Potentiometric gas sensor for carbon dioxide using solid electrolytes

Abstract Small insert-type CO 2 sensors are constructed by coating Na 2 CO 3 on the one side of a tip-shaped solid electrolyte of NASICON or “beta”-alumina, and the electromotive force (EMF) is examined at temperatures between 600 and 1000 K. The EMF depends only on the partial pressure of CO 2 and is expressed by the Nernst equation because the activity of Na 2 O in solid electrolytes remains constant. The high actyivity of Na 2 O results in the formulation of Na 2 CO 3 on the other side of the solid electrolyte tip, giving the EMF to be zero. The response of the sensor is quite rapid. The hybrid CO 2 O 2 sensor is designed by joining the NASICON CO 2 sensor with a stabilized zirconia oxygen sensor. It is revealed by the EMF measurement on the hybrid sensor that the CO 2 sensor functions at oxygen partial pressures above 10 −4 Pa.