Development Of A Potentiometric Carbon Dioxide Gas Sensor

Author : Inhee Lee
Publisher :
ISBN 13 :
Total Pages : 189 pages
Book Rating : 4.:/5 (679 download)

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Download or read book Development of Ceramic Li-electrolyte Based CO2 Sensors for Temperatures Ranging from Ambient to High Temperature written by Inhee Lee and published by . This book was released on 2009 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Solid-state electrochemical CO2 gas sensors composed of an electrolyte and two porous electrodes have been used extensively in the automobile and bio-chemical industry. Based on the field of application, the working temperature of the sensor ranges from room temperature to 600 °C. Two potentiometric CO2 sensors that work at different temperature ranges were developed in this work. A potentiometric CO2 gas sensor with Li3PO4 electrolyte and BaCO3coated Li2CO3sensing electrode was developed and the sensing electrode was characterized in order to understand its sensing mechanism under humid conditions. This potentiometric CO2 sensor showed humidity-interference-free sensing response for high CO2 concentrations (5~25%) at high temperatures (T> 400 °C). In addition, the sensor showed good reproducibility and long-term stability under humid conditions. In the sensing electrode, the BaCO3layer improved the resistance against humidity as a chemical barrier, while the inner Li2CO3layer was responsible for the CO2 sensing. However, the sensor in which the eutectic layer covered the entire sensing electrode showed good sensing behavior under dry and humid conditions. Lately, low-temperature CO2 sensors have been attracting attention due to their low power consumption and easy sensor miniaturization, since a heater is unnecessary. We have developed a low-temperature CO2 sensor based on lithium lanthanum titanate (LLT) electrolyte in dry conditions that requires further improvement. Lithium lanthanum titanate (LLT) electrolytes were prepared by a conventional solid-state method. The impedance of the LLT electrolyte was measured over the temperature range of 300 to 473 K and the frequency range of 5 Hz and 13 MHz. Activation energies for the Li ionic conduction for grain boundary and grain were estimated to be 0.47 and 0.31 eV, respectively. It was found that LLT is a good ionic conductor at low temperatures and a good candidate as an electrolyte for low-temperature electrochemical cells. A La2/3-xLixTiO3LLT)-based CO2 sensor with a mixture of CeO2, Au, and Li2CO3as the sensing electrode has been developed and shown to have relatively stable sensing behaviors at 200 °C under dry conditions. However, this sensor showed non-Nernstian behavior because electrochemical reactions were not fast enough on the sensing electrode and the solid electrolyte may have some electronic conduction. In addition, the observed sensitivity was less than the theoretical prediction. By adding K2CO3on the sensing electrode, the sensitivity of the low-temperature CO2 sensor was slightly improved. However, the sensing signals of the sensors were degraded by water vapor under humid conditions due to the formation of KHCO3or K2CO3mH2O (m= 2, 3, or 6). To optimize the low-temperature CO2 sensor, a more active sensing electrode is needed, which may be achieved by controlling the size of particles and their distribution on the electrode. In addition, a thinner electrolyte with pure ionic conduction is also required.