Long-term stability of potentiometric CO2 sensors based on Nasicon as a solid electrolyte

Five solid-state potentiometric CO2 sensors of the type: CO2, O2, Ag, M2CO3–BaCO3 |Nasicon| X, Pt, O2 (where M=Li or Na, X—Na2O activity buffer) were investigated. The effects of electrode composition and operating temperature on long-term performance of sensors were determined. It was found that the sensors with Na2Ti6O13/Na2Ti3O7 reference electrode show stable signal during 1000 h. No effect of the sensing electrode composition was observed. The optimal operating temperature of the studied sensors was 748 K. The formation of liquid phase at this temperature at the sensing electrode/solid electrolyte interface is suspected to be responsible for improvement of the sensors performance. The reactivity between sensing electrode and solid electrolyte materials at higher temperatures leads to sensors instability.