| Summary: | 碩士 === 國立成功大學 === 化學工程學系 === 87 === Carbon monoxide, as a toxic gas, is produced from incomplete oxidation of fuel, e.g. gasoline and natural gas. Electrochemical CO sensor is one of the commonly used sensors. One of the research topics of this type pf sensor is using polymer solid electrolyte. However, the polymer film has to contact with liquid electrolyte to maintain high conductivity. There are three parts in this study: 1. Humidifying Nafion film by gas flowing through saturated salt, and studying the performance of electrode without water contact; 2. Preparing Pt on Nafiona for different types of electrode arrangement with impregnation-reduction method, and investigating the sensing behaviors of these electrodes; and 3. Modifying electrode with Sn to improve the sensitivity of CO.
With PtW/Nafiona electrode, the sensitivity was found 0.12 μA/ppm CO for the concentration below 1000 ppm. When Sn was used to modify the electrode to form Sn/PtW/Nafiona, the sensitivity in the range of 0~400 ppm CO was 0.67 μA/ppm CO, about 6 times of that with PtW/Nafiona. However, the sensitivity decreased to 0.23 μA/ppm CO in the range of 400~1000 ppm CO.
With PtW/Nafiona/PtC electrode in [NH,NH] system, the sensitivity was 0.137 μA/ppm CO for the concentration below 100 ppm CO. With Sn-modified electrode, the sensitivity was 0.38 μA/ppm CO, about 3 times of that with PtW/Nafiona/PtC. In [AH,AH] system, O2 seriously affected CO sensing behaviors on PtW/Nafiona/PtC. Sn-modified electrode was also affected seriously by existence of O2.
The performance of PtW-PtC/Nafiona/PtR electrode in [NH,NH] system was studied. The HCl-pretreated electrode had the higher sensitivity than that pretreated with HClO4 or H2-SO4. The sensitivity was 0.36 μA/ppm CO in the concentration below 1000 ppm.
With PtW /Nafiona/PtC-PtR electrode in [NH,NH] system, the sensitivity was 0.37 μA/ppm CO in the concentration below 1000 ppm at the suitable potential, 0.0 V (vs. PtR). In [AH,NH] system, O2 still seriously affected CO sensing behaviors on PtW/Nafiona/PtC-PtR. The sensitivity decreased to 0.04 μA/ppm CO. Besides, when the area ratio of PtC to PtC increased, the range of potential for constant background current expended to more negative range. Since the sensing current was larger at more negative potential (-0.1 V vs. PtR). The sensitivity at more negative potentials were larger than 0.7 μA/ppm CO.
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