Glass-Coated Mixed Conducting Cobaltites as Solid-Reference Electrode Materials for NASICON-Based Potentiometric CO[sub 2] Sensors

Abstract

To improve the stability of Na3Zr2Si2PO12 (NASICON)-based potentiometric CO2 sensors fitted with carbonate/Au layers (sensing electrode), mixed conducting oxides of Li0.4CoO2 and Na0.6CoO2 were examined for their applicability to solid-reference electrodes in terms of their stability against CO2 and humidity. Compared with the Na0.6CoO2 electrode, the Li0.4CoO2 electrode showed far better stability against CO2 . When the Li0.4CoO2 electrode was coated with a layer of glass, the electrode showed no response to CO2 (200–2000 ppm) and little interference from humidity [21–86% relative humidity (RH)] at 450°C . A CO2 sensor device using Li2CO3–BaCO3 and a glass-coated Li0.4CoO2 showed stable electromotive force (emf) responses to CO2 in humid air (86% RH) at 450°C . The emf of the device was also stable even after it was exposed to humid air (86% RH) containing CO2 (400 ppm) at room temperature for 1–2 days. The present study indicates the promising features of the glass-coated Li0.4CoO2 as a stable solid-reference material for NASICON-based CO2 sensors.

Application of a Solid Electrolyte CO2 Sensor for the Analysis of Standard Volatile Organic Compound Gases

“…The use of a cheap, compact, and efficient CO 2 sensor in place of a nondispersive infrared (NDIR) detector is the key to the system. Through continuous extensive studies, we have developed a high-performance solid electrolyte CO 2 sensor, in which NASICON (Na 3 Si 2 Zr 2 PO 4 ; Na + conductor) and binary carbonate (Li 2 CO 3 −BaCO 3 ) are used as the solid electrolyte and the sensing layer, respectively. − This sensor can detect CO 2 in ppm concentrations without interference from other gases like water vapor, O 2 , CO, H 2 , NOx, and hydrocarbons. Furthermore, we successfully improved the stability of the sensor under high humidity conditions by using a stable solid reference electrode. , Thus, the sensor can effectively detect CO 2 formed by catalytic combustion of VOCs without interference from water vapor concurrently formed.…”

“…Through continuous extensive studies, we have developed a high-performance solid electrolyte CO 2 sensor, in which NASICON (Na 3 Si 2 Zr 2 PO 4 ; Na + conductor) and binary carbonate (Li 2 CO 3 -BaCO 3 ) are used as the solid electrolyte and the sensing layer, respectively. [23][24][25][26] This sensor can detect CO 2 in ppm concentrations without interference from other gases like water vapor, O 2 , CO, H 2 , NOx, and hydrocarbons. Furthermore, we successfully improved the stability of the sensor under high humidity conditions by using a stable solid reference electrode.…”