Effects of redox system structure on electron-transfer kinetics at ordered graphite and glassy carbon electrodes

Abstract

The basal plane of highly ordered pyrolytic graphite (HOPG) serves as an ordered model of more commonly used electrode surfaces such as glassy carbon (GC) and pyrolytic graphite. The defect density on the basal plane HOPG was reduced by careful cleaving and cell design and was verified to be low by requiring that AEp for Fe(CN)6*123"/4" (1 M KCI) be greater than 700 mV for a 0.2 V/s scan rate. Then a variety of redox systems were examined on "validated" HOPG surfaces, and variations In the electron transfer rate constant, Ab°, were observed. All 13 redox systems exhibited relatively fast kinetics on laser activated GC (A® > 0.03 cm/s for eight Inorganic systems), and In several cases A® exceeded the Instrumental limit. On HOPG, however, A£p varied greatly for the 13 systems, ranging from 66 to >1200 mV. The reasons for this variation fall into three general classifications. First, reactions Involving proton transfer (e.g. catechols) were all slow on HOPG, Implying some role of the surface In mediating multistep processes. Second, the observed rate correlated with the exchange rate for homogeneous electron transfer, but the heterogeneous rates on HOPG were 3-5 orders of magnitude slower than that predicted from simple Marcus theory. Third, the physical properties of HOPG, such as density of electronic states and hydrophoblclty, may depress A® relative to GC and metals.

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

“…The well-known scotch tape method was used to cleave HOPG. 23,[27][28][29]33,41,[45][46][47][48][49] Similarly, the CV response of pBDD was measured either with or without polishing the electrode surface between each CV, and we again state when each method was used. The pBDD electrode was polished with alumina particles (ca.…”

Molecular Functionalization of Graphite Surfaces: Basal Plane versus Step Edge Electrochemical Activity

“…AM, ZYA, SPI-1 and SPI-3 grade HOPG surfaces were freshly prepared for voltammetry measurements by peeling back the top layers of HOPG with Scotch tape, with the cleaving direction maintained to avoid deformation, until the tape was totally covered with HOPG, as routinely done in the literature. 27,37,40,41,49,50,57,[59][60][61] Fresh surfaces of AM HOPG were also revealed by mechanically cleaving with a clean razor blade, inserted perpendicular to the basal plane with a gentle rocking motion until a small piece delaminated spontaneously, as adopted elsewhere. 27,51,62 Both procedures were used for the macroscopic studies of AM grade HOPG, with samples respectively labelled as AM S and AM M .…”

“…40,49,50 Moreover, microscopic and nanoscopic measurements have reported high intrinsic activity of the basal surface, 40,41,49,[51][52][53][54][55] in contrast with the earlier literature, which proposed that the basal surface of HOPG was inert or largely inert. 56,57 In this paper we report detailed investigations of the adsorption and electrochemistry of AQDS on HOPG, with the particular goal of elucidating whether it is an appropriate measure for determining step edge density. More generally, this serves as an important model system to introduce new methodology for localized quantitative measurements of adsorption.…”

Structural effects in electron transfer reactions: comparative interfacial electrochemical kinetics for cis- versus trans-dioxorhenium(V)(bi)pyridine oxidation

“…McCreery has shown that HOPG electrodes attenuate interfacial ET rates by ca. 3-4 orders of magnitude [19].…”