Sensing properties and interfacial structure of solid electrolyte CO2 sensor attached with Na2CO3-based auxiliary phase

Potentiometric devices for which a disc of NASICON (Na+ conductor, Na3Zr2Si 2PO12) was attached with an auxiliary phase of Na2CO3 (I) or Na2CO3-BaCO3 ( 2 : 3 in molar ratio) (II) were investigated for CO2 sensing properties and the structure of hetero-junctions involved. SEM observation combined with EPMA analysis indicated that, for device (I), a corrosion layer (20-30 mu m ) rich in Na content was formed inside NASICON. The corrosion layer was est imated to consist mainly of Na2ZrSiO5 and Na2ZrO3 from separate experiments using powder samples. For device (II), in contrast, such a corrosion layer was hardly formed between the carbonate and NASICON. This difference in ju nction structure could account well for the difference in CO2 sensing capab ility at lower temperature between the devices.