Ion Exchange Capacity Of Membranes Research Articles

Novel sulfonated polysulfone ion exchange membranes for ionic polymer–metal composite actuators

A series of sulfonated polysulfone (SPSU) membranes with different degrees of sulfonation were prepared for fabricating cost-effective and high-performance ionic polymer–metal composite (IPMC) actuators. The experimental results show that the ion exchange capacity and water uptake of SPSU membranes increase with increasing their degree of sulfonation, and the proton conductivities of these hydrated membranes are subsequently enhanced. Compared with the commercial Nafion 117 ion exchange membrane, these SPSU membranes have higher ion exchange capacity and water uptake ability. Furthermore, the higher molecular rigidity of the SPSU membranes leads to higher tensile moduli in both dry and wet states than the Nafion membrane. The IPMC actuators made of the SPSU membranes demonstrate the large bending strain, fast response and excellent fatigue resistance under electric stimulation. Their electromechanical behaviors can be controlled by adjusting the sulfonation level of the SPSU ion exchange membranes.

Influence of the basic membrane properties of the disulfonated poly(arylene ether sulfone) copolymer membranes on the vanadium redox flow battery performance

This article focuses on structure–property–performance relationship of directly copolymerized disulfonated poly(arylene ether sulfone) membranes (BPSH) utilized in vanadium redox flow batteries (VRFBs). Degree of disulfonation was systematically altered from 25 to 45M percent by introducing controlled amount of disulfonated monomer into the copolymer structure. For the first time with this study the relation has been established between VRFB cell performances and basic membrane properties such as ion exchange capacity (IEC), water uptake, proton conductivity, and vanadium (VO2+) permeability of BPSH membranes. BPSH with 25M percent disulfonation (BPSH 25) showed delay time during discharging process due to the fluctuation of the discharging voltage caused by poor proton conductivity, 23mScm−1. Therefore, columbic efficiencies became greater than 100 percent for BPSH 25 indicating higher discharging time than charging time. On the other hand, the best performance in the series was observed with BPSH 35. Since it had almost three times higher proton conductivity than BPSH 25 and about 100 times lower vanadium permeability (1.6×10−13m2s−1) than BPSH 45. Although BPSH 45 had the highest proton conductivity (140mScm−1), its performance was deteriorated due to higher vanadium permeability (1.6×10−11m2s−1). It was also demonstrated that water uptake values of the series scales with the vanadium permeabilities. As a result, several basic membrane parameters were controlled and presented as tunable properties, which were function of VRFB performance.

Quaternary phosphonium-functionalized poly(ether ether ketone) as highly conductive and alkali-stable hydroxide exchange membrane for fuel cells

A series of quaternary phosphonium-functionalized poly(ether ether ketone)s (PEEK-QPOHs) have been synthesized by phosphorization reaction, and their membranes have been prepared by a solution casting method. Ion exchange capacity (IEC) of PEEK-QPOH membranes ranges from 0.89 to 1.19mmolg−1 with the degree of chloromethylation from 70% to 126%. Not only are PEEK-QPOH polymers soluble in typical high-boiling-point membrane-forming solvents, but also they are soluble in some low-boiling-point water-miscible solvents (low alcohols), implying their ability to serve as both membranes and ionomers. PEEK-QPOH membranes showed high hydroxide conductivity, e.g., a PEEK-QPOH 126% membrane (with IEC of 1.19mmolg−1) exhibited 61 and 89mScm−1 at 20°C and 60°C, respectively. Based on the same polymer backbone of PEEK, quaternary phosphonium-functionalized PEEK membranes are more hydroxide-conductive and more alkali-stable than quaternary ammonium- and imidazolium-functionalized counterparts. All these properties indicate PEEK-QPOH is one of the most promising HEM materials for potential applications in alkaline membrane fuel cells.

A New Kind of Electro-Active Nano-Composite Actors Based on SSMA-Reinforced Nafion

Ionic polymer metal composite actuators (IPMCs), a new kind of smart material, have taken much attention as suitable candidates for the next generation actuators, micro-electromechanical systems, medical devices and micro air vehicles. In this paper, a new kind of IPMCs was developed by incorporating sulfonated poly (styrene-co-maleic anhydride) (SSMA) into the Nafion structure to overcome some of the major drawbacks of traditional electro-active polymers. The results show that the ion exchange capacity and water uptake ratio of the SSMA-Nation membrane increased dramatically. Compared with general IPMCs, the maximum bending displacement and the maximum blocking force of the SSMA-reinforced IPMCs improved greatly: the 1 wt.% SSMA-IPMC exhibited the maximum bending displacement of 11 mm up to 1.4 times, while the 5 wt.% SSMA-IPMC exhibited the maximum blocking force of 26 mN up to 1.2 times.

Fabrication and electrochemical characterization of PVC based electrodialysis heterogeneous ion exchange membranes filled with Fe3O4 nanoparticles

In this research, novel polyvinylchloride based electrodialysis heterogeneous cation exchange membranes were prepared by casting technique. Iron oxide nanoparticle was also employed as additive in membrane fabrication. The effect of additive concentration on electrochemical properties of homemade membranes was studied. SOM images showed uniform particles distribution and relatively uniform surfaces for the membranes. Membrane water content and ion exchange capacity were increased initially by increase in additive loading ratio to 2%wt and then showed decreasing trend by higher additive content to 8%wt. Membrane potential, permselectivity and transport number all were enhanced with increase of additive content in sodium and barium chloride ionic solutions. They showed different behaviors for the membranes in lead nitrate ionic solution. Membranes exhibited lower potential, selectivity and transport number for bivalent ions compared to monovalent ones. Permeability and flux were enhanced initially in sodium and barium chloride ionic solutions by increase in additive content up to 2%wt and then began to decrease by more additive loading. The electrodialysis experiment results showed that dialytic rate of lead ions removal was increased obviously by increase of additive concentration. Modified membranes showed better electrochemical properties compared to pristine one.

Preparation and Properties of Poly (phthalazinone Ether Ketone) Based Anion Exchange Membranes for Vanadium Redox Flow Battery

Poly (phthalazinone ether ketone) anion exchange membranes with pyridinium groups (PyPPEK) for vanadium redox flow battery were prepared from chloromethylated poly (phthalazinone ether ketone) and pyridine. The chemical structure of PyPPEK was characterized by using FT-IR spectrum. Compared with quaternary ammonium group containing poly (phthalazinone ether ketone), PyPPEK membrane showed low ion exchange capacity, low swelling ratio and comparable tensile strength. Columbic efficiencies of VRB with anion exchange membranes were higher than that of VRB with Nafion117 membrane. When the ion exchange capacity of PyPPEK membrane was 1.40 mmol·g-1, energy efficiency of VRB with the membrane was higher than that of VRB with Nafion117 membrane at charge-discharge current densities ranging from 20 mA·cm-2 to 50 mA·cm-2.

Preparation of phase-transfer catalytic porous membrane by γ-ray irradiation grafting and its application in nucleophilic substitution reaction

Phase-transfer catalytic porous polyethylene membranes, prepared by γ-ray irradiation grafting of 4-vinyl pyridine and quaternization, were tested in nucleophilic substitution reaction. The effects of grafting conditions (irradiation dose, 4-vinyl pyridine concentration) and quaternization parameters (temperature, time, concentration of reagent) were investigated. It was found that, the grafting degree initially increases with irradiation dose or 4-vinyl pyridine concentration and then decreases. The ion exchange capacity and quaternization ratio of membranes rise with quaternization temperature, time, and reagent concentration. The quaternized membranes exhibit good phase-transfer activity in nucleophilic substitution reaction between n-bromooctane and KI aqueous solution. The n-bromooctane conversion and the observed reaction rate constant rise with the increase in ion exchange capacity of membranes or reaction temperature. This paper provides a novel and promising method for phase transfer catalysis.

The importance of water transport on short-side chain perfluorosulfonic acid membrane fuel cells operating under low relative humidity

Polarization curves of fuel cells incorporating PFSA short-side chain (SSC) ionomer membranes having ion exchange capacity (IEC) 1.30, 1.37, 1.43 and 1.50 meq g−1 and NRE-211 are compared. Under low humidity conditions, fuel cells incorporating SSC membranes show higher performance than NRE-211. SSC PFSA membranes possessing an IEC of 1.37 meq g−1 exhibit the highest performance. Differences in fuel cell polarization curves are due to differences in the high frequency resistance, which in turn is found related to ex-situ measurements of both the effective proton mobility and the rate of water flux through the membrane, which also exhibit a maximum for membranes of IEC 1.37 meq g−1. Water permeation and proton mobility are shown to be inherently linked, but it is found that simply increasing the membrane's IEC does not necessarily translate to increased water transport and effective proton mobility, despite the increased water content.

Hydroxide exchange composite membrane based on soluble quaternized polyetherimide for potential applications in fuel cells

A series of soluble quaternized polyetherimides (QAPEIs) have been successfully synthesized by homogeneous quaternization in trimethylamine aqueous solution. 1H NMR spectra confirm the successful synthesis of QAPEI. The QAPEIs exhibit good solubility in membrane-preparation solvents, making it possible to prepare the QAPEI composite membrane. Novel composite hydroxide exchange membranes have been prepared by incorporating QAPEIs with polytetrafluoroethylene (PTFE) membranes. The SEM images, gas permeation measurements and FTIR spectra show that the QAPEI is successfully filled in PTFE membrane and the resulted composite membrane is dense and smooth. The ion exchange capacity of composite membranes ranges from 0.35 to 0.58 mmol g−1. The composite membranes have appropriate water uptake (≤154%) and moderate swelling ratio (≤42%) even at 60 °C. The hydroxide conductivity of the composite membrane reaches 11.9 mS cm−1 at 20 °C that increases to 35.2 mS cm−1 at 60 °C. TGA curve shows that the composite membrane possesses high thermal stability (TOD: 210 °C). All these properties indicate that the QAPEI/PTFE composite membranes are good candidates for use as HEMs in HEM fuel cells.

Preparation and properties of novel sulfonated poly(arylene ether ketone) random copolymers for polymer electrolyte membrane fuel cells

Two series of novel poly(arylene ether ketone)s were prepared using direct copolymerization of 3,3′-disulfonated-4,4′-difluorobenzophenone (SDFB) as synthesized sulfonated dihalide and difluorobenzophenone (DFB) as nonsulfonated dihalide monomer with 4,4′-(1,4-phenylene diisopropylidene) bisphenol (BP) or 4,4′-(1,3-phenylene diisopropylidene) bisphenol (BM). Copolymers were synthesized by polycondensation in different degrees of sulfonation (25–45%). 1H NMR and FT-IR spectroscopy, dynamic mechanical thermal analysis, thermogravimetric analysis, and tensile test were used for characterization of prepared membranes. Inherent viscosity of synthesized copolymers was between 1.08 and 2.63dL/g. Copolymers showed acceptable properties as proton exchange membrane for fuel cells. Ion exchange capacity of membranes was between 0.76 and 1.46meq/g. Membranes showed proton conductivities increased by increasing in degree of sulfonation and reached to 0.08S/cm. Prepared membranes were thermally stable up to 260°C and water uptake of these samples were in the range of 11–27wt%.

Synthesis and properties of sulfonated polyarylene ether nitrile copolymers for PEM with high thermal stability

A series of sulfonated polyarylene ether nitrile copolymers (SPEN) were synthesized by the nucleophilic aromatic substitution polymerization of 2, 6-difluorobenzonitrile with different ratios of hydroquinonesulfonic acid potassium salt and bisphenol A in the presence of K2CO3. The synthesized SPEN exhibited good solubility in polar organic solvents such as N-methylpyrrolidone, N, N’-dimethylformamide, dimethylacetylamide and dimethylsulfoxide. These copolymers can be easily processed into membranes by a facile solution-casting method. The representative membranes in acid form were obtained and their chemical structures were characterized by Fourier transform infrared analysis. The thermal properties, mechanical properties, proton conductivity, water uptake and ion exchange capacity of copolymer membranes were also investigated. The results showed that they had high glass transition temperatures ranging from 189 °C to 245 °C and good thermal and thermo-oxidative stability with the 5 wt.% loss temperatures in the range of 328–378 °C in nitrogen and 329–379 °C in air, respectively. They also exhibited good mechanical property with the tensile strength in the range of 45–62 MPa in the dry state and 23–45 MPa in the wet state. Furthermore, these copolymer membranes exhibited good water uptake ranging from 9.7 % to 57.74 % and outstanding ion exchange capacity in the range of 0.64–1.99 mmol/g. Thus, the membranes had good proton conductivities in the range of 2.47 × 10−5–1.71 × 10−3 s/cm at room temperature and 55 % RH.

Solution casting Nafion/polytetrafluoroethylene membrane for vanadium redox flow battery application

Solution casting method was adopted using Nafion and polytetrafluoroethylene (PTFE) solution to prepare Nafion/PTFE blend membranes for vanadium redox flow battery application. The physicochemical properties of the membranes were characterized by using water uptake, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermal analysis (TA). The electrochemical properties of the membranes were examined by using electrochemical impedance spectroscopy (EIS) and single cell test. Despite the high miscibility of PTFE with Nafion, the addition of hydrophobic PTFE reduces the water uptake, ion exchange capacity (IEC) and conductivity of blend membranes. But PTFE can increase the crystallinity, thermal stability of Nafion/PTFE membranes and reduce the vanadium permeability. The blend membrane with PTFE (30wt%, N0.7P0.3) was chosen and investigated for VRB single cell test. The energy efficiency of this VRB with N0.7P0.3 membrane was 85.1% at current density of 50mAcm−2, which was superior to that of recast Nafion (r-Nafion) membrane (80.5%). Self-discharge test shows that the decay of open circuit potential of N0.7P0.3 membrane is much lower than that of r-Nafion membrane. More than 50 cycles charge–discharge test proved that the N0.7P0.3 membrane possesses high stability in long time running. Chemical stabilities of the chosen N0.7P0.3 membrane are further proved by soaking the membrane for 3 weeks in highly oxidative V(V) solution. All results suggest that the addition of PTFE is a simple and effective way to improve the performance of Nafion for VRB application.

Fabrication of (polyvinyl chloride/cellulose acetate) electrodialysis heterogeneous cation exchange membrane: Characterization and performance in desalination process

In this research, polyvinylchloride (PVC)/cellulose acetate (CA) blend heterogeneous cation exchange membranes were prepared by solution casting technique using tetrahydrofuran as solvent and cation exchange resin powder as functional groups agent. CA was employed in membrane fabrication to improve the hydrophilicity of membranes. The effect of blend ratio of polymers binder (PVC to CA) on physico-chemical characteristics of home-made membranes was studied. Scanning optical microscopy (SOM) images showed uniform particles distribution and relatively uniform surfaces for the membranes. Membrane water content and surface hydrophilicity were enhanced with increase of CA blend ratio in casting solution. Membrane ion exchange capacity was also improved slightly with increase of CA ratio in prepared membranes. Membrane fixed ion concentration, membrane potential, charge density, permselectivity, transport number and areal electrical resistance all showed decreasing trends by the increase in CA blend ratio in casting solution. Results revealed that ionic permeability and flux were initially enhanced by the increase of CA concentration up to 20%wt in casting solution and then showed decreasing trend by more CA loading from 20 to 50%wt. These parameters were enhanced again by more increase in CA ratio from 50 to 100%wt in prepared membranes.

Blend membranes for direct methanol and proton exchange membrane fuel cells

Abstract Sulphonated polystyrene ethylene butylene polystyrene (SPSEBS) prepared with 35% sulphonation was found to be highly elastic and enlarged up to 300%–400% of its initial length. It absorbed over 110% of water by weight. A major drawback of this membrane is its poor mechanical properties which are not adequate for use as polymer electrolytes in fuel cells. To overcome this, SPSEBS was blended with poly(vinylidene fluoride) (PVDF), a hydrophobic polymer. The blend membranes showed better mechanical properties than the base polymer. The effect of PVDF content on water uptake, ion exchange capacity and proton conductivity of the blend membranes was investigated. This paper presents the results of recent studies applied to develop an optimized in-house membrane electrode assembly (MEA) preparation technique combining catalyst ink spraying and assembly hot pressing. Easy steps were chosen in this preparation technique in order to simplify the method, aiming at cost reduction. The open circuit voltage for the cell with SPSEBS is 0.980 V which is higher compared to that of the cell with Nafion 117 (0.790 V). From this study, it is concluded that a polymer electrolyte membrane suitable for proton exchange membrane fuel cell (PEMFC) and direct methanol fuel cell (DMFC) application can be obtained by blending SPSEBS and PVDF in appropriate proportions. The methanol permeability and selectivity showed a strong influence on DMFC performance.

Sulfonated multiwalled carbon nanotube/sulfonated poly(ether sulfone) composite membrane with low methanol permeability for direct methanol fuel cells

AbstractAn organic/inorganic composite membrane was prepared based on sulfonated poly(ether sulfone) (s‐PES) embedded with sulfonated multiwalled carbon nanotubes (s‐MWNTs). The ion exchange capacity (IEC), proton conductivity, and water uptake of the SPES membranes increased with increasing s‐MWNTs content. The increased water uptake was attributed to hydrogen bond formation between the carbonyl group of the s‐MWNTs and a water molecule. The composite membranes exhibited proton conductivities ranging from 3.9281 × 10−4 to 7.0788 × 10−3 S/cm at 80°C, as well as low methanol permeability ranging from 4.4405 × 10−10 to 9.1008 × 10−10 cm2 s−1 at 25°C. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

PEMFC용 설폰화 Poly(ether ether ketone) (SPEEK) 전기방사 나노섬유 이온교환막의 제조 및 특성

전기방사 방법으로 sulfonated poly(ether ether ketone) (SPEEK) 나노섬유를 제조하고, 압축성형법으로 고분자 전해질막 연료전지(polymer electrolyte membrane fuel cell, PEMFC)용 나노섬유막을 제조하였다. SPEEK의 최대 설폰화율은 95% 이었고 초기 열분해 온도는 약 <TEX>$280^{\circ}C$</TEX>로 PEEK 보다 낮았으며 접촉각은 설폰화도가 증가함에 따라 감소하였다. 전기방사 나노섬유의 최적 인가전압, 유속, 방사거리(tip to collector distance, TCD) 및 농도는 각각 22 kV, 0.3 mL/hr, 5 cm, 23 wt% 이었고 평균 섬유직경은 47.6 nm 이었다. 한편, SPEEK 이온교환 나노섬유막의 함수율 및 이온교환용량은 설폰화 시간과 설폰화제 함량이 증가함에 따라 증가하였으며 최적값은 각각 20%, 2.03 meq/g으로 Nafion 117 보다 우수하였다. 막의 전기저항은 설폰화 시간이 증가함에 따라 감소하였고 그 값은 0.58~0.06 <TEX>${\Omega}{\cdot}cm^2$</TEX>로 측정되었다. 또한 막의 수소이온전도도는 설폰화 시간이 증가함에 따라 증가하였으며 최대 0.099 S/cm로 Nafion 117 보다 우수하였다. Sulfonated poly(ether ether ketone) (SPEEK) nanofibers were prepared by electrospinning. The nanofibrous membrane for polymer electrolyte membrane fuel cell (PEMFC) was fabricated by compression molding. The maximum degree of sulfonation was 95% and the initial thermal degradation temperature was <TEX>$280^{\circ}C$</TEX> and it's value was lower than that of PEEK. The contact angle of SPEEK increased with decreasing the degree of sulfonation. The optimum voltage, flow rate, tip to collector distance (TCD) and concentration of electrospinning conditions were 22 kV, 0.3 mL/hr, 15 cm, and 23 wt%, respectively. The average nanofibrous diameter was 47.6 nm. The water uptake and ion exchange capacity of SPEEK nanofibrous membrane increased with increasing the sulfonation time and the amount of sulfonating agent. The electrical resistance and proton ionic conductivity of SPEEK membrane increased with decreasing and increasing the sulfonation time, respectively. Their values were 0.58~0.06 <TEX>${\Omega}{\cdot}cm^2$</TEX>and 0.099 S/cm.

Characterization of poly(vinylchloride) (PVC) based cation exchange membranes prepared with ionic liquid

In this study, poly(vinylchloride) (PVC) based heterogenous strong acidic cation exchange membranes were prepared by the solution casting technique by using suspension polymerized polyvinylchloride (S-PVC) and emulsion polymerized polyvinylchloride (E-PVC) as binders, dioctyl phthalate (DOP) and ionic liquid (IL) tetradecyl(trihexyl)phosphoniumdecanoate as plasticizers and ion exchange resin as functional group agent. The main goal of this work was to evaluate the effects of polymer binder type, plasticizer type and bider/plasticizer ratio on pyhsicochemical, morphological and electrochemical properties of the prepared membranes. Physicochemical characterization consisted of water contents, dry and wet densities, porosities, ion exchange capacities of membranes and isotherm studies. Scanning Electron Microscopy (SEM) analysis was used to perform morphological characterization. Water contents of the membranes were found between 30% and 40% while density values were in the 0.7–1.2g/cm3 range. Porosities were found between 0.2 and 0.4 and ion exchange capacities changed between 1.2 and 2.8meq Na+/g-dry. Electrochemical characterization included transport numbers of membranes determined by the membrane potential method. Transport number for the membranes prepared with dioctyl phthalate (DOP) was found to be around 0.5 whereas this figure was 1.0 for the membranes prepared with IL. Diffusivity values of Na+ ions across the membrane were calculated by using the Donnan dialysis method and found in order of magnitude-5.

Imidazolium-functionalized polysulfone hydroxide exchange membranes for potential applications in alkaline membrane direct alcohol fuel cells

A series of imidazolium-functionalized polysulfones were successfully synthesized by chloromethylation-Menshutkin two-step method. PSf-ImOHs show the desired selective solubility: insoluble in alcohols (e.g., methanol and ethanol), and soluble in 50 vol.% aqueous solutions of acetone or tetrahydrofuran, implying their potential applications for both the alcohol-resistant membranes themselves and the ionomer solutions in low-boiling-point water-soluble solvents. PSf-ImOH also possesses very high thermal stability (TOD: 258 °C), higher than quaternary ammonium and quaternary phosphonium functionalized polysulfones (TOD: 120 °C and 186 °C, repsectively). Ion exchange capacity (IEC) of PSf-ImOH membranes ranges from 0.78 to 2.19 mmol g−1 with degree of chloromethylation from 42% to 132% of original chloromethylated polysulfone. As expected, water uptake, swelling ratio, and hydroxide conductivity increase with IEC and temperatures. With 2.19 mmol g−1 of IEC, the PSf-ImOH 132% membrane exhibits the highest hydroxide conductivity (53 mS cm−1 at 20 °C), higher than those of all other reported polysulfone-based HEMs (1.6–45 mS cm−1) and other imidazolium-functionalized HEMs (19.6–38.8 mS cm−1). In addition, PSf-ImOH membranes have low methanol permeability of 0.8–4.7 × 10−7 cm2 s−1, one order of magnitude smaller than that of Nafion212 membrane. All these properties indicate imidazolium-functionalized polysulfone is very promising for potential applications in alkaline membrane direct alcohol fuel cells.

Preparation and characterization of poly (vinyl chloride)-blend-poly (carbonate) heterogeneous cation exchange membrane: Investigation of solvent type and ratio effects

In this research polyvinylchloride/polycarbonate blend heterogeneous cation exchange membranes were prepared by solution casting technique using cation exchange resin powder as functional groups agent. Tetrahydrofuran (THF) and dimethylformamide (DMF) were utilized as solvents. The effect of solvent type and ratio (THF/DMF mixture) on properties of prepared membranes was studied. SEM and SOM images showed relatively uniform particle distribution and also uniform surface for the membranes. Images showed that at high DMF ratio decrease of polymer conformation with particles surface reduces the compatibility of polymer-particle. The membrane ion exchange capacity and permeability were enhanced initially by increase of DMF ratio up to 5% (v/v) in casting solution and then they began to decrease with more DMF ratio. Results showed that membrane potential, transport number, selectivity and thermal stability all were decreased by DMF ratio increasing. Conversely, membrane water content, specific surface area and roughness showed opposite trends. Membrane electrical resistance initially declined by increase in DMF content up to 15% (v/v) and then it began to increase. The increase of electrolyte concentration also led to decrease in membrane transport number and selectivity. Membrane with (95:5) (v/v) solvent ratio (THF:DMF) exhibited more appropriate performance compared to others.

Overlimiting current by interactive ionic transport between space charge region and electric double layer near ion-exchange membranes

In electrodialysis, a theoretical understanding of overlimiting current (greater ionic transport beyond the electroneutrality limit) has not been clearly demonstrated, despite two hypothetical explanations: the water splitting reaction and electro-convection. To suggest another possible mechanism for this phenomenon, the Nernst-Planck-Poisson equations were solved via the Painlevé equation of the second kind. Numerical simulations found that the initiation of overlimiting current involves a substantial redistribution of the ionic charge near the membrane surface. To maintain a constant ionic charge in the aqueous phase near the membrane while the non-electroneutral space charge region grows, the shrinking electric double layer in the aqueous-phase releases ionic charges toward the membrane. Frequent repetition of this charge redistribution can contribute additional current above the limiting current without a large investment of electrical potential. A sensitivity study found that the relationship between the growth of the space charge region and applied potential is independent of the membrane's ion exchange capacity and the ionic diffusivity; however, the amount of the ionic charge created in the space charge region was greater with a greater bulk concentration or with an electrolyte solvent of a greater permittivity. These findings are consistent with previous experimental studies in the overlimiting current regime.