CO2 sensing characteristics of a solid-state electrochemical sensor based on a sodium ionic conductor

Abstract

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.