Preparation of planar CO2 sensor based on solid-electrolyte NASICON synthesized by sol–gel process

A sol–gel process based primarily on inorganic reagents as raw material was employed to synthesize the solid-electrolyte material of NASICON. The synthesizing process and the resulted material were characterized by means of TG, DTA, XRD and FT-IR. The results indicated that the sintering reaction could be completed at around 900 °C within 8 h without the detectable appearance of ZrO2 phase. Furthermore, the resulted solid-electrolyte was used as the basic material for the fabrication of a planar-type CO2. The measurements showed that the output electromotive force (EMF) followed Nernst equation well in CO2 volume concentration ranging from 0.01% to 0.1% and its response and recovery time was less than 15 and 28 s, respectively. In order to enhance the resistance from other gases such as sulfide, H2, CH4, CO, humidity and so on, a noble metal doped active carbon cap was utilized in package, its filtering effect was investigated as well.