Abstract
Potentiometric CO2 sensors based on NASICON (Na1+xZr2Si2PO12) were fabricated by combining with a Li2CO3-BaCO3 (1:2 in molar ratio) auxiliary phase. The CO2 sensing properties of NASICON (x = 0, 1, 2, 2.75) sensors were investigated under dry condition at 450°C. The electromotive force (EMF) values of NASICON sensors were proportional to the logarithm of CO2 concentrations in the range of 250 to 2500 ppm. When exposed to dry air containing 250 ppm CO2, the EMF values of each sensor continuously changed toward a negative potential. From a X-Ray Diffraction (XRD) measurement, it was confirmed that new crystal phases such as Li2ZrO3, ZrO2, Na2Zr(PO4)2 and Na5Zr(PO4)3 were formed at the interface between sensing electrode and solid-state electrolyte, because of reaction between Li2CO3 and NASICON. The result of XRD measurement suggested that the base-EMF change closely related with the decrease of Li+ activity in auxiliary phase and Na2O activity in NASICON.
