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We extend the analytical theory of propagating concentration polarization (CP) to describe and compare the effects of constant-voltage versus constant-current conditions on the transient development of CP enrichment and depletion zones. We support our analysis with computational and experimental results. We find that at constant voltage, enrichment and depletion regions spread as [t.sup.1/2] as opposed to the previously observed [t.sup.1] scaring for constant current conditions. At low, constant voltages, the growth and propagation of CP zones can easily be misinterpreted as nonpropagating behavior. 10.1021/ac100432q

Electrochemical studies on the Fc + [e.sup.-] [left and right arrow] [Fc.sup.+] (Fc = ferrocene) process have been undertaken via the oxidation of Fc and reduction of [Fc.sup.+] as the hexafluorophosphate (P[F.sup.-.sub.6]) or tetrafluoroborate (B[F.sub.4]) salts and their mixtures in three ionic liquids (ILs) (1-butyl-1-methylpyrrolidinium bis[(trifluoromethyl)sulfonyl]imide, 1-butyl-3-methylimidazolium tetrafluoroborate, and 1-butyl-3-methylimidazolium hexafluorophosphate). Data obtained at macro- and microdisk electrodes using conventional dc and Fourier-transformed large-amplitude ac (FT-ac) voltammetry reveal that diffusion coefficients for Fc and [Fc.sup.+] differ significantly and are a function of the Fc and [Fc.sup.+] concentration, in contrast to findings in molecular solvents with 0.1 M added supporting electrolyte media. Thus, the Faradaic currents associated with the oxidation of Fc ([Fc.sup.0/+]) and reduction of FcP[F.sub.6] or FcB[F.sub.4] ([Fc.sup.+/0]) when both Fc and Fc are simultaneously present in the ILs differ from values obtained when individual Fc and [Fc.sup.+] solutions are used. The voltammetry for both the [Fc.sup.0/+] and [Fc.sup.+/0] processes exhibited near-Nernstian behavior at a glassy carbon macrodisk electrode and a platinum microdisk electrode, when each process was studied individually in the ILs. As expected, the reversible formal potentials (E[degrees]') and diffusion coefficients (D) at 23 [+ or -] 1 [degrees]C were independent of the electrode material and concentration. However, when Fc and FcP[F.sub.6] or FeB[F.sub.4] were both present, alterations to the mass transport process occurred and apparent D values calculated for Fc and [Fc.sup.+] were found to be about 25-39% and 32-42% larger, respectively, than those determined from individual solutions. The apparent value of the double layer capacitance determined by FT-ac voltammetry from individual and mixed Fc and [Fc.sup.+] conditions at the GC electrode was also a function of concentration. Double layer capacitance values increased significantly with the concentration of Fc and FcP[F.sub.6] or FcB[F.sub.4] when species were studied individually or simultaneously, but had a larger magnitude under conditions where both species were present. Variation in the structure of the ILs and hence mobillties of the ionic species, when Fc and FcP[F.sub.6] or FcB[F.sub.4] are simultaneously present, is considered to be the origin of the nonadditivity of the Faradaic currents and variation in capacitance. 10.1021/ac9020159

Research is presented describing the study of ion-exchange membranes and current efficiency.

A diabatic 3 x 3 potential matrix is presented. This matrix is used to investigate the three adiabatic-diabatic transformation angles that make up the corresponding 3 x 3 adiabatic-diabatic transformation matrix.

The intensity of the hydrodynamic convection generated by conventional disk millielectrodes in magnetic fields was studied. The generated convection was found to be intimately related to the nature of the faradaic process and that the mass-transfer limited current i(sub l) was proportional to n3/2 where n is the number of electrons involved in the heterogeneous electron transfer. A feedback mechanism that relies on the dependence of the faradaic current on the hydrodynamic velocity profile within the electrolytic conductor, and of the hydrodynamic velocity profile on the current.

The current-voltage curves of a composite bipolar membrane (CBM) were experimentally measured for the various mole fractions of methanol-water, ethanol-water and n-propanol-water mixed solution systems using 0.1 mol/L LiCl as electrolyte for each solution system. Results showed that a CBM has the characteristics of a bipolar membrane. The current-voltage curves showed that the maximum local effective value of a CBM resistance will increase with an increase in the mole fraction of alcohol. This is attributable to the weaker dissociative ability of alcohol as compared to water.

The temporal shape of both the discharge current and the photocurrent from a pulsed hollow cathode discharge is reported for aluminum, molybdenum, and titanium cathodes. Features which are characteristic of the discharge are discussed in terms of the physical processes involved. A circuit model of hte discharge is presented and used to explain the discharge behavior. The effect of supply overvoltage and cathode material on pulse shape is reported and discussed., The characterization of discharge current temporal profiles and typical pulse parameter photocurrents is discussed. Cathodes made of aluminum, titanium and molybdenum were used to derive the pulse shape and temporal emission signal data used in the experiments. Discharge behavior was explained by a circuit model. The utility of pulsed hollow cathode discharge for atomic energy spectroscopic analysis was demonstrated.

In several commercial capillary electrophoretic instruments, the potential is increased linearly at the beginning of a separation from zero to the programmed value. The ramp time can be as long as 20 s, resulting in grossly distorted mobility values when the migration times are commensurable with the ramp times. An expression is proposed to correct for the effects of the reduced field strength during the initial potential ramp.