The cyclic voltammetric response of electrochemically heterogeneous surfaces

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

“…Given the strong views in the literature that defects, originally focused on step edges, 21,22,24,25,27,28,91 but recently extended to point defects, 92 are the only sites for ET on HOPG even for outersphere processes, we can further analyse our data in terms of a partially active surface model for charge transfer (schematic Figure 10). 93 In line with this older work, we assume that the basal plane is inert, with two types of active site, i.e.…”

“…A host of literature 2, [21][22][23][24][25][26][27][28][29][30] in the past 2 decades resulted in a dominant opinion that step edges were responsible for all, or nearly all, of the observed electrochemical activity of HOPG electrodes. For example, studies of Fe(CN) 6 3-/4-found standard rate constant, k 0 , values at the basal plane ranging from nearly zero (k 0 < 10 -9 cm s -1 ) 31 to little activity (k 0 < 10 -6 cm s -1 ) 22,24 .…”

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

“…53 The pBDD had a roughness of 1-2 nm within a facet and 1-5 nm between grains, flat on the scale of SECCM and voltammetric measurements. 51 Studies of basal plane HOPG employed one of three different grades: either ZYB or SPI-3 grade (SPI Supplies, West Chester, PA), or an ungraded HOPG sample of the highest quality, 30 originating from Dr. Arthur Moore at Union Carbide (now GE Advanced Ceramics), and kindly provided by Prof. R. L. McCreery of the University of Alberta, Canada, which we refer to throughout as "AM grade"). All HOPG samples were cleaved with Scotch tape to remove surface layers and reveal a fresh surface for study.…”

“…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.…”

Intrinsic electrochemical activity of single walled carbon nanotube–Nafion assemblies

“…In the diffusional domain approach, the individual active sites were approximated as electrochemically active discs of radius r 1 within cylinders of radius r 2 , with inert Here, we make the assumptions that the defects are of uniform size (r 1 = 0.5 or 1 nm), the individual diffusion domains can be approximated to a cylinder, 79,80 and transport in the Nafion film can be described by Fick's laws of diffusion. The defect radius is assumed to be the same as the radius of a SWNT, which provides a generous approximation of the area for an active site on the sidewall.…”