Influence of Tip and Substrate Properties and Nonsteady-State Effects on Nanogap Kinetic Measurements: Response to Comment on “Impact of Adsorption on Scanning Electrochemical Microscopy Voltammetry and Implications for Nanogap Measurements”

Abstract

However, beyond the adsorption/desorption phenomena that we have highlighted, ion current rectification is an important consideration in ion-flux measurements with charged glass nanopipets, 34 nanopores, 35 and scanning ion conductance microscopy 34,36 and so there may be UME glass-charge effects to consider for nanogap SECM voltammetry.

Voltammetric Measurement of Adsorption Isotherm for Ferrocene Derivatives on Highly Oriented Pyrolytic Graphite

“…The unverified adsorption parameters reported in the previous studies 15,16 were inappropriately used to argue very small effects of surface adsorption on SECM-based nanogap voltammetry. 16,20 By contrast, adsorption parameters were determinable reliably in this study by analyzing the entire voltammogram without kinetic complications 12 even at fast scan rates of up to 10 V/s, not only because good background subtraction was possible, owing to the low capacitance of HOPG, 31 but also because only one form of a redox couple was adsorbed on HOPG. 3 Adsorption parameters are not determinable from CV when both forms of a redox couple are adsorbed on the electrode surface under equilibrium conditions.…”

“…In addition, the Langmuir isotherm was only assumed to assess the effect of surface adsorption on SECM-based nanogap voltammetry of FcTMA + at HOPG. 16,20 In this work, we analyze CV of ferrocene derivatives at the basal plane of HOPG by the finite element method with the Frumkin isotherm to separately parametrize ferrocene−HOPG and ferrocene−ferrocene interactions. The Frumkin isotherm is based on the Bragg−Williams approximation 21 and is given by 22…”

“…The recent CV studies , assumed, without experimental verification, that cyclopentadienyl rings of adsorbed ferrocene derivatives are closely packed despite the existence of substituents. In addition, the Langmuir isotherm was only assumed to assess the effect of surface adsorption on SECM-based nanogap voltammetry of FcTMA + at HOPG. , …”

Double layer effects in voltammetric measurements with scanning electrochemical microscopy (SECM)

“…For example, our previous measurement of FcTMA 2+ adsorption at glass [30] showed the accumulation of FcTMA 2+ for the glass/solution interface. Adsorption of redox couples, on both the glass and electrodes, even at low levels, will change the interfacial charge and properties dynamically during a voltammetric scan and is increasingly recognised as an important consideration in nanoconfined systems [40,70,71] and we have recently pointed out the importance of thoroughly characterising all surface and interfaces deployed in nanoscale systems [72]. We haven't treated this aspect herein, in order to keep the modelling tractable, but the model could be developed further in the future.…”

Bioelectronics and Interfaces Using Monolayer Graphene

“…The recent development of scanning or local electrochemical methods such as Scanning Electrochemical Microscopy (SECM) and Scanning Electrochemical Cell Microscopy SECCM have contributed significantly to the understanding of the ET kinetics on basal plane and at the edges . More than 25 years ago it was predicted that the range of ET rate constant potentially accessible using SECM is 1< k 0 <20 cm −1 , for redox species with typical diffusion coefficient in the order of 10 −5 cm 2 s −1 . This is a promising approach for determining locally the ET rate of single carbon nanotubes and graphene electrodes.…”