CO2 sensing characteristics of a solid-state electrochemical sensor based on a sodium ionic conductor
The sensing characteristics of a CO2 gas sensor with Na2CO3, NaHCO3 or NaOH coated on the sensing electrode have been investigated. Emf and response behaviour for CO2 at 450 °C were independent of the coated materials, since NaHCO3 and NaOH reacted with CO2, resulting in the formation of Na2CO3. The existence of NaOH or NaHCO3 in the Na2CO3 layer induced an increase in the emf. The existence of water in the test gas induced a decrease in the emf. Sodium oxides were formed on platinum electrodes from NaOH formed by the exposure to the test gas containing water vapour at a high temperature. After cutting off the water vapour, sodium oxides reacted with CO2, resulting in the formation of Na2CO3.