Shotaro Kishi

Planar NASICON-based CO2 sensor using BiCuVOx /Perovskite-type oxide as a solid-reference electrode

To improve the stability of a NASICON (Na 3 Zr 2 Si 2 PO 12 ; Na + conductor)-based potentiometric CO 2 sensor under humid conditions, a composite of BiCuVO x (Bi 2 Cu 0.1 V 0.9 O 5.35 ) and perovskite-type oxide (La 0.6 Sr 0.4 Co 0.78 Ni 0.02 Fe 0.2 O 3 ) was used as a solid-reference electrode. The CO 2 sensing properties and stability of a NASICON-based planar device fitted with Li 2 CO 3 -BaCO 3 (auxiliary phase) and the composite reference electrode were examined under humid conditions. The planar device mounted on an alumina substrate with a Pt heater showed stable electromotive force (emf) responses to changes in the CO 2 concentration (100-400 ppm) at 400 and 450°C in humid air without degradation. The sensor device also exhibited a good warming-up characteristic, i.e., the emf of the device quickly reached a steady and constant value when the sensor operation was restarted even after the sensor was exposed to humid air (86% relative humidity at 25°C) at room temperature for a long time.

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

Preparation and analysis of standard VOC (volatile organic compound) gases are needed when developing and evaluating the performance of analytical methods or instruments to detect VOCs. In this study, we designed and developed a simple system for the analysis of VOCs based on their decomposition into CO(2) by a combustion catalyst and their subsequent detection using a solid electrolyte CO(2) sensor. In this sensor, NASICON (Na(3)Si(2)Zr(2)PO(4); Na(+) conductor) and binary carbonate (Li(2)CO(3)-BaCO(3)) were used as the solid electrolyte and the sensing layer, respectively. This developed system proved to be effective in determining the concentrations of standard gases, including VOCs (ethanol, formaldehyde, and toluene), CO, and hydrocarbons in parts per million concentrations (10-500 ppm). The system also could continuously monitor the variations in ethanol vapors prepared by a diffusion method where liquid ethanol was heated at 25 and 50 degrees C. The advantages and limitations of our developed analytical system are also discussed.

Preparation and measurement of standard organic gases using a diffusion method and a NASICON-based CO2 sensor combined with a combustion catalyst

The development of new analytical methods for the detection of volatile organic compounds (VOCs) requires the preparation of standard gases at various concentrations. In this study, using a diffusion method where liquid samples were heated and vaporized under a carrier gas flow, we prepared standard organic gases containing acetone or 2,6-diisopropylphenol (propofol), which are breath markers for diabetes and anesthesia depth, respectively. A Pt/Al2O3 combustion catalyst was used in conjunction with a NASICON (Na3Zr2Si2PO12; Na+ conductor)-based CO2 sensor for the continuous determination of organic concentrations in the sample gas streams; the catalyst allowed for conversion of ppm concentrations of acetone or propofol to CO2. The results demonstrate that the present system is feasible for the preparation and concentration determination of standard VOC gases.

Glass-Coated Mixed Conducting Cobaltites as Solid-Reference Electrode Materials for NASICON-Based Potentiometric CO2 Sensors

To improve the stability of Na 3 Zr 2 Si 2 PO 12 (NASICON)-based potentiometric CO 2 sensors fitted with carbonate/Au layers (sensing electrode), mixed conducting oxides of Li 0.4 CoO 2 and Na 0.6 CoO 2 were examined for their applicability to solid-reference electrodes in terms of their stability against CO 2 and humidity. Compared with the Na 0.6 CoO 2 electrode, the Li 0.4 CoO 2 electrode showed far better stability against CO 2 . When the Li 0.4 CoO 2 electrode was coated with a layer of glass, the electrode showed no response to CO 2 (200-2000 ppm) and little interference from humidity [21―86% relative humidity (RH)] at 450°C. A CO 2 sensor device using Li 2 CO 3 ―BaCO 3 and a glass-coated Li 0.4 CoO 2 showed stable electromotive force (emf) responses to CO 2 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 CO 2 (400 ppm) at room temperature for 1―2 days. The present study indicates the promising features of the glass-coated Li 0.4 CoO 2 as a stable solid-reference material for NASICON-based CO 2 sensors.

Nasicon-Based Planar-Type CO2 Sensor Attached with Solid Reference Electrode Stable Under High Humid Conditions

In order to improve the stability of a NASICON (Na₃Zr₂Si₂PO₁₂; Na⁺ conductor)-based potentiometric CO₂ sensor under humid conditions, a new solid-reference electrode of the BiCuVOx (Bi₂Cu_0.1V_0.9O_5.35)/perovskite-type oxide (La_0.6Sr_0.4Co_0.78Ni_0.02Fe_0.2O₃) composite was investigated. The fabricated electrochemical cell (CO₂+O₂, Au/Li₂CO₃-BaCO₃/ NASICON/ BiCuVOx-La_0.6Sr_0.4Co_0.78Ni_0.02Fe_0.2O₃, O₂) responded well to changes in CO₂ concentration (100-400 ppm) at 400-450degC under high humid conditions (86% RH) without degradation. The sensor device also exhibited a good warming-up characteristic, i.e., the electromotive force of the device quickly reached a steady and constant value when the sensor operation is re-started even after the sensor was exposed to high humid air at room temperature.