Effect of macrostructural control of an auxiliary layer on the CO2 sensing properties of NASICON-based gas sensors

Macrostructural effects of an auxiliary electrode on the CO2 gas sensing properties of NASICON (Na3Zr2Si2PO12) solid-electrolyte sensors were investigated. The sensor with a porous Li2CO3–BaCO3-based auxiliary layer (mp-Sensor), which was prepared by utilizing constituent metal acetates and polymethylmethacrylate microspheres as a template, showed faster CO2 response and recovery and smaller cross-response against humidity changes than those obtained with a dense auxiliary layer without pores (d-Sensor). The magnitude of CO2 response of mp-Sensor was slightly larger than the theoretical one, probably due to the existence of impurities which might have reacted with CO2 in the auxiliary layer. On the other hand, c-Sensor with a thicker and dense auxiliary layer, which was prepared by commercially available carbonates, showed smaller CO2 response and larger cross-response to humidity than mp-Sensor and d-Sensor. Thus, the use of the porous auxiliary layer prepared by constituent metal acetates was confirmed to be effective for improving the CO2 sensing properties along with the large CO2 response and small cross-response to humidity.