Electrochemistry of Fe^3+/2+ at highly oriented pyrolytic graphite (HOPG) electrodes: kinetics, identification of major electroactive sites and time effects on the response

Abstract

A note on versions:The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP url' above for details on accessing the published version and note that access may require a subscription. derived from simulation of the experimental results, which fell into the range of the values reported for metal eletrodes, e.g. platinum and gold, despite the remarkable difference in density of electronic states (DOS) between HOPG and metal electrodes. This provides further evidence that outer-sphere redox processes on metal and sp 2 carbon electrodes appear to be adiabatic. Complementary surface electroactivity mapping of HOPG, using scanning electrochemical cell microscopy, reveal the basal plane to be the predominant site for the Fe 3+/2+ redox process. It is found that time after cleavage of the HOPG surface has an impact on the surface wettability (and surface contamination), as determined by contact angle measurements, and that this leads to a slow deterioration of the kinetics. These studies further confirm the importance of understanding and evaluating surface structure and history effects in HOPG electrochemistry, and how high resolution measurements, coupled with macroscopic studies provide a holistic view of electrochemical processes.

Scanning electrochemical cell microscopy: New perspectives on electrode processes in action

“…Most importantly, as with any high resolution measurement, one should carefully checkwhen possiblethat measurements at the nanoscale map onto macroscale responses. This aspect is well-illustrated by studies of sp 2 carbon 9 electrode materials, where macroscopic kinetics measurements can be made within seconds of preparing a surface and compare very well with SECCM [4,26].…”

“…SECCM scans can often be started within a few minutes of preparing a surface and one can check the fidelity of the scan response at similar types of surface site that are encountered at different points in the image [25,26]. Most importantly, as with any high resolution measurement, one should carefully checkwhen possiblethat measurements at the nanoscale map onto macroscale responses.…”

Imaging the reactivity and width of graphene's boundary region

“…7,18 This is in stark contrast to results by Unwin and co-workers who interpreted their elegant high-resolution electrochemical imaging experiments as the basal plane displaying a faster electron transfer. 19,20 The interruption of the regular hexagonal structure at graphene's edges manifests itself through the emergence of the so-called D peak (B1360 cm À1 ) in the Raman spectra, which indicates defects in the graphene lattice. 10 Strano and co-workers even observed an increased D peak intensity around the edges after chemical functionalisation.…”

Electrochemical properties of vertically aligned graphenes: tailoring heterogeneous electron transfer through manipulation of the carbon microstructure

“…The electrochemical properties of graphene have been reported recently to be dependent upon its ake/lateral size, [11][12][13] the number of stacked layers, 14,15 its manufacturing process and resultant defect and contaminant content, 6,16,17 and by its geometry/structure. [18][19][20] In terms of general electrochemical reactivity at 2D carbon nanomaterials, there is an on-going debate encompassing both computational and experimental studies, exploring the electron transfer properties of edge plane like-sites/defects [21][22][23][24][25] and basal/terrace planes, 26,27 with some contradictory reports as to the respective electrocatalytic properties.…”