Polyelectrolyte Membranes Research Articles

Exploring the hydrated microstructure and molecular mobility in blend polyelectrolyte membranes by quantum mechanics and molecular dynamics simulations

QMs and MD simulations were employed to investigate the effect of water contents and temperatures on structural and dynamical behaviors of blended PEMs.

Enhancement of ‘dry’ proton conductivity by self-assembled nanochannels in all-solid polyelectrolytes

Nanoscale proton-channels endow a polyelectrolyte membrane with exciting anhydrous proton conductivity, making it attractive for high-temperature PEMFC applications.

Bipolar Interfacial Polyelectrolyte Membrane Fuel Cell Ⅱ: Optimization of Cathode Catalyst Layer

Bipolar fuel cell (BPFC) is a new kind polymer electrolyte membrane fuel cell (PEMFC) with acidic-alkaline bipolar interface formed by acidic and alkaline polyelectrolyte both used in one cell. BPFC has shown some novel characterizations: (1) water generated at the bipolar interface would provide the possibility to devise self-humidification over the entire cell, which would simplify the water manager system; (2) alkaline cathode with facilitated electrokinetics allows for the use of lower catalyst loading or non-noble catalysts, such as silver and nickel. In our previous work, the effect of bipolar membrane electrode configuration on the cell output performance was evaluated and the optimal configuration was achieved. The BPFC with optimal membrane electrode configuration has been operated under completely self-humidifying conditions for prolonged periods successfully. However, there exists a big gap with the cell performance between BPFC and the state-of-art PEMFC. In order to improve the fuel cell performance, optimization of the membrane electrode configurations and further advances in fabricating bipolar interface had been conducted in our previous work. Another issue that affects the performance of the fuel cell is the structure and composition of the catalyst layer. Since the oxygen reduction reaction (ORR) at cathode influenced the fuel cell performance a lot, the improvement of electrode was mainly focused on the cathode catalyst layer. In the present work, thin hydrophilic electrode and thick hydrophobic electrode were used as cathode for BPFC. The influence of ionomer binder, quaternary ammonium polysulfone (QAPSF) in thin hydrophilic electrode and polytetrafluoroethylene (PTFE) in thick hydrophobic electrode, concentration on BPFC performance was studied. The results indicated that the optimal content of QAPSF in thin hydrophilic cathode was 20 wt%, and the peak power density of BPFC reached to 186.1 mW/cm at 25 °C without humidification. While the PTFE in the thick hydrophobic cathode was also 20 wt% with a peak power density of 461.5 mW/cm at 40 °C without humidification. Due to the high demand of alkaline cathode for drainage, the thick hydrophobic electrode behaved better than thin hydrophilic electrode in BPFC.

Effect of mineral organization on mechanical properties of constructs composed of fused and actively mineralized micromodules

Event Abstract Back to Event Effect of mineral organization on mechanical properties of constructs composed of fused and actively mineralized micromodules Kevin B. Miles1, Tristan Maerz2 and Howard W. Matthew1 1 Wayne State University, Chemical Engineering and Materials Science, United States 2 Beaumont Health System – Research Institute, Orthopaedic Research Laboratories, United States Introduction: A modular bone tissue engineering (TE) approach that builds larger, implantable constructs from small cell laden modules could circumvent some pitfalls of traditional bone TE (limited cell migration, inadequate scaffold mineralization, etc.). One modular TE strategy relies on composites of natural polyelectrolytes, such as glycosaminoglycans (GAGs) and chitosan, to construct modular units. Chondroitin 4-sulfate (C4S), the primary GAG in bone, facilitates hydroxyapatite (HAP) nucleation in vitro [1]. In addition, exogenous HAP can stimulate osteogenesis of mesenchymal stem cells (MSCs) [2]. The modular TE design described here involves the encapsulation of mesenchymal stem cells (MSCs) and HAP in a polyelectrolyte membrane composed of C4S and chitosan (Ct) to create micromodular units capable of being fused into larger implantable constructs. The influence of the extent and location of mineral deposition within the micromodules on fused construct mechanical properties is presented here. Methods: HAP and MSCs were encapsulated in spherical C4S/ct micromodules by polyelectrolyte complexation [3]. Four conditions were investigated: micromodules formed without exogenous HAP cultured in standard medium (E) or osteogenic medium (O) for four weeks, and similar micromodules containing HAP microgranules (cultured in standard, EH or osteogenic, OH medium). After 4 weeks of culture, micromodules were fused by the deposition of additional C4S/chitosan polyelectrolyte complex between the micromodules, to create larger fused constructs. The extent and organization of mineral deposition within micromodules/constructs was determined by μCT analysis after 4 weeks of static culture. Yield stresses under uniaxial compression were determined for each construct. Results and Discussion: Complexation between C4S and chitosan was found to adequately fuse mineralized micromodules containing differentiating MSCs (Fig. 1a and 1b). μCT analysis demonstrated that significant mineral deposition occured on the C4S/chitosan membrane enveloping the HAP and osteogenic MSCs (Fig. 1c). Moreover, fused constructs fabricated from micromodules containing osteogenic MSCs (O and OH micromodules) exhibited significantly higher compressive yield points (Fig. 2), compared to micromodules containing standard cultured MSCs (EH and E). Including HAP in the micromodules significantly enhanced the mechanical properties of tissue constructs created from fused micromodules. Interestingly, the location of mineralization was the primary determinant of mechanical properties: constructs composed of actively mineralized micromodules without HAP (O) had significantly higher yield stresses than the non-mineralized constructs containing HAP (EH), possibly due to the localization of mineral deposition to the micromodule C4S/Ct membranes (Fig. 1d). This data strongly suggests that mineralization reinforces the C4S/chitosan membranes, so that compressive stresses are effectively dissipated across the micromodules, resulting in fused constructs with higher compressive strength. Conclusion: The mechanical properties demonstrate that the in vitro mineralization of the C4S/chitosan module membrane is the primary determinant of mechanical properties in the fused constructs. Results show this micromodular unit design can form the basis of a modular TE solution to regenerate mechanically robust bone.

Embedding sulfonated lithium ion-sieves into polyelectrolyte membrane to construct efficient proton conduction pathways

In this study, acidified lithium ion-sieves (HMOs) containing unique inner ionic channels suitable for the transfer of H+ are selected as proton-conductive fillers to prepare hybrid membranes for the first time. By using facile distillation-precipitation polymerization process, two types of sulfonated HMOs (SHMOs) are prepared: L-SHMOs, which are modified by sulfonate polyelectrolyte layer, and B-SHMOs, which are sulfonate polyelectrolyte brushes. The results demonstrate that these fillers improve the thermal and mechanical stabilities of chitosan (CS) control membranes. The incorporation of pristine HMOs enhances the water uptakes and proton conduction abilities of hybrid membranes at suitable loading. By comparison, SHMOs-filled membranes possess higher proton conductivities than those of HMO-filled membranes, owing to the additional proton hopping sites of –SO3H and acid-base pairs (–SO3−···+3HN–). Moreover, B-SHMO-filled membranes exhibit superior proton conductivities over L-SHMO-filled ones, demonstrating that the polymer brushes on HMOs allow more –SO3H groups to form acid-base pairs with CS chains. Particularly, CS/B-SHMO-12 obtains the highest hydrated and anhydrous conductivities of 0.0224Scm−1 and 10.03mScm−1, enhancing by 91.4% and 98.6% respectively compared with those of CS control membrane under identical conditions. The enhanced proton conductivities offer SHMO-filled membranes elevated cell performances.

Effect of constrained amorphous region on properties of acid–base polyelectrolyte membranes based on sulphonated poly(ether ether ketone) and a nonconjugated diamine

The phenomenon of polymer chains being restrained from participating in relaxation mechanisms has been discussed for a number of situations in the field of polymer science. In the present study we invoke the same as a mechanistic origin of property improvement in an acid–base polymeric membrane for fuel cell application. Sulfonated polyether ether ketone (sPEEK) and a non conjugated diamine (3, 3′ dichloro 4,4′ diaminodiphenylmethane) were used as the acid and base components, respectively to prepare the membranes by a facile solvent casting process. The ionic cross-link induced constrained amorphous region (C) in the acid–base membranes is quantified as a function of basic component loading from the relative depression in the dissipation factor, tan δ using dynamic mechanical analysis (DMA); found to be a staggering 62% at 25% basic component loading. The significantly higher C values are attributed to strong acid–base interactions as established from morphological investigations by field emission scanning electron microscopy (FESEM), FTIR studies and IEC measurements. Consequent to the existence of constrained amorphous region of reduced mobility, significant improvement in thermomechanical properties, (~5 fold increase in storage modulus, 2 fold increase in tensile strength and ~100°C increase in glass transition temperature compared to pristine sPEEK) thermal, dimensional as well as oxidative stability, of the acid–base membranes are observed compared to the pristine SPEEK membrane. We envisage that the hitherto unexplored acid–base membranes derived from an acidic polymer and a small molecule non-conjugated diamine can also be suitable candidates for fuel cell applications. In addition these fundamental studies are expected to provide insights into mechanistic origins of the property improvements in acid–base membranes.

Phosphoric acid functional UV-cured proton conducting polymer membranes for fuel cells

This paper reports the preparation and characterization of 10-methacryloyloxydecyl-dihydrogenphosphate (MDP)-based UV-curable proton-conducting polymer membranes (UVcPMs). Poly(ethylene glycol diacrylate) (PEGDA), as cross-linking agent, and N-vinyl-2-pyrrolidone (NVP), as reactive diluent, were used to arrange the mechanical and physical properties of the resulting membrane. The membrane formulation polymerized under UV irradiation and membranes were characterized by using Fourier transform infrared (FT-IR), thermal gravimetric analysis (TGA) and electrochemical impedans spectroscopy (EIS). The water uptakes, the volume swelling ratio and ion exchange capacity (IEC) measurement of the membranes were performed. The IEC values increase with an increase in MDP monomer content. Proton conductivities were measured as a function of the weight fraction of MDP content of the membrane. The conductivities are of the order of 10−4–10−3 Scm−1. The morphology of the membranes was also investigated by Atomic Force Microscopy (AFM). MDP-based UV-cured polymers are first reported as polyelectrolyte membranes.

Influence of synthesis conditions on the performance of chitosan–Heteropolyacid complexes as membranes for low temperature H2–O2 fuel cell

Flat, free-standing chitosan/phosphotungstic acid (PTA) polyelectrolyte membranes were prepared by in-situ ionotropic gelation process at room temperature on porous alumina support firstly impregnated by H3PW12O40. Scanning electron microscopy revealed the formation of compact and homogeneous membranes, whose thickness resulted to be dependent on chitosan concentration and reticulation time. X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) evidenced the formation of almost amorphous membrane without appreciable concentration of not protonated NH2 groups and PTA3− ions with preserved Keggin structure. Membranes were tested as proton conductor in low temperature H2–O2 fuel cell allowing to get peak power densities up to 300 mW cm−2. Electrochemical impedance measurements allowed to estimate polyelectrolytes' conductivity up to 28 mS cm−1 at room temperature.

(1)H NMR Analysis of Water Freezing in Nanospace Involved in a Nafion Membrane.

Water involved in a polyelectrolyte membrane of Nafion has recently been revealed to comprise three distinctive molecular species with respect to molecular motion correlated with the hydrogen bonding structure by using (1)H NMR, infrared, and mass spectrometries. The three species are assigned to the condensed water, hydration water, and strongly bounded water on the sulfonic acid group. In the present study, on the contrary to an expectation on this schematic, even the condensed water is found unfrozen when the membrane is cooled down to -50 °C, and a freezing begins when it is cooled down to -60 °C or lower. Two-thirds of the condensed water remains unfrozen even at -80 °C, which is attributed to the effect of nanospace where the water molecules are too short to construct the ice-like structure. The reduction of rotational motion of water is, on the other hand, commonly found for all the water species revealed via the calculation of the activation energies.

Self-Assembly, Transport, and Thermodynamics in Nafion Membranes: Insight from Dissipative Particle Dynamics Simulation

Composed of perfluorinated backbone with sulfonate sidechains, Nafion self-assembles upon hydration and segregates into interpenetrating hydrophilic and hydrophobic subphases. This segregated morphology determines the transport properties of Nafion membranes that are widely used as compartment separators in fuel cells and other electro-chemical devices, as well as permselective diffusion barriers in protective fabrics. We introduce a coarse-grained model of Nafion, which accounts explicitly for polymer rigidity and electrostatic interactions between anionic sidechains and hydrated metal cations. By means of dissipative particle dynamics (DPD) and Monte Carlo (MC) simulations, we explore geometrical, transport, and sorption properties of hydrated Nafion-type polyelectrolyte membranes. Novel methodology will be presented for calculating water adsorption isotherms and transport coefficients as a function of the degree of hydration.

Layer-by-layer assembly of aquaporin Z-incorporated biomimetic membranes for water purification.

We fabricated a biomimetic nanofiltration (NF) membrane by immobilizing an Aquaporin Z (AqpZ)-incorporated supported lipid bilayer (SLB) on a layer-by-layer (LbL) complex polyelectrolyte membrane to achieve excellent permeability and salt rejection with a high stability. The polyelectrolyte membranes were prepared by LbL assembly of poly(ethylenimine) (PEI) with positive charges and poly(sodium 4-styrenesulfonate) (PSS) with negative charges alternately on a porous hydrolyzed polyacrylonitrile (H-PAN) substrate. AqpZ-incorporated 1,2-dioleloyl-sn-glycero-3-phosphocholine (DOPC)/1,2-dioleoyl-3-trimethylammo-nium-propane (chloride salt) (DOTAP) vesicles with positive charges were deposited on the H-PAN/PEI/PSS polyelectrolytes membrane surface. The resulting biomimetic membrane exhibited a high flux of 22 L·m(-2)·h(-1) (LMH), excellent MgCl2 rejection of ∼97% and NaCl rejection of ∼75% under an operation pressure of 0.4 MPa. Due to the attractive electrostatic interaction between SLB and the polyelectrolyte membrane, the biomimetic membrane showed satisfactory stability and durability as well as stable NF flux and rejection for at least 36 h. In addition, the AqpZ-containing biomimetic membrane was immersed in a 0.24 mM (critical micellar concentration, CMC) Triton X-100 solution for 5 min. The flux and rejection were slightly influenced by the Triton X-100 treatment. The current investigation demonstrated that the AqpZ-incorporated biomimetic membranes fabricated by the LbL method led to excellent separation performances and robust structures that withstand a high operation pressure for a relatively long time.

High cell density cultivation of human leukemia T cells (Jurkat cells) in semipermeable polyelectrolyte microcapsules

The ex vivo expansion of human T cells is of considerable scientific and medical interest. Currently, this requires the addition of massive amounts of stimuli. Here, human leukemia T cells (Jurkat cells) were used as model cells to demonstrate the in vitro expansion of T cells in the absence of added stimuli after encapsulation in semipermeable sodium cellulose sulfate/poly(diallyldimethyl) ammonium chloride polyelectrolyte membrane capsules (molecular weight cutoff <10 kDa, average diameter ca. 800 μm). For comparison, free and encapsulated cells were cultivated in standard T‐flasks and spinner bottles (both 50 mL culture medium) as well as in hanging drops (35 μL, only nonencapsulated cells). Encapsulation led to a significantly higher specific growth rate, a prolonged exponential growth phase together with a reduced tendency for apoptosis, as evidenced by shifts in the cell cycle distribution toward the S and G2/M phases together with a reduced percentage of cells in the sub‐G0/G1 phase. As a consequence, very high cell densities (>140×106 cells/mLcapsule) were obtained in the capsules, particularly for the spinner cultivations. No evidence for nonspecific activation/stimulation, that is IL‐2 and CD25 expression, was found, while specific stimulation by phorbol‐12‐myristate‐13‐acetate/ionomycin was still possible. Since Jurkat cells commonly serve as model cells for primary T lymphocytes, the proposed method may present a strategy for high‐density proliferation of primary human T lymphocytes.

Characterization of Nafion nanocomposites with spheric silica, layered silicate, and amphiphilic organic molecule and their actuator application

Nafion nanocomposite membranes with spheric silica, layered silicate (montmorillonite; MMT), and an amphiphilic organic molecule (10-camphorsulfonic acid; CSA) have been investigated as polyelectrolytes for ionic polymer-metal composite (IPMC) actuators. An organosilane (3-mercaptopropyltrimethoxy silane; 3-MPTMS) was grafted on the surfaces of silica and MMT, and the thiol groups on the fillers were sulfonated to endow them with additional hopping sites. The incorporation and modification of the fillers in the Nafion matrix greatly altered the internal morphologies of hydrophilic ion-rich and hydrophobic fluorocarbon regions, followed by changes in mechanical properties, dimensional stabilities, and mass transport kinetics. Finally, the Nafion nanocomposite membranes were engaged as the polyelectrolytes of an IPMC actuator, and actuation performance was analyzed, being associated with the internal morphology-driven diffusion characteristics and capacitances in the polyelectrolyte membranes and the resulting efficiency of charge-to-deformation.

Bipolar Interfacial Polyelectrolyte Membrane Fuel Cell I:Structure of Membrane Electrode Assembly

Although considered as the most viable approach for mobile powers, traditional polymer electrolyte membrane fuel cells require burdensome humidification and water management systems. The bipolar fuel cell (BPFC) or hybrid mem- brane fuel cell won noticeable interest because its potential self-humidification. BPFC is a novel polyelectrolyte membrane fuel cell involving both anion and cation polyelectrolyte and a new kind of acidic-alkaline bipolar reaction interface was pre- sented in the cell. The potential advantages of a BPFC are twofold: (a) the alkaline cathode with inherently faster kinetics that allows use of non-platinum catalysts, thereby significantly reducing the total cost of a fuel cell; (b) the water generation or dissociation reaction takes place at the bipolar interface providing the possibility to devise self-humidification over the entire cell. Despite the BPFC have such attractive potentials, the BPFC developed to date had not yet demonstrated these feature and have operated at very modest power densities. As the development of BPFC is still in their infancy, it still remains un- certain how the bipolar interface works and effects in the cell. In the present study, four types of bipolar membrane electrode configuration containing two or one kind of bipolar interface, either water generation or dissociation interfaces, were fabri- cated to evaluate the effect of bipolar interface on the cell output performance. Results show that the preferred configuration with only one bipolar interface generating water can benefit the cell output. The reason could be the faster water formation reaction kinetics in this kind of bipolar interface and lower interfacial potential loss with only one bipolar interface. Within this preferred membrane electrode configuration, we have realized and demonstrated the BPFC that operate under completely self-humidifying conditions for prolonged periods successfully. As we can see, optimization of the membrane electrode con- figurations and further advances in fabricating bipolar interface would open the way for the development of practical self-regulating portable fuel cells. Keywords bipolar interface; membrane electrode configuration; self-humidifying; polyelectrolyte membrane; fuel cell

A durable anion conducting membrane with packed anion-exchange sites and an aromatic backbone for solid-state alkaline fuel cells

A durable polyelectrolyte membrane with highly cross-linked aromatic packed anion-exchange sites that enable high OH− ion transport, simultaneously restricting methanol cross-over for solid-state alkaline fuel cells.

Preparation of a ROMP-type imidazolium-functionalized norbornene ionic liquid block copolymer and the electrochemical property for lithium-ion batteries polyelectrolyte membranes

Solid polymer electrolytes with high ionic conductivity have been prepared based on an imidazolium-functionalized norbornene ionic liquid block copolymer.

High proton conductivity of sulfonated methoxyphenyl-containing poly(arylene ether ketone) for proton exchange membranes

A polyelectrolyte membrane based on sulfonated methoxyphenyl-containing poly(arylene ether ketone) (SMP-PAEK) was obtained, which exhibited suitable proton conductivities and excellent mechanical properties.

Improved antifouling performance of polyethersulfone (PES) membrane via surface modification by CNTs bound polyelectrolyte multilayers

This study investigated the improved anti-fouling properties of CNTs bound polyelectrolyte membrane and proposed the mechanisms for anti-fouling.

ETFE-g-pentafluorostyrene: Functionalization and proton conductivity

In this study we propose a relatively simple and versatile method for the preparation of a polyelectrolyte membrane based on poly(pentafluorostyrene) (PFS) owing proton exchange functionalities for proton conducting applications. The method includes two steps: grafting of the PFS from an irradiated ETFE film, followed by post-functionalization. The advantage of our approach lies in grafting a polymer with highly reactive functional groups suitable for efficient post-sulfonation/phosphonation. The grafting step is optimized both in terms of the system (bulk, non-/solvent and gas-phase grafting) and the conditions (radiation doses, time and temperature) used. The kinetics of the grafting shows a linear increase of grafting degree with both time and temperature suggesting a lower diffusion control and a reduced termination reaction rate for the optimized grafting process. Both phosphonation and sulfonation of the PFS grafted ETFE result in a corresponding high functionalization degree of 50% and 70% with IEC values of 1 and 1.5mequivg−1 and conductivities of 170 and 90mScm−1 at 120°C, 90% RH for the sulfonated and phosphonated ETFE-g-PFS respectively. The high conductivity is attributed to the homogeneous distribution of the PFS within the ETFE matrix (EDX-SEM micrographs) and relatively high acidities of the sulfonic and the phosphonic acids.

Polyelectrolyte Nanocomposite Membranes Using Imidazole-Functionalized Nanosilica for Fuel Cell Applications

The preparation and characterization of a new type of nanocomposite polyelectrolyte membrane, based on DuPont Nafion/imidazole-modified nanosilica (Im-Si), for direct methanol fuel cell applications is described. Related to the interactions between the protonated imidazole groups, grafted on the surface of nanosilica, and negatively charged sulfonic acid groups of Nafion, new electrostatic interactions can be formed in the interface of Nafion and Im-Si which result in both lower methanol permeability and also higher proton conductivity. Physical characteristics of these manufactured nanocomposite membranes were investigated by scanning electron microscopy, thermogravimetry analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, water uptake, methanol permeability, and ion-exchange capacity, as well as proton conductivity. The Nafion/Im-Si membranes showed higher proton conductivity, lower methanol permeability and, as a consequence, higher selectivity parameter in comparison to the neat Nafion or Nafion/silica membranes. The obtained results indicated that the Nafion/Im-Si membranes could be utilized as promising polyelectrolyte membranes for direct methanol fuel cell applications.