Showing papers on "Supporting electrolyte published in 1987"

Modeling ionic strength effects on cation adsorption at hydrous oxide/solution interfaces

Abstract: The effects of changes in ionic strength on the adsorption behavior of selenite (SeO32−) and selenate (SeO42−) on goethite and hydrous ferric oxide have been modeled using a generalized version of the triple-layer surface complexation model. Selenite adsorption, which is relatively unaffected by changes in ionic strength, is best modeled assuming that selenite forms an inner-sphere (surface coordination) complex; selenate adsorption, which is markedly reduced by increasing ionic strength, is best modeled assuming that selenate forms an outer-sphere (ion-pair) surface complex. The modeling results suggest that it is possible to distinguish between inner-sphere and outer-sphere anion surface complexes by studying the effects of ionic strength on anion partitioning.

Permselectivities of polyelectrolyte electrode coatings as inferred from measurements with incorporated redox probes or concentration cells

Abstract: Permselectivities of coatings and membranes prepared from polyanionic Nafion and from a new type of polycationic copolymer were evaluated by two methods. (i) Electroactive couples incorporated in coatings on graphite electrode surfaces served as redox probes whose apparent formal potentials changed as the concentration of supporting electrolyte was varied. The magnitude of those changes allowed the permselectivities of the coating to be surmised. (ii) Thicker layers of the polyelectrolytes were used as membranes to separate supporting electrolyte solutions of differing concentrations. The potential difference between reference electrodes placed on either side of the membrane allowed the permselectivities of the membranes to be judged. Both of the methods indicated nearly ideal permselectivity of Nafion coatings and membranes at supporting electrolyte concentrations below ca. 2 M. Ideal permselectivity continued to be registered for a Nafion membranes by the redox probe method even after the membrane had been punctured so that the bulk cation transference number was far from unity. For the polycationic copolymer, both methods indicated increasing deviations from ideal anion permselectivity as the concentration of the supporting electrolyte was increased. Interpretations and some consequences of the observations are presented.

The Electrochemical Behavior in Aqueous Media of Conducting Polymers II . The Insoluble Fractions Obtained on the Cu(II) Catalyzed Polymerization of (2,5‐Dibromo‐3‐Group IV Substituted) Thiophenes

Abstract: : The chemical polymerization of (2,5-dibromo-3-substituted) thiophenes utilizing Cu(II)Cl2 as a copromoter yields an amorphous insoluble polymer fraction which exhibits a very high electronic conductivity. These materials have been used as electrode materials. The redox chemistry of the Cu(II) containing polymer in contact with supporting electrolyte only shows a distinct internal (Cu(II)/Cu(I) cyclic voltammetric wave. No redox behavior for the thiophene ring system is observed. This material is very stable in aqueous media and appears to be conducting at positive and negative electrode potentials (contrary to the redox response of electrodeposited polythienylene films). The lack of 3-substituent steric effects is discussed. The similarities and, more important, the dissimilarities of the properties of these polymers and Cu(II)-dithiolate complexes are also discussed.

Overlayer Formation as a Source of Stability in the N‐Type Photoelectrochemical Cell: The Cell

Abstract: The stability of in a electrolyte is demonstrated to be due to the formation of a overlayer. Mediated hole transfer through the overlayer to solution competes with photoanodic decomposition of the electrode. The charge transfer energetics and kinetics of the overlayer are very sensitive to the supporting electrolyte cation. Variations in supporting electrolyte allow maximization of overlap between the semiconductor states and the filled levels of the surface couple. This leads to enhanced energy conversion efficiencies and minimization of electrode decomposition. For the electrode, a supporting electrolyte containing both K+ and Cs+ is found to maximize cell performance. A surface state responsible for deleterious electron transfer through the barrier is observed ~600 mV positive of the conduction bandedge. Cells with monochromatic efficiencies in excess of 20% (488 nm) can be obtained by considering the overlayer properties.

Effects of solution conditions on the surface-enhanced Raman scattering of cyanide species at Ag electrodes

Abstract: The effect of solution pH and supporting electrolyte anion on the SERS behavior of cyanide species adsorbed at Ag electrodes is described. Signals for the nu(CN) band are observed in both acidic (pH 2) and basic (pH 11) media in ClO/sub 4//sup -/, Cl/sup -/, and SO/sub 4//sup 2 -/ supporting electrolytes. The frequency and intensity of the nu(CN) band are a function of electrode potential in all media. The potential at which the SERS signal reaches a maximum intensity is slightly dependent on the anion of the supporting electrolyte in basic media, but is a strong function of the anion in acidic media. In acid solution, HCN is adsorbed. Two unresolved bands occur in the nu(CN) region in acidic media and several possible assignments are proposed. The assignment that best explains all of the experimental data involves both end-bonded and side-bonded HCN. The effect of supporting electrolyte anion on the SERS response is explained in terms of the relative abilities of these anions to influence the self-association of HCN in the interface.

A method and apparatus for the determination of electrochemically active components in a process stream

Abstract: A method and apparatus for determining electrochemically active components in a process stream. The method comprises the steps of providing a sample in which the components are contained, and depositing the components onto a working electrode, altering the environment of the working electrode so that it is immersed in a supporting electrolyte by effecting a matrix exchange and stripping the deposited electrochemically active components from the working electrode into the supporting electrolyte. The method and apparatus utilize a measurement cell which comprises a vessel (10) for containing the supporting electrolyte and a mercury drop electrode (150). A flow injector (16) is used to inject a flow of a sample electrolyte which contains the electrochemically active component; and into the vessel so that the sample electrolyte surrounds the mercury drop electrode and then sinks away from the mercury drop electrode (150) to the bottom of the vessel where it is removed via an outlet (20) to thereby leave the mercury electrode (150) immersed in the supporting electrolyte. The deposited impurities are stripped from the working electrode using variable time domain transient electrochemical stripping voltammetry. The sequence of steps including the deposition of the impurities from an injected flow of electrolyte sample are repeated under microprocessor control (50).

Structure and amounts of counter ions in polypyrrole films prepared from aqueous solutions of sodium tosylate

Abstract: A series of conducting polypyrrole films was prepared from aqueous TsONa solution of different concentrations, and investigated by means of elemental analyses and scanning electron microscopy. The results show that the different concentrations of the supporting electrolyte TsONa do not only cause different amounts of counter ions in the film, but also cause a different structure and morphology of the film.

Electro-oxidation rate ofp-tert-butyltoluene in a bipolar packed-bed electrode cell

Abstract: The side chain methoxylation ofp-tert-butyltoluene was carried out in a bipolar packed-bed electrode cell in which graphite pellets of diameter 4.74 mm and length 5mm were randomly packed in nine layers separated by inert mesh spacers. The reaction consisted of main consecutive reactions leading top-tert-butylbenzyl methyl ether andp-tert-butylbenzaldehyde dimethyl acetal (TBDA) and polymerization reactions. Overall reaction rate coefficients for each reaction step, current efficiency and energy consumption were determined on the basis of a reactor model. The selectivity and the current efficiency for TBDA increased with increasing current, but the energy consumption began to rise when the current exceeded 0.8 A. An addition of supporting electrolyte suppressed the overall reaction rate coefficients, although it decreased the energy consumption.

A study of metal ion adsorption at low suspended-solid concentrations

Abstract: A procedure for conducting adsorption studies at low suspended solid concentrations in natural waters (<50 mg l−1) is described. Methodological complications previously associated with such experiments have been overcome. Adsorption of zinc ion onto synthetic colloidal titania (TiO2) was studied as a function of pH, supporting electrolyte (NaCl) concentration (0·1-0·002 m) and particle concentration (2–50 mg l−1). The lack of success of the Davis Leckie site bonding model in describing Zn(II) adsorption emphasizes the need for further studies of adsorption at low suspended-solid concentrations.

Determination of lead and cadmium in biological samples by potentiometric stripping analysis

Abstract: The determination of lead and cadmium in biological materials was carried out by potentiometric stripping analysis. Supporting electrolyte was a mixture of NaCl and HCl. In the presence of 4% lumatom in methanol, oxidation potentials of −0.46 V for Pb and −0.68 V for Cd were found (vs. SCE). The method was applied to different standard reference materials (leaves, needles, hair) and was also compared with the differential pulse anodic stripping technique. The latter presented considerable difficulties, in particular by the interference of oxygen.