The performance and long-time stability of potentiometric CO2 gas sensors based on the (Li–Ba)CO3∣NASICON∣(Na–Ti–O) electrochemical cells

Solid-state potentiometric CO2 sensors were fabricated using Na+ conductor (Na3Zr2Si2PO12) as a solid electrolyte, Li2CO3–BaCO3 fused carbonate with different compositions as a sensing electrode and the Na2Ti6O13–Na2Ti3O7 or TiO2–Na2Ti6O13 two phase systems as a reference electrode. The measured electromotive force of the investigated cells was found to be linear with the logarithm of CO2 partial pressure in the range 100–12 600 ppm of CO2 and in the temperature range 300–500 °C. The response time was ca. 40–120 s. The sensors exhibited reproducible signal during short-time experiments (<24 h). However, the unstable behaviour was observed during long-time measurements (several weeks) in case of some sensors, and it was found to be sensor composition dependent. A sensing mechanism is proposed on the basis of the sensing characteristics obtained. The possible explanation of the observed long-time instability of investigated sensors is also given.