Carbon-Supported Fe鈥揘x Catalysts Synthesized by Pyrolysis of the Fe(II)鈥?,3,5,6-Tetra(2-pyridyl)pyrazine Complex: Structure, Electrochemical Properties, and Oxygen Reduction Reaction

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• 作者：Amado Vela虂zquez-Palenzuela ; Lei Zhang ; Liucheng Wang ; Pere Llui虂s Cabot ; Enric Brillas ; Ken Tsay ; Jiujun Zhang
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：July 7, 2011
• 年：2011
• 卷：115
• 期：26
• 页码：12929-12940
• 全文大小：1203K
• 年卷期：v.115,no.26(July 7, 2011)
• ISSN：1932-7455

文摘

Carbon-supported Fe鈥揘_x/C catalysts were synthesized at several pyrolysis temperatures such as 600, 700, 800, and 900 掳C in the effort to investigate the temperature effect on the catalyst structures. The Fe contents in the synthesized catalysts were found to be about 1 wt % more than that in the Fe鈥揟PPZ/C precursor complex (5 wt %), indicating that both the carbon support and complex ligand might be decomposed during the pyrolysis. X-ray diffraction (XRD) analysis revealed that the samples at 600鈥?00 掳C had no iron species segregation, while that formed at 900 掳C showed the formation of Fe₃C and Fe₃O₄, confirmed by transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and energy dispersive X-ray analysis (EDX) measurements. TEM images clearly showed that the large sizes of Fe₃C and Fe₃O₄ species with a diameter of about 500 nm were wrapped up by a thin carbon layer. For Fe states, X-ray photoelectron spectroscopy (XPS) data revealed that Fe³⁺ was the dominant Fe species in the Fe鈥揘_x/C sample. Several nitrogen-containing species such as pyridinic N, the Fe鈥揘(pyr) bond, quaternary N,N-oxides, as well as graphitic nitrogen were identified by XPS in the catalyst samples. Electrochemical characterization revealed a reversible Fe(III)鈥揘_x/Fe(II)鈥揘_x redox wave at 0.63 V vs RHE, which is believed to be the active sites for the oxygen reduction reaction (ORR). The density of this active site was found to be dependent on the pyrolysis temperature, and high densities were obtained in the temperature range of 700鈥?00 掳C. In addition, the morphology of the catalyst samples was also analyzed using the change of double-layer charge with the potential scan rate. Furthermore, the Fe鈥揘_x/C catalysts were found to have strong catalytic activity toward oxygen reduction reaction with an overall electron transfer number of 3.6.