Relationship between aging time and EMF change of potentiometric CO2 device using Na1+xZr2SixP3-xO12 (0 < x < 3)

Four kinds of NASICON (Na(1+x)Zr(2)Si(x)P(3-x)O(12), x =1, 1.5, 2 or 2.75)-based CO(2) devices were combined with a Li(2)CO(3)-BaCO(3) (1:2 in molar ratio) auxiliary phase to investigate their CO(2) sensing properties. The EMF values of NASICON devices were correlated linearly with the logarithm of CO(2) concentrations in the range of 250-2500 ppm at 450 degrees C. When exposed to 250 ppm CO(2) for 200 h under dry condition, the EMF of each NASICON device decreased with aging time. To research the cause of the EMF drift, a mixture that consists of NASICON and Li(2)CO(3) was heated at 750 degrees C in air. From X-ray diffraction measurement, it was confirmed that alkali-rich crystal phases such as Li(2)ZrO(3) and Na(5)Zr(PO(4))(3) were formed instead of Na(3)Zr(2)Si(2)PO(12) phase. This Suggests that the EMF drift relates with the formation of alkali-rich crystal phase at the interface between NASICON and auxiliary phase. (C) 2009 Published by Elsevier B.V.