Electrochemical oxidation of primary amine in ionic liquid media: Formation of organic layer attached to electrode surface

Electrochemical oxidation of primary amine in ionic liquid media has been investigated. The ionic liquid chosen for this study was 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Two primary amine compounds are used for this study; 4-nitrobenzylamine and 2-aminoethylferrocenylmethylether. The oxidation of the amino compounds in ionic liquid conduces to the modification of the electrode surface. The modified electrodes were characterized by cyclic voltammetry and XPS analysis. Both techniques support the presence of an organic layer strongly attached onto the electrode surface. The surface concentration of the attached group obtained in this media was found to be around 1 to 3 × 10^?10 mol cm^?2. The use of ionic liquid as media for the grafting leads to decrease of the surface concentration of the grafted layer; and the formation of less dense layer compared with classical solvent such as acetonitrile.     

Electrosynthesis of well-organized nanoporous poly(3,4-ethylenedioxythiophene) by nanosphere lithography

The electrodeposition of poly(3,4-ethylenedioxythiophene) (PEDOT) films from aqueous surfactant solution through a two-dimensional poly(styrene) (PS) template onto indium tin oxide (ITO) substrate has been investigated. The polymer grows in the interstitial spaces of the self-assembled PS spheres which were subsequently removed by dissolution in tetrahydrofuran (THF). Surface characterization by scanning electron microscopy (SEM) and atomic force microscopy (AFM) reveals that two-dimensional nanoporous honeycomb PEDOT structures can easily be obtained by using PS spheres of different sizes. Gold electrodeposition onto the nanostructured PEDOT electrode was investigated and SEM images show preferential formation of nanoparticles (NP) on the wall and the rim of the PEDOT film but metal clusters inside the pores are also observed.     

Formation of negative oxidation states of platinum and gold in redox ionic liquid: Electrochemical evidence

The electrochemical reduction of noble metal electrodes in the presence of redox ionic liquid, 1-ferrocenylethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [FcEMIM][TFSI], was investigated by cyclic voltammetry. Our experiments suggest the formation of metal with negative oxidation states, in the cases of platinum and gold electrodes [M_n⁻, FcEMIM⁺]. By analogy with the previous work, the formation of these phases is concomitant with the insertion of the supporting electrolyte; which correspond in our experimental condition to the redox cation of the ionic liquid. As an exciting result, the electrochemical investigations of the reduced electrode in electrolytic solution, containing solvent and supporting electrolyte, evidence the presence of the ferrocene groups at the electrode surface. Moreover, the reduced electrode exhibits the presence of the ferrocene even after, contact with air, after ultrasound, and after physical polishing, highlighting the large stability of this organo-metallic phases formed in this media. The AFM investigations demonstrate the morphological change of the platinum surface after the reduction process. Finally, our works bring a formal electrochemical proof of the presence of the ionic liquid cation inside the electrode material after the cathodic treatment in this media.     

Ionic liquid viscosity effects on the functionalization of electrode material through the electroreduction of diazonium

The electrochemical reduction of 4-nitrophenyl diazonium, NPD, in different ionic liquids presenting different viscosities has been investigated. The electrochemical studies show that the reduction of diazonium leading to the formation of its corresponding radical occurs whatever the viscosity of the grafting media. Following that, the presence of an organic layer attached to the electrode after electrochemical treatment was evidenced by cyclic voltammetry (CV) in acidic media thanks to the presence of nitro groups. Moreover, infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) confirm the presence of a nitrophenyl (NP) layer attached to the electrode material. Next, the examination of the electrochemical data through the measurement of the charge, corresponding to the reduction of the attached nitrophenyl (NP) moieties, shows that the surface concentration of NP, Γ(NP), decreases when the viscosity, η, of the grafting media increases. Additionally, in the case of the more viscous ionic liquid, N-tributyl-N-methylammonium bis(trifluoromethylsulfonyl)imide [Bu(3)MeN] [NTf(2)], a cosolvent has been added leading to fine decrease of the viscosity. The IR and CV investigations of the modified electrodes demonstrate the decrease of the amount of the attached molecules when the viscosity of the grafting media increases. In addition, a correlation between Γ(NP) as function of 1/η was observed. Finally, XPS and AFM experiments lead to an estimate of the thickness of the attached layer. As a result, both methods are in perfect agreement and thicknesses of 4 and 1 nm are measured after grafting in acetonitrile and in pure ionic liquid [Bu(3)MeN] [NTf(2)], respectively. By comparison with classical solvent, the use of viscous ionic liquid for the grafting leads to a decrease in the amount of the attached molecules and conduce to the formation of thinner or less dense layer.     

New chemical synthesis of functionalized arylzinc compounds from aromatic or thienyl bromides under mild conditions using a simple cobalt catalyst and zinc dust

A new chemical method for the preparation of arylzinc intermediates is described in acetonitrile, on the basis of the activation of aryl bromides by low-valent cobalt species arising from the reduction of cobalt halide by zinc dust. This procedure allows for the synthesis of a variety of functionalized aryl- and thienylzinc species in good to excellent yields. The versatility and the simplicity of that original method represent an alternative to most known procedures.     

Microelectrodes modification through the reduction of aryl diazonium and their use in scanning electrochemical microscopy (SECM)

This work is devoted to the study of the electrochemical grafting of nitrophenyl groups onto platinum ultramicroelectrode (UME). The grafting was made using the electrochemical reduction of nitrophenyldiazonium. Our results demonstrate the possibility to reduce the diazonium onto Pt UME. As consequence the electrochemical reduction leads to the attachment of nitrophenyl groups onto the UME surface. Following that, the modified UME was characterized using electrochemical techniques. In addition, the electrochemical response of the modified UME in the presence of reversible redox couple, ferrocene, has been studied. The main remark is that the steady state current observed at the UME is not affected by the presence of the nitrophenyl layers. Finally, from this last point we demonstrate the possibility to achieve scanning electrochemical microscopy (SECM) using modified platinum UME.     

Electrochemical investigation of thin PEDOT film above an insulating substrate using scanning electrochemical microscopy

Thin layer of conducting polymer, poly(3,4-ethylenedioxythiophene) PEDOT, deposited on insulating substrates was electrochemically investigated. This study was performed through the reaction with a series of electrogenerated mediators at a microelectrode operating in the configuration of a scanning electrochemical microscope (SECM). The method proves to be a convenient tool for investigating redox properties of the electroactive materials onto insulating substrate and the occurrence of electron transfers across the modified substrate. The SECM results demonstrate the possibility of the regeneration of the mediator at the modified surface even if the used substrate is an insulator. The regeneration rate depends on the standard redox potential of the mediator, on the switching potential of the polymer and on its initial oxidation state. In addition, the obtained data could be analyzed through the construction of the steady state voltammograms allowing the extraction of the electrochemical properties of the thin organic layer deposited onto insulating surface.     

Chemical capacitance of nanoporous-nanocrystalline TiO2 in a room temperature ionic liquid

The electrochemical behaviour of nanoporous TiO(2) in a room temperature ionic liquid (RTIL), 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide (EMITFSI), was investigated by cyclic voltammetry (CV) and impedance spectroscopy. Exponentially rising currents in voltammetry were attributed to the charging/discharging of electrons in the TiO(2) film and a charge transfer mechanism. The main features of the voltammetry and impedance followed the same trends in the ionic liquid as in other organic solvents and also in aqueous electrolytes. In the presence of lithium ions, the onset potential of the charge accumulation increased due to the change of the initial position of the TiO(2) conduction band. The results show that substitution of organic solvents contained in solar cells, supercapacitors or other electrochemical devices is in general feasible, though requires some adjustment in the electrolyte composition for optimal performance.     

Spiral demystified

Spiral acquisition schemes offer unique advantages such as flow compensation, efficient k-space sampling and robustness against motion that make this option a viable choice among other non-Cartesian sampling schemes. For this reason, the main applications of spiral imaging lie in dynamic magnetic resonance imaging such as cardiac imaging and functional brain imaging. However, these advantages are counterbalanced by practical difficulties that render spiral imaging quite challenging. Firstly, the design of gradient waveforms and its hardware requires specific attention. Secondly, the reconstruction of such data is no longer straightforward because k-space samples are no longer aligned on a Cartesian grid. Thirdly, to take advantage of parallel imaging techniques, the common generalized autocalibrating partially parallel acquisitions (GRAPPA) or sensitivity encoding (SENSE) algorithms need to be extended. Finally, and most notably, spiral images are prone to particular artifacts such as blurring due to gradient deviations and off-resonance effects caused by B₀ inhomogeneity and concomitant gradient fields. In this article, various difficulties that spiral imaging brings along, and the solutions, which have been developed and proposed in literature, will be reviewed in detail.