Membrane Mass Transport Research Articles

PH and potential-controlled multi-modal mass transport in block copolymer nanochannel membranes

Inspired by the hydrophobic gating for achieving fast and selective ion/molecular transport in cell membranes, wetting/dewetting transition in solid-state nanopores controlled by external stimuli such as voltage, pH, electrostatics, and light have attracted increasing attention. For an accurate and better understanding, a single nanopore or low-density array of nanopores was preferred to investigate the wetting and dewetting transitions owing to their well-defined chemical functions and physical structures. However, high-density nanochannel membranes capable of processing high-throughput and multi-modal mass transport are more beneficial with the aim of practical use. In this regard, pH- and potential-responsive nanochannel membranes consisting of a polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP) are prepared to demonstrate a multi-modal transport system with high-throughput capability. At pH < pKa(P4VP) (pKa ∼ 4.8), the cylindrical P4VP nanodomains are hydrophilic and positively charged, acting as an anion-exchange membrane. In contrast, at pH > pKa(P4VP), the P4VP domains switch to be charge-neutral and hydrophobic, naturally blocking the mass transport through the nanochannels. Applying a sufficiently positive potential to a BCP membrane-coated electrode may induce oxidative wetting in the hydrophobic nanochannels to facilitate mass transport across the membrane with no charge-selectivity. Releasing the bias makes the hydrophobic nanochannel membranes retrieve the original dewetted state, blocking the transport again. In addition, direct observation of the wetting-dewetting transition dynamics in the hydrophobic nanochannels is investigated by monitoring potential-correlated electrochemiluminescence (ECL) signals arising from Ru(bpy)32+ and co-reactant tripropylamine (TPA) under potential modulations. ECL signals tend to decrease with increasing membrane thickness ranging from 0 nm to 820 nm because it requires higher potentials to induce wetting in the nanochannels due to elongated hydrophobic nanochannels. The multi-modal transport system developed in the present work will be useful for applications such as water treatment, biosensors, and smart valve systems like controlled drug release/delivery.

Nafion Matrix and Ionic Domain Tuning for High‐Performance Composite Proton Exchange Membranes

AbstractAlthough proton exchange membranes (PEMs) are widely deployed in an array of commercial applications, limitations linked to their proton conductivity, water retention, and gas permeability still limit ultimate device performance. While ex situ studies have shown additives can enhance membrane stability and mass transport, to date few have demonstrated that these performance enhancements are maintained when tested in commercially relevant electrochemical technologies, such as fuel cells or electrolyzers. Herein, a new multifunctional additive, 2D poly(triazine imide) (PTI), is demonstrated for composite PEMs, which is shown to boost proton conductivity by 37% under optimal high relative humidity (RH) conditions and 67% at low RHs. PTI also enables major improvements (over 55%) in both current and power densities in industrially relevant PEM fuel cells (PEMFCs). Most importantly, in situ and ex situ characterization suggests that the enhanced performance is due to polymer aggregate‐PTI clusters that form with increasing 2D character and improved long‐range connectivity, while acid‐base interactions with pyridinic nitrogen facilitate the critical proton hopping mechanism at all RHs. Hence, this work offers both a new membrane concept with proven benefits for important electrochemical technologies, as well as design principles for future optimization of proton transport and water management within PEMs.

Random Walks and Sticky Surfaces: Single-Molecule Measurements of Solute Diffusion in Ethanol/Water-Filled Anodic Alumina Nanopores

Nanoporous anodic aluminum oxide (AAO) membranes are now being explored for use in advanced chemical separations, including in the dehydration of biofuels such as ethanol. Optimization of membrane performance requires an in-depth understanding of how solvent mixtures and solutes behave under nanoconfinement. In this work, the diffusion of rhodamine B (RhB) dye through 10 and 20 nm AAO nanopores filled with a series of ethanol/water mixtures (0–33% water) is explored by fluorescence correlation spectroscopy (FCS). RhB was found to diffuse through the pores by two distinct mechanisms with mean diffusion coefficients, Df and Ds, reflecting fast and slow diffusive motions, respectively, with values that differ by nearly 2 orders of magnitude. Both Df and Ds increased with pore size and were significantly smaller than Db, the RhB diffusion coefficient in bulk liquid. Mean Df values follow a composition-dependent trend that closely mimics the viscosity dependence of Db. Additional slowing of fast RhB diffusion is attributed to both hydrodynamic drag and electrostatic interactions with the nanopore surface. The mean Ds values exhibit a different trend with increasing water content, revealing an increase in Ds and a decrease in the contributions of slow diffusion to the observed dynamics. The fluorescence time transient data used in the analysis show that the slow diffusion process is strongly hindered and likely involves frequent adsorption of RhB to the pore surfaces. These results provide new insights into the detailed molecular-level mechanisms of mass transport in nanoporous AAO membranes.

Discrete effects on the source term for the lattice Boltzmann modelling of one-dimensional reaction–diffusion equations

This work presents a detailed numerical analysis of one-dimensional, time-dependent (linear) reaction–diffusion type equations modelled with the lattice Boltzmann method (LBM), using the two-relaxation-time (TRT) scheme, for the D1Q3 lattice. The interest behind this study is twofold. First, because it applies to the description of many engineering problems, such as the mass transport in membranes, the heat conduction in fins, or the population growth in biological systems. Second, because this study also permits understanding the general effect of solution-dependent sources in LBM, where this problem offers a simple, yet non-trivial, canonical groundwork. Without recurring to perturbative techniques, such as the Chapman-Enskog expansion, we exactly derive the macroscopic numerical scheme that is solved by the LBM-TRT model with a solution-dependent source and show that it obeys a four-level explicit finite difference structure. In the steady-state limit, this scheme reduces to a second-order finite difference approximation of the stationary reaction–diffusion equation that, due to artefacts from the source term discretization, may operate with an effective diffusion coefficient of negative value, although still remaining stable. Such a surprising result is demonstrated through an exact stability analysis that proves the unconditional stability of the LBM-TRT model with a solution-dependent source, in line with the already proven source-less pure diffusion case (Lin et al., 2021). This proof enlarges the confidence over the LBM-TRT model robustness also for the (linear) reaction–diffusion problem class. Finally, a truncation error analysis is performed to disclose the structure of the leading order errors. From this knowledge, two strategies are proposed to improve the scheme accuracy from second- to fourth-order. One exclusively based on the tuning of the LBM-TRT scheme free-parameters, namely the two relaxation rates and the lattice weight coefficient, and the other based on the redefinition of the structure of the relaxation rates, where the leading order truncation error is absorbed into one of the relaxation rates, liberating the other to improve additional features of the scheme. Numerical tests presented in the last part of the work support the ensemble of theoretical findings.

Oxygen Plasma-Mediated Microstructured Hydrocarbon Membrane for Improving Interface Adhesion and Mass Transport in Polymer Electrolyte Fuel Cells.

Developing a method for fabricating high-efficient and low-cost fuel cells is imperative for commercializing polymer electrolyte membrane (PEM) fuel cells (FCs). This study introduces a mechanical and chemical modification technique using the oxygen plasma irradiation process for hydrocarbon-based (HC) PEM. The oxygen functional groups were introduced on the HC-PEM surface through the plasma process in the controlled area, and microsized structures were formed. The modified membrane was incorporated with plasma-treated electrodes, improving the adhesive force between the HC-PEM and the electrode. The decal transfer was enabled at low temperatures and pressures, and the interfacial resistance in the membrane-electrode assembly (MEA) was reduced. Furthermore, the micropillar structured electrode configuration significantly reduced the oxygen transport resistance in the MEA. Various diagnostic techniques were conducted to find out the effects of the membrane surface modification, interface adhesion, and mass transport, such as physical characterizations, mechanical stress tests, and diverse electrochemical measurements.

Coupled FEM and CFD Modeling of Structure Deformation and Performance of PEMFC Considering the Effects of Membrane Water Content

Based on a coupled finite element method (FEM) and computational fluid dynamics (CFD) model, the structural deformation and performance of a proton exchange membrane fuel cell (PEMFC) under different membrane water contents are studied. The water absorption behavior of the membrane is investigated experimentally to obtain its expansion coefficient with water content, and the Young’s modulus of the membrane and catalyst (CL) are obtained through a tensile experiment. The simulation results show that the deformation of the membrane increases with water content, and membrane swelling under the channel is larger than that under the rib, forming a surface bump under the channel. The structural changes caused by the membrane water content have little effect on the performance of PEMFC in the low-current density range; while its influence is significant in the medium- and high-current density range. A medium membrane water content value of 12 achieves the best fuel cell performance due to the balance of membrane resistance and mass transport.

Pervaporation as a Successful Tool in the Treatment of Industrial Liquid Mixtures.

Pervaporation is one of the most active topics in membrane research, and it has time and again proven to be an essential component for chemical separation. It has been employed in the removal of impurities from raw materials, separation of products and by-products after reaction, and separation of pollutants from water. Given the global problem of water pollution, this approach is efficient in removing hazardous substances from water bodies. Conventional processes are based on thermodynamic equilibria involving a phase transition such as distillation and liquid–liquid extraction. These techniques have a relatively low efficacy and nowadays they are not recommended because it is not sustainable in terms of energy consumption and/or waste generation. Pervaporation emerged in the 1980s and is now becoming a popular membrane separation technology because of its intrinsic features such as low energy requirements, cheap separation costs, and good quality product output. The focus of this review is on current developments in pervaporation, mass transport in membranes, material selection, fabrication and characterization techniques, and applications of various membranes in the separation of chemicals from water.

Large-Area 2D Covalent Organic Framework Membranes with Tunable Single-Digit Nanopores for Predictable Mass Transport.

The potential of covalent organic frameworks (COFs) for molecular separations remains unrealized because of challenges transforming nanoscale COF materials into large-area functional COF membranes. Herein, we report the synthesis of large-area (64 cm2), ultrathin (24 nm), β-ketoenamine-linked 2D COFs using a facile interfacial polymerization technique. Angstrom-level control over single-digit nanopore size (1.4-2.0 nm) is achieved by direct integration of variable-length monomers. We apply these techniques to fabricate a series of large-area 2D COF membranes with variable thicknesses, pore sizes, and supporting materials. Tunable 2D COF properties enable control over COF membrane mass transport, resulting in high solvent fluxes and sharp molecular weight cutoffs. For organic solvent nanofiltration, the 2D COF membranes demonstrate an order-of-magnitude greater permeance than the state-of-the-art commercial polymeric membrane. We apply continuum models to quantify the dominance of pore passage resistance to mass transport over pore entrance resistance. A strong linear correlation between single-digit nanopore tortuosity and 2D COF thickness enables solvent fluxes to be predicted directly from solvent viscosity and COF membrane properties. Solvent-nanopore interactions characterized by the membrane critical interfacial tension also appear to influence mass transport. The pore flow transport model is validated by predicting the flux of a 52 nm thick COF membrane.

Following mass transport through barrier membranes with confocal Raman microscopy

AbstractThis work describes a setup to characterize the effective diffusivity of barrier membranes to mass transport. Membranes with controlled and well‐defined barrier microstructures are produced from an elastomeric polydimethylsiloxane (PDMS) matrix. Physical obstacles to mass transport are generated by carving in the matrix microscopic holes with well‐defined shapes and in specific positions. Lateral Raman mapping is used to follow mass transport of a penetrant molecule, hexadecanol (HDOL), in the carved matrix. The influence of circular and elongated holes over mass transport is examined by monitoring the HDOL Raman intensity over time, after it passes the barrier microstructure. Results are compared with computer simulations of mass transport and excellent agreement is found. It is shown that holes act as bidimensional barriers to HDOL and that the effective diffusion coefficient of HDOL in the barrier membrane is reduced with respect to that of the homogenous material. Overall, Raman measurements provide a valuable base of data generation to contrast theoretical models of mass transport in heterogeneous barrier membranes.

Modelling the Molecular Permeation through Mixed-Matrix Membranes Incorporating Tubular Fillers.

Membrane-based processes are considered a promising separation method for many chemical and environmental applications such as pervaporation and gas separation. Numerous polymeric membranes have been used for these processes due to their good transport properties, ease of fabrication, and relatively low fabrication cost per unit membrane area. However, these types of membranes are suffering from the trade-off between permeability and selectivity. Mixed-matrix membranes, comprising a filler phase embedded into a polymer matrix, have emerged in an attempt to partly overcome some of the limitations of conventional polymer and inorganic membranes. Among them, membranes incorporating tubular fillers are new nanomaterials having the potential to transcend Robeson’s upper bound. Aligning nanotubes in the host polymer matrix in the permeation direction could lead to a significant improvement in membrane permeability. However, although much effort has been devoted to experimentally evaluating nanotube mixed-matrix membranes, their modelling is mostly based on early theories for mass transport in composite membranes. In this study, the effective permeability of mixed-matrix membranes with tubular fillers was estimated from the steady-state concentration profile within the membrane, calculated by solving the Fick diffusion equation numerically. Using this approach, the effects of various structural parameters, including the tubular filler volume fraction, orientation, length-to-diameter aspect ratio, and permeability ratio were assessed. Enhanced relative permeability was obtained with vertically aligned nanotubes. The relative permeability increased with the filler-polymer permeability ratio, filler volume fraction, and the length-to-diameter aspect ratio. For water-butanol separation, mixed-matrix membranes using polydimethylsiloxane with nanotubes did not lead to performance enhancement in terms of permeability and selectivity. The results were then compared with analytical prediction models such as the Maxwell, Hamilton-Crosser and Kang-Jones-Nair (KJN) models. Overall, this work presents a useful tool for understanding and designing mixed-matrix membranes with tubular fillers.

Stable cation-controlled reduced graphene oxide membranes for improved NaCl rejection

Reduced graphene oxide (rGO) membranes have drawn intensive attention in applications of desalination and molecular sieving, owing to their stable and selective two-dimensional (2D) channels. However, their performance, particularly the selectivity for water and ions separation, is still under the theoretical limit. In this research, we incorporated potassium cations (K+) into the laminar channels of rGO membranes to form stable and selective K-controlled rGO (K-rGO) membranes for water and NaCl separation. These K-rGO membranes can be prepared by either thermally reducing K-controlled GO (K-GO) membranes in air or by soaking rGO membranes thermal-reduced in air (Air-rGO) in KCl solutions. Compared with reported K-GO and Air-rGO membranes, as-prepared K-rGO membranes exhibit narrower interlayer spacing in NaCl solutions due to the strong K+-π interaction between K+ and π-electron cloud on rGO nanosheets. This strong K+-π interaction can stabilize and confine 2D nanochannels and prevent the permeation of other cations, such as Na+, into rGO laminates, contributing to the enhanced NaCl rejection (91%) of K-rGO membranes. This work advances the understanding of the mass transport in rGO membranes and provides new insights into the design of selective 2D membranes for desalination, ionic sieving and other environmental applications.

Computational fluid dynamics analysis of mini membrane module flow behavior

A newly developed green ultrafiltration membrane has been successfully made by utilizing natural antibiofoulant impregnated cellulose acetate mixed matrix membranes. The extract impregnated into cellulose acetate polymer to form mixed matrix membranes with higher and foodgrade antibiofouling properties. In order to evaluate mixed matrix membrane mass transport, a specialized mini membrane modules has been developed. This study utilizing computational fluid dynamics (CFD) simulation to evaluate fluid distribution in rectangular, quadrilateral and circular narrow channels. Three different superficial velocities which are normally found in spiral wound membrane modules were evaluated, i.e. 0.11, 0.16 and 0.2 m/s. Trans-membrane pressure normally used in ultrafiltration processes were evaluated, i.e. 50, 100, and 150 kPa. Based on CFD analysis, circular channel provides a more uniform and distributed velocity stream compare to the others. The circular shape also provide advantage on managing superficial feed flow inside the membrane channel, compared with rectangular and quadrilateral shapes channel. The mini membrane modules potentially reduces laboratory scale research cost, while maintaining the similar operating variables of larger scale.

Theory of Multicomponent Phenomena in Cation-Exchange Membranes: Part II. Transport Model and Validation

Multicomponent mass-transport in cation-exchange membranes involves the movement of multiple species whose motion is coupled one to another. This phenomenon mediates the performance of numerous electrochemical and water purification technologies. This work presents and validates against experiment a mathematical model for multicomponent mass transport in phase-separated cation-exchange membranes (e.g., perfluorinated sulfonic-acid ionomers). Stefan-Maxwell-Onsager theory describes concentrated-solution transport. Hydrodynamic theory provides constitutive relations for the solute/solvent, solute/membrane, and solvent/membrane friction coefficients. Classical porous-medium theories scale membrane tortuosity. Electrostatic relaxation creates friction between ions. The model uses calculated ion and solvent partitioning between the external solution and the membrane from Part I of this series and incorporates the corresponding ion speciation into the transport coefficients. The proposed transport model compares favorably to properties (e.g., membrane conductivity, transference numbers, electroosmosis, and permeability) measured in dilute and concentrated aqueous binary and ternary electrolytes. The results reveal that the concentration and type of ions in the external solution alter the solvent volume fraction and viscosity in the hydrophilic pathways of the membrane, changing macroscale ionomer conductivity, permeability, and transference numbers. This work provides a physicochemical framework to predict ion-exchange-membrane performance in multicomponent systems exhibiting coupled transport.

Absorptive Dissolution Testing: An Improved Approach to Study the Impact of Residual Crystallinity on the Performance of Amorphous Formulations

Amorphous solid dispersions typically improve the oral bioavailability of poorly soluble drugs. However, residual crystallinity is always a concern, in terms of potential impact on the product stability and performance. Consequently, in vitro tools that allow biorelevant assessment of residual crystallinity are of interest. The goal of the present study was to use absorptive dissolution testing to evaluate the impact of different levels of crystallinity in an amorphous formulation on membrane mass transport kinetics and supersaturation-time profiles. Partial crystallinity was induced in commercially available tacrolimus formulations by exposure to moderate temperature and high relative humidity. A hollow fiber membrane was coupled to a dissolution vessel to create an absorptive dissolution testing apparatus, and concentration-time profiles were simultaneously monitored during dissolution (donor compartment) and after absorption across the membrane (receiver compartment). The coupled dissolution-absorption measurements indicated that residual crystallinity impacted the absorption profiles in a manner that depended on the volume of fluid used for the dissolution measurement. A high percentage of residual crystallinity hampered the drug release from the formulation. Higher supersaturation in nonsink dissolution conditions improved mass transfer rates; however, the presence of seed crystals led to rapid desupersaturation. Further systematic studies to delineate the interplay between the rate of absorption and desupersaturation revealed that for a given dissolution rate, the crystallization rate would supersede the absorption rate only at high supersaturations. Thus, seeds have a lower impact on absorption when the overall supersaturation generated is lower. This study underscores the importance of considering competing physical processes when evaluating amorphous formulations. A further consideration highlighted is that different fluid volumes may impact the absorption profile for supersaturating dosage forms. Absorptive dissolution testing appears to be a potentially valuable tool to mechanistically investigate amorphous solid dispersion formulation release and phase behavior under more biorelevant conditions.

Mesoscopic modeling of mass transport in viscoelastic phase-separated polymeric membranes embedding complex deformable interfaces

Phase-separated polymeric membranes turn out to offer an alternative and promising solution for enhancing the limited performance exhibited by homopolymer membranes in separation techniques. Here, in order to properly describe mass transport in immiscible membranes embedding a dividing deformable complex interface, we rigorously derive, by using non-equilibrium thermodynamics and continuum mechanics approaches, a genuinely non-linear mesoscopic formulation that extends Fick’s laws and explicitly incorporates the coupling arising between diffusion and structure changes. Thereby, in addition to the penetrants’ mass fraction c, three additional independent structural state variables are adopted, namely the macromolecular chain conformation tensor m; and a scalar Q and a second-rank tensor q respectively for the size and shape anisotropy of the interface area. Our model consists of coupled PDEs and ODEs time evolution equations respectively for the bulk and the boundary dynamics, and provides an expression for the distribution of internal stresses. Our findings show among others that the mechanical changes occurring in the membrane internal structure may have an important effect on mass transport which may consequently exhibit a non-Fickian character. Moreover, the model is also capable of providing the mesoscopic details of the structure changes induced by diffusion. Scaling analysis leads to the emergence of several groups of physical parameters whose influence on mass transport is illustrated; and quantitative as well as qualitative agreements with sorption data (taken from literature) of Toluene in a PP/NBR membrane at different PP contents are shown. Unsteady mass fluxes are also calculated for permeation of PP/NBR to toluene, xylene and benzene and respective time lags are predicted.

Polytetrafluoroethylene content in standalone microporous layers: Tradeoff between membrane hydration and mass transport losses in polymer electrolyte membrane fuel cells

Fuel cell performance testing and in operando synchrotron radiography were used to investigate the effect of polytetrafluoroethylene (PTFE) in standalone microporous layers (MPLs) on mass transport and membrane hydration. Two standalone MPLs with 20 wt% and 30 wt% PTFE were fabricated and tested with inlet gas relative humidity (RH) between 50 and 100%. This study demonstrates that the performance of a fuel cell using a standalone MPL with 30 wt% PTFE decreases when the RH of the inlet gases is increased from 50% to 100%, whereas the performance of a fuel cell using a standalone MPL with 20 wt% PTFE remains stable over the same relative humidity range. Furthermore, this study demonstrates that a tradeoff between membrane hydration and mass transport losses must be considered when increasing the PTFE content within the MPL. Higher PTFE content led to greater liquid water accumulation adjacent to the catalyst layer. The greater liquid water accumulation adjacent to the catalyst layer improved membrane hydration and proton conductivity but also led to an increase in mass transport resistance. Standalone MPLs with higher PTFE content did not support high current density operation because the mass transport limitations outweighed the benefits of improved membrane hydration.

Relationship between amorphous solid dispersion in vivo absorption and in vitro dissolution: phase behavior during dissolution, speciation, and membrane mass transport

Enzalutamide is a fast crystallizing, hydrophobic compound that has solubility limited absorption in vivo. Given the low aqueous solubility of this compound, it was of interest to evaluate amorphous formulations in vitro and in vivo. Amorphous solid dispersions (ASD) of enzalutamide were prepared with the hydrophilic polymers, hydroxypropyl methylcellulose acetate succinate (HPMCAS) and copovidone (PVPVA). A side-by-side diffusion cell was developed as an in vitro characterization tool to discriminate enzalutamide ASDs based upon the solute thermodynamic activity achieved during dissolution and its impact on the subsequent membrane transport rates, phase behavior, and drug speciation. The same formulations were then tested in vivo in rats using oral dosing of ASD suspensions. Different levels of plasma exposure were observed between the ASDs, which could be correlated to the phase behaviors of the ASDs following dissolution. Unsurprisingly, ASDs that underwent crystallization show lower plasma exposures. However, differences were also observed between ASDs that dissolved to form nanosized amorphous drug aggregates versus those that dissolved to yield only supersaturated solutions, with the former outperforming the latter in terms of the plasma exposure. These observations highlight the importance of thoroughly understanding the phase behavior of an amorphous formulation following dissolution and the need to discriminate between different types of precipitation, specifically crystallization versus glass liquid phase separation to form nanosized amorphous aggregates.

Influence of composition and concentration of saline water on cation exchange behavior in forward osmosis desalination

Thin film composite (TFC) membranes are the gold standard for the application of forward osmosis (FO) in seawater desalination and wastewater treatment. However, bidirectional mass transport phenomena in this process still hinder its wider application. A deeper understanding of ion transport behavior in various solution conditions is critical for the fabrication of FO membrane and future development of FO process. In this work, we systematically investigated the influences of solution chemistry on ion mass transport in TFC FO membranes. Our results suggested that the mass transports of cations were much larger than those of anions in FO processes, and monovalent cations with smaller hydrated radius could induce greater cation exchange than divalent cations. Though anions did not participate in the cation exchange processes directly, cations paired with nitrate could transport through the TFC membrane more readily than those paired with chloride or sulfate. Additionally, a set of experiments with series solution concentrations confirmed the existence of cation transport bottleneck for one TFC FO membrane. We found that the cation transport capacity of TFC membranes was mainly determined by the concentration of feed solution and the generation of cation exchange behavior was independent of water transport. Engineering implications of our findings for FO application were also discussed.

Amplified CPEs enhancement of chorioamnion membrane mass transport by encapsulation in nano-sized PLGA particles

Chemical penetration enhancers (CPEs) have long been used for mass transport enhancement across membranes. Many CPEs are used in a solution or gel and could be a solvent. The use of CPEs is mainly limited due to their toxicity/irritation levels. This study presents the evaluation of encapsulated CPEs in nano-sized polymeric particles on the chorioamnion (CA) membrane mass transport. CPEs’ mass encapsulated in nanoparticles was decreased by 10,000-fold. Interestingly, this approach resulted in a 6-fold increase in mass transport across the CA. This approach may also be used with other CPEs' base applications necessitating lower CPE concentration. Applying Ultrasound (US) has shown to increase the release rate of and also the mass transport across the CA membrane. It is proposed that encapsulated CPEs penetrate into the CA membrane thus prolonging their exposure, possibly extending their penetration into the CA membrane, while insonation also deepens their penetration into the CA membrane.

Species Uptake and Mass Transport in Membranes for Vanadium Redox Flow Batteries

In this contribution, we provide a synthesis of results to date describing uptake and mass transport of water, vanadium species and protons in Nafion membranes for use as separators in VRFBs. Resistance issues as well as species cross-over are important contributors to performance loss in VRFBs. After a brief discussion of our state-of-the-art cell performance, we consider the uptake and transport of various species through a number of membrane materials. We draw together numerous previous studies and augment them with new data to provide a summary of our present state of understanding of the experimental facts regarding membrane behavior.