Fabrication of CO2 sensor using NASICON thick film

The condition of screen-printing paste was explored to densify a thick film of Na+ conductor, Na3Zr2Si2PO12 (NASICON) deposited on an alumina substrate. A fair well-densified NASICON thick film was found to be obtained from a paste consisting of NASICON powder and ethylene glycol dispersant by screen-printing and calcination at 1000 °C. The resulting planar sensor showed good CO2 sensing capability even under humid conditions, although the emf tended to shift upward with increasing relative humidity. In order to reduce the disturbance by humidity, applicability of an oxide-ionic conductor of Bi2Me0.1V0.9O5.35 as a counter electrode material was examined. The oxide-incorporated devices, of both disk type and planar, exhibited stable CO2 sensing properties under dry as well as humid conditions. In addition, the dependence of emf on RH could be reduced considerably with the oxide-incorporated devices. It was found, however, that the RH dependence of emf originates from both of the sensing and counter electrodes so that the RH dependence of both electrodes should be tackled with to eliminate the RH dependence of the devices.