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As an alternative to the usual commercial reference and quasi-reference electrodes (QREs), we propose metal (Pt, stainless steel) coated with partially oxidized polypyrrole as a QRE. The electrode is easily fabricated by cyclic voltammetry (CV) with the metal electrode in an acetonitrile or CH2Cl2 solution of 10 mM pyrrole containing 0.1 M Bu4NPF6. These QREs were more stable than the widely used metal (e.g., Ag, Pt) wire QRE as demonstrated by testing in several aqueous and organic media, with the stability checked by CV with ferrocenemethanol as the redox species. The results obtained demonstrate good stability of these QREs over a period of 1 day and relatively reproducible potential in a given solvent and supporting electrolyte. This electrode has the advantage that it does not contaminate the test solution with ions or solvent fro...
Scanning electrochemical microscopy offers interesting possibilities for investigating both transport properties in room-temperature ionic liquids (RTILs) and reactions occurring at the ionic liquid/substrate interface. Besides the expected difficulties related to the lower diffusion coefficients for species dissolved in RTILs arising from the higher viscosity of RTILs, the major problem comes from the inequality of the diffusion coefficients between the oxidized and reduced forms of the redox mediator used to probe the interfaces. This question was treated by an extension of the model originally presented by Martin and Unwin (Martin, R. D.; Unwin, P. R. J. Electroanal. Chem. 1997, 439, 123) and was adapted to the specific aspects of SECM in ionic liquids. The inequalities of diffusion coefficients lead to large anomalies in the curren...
p-Si type electrodes modified with different organic monolayers were investigated by reaction with radical anion and cation electrogenerated at a microelectrode operating in the configuration of a scanning electrochemical microscope. The method proves to be a convenient tool for investigating both the quality and the redox properties of the layer as previously demonstrated on metallic electrodes especially when the sample cannot be electrically connected. Approach curves recorded with the different mediators were used to investigate the electron-transfer rates across alkyl monolayers bound to p-type silicon substrates. Preliminary results indicate that the interfacial electron transfer occurs via electron tunneling through the organic layer as generally described for SAMs grafted on gold electrodes.
Electropolymerization of substituted dithiafulvenes is a convenient way to produce conjugated TTF electroactive films. When flexible polyoxyethyl chains link a conjugated TTF, the properties of the electroactive units in the film are the same as those observed in solution. This is illustrated with the existence of molecular movements in the TTF core that were previously described in solution and are clearly detected in the film. With this linker, morphologic investigations performed by in situ EC-AFM show a regular film formation leading to a continuous deposit with no special structures
The redox activity of a ferrocenyl monolayer grafted on an n-type Si111 substrate was investigated by scanning electrochemical microscopy (SECM) in conditions where the substrate plays the role of an insulator. This approach permits the differentiation between the different possible electron-transfer and mass-transport pathways occurring at the interface. As an exciting result, the thin ferrocenyl monolayer behaves like a purely conducting material, highlighting very fast electron communication between immobilized ferrocenyl headgroups in a 2D-like charge-transport mechanism.
Highly oriented YNixMn1−xO3 thin films on SrTiO3 (100) substrates were achieved by using pulsed laser deposition for x = 0.33 and x = 0.50. We used a combination of X-ray diffraction, scanning electron microscopy, atomic force microscopy, and magnetic-property measurements. The magnetic transition temperatures (Tc) of the as-grown films are higher than the corresponding bulk values (typically 85 K instead of 80 K, for x = 0.5, and 60 K instead of 50 K, for x = 0.33). Our magnetic measurements also suggest a spin-glass characteristic in the x = 0.33 films, while a cluster glasslike behavior is observed for the films with x = 0.5, which is quite different from that of the bulk samples. Finally, the influence of post-deposition heat treatment on the magnetic properties of the as-grown films is discussed
Electrochemical "reduction" of Pt was investigated using electrochemical and X-ray photoelectron spectroscopy (XPS) techniques. This transformation of a platinum metal, which is possible with a large variety of organic and inorganic cations, was investigated in DMF containing CsI salts chosen as a test system. Experiments show that considerable modifications of the chemical nature of the starting material accompany the morphological changes that were previously reported. With rather mild reduction conditions, cesium-platinides-like structures were detected. XPS investigations bring a direct spectroscopic evidence for the formation of a reduced platinum state from a metallic electrode held at a negative potential. XPS spectra clearly showed a significant and continuous shift of the Pt formal oxidation degree with the injected charge of ...
The reaction of platinum metal with an organic molecular radical anion leads to the formation of iono-metallic phases where Pt exists under negative oxidation states. This puzzling transformation of a "noncorrodible metal" was examined using localized electrochemical techniques in dimethylformamide containing different tetra-alkylammonium salts chosen as test systems. Our experiments demonstrate that the platinum metal is locally reduced as soon as the Pt faces relatively moderate reducing conditions, for example, when the Pt is used as a negative electrode or when the metal is in the presence of a reducing agent such as an organic radical anion. Scanning electrochemical microscopy (SECM) analysis, current-distance curves, and transient mode responses provide detailed descriptions of the reactivity of Pt to form negative oxidation stat...
Electrochemical and mass-transport properties of a redox-active ionic liquid, 1-(ferrocenylmethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (FcEmiTFSI), were investigated for the pure compound and for solutions in acetonitrile (ACN) and in a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmiTFSI). Cyclic voltammetry data were compared with those obtained for the oxidation of ferrocene (Fc) in EmiTFSI and ACN. The half-potential of FcEmiTFSI/Fc+EmiTFSI is higher than that of Fc/Fc+ in both media. The apparent heterogeneous rate constants View the MathML sourcekapp° of FcEmiTFSI and Fc were determined in both solvents. The values of View the MathML sourcekapp° for these two redox probes in the same solvent are of the same order of magnitude. However, View the MathML sourcekapp°...
Herein, we report the variation of localized surface plasmon resonance (LSPR) of gold nanoparticle (NP) arrays covered by poly(3,4-ethylenedioxythiophene) (PEDOT) as a function of the electronic state of the polymer. Giant shifts and fine-tuning of the LSPR of gold NPs surrounded by PEDOT/sodium docecyl sulfate have been achieved. The color variations of plasmonic/conducting polymer (CP) devices are given not only by changes of the optical properties of the CP upon doping but also by a close synergy of the optical properties of CP and NP. Such systems can considerably extend the field of CP-based electrochromic devices.
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