Oleksiy V. Klymenko

Oxidation of N,N,N′,N′-tetraalkyl-para-phenylenediamines in a series of room temperature ionic liquids incorporating the bis(trifluoromethylsulfonyl)imide anion

Abstract The five room temperature ionic liquids: 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([CnMIM][N(Tf)2], n=2, 4, 8, 10) and n-hexyltriethylammonium bis(trifluoromethylsulfonyl)imide ([N6222][N(Tf)2]) were investigated as solvents in which to study the electrochemical oxidation of N,N,N′,N′-tetramethyl-para-phenylenediamine (TMPD) and N,N,N′,N′-tetrabutyl-para-phenylenediamine (TBPD), using 20 μl micro-samples under vacuum conditions. The effect of dissolved atmospheric gases on the accessible electrochemical window was probed and determined to be less significant than seen previously for ionic liquids containing alternative anions. Chronoamperometric transients recorded at a microdisk electrode were analysed via a process of non-linear curve fitting to yield values for the diffusion coefficients of the electroactive species without requiring a knowledge of their initial concentration. Comparison of experimental and simulated cyclic voltammetry was then employed to corroborate these results and allow diffusion coefficients for the electrogenerated species to be estimated. The diffusion coefficients obtained for the neutral compounds in the five ionic liquids via this analysis were, in units of 10−11 m2 s−1, 2.62, 1.87, 1.12, 1.13 and 0.70 for TMPD, and 1.23, 0.80, 0.40, 0.52 and 0.24 for TBPD (listed using the same order for the ionic liquids as stated above). The most significant consequence of changing the cationic component of the ionic liquid was found to be its effect on the solvent viscosity; the diffusion coefficient of each species was found to be approximately inversely proportional to viscosity across the series of ionic liquids, in accordance with Waldens rule.

A new approach for the simulation of electrochemiluminescence (ECL).

The validity and accuracy of our new numerical approach implemented in KISSA-1D software when applied to a theoretical study of different types of electrochemiluminescence (ECL) is established by comparison with existing analytical solutions and others specifically derived in this work, as well as with independent numerical solutions obtained by using commercial software. The efficiency and comprehensiveness of this approach are illustrated by using a representative series of published ECL reaction schemes taken as typical case studies when ECL is generated by a single electrode under amperometric or voltammetric conditions, even when rate constants used in the simulations far exceed any of their realistic experimental limits.

The electro-oxidation of N,N-dimethyl-p-toluidine in acetonitrile:: a microdisk voltammetry study

The oxidative dimerisation reaction of N,N-dimethyl-p-toluidine (DMT) in acetonitrile was studied by cyclic voltammetry using a range of concentrations from 1 to 70 mM at microdisk electrodes of radii 10, 12.5, and 50 μm using scan rates from 20 mV s-1 to 6 V s-1. Theory was developed to simulate the following mechanism using the ADI method and comparison made to experimental voltammograms.The mechanism was found to be consistent with the observed data under all experimental conditions employed. The following rate constants were inferred: k1=(5.9±2.2)×105 cm3 mol-1 s-1, k-1≈0, and k2=(9.2±3.8)×108 cm3 mol-1 s-1.

The high speed channel electrode applied to heterogeneous kinetics: The oxidation of 1,4-phenylenediamines and related species in acetonitrile

The application of the high-speed microband channel electrode to the study of the heterogeneous electron transfer kinetics of the oxidation of some N-substituted phenylenediamines is described. Experiments to investigate the standard electrochemical rate constant, k0, of the oxidation of 1,4-phenylenediamine (PPD), N,N-dimethyl-1,4-phenylenediamine (DMPD), and N,N-diethyl-1,4-phenylene-diamine (DEPD) in acetonitrile solutions containing 0.10 M tetrabutylammonium perchlorate (TBAP) are reported for 2.5 and 5 μm platinum microband electrodes using a range of centre-line velocities from 12 to 25 m s−1. The measured values of k0 for PPD, DMPD, and DEPD are 0.84±0.16, 3.15±0.30 and 1.64±0.25 cm s−1, respectively. The respective formal oxidation potentials are also found to be 0.287±0.002, 0.245±0.001, and 0.208±0.003 V (all measured vs. Ag). Experiments are also presented using “fast scan” cyclic voltammetry to obtain measurements of the heterogeneous rate constants for PPD, DMPD and DEPD to compare between the steady-state channel electrode and the ‘established’ transient methodologies. Scan rates in the range 102–104 V s−1 were used to measure peak separations with the resulting k0 values of 0.51±0.05, 1.89±0.10, and 1.28±0.20 cm s−1, respectively. The use of steady-state voltammetry obviates the need for capacitative corrections, perhaps suggesting a greater reliability in the resulting data.

The theory of electrodeposition in the presence of forced convection:: Transport controlled nucleation of hemispheres

Abstract A new equation to describe the diffusion controlled nucleation of hemispherical centres under conditions of forced convection is derived, in a manner similar to that of the Scharifker and Mostany equation (J. Electroanal. Chem. 177 (1984) 13). It has been shown that the transients measured under these conditions should show a monotonically rising transient, followed by convergence to a limiting current. The accuracy and validity of the model is tested by comparison with experimental data obtained using a 5 mM Co/Co 2+ system, sonicated at 66 W cm −2 . Excellent fits are obtained, and the parameters derived are in agreement with those derived from independent experiments.

An improved configuration for simultaneous electrochemical ESR studies: a tubular electrode in a cylindrical cavity

An improved configuration for simultaneous electrochemical ESR is described in which a tubular flow cell occupies a cylindrical TE011 ESR cavity. The minimisation of dielectric loss allowed good cavity Q-values to be achieved, resulting in a high level of sensitivity and allowing good quality spectra to be attained for the N,N,N′, N′-tetramethyl-para-phenylenediamine (TMPD) radical cation and the 1,2,4,5-tetrachlorobenzoquinone (para-chloranil) and nitrobenzene radical anions. The theory describing the convective and diffusive mass transport in the tubular arrangement, along with its influence on the steady state ESR signal intensity for these stable radicals is fully developed and shown to be in good agreement with experimental results. The transient ESR response is also considered and shown to agree well with the theory presented in the literature at flow rates for which the Leveque approximation holds.

A novel approach to the simulation of electrochemical mechanisms involving acute reaction fronts at disk and band microelectrodes.

A new simulation algorithm is presented for describing the dynamics of diffusion reactions at the most common microelectrode 1D (planar, cylindrical, spherical) and 2D geometries (band, disk) for electrochemical mechanisms of any complexity and involving fast homogeneous reactions of any kind. A series of typical electrochemical mechanisms that create the most severe simulation difficulties is used to establish the exceptional performance and accuracy of this algorithm, which stem from the combination of (quasi)conformal transformation of space and a new method for auto-adaptive grid compression.

The application of fast scan cyclic voltammetry to the high speed channel electrode

The application of fast-scan cyclic voltammetry methods to the high-speed microband channel electrode (Rees et al. J. Phys. Chem. 99 (1995) 7096) is reported. Theory is presented to simulate cyclic voltammograms for a simple electron transfer under high convective flow rates within the high-speed channel. Experiments are reported for the oxidation of 9,10-diphenylanthracene (DPA) in acetonitrile solution containing 0.10 M tetrabutylammonium perchlorate (TBAP) for both 12.5 and 40 μm platinum microband electrodes using a range of scan rates from 50 to 3000 V s−1 and centre-line flow velocities from 12 to 25 m s−1. Analysis of the voltammograms yielded values for k0 and α for DPA which were measured to be 0.80±0.27 and 0.52±0.07 cm s−1, respectively. The range of applicability of this method was also investigated. Experiments are also presented using steady-state linear sweep voltammetry to obtain accurate measurements of the heterogeneous kinetic parameters for DPA at a platinum microband electrode. The measured value of k0 for DPA was found to be 0.94±0.16 cm s−1, with α=0.53±0.02 and a formal oxidation potential of 1.40±0.01 V (vs. Ag).

Liquid-liquid processes and kinetics in acoustically emulsified media

The measurement of liquid-liquid kinetics in acoustically emulsified media is shown to be conveniently achieved via the monitoring of bulk concentrations. This is exemplified with reference to the extraction of copper from an aqueous solution by the ligand 5-nonyl-salicylaldoxime in ethyl acetate. The speed of the extraction under ultrasound compares favourably with that seen under conventional stirring and the benefits are illustrated with reference to the extraction of copper from industrial effluent.

Electrochemical Determination of Flow Velocity Profile in a Microfluidic Channel from Steady-State Currents: Numerical Approach and Optimization of Electrode Layout

In this article, the numerical approach for flow profile reconstruction in a microfluidic channel equipped with band microelectrodes introduced previously by the authors, based on transient currents, is extended to the exclusive use of steady-state currents. It is shown that, although the currents obey steady state, the flow velocity profile in the channel may be reconstructed rapidly with a high accuracy, provided a sufficient number of electrodes performing under steady state are considered. The present theory demonstrates how the electrode widths and sizes of gaps separating them can be optimized to achieve better performance of the method. This approach has been evaluated theoretically for band microelectrode arrays embedded into one wall of a rectangular channel consisting of three, four, or five electrodes, all of which are operated in the generator mode. The results prove that the proposed approach is able to accurately recover the shape of the flow profile in a wide range of Peclet numbers and flow types ranging from the classical parabolic Poiseuille flow to constant electro-osmotic-type flow.