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  • 1.
    Behm, Mårten
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Electrochemical production of polysulfides and sodium hydroxide from while liquor .2. Electrolysis in a laboratory scale flow cell1997In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 27, no 5, p. 519-528Article in journal (Refereed)
    Abstract [en]

    Electrochemical production of polysulfide-containing white liquor and pure sodium hydroxide solution was investigated at 90 degrees C in a laboratory scale flow cell. A mixed iridium-tantalum oxide coated titanium electrode was used as the anode and the two electrolyte compartments were separated by a cation-exchange membrane. The process was demonstrated at current densities up to 5 kA m(-2), resulting in high current efficiencies for both products. The previously reported autocatalytic effect of polysulfide ions was confirmed, and its technical implications on the use of three-dimensional electrodes were demonstrated and discussed. The current efficiency was found to depend strongly on the degree of conversion of sulfur(-II) to sulfur(0). The anode material showed favourable properties, with respect to activity and selectivity, but suffered from limited durability.

  • 2.
    Behm, Mårten
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Electrochemical production of polysulfides and sodium hydroxide from white liquor .1. Experiments with rotating disc and ring-disc electrodes1997In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 27, no 5, p. 507-518Article in journal (Refereed)
    Abstract [en]

    Electrochemical oxidation of white liquor in a membrane cell is a process of great potential for the pulp and paper industry. The process produces polysulfide-containing white liquor in the anode chamber, and pure sodium hydroxide solution in the cathode chamber. The anode reaction has been investigated using cyclic voltammetry at temperatures between 25 and 90 degrees C on rotating disc and ring-disc electrodes. It was further investigated using chronoamperometry on rotating disc electrodes at 90 degrees C. The experiments, which were mainly run in dilute alkaline sulfide solutions, using platinum electrodes, show that the electrochemical production of polysulfide ions, at lower anode potentials (-0.1 to +0.1 V vs SCE), proceeds via formation of elemental sulfur on the electrode surface. The sulfur is dissolved by hydrosulfide and polysulfide ions producing (longer-chain) polysulfide ions. The rate of dissolution, and thus the overall reaction rate, increases strongly with temperature. Polysulfide ions have an autocatalytic effect on the anode reaction due to their ability to dissolve adsorbed sulfur. At higher anode potentials (greater than or equal to 0.2 V vs SCE), a change of reaction mechanism is observed. In this region the reaction rate depends on electrode potential and is not catalysed by polysulfide ions.

  • 3.
    Behm, Mårten
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Graphite as anode material for the electrochemical production of polysulfide ions in white liquor1999In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 29, no 4, p. 521-524Article in journal (Refereed)
  • 4.
    Behm, Mårten
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Nickel as anode material for the electrochemical production of polysulfides in white liquor1999In: Journal of New Materials for Electrochemical Systems, ISSN 1480-2422, Vol. 2, no 1, p. 11-18Article in journal (Refereed)
    Abstract [en]

    This paper is concerned with new anode materials for the electrochemical oxidation of white liquor. This electrosynthesis process is run in a membrane cell where polysulfide ions are produced in the white liquor of the anode chamber, while a pure sodium hydroxide solution is generated in the cathode chamber: If the noble metal oxide coated anodes that were used in a previous investigation could be successfully replaced by nickel, important reductions in investment costs would be possible. The stability and catalytic activity of nickel as anode material were investigated using cyclic voltammetry and chronoamperometry on rotating disc electrodes, combined with surface analysis. Furthermore, porous nickel was tested in a flow cell, with galvanostatic electrolysis. The results show that nickel has good activity for sulfide oxidation, but a nickel oxide/sulfide surface layer is formed which deactivates the electrode at E greater than or equal to -0.2 V, probably due to the increasing proportion of poorly conducting Ni(II) oxide. Carbon precipitation, and peeling of a thin film of the metal were observed with SEM. High current efficiency and an overpotential of less than 0.2 V were obtained with a porous nickel electrode at a geometric current density of 3 kA m(-2). Corrosion did not appear to be a problem, and nickel should also be suitable as substrate material for more active anode coatings.

  • 5.
    Cornell, Ann
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Lindbergh, Göran
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    The effect of addition of chromate on the hydrogen evolution reaction and on iron oxidation in hydroxide and chlorate solutions1992In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 37, no 10, p. 1873-1881Article in journal (Refereed)
    Abstract [en]

    The addition of chromate to the electrolyte has been shown in previous papers to hinder almost completely the electroreduction of hypochlorite, while the hydrogen evolution reaction can still proceed on the cathode surface. The effect of chromate on the latter reaction has been studied with cyclic voltammetry and by measuring polarization curves for iron electrodes in both chlorate and hydroxide electrolyte. For the sake of comparison, the investigations have also included the effects on the gold electrode in hydroxide solution. The results showed that the kinetics is changed in a way that decreases the differences in electrocatalytic activity between different electrode materials. Also, the innermost layer of the chromium hydroxide film seems to be the most active part in the HER. The chromate also affects the oxidation of the iron surface. A practical result of this is that the activity for the HER on corroded iron in chlorate electrolyte depends on whether the electrolyte contained chromate during the period of corrosion. The activation becomes much smaller if chromate is present.

  • 6.
    Cornell, Ann
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Ruthenium Dioxide as Cathode Material for Hydrogen Evolution in Hydroxide and Chlorate Solutions1993In: Journal of The Electrochemical Society, Vol. 140, no 11, p. 3123-3129Article in journal (Refereed)
    Abstract [en]

    Ruthenium dioxide as electrocatalyst on an activated cathode for chlorate production was investigated with respect toits activity towards hydrogen evolution, hypochlorite reduction, and chlorate reduction, respectively. Investigations weremade in the presence, as well as in the absence, of a chromium hydroxide film in 1M NaOH and in typical chlorateelectrolyte. Low overvoltages for hydrogen evolution were found and, at technical current densities, an effect of catalystcoating thickness. Commercial DSA® electrodes with RuO2 as the active compound were tested as cathodes and were lessactive but more stable than the coatings produced by us. Hypochlorite and chlorate were reduced in the absence ofchromate, chlorate reduction being fast on ruthenium dioxide compared to the other electrode materials and by far thedominating cathodic reaction in chlorate electrolyte without chromate and hypochlorite at 70°C, 3 kA/m2

  • 7.
    Fontes, Eduardo
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Lagergren, Carina
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Lindbergh, Göran
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Influence of gas phase mass transfer limitations on molten carbonate fuel cell cathodes1997In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 27, no 10, p. 1149-1156Article in journal (Refereed)
    Abstract [en]

    The purpose of this paper is to elucidate to what extent mass transfer limitations in the gas phase affect the performance of porous molten carbonate fuel cell cathodes. Experimental data from porous nickel oxide cathodes and calculated data are presented. One and two-dimensional models for the current collector and electrode region have been used. Shielding effects of the current collector are taken into account. The mass balance in the gas phase is taken into account by using the Stefan-Maxwell equation. For standard gas composition and normal operating current density, the effect of gas-phase diffusion is small. The diffusion in the gaseous phase must be considered at operation at higher current densities. For low oxygen partial pressures, the influence of mass transfer limitations is large, even at low current densities. To eliminate the influence of conversion on polarization curves recorded on laboratory cell units, measurements should always be performed with a five to tenfold stoichiometric excess of oxygen. Two-dimensional calculations show rather large concentration gradients in directions parallel to the current collector. However, the influence on electrode performance is still small, which is explained by the fact that most of the current is produced close to the electrolyte matrix.

  • 8.
    Fontes, Eduardo
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Lagergren, Carina
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Mathematical modelling of the MCFC cathode: On the linear polarisation of the NiO cathode1997In: Journal of Electroanalytical Chemistry, ISSN 0022-0728, E-ISSN 1873-2569, Vol. 432, no 1-2, p. 121-128Article in journal (Refereed)
    Abstract [en]

    Experimental polarisation curves for the porous lithiated NiO cathode used in molten carbonate fuel cells very often exhibit a linear shape over a wide potential range. It is shown by means of mathematical modelling that this linear behaviour can be explained by the interplay of intrinsic electrode kinetics, diffusion of electroactive species through an electrolyte film and the effective ohmic resistance of the pore electrolyte, providing that the cathodic transfer coefficient has a value of about 1.5. In contrast, with the generally assumed value of 0.5 of this transfer coefficient and with reasonable values of the effective electrolyte conductivity, predicted polarisation curves will always bend downwards over the overvoltage region of interest. The evolution of the polarisation curves with increasing electrolyte fill can be simulated by a model according to which the electroactive surface area becomes gradually blocked with the increasing amount of electrolyte.

  • 9.
    Fontes, Eduardo
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Lagergren, Carina
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    MATHEMATICAL-MODELING OF THE MCFC CATHODE1993In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 38, no 18, p. 2669-2682Article in journal (Refereed)
  • 10.
    LAGERGREN, CARINA
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    LINDBERGH, GÖRAN
    KTH, Superseded Departments, Chemical Engineering and Technology.
    SIMONSSON, DANIEL
    KTH, Superseded Departments, Chemical Engineering and Technology.
    INVESTIGATION OF POROUS ELECTRODES BY CURRENT INTERRUPTION APPLICATION TO MOLTEN CARBONATE FUEL CELL CATHODES1995In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 142, no 3, p. 787-797Article in journal (Refereed)
    Abstract [en]

    A transient agglomerate model for simulation and analysis of experimental data, obtained by current interruption on porous molten carbonate fuel cell cathodes, is presented. The initial fast change of the potential after current interruption on a polarized NiO electrode is due to the closed-circuit potential distribution in the electrode. Conventional estimation of the iR corrected overvoltage by current interruption on porous electrodes, with finite electronic conductivity in the solid phase and a finite ionic conductivity of the pore electrolyte, leads to an overcompensation of the external potential drop and an underestimation of the total steady-state overvoltage due to the internal currents passing in the electrode after interruption. The overcompensation of the external potential drop is directly proportional to the geometric current density and to the thickness of the electrode and inversely proportional to the sum df the effective conductivities in the electrode matrix and the pore electrolyte.

  • 11.
    Lagergren, Carina
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    The effects of oxidant gas composition on the polarization of porous LiCoO2 electrodes for MCFC1997In: Carbonate Fuel Cell Technology IV / [ed] J. R. Selman, I. Uchida, H. Wendt, D. A. Shores and T. F. Fuller, 1997, p. 329-Conference paper (Other academic)
  • 12.
    Lagergren, Carina
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    The effects of oxidant gas composition on the polarization of porous LiCoO2 electrodes for the molten carbonate fuel cell1997In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 144, no 11, p. 3813-3818Article in journal (Refereed)
    Abstract [en]

    Stationary polarization curves were obtained for porous lithium cobaltite cathodes under varying temperatures and oxidant compositions. The exchange current densities were determined from the slope at low overpotentials by means of numerical calculations, taking into account the current density distribution. Positive influences on the exchange current density were found both for the partial pressure of oxygen and carbon dioxide. The results are similar to earlier data obtained from measurements on NiO electrodes. The values are not consistent with either the peroxide mechanism or the superoxide mechanism, two mechanisms often proposed in the literature.

  • 13.
    Lindbergh, Göran
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Effect of chromate addition on cathodic reduction of hypochlorite in hydroxide and chlorate solutions1990In: Journal of the Electrochemical Society, Vol. 137, no 10, p. 3094-3099Article in journal (Refereed)
    Abstract [en]

    The cathodic reduction of chromate and its effect on the reduction of hypochlorite have been studied by cyclic voltammetry, using a rotating disk electrode of platinum in IM NaOH solution as well as in an electrolyte with a composition and temperature which were typical for industrial chlorate synthesis. It was found that in both electrolytes a thin film of presumably Cr(OH)3, with a thickness of only one or two molecular layers, is formed. After formation of this film in a cathodic sweep of the potential, the hypochlorite reduction reaction is almost completely inhibited in the reversed sweep, up to the potential region for dissolution of the formed film. From the experimental results and a theoretical analysis of the mass transfer rate of hypochlorite ions to the cathode surface, it is concluded that the addition of chromate to the electrolyte in the industrial chlorate process leads to the formation of a thin film on the cathode surface, which hinders electron transfer at the reduction of hypochlorite.

1 - 13 of 13
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