0.5M H2SO4中Ti-Cu、Ti-Co二元薄膜觸媒對氧還原之催化反應

Catalytic activity of Ti-Cu and Ti-Co films for oxygen reduction reaction in 0.5 M sulfuric acid solution

朱恆慶(Heng-Ching Chu)

指導教授 ： 林景崎

國立中央大學/工學院/機械工程學系/碩士(2007年)

摘要

本研究由磁控濺鍍法製備不同比例之鈦-銅(Ti-Cu)與鈦-鈷(Ti-Co)金屬二元薄膜觸媒。在0.5M硫酸溶液中，以慢速極化掃描(SSV)、循環伏安法(CV)、旋轉碟型電極(RDE)與塔弗極化作圖法(Tafel-Plot)等電化學技術，來研究其在0.5M H2SO4對氧還原反應(ORR)之催化作用。此外以能量散佈光譜儀(EDS)來分析薄膜所含之元素，以X光光電子質譜儀(XSP)等來解析反應前後薄膜化學狀態之變化，綜合以上結果來探討不同薄膜對氧還原反應。
電化學技術中，SSV結果顯示：Ti-Cu與Ti-Co兩系統對ORR反應均有催化作用。在Ti-Cu系統中，Cu含量約在50~90 atom%之間；在Ti-Co系統中，Co含量約在40~60 atom%之間，均有良好催化效果。由SSV掃描圖中之可以獲得ORR的氧還原之起始電位(Eonset)及其還原電流。比較兩種二元系統之還原起始電位得知：Ti-Cu系統之Eonset(0.6~0.7V)低於Ti-Co系統之Eonset(1V)。系統之Eonset結果顯示，Ti-Cu系統對ORR反應之過電位較大，不如Ti-Co系統。在0V與0.2V電位下之ORR反應之還原電流，且此電流隨Cu、Co濃度增加而增大。在同合金濃度下Ti-Co系統大於Ti-Cu系統，例如在0.2V下Ti50-Cu50系統之還原電流(28.57μA/cm2)低於Ti50-Co50系統之還原電流(272.14μA/cm2)。CV圖譜有助於理解薄膜系統在0.5M H2SO4中之反應結果。CV結果顯示：Ti-Cu系統在第一次掃描中在0.5V處有強且寬的銅的氧化峰出現，此氧化峰為Cu氧化成Cu+和Cu2+。而在第二次掃描中僅在0.3V出現小的峰值，此氧化峰為Cu氧化成Cu2+。相較之下Ti-Co系統在0~1.2V間有對稱之還原及氧化峰，並無其他峰值出現。在0.5M H2SO4中Ti-Co系統比Ti-Cu系統穩定。RDE實驗結果配合Koutecky-Levich方程式可推算ORR反應中參與反應之電子數。在Ti-Cu系統中電子轉移數為4；而Ti-Co系統電子轉移數為3。Tafel極化結果顯示：Ti-Cu與Ti-Co兩系統中各成份之交換電流密度(j0，μA/cm2)大小依序為Co (1.26 x 10-8) > Cu (8.54 x 10-9) > Ti (1.21 x 10-10).

關鍵字

氧還原反應 ； 鈷 ； 電化學觸煤 ； 銅 ； 鈦

並列摘要

Catalytic activity of Ti-Cu and Ti-Co films for oxygen reduction reaction (ORR) in the 0.5M H2SO4 was investigated in this work. Ti-Cu and Ti-Co films in variant compositions were prepared with magnetron sputtering method. Electrochemical technologies such as slow scan voltammetry (SSV), Tafel-Plot (TP), cyclic voltammetry (CV), and rotating disk eelectrode (RDE) were employed to study the electrochemical behavior of the films. Energy dispersive spectrometry (EDS) and x-ray photoelectron spectrometer (XPS) were applied to analyze the composition of the films before and after electrochemical testing.
The results of SSV indicated that both Ti-Cu and Ti-Co films were catalytically active for ORR. Ti-Co films were more active than Ti-Cu. The catalytic activity increases with increasing the concentration of Co (from 40-60 at%) in Ti-Co films and that of Cu (from 50 to 90 at%) in Ti-Cu. With higher catalytic activity, Ti-Co film revealed higher onset potential (i.e., at 1.0 V) than Ti-Cu (i.e., 0.6~0.7V). At a constant potential of 0.2V, a film of Ti50Co50 indicated a greater reduction current density (272.14μA/cm2) than Ti50-Cu50 (i.e., 28.57μA/cm2).
Resulting from CV, there was a strong broad oxidation peak at 0.5V on the first scan cycle of the Ti-Cu films. This peak disappeared on the second cycle and a week small one present at lower potential (i.e., 0.3 V) instead of it. The strong broad peak is ascribed the oxidation of Cu to Cu+ and Cu2+ and the weak small one to only oxidation of Cu to Cu+. The cyclic voltammogram depicted that Ti-Co films revealed only a symmetrical and smooth loop in the potential range from 0 to 1.2V. No any peak was present on the loop. This phenomenon implied that Ti-Co was more stable than Ti-Cu. The instability of Ti-Cu film was due to dissolution of Cu in 0.5M H2SO4. .Using the RDE data and Koutecky-Levich equation, the number of electron transferred in the ORR process was estimated. Almost four electrons were transferred on the Ti-Cu and about three electrons were transferred on the Ti-Co films.
Tafel plot provided the evaluation of exchange current density for ORR. The exchange current density (μA/cm2) decreases in the order Co (1.26 x 10-8) > Cu (8.54 x 10-9) > Ti (1.21 x 10-10).

並列關鍵字

Oxygen reduction reaction ； electrocatalyst ； Cobalt ； Cupper ； Titania

參考文獻

[Yi] 衣寶廉,“燃料電池-原理與應用”,五南出版社, 2003

[Hu] Feng-Ping Hu , Xiao-Gang Zhang , Fang Xiao , Jun-Ling Zhang, Carbon, 43, 2005, pp.2931–2936

[Jal] V. Jalan, E.J. Taylor, J. Electrochem. Soc., 130, 1983, p.2299

[Jia] T. Jiang, G.M. Brisard, Electrochimica Acta, 52, 2007, pp.4487-4496

[Joh] John F. Moulder, William F. Stckle, Handbook of X-ray Photoelectron Spectroscopy, Physical Electronics Inc., 1995