Electrochemistry at highly oriented pyrolytic graphite (HOPG): lower limit for the kinetics of outer-sphere redox processes and general implications for electron transfer models

Abstract

Original citation:Zhang, Guohui, Cuharuc, Anatolii S., Güell, Aleix G. and Unwin, Patrick R.. (2015) Electrochemistry at highly oriented pyrolytic graphite (HOPG) : lower limit for the kinetics of outer-sphere redox processes and general implications for electron transfer models. Physical Chemistry Chemical Physics (Number 17). pp. 11827-11838. Permanent WRAP url: http://wrap.warwick.ac.uk/67805 Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes this work of researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.Copies of full items can be used for personal research or study, educational, or not-forprofit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. Publisher statement:First published by Royal Society of Chemistry 2015 http://dx.doi.org/10.1039/C5CP00383K 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. This simple configuration allows measurements to be made on a very short time scale after cleavage of HOPG, so as to minimise possible effects from (atmospheric) contamination, and with minimal, if any, change to the HOPG surface. However, the droplet-cell geometry differs from more conventional electrochemical setups and is more prone to ohmic drop effects. The magnitude of ohmic drop is elucidated by modelling the electric field in a typical droplet configuration. These simulations enable ohmic effects to be minimised practically by optimising the positions of the counter and reference electrodes in the droplet, and by using a concentration ratio of electrolyte to redox species that is higher than used conventionally . It is shown that the ET kinetics for all of the redox species studied herein is fast on all grades of HOPG and lower limits for ET rate constants are deduced. For IrCl 6 2-/3-and Fe(CN) 6 3-/4-, ET on HOPG is at least as fast as on Pt electrodes, and for Ru(NH 3 ) 6 3+/2+ ET kinetics on HOPG is comparable to Pt electrodes. Given the considerable difference in the density of electronic states (DOS) between graphite and metal electrodes, the results tend to suggest that the DOS of the electrode does not play an important role in the ET kinetics of these outer-sphere redox couples over the range of values encompassing HOPG and metals. This can be rationalised because the DOS of all of these different electrode ma...

Impact of Adsorption on Scanning Electrochemical Microscopy Voltammetry and Implications for Nanogap Measurements

“…63 Comparison of experimental to computed diffusional waves (using precise diffusion coefficients) showed that the experimental currents exceeded the simulated ones (see SI, Section S-2, Figure S-1 (c)), whereas the reverse scan voltammetry fitted quite well. Thus, while FcTMA + adsorbs at the HOPG electrode, FcTMA 2+ that is produced does not adsorb appreciably and a significant proportion of FcTMA 2+ produced by the oxidation of adsorbed FcTMA + , diffuses away from the electrode on this timescale.…”

“…Fresh HOPG basal surfaces were prepared by gently pressing down Scotch tape on to the sample and pullingoff the top layers, as reported extensively in the literature. 33,[60][61][62][63] Cyclic Voltammetry and SECM Instrumentation cm 2 ) with the counter and reference electrode placed into the droplet. 63 An advantage of this electrochemical cell is that it can be assembled and used within seconds of sample cleavage, 63 minimizing surface contamination.…”

Nanoscale Electrocatalysis of Hydrazine Electro-Oxidation at Blistered Graphite Electrodes

“…[13][14][15] This is particularly true of graphite, which comprises stacked graphene layers with weak van der Waals force present between the layers. 7 While outer sphere redox processes, and some more complex electron-proton coupled processes, occur readily at the basal structure of graphite, [16][17][18][19][20][21] electrocatalytic (bond-breaking) reactions often require additional efforts to promote the electrochemical activity. There are 3 broad, and somewhat interrelated, approaches and effects to consider: (i) selective doping of sp 2 materials by various heteroatoms (e.g.…”

Electrochemical oxidation of dihydronicotinamide adenine dinucleotide (NADH): comparison of highly oriented pyrolytic graphite (HOPG) and polycrystalline boron-doped diamond (pBDD) electrodes

“…22,40,41 In the case of outer sphere redox processes, electron transfer rates are at least as fast at HOPG as on platinum. 27 The studies reported herein on the electrochemical oxidation of NADH at HOPG and oxygen-terminated pBDD reinforce, and amplify, the recent models on the properties and activity of these electrode materials, while also providing detailed new insights on adsorption and surface fouling (contamination) processes. These measurements are complemented with high resolution scanning electrochemical cell microscopy (SECCM) 42,43 experiments to map the electrochemical activity of HOPG and pBDD and confirm the macroscopic findings.…”

“…It comprises of extensive basal terraces with a low density of point defects, 26,27 and a step edge density that depends on the grade (quality) of the HOPG. 28,29 Although early work considered the basal surface of HOPG to have ultra-low (or no) electrochemical activity, 27,[29][30][31][32][33][34][35][36][37][38][39] recent studies have highlighted the high activity of the basal surface for both simple redox reactions and more complex coupled electron-proton transfer processes. 22,40,41 In the case of outer sphere redox processes, electron transfer rates are at least as fast at HOPG as on platinum.…”