Identification of electrode surface blocking by means of thin-layer cell

Baltrūnas, G.; Valiūnas, Raimondas; Popkirov, G.

doi:10.1016/j.electacta.2007.05.040

Cited by 12 publications

(10 citation statements)

References 11 publications

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“…According to this approach, the presence of inert (nonconducting) areas on the surface of heterogeneous membranes leads to a decrease in the limiting electrodiffusion current as compared with values calculated based on the Levich theory. The limit ing current i lim depends on the correlation of the inert surface fraction Θ and the effective radius of conducting areas R found by processing the surface microimages for membranes under study [23,24]:…”

Section: Methodsmentioning

confidence: 99%

Transfer of electrolyte ions and water dissociation in anion-exchange membranes under intense current conditions

et al. 2012

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Polarization characteristics of electromembrane systems (EMS) based on the Russian commer cial heterogeneous membranes MA 40 and MA 41, the anion exchange heterogeneous membrane AMH (Mega, Czech Republic), and the modified membrane MA 40M are studied by the method of rotating mem brane disk in dilute sodium chloride solutions. The effective transport numbers of ions are found; the partial voltammetric characteristics (VAC) with respect to chloride and hydroxyl ions are measured; the limiting cur rent densities are calculated as a function of the membrane disk rotation rate. In terms of the theory of the overlimiting state of EMS, based on experimental VAC and the dependences of the effective transport num bers on the current density, the following internal parameters of systems under study are calculated: the space charge and electric field strength distribution over the diffusion layer and the membrane. It is shown that water dissociation can be virtually completely eliminated by substituting chemically stable quaternary ammo nium groups inert with respect to water dissociation in the surface layer of a heterogeneous anion exchange membrane MA 40 for the active ternary and secondary functional amino groups. The maximum electric field strength values at the membrane/solution interface, which were found in the framework of the theory of over limiting state, turned out to be close for all anion exchange membranes studied, namely, (7-9) × 10 6 V/cm. This suggests that it is the nature of ionogenic groups in the surface layer rather than the field effect that plays the decisive role in the membrane ability to accelerate the water dissociation reaction. It is proved experimen tally that in highly intense current modes of the electrodialysis process, the thermal hydrolysis of quaternary ammonium bases occurs in strongly basic MA 41 and AMH membranes by the Hofmann reaction to form ternary amino groups catalytically active in water dissociation reaction. Based on the concept on the catalytic mechanism of water dissociation, the fraction of ternary amino groups formed by thermal hydrolysis in the surface layer (the space charge region) of monopolar anion exchange membranes MA 41 and AMH is assessed quantitatively as 0.7 and 6.5%, respectively.

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Section: Methodsmentioning

confidence: 99%

Transfer of electrolyte ions and water dissociation in anion-exchange membranes under intense current conditions

et al. 2012

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“…Electrochemical responses of materials having heterogeneous surface mainly depend on the parameters of surface heterogeneity [15,274,291]: on the size and shape [292,293], as well as the surface fraction [274,292,[294][295][296] of conductive and nonconductive areas. Most of mathematical descriptions of ionic transport in electrochemical systems are restricted to 1D geometry [296], not relevant to a heterogeneous permselective surface.…”

Section: The Use Of Electric Current Stream Function Comparison Withmentioning

confidence: 99%

Modelling of Ion Transport in Electromembrane Systems: Impacts of Membrane Bulk and Surface Heterogeneity

et al. 2018

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Artificial charged membranes, similar to the biological membranes, are self-assembled nanostructured materials constructed from macromolecules. The mutual interactions of parts of macromolecules leads to phase separation and appearance of microheterogeneities within the membrane bulk. On the other hand, these interactions also cause spontaneous microheterogeneity on the membrane surface, to which macroheterogeneous structures can be added at the stage of membrane fabrication. Membrane bulk and surface heterogeneity affect essentially the properties and membrane performance in the applications in the field of separation (water desalination, salt concentration, food processing and other), energy production (fuel cells, reverse electrodialysis), chlorine-alkaline electrolysis, medicine and other. We review the models describing ion transport in ion-exchange membranes and electromembrane systems with an emphasis on the role of micro-and macroheterogeneities in and on the membranes. Irreversible thermodynamics approach, "solution-diffusion" and "pore-flow" models, the multiphase models built within the effective-medium approach are examined as the tools for describing ion transport in the membranes. 2D and 3D models involving or not convective transport in electrodialysis cells are presented and analysed. Some examples are given when specially designed surface heterogeneity on the membrane surface results in enhancement of ion transport in intensive current electrodialysis.Recently, Svoboda et al. [13] developed a specific scanning cell for the analysis of heterogeneous IEM structure by micro-computed tomography, which provides volume reconstruction of the studied material. The unique working principle of the cell allows one to scan membranes not only in their dry state but also in fully swollen state. The micro-computed tomography showed that there are profound changes in the structure of the IEM associated with their transition from the dry state into the swollen one. This study applied to the heterogeneous cation-exchange membrane (CEM) coming from Mega a.s., Czech Republic showed that swelling of the membrane is caused by the swelling of the ion-exchange resin. Its volume increased nearly three times after exposure to deionized water, while the overall membrane volume increased by 50%. If the membrane contained approximately 28%vol. of the resin in the dry state, this content increased to 52%vol. after swelling.Micro-computed tomography not only allows one to analyse volumetric composition of the membrane bulk but also to quantify the composition of the surface. By using two different methods, Vobecka et al. [14] evaluated the fraction of the conductive area (e.g., the ion-exchange resin) on the surface of an AEM and CEM in the swollen state. The obtained results showed that the volume fraction of the conductive domains does not correspond to the surface fraction of these domains and thus the volume composition is not reflected on their surface. For example, the volume fraction of the conductive domains for the st...

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“…By taking into account the electric nonuniformity of the heterogeneous membrane surface, an improved version of this equation was obtained [2,3]. The elec trodiffusional transfer of ions in electrolytes was theo retically described for a system with a metal electrode [2].…”

Section: Introductionmentioning

confidence: 99%

“…The elec trodiffusional transfer of ions in electrolytes was theo retically described for a system with a metal electrode [2]. As applied to the electrodiffusional transfer of electrolyte ions through ion exchange membranes with heterogeneous surfaces, the modernized version of Eq.…”

Section: Introductionmentioning

confidence: 99%

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Electroconvection in systems with heterogeneous ion-exchange membranes

et al. 2012

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The results of studying the surface morphology of heterogeneous cation (MK 40) and anion exchange (MA 40) membranes and calculating the structure of electroconvective vortices generated by the electric body force are shown. The body force and its distribution are estimated by taking into account real parameters of the membrane surface morphology. The calculations of vortices were carried out by solving the Navier-Stokes equation with the no slip boundary condition and the preset body force distribution. It is shown that the body force induced by the flowing current can generate pairs of electroconvective vortices (electroosmosis of the second kind), where the size of induced vortices is comparable with the intermembrane gap in electrodialysis cells.

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Identification of electrode surface blocking by means of thin-layer cell

Cited by 12 publications

References 11 publications

Transfer of electrolyte ions and water dissociation in anion-exchange membranes under intense current conditions

Transfer of electrolyte ions and water dissociation in anion-exchange membranes under intense current conditions

Modelling of Ion Transport in Electromembrane Systems: Impacts of Membrane Bulk and Surface Heterogeneity

Electroconvection in systems with heterogeneous ion-exchange membranes

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