Ian Cutress

The construction and use of a dual-microdisk electrode system is reported in which two microdisk electrodes are positioned close to each other with a separation of ∼10 μm. Experiments are reported in which the species generated on one disk is ‘collected’ on the second. The current–time responses of each electrode in generator–collector mode following a potential step on the generator electrode are measured and shown to be in excellent agreement with simulations made using the explicit digital… Show more

The construction and use of a dual-microdisk electrode system is reported in which two microdisk electrodes are positioned close to each other with a separation of ∼10 μm. Experiments are reported in which the species generated on one disk is ‘collected’ on the second. The current–time responses of each electrode in generator–collector mode following a potential step on the generator electrode are measured and shown to be in excellent agreement with simulations made using the explicit digital GPU approach. The use of this approach in measuring the diffusion coefficients of electro-generated species is explained and applied to the hexaammineruthenium system. Show less

Electrochemical simulation is employed to investigate voltammetry in solutions of very low concentrations. Using Monte Carlo random-walk simulations, potential-step chronoamperometry is considered from the perspective of individual species under Brownian motion in solution interacting with an electroactive surface for electron transfer. This allows the exploration of stochastic versus statistical diffusion, where the latter is described by continuous theory (Fick’s laws of diffusion). This… Show more

Electrochemical simulation is employed to investigate voltammetry in solutions of very low concentrations. Using Monte Carlo random-walk simulations, potential-step chronoamperometry is considered from the perspective of individual species under Brownian motion in solution interacting with an electroactive surface for electron transfer. This allows the exploration of stochastic versus statistical diffusion, where the latter is described by continuous theory (Fick’s laws of diffusion). This approach details individual electron transfer events, and the stochastic nature of voltammetry under ultra-low concentration conditions. An optimisation in this work over previous random-walk simulations is the realisation of true spherical diffusion, rather than the bipyramidal diffusion approximation. Graphic Processors are used for the simulations, due to the independence of the particles in the system, resulting in a ∼1000× speed increase over conventional computer processors. Show less

The stochastic limit at which fully-reversible cyclic voltammetry can accurately be measured is investigated. Specifically, Monte Carlo GPU simulation is used to study low concentration cyclic voltammetry at a microdisk electrode over a range of scan rates and concentrations, and the results compared to the statistical limit as predicted by finite difference simulation based on Fick’s Laws of Diffusion. Both Butler–Volmer and Marcus–Hush electrode kinetics are considered, simulated via… Show more

The stochastic limit at which fully-reversible cyclic voltammetry can accurately be measured is investigated. Specifically, Monte Carlo GPU simulation is used to study low concentration cyclic voltammetry at a microdisk electrode over a range of scan rates and concentrations, and the results compared to the statistical limit as predicted by finite difference simulation based on Fick’s Laws of Diffusion. Both Butler–Volmer and Marcus–Hush electrode kinetics are considered, simulated via random-walk methods, and shown to give identical results in the fast kinetic limit. Show less

Recent work on faradaic processes occurring during thermal nanoparticle–electrode collisions contrasts significantly from analogous research using ultrasonically-driven microparticles, where no faradaic signals were found. It is suggested that this might be explained by the differences in both particle size and contact time. To investigate this, we present results from adapted Monte Carlo random walk simulations. Using the underpotential deposition of thallium onto silver nanoparticles as a… Show more

Recent work on faradaic processes occurring during thermal nanoparticle–electrode collisions contrasts significantly from analogous research using ultrasonically-driven microparticles, where no faradaic signals were found. It is suggested that this might be explained by the differences in both particle size and contact time. To investigate this, we present results from adapted Monte Carlo random walk simulations. Using the underpotential deposition of thallium onto silver nanoparticles as a model system, it is found that an estimated minimum contact time of ca. 10−4 s is required to deposit a complete monolayer (from a 10 mM solution) onto a nanoparticle of radius 45 nm. Show less

Electrochemical simulation via the solution of Fick’s Laws is a widely used technique to corroborate experimental results with well defined theory. This paper analyses use of ‘off-the-shelf’ finite element (FEM) software COMSOL Multiphysics™ in one, two and three-dimensional quantitative problems and under homogeneous and heterogeneous kinetic systems. Conclusions indicate that two-dimensional problems are within an order of magnitude of accuracy of finite difference simulations and analytical… Show more

Electrochemical simulation via the solution of Fick’s Laws is a widely used technique to corroborate experimental results with well defined theory. This paper analyses use of ‘off-the-shelf’ finite element (FEM) software COMSOL Multiphysics™ in one, two and three-dimensional quantitative problems and under homogeneous and heterogeneous kinetic systems. Conclusions indicate that two-dimensional problems are within an order of magnitude of accuracy of finite difference simulations and analytical solutions, as long as the problem is well defined in the software and care is taken with regards to appropriate meshing and boundary conditions. Three-dimensional simulations relating to microdiscs result in steady-state current values not quantitatively compatible with experimental observations or analytical solutions. Show less

The use of microband electrodes in electrochemistry has expanded in recent years due to enhanced current densities, ease of fabrication, and available theory. This paper, through explicit three-dimensional finite difference GPU simulation, simulates mass transport to square and rectangular (finite band) microelectrodes and quantifies the response of a finite band at any given length to width ratio, including the validation of an equation for the chronoamperometric response. In addition, the… Show more

The use of microband electrodes in electrochemistry has expanded in recent years due to enhanced current densities, ease of fabrication, and available theory. This paper, through explicit three-dimensional finite difference GPU simulation, simulates mass transport to square and rectangular (finite band) microelectrodes and quantifies the response of a finite band at any given length to width ratio, including the validation of an equation for the chronoamperometric response. In addition, the power of explicit simulations harnessed to modern computing hardware is emphasised. Show less

The use of graphics processors under the heading GPGPU (general-purpose computation on GPUs (graphics processing units)) promises a computational advance which may greatly facilitate the use of explicit digital simulation for non-trivial problems. This paper illustrates the use of GPGPU for the simulation of mass transport processes at elliptically shaped electrodes and for deformed microelectrodes. Under explicit algorithm conditions, this paper finds a mid-range commercial GPU affords a… Show more

The use of graphics processors under the heading GPGPU (general-purpose computation on GPUs (graphics processing units)) promises a computational advance which may greatly facilitate the use of explicit digital simulation for non-trivial problems. This paper illustrates the use of GPGPU for the simulation of mass transport processes at elliptically shaped electrodes and for deformed microelectrodes. Under explicit algorithm conditions, this paper finds a mid-range commercial GPU affords a fivefold increase in simulation speed, at an eighth of the cost, over a 16-thread high-range professional workstation PC. This work shows also the difficulties of confirming the regularity of size and shape, from purely voltammetric studies, of microdisc electrodes. Show less

Microwave-assisted electrochemistry is critically discussed with a focus on the fundamental aspects of the processes involved and its applications in electroanalysis. The concept of direct and nondirect heated electrodes is discussed, and simulation work is evaluated. Microwave-assisted electrochemistry predominantly results in higher current responses (up to 2 magnitudes higher) due to increased temperature and mass transport to the active electrodes. Temperature gradients at… Show more

Microwave-assisted electrochemistry is critically discussed with a focus on the fundamental aspects of the processes involved and its applications in electroanalysis. The concept of direct and nondirect heated electrodes is discussed, and simulation work is evaluated. Microwave-assisted electrochemistry predominantly results in higher current responses (up to 2 magnitudes higher) due to increased temperature and mass transport to the active electrodes. Temperature gradients at microwave-affected electrodes may exceed 105 K/cm, with temperature hotspots found in the thin diffusion layers set up at ultramicroelectrodes. Research into microwave-assisted electroanalysis can lead to enhanced capillary electrophoresis detection, improved stripping voltammetry and development of new high temperature methods. Show less

Anodic stripping voltammetry (ASV) is an extremely powerful tool for detection of metal ions in solution through a two step process of preconcentration of the metal at the electrode surface, followed by electrodissolution. The second phase produces an electroanalytical response proportional to the amount of material deposited in the first phase. This paper utilizes theory to explore the electrochemical signals produced when considering ASV at a microelectrode or ultramicroelectrode arrays. The… Show more

Anodic stripping voltammetry (ASV) is an extremely powerful tool for detection of metal ions in solution through a two step process of preconcentration of the metal at the electrode surface, followed by electrodissolution. The second phase produces an electroanalytical response proportional to the amount of material deposited in the first phase. This paper utilizes theory to explore the electrochemical signals produced when considering ASV at a microelectrode or ultramicroelectrode arrays. The theory outlined is applicable mostly to thin mercury film absorption and metal adsorption. Show less