Fabrication and characteristics of CO2-gas sensor using Li2CO3–Li3PO4–Al2O3 electrolyte and LiMn2O4 reference electrode

Fabrication of solid-state potentiometric CO2 sensor was simplified by using Li2CO3–Li3PO4–Al2O3 mixture for both a solid electrolyte and sensing electrode. LiMn2O4 was used as the reference electrode to improve an electrochemical stability of the sensor. The emf of the sensor showed a good accordance with theoretical Nernst slope (n=2) for CO2 gas concentration in the range of 100–10,000 ppm above 350°C. The emf of the sensor was constant regardless of oxygen partial pressure at the high temperature above 5 kPa. It however, a little depended on oxygen partial pressure as the pressure decreased below 5 kPa. The oxygen-dependency of the sensor gradually disappeared as the operating temperature increased. The sensing behavior of CO2 sensor was affected by the presence of water vapor, but its effect was small comparing with other sensors. The CO2 sensor also showed superior long-term stability.