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研究生:邱秋燕
研究生(外文):Chiou-Yen Chiou
論文名稱:電流式二氧化硫氣體感測器之研究
論文名稱(外文):Study of Amperometric SO2 Gas sensor
指導教授:周澤川
指導教授(外文):Tse-Chuan chou
學位類別:博士
校院名稱:國立成功大學
系所名稱:化學工程學系
學門:工程學門
學類:化學工程學類
論文種類:學術論文
論文出版年:1999
畢業學年度:87
語文別:中文
論文頁數:138
中文關鍵詞:氣體擴散電極固態高分子電解質二氧化硫感測器電流式氣體感測器離子交換膜
外文關鍵詞:gas diffusion electrodesolid polymer electrolyteSO2 sensorAmperometric gas sensorNafion
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廢氣之排放是造成空氣品質不良之主要原因,特別是二氧化硫遇到雨水形成酸雨對人類及自然環境造成嚴重的傷害,因此二氧化硫之監測就顯得重要。
本文擬以金屬觸媒分散之氣體擴散電極及固態高分子(SPE)電極為感測電極探討鐵弗龍含量、氣體流量、觸媒種類、觸媒顆粒大小、氣體流率、干擾氣體如氧氣、一氧化碳、一氧化氮與二氧化氮等,對二氧化硫氣體感測器之影響,以及電極之穩定性、毒化與再生方式。
分別以含浸法及膠體法(colloid)製備電極觸媒,並以X 光繞射法及X光吸收光譜術進行觸媒之粒徑分析,由實驗結果配合X-ray數據分析之結果得知當金觸媒之負載量為5%時,以含浸法製備之觸媒其平均粒徑為210A。膠體法實驗中,分別以非離子型介面活性劑(Triton X-100)和聚乙烯二呲咯烷酮(poly-N-vinyl-2-pyrrolidone)為分散劑,製備之觸媒其平均粒徑為39、33A。以此三種電極觸媒製備氣體擴散電極,並於穩定狀態下進行二氧化硫之感測其靈敏度分別為1.428、1.907、2.269μA/cm2∙ppm,以上之結果乃因觸媒顆粒愈小其分散度愈高,其反應之真實面積愈大所致。
鐵氟龍之作用除當黏著劑外,主要之目的乃控制電極之親水與疏水性,因此鐵氟龍之含量與液即電解液、氣即反應氣體與固即含金屬觸媒之碳粉,三相反應有著密不可分之關係,實驗結果得知當鐵氟龍含量20~40%時感測器之穩態電流最高。此外,穩態電流隨氣體流率之增加而上升,但當氣體流率大於350ml/min,穩態電流與應答時間不再受氣體流率之影響,此時擴散阻力來自多孔性電極內之擴散阻力。分別以鉑、金、CoPc為電極觸媒,鉑與金之應答電流非常相近,但CO對鉑觸媒之干擾較嚴重,以CoPc為電極觸媒因部份二氧化硫經由化學反應因此穩態電流較低。CO、O2、NO2對金觸媒之氣體擴散電極無干擾,但NO氣體則有顯著之影響。感測時,二氧化硫氣體在電極表面氧化,其氧化產物與金屬觸媒形成強吸附,不易自電極表面脫附造成電極觸媒中毒,以電化學方式使二氧化硫及其氧化產物自電極表面脫附,並以伏安循環掃描法使電極觸媒恢復電極之初始活性,為避免脫附不完全在後續掃描過程產生硫原子吸附在電極表面,脫附之電位為1200mV,脫附時間4分鐘。
以metal-Nafion電極為二氧化硫之感測,以化學法製備Pt/SPE及Pd/SPE電極,金屬之負載量分別為1.595、0.114 mg/cm2,以蒸鍍法製備之Au/SPE電極,金之負載量為0.126 mg/cm2,以此三種高分子電極做為二氧化硫之感測電極,在穩定狀態下進行擴散阻力之探討,以穩態電流對氣體濃度作圖求電極整體之擴散阻力 ,換算電極之靈敏度分別為2.266、0.176及0.917μA/cm2∙ppm。當氣體流率為100ml/min時,Pt/SPE、Pd/SPE及Au/SPE電極之90%應答時間分別為40、41、27秒,O2對此三種電極均無干擾;CO對Pt/SPE有嚴重之干擾,對Pd/SPE之影響次之,對Au/SPE無影響;NO對此三種電極均無干擾;NO2對此三種電極均有顯著之干擾。
Emission of exhaust or flue gases are the main sources of air pollution. Specially, sulfur dioxide (SO2) can react with moisture in atmosphere to form acid rain, which has significantly affected on human health and environment. Therefore, monitoring of SO2 becomes an important issue for environmental protection and control.
In this work, gas diffusion electrodes based on the dispersed metal catalysts and solid polymer electrodes (SPE) were fabricated for gas sensing. In order to know their influence on the performance of SO2 gas sensors, several factors were investigated, including catalyst type, metal particle size, Teflon content, gas flow rate, and the presence of interfering gases such as O2, CO, NO, and NO2. The stability, poisoning, and regeneration of the electrode were also studied.
Two methods were employed to prepare the electrode catalysts, namely impregnation and colloidal methods. The supported metal particle size was estimated by using X-ray diffraction and X-ray absorption spectroscopy. It was found that the average metal particle size was 210A on the gold catalyst at a loading of 5 wt% via impregnation. On the other hand, colloidal method leads to the average metal particle sizes of 39 and 33 A when surfactant Triton X-100 and ploy-N-vinyl-2-pyrrolidone, respectively, were utilized as the dispersion agent. The sensitivity of SO2 sensing at steady state by these sensors was found to be 1.428, 1.907, and 2.269μA/cm2∙ppm for the gas diffusion electrodes based on these three catalysts. This evidence indicates that higher sensitivity comes from catalysts with smaller metal particle size and hence higher dispersion as well as higher active surface area.
In addition to play the role of binder, Teflon was adopted to modify the hydrophilic and hydrophobic properties of electrode. Accordingly, the effect of Teflon content on the reaction rate among the relationship of liquid i.e. electrolyte-gas i.e. reactant-solid i.e. catalyst powder ternary phases. 20~40% Teflon content electrode was found to give the maximum steady-state current on gas sensors. This steady-state current increases with gas flow rate. However, when the gas flow rate was larger than 350 ml/min, both steady-state current and response time became constant because diffusion through the porous electrode dominated mass transfer resistance.
Regarding the effect of different electrode catalysts, a comparison in performance was made among Pt/C, Au/C, and CoPc/C active sites of the electrodes as follows: The response current of Pt was similar to that of Au, but the former was interfered by CO to a greater extent. NO exhibited significant interference on the gas diffusion electrode based on Au catalyst while with negligible interference by CO, O2, and NO2. Due to the chemical reaction of SO2 in sensing, lower steady-state current was obtained on the electrode based on CoPc/C electrode. The SO2 molecules were oxidized on the electrode surface and the product was strongly adsorbed on the metal catalyst, leading to poisoning of the electrode catalyst. The SO2 and its oxidation products can be removed from the electrode surface by electrochemical treatment. Application of cyclic voltammetry serves to restore the initial activity of the electrode. To avoid the possibility of incomplete desorption of sulfur species in subsequent scans, the voltage for desorption was 1200 mV with a period of 4 min.
Metal-Nafion electrodes were also prepared and applied as SO2 sensors. The Pt/SPE and Pd/SPE electrodes were prepared by using chemical method to have metal loading of 1.595 and 0.114 mg/cm2 respectively. On the other hand, an Au/SPE electrode with Au loading of 0.126 mg/cm2 was prepared via chemical vapor deposition. The diffusion resistance was studied when these three solid polymer electrodes work as SO2 sensors at steady state. The bulk diffusion resistance, , can be obtained by plotting steady-state current versus gas concentration. The corresponding sensitivity was calculated to be 2.266, 0.176, and 0.917μA/cm2∙ppm. The 90% response time was 40, 41, and 27 sec for Pt/SPE, Pd/SPE, and Au/SPE, respectively, at 100 ml/min gas flow rate. No interference from O2 and NO was observed for all three electrodes. In contrast, NO2 exhibited significant interference on these electrodes. Finally, it is interesting to note that the interference of CO on Pt/SPE was more serious than that on Pd/SPE. The Au/SPE was hardly affected by CO gas.
封面
目錄
中文摘要
英文摘要
誌謝
圖目錄
表目錄
符號說明
第一章 緒論
1.1氣體感測器之發展及其現況
1.2二氧化硫氣體感測器
1.3二氧化硫氣體之電化學反應
1.4氣體擴散電極
1.5固態高分子電極
1.6研究動機與本文大綱
第二章 實驗方法
2.1 藥品及儀器
2.1.1藥品
2.1.2儀器
2.2 Au/C電極觸媒之製備方法
2.2.1 碳粉前處理
2.2.2 含浸法
2.2.3 膠體法
2.3 電極觸媒之特性分析
2.3.1 程溫還原法
2.3.2 X光繞射法
2.3.2 X光吸收光譜術
2.4 氣體擴散電極之製備
2.5 固態高分子電極之製備
2.2.1 Au-Nafion電擊之製備
2.5.2 Pt-Nafion電擊之製備
2.5.3 Pd-Nafion電擊之製備
2.6 感測器之組裝
第三章 二氧化硫氣體之感測模式
3.1 Au/SPE、Pt/SPE、Pd/SPE電極之感測模式
3.1.1 非穩定狀態下之感測行為
3.1.2 穩定狀態下行為模式之探討
3.2 氣體擴散電極之感測模式
3.2.1 非穩定狀態之下感測行為
3.2.2 穩定狀態下行為模式之探討
第四章 電極觸媒之特性分析
4.1 前言
4.2 含浸時間之影響
4.3 程溫還原
4.4 X光繞射法
4.4.1 原理
4.4.2 結果語討論
4.5 X光吸收光譜術
4.5.1 原理
4.5.2 數據分析
4.5.3 結果與討論
第五章 氣體擴散電極之製備與其應用於二氧化硫氣體之感測
5.1 前言
5.2 鐵弗龍含量對二氧化硫氣體感測之影響
5.3 氣體流率對二氧化硫氣體感測之影響
5.4 金觸媒顆粒大小對二氧化硫氣體感測器靈敏之影響
5.5 不同觸媒對二氧化硫氣體感測之影響
5.6 感測器之穩定性與再生
5.7 他種氣體之干擾
5.8 結果
第六章 固態高分子電極製備與其應用於二氧化硫氣體之感測
6.1 前言
6.2 固態高分子電極之特性分析
6.2.1 金屬之負載量與活性面積
6.2.2 電極表面觀察與縱向分佈
6.4 氣體流率對二氧化硫氣體之感測之影響
6.5 電極種類對二氧化硫氣體感測器靈敏之影響
6.6 他種氣體之干擾
6.7 結論
第七章 綜合討論,總結與未來工作建議
7.1 綜合討論
7.2 總結
7.3 未來工作建議
第七章 參考文獻
自述
著作
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