Search results for "Dielectric Spectroscopy"
showing 10 items of 243 documents
Improvement in photocatalytic activity of stable WO3 nanoplatelet globular clusters arranged in a tree-like fashion: Influence of rotation velocity d…
2016
This study investigates the influence of controlled hydrodynamic conditions during anodization of tungsten (W) on the morphological, electrochemical and photocatalytic properties of a novel WO3 nanostructure: globular clusters of nanoplatelets associated in a tree-like fashion. For this purpose different techniques such as Field-Emission Scanning Electronic Microscopy (FE-SEM), electrochemical impedance spectroscopy (EIS) measurements, Mott-Schottky (M-S) analysis and photoelectrochemical water splitting tests have been carried out. Photoanodes obtained at 375 rpm showed the best photoresponse, much higher than that of conventional WO3 nanoplatelets, which can be ascribed to a noteworthy in…
Enhancement of photoelectrochemical activity for water splitting by controlling hydrodynamic conditions on titanium anodization
2015
This work studies the electrochemical and photoelectrochemical properties of a new type of TiO2 nanostructure (nanosponge) obtained by means of anodization in a glycerol/water/NH4F electrolyte under controlled hydrodynamic conditions. For this purpose different techniques such as Scanning Electronic Microscopy (SEM), Raman Spectroscopy, Electrochemical Impedance Spectroscopy (EIS) measurements, Mott–Schottky (M−S) analysis and photoelectrochemical water splitting tests under standard AM 1.5 conditions are carried out. The obtained results show that electron–hole separation is facilitated in the TiO2 nanosponge if compared with highly ordered TiO2 nanotube arrays. As a result, nanosponges en…
The Effect of Ni Doping on the Performance and Electronic Structure of LSCF Cathodes Used for IT-SOFCs
2018
We investigated the effect of nickel doping on the electronic structure and performance of nanostructured La0.6Sr0.4Co0.2Fe0.8-0.03Ni0.03O3-delta prepared by the one-pot sol gel method. The commercial undoped La0.6Sr0.4Co0.2Fe0.8O3-delta (ISCF0.8) was used as reference. Moreover, for comparison, Ni (3 mol %) was deposited by wetness impregnation over the La0.6Sr0.4Co0.2Fe0.8O3-delta. We show by in situ X-ray absorption spectroscopy at 900 degrees C under air flow that nickel enters the B perovskite site of the material and favors the stabilization of the cobalt oxidation state, as evidenced by the delay in the decrease of the average Co valence with respect to undoped samples. Our results a…
Hexasubstituted Benzenes with Ultrastrong Dipole Moments
2015
Hexasubstituted benzenes have been synthesized with the highest known dipole moments, as determined by dielectric spectroscopy and DFT methods. Based on the preparation of 4,5-diamino-3,6-dibromophthalonitrile, combined with a novel method to synthesize dihydrobenzimidazoles, these benzene derivatives have dipole moments in excess of 10 debye. Such dipole moments are desirable in ferroelectrics, nonlinear optics, and in organic photovoltaics. Structure determination was achieved through single-crystal X-ray crystallography, and the optical properties were determined by UV/Vis absorption and fluorescence spectroscopy.
Chloride role in the surface of nickel electrode
1998
The chloride ion participation in the dissolution process on nickel electrodes in acid media as well as in the formation of the passive layer and in the pitting corrosion induction were studied. Composite electrodes containing nickel powder dispersed in a polymeric matrix show similar processes to those observed in polycrystalline nickel. Furthermore, phenformine hydrochloride inhibits the dissolution process due to the adsorption of the organic cation on the metal surface, although it does not protect the metal from pitting corrosion. Electrochemical impedance spectroscopy data allowed us to propose a physical model for the role of chloride ion in the dissolution and passivation processes …
Electrochemical impedance spectroscopy of conductor-insulator composite electrodes: properties in the blocking and diffusive regimes
1998
Abstract The electrochemical response of graphite + high-density polyethylene composite electrodes as a function of the conductivity load was investigated. Percolation theory was used in order to explain the electrochemical behaviour of this type of composite electrode. In the blocking regime the electrochemical impedance of this electrode material behaved as R 0 + q · ( ω j) − η , where R 0 represents the uncompensated resistance of the cell. Its value depended on the graphite volume proportion ( ν ) with a power law R 0 ∞ ( ν — ν c ) − t with a critical exponent t = 3.2 ± 0.1 which is close to the mean field value, t = 3. With potassium chloride concentrations greater than 0.7 M, the unco…
Dynamic properties of solvent confined in silica gels studied by broadband dielectric spectroscopy
2007
Abstract We report the results of a broadband (10−2–107 Hz) dielectric spectroscopy study on a solvent system (glycerol–water solution) confined in a porous silica matrix. The dielectric relaxation of the system is studied as a function of both temperature (120–280 K) and solvent composition (0–36 glycerol molar percentage), at constant matrix composition. Our data show that glycerol–water systems confined inside silica gel are characterized by a very complex dynamics quite different from that observed in solution, thus indicating that confinement may deeply modify solvent dynamics. Indeed in addition to the relaxation processes similar to those occurring in bulk samples, new dielectric rel…
Dielectric spectroscopy and molecular dynamics of methylene chloride CH2Cl2
1991
Abstract Precise measurements of the complex permittivity of methylene chloride (CH 2 Cl 2 ) at 293 K have been made at frequencies in the range 50–310 GHz. These, when combined with earlier results, have made possible a determination of the complex permittivity over the entire zero to THz frequency region. These results show a distribution of dielectric relaxation times. The value of the Cole-Cole distribution parameter, α, was 0.03 and that of the relaxation time, τ, was 2.07 ps. A comparison of the power absorption, A (ω), spectra of pure methylene chloride with the normalized dilute solution spectra shows that: (a) the integrated absorption intensity of the pure liquid is 20% greater th…
Dielectric breakdown strength of epoxy bimodal-polymer-brush-grafted core functionalized silica nanocomposites
2014
The central goal of dielectric nanocomposite design is to create a large interfacial area between the matrix polymer and nanofillers and to use it to tailor the properties of the composite. The interface can create sites for trapping electrons leading to increased dielectric breakdown strength (DBS). Nanoparticles with a bimodal population of covalently anchored molecules were created using ligand engineering. Electrically active short molecules (oligothiophene or ferrocene) and matrix compatible long poly(glycidyl methacrylate) (PGMA) chains comprise the bimodal brush. The dielectric breakdown strength was evaluated from recessed samples and dielectric spectroscopy was used to study the di…
Dielectric spectroscopy measurements of the sub-Tg relaxations in amorphous ethyl cellulose: A relaxation magnitude study
2005
Amorphous ethyl cellulose exhibits three secondary relaxations at temperatures below its glass transition. The fitted parameters that describe these processes and the comparison with other polysaccharides allow to ascribe the relaxations to lateral groups on one hand and to local main chain motion on the other hand. Their contributions to the dielectric constant overlap and induce a broad dielectric losses peak. The amplitude of one of these relaxations is found to decrease regularly with time. It is believed it comes from a gradual change of the polar groups chemical environment that constrains their motion.