the EMF of the sensor does not change after exposure to high humidity atmosphere. Au-NiO-Li₂CO₃/Li₂TiSiO₅/Au can be considered to serve as a high humidity-resisting system for solid electrolyte CO₂ sensors.