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Electrochemical simulation is used to validate the geometry of commercially manufactured interdigitated array electrodes intended for use in generator–collector experiments, consisting of two interlocked arrays of band electrodes. A working surface is generated showing peak current as a function of scan rate and the inter electrode distance when cyclic voltammetry is performed at a single array of band electrodes. This working curve is then used to establish accurate electrode widths and inter-electrode distances of an interdigitated band array using a fully supported aqueous solution of ruthenium hexamine trichloride as a test system by running voltammetry at one of the two arrays at a time. Both arrays are then used at the same time to perform cyclic voltammetry to validate the established electrode geometries of 9.9 and 10.7 μ m for the electrode widths in the two arrays, and 10.5 μ m for the distance between adjacent electrodes. Cyclic voltammetry in generator–collector mode is then carried out, and these parameters used to successfully simulate the experimental data. The level of precision determined is essential for the quantitative interpretation of generator–collector measurements using interdigitated electrodes.

Recent progress in the theory and practice of voltammetry is surveyed and evaluated. The transformation over the last decade of the level of modelling and simulation of experiments has realised major advances such that electrochemical techniques can be fully developed and applied to real chemical problems of distinct complexity. This review focuses on the topic areas of: multistep electrochemical processes, voltammetry in ionic liquids, the development and interpretation of theories of electron transfer (Butler-Volmer and Marcus-Hush), advances in voltammetric pulse techniques, stochastic random walk models of diffusion, the influence of migration under conditions of low support, voltammetry at rough and porous electrodes, and nanoparticle electrochemistry. The review of the latter field encompasses both the study of nanoparticle-modified electrodes, including stripping voltammetry and the new technique of 'nano-impacts'.

Asymmetric Marcus–Hush (AMH) theory is applied for the first time in ionic solvents to model the voltammetric reduction of oxygen in 1-butyl-1-methylpyrrolidinium bis-(trifluoromethylsulfonyl)-imide and of 2-nitrotoluene (2-NT), nitrocyclopentane (NCP), and 1-nitro-butane (BuN) in trihexyltetradecylphosphonium tris(pentafluoroethyl)trifluorophosphate on a gold microdisc electrode. An asymmetry parameter, γ, was estimated for all systems as −0.4 for the reduction of oxygen and −0.05, 0.25, and 0 ± 0.05 for the reductions of 2-NT, NCP, and BuN, respectively, which suggests equal force constants of reactants and products in the case of 2-NT and BuN and unequal force constants for oxygen and NCP where the force constants of the oxidized species are greater than the reduced species in the case of oxygen and less than the reduced species in the case of NCP. Previously measured values for α, the Butler–Volmer transfer coefficient, reflect this in each case. Where appreciable asymmetry occurs, AMH theory was seen...

The voltammetry for the reduction of 2-nitrotoluene at a gold microdisk electrode is reported in two ionic liquids: trihexyltetradecylphosphonium tris(pentafluoroethyl)trifluorophosphate ([P14,6,6,6][FAP]) and 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([Emim][NTf2]). The reduction of nitrocyclopentane (NCP) and 1-nitrobutane (BuN) was investigated using voltammetry at a gold microdisk electrode in the ionic liquid [P14,6,6,6][FAP]. Simulated voltammograms, generated through the use of Butler–Volmer theory and symmetric Marcus–Hush theory, were compared to experimental data, with both theories parametrizing the data similarly well. An experimental value for the Marcusian parameter, λ, was also determined in all cases. For the reduction of 2-nitrotoluene, this was 0.5 ± 0.1 eV in both solvents, while for NCP and BuN in [P14,6,6,6][FAP], it was 2 ± 0.1 and 5 ± 0.1 eV, respectively. This is attributed to the localization of charge on the nitro group and the primary nitro alkyl’s increase...

Microelectrode voltammetry is used to study the electrochemical reduction of dioxygen, O2, in the room-temperature ionic liquid trihexyl(tetradecyl)phosphonium trifluorotris(pentafluoroethyl)phosphate [P6,6,6,14][FAP]. The nature of the unusual voltammetric waves is quantitatively modeled via digital simulation with the aim of clarifying apparent inconsistencies in the literature. The reduction is shown to proceed via a two-electron reaction and involve the likely capture of a proton from the solvent system. The oxidative voltammetric signals seen at fast scan rates are interpreted as resulting from the reoxidation of HO2•–. In the presence of large amounts of dissolved carbon dioxide the reductive currents decrease by a factor of ca. two, consistent with the trapping of the superoxide radical, O2•–, intermediate in the two-electron reduction process.

Theory is developed for the rate of irreversible adsorption of nanoparticles from solution onto an electrode surface, including the effects of hindered diffusion of large nanoparticles. The effect of nanoparticle size on adsorption processes is studied, and found to be significant for large particles, where the nanoparticle radius to electrode radius ratio is larger than 1 × 10-3. The extent of adsorption in a typical electrochemical nanoparticle experiment at a 5 μm radius hemispherical electrode is studied for different adsorption rate constants, along with the effect this has on concentration of nanoparticles in the vicinity of the electrode and the frequency of impacts of nanoparticles on the electrode. For fast adsorption rate constants, significant and long lasting (in extreme cases greater than 4 h) concentration gradients can form, necessitating careful experimental practice.© 2013 Elsevier B.V. All rights reserved.

This thesis is concerned with the simulation of various electrochemical experiments and its application to electroanalysis. Chapter 1 outlines the fundamental principles of electrochemistry which are of importance for the reading of this thesis. Chapter 2 then outlines the methods used in the numerical simulation of electrochemical experiments. Chapters 3 and 4 are concerned with the electrochemistry of nanoparticles, and how this is affected by the presence of near wall hindered diffusion. In Chapter 3, a computational model to simulate anodic particle coulometry of nanoparticles in the presence of hindered diffusion is developed, and the effect of this hindered diffusion investigated. The model is then applied to simulate experimental data. Chapter 4 looks at the effect of hindered diffusion on the adsorption of nanoparticles on electrode surfaces, and investigates the effects of this adsorption on electrochemical experiments with nanoparticles generally. Chapters 5, 6 and 7 are concerned with band electrodes in isolation, in a pair and in an array respectively. In Chapter 5, a model to simulate double potential step chronoamperometry at an individual band electrode is developed, and used to successfully simulate experimental data. Chapter 6 looks at dual band electrodes used in generator-collector mode, and how this can be used to simultaneously measure the concentration of two species in solution. Chapter 7 looks at interdigitated arrays of band and ring electrodes in generator-collector mode, and develops a model to simulate cyclic voltammetry in both cases, as well as investigating under what conditions interdigitated ring arrays may be modelled as interdigitated band arrays. Chapter 8 develops a model to simulate chronoamperometry and cyclic voltammetry at porous electrodes, and investigates the consequences for electroanalysis of having a porous layer. Finally, Chapter 9 investigates the Marcus-Hush theory of electron transfer kinetics, and looks at the effect of the kinetically limited currents resulting from this theory to the equivalence relation between microdisc electrodes and sphere-on-a-surface electrodes.

A general, simple, analytical expression for the steady state voltammetric response at electrodes of three different geometries is developed. These geometries have both uniform (isolated microsphere) and nonuniform (microdisc and microsphere supported on an electroinactive surface) accessibility. The expression is applicable over the full range of electrochemical reversibility and for any initial concentrations of both species in the redox couple of interest. By making the assumption that, in all cases, the concentration of each species across the electrode surface is constant (representing an average of the true concentration profile), an equation describing the steady state voltammetric wave is deduced. Although approximate, the developed equation has a high degree of accuracy when compared to simulated results. This method, based on sound physical principles, is open to extension to other geometries and represents an advantage of previous solutions largely restricted to microdiscs. © 2013 American Chemical Society.

Two flat gold electrodes are placed vis-a-vis with an epoxy spacer layer that is etched out to give a ca. 100 μm-deep electrochemically active trench. A water-insoluble oil phase, here the redox system N,N-diethyl-N'N'-didodecyl-phenylenediamine (DDPD) in 4-(3-phenylpropyl)-pyridine (PPP), is immobilized into the trench to allow anion transfer upon oxidation of DDPD (oil) to DDP⁺ (oil). In "mono-potentiostatic mode" quantitative transfer/expulsion of anions into the trench oil phase occurs. However, in "bi-potentiostatic mode" feedback currents dominated by rapid plate-to-plate diffusion normal to the electrode surfaces are observed. Comparison of "normal" diffusion and "lateral" diffusion shows that the rate of diffusion-migration charge transport across the oil film is anion hydrophobicity dependent.

The voltammetry for the reduction of oxygen at a microdisc electrode is reported in two room temperature ionic liquids: 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide ([Bmpyrr][NTf2]) and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) imide ([P 14,6,6,6][NTf2]) at 298 K. Simulated voltammograms using Butler-Volmer theory and Symmetric Marcus-Hush (SMH) theory were compared with experimental data. Butler-Volmer theory consistently provided experimental parameters with a higher level of certainty than SMH theory. A value of solvent reorganisation energy for oxygen reduction in ionic liquids was inferred for the first time as 0.4-0.5 eV, which is attributable to inner-sphere reorganisation with a negligible contribution from solvent reorganisation. The developed Butler-Volmer and Symmetric Marcus-Hush programs are also used to theoretically study the possibility of kinetically limited steady state currents, and to establish an approximate equivalence relationship between microdisc electrodes and spherical electrodes resting on a surface for steady state voltammetry for both Butler-Volmer and Symmetric Marcus-Hush theory. © 2014 Elsevier B.V. All rights reserved.