Microwave activation in ionic liquids induces high temperature-high speed electrochemical processes

Self-focusing of intense microwave radiation at the tip of a 25 microm diameter platinum disk microelectrode immersed into the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM(+)PF(6)(-)) containing 1 mM ferrocene causes dramatically (two orders of magnitude) enhanced voltammetric current signals and temperatures in excess of 600 K (at the electrode surface)--extreme conditions sufficient for condensed phase pyrolysis processes to occur.     

Electrocatalytic reduction of alkyl iodides in tetrahydrofuran at silver electrodes

Recent interest in the electrocatalytic activity of silver towards the reduction of alkyl iodides has led us to investigate whether the effect is observed in tetrahydrofuran (THF) at room temperature. Using platinum electrodes in THF for the reduction of alkyl halides at 298 K has been hampered by the solvent window, which ‘obscures’ the voltammetric signals of interest. In order to overcome these problems, voltammetry has been performed at low temperature and was shown to extend the voltammetric window, leading to accurate electrochemical analyses and even novel changes in mechanism(s) of the reactive species following electron‐transfer (ET). Herein, it is shown that for a primary and tertiary alkyl iodide in THF, electroreduction at silver leads to a significant shift in the reduction potential to more positive values compared to platinum. In addition, following reduction, a characteristic series of oxidation peaks are observed and are shown to be due to the specific activity of iodide ions towards silver following reductive cleavage of the parent alkyl iodide. This characteristic feature is not observed with other halide ions: bromide and chloride. Preparative electrolyses at controlled‐potential have suggested that the reduction of the above alkyl iodides is a one‐electron concerted process. The ‘free’ iodide ions act as a monitor of reaction progression, and the carbon‐centred radical either dimerises and/or abstracts a hydrogen atom from the electrolyte/solvent; 1‐iodoadamantane giving percentage yields of 58% adamantane and 39% 1,1'‐biadamantane, the primary alkyl iodide, prepared in‐house, giving 67% R‐H and 25% R‐R. Copyright © 2007 John Wiley & Sons, Ltd.     

Some Isoperimetric Inequalities in Electrochemistry and Hele Shaw Flows

Isoperimetric inequalities are applied to a moving-boundaryproblem for doubly-connected domains. This problem occurs forexample in electrochemistry, in which case the domains in questionare the electrolyte of an electrolytic cell. The two electrodessurrounding the electrolyte are assumed to grow or dissolve,at different rates in general, by electrochemical reaction.We obtain optimal estimates showing, for example, that the leastchange in volume of each electrode always occurs in sphericalsymmetry.     

The Mediated Detection of Hydrogen Sulfide in Room Temperature Ionic Liquids

The detection of H₂S was studied using several mediators in room temperature ionic liquids (RTILs) at a microelectrode. Each mediator was characterised voltammetrically, and H₂S was added to observe if any mediation took place. A successful mediator was 3,5‐tert‐butyl‐obenzoquinone. Cyclic voltammetry was carried out in [C₂mim][NTf2]. A reductive wave was observed and attributed to the two‐electron reduction of the mediator. No oxidative signal was observed. H₂S was flowed through the system. Cyclic voltammograms showed a decrease in the reductive wave of the mediator and the onset of an oxidative signal due to the reaction between the mediator and H₂S to form an adduct. This reaction is reversible and on purging the system with N₂, the original reductive signal of the mediator was recovered.     

A Comparison of Electron Transfer Kinetics of Three Common Carbon Electrode Surfaces in Acetonitrile and in Room Temperature Ionic Liquid 1‐Butyl‐3‐Methylimidiazonium Hexafluorophosphate: Correlation to Surface Structure and the Limit of the Diffusion Domain Approximation

We report the comparison of electron transfer kinetic parameters of the ferrocene redox couple in both acetonitrile and in room temperature ionic liquid (RTIL) 1‐butyl‐3‐methylimidiazonium hexafluorophosphate ([C₄mim] [PF₆]), using edge plane pyrolytic graphite (EPPG), basal plane pyrolytic graphite (BPPG) and glassy carbon (GC) electrodes. Each electrode surface was characterized using SEM and AFM and the surface morphology was analyzed in terms of surface heterogeneity including the distribution of edge plane defects. The experimental data were modeled using both one and two dimensional simulations to correlate the electron transfer parameters obtained with the different surface structure of each electrode. Furthermore, we show that the diffusion domain approximation (commonly used to accurately simulate electron transfer kinetics at graphitic surfaces) breaks down when a BPPG electrode is used in RTIL and demonstrate the near impossibility of assigning rate constant to the basal plane surface.     

Additive Differential Pulse Voltammetry for the Study of Slow Charge Transfer Processes at Spherical Electrodes

The application of additive differential pulse voltammetry to the study of the kinetics of a charge transfer process is studied. A simple analytical solution is presented, valid for spherical electrodes of any size and for electrode processes of any reversibility. From this solution, valuable diagnostic criteria for the elucidation of the electrochemical reversibility are established based on the variation of the ADPV signal with the duration of the potential pulses, the electrode radius and the pulse height. Working curves for the determination of the kinetic parameters are also given. The value of the ADPV technique is experimentally demonstrated by studying the kinetics of the reduction of 3‐nitrophenolate^? and europium³⁺ at mercury hemispherical microelectrodes.     

Spatial-spectral distribution of Rabi radiation generated in plasma

We report observation and control of the spatial-spectral distributions of coherent, dynamic Rabi sideband radiation. The Rabi sidebands result from the interaction of a shaped picosecond probe laser of intensity 10(10) W cm(-2), with neutral excited atomic oxygen generated in a laser-induced microplasma. The spatial-spectral distribution is measured and compared for picosecond laser pulses having either an asymmetric temporal shape or a Gaussian temporal shape. The resulting spatial-spectral distributions are in quantitative agreement with theoretical predictions that account for the radial intensity distribution of the picosecond probe pulse.