关键词： corrosion   paint coatings   scanning electrochemical microscopy   polyurethane   iron dissolution   oxygen reduction  

摘要： The scanning electrochemical microscope (SECM) is a non-optical scanning microscopic instrument capable of imaging highly localized electrical currents associated with charge transfer reactions occurring in the vicinity of the surface of coated metals. The SECM tip operates as working microelectrode in an electrochemical cell under potentiostatic control. Microelectrode current and position is recorded as the tip is scanned very near a coated sample at a constant Z height, and variations in the faradaical current measured at selected tip potential values can be related to changes in the local concentration of electroactive species involved in corrosion reactions occurring at the substrate. Carbon steel samples coated with polyurethane in which a holiday was produced prior to immersion in different aqueous electrolytes were investigated with this technique. The release of Fe(II) ionic species into the solution phase from local anodic sites, as well as the consumption of dissolved oxygen at the corresponding cathodic locations was successfully monitored. (c) 2005 Elsevier Ltd. All rights reserved.

关键词： electrochemistry   energy   membranes   system engineering   hydrogen production IS (S-I) process   thermal efficiency  

摘要： One of the key reactions for efficient hydrogen production using the water-splitting iodine-sulfur (IS or S-I) process is the Bunsen reaction (SO2 + I-2 + 2H(2)O = H2SO4 + 2HI). The Bunsen reaction was examined using an electrochemical cell with a cation exchange membrane as the separator. The optimal molalities of anolyte and catholyte were evaluated by total thermal efficiency using the heat/mass balance of the IS process. The I-2/HI ratio had little effect on the required total voltage;the I-2/HI ratio can be reduced to 0.5 without decreasing the total thermal efficiency. On the other hand, HI and H2SO4 molality greatly affected the total thermal efficiency. The total thermal efficiency increased with increasing HI molality up to 16.7 mol kg(-H2O)(-1) and the maximum thermal efficiency was found at 15.3 mol kg(-H2O)(-1) of H2SO4. Membrane resistances are very important parameters affecting the efficiency. The total thermal efficiency increased by 3.0% at a current density of the electrochemical cell of 10.0A dm(-2) by increasing the operating temperature from 313 to 363 K. (c) 2005 Elsevier Ltd. All rights reserved.

关键词： Bayesian updating   normal process   electrolyte impurity  

摘要： The paper describes the establishment of prior, posterior and predictive distributions for parameters of a normal (Gaussian) electrochemical process with detailed numerical illustrations provided also for the estimation of certain probabilities. (C) 2004 Elsevier Ltd. All rights reserved.

关键词： phase field models   PITT   GITT   Li-ion batteries   intercalation   diffusion   Fick's equation   Chebyshev-spectral methods   Cahn-Hilliard equation   Allen-Cahn equation   gradient energy coefficient   computer simulations  

摘要： In this paper, we apply phase field models to move beyond Fick's law in describing Li diffusion in secondary battery electrodes. Phase field models are potentially more accurate and allow simpler tracking of phase boundaries than Fick's equation. The phase field models are implemented using the highly accurate but fast Chebyshev-spectral method. Using the phase field we investigate to what extent non-Fickian behavior can affect results from experimental techniques for measuring diffusion coefficients, such as Galvanostatic Intermittent Titration Technique (GITT) and Potentiostatic Intermittent Titration Technique (PITT). We show that GITT and PITT can still accurately measure the diffusion coefficient in systems described by phase field models even when significant gradient energy terms are present. (C) 2004 Elsevier Ltd. All rights reserved.

关键词： Anode materials   Anions   Carbon   Materials   Nickel  

摘要： A thorough study of all the steps involved in a typical industrial nickel hydroxide based active material preparation process has been carried out. The influence of the parameters involved in the reaction, graphite addition, sedimentation, washing, and homogenization steps upon the properties of the final product was determined. The results indicate that no significant particle growth takes place during the sedimentation step and it could thus be suppressed from the process, a fact that would result in cost and time savings. On the other hand, the sometimes disregarded final homogenization step turned out to be crucial in view of obtaining optimal electrochemical performances. Indeed, simple low cost additional milling treatments were found to significantly increase the electrochemical yields and are advisable for implementation in the industrial process.

关键词： hydroxylamine   radical amino cation   electrophilic amination   radical aromatic substitution  

摘要： Electrolysis of the system Ti(IV)-NH2OH-C6H6 in an 11 M H2SO4 solution shows that using an organic solvent (acetic acid, acetonitrile) during cathodically initiated amination of aromatic substrates permits the production of aromatic amines with the overall yield by hydroxylamine reaching 91%. Due to a chain mechanism of radical substitution, the benzene amination in electrolytes containing 5 M CH3COOH and 5.5 M CH3CN terminates largely upon consuming 70-75 and 50-55% of the charge required theoretically for a one-electron process. The maximum efficiency of electrochemical amination is observed at low hydroxylamine conversions and the overall current efficiency for mono- and disubstituted products of the benzene amination may exceed in these conditions 750%.

关键词： organic-inorganic hybrid phase   polysiloxane-immobilized amine ligands   sorption   mercury   modified electrodes  

摘要： Transport of mercury species in aquatic media is strongly affected by sorption processes on both organic and inorganic particles, and such mass transfer reactions are governed by speciation of this contaminant in the environment. The present research investigates the uptake of inorganic Hg-II species by sorbent materials based on polysiloxane-immobilized amine or thiol ligands, with the goal to highlight the effect of speciation on the sorption processes. Mercury binding was studied as a function of pH and chloride concentration to cover a wide range of species, including some among the most widely encountered forms in natural medium (HgCl42-, HgCl3,- HgCl2, Hg(OH)(2)). It was found on the one hand that all these species are liable to be removed from solution by strong binding to silica gels grafted with mercaptopropyl groups. On the other hand, the use of silica bearing aminopropyl moieties has led to the selective accumulation of anionic chloro-complexes of Hg-II in acidic medium in the presence of high chloride concentration and to the uptake of Hg-II hydroxide around neutral pH, while HgCl2 cannot be adsorbed on this material. The former reaction involves electrostatic interactions between HgCl42- or HgCl3- and the ammonium form of polysiloxane-immobilized an-line ligands, and the latter is driven by complexation of Hg-II species to the unprotonated amine groups. The interest of electrochemistry at carbon paste electrodes modified with these adsorbents for characterizing the sorption processes was also described by applying the following sequence "voltammetric detection subsequent to open-circuit accumulation". This approach allows the in situ determination of the amount of mercury in the organic-inorganic hybrid phase, as a function of speciation in solution and without significant modification in the solution-phase concentrations, so that the adsorption and ion-exchange isotherms can be obtained very easily and without requiring additional treatment of the sol

关键词： self-assembled monolayers (SAMs)   electrochemical impedance spectroscopy (EIS)   electrochemical noise (EN)   defect   pitting  

摘要： 1-Octadecanethiol (C18SH) monolayers were self-assembled on the fresh and active copper surface pretreated by nitric acid etching method. The surface properties of the alkanethiol-modified copper electrode in halide-containing solutions were characterized systematically by using several electrochemical methods, including polarization curves, cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN). The results show that C18SH self-assembled monolayers (SAMs) onto copper provide a flexible method that can protect the underlying copper against corrosion. With the immersion time of SAMs-coated copper electrode in NaCl and HCl corrosive solutions increasing, a slow loss of corrosion protection ability of SAMs indicates dynamic processes occurring at the electrode/solution interface and in the monolayers, such as expansion of the defects and transport of corrosive ions through defects of SAMs. Electrochemical noise (EN) is employed to detect the alkanethiol-modified copper surfaces immersed in HCl solution. This observation suggests the pitting process associate with dynamic processes in the I-octadecanethiol layer. (C) 2003 Elsevier Ltd. All rights reserved.

关键词： gold   thiourea   adsorbates   formamidine disulphide   electro-oxidation   dissolution  

摘要： The electrochemical behaviour of thiourea (TU) on gold in acid solutions is investigated in the range -0.2 to 1.7 V (versus standard hydrogen electrode) by conventional and triangularly potential modulated voltammetry, rest potential (E-rest) measurements, rotating disk and rotating ring-disk techniques. The value of E-rest is determined by an electrochemical reaction involving formamidine disulphide (FDS), adsorbed TU and soluble [Au(TU)(2)](+) species. For TU concentrations (c(TU)) in the range 1 less than or equal to c(TU) less than or equal to 50 mM, E-rest decreases linearly with log c(TU) with a slope of approximately -0.090 V decade(-1), while in the range 0.1 less than or equal to c(TU) less than or equal to 0.25 mM, it approaches -0.120 V decade(-1). Conventional and triangularly modulated voltammetry data indicate the quasi-reversible adsorption of TU occurring in the range -0.2 less than or equal to E less than or equal to 0.1 V, and the electro-oxidation of TU to FDS in the range 0.2 less than or equal to E less than or equal to 0.9 V, occurring simultaneously with the electrodissolution of gold yielding soluble [Au(TU)(2)](+) species. Both the electro-oxidation of TU and the electrodissolution of gold are under mass transfer control influenced by adsorbate formation. Different adsorbates from TU are produced depending on the adsorption potential and time. The electro-oxidation of these adsorbates in the range 0.9-1.7 V yields sulphate, carbon dioxide and CN residues. Reaction products are consistent with previous STM and FTIRS data. Comparative electrochemical data from FDS- and sulphide-containing solutions are also presented. Reaction pathways in which the participation of different adsorbates is considered, are discussed. (C) 2003 Elsevier Science B.V. All rights reserved.

关键词： conducting polymers   polyaniline   quinones   graphite   mechanisms  

摘要： The electrochemical peculiarities of classical redox systems with solid-state reagents (non-soluble quinones, intercalation compounds of graphite) as well as polyaniline-type conducting polymers have been considered. The conducting polymers show a significant non-faradaic component of the electrochemical mechanism. The essential differences of faradaic and non-faradaic systems in equilibrium behavior, trends of galvanostatic charge-discharge curves and cyclic voltammograms have been shown, and criteria for the identification of these mechanisms are proposed. Our investigations of the current-producing mechanism for the polyaniline electrode have shown that at least within a narrower range of potentials DeltaE(n) from 0.30-0.40 to 0.80-0.90 V versus SHE (depending on pH value) the 'capacitor' model of ion electrosorption/desorption in well conducting emeraldine salt phase is more preferable. Nevertheless, such a model should take into account the transport of both anions and protons (cations in a general case). Besides the possibilities of redox processes at the limits and beyond this range of potentials DeltaE(n) should be taken into account. At the same time, these processes can lead to the fast formation of thin passive layers of new poorly conducting phases (leucoemeraldine salt, leucoemeraldine base, etc.) near the current collector. The formation of such phases, even in a small amount, rapidly inhibits and discontinues the electrochemical process. (C) 2001 Elsevier Science Ltd. All rights reserved.