Studies on Carbon Monoxide Gas Sensor Based on YSZ Electrolyte

• Main Authors: MingYao Cheng, 鄭銘堯
• Other Authors: BingJoe Hwang
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/04005596640538123314

碩士 === 國立臺灣科技大學 === 化學工程系 === 88 === Abstract A novel mixed ionic-electronic conductor was prepared and applied in the development of a CO sensor. The first step, the pressed YSZ disks were sintered and then working and counter electrodes were fabricated on different sides of disks by a screen-printing method. Mixed ionic electronic conductors were prepared by electroless deposition of Pt on YSZ powders. The working electrodes were obtained by mixing Pt pastes with Pt-YSZ powders in different ratios. Next, g-Al2O3 layer was further coated on the counter electrode by a screen-printing method. A proper potential between working and counter electrodes was applied to detect the concentration of CO. At working electrode（anode）, CO would be oxidized by oxygen ions transferred from counter electrode（cathode）. CO oxidation would cause the resistance reduction at working electrode and raise the current. The currents change caused by the introduction of CO/N2 gas was used to detect the concentration of CO. Since both the response currents and the background currents increase simultaneously as the sensing temperature and the applied potential increase. The sensitivity was insignificantly improved by raising the temperature and the applied potential in the Pt/YSZ/Pt system. For example, sensitivity is raised from 0.2328nA/ppm CO to 0.4293nA/ ppm CO when temperature increased from 600℃ to 700℃ at 300mV. And if increasing the applied potential from 300mV to 500mV at 600℃, sensitivity is raised from 0.2328nA/ppm CO to 0.383nA/ppm CO. When the Pt-YSZ powder was introduced in the working electrode in the Pt/YSZ/Pt-YSZ system, the sensitivity was enhanced dramatically in the detection of CO. It was found that the working electrode of the sensor element modified with 10wt﹪Pt-YSZ/ Pt pastes showed the highest sensitivity of 2.11nA/ppm CO at 250mV and 600℃. It is almost 21 times to the sensitivity（0.104nA/ppm CO）of the sensor element with a pure Pt working electrode at same sensing conditions. It was proved that electrodes modified with mixed ionic-electronic conductors could enlarge the three-phase boundaries of electrodes and raise the sensitivity of the sensor elements. At CO concentrations higher than 5000ppm (CO/N2), response time for the modified sensor element was around 300 sec shorter than that of the Pt/YSZ/Pt sensor. Meanwhile, the response time decreases with an increase in the concentration of CO.