- 學位論文
改善電鍍技術製備以奈米碳管為載體之直接甲醇燃料電池陽極觸媒層
An improved electrodeposition technique for preparing the CNTs supported catalyst for direct methanol fuel cell applications
摘要
近年來，由於燃料電池技術突破性的發展，受到全世界各地高度的重視，並被認為是未來能源之星（Power of Future）。因為其與傳統的電力供應系統比較起來，燃料電池不但能提高能源效率，並且能降低環境的污染。其中，直接甲醇燃料電池被視為解決未來能源危機的重要選擇，但在目前仍有很多方面的瓶頸。本實驗期望提升陽極觸媒的催化效能，並採用鉑釕二元合金組合抑制ㄧ氧化碳的毒化現象，以獲得較高的電池功率密度。 理想的觸媒載體需要有大表比面積、高導電度及在酸鹼環境下穩定的特性，本實驗選用直接成長於碳布之奈米碳管為觸媒載體，主要功能是將具有催化功能的催化劑（鉑釕二元合金）有效的分佈在其表面上，得到較小顆粒之催化劑及更佳的質量活度；並改變親水處理時氧氣分壓、使用雙面成長奈米碳管之碳布及超音波震盪器，以提高電鍍效率，增加觸媒的載量，達到觸媒活性面積的增加及電鍍的最佳化，進一步期許降低電鍍成本及縮短製程時間。 製備完成之陽極觸媒藉由各種不同的電化學（循環伏安法、動態極化掃瞄等）及物理特性（穿透式電子顯微鏡、掃描式電子顯微鏡、感應 X光粉末繞射、霍氏轉換紅外光譜等）進行分析，深入探討其電化學特性（甲醇氧化機制、觸媒效率、觸媒毒化、半電池電位電流、質量活度等）和物理性質（半電池之表貌結構變化、觸媒合金的形貌、分佈情形及團聚等）。 研究結果發現，使用雙面成長奈米碳管之碳布通入空氣作硫酸親水處理之後進行超音波震盪器之定電位電鍍，於循環伏安法下可獲得最大的甲醇氧化峰電流值，感應耦合電漿分析可知是由於觸媒載量顯著提升之結果；X光粉末繞射及穿透式電子顯微鏡分析下所得之觸媒粒徑縮小至約2∼3 nm之間，且均勻高密度的分佈於奈米碳管表面，但從掃描式電子顯微鏡觀察，表面團聚現象更加嚴重；若增加釕前驅物濃度，則可以有效降低毒化現象、延長電池壽命並提升If / Ib值，但伴隨著甲醇氧化峰電流密度亦隨之下降，是故無法兩全其美。
並列摘要
In recent years, as a result of the fuel cell technology unprecedented development, the whole world attached great importance to fuel cell which was considered would be the “Power of Future”. Compared with the traditional electric power supply system, the fuel cell not only can enhance the energy efficiency and can reduce the environmental pollution. Among them, the direct methanol fuel cell (DMFC) was regarded as the best choice to solve the energy crisis in the future. But there were still various bottlenecks at present. This experiment expected the promotion for mass activity of anode catalyst and used platinum ruthenium binary alloy for suppression of carbon monoxide poisoning phenomenon. Then we could obtain the higher power density of cell. The ideal catalyst support need have large specific surface area, good electronic conductivity and stability under the environment of strong acid or alkali solution. Carbon nanotubes directly grown on carbon cloth were prominent materials as the catalyst supports that exhibited special properties which make them suitable for application in several technological areas. In our studies, we changed the partial oxygen at hydrophilical treatment, used two-sides carbon nanotubes and ultrasonic shaker in order to improve the electrodeposition efficiency, increase loading of electrocatalysts and mass activity. Further we would achieve electrodeposition optimization and reduce the cost and time. Electrochemical and physical characteristics of the prepared catalysts through cyclic voltammetry (CV), transmission electron microscopy (TEM), scanning electron microscopy (SEM), inductively coupled plasma-mass spectrometer (ICP-MS), X-ray powder diffraction (XPRD) and Fourier-transform infrared spectrometer (FTIR) were carried out. Finally we discussed methanol oxidation on these catalysts, efficiency, CO poisoning, mass activity, distribution and agglomeration. According to the experiment observations, the two-sides CNTs supported specimens which were potentiostatic deposited in the ultrasonic shaker after hydrophilical treatment under air flow conditions would obtain the largest forward peak current density because of the catalyst loadings increasing. TEM and XPRD analyses exhibited that well-dispersed Pt-Ru nanoparticles were observed on the CNTs and particle sizes of electrocatalysts were between 2 and 3 nanometers. But the results from SEM observation, the agglomerations were more serious. If increasing ruthenium concentration, the CO poisoning could decrease and the life of cell would be lengthening.