以電鍍法製備鈀銀合金薄膜與其儲氫後之應用

Preparation of Palladium-Silver alloy membrane by electroplating and applications after hydrogen storage

吳勇毅(Yung-Yi Wu)

指導教授 ： 胡啟章

國立清華大學/工學院/化學工程學系/碩士(2014年)

摘要

中文摘要
常見的鈀銀合金薄膜製備方式以無電電鍍法為主，再將其進行熱處理形成鈀銀合金而得，製程上具有步驟較為繁瑣、耗時較長、薄膜厚度難以控制…等缺點;另一方面，無電電鍍法所使用的還原劑多為聯氨和次磷酸鹽類，此種還原劑本身具有毒性，無論是對人體或環境均有危害，應盡可能地避免，故本研究希望能夠藉由電鍍的製備方式來取代還原劑之使用。首先，由初步測試發現鈀銀組成會隨著添加劑與電鍍參數的不同而有所改變，為了更有效率地瞭解該電鍍系統之顯著因素，且從文獻中可得知鈀銀合金薄膜組成約為3:1時，較利於氫氣穿透且穩定性較佳，於是利用部分因素實驗設計法控制鈀銀組成。
而根據實驗結果可發現所得鍍層的鈀銀比例均非常接近鍍浴中鈀銀離子的比例，表示該鍍浴已接近平衡電鍍系統。隨後藉由固定鍍浴總濃度並僅改變鈀銀離子濃度比例的方式，可得到鍍層Pd/Ag與鍍浴Pd2+/Ag+之關係圖及其操作方程式。然而，為了更有效地抑制樹枝狀結構的發生，以加入含胺官能基之添加劑，如:Lugalvan G35、Lugalvan IZE、Lugalvan P來做比較，研究發現當Lugalvan G35與Lugalvan P同時存在於鍍浴中即可達到相當平整的表面形態，且亦可將鈀銀比例控制約3:1。在材料分析方面，分別利用能量散射光譜儀(EDX)、場發射電子顯微鏡(FE-SEM)及X光晶格繞射(XRD)測量鈀銀合金組成、表面形態及結晶性變化。
接著則是針對黏著性最佳的鍍層進行電化學行為分析，根據文獻中的理論模型，以電化學方法估算氫於不同鈀銀組成之鍍層中的擴散係數，測得擴散係數的大小為Pd3Ag1＞Pd5Ag1＞Pd＞Pd2Ag1＞Pd1Ag1，證實了鈀與銀的比例為3:1之鈀銀合金薄膜較利於作為氫氣穿透薄膜之應用。最終則根據不同組成的鈀銀電極與氫擴散係數的關係，在電化學參考電極的應用上選擇純鈀電極，由常溫常壓鍍浴環境的電位穩定性測試可發現氫化鈀電極的參考電位約為50～85 mV(vs. RHE)且可穩定長達數小時，將氫化鈀電極實際作為電化學參考電極應用時，發現氫化鈀電極無論在常溫、高溫或超臨界流體環境中均可作為電化學參考電極之使用。

關鍵字:鈀銀合金薄膜、電鍍、實驗設計法、含胺官能基之添加劑、氫化鈀電極、電化學參考電極應用

關鍵字

鈀銀合金薄膜 ； 電鍍 ； 實驗設計法 ； 含胺官能基之添加劑 ； 氫化鈀電極 ； 電化學參考電極應用

並列摘要

Abstract
The general practice for the synthesis of Pd-Ag alloy membrane consists of the electroless deposition of layers of Pd and Ag alternately, which are then annealed to form Pd–Ag alloy. However, there are some disadvantages in the above manufacturing process, such as complicated steps, time-consuming and difficult to control the membrane thickness. On the other hand, the most common reducing agents used in electroless method are hydrazine (N2H4) and sodium hypophosphite (NaH2PO2), which are very toxic to human body and environment, so it must be avoided to use as much as possible. Hence, the goal of this study is to prepare the alloy by using electroplating method without any toxic reducing agent. Firstly, preliminary results of this study found that the composition of Pd and Ag can be varied with additives and plating parameters. Because most of literatures have reported that Pd-Ag membrane composed of approximately 75 % Pd content, which is suitable for hydrogen permeation and stability. Furthermore, the fractional factorial design (FFD) was carried out in order to efficiently find out the significant factors during the electroplating bath system, which is used to control the composition of Pd-Ag deposition.
In this study, the Pd-Ag ratios in all the deposits are almost equivalent to its proportion in plating solution, which shows the electroplating process of Pd-Ag system is approaching equilibrium codeposition. On the other hand, the operational equation and relation between Pd/Ag ratio in Pd-Ag deposits and Pd2+/Ag+ ratio in plating solutions were obtained by fixing the total concentration of the plating bath and varying the Pd2+/Ag+ concentration ratios. However, in order to reduce the dendritic structures during the deposition process on the surface, the additives containing amino-group, such as Lugalvan G35, Lugalvan IZE and Lugalvan P were added to inhibit the formation of dendrites efficiently. These results show that the relatively smooth surface morphology could be achieved with plating bath containing Lugalvan G35 and Lugalvan P simultaneously. The ratio of Pd/Ag in this deposit was almost equal to 3. The surface morphology, material compositions, and crystalline structure of the as prepared alloy were characterized by using scanning electron microscopic (SEM), energy-dispersive X-ray (EDX) spectroscopic, and X-ray diffraction (XRD) analysis respectively.
For study of hydrogen adsorption/desorption, the Pd-Ag electrodes with best adhesion were chosen and electrochemical analyses were carried out. The hydrogen diffusion coefficient in the deposition with various Pd-Ag compositions can be evaluated according to the theoretical models in the previous reported literatures. The order of diffusion coefficients is listed below: Pd3Ag1＞Pd5Ag1＞Pd＞Pd2Ag1＞Pd1Ag1, indicating that the Pd-Ag membrane with Pd/Ag ratio of 3 is more suitable for application of hydrogen permeation membrane. Finally, based on the relation between electrodes with different Pd-Ag compositions and hydrogen diffusion coefficients, the pure Pd electrode was chosen for application of electrochemical reference. From the potential stability test in normal plating bath condition, the stable potential of palladium-hydride is about 50～85 mV(vs. RHE) and last several hours. Furthermore, the palladium-hydride electrodes can be practically used as an electrochemical reference electrode even at high temperature or in supercritical fluid conditions.
Keywords: Pd-Ag alloy membrane, electroplating; fractional factorial design; additives containing amino-group; palladium-hydride electrode; electrochemical reference applications

並列關鍵字

Pd-Ag alloy membrane ； electroplating ； fractional factorial design ； additives containing amino-group ； palladium-hydride electrode ； electrochemical reference applications

參考文獻

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