Single and dual-solute transport in quaternary ammonium-functionalized anion exchange membranes: Isolating the impact of water volume fraction

In this review, previous researches related to water transport in PEMFC are comprehensively reviewed. The state and transport mechanism of water in different components are elaborated in detail. The water transport in anion exchange membrane fuel cell (AEMFC) and the novel bipolar membrane fuel cell (BPMFC) are also discussed based on the cases in PEMFC. The water transport mechanism in AEMFC and BPMFC are similar to that of PEMFC, while the water management would be much difficult since the limitation properties of anion exchange membrane. In another hand, the difference between electrode reactions and membrane interface reactions for BPMFC make the transport of water more complicated. Fully understand the water transport in membrane electrode assembly is important in the develop of novel self-humidification fuel cells. As a result, the attractive cell configuration of BPMFC would make it a potential candidate for smart self-humidification fuel cells.

![Figure][1] J. Patrick Kampf Torrey Pines Institute for Molecular Studies, San Diego, California ![Figure][1] Alan M. Kleinfeld Torrey Pines Institute for Molecular Studies, San Diego, California akleinfeld{at}tpims.org The mechanism of free fatty acid (FFA)

We have previously introduced an optical technique for recording the transport of fluorescent substrates by single membrane transporters. Referred to as optical single-transporter recording (OSTR), the method was restricted to cases in which membrane transporters occurred at extremely small densities, namely at one or a few transporters per cell. Here we describe the extension of OSCR from whole cells harbouring a small number of transporters to small membrane patches containing transporters at normal densities. A technique was developed for firmly attaching cells to isoporous filters, i.e. very thin transparent sheets containing homogeneous populations of cylindrical pores. The flux of fluorescent transport substrates across the tiny membrane pieces spanning the filter pores was measured by scanning microphotolysis, a combination of fluorescence microphotolysis and confocal laser scanning microscopy. The technique was tested by attaching erythrocytes to filters containing pores of 1.2, 2.0 or 3.0 microns diameter. After treating filter-attached erythrocyte membranes with streptolysin O, the transport of the fluorescent protein B-phycoerythrin through single streptolysin O pores was observed. From the flux data the functional radius of the streptolysin O pore was derived to be 12.5 +/- 0.9 nm, in very good agreement with previous electron microscopic estimates. The new technique features a number of unique properties: (i) the size of the membrane patch can be chosen within wide limits according to transporter density, (ii) transport can be recorded on many membrane patches in parallel, (iii) both influx and efflux may be analysed employing either photobleaching of fluorescent or photorelease of caged nonfluorescent substrates, (iv) two or more transport substrates may be monitored simultaneously. The new technique can be used, for instance, for analysing the activity of protein/particle pumps, a membrane transport domain not previously accessible to a single-transporter analysis.

Sizes and dynamics of single membrane transporters on single living cells, Pseudomonas aeruginosa, were directly measured showing transported substrates up to 80 nm in diameter, which is one order magnitude larger than the reported exclusion limit of the outer membrane, over times of seconds to hours. The uptake and efflux dynamics depend on size and concentration of substrates, incubation time, and mutants. The strikingly active efflux of substrates by mutants devoid of pump proteins was observed, suggesting that substrates trigger the assembly of a new extrusive system. This new observation is in excellent agreement with the recent results of genome project analysis showing that P. aeruginosa encode more than a dozen unidentified efflux pump proteins. An extraordinary heterogeneity of size and dynamics of membrane transport mechanisms was observed, demonstrating real-time transformation of membrane permeability and an active extrusion system. This constitutes the first direct observation of living membrane transportation triggered by substrates with a variety of sizes at the single membrane pump level and opens up the new possibility of direct measurements of membrane active extrusion mechanisms for advancing the understanding of multidrug resistance and living molecular pumps.

Membrane transport system modeled by network thermodynamics

Anion exchange membrane (AEM) fuel cells are emerging energy conversion technologies. A significant challenge in these devices lies in the core component, the AEM, which must possess high ionic conductivity to minimize Ohmic losses and exhibit chemical stability in highly basic conditions. A significant amount of effort has been expended to develop new anion exchange polymers with enhanced transport functionality. However, understanding of how anion transport in these polymers is related to hydration and nano-morphology is far from adequate. In this work, we report a systematic study on PAP-TP-85, an AEM with promising cell performance.1 A commercial AEM (Fuma FAA3) is used for comparison in this study. Membrane water uptake and anion conductivity in liquid and vapor as well as the impact of various anion forms on these properties are investigated. Small-angle X-ray scattering (SAXS) is used to probe hydrated AEM nanostructure, which is correlated to the membrane uptake and transport properties. Our results show that these AEMs lack a phase-separated nanostructure, regardless of their counter-anion form and hydration level. This is associated with their weak electrolytes behavior, which also explains their lower ion conductivity values (compared to proton exchange membranes), despite having higher water content and greater ion exchange capacity (IEC). Water content plays a more significant role than the temperature in controlling the anion conductivity of these weak electrolytes in water vapor. Comparing the water content in liquid vs. saturated vapor, both AEMs show Schroeder’s paradox regardless of counter-anion form. This study also demonstrates the importance of hydration level and ion concentration for anion transport in amorphous AEMs and provides further understanding into their parameters governing their structure-transport relationship and sheds light into designing AEMs with improved performance. Wang, J.; Zhao, Y.; Setzler, B. P.; Rojas-Carbonell, S.; Ben Yehuda, C.; Amel, A.; Page, M.; Wang, L.; Hu, K.; Shi, L.; Gottesfeld, S.; Xu, B.; Yan, Y., Poly(aryl piperidinium) membranes and ionomers for hydroxide exchange membrane fuel cells. Nature Energy 2019.

Salinity gradient energy technologies, such as reverse electrodialysis (RED) and capacitive mixing based on Donnan potential (Capmix CDP), could help address the global need for noncarbon-based energy. Anion exchange membranes (AEMs) are a key component in these systems, and improved AEMs are needed in order to optimize and extend salinity gradient energy technologies. We measured ionic resistance and permselectivity properties of quaternary ammonium-functionalized AEMs based on poly(sulfone) and poly(phenylene oxide) polymer backbones and developed structure-property relationships between the transport properties and the water content and fixed charge concentration of the membranes. Ion transport and ion exclusion properties depend on the volume fraction of water in the polymer membrane, and the chemical nature of the polymer itself can influence fine-tuning of the transport properties to obtain membranes with other useful properties, such as chemical and dimensional stability. The ionic resistance of the AEMs considered in this study decreased by more than 3 orders of magnitude (i.e., from 3900 to 1.6 Ω m) and the permselectivity decreased by 6% (i.e., from 0.91 to 0.85) as the volume fraction of water in the polymer was varied by a factor of 3.8 (i.e., from 0.1 to 0.38). Water content was used to rationalize a tradeoff relationship between the permselectivity and ionic resistance of these AEMs whereby polymers with higher water content tend to have lower ionic resistance and lower permselectivity. The correlation of ion transport properties with water volume fraction and fixed charge concentration is discussed with emphasis on the importance of considering water volume fraction when interpreting ion transport data.

Understanding the volume fraction of water-oil-gas three-phase flow is of significant importance in oil and gas industry. The current research attempts to indicate the ability of adaptive network-based fuzzy inference system (ANFIS) to forecast the volume fractions in a water-oil-gas three-phase flow system. The current investigation devotes to measure the volume fractions in the stratified three-phase flow, on the basis of a dual-energy metering system consisting of the 152Eu and 137Cs and one NaI detector using ANFIS. The summation of volume fractions is equal to 100% and is also a constant, and this is enough for the ANFIS just to forecast two volume fractions. In the paper, three ANFIS models are employed. The first network is applied to forecast the oil and water volume fractions. The next to forecast the water and gas volume fractions, and the last to forecast the gas and oil volume fractions. For the next step, ANFIS networks are trained based on numerical simulation data from MCNP-X code. The accuracy of the nets is evaluated through the calculation of average testing error. The average errors are then compared. The model in which predictions has the most consistency with the numerical simulation results is selected as the most accurate predictor model. Based on the results, the best ANFIS net forecasts the water and gas volume fractions with the mean error of less than 0.8%. The proposed methodology indicates that ANFIS can precisely forecast the volume fractions in a water-oil-gas three-phase flow system.

Electrospinning is a promising technique for polymeric ion exchange membrane (IEM) fabrication because it enables good control of microstructural and morphological properties. Recent work1 developed a fiber network model to predict carbonate-free electrospun IEM hydroxide conductivity based on a simulation of randomly oriented conducting fibers and a subsequent application of Kirchoff’s circuit laws to solve the equivalent resistor network. A promising application for electrospun membranes is in anion exchange membrane (AEM) fuel cells. By controlling the microstructure and morphology via electrospinning, electrospun AEMs could exhibit improved transport properties compared to AEMs fabricated using other techniques. The transport properties of these other classes of AEMs, referred to as “bulk membranes”, have also been investigated2, including the effects of carbon dioxide absorption3–5 which is a problem in AEM fuel cell operation. The missing link therefore, is to characterize the effects of carbon dioxide on electrospun AEMs. The bulk membrane models2–5 describe ion transport in a water-saturated bulk material. On the other hand, the fiber network model describes transport in layers of randomly oriented saturated (and therefore conducting) fibers imbedded in a non-conducting hydrophobic matrix. The mapping procedure is a means of converting the layered fiber configuration into an equivalent bulk configuration based on maintaining the volume fraction of water in the process. Scaling laws are given for mapping the fiber network parameters to those of an equivalent bulk membrane. The equivalent bulk membrane yields the same conductivity as the fibrous membrane for the carbonate-free case, and is then used to assess the effects of CO­2 (i.e. carbonates) following the established procedure5. Acknowledgements Financial support from the Army Research Office (award number W911NF-14-1-0298) is gratefully acknowledged. The authors would also like to acknowledge the support of and discussions with Dr. Cynthia Lundgren and Dr. Deryn Chu of the U.S. Army Research Laboratory. References DeGostin, M. B., Peracchio, A. A., Myles, T. D., Cassenti, B. N. & Chiu, W. K. S. Charge transport in the electrospun nanofiber composite membrane’s three-dimensional fibrous structure. J. Power Sources 307, 538–551 (2016).Grew, K. N. & Chiu, W. K. S. A Dusty Fluid Model for Predicting Hydroxyl Anion Conductivity in Alkaline Anion Exchange Membranes. J. Electrochem. Soc. 157, B327 (2010).Myles, T. D., Grew, K. N., Peracchio, A. A. & Chiu, W. K. S. Transient ion exchange of anion exchange membranes exposed to carbon dioxide. J. Power Sources 296, 225–236 (2015).Grew, K. N., Ren, X. & Chu, D. Effects of temperature and carbon dioxide on anion exchange membrane conductivity. Electrochem. Solid-State Lett. 14, B127–B131 (2011).Wrubel, J. A. et al. Anion Exchange Membrane Ionic Conductivity in the Presence of Carbon Dioxide under Fuel Cell Operating Conditions. J. Electrochem. Soc. 164, F1063–F1073 (2017).

Transport of a redox active molecule through the separator in a flow battery is an important source of inefficiency and electrolyte imbalance. This transport occurs by diffusion, migration, and convection, with driving forces that change with state of charge. Typically, only diffusive permeability and conductivity are measured to characterize transport in membranes, because they are straightforward experiments. The Nernst-Planck-Einstein equation for transport in electrolyte solutions suggests that this may be sufficient because the transference number of an ion can be calculated from its diffusion coefficient and conductivity.We measured transport of four vanadium cations through Nafion (cation exchange), Fumasep FAPQ-330 (anion exchange), and polybenzimidazole as a function of current density. The measurements were made using a cell with three membranes and four flow compartments designed to collect vanadium passing through sample separators and into receiver compartments. These experiments were augmented with independent sorption and conductivity measurements to assist interpretation in the context of Nernst-Planck-Einstein.The figure shows the sum of the partial current densities of V2+ and V3+ versus current density for the three membranes. Partial currents at zero total current are proportional to diffusive permeability and slopes at currents greater than zero approximate transference numbers. Transport of vanadium cations is hindered by an anion exchange membrane more than a cation exchange membranes as expected. The gaps in transport observed at zero current widen as current increases. Further data, not shown here, taken with VO2+ and VO2 + ions on the same membranes indicate that transport is strongly influenced by the nature of the cation. All experimental results are compared to predictions from Nernst-Planck-Einstein.Acknowledgements This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. Figure 1

The capability of radial basis function to forecast the volume fractions of the annular three-phase flow of gas-oil-water

Erythrocytes are endowed with functional entities that support either cellular functions or the systemic delivery of O2 from lung to tissue and removal of CO2 from tissue to lung. The latter depend largely on the blood's circulatory capacity. They are associated, respectively, with cytosolic haemoglobin and the major membrane polypeptide band 3 (anion exchanger 1, AE1). As a membrane transporter, AE1 mediates Cl-/HCO3- exchange, thus enhancing the blood capacity for carrying CO2 and for acid-base homeostasis. By interacting with lipids and proteins, the multifunctional AE1 tethers the membrane cytoskeleton multiprotein complex to the membrane and confers upon erythrocytes both mechanical and viscoelastic properties. Those in turn allow cells to withstand the shear forces of circulation and squeeze through capillaries. Most other major membrane transporters are apparently essential for maintaining a stable erythrocyte cell shape and flexibility via a functional membrane cytoskeleton. These include the membrane transporters of glucose, nucleoside and purine for fueling the Na/K and Ca pumps via ATP production, and of amino acid and oxidized glutathione transport for maintaining the cell redox status. All membrane transporters detected in mature erythrocytes are synthesized early in erythrocyte differentiation. Their contribution to erythrocyte and to systemic physiology is presently being re-assessed by targeted gene disruption and replacement. For example, organisms with reduced or disrupted AE1 gene expression showed major erythrocyte instabilities and defective anion exchange capacity and acidosis, but remain alive.

Hydroxide transport and chemical degradation in anion exchange membranes: a combined reactive and non-reactive molecular simulation study

In this paper, the volume fractions in the annular three-phase flow are measured based on a dual energy metering system consisting of $$^{152}$$ Eu and $$^{137}$$ Cs and one NaI detector, and then modeled by fuzzy logic. Since the summation of volume fractions are constant (equal to 100%), therefore the fuzzy network must predict only two volume fractions. In this study, three fuzzy networks are applied. The first network is utilized to predict the gas and water volume fractions. The next one is applied to predict the gas and oil volume fractions, and the last one to predict the water and oil volume fractions. In the next step, the numerically obtained data from MCNP-X code, must be imported to the fuzzy models. Then, the average errors of these three networks are computed and compared. The network which has the least error is selected as the best predictor model. According to the modeling results, the best fuzzy network, predicts the gas and water volume fractions with the mean relative error of less than 0.3%, which shows that the fuzzy logic can predict the results precisely.

Host-guest interaction induced ion channels for accelerated OH− transport in anion exchange membranes