Effect Of Ion Exchange Capacity Research Articles

Evaluation of sulfonated chitosan-g-sulfonated polyvinyl alcohol/polyethylene oxide/sulfated zirconia composite polyelectrolyte membranes for direct borohydride fuel cells: Solution casting against the electrospun membrane fabrication technique

To improve the mechanical properties of proton exchange membranes, consequently improving the performance of direct borohydride fuel cells, the present study prepared sulfonated chitosan-g-sulfonated polyvinyl alcohol/polyethylene oxide doped with sulfated zirconia composite (SCS-g-SPVA/PEO/SZrO2) polyelectrolyte membranes. Two fabrication techniques were followed, solution casting and electrospinning, to have the membranes in film and fiber forms and study the effect of the different forms on the membrane’s physicochemical properties. For the casting technique, different concentrations of SZrO2 (1-3 wt%) were used, while the optimum concentration of SZrO2 (3 wt%) was used in the electrospun one (SCS-g-SPVA/PEO/SZrO2-CF). SCS-g-SPVA/PEO/SZrO2-C membranes were prepared in a single step. The grafting and the crosslinking were carried out using glutaraldehyde and sulfosuccinic acid as sulfonating agents for chitosan and PVA and coupling agents simultaneously using click chemistry. On the other hand, SCS-g-SPVA/PEO/SZrO2-CF membranes were prepared in two steps. They were fabricated with electrospinning and then dipped into the coupling and crosslinking solutions. The casting membranes’ physicochemical properties were improved by increasing the SZrO2 content. The experimental results further show that the fabrication procedure significantly influences the physicochemical properties of the membranes. For instance, the composite fiber membrane demonstrated higher selectivity and higher ion exchange capacity (IEC) than the casting membrane. Furthermore, by using the response surface methodology model, the effects of ion exchange capacity, water uptake, and oxidative stability were optimized as three independent variables that affected the ionic conductivity of SCS-g-SPVA/PEO/SZrO2-3C. The optimized ionic conductivity of the SCS-g-SPVA/PEO/SZrO2-3C membrane was 13.6 mS cm−1, achieved at the maximum point of the polynomial model, with an IEC of 0.74 meq g−1, ∼92% water uptake, and about 93% oxidative stability.

Oligomeric chain extender-derived poly(p-phenylene)-based multi-block polymer membranes for a wide operating current density range in polymer electrolyte membrane water electrolysis

Hydrocarbon-based membranes can extend the operating current range of a polymer electrolyte membrane water electrolyzer (PEMWE) because of their low gas permeability and high proton conductivity. However, increasing the ion exchange capacity for sufficiently high proton conductivity leads to poor mechanical stability and increased gas permeability for hydrocarbon-based membranes. This study presents a poly(p-phenylene)-based multiblock polymer with an oligomeric chain extender (CE-sPP-PPES) for improved mechanical stability and extended operating current range. With the introduction of a chain extender, the mechanical and chemical stability were notably enhanced. The effects of ion exchange capacity on mechanical properties, proton conductivity, and hydrogen crossover were investigated compared to a Nafion membrane. The CE-sPP-PPES-based PEMWE has a 2.1 times wider operating current range than a Nafion-based PEMWE because of its smaller ohmic overvoltage and lower gas crossover at an optimal ion exchange capacity, demonstrating the possibility of a new hydrocarbon-based membrane for PEMWE.

Impact of side-chains in poly(dibenzyl-co-terphenyl piperidinium) copolymers for anion exchange membrane fuel cells

Anion exchange membrane fuel cells (AEMFCs) have experienced rapid advancement in the past few years due to the discovery of high-performance AEMs and ionomers. Here, we report a series of side-chain-type poly(dibenzbeyl-co-terphenyl piperidinium) ( s -PDTP) copolymers as ionomers and membranes for AEMFC applications. The features of aryl ether-free PDTP polymer backbone and pendent ammonium groups endow both high alkaline stability and excellent micromorphology to s -PDTP copolymers. These ion-exchange-capacity (IEC)-controlled s -PDTP membranes possess high OH − conductivity >120 mS cm −1 at 80 °C, reasonable molecular weight (M w = 150–290 kDa), and excellent ex-situ durability in 1 M NaOH at 80 °C for 1000 h (∼90% conductivity remaining). For ionomer research, s -PDTP ionomers with moderate IEC (∼3.0 mmol g −1 ) and rational water uptake (∼200%) exhibit optimal AEMFC performance based on a PDTP membrane compared to high-IEC or low-IEC s -PDTP ionomers (>3.4 mmol g −1 or <2.4 mmol g −1 ). Based on Pt/C, s -PDTP-based AEMFCs reach a peak power density (PPD) of 1.47 W cm −2 in H 2 –O 2 and 1.04 W cm −2 in H 2 -air (CO 2 -free) at 80 °C. • IEC-controlled side-chain-type poly(aryl-co-aryl piperidinium)s is developed. • The effect of IECs on the performance of s-PDTP- x ionomers and AEMs is elucidated. • s-PDTP- x copolymers display excellent durability >1000 h in 1 M NaOH at 80 °C. • s-PDTP-based AEMFCs reach power densities of 1.04 W cm −2 in H 2 -air.

Effect of ion exchange capacity and water uptake on hydroxide transport in PSU-TMA membranes: A DFT and molecular dynamics study

Anion Exchange Membranes (AEMs) are nowadays used in a very wide range of different applications, from electrodialytic systems for water treatment, to Fuel Cells for energy generation. In many of these cases, the AEM is in contact with water molecules, either in aqueous or gas phase, which can strongly interact with the AEM polymer, thus affecting membrane properties. The role of water in fully swollen AEM and its effect on the diffusion of hydroxide is the focus of this work. Density Functional Theory (DFT) based calculations were merged with Molecular Dynamics (MD) simulations coming to a more accurate description of the ionic exchange capacity effect on the hydroxide ion diffusion in AEM. Hydration of the polysulfone-tetramethylammonium (PSU-TMA), one of the most studied systems in Alkaline anion exchange Membrane Fuel Cells (AMFC), was determined by DFT developing an efficient algorithm. The ab-initio calculations predicted water uptake, at different Ion Exchange Capacity (IEC), resulted in good agreement with the experimental data. The theory-experiment comparison identified a threshold range of 1.2–1.7 meq/g as critical IEC at which over-swelling of functionalized polymer matrix occurs. From this comparison, three IEC values were chosen to perform MD simulations in order to evaluate the hydroxyl diffusion coefficients as a function of the different IEC where the ab-initio water uptake and partial charges, utilized in the force-field, were adopted. Diffusion coefficients in the bulk of the membrane were calculated through the Mean Square Displacement (MSD) over 100 ns MD trajectories, and then compared with the values obtained by the analytical Mackie-Meares's model, finding good agreement between the two computational methodologies. In addition, the computed diffusion coefficients were compared with the experimental conductivity data with a fair agreement. It is worth noting that, thanks to the minimization of adjustable parameters, the present work can be easily adapted to study any type of Ion Exchange Membrane (IEM) and counter-ions diffusion.

Effect of Ion Exchange Capacity on Salt Removal Rate in Membrane Capacitive Deionization Process

Effect of Ion Exchange Capacity on Salt Removal Rate in Membrane Capacitive Deionization Process

Commercial perfluorosulfonic acid membranes for vanadium redox flow battery: Effect of ion-exchange capacity and membrane internal structure

A series of perfluorosulfonic membranes is screened for application in vanadium redox flow batteries (VRFB): membranes of constant thickness 50 µm with different ion-exchange capacities ranging from 0.56 to 1.15 mol eq. g−1. Diffusion flux of each vanadium ion occurring in VRFB electrolytes through each examined membrane is measured by UV/Vis spectroscopy. Permeation of V2+ ions contributes most to the self-discharge losses and the mechanism of vanadium ions permeation is discussed for all oxidation states. The membranes are characterized in the single-cell by electrochemical impedance spectroscopy, load curve measurements with linearly increasing current and charge-discharge cycles at various current densities ranging from 50 to 200 mA cm−2. Generally, at lower current densities the permeation of vanadium ions decreases the battery efficiency and thus lower ion-exchange capacity membranes are more suitable. Concurrently, at higher current densities the battery efficiency is decreased by the membrane resistance and thus higher ion-exchange capacity membranes are optimal. However, membrane ion-exchange capacity is not the only characteristic that affects the VRFB performance. Small-angle X-ray scattering of membranes revealed the effect of polymer molecular architecture on the size of hydrophilic domains which affects the membrane transport properties.

Morphology of Elastomeric Anion Exchange Membranes: A Dissipative Particle Dynamics Study

The design and optimization of stable and highly conductive anion exchange membranes (AEMs) is essential to the development of energy and conversion technologies.1 , 2 There has been an increased interest and research to address the low stability and ionic conductivity of polymeric AEMs. However, a fundamental understanding of stability and transport in AEMs is still in its infancy3 and the effects of the choice of the cationic functional group and polymer architecture are still not known. Recently developed elastomeric AEMs4 exhibiting satisfactory chemical stability are investigated in this study. These AEMs are based on the elastomeric triblock copolymer, polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS), that are functionalized with various cationic groups. Dissipative particle dynamics (DPD) is a meso-scale simulation technique5 , 6 which enables the simulation of large time- and length-scales with reasonable computational expense has been selected to investigate the morphology and dynamical behavior of such systems. The system of hydrated AEM is coarse-grained to a degree that the consideration of both chemical distinction and fine structural variants are satisfied. The structures of the DPD beads were optimized using first principles electronic structure calculations and the interaction parameters were determined using a recently developed methodology.7 The effects of several microstructural parameters including the length of the tether chains, type of the cationic group (trimethylammonium [(CH3)3NH]+; dimethylimidazolium [DMIm+]; and triphenylphosphonium [(C6H5)3PH]+ ), and the polymer architecture on the morphology and transport of anions in the aforementioned elastomeric AEMs were investigated. The effect of water content in the membrane and the effect of ion exchange capacity (IEC) were also studied. The results are compared with the widely studied proton exchange membrane Nafion.

The effect of hydrophobicity in alkaline electrodes for passive DMFC

The effect of hydrophobicity in alkaline electrodes has been investigated in an effort to improve their performance in passive direct methanol fuel cells. Two approaches have been used to increase the hydrophobicity within the electrodes. One is using a more hydrophobic ionomer, and the other is introducing polytetrafluoroethylene (PTFE) into the catalyst layer. Two types of anion exchange ionomers with different hydrophobicity have been synthesized for this study. The effect of ion exchange capacity, ionic conductivity, and water uptake of the ionomers on the electrode performance has been studied using a half-cell test. The use of a hydrophobic ionomer resulted in enhanced cathode performance even though the ionic conductivity was lower than the more hydrophilic ionomer. Also, the addition of PTFE improved both the cathode and anode performance. The improved alkaline electrode performance was compared to a traditional acid electrode using Nafion as the ionomer. The performance increased threefold as a result of higher hydrophobicity in alkaline electrode.

Water, proton, and oxygen transport in high IEC, short side chain PFSA ionomer membranes: consequences of a frustrated network

The effect of ion exchange capacity (IEC) on the water sorption properties of high IEC, short side chain (SSC) PFSA ionomer membranes, and the relationships between water content, proton conductivity, proton mobility, water permeation, oxygen diffusion, and oxygen permeation are investigated. SSC PFSA ionomer membranes possessing 1.3, 1.4, and 1.5 mmol g(-1) IEC are compared to a series of long side chain (LSC) PFSA ionomer membranes ranging in IEC from 0.9 to 1.13 mmol g(-1). At 25 °C, fully-hydrated SSC ionomer membranes are characterized as possessing higher water contents (56-75 vol%), moderate λ values (15-18), high analytical acid concentrations (2-2.8 M), and moderate conductivity (88-115 mS/cm); but lower than anticipated effective proton mobility. Complementary measurements of water permeability, oxygen diffusion, and oxygen permeability also yield lower than expected values given their much higher water contents. Potential benefits afforded by reducing the side chain length of PFSA ionomer membranes, such as increased crystallinity, higher IEC, and high hydrated acid concentration are offset by a less-developed, frustrated hydrophilic percolation network, which provides a motivation for future improvements of transport properties for this class of material.

Anionic–cationic bi-cell design for direct methanol fuel cell stack

A new fuel cell stack design is described using an anion exchange membrane (AEM) fuel cell and a proton exchange membrane (PEM) fuel cell in series with a single fuel tank servicing both anodes in a passive direct methanol fuel cell configuration. The anionic–cationic bi-cell stack has alkaline and acid fuel cells in series (twice the voltage), one fuel tank, and simplified water management. The series connection between the two cells involves shorting the cathode of the anionic cell to the anode of the acidic cell. It is shown that these two electrodes are at essentially the same potential which avoids an undesired potential difference and resulting loss in current between the two electrodes. Further, the complimentary direction of water transport in the two kinds of fuel cells simplifies water management at both the anodes and cathodes. The effect of ionomer content on the AEM electrode potential and the activity of methanol oxidation were investigated. The individual performance of AEM and PEM fuel cells were evaluated. The effect of ion-exchange capacity in the alkaline electrodes was studied. A fuel wicking material in the methanol fuel tank was used to provide orientation-independent operation. The open circuit potential of the bi-cell was 1.36 V with 2.0 M methanol fuel and air at room temperature.

Triazole and triazole derivatives as proton transport facilitators in polymer electrolyte membrane fuel cells

Some basic aspects pertaining to the application of triazole and its derivatives as proton transport facilitators for membranes for high temperature fuel cell operations are investigated. Performance as proton transport facilitators is studied for compounds in their native solid state and as a dopant in a polymer membrane. Some key parameters which influence the proton transport in the system are the proton affinity, pKa or acidity, activation energy and the ease of formation of hydrogen bonding network. Theoretical calculations of the proton affinity of the compounds are presented. The effect of proton affinity of the compound on the activation energies for proton transport is investigated. Proton conductivity is measured for acid doped triazoles in both pellet form (powder triazole mixed with acid) and in composite forms wherein the acid group is contained in a polymer matrix. The effect of formation of a hydrogen bonding network by the triazoles and its impact on the proton conductivity are studied. Also, the effect of ion exchange capacity (IEC) of the host polymeric electrolytes and loading of triazoles in the composites were investigated.

Effect of cathode binder IEC on kinetic and transport losses in all-SPEEK MEAs

The effect of ion exchange capacity (IEC) and loading of sulfonated polyether ether ketone (SPEEK) binder on PEFC cathode performance was studied. MEAs were prepared by decal transfer onto a SPEEK membrane (IEC-1.75 mequiv./g). The IEC of SPEEK binder in the MEA cathode was varied between 1.3 and 2.1 mequiv./g. Cathodes prepared with 30 wt.% SPEEK loading had an electrochemically active surface area (ECA) that was 25% lower than a Nafion ® bonded electrode with similar loading. Polarization curves were obtained at 80 °C and 75% RH with hydrogen as fuel and air and oxygen (O 2 ) as oxidants. Polarization data was analyzed to determine the relative contributions of different sources of polarization, namely membrane ohmic losses, electrode ohmic losses, and mass transport losses in the gas diffusion layer, binder film and electrodes. The electrode ohmic and mass transport losses decreased with increase in SPEEK IEC. However, even for the highest SPEEK IEC, these losses were higher than those obtained in a Nafion ® bonded electrode. This was attributed to the lower proton activity and O 2 permeability in SPEEK. The loading of SPEEK in the electrode was found to influence performance in the activation controlled region, with a loading of 7.5 wt.% giving the highest performance. However, gains in this region were negated at higher current densities due to enhanced ohmic and transport losses and MEAs with all binder loadings between 7.5 and 30 wt.% had similar limiting currents.

Influence of Membrane Ion Exchange Capacity on the Catalyst Layer Performance in an Operating PEM Fuel Cell

The effect of ion exchange capacity (IEC) of polymer electrolyte membranes (PEMs) on cathode catalyst layer operation is investigated using a hydrogen/oxygen proton exchange membrane fuel cell (PEMFC) and a series of tetrafluoroethylene--polystyrene sulfonic acid (ETFE--PSSA) membranes. The electrochemically active surface area (ESA) of the catalyst layer reveals a slight dependence on IEC. The steady-state beginning-of-life polarization curves show an increase in fuel cell performance with increased IEC. The membrane’s IEC and molecular structure controls the water content within, and regulates the water balance in the complete MEA. Comparing half-fuel-cell and fuel cell systems reveals that the ESA in the latter is lower as a result of reduced wetting of the catalyst layer but this is offset by an order of magnitude improvement of the effective diffusion. Consequently oxygen reduction reaction (ORR) performance is higher in the fuel cell system. The balance between electro-osmotic flux and hydraulic counterflux in the membrane is employed to explain the distinct effects of IEC in the half fuel cell and fuel cell systems. The two types of measurements thus provide a convenient tool for studying the interplay of different mechanisms of water flux in the membrane.

The role of membrane ion exchange capacity on membrane|gas diffusion electrode interfaces: a half-fuel cell electrochemical study

The effect of ion exchange capacity (IEC) of tetrafluoroethylene- g-polystyrene sulfonic acid membranes (ETFE- g-PSSA) on the electrochemical oxygen reduction reaction at the membrane|catalyst layer interface is investigated. In the half-fuel cell system the catalyst layer is hot-pressed to an ETFE- g-PSSA membrane forming a half-membrane electrode assembly (HMEA). The working electrode is exposed to liquid electrolyte at the membrane side and to O 2 gas at the gas diffusion layer side. Measurement of electrochemically active surface area by CO stripping reveals that membranes with higher IECs result in higher active surface areas of the electrode. In contrast, they exhibit lower oxygen reduction performances. The experimental results are analyzed using the agglomerate model. The extracted effective diffusion coefficients of oxygen (0.62–1.25 × 10 −5 cm 2 s −1) and O 2 solubility (2.03–2.80 mmol l −1) in the catalyst layers are close to the corresponding values found in fully hydrated ETFE- g-PSSA bulk membranes and H 2SO 4. Percolation theory reveals that ∼71–77% of void space in the catalyst layer is filled with water. The membrane IEC regulates the extent of flooding in the cathode, which in turn affects its electrochemical characteristics. The predominant mode of O 2 transport in the half-fuel cell is diffusion through the electrolyte phase or flooded area.

Effects of ion exchange capacities on attachment and growth of anchorage-dependent HeLa cell

An effect of ion exchange capacity of petri dish on cell attachment and growth of an anchorage-dependent animal cell was studied. We proposed a new idea to analyze cell attachment kinetics. As the experimental result of cell attachment to a petri dish, the attachment rate constant and the maximum number of attached cells both increase with increasing the ion exchange capacity. However, no direct correlation between the ion exchange capacity and the cell growth was observed. An influence of ion exchange capacity on the cell growth of initially attached cells onto the petri dish with different ion exchange capacities was examined. The specific growth rate of initially attached cells decreased with increasing the ion exchange capacity. The detrimental effect of the ion exchange capacity on the specific growth rate of the initially attached cells exists during the cell cultivation period. In the ion exchange capacity of 27 meq/m2, the specific growth rate drastically decreased. It is considered that there is optimum value of the ion exchange capacity for the cell growth and attachment. It is concluded that the optimum ion exchange capacity is 18 meq/m2.

Polyphosphazene membranes. IV. Polymer morphology and proton conductivity in sulfonated poly[bis(3-methylphenoxy)phosphazene] films

The microstructure of sulfonated poly[bis(3-methylphenoxy)phosphazene] was studied using wide- and small-angle X-ray diffraction. A reflection peak, attributed to the presence of ionic clusters, was observed in the small-angle X-ray diffraction patterns of hydrated and dry polymers with an ion-exchange capacity (IEC) ≥0.6 mmol/g. The Bragg spacing from the ionic cluster structure was about 30 Å for the nonhydrated polymer and 50 to 90 Å for fully hydrated films. The effects of IEC, cation form of the polymer, temperature, and polymer water content on the cluster structure were investigated. The specific proton conductivity of water-swollen, sulfonated poly[bis(3-methylphenoxy)phosphazene] films at 25°C increased with increasing IEC, with a maximum conductivity of 0.1 S/cm at a polymer ion-exchange capacity of 1.6 mmol/g. The water-content percolation threshold for conductivity was between 17.5 and 25 vol %, and decreased with polymer IEC. The temperature dependence of proton conductivity for 1.2 mmol/g IEC poly[bis(3-methylphenoxy)phosphazene] membranes exhibited Arrhenius behavior with an apparent activation energy of 27.8 and 36.7 kJ/mol for crosslinked and noncrosslinked polymers, respectively. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 49–59, 2001