Edward O. Barnes

Generator-collector double electrode systems: A review

A variety of generator-collector systems are reviewed, from the original rotating ring-disc electrodes developed in the 1950s, to very recent developments using new geometries and microelectrodes. An overview of both theoretical and experimental aspects are given, and the power of these double electrode systems in analytical electrochemistry is illustrated with a range of applications.

Recent Advances in Voltammetry.

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’.

Voltammetry at porous electrodes: A theoretical study

Abstract Theory is presented to simulate both chronoamperometry and cyclic voltammetry at porous electrodes fabricated by means of electro-deposition around spherical templates. A theoretical method to extract heterogeneous rate constants for quasireversible and irreversible systems is proposed by the approximation of decoupling of the diffusion within the porous electrode and of bulk diffusion to the electrode surface.

Dual band electrodes in generator–collector mode: Simultaneous measurement of two species

Abstract A computational model for the simulation of a double band collector–generator experiment is applied to the situation where two electrochemical reactions occur concurrently. It is shown that chronoamperometric measurements can be used to take advantage of differences in diffusion coefficients to measure the concentrations of both electroactive species simultaneously, by measuring the time at which the collection efficiency reaches a specific value. The separation of the electrodes is shown to not affect the sensitivity of the method (in terms of percentage changes in the measured time to reach the specified collection efficiency), but wider gaps can provide a greater range of (larger) absolute values of this characteristic time. It is also shown that measuring the time taken to reach smaller collection efficiencies can allow for the detection of smaller amounts of whichever species diffuses faster. The case of a system containing both ascorbic acid and dopamine in water is used to exemplify the method, and it is shown that mole fractions of ascorbic acid between 0.055 and 0.96 can, in principle, be accurately measured.

A gold-gold oil microtrench electrode for liquid-liquid anion transfer voltammetry

Two flat gold electrodes are placed vis‐à‐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 DDPD+ (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.

Interdigitated ring electrodes: Theory and experiment

Abstract The oxidation of potassium ferrocyanide, K4Fe (CN)6, in aqueous solution under fully supported conditions is carried out at interdigitated band and ring electrode arrays, and compared to theoretical models developed to simulate the processes. Simulated data is found to fit well with experimental results using literature values of diffusion coefficients for Fe ( CN ) 6 4 - and Fe ( CN ) 6 3 - . The theoretical models are used to compare responses from interdigitated band and ring arrays, and the size of ring array required to approximate the response to a linear band array is investigated. An equation is developed for the radius of ring required for a pair of electrodes in a ring array to give a result with 5% of a pair of electrodes in a band array. This equation is found to be independent of the scan rate used over six orders of magnitude.

New Chemical Insights Using Weakly Supported Voltammetry: Ion Pairing in the EC2 Reduction of 2,6-Diphenylpyrylium in Acetonitrile

Pairing effect: Varying the concentration of support electrolyte in the electrochemical EC(2) reduction of 2,6-diphenylpyrylium reveals the presence of ion pairing between the electroactive species and BF(4)(-). Experiment and theory are shown to be in good agreement only if ion pairing is included in the simulations. This previously unanticipated effect is only observable if voltammetry is performed under conditions of weak support.

New Chemical Insights Using Weakly Supported Voltammetry: The Reductive Cleavage of ArylBr Bonds is Reversible

Cyclic voltammetry carried out at a wide range of supporting electrolyte concentrations and compositions can elucidate additional kinetic and mechanistic details of the electrochemical reduction of aryl halides. The cleavage of the C-Br bond is reversible, driven by H abstraction and the second electron transfer. This is a new chemical insight, as the cleavage of such bonds has usually been regarded as irreversible.