Carbon dioxide gas sensors based on a lithium ionic conductor Li2TiSiO5

Abstract

Recently sodium ionic conductors such as NASICON (Na3Zr2Si2PO12) have been used as the solid electrolyte for EMF (electromotive force) type CO2 sensors. However, it has been hard to obtain a sufficiently high quality in this type of sensor, partly due to the low humidity-resistance of NASICON and partly because of its poor initial response of EMF to CO2 pressure. For the purpose of improving the humidity-resistance and the initial response of EMF of the solid electrolyte CO2 sensors, Li2TiSiO5 is employed as the sensing material instead of NASICON. It is composed of the following electrochemical cell: CO2+Air/Au+Li2CO3Li2TiSiO5/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. The initial 90% response of EMF is steadied within 4 min. These experimental results make it possible to use the sensor in the environments.