A New View of Electrochemistry at Highly Oriented Pyrolytic Graphite

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• 作者：Anisha N. Patel ; Manon Guille Collignon ; Michael A. O鈥機onnell ; Wendy O. Y. Hung ; Kim McKelvey ; Julie V. Macpherson ; Patrick R. Unwin
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：December 12, 2012
• 年：2012
• 卷：134
• 期：49
• 页码：20117-20130
• 全文大小：762K
• 年卷期：v.134,no.49(December 12, 2012)
• ISSN：1520-5126

文摘

Major new insights on electrochemical processes at graphite electrodes are reported, following extensive investigations of two of the most studied redox couples, Fe(CN)₆^{4鈥?3鈥?/sup> and Ru(NH₃)₆3+/2+. Experiments have been carried out on five different grades of highly oriented pyrolytic graphite (HOPG) that vary in step-edge height and surface coverage. Significantly, the same electrochemical characteristic is observed on all surfaces, independent of surface quality: initial cyclic voltammetry (CV) is close to reversible on freshly cleaved surfaces (>400 measurements for Fe(CN)₆4鈥?3鈥?/sup> and >100 for Ru(NH₃)₆3+/2+), in marked contrast to previous studies that have found very slow electron transfer (ET) kinetics, with an interpretation that ET only occurs at step edges. Significantly, high spatial resolution electrochemical imaging with scanning electrochemical cell microscopy, on the highest quality mechanically cleaved HOPG, demonstrates definitively that the pristine basal surface supports fast ET, and that ET is not confined to step edges. However, the history of the HOPG surface strongly influences the electrochemical behavior. Thus, Fe(CN)₆4鈥?3鈥?/sup> shows markedly diminished ET kinetics with either extended exposure of the HOPG surface to the ambient environment or repeated CV measurements. In situ atomic force microscopy (AFM) reveals that the deterioration in apparent ET kinetics is coupled with the deposition of material on the HOPG electrode, while conducting-AFM highlights that, after cleaving, the local surface conductivity of HOPG deteriorates significantly with time. These observations and new insights are not only important for graphite, but have significant implications for electrochemistry at related carbon materials such as graphene and carbon nanotubes.}