Electrochemical Properties of Homogeneous and Heterogeneous Anion Exchange Membranes Coated with Cation Exchange Polyelectrolyte - MDPI
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
membranes Article Electrochemical Properties of Homogeneous and Heterogeneous Anion Exchange Membranes Coated with Cation Exchange Polyelectrolyte Xenia Nebavskaya 1, * , Veronika Sarapulova 1 , Dmitrii Butylskii 1 , Christian Larchet 2 and Natalia Pismenskaya 1 1 Kuban State University, 149 Stavropolskaya st., 350040 Krasnodar, Russia; vsarapulova@gmail.com (V.S.); dmitrybutylsky@mail.ru (D.B.); n_pismen@mail.ru (N.P.) 2 Institut de Chimie et des Matériaux Paris-Est, UMR7182 CNRS—Université Paris-Est, 2 rue Henri Dunant, 94320 Thiais, France; larchet@u-pec.fr * Correspondence: k.a.nebav@gmail.com; Tel.: +7-918-32-32-996 Received: 3 December 2018; Accepted: 6 January 2019; Published: 11 January 2019 Abstract: Coating ion exchange membranes with polyelectrolyte has been proven to be a cheap way to reduce concentration polarization and increase limiting current (for polyelectrolytes carrying fixed groups of the same sign of charge with respect to the membrane bulk), to create high monovalent selectivity, and to add the function of H+ /OH− ions generation (for polyelectrolytes bearing fixed groups of the opposite sign of charge with respect to the membrane bulk). In the latter case, the balance between the counterion transport and the H+ /OH− ions generation is affected by parameters of the substrate and the modifying layer. In this study we investigated the electrochemical characteristics of homogeneous Neosepta AMX-Sb and heterogeneous MA-41P membranes coated with one, two, or three layers of oppositely charged polyelectrolyte (the maximum thickness of each layer was 5 µm). It was found that the limiting current decreased earlier and the generation of H+ /OH− ions was stronger in the case of the heterogeneous membrane. The shift in the pH of the solution depended more on the generation of H+ /OH− ions at the modifying layer/solution interface than on the generation at the membrane/modifying layer interface, and in all cases water splitting started in the same range of potential drops over the membrane. Keywords: ion exchange membrane; polymer; membrane modification; current–voltage curve; limiting current 1. Introduction The modification of ion exchange membrane (IEM) surfaces with a polyelectrolyte layer was first proposed by Sata et al. [1], who aimed to improve monovalent selectivity through the introduction of a selective layer carrying fixed groups oppositely charged with respect to the fixed groups of membrane bulk. In practice, the samples with functional groups of modifying layers being oppositely charged to the groups in membrane bulk became bipolar membranes with two functions: desalination and H+ /OH− ions generation [2]. The great role in the electrochemical properties of such IEM is played by the bipolar junction between the membrane and the modifying layer, at which the H+ /OH− ions generation occurs. Further studies broadened the range of application of layered electrochemical materials. Membrane-coated electrodes attracted interest for various electrochemical applications [3–5]. In the case of IEM, for redox flow batteries, layered polyelectrolyte composite membranes showed good conductivity and low permeability to vanadium ions [6], and a thorough review of methods to achieve Membranes 2019, 9, 13; doi:10.3390/membranes9010013 www.mdpi.com/journal/membranes
Membranes 2019, 9, 13 2 of 13 high monovalent selectivity of IEM in the separation processes (including several techniques for coating surfaces with charged and uncharged layers) was recently published [7]. Surface modification of ion exchange membranes with polyelectrolytes was used for pH correction [8], for suppression of fouling [9,10] or scaling [11], and for facilitation of the electro-osmotic slip of water near the surface [12]. It was shown that excellent monovalent selectivity can be achieved for IEM using layer-by-layer coating with polyelectrolytes carrying functional groups of alternating charges [13,14], or even for multilayers applied at uncharged porous supports [15]. For these systems, very high separation factors and adequate electric resistance were reported. However, several possible additional properties of layered IEM, such as the ability to generate H+ and OH− ions, should be taken into account for possible applications. The balance between the transport of salt ions and the generation of H+ /OH− ions depends on the thickness of the applied layer. For asymmetric bipolar membranes produced by the pouring and spreading of relatively thick modifying layers, this dependence was studied by Zabolotsky et al. [8], who found that the water splitting increases (and salt ion transport decreases) with the layer thickness. For thinner layers, the details of such dependency are not yet known, hence one of the tasks of our study was to determine the effect of modifying-layer thickness on the electrochemical properties (limiting current density of salt counterion and ability for H+ /OH− ions generation) of resulting membranes in the cases of applied layers with low thickness. Another question not yet answered was the role of the electrical heterogeneity of membrane support. Heterogeneous membranes are cheaper than homogeneous ones, hence they can be used for the design of cheaper novel materials with improved monovalent selectivity and reasonable electrochemical properties. What makes the difference between the homogeneous and the heterogeneous membranes in this case is that the appearance of nonconductive zones at the surface of heterogeneous membranes make the current lines concentrated on conductive zones [16]. As a result, the local current density is higher on conductive zones, which causes stronger concentration polarization and water splitting. Modified homogeneous membranes [13] and modified heterogeneous membranes [8] were studied separately, but the differing methods of modification and testing protocols do not allow direct comparison of results. To study the effect of this difference, we compared the properties of two series of membranes based on supporting membranes differing in homogeneity. The homogeneous supporting membrane was produced by the paste method (Neosepta AMX-Sb) and the heterogeneous supporting membrane was produced by hot rolling (MA-41P). 2. Materials and Methods 2.1. Membranes and Materials All samples in this study were prepared from the stock of commercial MA-41P (Shchekinoazot, Russia) and Neosepta AMX-Sb (Astom, Tokyo, Japan) membranes purchased from their respective companies. Both membranes contained an ion exchange matrix of the same composition, poly(styrene-divinylbenzene) copolymer, which carried quaternary ammonium bases (Table 1). They differed in their degrees of heterogeneity. Data from manufacturers and from previous studies described the procedures of the commercial production of MA-41P and AMX-Sb as follows: During the production of the MA-41P, a mixture of powdered ion exchanger and powdered polyethylene was hot rolled between two layers of Nylon 6 reinforcing cloth. As determined from analysis of the surface fraction of the ion exchanger (based on scanning electron microscopy visualizations of Russian heterogeneous membranes in top view), only about 28% of the resulting membranes can conduct electrical current, even in a swollen state [17]. During the production of AMX-Sb, a mixture of finely powdered polyvinyl chloride and functionalized monomer was applied to reinforced polyvinyl chloride cloth, then heated for polymerization [18], so that the dimensions of heterogeneities were far smaller than in the case of the MA-41P [19] and, before coating, almost 100% of the commercial AMX-Sb membrane was electrically conductive [20].
PVC grains up to 100 nm in continuous phase of PE; Reinforcing material diameter [21] *; PVC cloth Nylon 6 cloth [22] Ion exchange capacity, mM/g (swollen sample) 1.28 ± 0.05 1.25 ± 0.05 Thickness, µm (swollen sample) 134 ± 3 545 ± 3 Resistance in 0.02 M NaCl solution (calculated 46 52 from current–voltage curves), Ohm Membranes 2019, 9, 13 3 of 13 * From visualization of the surface of cation exchange membranes prepared by the same method. Commercial membranes used in this study were chosen based on their broad use for electrodialysis. 1. Properties Table The AMX-Sb of AMX-Sb homogeneous and MA-41P anioncommercial exchangesubstrate membrane membranes. (AEM) operating in electrodialyzers [23] Property is recommended by its manufacturer AMX-Sb for a number of applications MA-41P including separation of monovalent ions. In Reference poly(styrene-divinylbenzene) copolymer which carries quaternaryin ED for [24], this type of AEM is cited as widely used Ion exchanger food industry applications. The MA-41P belongs to the MA-41bases ammonium series of membranes, which is Diameter currently of ion the exchange standard grains heterogeneous Russian continuous AEM phase routinely used both for 5–40studies µm [17]and in industry PVC grains up to 100 nm in continuous phase of PE; Nylon 6 [25–27]. Reinforcing The MA-41P membrane is known material for its mechanical stability and durability. diameter [21] *; PVC cloth cloth [22] Coupled with its low cost, these properties Ion exchange capacity, mM/g make the MA-41P membrane promising for the production of modified 1.28 ± 0.05 1.25 ± 0.05 membranes (swollen [28]. sample) Thickness, µm (swollen sample) 134 ± 3 545 ± 3 Prior to modification, the membranes were equilibrated with isopropyl alcohol. The dispersion Resistance in 0.02 M NaCl solution of (calculated Nafion was fromused for coating. Nafion used46in this study was perfluorinated current–voltage 52 ionomer, which contains sulfonic curves), groups. Ohm To produce the modifier, a 5% (wt.) commercial dispersion of ionomer in water and * Fromalcohols bought visualization of thefrom surfaceSigma-Aldrich of cation exchange was diluted prepared membranes fivefoldbywith isopropyl the same method.alcohol. The resulting dispersion was spread to produce the modifying layer as thin as possible (differing here from the approach Commercial used toused membranes produce in this the study asymmetric were bipolar chosen membranes based on their with relatively broad usethick for modifying layers [8]) onto the 5 cm × 5 cm samples electrodialysis. The AMX-Sb homogeneous anion exchange membrane (AEM) operating in fixed to glass; the membranes were then left to dry in air for 24 h. For spreading, the selected volume (0.25 mL electrodialyzers [23] is recommended by its manufacturer for a number of applications including in this case) was applied at the center of the samples separation and fixed of monovalent to glass ions. (which rests In Reference [24],at this the level type surface), of AEM is then theas cited dispersion widely used was inmanually ED for spread onto the membrane with a spatula (Figure 1) and left to food industry applications. The MA-41P belongs to the MA-41 series of membranes, which is currentlydry. Previous the standard Russian preparation heterogeneous of the modified AEM routinely membranesused bothfollowing this protocol for studies showed that and in industry the [25–27]. thickness of the single layer applied to homogeneous membranes The MA-41P membrane is known for its mechanical stability and durability. Coupled with its does not exceed 5 µm [29]. After that, the membranes were soaked in concentrated (6.15 M, or 36%) NaCl solution, and every 2 h the low cost, these properties make the MA-41P membrane promising for the production of modified solution was diluted two-fold. After four such dilutions, the membranes were transferred into 0.02 membranes [28]. M NaCl solution and left for 16 h. Prior to modification, the membranes were equilibrated with isopropyl alcohol. The dispersion of It should be noted that, according to the row of catalytic activity of functional groups [30], neither Nafion was used for coating. Nafion used in this study was perfluorinated ionomer, which contains sulfonic groups of Nafion nor quaternary ammonium bases of AMX-Sb/MA-41P boost the H+/OH− sulfonic groups. To produce the modifier, a 5% (wt.) commercial dispersion of ionomer in water and ions generation reaction. alcohols bought from Sigma-Aldrich was diluted fivefold with isopropyl alcohol. The resulting The thicknesses were measured for swollen commercial membranes and swollen modified dispersion membranes was withspread to produce However, a micrometer. the modifying it waslayer found asthat thintheas modification possible (differingdid nothere leadfrom to a the approach used to produce the asymmetric bipolar membranes detectable change in thickness, and that the thickness of commercial AMX-Sb and all composite with relatively thick modifying layers [8]) onto the membranes based 5 cmon×it 5were cm samples in range fixedof 134to± glass; 3 µm, the whilemembranes thickness were then left to of commercial dry in and MA-41P air for all 24 h.composite For spreading, the selected volume (0.25 mL in this case) was applied membranes based on it were in the range of 545 ± 3 µm (Table 1). Visualizations of cross at the center of the samples and sections fixed to glass of MA-41P(whichmembranes rests at themodified level surface),with athen thelayer single dispersion was manually of polyelectrolyte spread (Figure 1e)onto the showed membrane that thewith a spatula thickness of dry (Figure layers 1) and left applied to to dry. heterogeneous membranes was about 1 µm. Nafion chain spatula solvent reinforcing cloth inert binder ion exchanger Membranes 2019, 9, x FOR PEER REVIEW 4 of 13 (a) (b) (c) (d) (e) (f) Figure1.1. Sketch Figure Sketch of of the the process process of modification modification (a–d) (a–d)and andfragments fragmentsofofSEM SEMimages images of of resulting resulting membranes. (a) The commercial membrane to be subjected to modification (the membranes. (a) The commercial membrane to be subjected to modification (the sketch illustratessketch illustrates thethe caseofofAMX-Sb); case AMX-Sb);(b)(b)the the modifying modifying dispersion dispersion isisapplied; applied;(c) (c)ititisismanually manually spread spreadwith witha spatula; a spatula;(d)(d) thesolvent the solventevaporates, evaporates, leaving leaving the relatively relatively thin thinmodifying modifyinglayer. layer.(e) (e)AAfragment fragment ofof ananSEMSEM image image portrayingaacross portraying crosssection section of of MA-41P MA-41P membrane membrane modified modifiedwith withone onelayer layerofofpolyelectrolyte; polyelectrolyte; (f) (f) AA fragmentofofan fragment anSEM SEMimage imageshowing showing aa top top view view ofof the the same samemembrane. membrane. 2.2. Current–Voltage (I–V) Curves Current–voltage (I–V) curves of studied samples were obtained using a flow-through 4-chamber cell (Figure 2). In all cases tested, the AEM formed a desalination chamber with a Neosepta CMX cation exchange membrane. On the other side, the concentration chamber was separated from the
Membranes 2019, 9, 13 4 of 13 Previous preparation of the modified membranes following this protocol showed that the thickness of the single layer applied to homogeneous membranes does not exceed 5 µm [29]. After that, the membranes were soaked in concentrated (6.15 M, or 36%) NaCl solution, and every 2 h the solution was diluted two-fold. After four such dilutions, the membranes were transferred into 0.02 M NaCl solution and left for 16 h. It should be noted that, according to the row of catalytic activity of functional groups [30], neither sulfonic groups of Nafion nor quaternary ammonium bases of AMX-Sb/MA-41P boost the H+ /OH− Membranes 2019, 9, x FOR PEER REVIEW 4 of 13 ions generation reaction. The thicknesses were measured for swollen commercial membranes and swollen modified membranes with a micrometer. However, it was found that the modification did not lead to a detectable change in thickness, and that the thickness of commercial AMX-Sb and all composite membranes based on it were in range of 134 ± 3 µm, while thickness of commercial MA-41P and all composite (d) (e) (f) membranes based on it were in the range of 545 ± 3 µm (Table 1). Visualizations of cross sections Figure 1. Sketch of the process of modification (a–d) and fragments of SEM images of resulting of MA-41P membranes modified with a single layer of polyelectrolyte (Figure 1e) showed that the membranes. (a) The commercial membrane to be subjected to modification (the sketch illustrates the thickness of dry case of AMX-Sb); (b) theto layers applied heterogeneous modifying dispersion ismembranes was about applied; (c) it is manually 1 with spread µm.a spatula; (d) the solvent evaporates, leaving the relatively thin modifying layer. (e) A fragment of an SEM image 2.2. Current–Voltage (I–V) portraying Curves a cross section of MA-41P membrane modified with one layer of polyelectrolyte; (f) A fragment of an SEM image showing a top view of the same membrane. Current–voltage (I–V) curves of studied samples were obtained using a flow-through 4-chamber cell (Figure2.2.2). Current–Voltage In all cases(I–V) Curvesthe AEM formed a desalination chamber with a Neosepta CMX tested, cation exchange membrane.(I–V) Current–voltage Oncurves the other side, of studied the concentration samples chamber were obtained using was separated a flow-through 4-chamber from the cell (Figure 2). In all cases tested, the AEM formed a desalination chamber electrode chamber by the MA-41P membrane. The operating area was 2 cm × 2 cm, the intermembrane with a Neosepta CMX cation exchange membrane. On the other side, the concentration chamber was separated from the distance was 0.65 cm, and the operating solution was 0.02 M NaCl pumped at a flow rate of 0.46 cm/s. electrode chamber by the MA-41P membrane. The operating area was 2 cm × 2 cm, the The polarizing electrodes intermembrane were was distance made 0.65ofcm, polished platinum and the operating 2 cm × solution was2 cm 0.02 and thepumped M NaCl measurementat a flow electrodes were closed rateAg/AgCl of 0.46 cm/s.electrodes The polarizing connected electrodesto Luggin were made capillaries, the tips of polished platinum of which 2 cm × 2 cm and were the located at measurement electrodes were closed Ag/AgCl electrodes connected to Luggin both sides of the studied membrane against its geometrical center. The distance from the surface capillaries, the tips of was which were located at both sides of the studied membrane against its geometrical center. The distance around 0.5frommm.theThe setup was laboratory-assembled and based on the setup described surface was around 0.5 mm. The setup was laboratory-assembled and based on the setup in more detail in [31,32], described with severalin morechanges detail in in equipment. [31,32], with several changes in equipment. Figure 2. Principal scheme of the flow-through four-chamber electrodialysis cell (1) with an anion Figure 2. Principal scheme of the flow-through four-chamber electrodialysis cell (1) with an anion exchange membrane (AEM)(AEM) exchange membrane under study under study(A*); (A*);auxiliary cation auxiliary cation exchange exchange (C) and(C) andexchange anion anion exchange (A) (A) membranes; tanks with membranes; 0.02 tanks M0.02 with NaCl solutions M NaCl (2,3); solutions Luggin (2,3); Luggin capillaries capillaries (4)(4) with with Ag/AgCl Ag/AgCl electrodes (5); electrodes an Autolab(5);PGSTAT an Autolab PGSTAT N100 N100source/voltmeter power power source/voltmeter (6);and (6); and aa pH-sensitive pH-sensitive electrode (7) connected electrode (7) connected to to a Mettler Toledo SevenCompact S220 pH meter (8). Adapted from [32]. a Mettler Toledo SevenCompact S220 pH meter (8). Adapted from [32]. I–V curves were obtained in galvanodynamic mode. The current density was swept from 0 to I–V curves were 6.0 mA/cm obtained 2, increasing in galvanodynamic stepwise mode.Autolab at 2.5 µA/cm2 per second. The current PGSTATdensity N100 waswas used swept both to from 0 to 2 2 6.0 mA/cm , increasing stepwise at 2.5 µA/cm per second. Autolab PGSTAT N100 was used both to
Membranes 2019, 9, 13 5 of 13 create the current sweep and to register the potential drop over the membrane. The theoretical limiting current density was calculated by the Lévêque equation [33]: Membranes 2019, 9, x FOR PEER REVIEW 5 of 13 " 2 1/3 # z C FD h drop V0 over the membrane. The theoretical create the current sweep and jlim = 1 1 the potential theorto register 1.47 − 0.2 , h ( T limiting current density was calculated by − t 1 the ) LD 1 Lévêque equation [33]: where z1 and C1 are the charge and molar concentration ℎ of counterion in solution bulk, respectively; = 1.47 − 0.2 , ℎ − F is the Faraday constant; D is the diffusion coefficient of salt in solution; h is the intermembrane distance; T1 and t1 are the counterion transport number in the membrane and solution, respectively; where z1 and C1 are the charge and molar concentration of counterion in solution bulk, respectively; V 0 is the linear solution pumping rate; and L is the length of the desalination path. The D value was F is the Faraday constant; D is the diffusion coefficient of salt in solution; h is the intermembrane takendistance; equal toT1that at infinite dilution and 25 ◦ C, which is 1.61 × 10−9 m2 /s. For the experimental and t1 are the counterion transport number in the membrane and solution, respectively; V0 is theT1linear conditions, was solution assumedpumping to be equalrate; to 1 (since and L is thethe membranes length are highlypath. of the desalination selective The Dfor counterions value was in such takendilute solutions, equal and to that at at currents infinite dilution close andto25the °C,limiting which iscurrent 1.61 × density 10−9 m2/s. the Forinput of water splitting the experimental is found to be negligible), conditions, Т1 was assumed t1 toto0.603, be equal h to to 16.3 mm, (since theand L to 2.0 are membranes cm.highly The calculated selective forlimiting current counterions in such dilute density was 3.12 mA/cm . 2 solutions, and at currents close to the limiting current density the input of water splitting To is found determine to be such negligible), parameters ast1experimental to 0.603, h to 6.3 mm, and limiting L to 2.0 current cm. The density and calculated limiting the current at which current density was 3.12 mA/cm 2. the coupled effects of concentration polarization arise, the following procedure was employed: To determine such parameters as experimental limiting current density and the current at which The I–V curves were built in ∆φ vs. j coordinates, where ∆φ was the experimental potential the coupled effects of concentration polarization arise, the following procedure was employed: difference registered between Luggin capillaries and j was the experimental current density (Figure 3). The I–V curves were built in Δϕ vs. j coordinates, where Δϕ was the experimental potential Then,difference the tangents were drawn registered betweentoLuggin the initial sectionand capillaries of the I–V j was thecurve (the so-called experimental currentohmic densityregion), (Figureto the initial3).section of the plateau region and to the end of the overlimiting currents Then, the tangents were drawn to the initial section of the I–V curve (the so-called ohmic region), region. The slope of the first to the initial section of the plateau region and to the end of the overlimiting currents region. The slope due tangent depends on the resistance of the membrane. It shows if the resistance changed to modification. The intersection of the first tangent depends on the ofresistance tangentsofdrawn to the ohmic the membrane. It shows region if the and to thechanged resistance plateau region due givestothe modification. experimental Thelimiting intersection of tangents current. drawn to the The intersection of ohmic tangents region drawn andto to the the plateau plateau region region and to thegives the experimental overlimiting currentslimiting regioncurrent. givesThetheintersection point where of tangents drawn to the transition tothe theplateau region and overlimiting current to the range occurs. overlimiting currents region gives the point where the transition to the overlimiting current range occurs. 6 5 4 j (mA/cm2) 3 2 1 0 0 0.5 1 1.5 2 2.5 ∆φ (V) Figure 3. Determination Figure 3. Determination of of thetheexperimental experimental limiting currentand limiting current and the the current current at which at which the coupled the coupled effects of concentration effects polarization of concentration polarizationarise. TheThe arise. resistance resistanceof of thethe membrane membranecan canalso alsobe bedetermined determined from the slope from of thethe tangent slope of the drawn tangent to the initial drawn part ofpart to the initial theofcurve. the curve. In allIncases, the the all cases, difference differenceininpHpHbetween between the outletand the outlet andthe theinlet inletof of thethe desalination desalination chamber chamber was registered was registered together togetherwith withthe theI–V I–Vcurves curves with with aa Mettler MettlerToledo ToledoSevenCompact SevenCompact S220S220 pH meter pH meter (Shanghai, (Shanghai, China). China). Before Before thethe theoreticallimiting theoretical limiting current currentwas wasreached, reached, pHpH value waswas value recorded each each recorded 5 min (starting at the beginning of the experiment at 0 min). When the limiting current 5 min (starting at the beginning of the experiment at 0 min). When the limiting current was reached was reached and the water dissociation reaction was expected to intensify, the lap between the measurements was and the water dissociation reaction was expected to intensify, the lap between the measurements reduced to 2 min. Since the cation exchange membrane in all tests was the same (strongly acidic
Membranes 2019, 9, 13 6 of 13 was reduced to 2 min. Since the cation exchange membrane in all tests was the same (strongly acidic Membranes 2019, 9, x FOR PEER REVIEW 6 of 13 Neosepta CMX), the pH-metry data were used to evaluate the relative rate of generation of H+ and OH−Neosepta ions on theCMX),AEM. the pH-metry data were used to evaluate the relative rate of generation of H+ and OH− ions on the AEM. 3. Results and Discussion 3. Results Figure and Discussion 4 gives the I–V curves of studied membranes. It should be noted that even the experimental limiting current Figure of the commercial 4 gives MA-41P the I–V curves heterogeneous of studied membranes.membrane It should wasbelower notedthan that the theoretical even the experimental limiting limiting current current calculated by theofLévêque the commercial MA-41P equation. Thisheterogeneous can be explainedmembrane was lower by a higher than local current the theoretical limiting current calculated by the Lévêque equation. This can be explained density at the conductive zones due to the surface being partially occupied by nonconductive material,by a higher localtocurrent leading higherdensity at the conductive concentration polarization zones anddue to thedecrease a faster surface being partially of salt occupiednear concentration by the nonconductive material, leading to higher concentration polarization and a faster decrease of salt membrane surface. concentration near the membrane surface. Comparison of the I–V curves that were measured for homogeneous and heterogeneous Comparison of the I–V curves that were measured for homogeneous and heterogeneous membranes showed membranes showed that in in that general generalthe thechanges changes that occurredwith that occurred withelectrochemical electrochemical properties properties (due (due to their to their modification with polymer carrying the functional groups oppositely charged to groups in in modification with polymer carrying the functional groups oppositely charged to groups membrane membranebulk) were bulk) similar. were However, similar. However,there therewere were also peculiarities. also peculiarities. 6 5 increasing nb. 0 1 4 of layers 2 j (mA/cm2) 3 3 j lim theor 2 no coating 1 layer 1 2 layers 3 layers 0 0 0.5 1 1.5 2 2.5 3 ∆φ (V) (a) 6 3 2 1 5 4 0 j (mA/cm2) 3 0 j lim theor 1 no coating 2 2 3 1 layer increasing nb. 1 2 layers of layers 3 layers 0 0 0.5 1 1.5 2 2.5 3 ∆φ (V) (b) Figure Figure 4. I–V 4. I–V curves curves of of thethehomogeneous homogeneous AMX-Sb AMX-Sb membrane membraneand andits its modifications (a) and modifications the the (a) and heterogeneous MA-41P membrane and its modifications (b). Arrows show the heterogeneous MA-41P membrane and its modifications (b). Arrows show the increased number increased number of of changes occurring with the additional layers of Nafion applied. The dashed line shows the theoretical changes occurring with the additional layers of Nafion applied. The dashed line shows the theoretical limiting current calculated by the Lévêque equation. Numerals denote the number of applied layers limiting current calculated by the Lévêque equation. Numerals denote the number of applied layers ranging from zero (no coating, i.e., the commercial membrane) to three. ranging from zero (no coating, i.e., the commercial membrane) to three.
Membranes 2019, 9, 13 7 of 13 Membranes 2019, 9, x FOR PEER REVIEW 7 of 13 Firstly, it can be seen that in all cases the experimental limiting current density decreased with Firstly, it can be seen that in all cases the experimental limiting current density decreased with the increasing number of layers. Such changes are typical for monopolar ion exchange membranes the increasing number of layers. Such changes are typical for monopolar ion exchange membranes transforming into bipolar membranes due to the increasing thickness of the oppositely charged layer [8] transforming into bipolar membranes due to the increasing thickness of the oppositely charged layer when [8] thewhen bipolar the junction blocksblocks bipolar junction the transport of salt the transport ions.ions. of salt Secondly, Secondly, in all cases, the differential resistance ofmembranes, in all cases, the differential resistance of whichcould membranes, which couldbe be determined determined fromfrom the slope of theof I–V the slope curve the I–V in the curve underlimiting in the underlimitingcurrents currents region, didnot region, did notstrongly strongly change change withwith the the application of layers. application However, of layers. However, thethecharacter character of of changes thatoccurred changes that occurredwithwith modifications modifications of the of the AMX-Sb membrane differed from the character of changes that occurred with AMX-Sb membrane differed from the character of changes that occurred with modifications of the modifications of the MA-41PMA-41P membrane. membrane. Properties Properties of the of the MA-41Pchanged MA-41P changed gradually gradually (the (theexperimental experimental limiting currents limiting currents and currents at which the overlimiting current range starts to decrease step by and currents at which the overlimiting current range starts to decrease step by step with each step with each newlynewly applied layer), while properties of the commercial AMX-Sb and samples modified with one or two applied layer), while properties of the commercial AMX-Sb and samples modified with one or two layers of polymer only slightly differed, and the significant decline occurred only after three layers layers of polymer only slightly differed, and the significant decline occurred only after three layers were applied (Figure 5). were applied (Figure 5). 5 4 j (mA/cm2) 3 2 1 0 0 1 2 3 Number of layers (a) 5 4 j (mA/cm2) 3 2 1 0 0 1 2 3 Number of layers (b) exp FigureFigure 5. Dependence 5. Dependence of experimental of experimental limitingcurrent limiting current densities densities ( (i , ,circles) and current densities lim circles) and current densities of transition to the overlimiting current range (i , squares) on of transition to the overlimiting current range (icoupled , squares) on the number coupled the number of of applied layers applied of of layers polyelectrolyte for AMX-Sb (a) and MA-41P polyelectrolyte for AMX-Sb (a) and MA-41P (b). (b). Data Data of of pH-metry pH-metry showedshowed how water how water splitting splitting was balanced was balanced in theindesalination the desalination chamber chamber between between a cation and an anion exchange membrane. The H+ ions produced at the AEM and the OH − a cation and an anion exchange membrane. The H ions produced at the AEM and the OH− ions + produced at the cation exchange membrane entered the desalination chamber, and acidification of desalted solution provided evidence that the reaction occurred more strongly at anion exchange
Membranes 2019, 9, x FOR PEER REVIEW 8 of 13 ions produced at the cation exchange membrane entered the desalination chamber, and acidification Membranes 2019, 9, 13 8 of 13 of desalted solution provided evidence that the reaction occurred more strongly at anion exchange membranes, while alkalification of desalted solution showed that the reaction occurred more strongly membranes, while alkalification at cation exchange membranesof[34]. desalted Sincesolution the cationshowed that the exchange reaction occurred membrane (Neosepta more CMX)strongly was the at cation exchange membranes [34]. Since the cation exchange membrane (Neosepta same in all measurements, the difference in pH between the exit and the entrance of the desalination CMX) was the same inchamber all measurements, could be the useddifference to comparein pHthe between the exit intensity and thesplitting of water entranceatofdifferent the desalination chamber anion exchange could be used to compare the intensity of water splitting at different anion exchange membranes. membranes. −− In Inthe thecase caseofofcommercial commercialmonopolar monopolar membranes, membranes, it is known it is known [34] that [34] thethe that generation generation of+H of H /OH+/OH ions ionsoccurs occursonly onlyatatthe themembrane/desalted membrane/desalted solution solution boundary. boundary.In Inthe thecase caseof ofmonopolar monopolarmembranes membranes modified modifiedwithwithpolyelectrolyte polyelectrolytecarrying carryingthethefixed fixedgroups groupswith withthethecharge chargeopposite oppositeto tomembrane membranebulk, bulk, the thereaction reactioncancanoccur occurboth bothatatthe thesubstrate substratemembrane/modifying membrane/modifying layer layer (bipolar (bipolarjunction) junction)ororatatthe the modifying modifyinglayer/desalinated layer/desalinated solution solution boundaries boundaries (Figure (Figure6). 6). The Theelectrolyte electrolyteconcentration concentrationdecreases decreases faster fasteratatthe thebipolar bipolarjunction junctionsince sincethe thedelivery deliveryof ofsalt saltions ionstotothis thisinterface interfaceisishindered hinderedfromfrombothboth directions directionsby byelectrostatic electrostaticrepulsion repulsionforces, forces,meaning meaningthatthatthe thelimiting limitingstatestateisisreached reachedfaster fasteratatthis this boundary. boundary. ThisThis first firstlimiting limitingstate statecorresponds correspondstotothe theexperimental experimentallimitinglimitingcurrent. current. With Withfurther further increase increaseofofpotential potentialdrop,drop,twotwosituations situationsare arepossible: possible: either either growing growing potential potential drop drop will willcause cause increased increased transport transport of of salt salt ions ionsbybythe theelectromigration electromigrationmechanism mechanism(despite (despite counterions counterions for for thethe substrate substratemembrane membranebeing beingco-ions co-ionsfor forthe themodifying modifyinglayer), layer),or orgrowing growingpotential potentialdrop dropwill willcause cause intensive /OH−−ions intensiveHH++/OH ionsgeneration generationatatthethebipolar bipolarjunction. junction. DBL DBL Na+ Cl- Na+ Cl- Na+ Cl- ML (a) (b) DBL Na+ Cl- ML (c) Figure6.6.Limiting Figure Limitingstates statesreached reachedatatthe thecommercial commercialmembrane membrane(a), (a),atatthe themodifying modifyinglayer/substrate layer/substrate membrane membraneboundary boundaryofofthethemodified modifiedmembrane membrane(b) (b)and andatatthethemodifying modifyinglayer/desalted layer/desaltedsolution solution boundary boundaryofofthe themodified modifiedmembrane membrane(c). (c).Pink Pinkzone zonedenotes denotesthethesubstrate substratemembrane, membrane,DBL DBLdenotes denotes the the(depleted) (depleted)diffusion diffusionboundary boundarylayer layerandandMLMLdenotes denotesthe themodifying modifyinglayer. layer.Black Blacklines linesshow showthe the concentration concentrationprofile profileofofsalt saltand andgrey greylines linesshow showthe thefluxes fluxesofofsalt saltions. ions. The Theexperimental experimentalpH-metry pH-metrydata dataare aregiven givenininFigure Figure7.7.Dependences Dependencesof ofpH pHdifference differenceare aregiven given in Figure 7a,b together with experimental limiting current values, and it can be seen that in Figure 7a,b together with experimental limiting current values, and it can be seen that intensive intensive water watersplitting splittingstarted startedmuch muchlater laterthan thanthe thelimiting limitingcurrents currentswerewerereached. reached.In Inthese thesecases, cases,therefore, therefore, the + − the bipolar junction did not determine the beginning of H /OH ions generation. In all caseswater bipolar junction did not determine the beginning of H /OH + − ions generation. In all cases water splitting splittingstarted startedininthe thesame samerelatively relativelysmall smallwindow windowof ofpotential potentialdrops dropsover overthethemembrane membrane(denoted (denoted by empty black boxes in Figure 7c,d), and the corresponding current value decreased only due to increasing resistance from the system. This dependence of critical potential drop on the number of
Membranes 2019, 9, x FOR PEER REVIEW 9 of 13 by empty2019, Membranes black 9, 13boxes in Figure 7c,d), and the corresponding current value decreased only due 9 of to 13 increasing resistance from the system. This dependence of critical potential drop on the number of layers shows that the desalted solution/modifying layer boundary plays a more important role in layers shows of development thatH+the /OHdesalted solution/modifying layer boundary plays a more important role in − ions generation. development of H+ /OH− ions generation. j (mA/cm2) 0 0 2 4 6 ∆pH -1 no coating 1 layer 2 layers 3 layers -2 (a) j (mA/cm2) 0 0 2 4 6 ∆pH -1 no coating 1 layer 2 layers 3 layers -2 (b) ∆φ (V) 0 0 1 2 3 4 ∆pH -1 no coating 1 layer 2 layers 3 layers -2 (c) Figure 7. Cont.
Membranes 2019, 9, x FOR PEER REVIEW 10 of 13 Membranes 2019, 9, 13 10 of 13 Membranes 2019, 9, x FOR PEER REVIEW 10 of 13 ∆φ (V) 0 0 1 2 3 ∆φ (V) 4 ∆pH∆pH 0 0 1 2 3 4 -1 -1 no coating 1 layer 2no layers coating 31layers layer 2 layers -2 3 layers -2 (d) Figure 7. Dependence of the difference in pH between (d) the exit and entrance of the desalination chamber formed by CMX cation exchange membranes and AEMs based on AMX-Sb (a,c) and MA- Figure7.7.Dependence Figure Dependence of of thethedifference in pH difference inbetween pH betweenthe exit theand entrance exit of the desalination and entrance chamber of the desalination 41P (b,d) on current density (a,b) or potential drop over the membrane (c,d). Crosses show the formed by CMX cation exchange membranes and AEMs based on AMX-Sb chamber formed by CMX cation exchange membranes and AEMs based on AMX-Sb (a,c) and (a,c) and MA-41P (b,d)MA- on approximations of pH made for experimental limiting current densities based on pH values registered current density 41P (b,d) (a,b) ordensity on current potential drop (a,b) orover the membrane potential drop over (c,d). the Crosses membrane show(c,d). the approximations Crosses show the of for the two closest current densities. Squares denote the commercial membranes, diamonds represent pH made for experimental approximations of pH made limiting current densities for experimental based limiting on pH current valuesbased densities registered on pH for the two values closest registered the membranes with one layer of coating, triangles represent the membranes with two layers of current densities. for the two closestSquares denote theSquares current densities. commercial denote membranes, the commercialdiamonds represent membranes, the membranes diamonds represent coating, and circles represent the membranes with three layers of coating. with one layer of coating, triangles represent the membranes with two layers the membranes with one layer of coating, triangles represent the membranes with two layers of coating, and circles of represent coating, the and membranes circles with represent three the layers membranes of coating. with three layers of coating. The registered pH values (Figure 7) show the common trend between the homogeneous and heterogeneous The membranes: the H+/OH− 7) ions generation increased with the numberhomogeneous of applied layers, The registered registered pH pH values values (Figure (Figure 7) show show thethe common common trend trend between between the the homogeneous and and while water splitting wasthe heterogeneous much + stronger − ions in the caseincreased of modified membranes of based appliedon the heterogeneousmembranes: membranes: theHH+/OH /OH− ions generation generation increased withwith the the number of number applied layers, layers, heterogeneous while MA-41P membrane than modified membranes based on the homogeneous AMX-Sb whilewater watersplitting waswas splitting muchmuch stronger in the case stronger of modified in the case ofmembranes modified based membraneson the heterogeneous based on the membrane. MA-41P membrane than modified membranes based on the homogeneous AMX-Sb membrane. heterogeneous MA-41P membrane than modified membranes based on the homogeneous AMX-Sb A A hypothesis hypothesis can can be be suggested suggested regarding regarding the the differences differences in in behavior behavior of of AMX-Sb AMX-Sb and and MA-41P. MA-41P. membrane. It It was previously concluded wasA previously concluded from the peculiarities from the peculiarities of electrochemical properties of electrochemical properties of of andthe AMX-Sb the AMX-Sb hypothesis can be suggested regarding the differences in behavior of AMX-Sb MA-41P. membrane membrane modified modified with withNafion Nafion that the singular singularapplication ofof modifier leads to to formation notnotof It was previously concluded fromthat thethepeculiarities application of electrochemicalmodifier leads properties offormation the AMX-Sb aofcontinuous a continuous and even and even layer, but of island-like structures [29]. This is further supported by the membrane modified with layer, Nafionbut of the that island-like singularstructures application [29]. This is further of modifier leads tosupported formationby nottheof geometrical geometrical heterogeneity heterogeneity of of the the homogeneous homogeneous membrane membrane produced produced by Astom, by Astom, which which does does not not have have a continuous and even layer, but of island-like structures [29]. This is further supported by the aa flat flat surface but but instead instead possesses surfaceheterogeneity possesses repeating repeating hills hills and and valleys valleys [20,35] [20,35]by(Figure (Figure 8), where 8),which wheredoes the the modifier modifier geometrical of the homogeneous membrane produced Astom, not have might might be be accumulated accumulated in in the the valleys. valleys. Since Since the the application application of of a a second second layer layer does does not not lead lead to to such such big big a flat surface but instead possesses repeating hills and valleys [20,35] (Figure 8), where the modifier changes changes in in the the I–V I–V curve, curve, it it might might be be suggested suggested that, that, like like coating coating with with the the first first layer, layer, the the second-layer second-layer might be accumulated in the valleys. Since the application of a second layer does not lead to such big coating coating does not not lead lead to tocomplete completecontinuous continuouscoverage, coverage,whilewhilecoating coatingwith with a third layer might lead changesdoesin the I–V curve, it might be suggested that, like coating a third with the first layer layer, themight lead second-layer to to fullfull coverage. coverage. coating does not lead to complete continuous coverage, while coating with a third layer might lead to full coverage. Figure 8. Cross section of swollen AMX-Sb membrane. Adapted from [20]. Figure 8. Cross section of swollen AMX-Sb membrane. Adapted from [20]. Smaller limiting currents and stronger water splitting found for modified membranes based on Figure 8. Cross section of swollen AMX-Sb membrane. Adapted from [20]. Smaller MA-41P mightlimiting currents be explained byand stronger waterofsplitting the heterogeneity found for modified MA-41P—according to [17], membranes based only about 28% on of the MA-41P surface ofmight MA-41 beseries explained by theisheterogeneity membranes represented by ofion MA-41P—according to [17], exchanger. This causes onlycurrent higher about density 28% of Smaller limiting currents and stronger water splitting found for modified membranes based on the surface of areas at conductive MA-41 series and, as amembranes result, higheris represented concentration bypolarization ion exchanger. and This morecauses highercoupled pronounced current MA-41P might be explained by the heterogeneity of MA-41P—according to [17], only about 28% of density at conductive effects—which areasjudging in this case, and, asbya result, Figurehigher 7, wereconcentration polarization represented by and more water splitting. pronounced Additional factors the surface of MA-41 series membranes is represented by ion exchanger. This causes higher current coupled effects—which in this case, judging by Figure 7, were represented by water that may play a role in the difference are the possible preferable sorption of polyelectrolyte on the splitting. density at conductive areas and, as a result, higher concentration polarization and more pronounced coupled effects—which in this case, judging by Figure 7, were represented by water splitting.
Membranes 2019, 9, 13 11 of 13 grains of ion exchanger (due to electrostatic interaction between the oppositely charged fixed groups) and lessened sorption on (uncharged) polyethylene. This would cause the thickening of the layer on the conductive zones in comparison with a homogeneous surface, meaning that such materials might benefit from a decrease in the amount of added modifier. 4. Conclusions It was shown that spreading one or two thin layers of polymer, with functional groups oppositely charged with respect to the ones in membrane bulk, onto the surface of commercial homogeneous AMX-Sb membrane resulted in the creation of new membranes with resistance and limiting current comparable with the original one. As such, this method is suitable for the creation of materials that combine good transport properties of supporting membrane with monovalent selectivity, due to the oppositely charged layer that was applied. The application of a larger number of layers or the use of heterogeneous membrane led to a decrease of the limiting current and hastening of the onset of overlimiting mode, accompanied by growing H+ /OH− ions generation. In all cases, the H+ /OH− ions generation started in the same range of potential drops and this reaction was more active at the external (modifying layer/desalted solution) boundary than at the internal (modifying layer/substrate membrane) boundary. It was found that H+ /OH− ions generation was stronger, and that the limiting current decreased more readily, in the case of a heterogeneous membrane. Such peculiarities would require special attention if the heterogeneous membranes were to be used for the production of novel modified membranes. Author Contributions: Conceptualization, X.N.; Methodology, X.N.; Validation, V.S., D.B., and N.P.; Formal Analysis, X.N.; Investigation, V.S. and D.B.; Resources, C.L. and N.P.; Data Curation, X.N.; Writing—Original Draft Preparation, X.N.; Writing—Review & Editing, C.L. and N.P.; Visualization, X.N.; Supervision, C.L. and N.P.; Project Administration, X.N.; Funding Acquisition, X.N. and C.L. All authors have approved the final article. Funding: This research was funded by CNRS and RFBR grant number 18-58-16008_NCNIL_a. Conflicts of Interest: The authors declare no conflict of interest. References 1. Sata, T.; Izuo, R.; Mizutani, Y.; Yamane, R. Transport properties of ion-exchange membranes in the presence of surface active agents. J. Colloid Interface Sci. 1972, 40, 317–328. [CrossRef] 2. Zabolotskii, V.; Sheldeshov, N.; Melnikov, S. Heterogeneous bipolar membranes and their application in electrodialysis. Desalination 2014, 342, 183–203. [CrossRef] 3. Lin, Y.; Li, H.; Liu, C.; Xing, W.; Ji, X. Surface-modified Nafion membranes with mesoporous SiO2 layers via a facile dip-coating approach for direct methanol fuel cells. J. Power Sources 2008, 185, 904–908. [CrossRef] 4. Esposito, D.V. Membrane-Coated Electrocatalysts—An Alternative Approach to Achieving Stable and Tunable Electrocatalysis. ACS Catal. 2018, 8, 457–465. [CrossRef] 5. Labrador, N.Y.; Songcuan, E.L.; De Silva, C.; Chen, H.; Kurdziel, S.J.; Ramachandran, R.K.; Detavernier, C.; Esposito, D.V. Hydrogen Evolution at the Buried Interface between Pt Thin Films and Silicon Oxide Nanomembranes. ACS Catal. 2018, 8, 1767–1778. [CrossRef] 6. Luo, Q.; Zhang, H.; Chen, J.; You, D.; Sun, C.; Zhang, Y. Preparation and characterization of Nafion/SPEEK layered composite membrane and its application in vanadium redox flow battery. J. Membr. Sci. 2008, 325, 553–558. [CrossRef] 7. Luo, T.; Abdu, S.; Wessling, M. Selectivity of ion exchange membranes: A review. J. Membr. Sci. 2018. [CrossRef] 8. Zabolotskii, V.; Sheldeshov, N.; Melnikov, S. Effect of cation-exchange layer thickness on electrochemical and transport characteristics of bipolar membranes. J. Appl. Electrochem. 2013, 43, 1117–1129. [CrossRef] 9. Park, J.-S.; Lee, H.-J.; Choi, S.-J.; Geckeler, K.E.; Cho, J.; Moon, S.-H. Fouling mitigation of anion exchange membrane by zeta potential control. J. Colloid Interface Sci. 2003, 259, 293–300. [CrossRef]
Membranes 2019, 9, 13 12 of 13 10. Mulyati, S.; Takagi, R.; Fujii, A.; Ohmukai, Y.; Maruyama, T.; Matsuyama, H. Improvement of the antifouling potential of an anion exchange membrane by surface modification with a polyelectrolyte for an electrodialysis process. J. Membr. Sci. 2012, 417–418, 137–143. [CrossRef] 11. Andreeva, M.A.; Gil, V.V.; Pismenskaya, N.D.; Dammak, L.; Kononenko, N.A.; Larchet, C.; Grande, D.; Nikonenko, V.V. Mitigation of membrane scaling in electrodialysis by electroconvection enhancement, pH adjustment and pulsed electric field application. J. Membr. Sci. 2018, 549. [CrossRef] 12. Urtenov, M.K.; Uzdenova, A.M.; Kovalenko, A.V.; Nikonenko, V.V.; Pismenskaya, N.D.; Vasil’eva, V.I.; Sistat, P.; Pourcelly, G. Basic mathematical model of overlimiting transfer enhanced by electroconvection in flow-through electrodialysis membrane cells. J. Membr. Sci. 2013, 447, 190–202. [CrossRef] 13. White, N.; Misovich, M.; Yaroshchuk, A.; Bruening, M.L. Coating of Nafion membranes with polyelectrolyte multilayers to achieve high monovalent/divalent cation electrodialysis selectivities. ACS Appl. Mater. Interfaces 2015, 7, 6620–6628. [CrossRef] [PubMed] 14. Abdu, S.; Martí-Calatayud, M.C.; Wong, J.E.; García-Gabaldón, M.; Wessling, M. Layer-by-layer modification of cation exchange membranes controls ion selectivity and water splitting. ACS Appl. Mater. Interfaces 2014, 6, 1843–1854. [CrossRef] [PubMed] 15. Cheng, C.; Yaroshchuk, A.; Bruening, M.L. Fundamentals of selective ion transport through multilayer polyelectrolyte membranes. Langmuir 2013, 29, 1885–1892. [CrossRef] [PubMed] 16. Rubinstein, I.; Zaltzman, B.; Pundik, T. Ion-exchange funneling in thin-film coating modification of heterogeneous electrodialysis membranes. Phys. Rev. E 2002, 65, 1–10. [CrossRef] [PubMed] 17. Volodina, E.; Pismenskaya, N.; Nikonenko, V.; Larchet, C.; Pourcelly, G. Ion transfer across ion-exchange membranes with homogeneous and heterogeneous surfaces. J. Colloid Interface Sci. 2005, 285, 247–258. [CrossRef] 18. Mizutani, Y. Structure of ion exchange membranes. J. Membr. Sci. 1990, 49, 121–144. [CrossRef] 19. Garcia-Vasquez, W.; Ghalloussi, R.; Dammak, L.; Larchet, C.; Nikonenko, V.; Grande, D. Structure and properties of heterogeneous and homogeneous ion-exchange membranes subjected to ageing in sodium hypochlorite. J. Membr. Sci. 2014, 452, 104–116. [CrossRef] 20. Mareev, S.A.; Butylskii, D.Y.; Pismenskaya, N.D.; Larchet, C.; Dammak, L.; Nikonenko, V.V. Geometrical heterogeneity of homogeneous ion-exchange Neosepta membranes. J. Membr. Sci. 2018, 563, 768–776. [CrossRef] 21. Pismenskaya, N.D.; Nikonenko, V.V.; Melnik, N.A.; Shevtsova, K.A.; Belova, E.I.; Pourcelly, G.; Cot, D.; Dammak, L.; Larchet, C. Evolution with time of hydrophobicity and microrelief of a cation-exchange membrane surface and its impact on overlimiting mass transfer. J. Phys. Chem. B 2012, 116, 2145–2161. [CrossRef] 22. Monopolar Membranes-Innovative Company Shchekinoazot Ltd. Available online: http://www.azotom.ru/ monopolyarnye-membrany/ (accessed on 5 May 2018). 23. Ghalloussi, R.; Garcia-Vasquez, W.; Bellakhal, N.; Larchet, C.; Dammak, L.; Huguet, P.; Grande, D. Ageing of ion-exchange membranes used in electrodialysis: Investigation of static parameters, electrolyte permeability and tensile strength. Sep. Purif. Technol. 2011, 80, 270–275. [CrossRef] 24. Garcia-Vasquez, W.; Dammak, L.; Larchet, C.; Nikonenko, V.; Pismenskaya, N.; Grande, D. Evolution of anion-exchange membrane properties in a full scale electrodialysis stack. J. Membr. Sci. 2013, 446, 255–265. [CrossRef] 25. Vasil’eva, V.I.; Zhil’tsova, A.V.; Malykhin, M.D.; Zabolotskii, V.I.; Lebedev, K.A.; Chermit, R.K.; Sharafan, M.V. Effect of the chemical nature of the ionogenic groups of ion-exchange membranes on the size of the electroconvective instability region in high-current modes. Russ. J. Electrochem. 2014, 50, 134–143. [CrossRef] 26. Zabolotskii, V.I.; Chermit, R.K.; Sharafan, M.V. Mass transfer mechanism and chemical stability of strongly basic anion-exchange membranes under overlimiting current conditions. Russ. J. Electrochem. 2014, 50, 38–45. [CrossRef] 27. Melnikov, S.; Sheldeshov, N.; Zabolotsky, V.; Loza, S.; Achoh, A. Pilot scale complex electrodialysis technology for processing a solution of lithium chloride containing organic solvents. Sep. Purif. Technol. 2017, 189, 74–81. [CrossRef] 28. Kniaginicheva, E.; Pismenskaya, N.; Melnikov, S.; Belashova, E.; Sistat, P.; Cretin, M.; Nikonenko, V. Water splitting at an anion-exchange membrane as studied by impedance spectroscopy. J. Membr. Sci. 2015, 496. [CrossRef]
You can also read