Thick film planar CO2 sensors based on Na beta-alumina solid electrolyte

Abstract

Practical small-sized thick film CO2 sensor with self-heater was fabricated with Na beta-Alumina (NBA), Na2Ti6O13-TiO2, and Na2CO3 as a solid electrolyte, reference electrode, and a sensing electrode, respectively. The measured EMF from the sensor followed the Nernstian behavior with CO2 concentration change in the range of 400 to 600 degrees C (350-580 mW power consumption). However, in the aspect of stability, densification of the NBA thick film and prevention of Na2CO3 evaporation were needed. In this study, an Al2O3 porous layer deposited on Na2CO3 was effective in improving the durability during operation of the sensor. It is thought that Al2O3 suppresses evaporation of Na2CO3.