Performance and stability of potentiometric CO2 gas sensor based on the Pt, Li2CO3/Na2O–Al2O3–4SiO2//YSZ/Pt electrochemical cell

CO2 sensing characteristics were examined in dry condition for Pt, Li2CO3/Na2O–Al2O3–4SiO2 (NA4S)/YSZ/Pt structure. The electromotive force (emf) value was linearly increased with logarithm of CO2 concentration in the range of 10–10,000 ppm and the electron number was closed to 2.0. The electron number was hardly changed and the activity of alkali metal oxide in NA4S increased with time. As a reason to increase in the activity, the reaction of Li2CO3 as an auxiliary electrode with SiO2 in NA4S layer and the formation of lithium silicates are considered. The formation of Li2SiO3 was accelerated by using H2O, methanol or ethanol instead of α-terpineol as an additive for the mixing of Li2CO3 and silica. It was concluded that to depress the reaction with Li2CO3 and silica, the use of Li2CO3 mixed with α-terpineol for an auxiliary electrode was preferable.