利用逆微胞法製備白金與核殼式白金-鈷觸媒及其氧氣還原反應特性探討

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Title:	利用逆微胞法製備白金與核殼式白金-鈷觸媒及其氧氣還原反應特性探討
Other Titles:	Preparation and characterization of Pt and Corich core-Ptrich shell electrocatalysts by reverse micelle method for oxygen reduction reaction
Authors:	李政融 Lee, Zheng-Rong
Contributors:	杜景順 Do, Jing-Shan 東海大學化學工程與材料工程學系
Keywords:	氧氣還原反應;核殼式觸媒;金屬置換法;逆微胞法;電極穩定性 oxygen reduction reaction, core-shell structural electrocatalyst, transmetallation, reverse micelle, electrode stability
Date:	2009
Issue Date:	2011-02-22T07:44:40Z (UTC)
Abstract:	在氫氧式燃料電池中，陰極氧氣還原半反應動力較陽極的氫氣氧化半反應慢，使得全電池效能降低，因此在本研究中利用逆微胞法製備Pt/C，Pt-Co/C與Corich core-Ptrich shell/C電極觸媒，探討其氧氣還原反應特性並比較之，期望降低白金的用量與提高其氧氣還原動力。在製備Corich core-Ptrich shell/C的製備過程中，首先以逆微胞法製備Co粒子，再分別以金屬置換法(程序一)(Corich core-Ptrich shell/C-MT I)以及金屬置換法結合化學還原法(程序二)(Corich core-Ptrich shell/C-MT II)，將白金前驅鹽製備於鈷粒子上形成Pt殼層。接著將利用熱回火之處理方式修飾製備所得電極觸媒，並探討對氧氣還原反應特性與穩定性之影響。文中利用XRD (X-ray diffractometer)分析製備所得電極觸媒的晶粒大小與結晶性、TEM (transmission electron microscopy)觀察其顆粒大小與分散性、AAS (atomic absorption spectrophotometer)分析觸媒中Pt與Co組成。並在0.5M HClO4水溶液中，以循環伏安(cyclic voltammetry, CV)掃描法分析電極觸媒的電化學活性面積與穩定性。本研究亦將製備所得之電極觸媒製備為平板電極後，利用極化曲線(polarization curve)法探討氧氣還原反應特性。實驗結果顯示Corich core-Ptrich shell/C-MT II電極觸媒，經400℃熱回火處理2小時修飾後，具有最大之質量活性與比活性其值分別為16.4 A g-1與31.9 μA cm-2與商品化之Pt/C (E-TEK 20% Pt on XC-72R)比較，其質量活性與比活性分別為商品化Pt/C的1.64與2.47倍。　　在電極觸媒穩定性方面，經熱回火處理後之自製Pt/C電極觸媒所得之電化學活性面積穩定性改善了43 %，而於0.9 V(vs. RHE)時之氧氣還原反應電流密度之穩定性提昇了31%。但經熱回火處理之Corich core-Ptrich shell/C-MT II (Pt/Co原子比為1/5)因核心Co遷移至殼層，因而電化學活性面積穩定性降低了16 %，而氧氣還原反應電流密度之穩定性則下降了18 %。 The overall performance of H2/O2 fuel cell is generally limited by the slow oxygen reduction reaction (ORR) on the cathode compared with the hydrogen oxidation on anode. Therefore in this work were prepared Pt/C, Pt-Co/C, Corich core-Ptrich shell/C electrocatalysts via reverse micelle method. One of Corich core-Ptrich shell/C electrocatalysts were prepared by two procedure. In procedure I, first Co particles was prepared by reverse micelle method, and via transmetallation method prepared Corich core-Ptrich shell/C ( Corich core-Ptrich shell/C-MT I by Procedure I) . In procedure II, first prepared Co particles by reverse micelle method, and via transmetallation method prepared Corich core-Ptrich /C, final by chemical reduction method to increase Pt loading on Pt shell ( Corich core-Ptrich shell/C-MT II by Procedure I) .The catalysts were characterized by different techniques: XRD (X-ray diffraction), TEM (transmission electron microscope), and AAS (atomic absorption spectrophotometer). The electroactive areas and stability of home-made electrocatalysts were evaluated by cyclic voltammetry (CV). The polarization curve method for slab electrode in 0.5M HClO4 aqueous solution were used to study the electrocatalysts activity.The experimental results , Corich core-Ptrich shell/C-MT II (atomic ratio Pt/Co = 1/5) was prepared by Procedure II and via thermal annealing treatment electrocatalyst has the maximum MA and SA( 16.4 A g-1& 31.9 μA cm-2 ).The durative CV method was used to investigate the stability of home-made electrocatalysts. The stability of electroactive areas and the stability of ORR current density of home-made Pt/C electrocatalyst treated by annealing, it is rise 43% and 31%. However, the Corich core-Ptrich shell/C-MT II (atomic ratio Pt/Co = 1/5) electrocatalyst treated by annealing, the stability of electroactive areas and the stability of ORR current density decrease 16% and 18%.
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