Anal. Chem. 2002, 74, 4800-4804
A Carbon Dioxide Gas Sensor by Combination of Multivalent Cation and Anion Conductors with a Water-Insoluble Oxycarbonate-Based Auxiliary Electrode Nobuhito Imanaka,* Masayuki Kamikawa, and Gin-ya Adachi
Department of Applied Chemistry, Faculty of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
A compact and inexpensive carbon dioxide gas sensor was successfully realized by the combination of a divalent magnesium ionic conductor of Mg0.7(Zr0.85Nb0.15)4P6O24 and a divalent oxide anion conducting ZrO2-Y2O3 solid electrolyte with the water-insoluble Li- and Ba-codoped Nd2O2CO3 solid solution as the auxiliary electrode. The sensor response was continuous and reproducible, and the present sensor also demonstrated a theoretical Nernst response in the atmosphere where water vapor, nitrogen oxides, ammonia, etc., coexist. The exposure of the present sensor to water dew and variation in oxygen concentration does not interfere with the sensor response, which will be a great advantage in applying the in situ practical CO2 detection in combustion exhaust gas atmospheres. The suppression of carbon dioxide (CO2), which is one of the gas species causing global warming, has been focused on as a worldwide critical issue to be solved within the next decades. For the purpose of realizing effective CO2 suppression, in situ and real time CO2 monitoring tools are essential, and various types of CO2 detection methods have been reported. For example, CO2 detection by optical1-3 and electrochemical pH sensing4 methods have been proposed. The former has the advantage of a rapid response within 0.3 s; however, from the viewpoint of in situ CO2 monitoring in an emitted gas atmosphere where various gas species appear as ultrafine particles, optical apparatuses are not suitable for selective CO2 sensing, especially in a combustion exhaust gas atmosphere. As a result, another detection tool with a different mechanism should be developed. Electrochemical pH sensing measures the pH change when CO2 is dissolved in an internal electrolyte, and the response is as rapid as
