Edmund J. F. Dickinson

New electrochemical methods.

Influence of Convection of Mass Transport F Theories of Electron and Proton Transfer F Nanoelectrochemistry andDouble Layer Structure G Development of New Electrochemical Pulse Procedures G Stochastic Methods in Voltammetry G Stochastic Experiments in Confined Volumes G Nanofluidic Experiments H Stochastic Theory in Electrochemistry H Nanoparticle Electrochemistry I Bioelectrochemistry I Nanopores and Single Molecule Detection J Single-Cell Electrochemistry K Outlook L Author Information L Biographies L References M

Nanoparticle-modified electrodes

The behaviour of nanoparticle-modified electrodes is compared and contrasted with that of conventional unmodified macroelectrodes.

Chronoamperometry and Cyclic Voltammetry at Conical Electrodes, Microelectrodes, and Electrode Arrays : Theory

The finite difference method is used to simulate chronoamperometry, linear sweep voltammetry, and cyclic voltammetry at conical electrodes and microelectrodes. Techniques for the numerical simulation of these processes at microdiscs are adapted and extended to accurately model diffusion to the electroactive cone surface. Simulated results are analyzed, and trends are rationalized in terms of the cone apex angle, alpha. The diffusion domain approximation is used to extend the theory to regular and random arrays of conical electrodes.

Mass transport to and within porous electrodes. Linear sweep voltammetry and the effects of pore size: The prediction of double peaks for a single electrode process

We simulate an electrode modified with a conducting porous film, where the electrolysis occurs both at the surface of the film and within it, in order to study the effect of pore size on the peak current in linear sweep voltammetry. For redox systems with reversible electrode kinetics we find that for both very large and very small pores the peak current is given by the Randles-Ševčik equation. For intermediate pore size, however, we observe a greatly enhanced peak current. When considering systems with irreversible electrode kinetics a very similar pattern is observed, except for the case of very small pores. In this case the peak current is actually smaller than expected from the Randles-Ševčik equation because the peak splits into two distinct peaks; one due to “thin layer” diffusion within the film and another caused by planar diffusion from bulk solution. The experimental implications of this observation are significant given the widespread use of modified electrodes for analysis.

Volatilisation of ferrocene from ionic liquids: kinetics and mechanism

The evaporation of dissolved ferrocene from non-volatile ionic liquids under a flow of nitrogen gas has been monitored voltammetrically and modelled mathematically. The rate of volatilisation was found to depend on the surface tension of the ionic liquid, and a model is presented.

Dynamic Theory of Liquid Junction Potentials

A Nernst-Planck-Poisson finite difference simulation system is used to model the dynamic evolution of a liquid junction from a nonequilibrium initial condition to a condition of steady potential difference, in a linear semi-infinite space. Liquid junctions of Linganes type 1 (monophasic, unequal concentration) and type 2 (bi-ionic potential; biphasic, equal concentration) are considered, for the sake of simplicity. Analysis of the results shows consistency with known and novel asymptotic solutions. A comprehensive dynamic theory of the free liquid junction potential is presented, having considered the simulated concentration profiles and electric field in the system. This reveals a dynamically relaxing junction in which a diffuse layer continues to expand. This is advocated as physically realistic and shown to be consistent with a steady state potential difference, which arises after 10-1000 ns for typical aqueous systems, when the expanding diffuse layer has a corresponding size of 10-1000 nm. Hence, Plancks concept [Wied. Ann. 1890, 40, 561-576] that a steady state potential difference exclusively implies a static junction with equal fluxes of all species is shown to be false, for an unconstrained system.

The kinetics of ferrocene volatilisation from an ionic liquid.

The volatilisation of ferrocene (Fc), dissolved in the ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [C(4)mpyrr][NTf(2)], to the gas phase has been indirectly monitored by cyclic voltammetry and chronoamperometry. Simulation of the observed trends in concentration with time using a simple model allowed quantification of the process. Volatilisation of dissolved Fc under flowing wet and dry dinitrogen gas (N(2)) was found to be kinetically limited with a rate constant in the region of 2×10(-7) cm s(-1). The activation energy of diffusion for Fc was found to be 28.2±0.7 kJ mol(-1), while the activation energy of volatilisation of Fc from [C(4)mpyrr][NTf(2)] to dry N(2) was found to be 85±2 kJ mol(-1).

Dynamics of Ion Transfer Potentials at Liquid-Liquid Interfaces

The Nernst-Planck-Poisson finite difference method is used to simulate the dynamic evolution of a water-nitrobenzene system with initially equimolar concentrations of a monovalent salt present in both liquids. The effect of single ion partition coefficients on the evolution of the liquid junction is investigated. The results from simulations reveal two separable components of the potential difference, similar to the behavior observed in recent works on the dynamic theory of membrane potentials [Ward, K. R.; et al. J. Phys. Chem. B2010, 114, 10763-10773]: a localized static component purely dependent on the ratio of single ion partition coefficients and a dynamically expanding diffuse component dependent on the mean salt partition coefficient and the diffusion coefficients of the constituent ions.

Dynamics of ion transfer potentials at liquid-liquid interfaces: the case of multiple species.

The dynamic evolution of a water-nitrobenzene system with both solvents containing an initially equimolar mixture of two monovalent binary electrolytes, sharing a common cation, is simulated using the Nernst-Planck-Poisson finite difference method. The effect of single ion partition coefficients and diffusion coefficients on the evolution of potential across the liquid-liquid interface is investigated. Two separable components of the potential difference are observed: a static component localized at the liquid-liquid interface and a diffuse component with dynamic spatial expansion. The former is shown through novel calculations to be dependent on an apparent partition coefficient of the system, defined to be dependent on the partition coefficients of the two constituent salts such that the static component also depends on the single ion partition coefficient of the shared cation. The dynamic component depends on the same apparent partition coefficient; further, its dependence on the diffusion coefficients of the constituent ions is investigated, and the time scales of the potential difference formation are revealed. The evolution of the system can be described in three stages with short time behavior dominated by partition of ions and long-time behavior dominated by recovery of electroneutrality. The dynamics were correlated to those recently discussed for a simpler system [Zhurov, K. et al. J. Phys. Chem. B, 2011, 115, 6909-6921].