Carbon Dioxide Sensor Using Sodium Ion Conductor and Binary Carbonate Auxiliary Electrode

Abstract

A NASICON-basic CO = sensor was improved considerably when it was fitted with a Ba-Na binary carbonate electrode (Ba content: 46 atom percent). It responded to CO = very quickly with a 90 % response time of less than 8 s, at 550 ~ without being affected by water vapor. The electromotive force responses followed perfectly aNernst equation corresponding to a 2-electron reaction for CO = over a wide CO = concentration range at 450-600 ~ The sensor performance was stable for the test period of 200 days. X-ray diffraction analysis revealed that no free Na~.CO3 remained in the binary carbonate electrode, while scanning electron microscopy observation of the electrode revealed eposits of micro-needles containing both Ba and Na. It was concluded that the disappearance of free NasCO3 to form needle-like deposits gave rise to a resistance to water vapor and the quick response rates of the sensor element. Similar improvements were also observed for other bi-nary carbonate systems, such as Sr-Na and Ca-Na. CO2 emissions are a global issue. In addition, CO2 moni-toring and control in offices, homes, agricultural fields, and bio-related processes are of growing importance. Therefore, there are ever increasing needs for solid-state CO = sensors which are reliable, inexpensive, and compact.