Effects of electrode materials on CO2 sensing properties of solid-electrolyte gas sensors

The effect of oxide powder addition to a carbonate auxiliary electrode on the CO2-sensing properties of Na3Zr2Si2PO12 (NASICON) gas sensors has been investigated. CO2 was adsorbed on the surfaces of most of the oxides tested after treatment at 400 degrees C in dry air, while the coexistence of H2O reduced the amount of adsorbed CO2. However, the amount of CO2 adsorbed on the oxides was not correlated with the CO2 response of the NASICON sensors equipped with an electrode containing the oxide. The CO2 response increased and the humidity cross response decreased with a decrease in the resistance of the oxides. This result suggests that the strict conductivity control of auxiliary electrodes is an important factor for achieving high-performance potentiometric CO2 sensors.