- 學位論文
微波輔助合成奈米銀觸媒於複合碳電極及其特性研究
Microwave-assisted Synthesis and Characterization of Silver Nanocatalysts on Carbon-based Electrodes
摘要
本研究提供一種有效合成奈米銀微粒之技術，以微波輔助合成法沉積零維奈米銀於奈米碳管及氧化石墨烯表面，此奈米碳管/碳紙與氧化石墨烯/碳紙之複合碳材分別由觸媒化學氣相沉積法與化學反應法製備而得。零維奈米銀觸媒之特性則藉由掃描式電子顯微鏡、X光繞射儀、高解析穿透式電子顯微鏡、熱重分析儀、X-光光電子光譜、循環伏安及交流阻抗測試進行分析。 電化學測試系統中，循環伏安測試結果顯示奈米銀觸媒於1 M氫氧化鈉溶液環境下具有可逆的氧化還原反應。兩相比較下可發現，氧化石墨烯除了有較低之擴散阻抗外亦有較高之觸媒活性。交流阻抗結合等效電路分析，氧化石墨烯在降低觸媒與集電板之接觸阻抗中扮演了重要的角色，歸因於包覆碳紙之奈米片狀氧化石墨烯提供面接觸，相較於點接觸之奈米碳管，能降低其內部阻抗。 本研究更進一步以微波輔助合成法製備一維奈米銀線，經由掃描式電子顯微鏡、X光繞射儀及高解析穿透式電子顯微鏡分析此奈米銀線之結構。並藉由調整微波反應之時間，控制奈米銀線成長之長短。以一維奈米銀線作為觸媒進行電化學測試，一維奈米銀觸媒之氧化還原能力不及零維奈米銀觸媒，其原因為奈米銀線表面之保護劑聚乙烯吡咯烷酮降低了觸媒與電解液之接觸，導致觸媒使用率下降。然而以交流阻抗分析發現，奈米銀線因本身之一維結構提供電子一連續性之傳導途徑，因此有較低之電阻值，亦即有較優越之導電性。
並列摘要
The results presented in this work apparently show an efficient microwave synthesis of nanosized Ag particals deposits over carbon nanotubes (CNTs)- and graphene oxide (GO)-based electrodes. The CNTs and GO nanosheets over carbon paper (CP) electrodes were prepared by catalytic chemical vapor deposition (CVD) and chemical reaction, respectively. The zero-dimensional silver nanocatalyst electrodes are characterized by FE-SEM, XRD, HR-TEM, TGA, XPS, CV and EIS. Both Ag-CNT and Ag-GO electrodes exhibit redox reversibility with a potential region of 0 − 0.5 V vs. saturated calomel electrode (SCE) in 1 M NaOH. The CV measurement indicated that Ag-GO electrode represents not only low diffusion resistance but also high catalytic activity when compared with those of the Ag-CNT electrode. The EIS analysis incorporated with equivalent circuit confirms that the presence of GO plays a crucial role in lowering the interfacial resistance between active materials and current collector. This enhancement of the inner resistance, attributed to the fact that the GO nanosheets cover the CP substrate offers a plane contact, when compared with the point contact of CNTs. This study also synthesizes one-dimensional silver nanowires by using microwave assisted approach. The silver nanowires are characterized by FE-SEM, XRD, and HR-TEM. The length of nanowires can be well controlled by different microwave periods. One-dimensional silver catalyst exhibits the catalytic activity, showing a lower activity than zero-dimensional silver catalyst. Because the polyvinylpyrrolidone (PVP) reduces the surface area for contact with the electrolyte, such polymeric coating onto the Ag nanowires reduces the catalytic accessibility. However, the silver nanowires offers one-dimensional pathway for charge conductivity, thus leading to lower inner resistance, confirmed by the EIS analysis.