Improvement of warming-up characteristics of potentiometric CO2 sensor by using solid reference counter electrode

A planar type CO2 sensor device using NASICON (Na+ conductor, Na3Zr2Si2PO12) thick film was attached with a glass (SiO2:Na2O:B2O3:Al2O3 = 44:20:31:5, in molar ratio)-coated Na0.6CoO2 reference electrode to increase its feasibility under various conditions in practical. The fabricated device proved satisfactory CO2-sensing properties at steady operating temperature (450 °C) under dry and humid conditions. In the heat-cycle tests between the operating temperature and room temperature under various humid conditions, the planar device once aged, exhibited quick warm-up characteristics and well-reproducible EMF response to CO2 unless humidity was very high (e.g. 80%).