Electro-osmotic Drag Coefficient Research Articles

Proton Transport, Electroosmotic Drag and Oxygen Permeation in Polytetrafluoroethylene Reinforced Ionomer Membranes and Their Effects on Fuel Cell Performance

Abstract With the increasing need for high power density of proton exchange membrane fuel cells, new composite membranes have been explored for superior proton transport and gas impermeability. These membranes’ physicochemical properties usually deviate from existing empirical formulas, which are poorly understood, especially when mechanical deformation occurs. This poor understanding hinders development of novelty membranes and their fuel cell applications. Here, using polytetrafluoroethylene reinforced ionomer membrane as an example, we conducted extensive water absorption experiments to determine hydration levels at different water activities. Molecular dynamics simulations and electrochemical impedance spectroscopy were used to investigate the impacts of hydration level, external electric field strength, and tensile deformation on proton transport and electroosmotic drag coefficient, as well as the impact of hydration level and free volume ratio on oxygen permeability. We proposed mathematical correlations for these impacts and incorporated them into a single-cell voltage model to analyze their effects on fuel cell performance. Results show that an increase in the electric field strength alters the proton transport pattern, but has minimal impact on the electro-osmosis coefficient. The oxygen permeability coefficient of a deformed membrane with a free volume ratio of 28.57% is more than two orders of magnitude higher than that of a non-deformed membrane. The electro-osmatic drag coefficient imposes a larger influence on fuel cell performance than oxygen permeability

Tuning and Coupling Irreversible Electroosmotic Water Flow in Ionic Diodes: Methylation of an Intrinsically Microporous Polyamine (PIM-EA-TB).

Molecularly rigid polymers with internal charges (positive charges induced by amine methylation) allow electroosmotic water flow to be tuned by adjusting the charge density (the degree of methylation). Here, a microporous polyamine (PIM-EA-TB) is methylated to give a molecularly rigid anion conductor. The electroosmotic drag coefficient (the number of water molecules transported per anion) is shown to increase with a lower degree of methylation. Net water transport (without charge flow) in a coupled anionic diode circuit is demonstrated based on combining low and high electroosmotic drag coefficient materials. The AC-electricity-driven net process offers water transport (or transport of other neutral species, e.g., drugs) with net zero ion transport and without driver electrode side reactions.

Electro-osmotic drag coefficient of Nafion membrane with low water Content for Proton exchange membrane fuel cells

Proton exchange membrane fuel cells (PEMFCs) are recognized as promising clean power sources in automotive applications. However, there are still confusions and contradictions about the electro-osmotic drag (EOD) coefficient of Nafion membrane with low water content. In this work, the molecular dynamics (MD) simulation is utilized to predict the EOD coefficient in dehydrated Nafion membranes with low water content λ=1, 1.5 and 2 at 350 K for fuel cells under low relative humidity. Micro-structurally, it is found that when the dehydrated Nafion membrane gradually becomes more hydrated, or λ increases from 1 to 2, more water molecules are bound to Nafion side chains and larger atom clouds are formed. In order to predict the EOD coefficient, mass flows of hydronium ions and water molecules are analyzed. The hydronium ions flow much faster than water molecules in the direction of electric field. Consequently, based on the mass flow values, for the Nafion membrane with low water content λ=1, 1.5, and 2, values of the EOD coefficients are 0.098, 0.149 and 0.255, respectively. It is further discovered that the EOD coefficient for Nafion membrane with low water content exactly agree with the linear model nd=2.5λ/22.

Dynamic Water Transport through the Perfluorinated Sulfonic-Acid Membrane

IntroductionThe proton exchange membrane (PEM) is indispensable material for proton transport in PEFC. Since RH affects the effective proton conductivity and the effective oxygen diffusivity through the catalyst layer as well as the proton conductivity, the electroosmotic drag coefficient, the effective diffusivity of water, and the gas permeances of PEM, water behavior which determines relative humidity is most important.To estimate the PEFC performance over time, the dynamic change in transport properties of PEM should be reproduced over full range of operating temperature and moisture content. Though water diffusion in Nafion™ membrane was extensively investigated [1, 2], the transport properties have not been formulated as the function of both temperature and moisture content. In this study, the effective water diffusivity and the skin layer water transfer coefficient were formulated from the experimental results measured by the permeation method and the sorption/desorption method.Experimental–Permeation experimentsA Nafion™ membrane, NR-212, N115 or N117 with different thickness (at relative humidity, RH of 50 %), 51 μm, 127 μm, and 183 μm, respectively, was set in a Japan Automobile Research Institute (JARI) standard cell whose active area was reduced to 2.0 cm×2.0 cm. The cell was placed in the constant temperature and humidity oven (ESPEC, LHL-113). Nitrogen was supplied to both sides of the cell at 300 cm3/min (20 °C, 1 atm). The relative humidity of the supplied gas was controlled by the bubbler temperature. The water vapor flowing out of the cell was collected with an ice-cooled trap to estimate the water permeation flux of the membrane.–Sorption/desorption experimentsThe membrane was placed in a desiccator in which RH was controlled by saturated salt solution method at room temperature (22 °C). The weight of the membrane was recorded constantly. After reaching equilibrium, the membrane was placed in another RH condition and weighed.Results and discussionThe moisture content of the membrane, λ was calculated by a GAB sorption equation in which paraments were fit using reported water equilibrium experimental data [3, 4, 5, 6] as shown in Fig. 1. Schematic diagram of permeation mechanism is shown in Fig. 2. Water permeation flux through the membrane, N A (M) is expressed as follows: N A (M)=c (M) ρ (M) (λ -m -λm )/(1/k A++1/k A-+δ (M)/D eA (M)) (1)where c (M) is the ion-exchange capacity [mol/kg], ρ (M) is the density of dry membrane [kg/m3], λ is the moisture content, k A is the skin layer mass transfer coefficient [m/s], δ (M) is the membrane thickness [m] and D eA (M) is the effective diffusivity [m2/s]. The subscript A means absorbed water, m is the surface of the membrane, - is the supply side and + is the permeate side. Total resistances calculated by eq. (1) were plotted against the membrane thickness. D eA (M) and k A calculated from the trendlines are shown in Figs. 3 and 4, and Arrhenius plots of D eA (M) are shown in Fig. 5.Skin layer mass transfer coefficient, k A can be obtained directly from the sorption/desorption experiments at low temperature. k A obtained from the permeation and sorption/desorption experiments are summarized in Fig. 6 and they are located on an identical line. The transport properties at λ= 5 are expressed as follows as an example: D eA (M) = 3.35×10–5 m2 s–1 exp(–3760 K/T) k A = 1.27×105 ms–1 exp(–8330 K/T)Since these transport properties depend on the moisture content, the desorption is faster than sorption and vice versa even at completely same range of moisture content. This is because the moisture content in the skin layer is always different during sorption and desorption even with the same moisture content variation range.ConclusionsFrom the permeation experiments and the sorption/desorption experiments, the transport properties over wide range of temperature and moisture content of the perfluorinated sulfonic-acid membrane were formulated. Considering the change in k A and D eA depending on the moisture content, the sorption and desorption rate are unequal even in identical RH range.AcknowledgementThis work was supported by the FC Platform Program: Development of design-for-purpose numerical simulators for attaining long life and high-performance project (FY 2020–FY 2022) conducted by the New Energy and Industrial Technology Development Organization (NEDO), Japan.

Dynamic Water Transport through the Perfluorinated Sulfonic-Acid Membrane

Proton exchange membrane (PEM) is essential material for the proton transport in a polymer electrolyte fuel cell (PEFC). Since relative humidity (RH) in a cell affects the effective proton conductivity and the effective oxygen diffusivity through the catalyst layer as well as the proton conductivity, the electroosmotic drag coefficient, the effective diffusivity of water, and the gas permeances of the PEM, water behavior which determines relative humidity is important. To estimate the PEFC performance over time, the dynamic change in the moisture content of the PEM is needed to know. In this study, the PEM is considered to consist of a bulk layer and skin layers on both sides of the bulk layer. The bulk layer effective diffusion coefficient and the skin layer water transfer coefficient were formulated from the experimental results measured by the steady-state permeation method and the unsteady-state sorption and desorption method.

Electro-osmotic Drag and Thermodynamic Properties of Water in Hydrated Nafion Membranes from Molecular Dynamics.

One of the important parameters in water management of proton exchange membranes is the electro-osmotic drag (EOD) coefficient of water. The value of the EOD coefficient is difficult to justify, and available literature data on this for Nafion membranes show scattering from in experiments and simulations. Here, we use a classical all-atom model to compute the EOD coefficient and thermodynamic properties of water from molecular dynamics simulations for temperatures between 330 and 420 K, and for different water contents between λ = 5 and λ = 20. λ is the ratio between the moles of water molecules to the moles of sulfonic acid sites. This classical model does not capture the Grotthuss mechanism; however, it is shown that it can predict the EOD coefficient within the range of experimental values for λ = 5 where the vehicular mechanism dominates proton transfer. For λ > 5, the Grotthuss mechanism becomes dominant. To obtain the EOD coefficient, average velocities of water and ions are computed by imposing different electric fields to the system. Our results show that the velocities of water and hydronium scale linearly with the electric field, resulting in a constant ratio of ca. 0.4 within the error bars. We find that the EOD coefficient of water linearly increases from 2 at λ = 5 to 8 at λ = 20 and the results are not sensitive to temperature. The EOD coefficient at λ = 5 is within the range of experimental values, confirming that the model can capture the vehicular transport of protons well. At λ = 20, due to the absence of proton hopping in the model, the EOD coefficient is overestimated by a factor of 3 compared to experimental values. To analyze the interactions between water and Nafion, the partial molar enthalpies and partial molar volumes of water are computed from molecular dynamics simulations. At different water uptakes, multiple linear regression is used on raw simulation data within a narrow composition range of water inside the Nafion membrane. The partial molar volumes and partial molar excess enthalpies of water asymptotically approach the molar volumes and molar excess enthalpies of pure water for water uptakes above 5. This confirms the model can capture the bulklike behavior of water in the Nafion at high water uptakes.

Electro-Osmotic Flow of Water–Methanol Mixtures Through Nafion Membranes Revisited: Composition and Temperature Dependence

The electro-osmotic drag coefficient of water and methanol mixtures through Nafion 117 membranes was measured as a function of the composition at several temperatures between 25 and 60°C using a two-compartment capillary cell with Ag/AgCl electrodes. The electro-osmotic water drag in HCl aqueous solutions is higher than that reported in measurements where the membrane is in contact with pure water; hence, all the reported results were performed at the same acid concentration. It was found that the drag coefficient for pure methanol is about 40% higher than that for water at all the temperatures studied as a consequence of the expanded nanostructure of Nafion in methanol. The drag coefficients of the water–methanol mixtures exhibit a high non-linearity, which can be explained by considering the Nafion sorption in the binary solvent. The electro-osmotic flow in pure methanol is similar to that of 5 M methanol aqueous solutions, which opens the opportunity to use pure methanol in DMFCs. The methanol crossover due to permeability can be minimized. Controversial results with previous studies are also addressed.

Theoretical description and experimental characterization of water content distributions in hydrogen PEM fuel cells

An analytical solution of water mass balance equation was obtained considering diffusion and electroosmotic drag fluxes under non steady state regimes. The theoretical predicted profiles in a membrane electrode assembly were compared experimentally in a single polymer electrolyte hydrogen/oxygen fuel cell changing operating conditions such as, flow velocity, current density and temperature. The specific anodic and cathodic areas were calculated using the carbon monoxide anodic stripping method (ca. 17000 cm2). The electroosmotic drag coefficient was determined with electrochemical isopiestic methods showing temperature invariance, i.e. 2.3 between 313 and 353 K for water contents less than 5, but when reaching 20 it increased to 3.2.Polarization curves were attained galvanodynamically in a single fuel cell showing a strong dependence on water residence (performing with distinct water amounts and conditions). Internal resistance (0.59 to 0.24 Ω cm−2) and open circuit potentials (0.90 to 0.38 V) were affected by water reduction (from 0.8 to 0.4 units). Continuous water recycling of the fuel cell was adopted to preserve the shape and characteristic parameters of the fuel cell under full operation with excellent results.

Effective electroosmotic transport of water in an intrinsically microporous polyamine (PIM-EA-TB)

Tertiary-amine-based Polymers of Intrinsic Microporosity (PIMs) provide a class of highly porous molecularly rigid materials for the electrochemical transport of both ionic and neutral species. Here, the transport of water molecules together with chloride anions (i.e. the electroosmotic drag coefficient) is studied for the intrinsically microporous polyamine PIM-EA-TB immersed in aqueous 0.01 M NaCl (i) when protonated for pH < 4 or (ii) when not protonated for pH > 4. Preliminary data suggest that in both cases a high electroosmotic drag coefficient is observed based on direct H2O transport into a D2O-filled compartment (quantified by 1H-NMR). For PIM-EA-TB there is a strong pH dependence with a higher electroosmotic drag coefficient in less acidic solutions (going from approx. 400 H2O per anion at pH 3 to approx. 4000 H2O per anion at pH 7), although the underlying absolute rate of water transport at a fixed voltage of −1 V appears to be essentially pH independent. Water transport through the PIM-EA-TB microchannels is rationalised based on the relative populations of chloride anions and of water in the micropores (essentially a ‘piston’ mechanism).

Modelling the Proton-Conductive Membrane in Practical Polymer Electrolyte Membrane Fuel Cell (PEMFC) Simulation: A Review.

Theoretical models used to describe the proton-conductive membrane in polymer electrolyte membrane fuel cells (PEMFCs) are reviewed, within the specific context of practical, physicochemical simulations of PEMFC device-scale performance and macroscopically observable behaviour. Reported models and their parameterisation (especially for Nafion 1100 materials) are compiled into a single source with consistent notation. Detailed attention is given to the Springer–Zawodzinski–Gottesfeld, Weber–Newman, and “binary friction model” methods of coupling proton transport with water uptake and diffusive water transport; alongside, data are compiled for the corresponding parameterisation of proton conductivity, water sorption isotherm, water diffusion coefficient, and electroosmotic drag coefficient. Subsequent sections address the formulation and parameterisation of models incorporating interfacial transport resistances, hydraulic transport of water, swelling and mechanical properties, transient and non-isothermal phenomena, and transport of dilute gases and other contaminants. Lastly, a section is dedicated to the formulation of models predicting the rate of membrane degradation and its influence on PEMFC behaviour.

On the Nature of Electro-Osmotic Drag

Electro-osmotic drag (EOD) is usually thought of as a transport mechanism of water inside and through the polymer electrolyte membrane (PEM) in electrochemical devices. However, it has already been shown that the transport of dissolved water in the PEM occurs exclusively via diffusion, provided that the EOD coefficient nd is constant. Consequently, EOD is not a water transport mechanism inside the electrolyte membrane, and this means that its nature is not yet understood. This work proposes a theory that suggests that the root of the EOD is located in the catalyst layers of the electrochemical device where the electric current is generated, and consequently could be linked to one or more of the elementary reaction steps. It is therefore also conceivable that EOD exists at one electrode in an electrochemical device, but not in the other. Moreover, the EOD coefficient nd may depend on the current density as well as the oxidization level of the catalyst. The last consequence, if EOD is linked to an elementary reactions step, it could also be part of the rate-determining elementary step, and this could open pathways to increase the reaction kinetics by finding ways of enhancing the water/hydronium ion transport out of or into the polymer phase.

Water transport according to temperature and current in PEM water electrolyzer

Recently, various studies have been conducted on hydrogen energy as a means of replacing conventional fuels. Polymer electrolyte membrane water electrolyzers (PEMWEs) are being studied as a means of producing hydrogen for renewable energy. The PEMWE can be operated over a wider range than other types of water electrolyzers and can be connected to a renewable energy source, such as solar or wind. However, further studies are required because the water accompanying the hydrogen in the cathode presents a problem regarding hydrogen purity and storage. The phenomenon of water transport which is occurred on the PEMWE is analyzed by electro-osmotic drag and diffusion in the membrane. Electro-osmotic drag coefficients which are calculated by mass flow rate of discharged water with hydrogen are compared to the results of previous studies. The results of Electro-osmotic drag coefficient are different from previous studies at each operating condition. This difference is considered to be caused by the capacity of PEMWE such as active area and the number of cell.

PEMFCs multiscale modeling: Determination of overpotential with description of electron transfer in cathodic EDL at different O2 concentrations

The effect of the formation of the electrical double layer (EDL) as a function of O2 concentrations in Pt/H2O interface in a proton-exchange membrane fuel cell (PEMFC) is analyzed in this work. The overpotential associated with the existence of the EDL is calculated at typical fuel cell O2 concentrations by using molecular dynamics (MD). The calculated overpotentials are in the range of −8.865 × 10−6 – 0.0086V for oxygen molar fractions in the cathode between 0 and 0.1273. These overpotential values are included in the ORR kinetic equations of a multiscale model for PEMFCs developed in a previous work to estimate the global electroosmotic drag coefficient and compare it with experimental data from literature. It was found an improvement of the accuracy of the model, at air fed hydration levels of 50% and 70% in the cathode, if the overpotential calculation is carried out considering the electron transfer in the entire interface, not only in the outer Helmholtz plane (OHP) thus, modifying the Frumkin effect calculation.

Experimental parameter uncertainty in proton exchange membrane fuel cell modeling. Part I: Scatter in material parameterization

Ever since modeling has become a mature part of proton exchange membrane fuel cell (PEMFC) research and development, it has been plagued by significant uncertainty lying in the detailed knowledge of material properties required. Experimental data published on several transport coefficients are scattered over orders of magnitude, even for the most extensively studied materials such as Nafion membranes, for instance. For PEMFC performance models to become predictive, high-quality input data is essential. In this bipartite paper series, we determine the most critical transport parameters for which accurate experimental characterization is required in order to enable performance prediction with sufficient confidence from small to large current densities. In the first part, a macro-homogeneous two-phase membrane-electrode assembly model is furnished with a comprehensive set of material parameterizations from the experimental and modeling literature. The computational model is applied to demonstrate the large spread in performance prediction resulting from experimentally measured or validated material parameterizations alone. The result of this is a ranking list of material properties, sorted by induced spread in the fuel cell performance curve. The three most influential parameters in this list stem from membrane properties: The Fickean diffusivity of dissolved water, the protonic conductivity and the electro-osmotic drag coefficient.

Measuring electro-osmotic drag coefficients in PFSA membranes without any diffusion assumption

Absrtract An original set-up derived from the now standard hydrogen pump set-up is presented. The system enables isolation of the electro-osmosis as the lone macroscopic mass transport phenomenon, by minimizing or suppressing other external gradients, keeping the total pressure as the unique adjustment macroscopic parameter. The Electro-Osmotic Drag (EOD) coefficient was determined using 4 Nafion™ MEA (XL, 115, 117, 1110) as material, for temperature values in the 50–80 °C range, relative humidity (RH) values in the 30–90% range and current densities ranging from 1.2 up to 1000 mA cm−2. Pure Nafion™membranes exhibit the same behaviours with EOD coefficients between 0.8 and 1 and which do not depend on the current density or RH. Nafion™ XL based MEA show a singular behaviour with an EOD coefficient sometime as low as 0.4 and which depends on the RH.

Effects of water nanochannel diameter on proton transport in proton‐exchange membranes

ABSTRACTThe effects of water nanochannel diameter on proton transport pathways and properties have been studied using reactive molecular dynamics simulations. The proton distributions and diffusivities have been evaluated using the cylinder model of water domains at various diameters that is the most typical proposed morphological model in proton‐exchange membranes. The proton distributions are analyzed to clarify proton pathways by classifying the water channel into two regions in parallel: an inner channel (free water) and an outer channel (bound water). For all the water contents, the nonmonotonic trends that show a peak at a certain diameter are found to be observed in the proton diffusivity, which is dominated by the proton diffusivity in the free water region and has a strong correlation with the proton distribution that is controlled by the balance between the volume fraction of free water and the surface density of sulfonate groups. The electroosmotic drag coefficients are found to increase monotonically with increasing channel diameter as a result of the increase in the volume fraction of free water. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 867–878

Experimental parameter uncertainty in proton exchange membrane fuel cell modeling. Part II: Sensitivity analysis and importance ranking

Numerical modeling of proton exchange membrane fuel cells is at the verge of becoming predictive. A crucial requisite for this, though, is that material properties of the membrane-electrode assembly and their functional dependence on the conditions of operation are known with high precision. In this bipartite paper series we determine the most critical transport parameters for which accurate experimental characterization is required in order to enable the simulation of fuel cell operation with sufficient confidence from small to large current densities. In Part II, we employ the two-phase model developed in Part I to carry out extensive forward uncertainty propagation analyses. These include the study of local parameter sensitivity in the vicinity of a baseline parameter set, and a global sensitivity analysis in which a broad range of operating conditions and material properties is covered. A comprehensive ranking list of model parameters is presented, sorted by impact on predicted fuel cell properties such as the current-voltage characteristics and water balance. The top five in this list are, in this order: The membrane hydration isotherm, the electro-osmotic drag coefficient, the membrane thickness, the water diffusivity in the ionomer and its ionic conductivity.

Development of an Ion Exchange Membrane Characterization Protocol

The development of electrochemical devices for electric energy generation has been in constant growth in recent years because environmental challenges provide a driving force for many of today’s studies of electrochemical materials [1], among these are destacable: fuel cells, reverse electrodialysis cells, redox flow batteries, bio electrochemical systems (microbial fuel cells), etc. A key component in the behavior of all of them is the ion exchange membranes, which have high commercial value, so in the development of these technologies the need for local production is presented to make their application cheaper, so its complete characterization is required to determine if they are applicable in these technologies. This paper presents the experimental protocol developed and the results of its application to the membrane characterization of Nafion® 117, material of extended use and which its properties are widely known, in order to validate the methodology proposed with the existing literature . The characterization consists in a series of laboratory tests that deliver the most important properties of the membrane. Initially a pre-treatment of the membrane is carried out to bring it to a reproducible condition and then its properties are measured as conductivity both by a voltammetric method with controlled current and by electrochemical impedance; electroosmotic drag coefficient from measurement of potentials [2], [3], permeability to substances such as ethanol; and thermal stability. It is expected that the proposed protocol and the results obtained will be useful in the characterization of membranes, both protonic and anionic, that are currently being developed in multiple universities and educational centers around the world, as well as at the Universidad Nacional de Colombia - Sede Medellín, to make competitive these energy production technologies that use this type of solid electrolyte [4], [5].

Multiscale Modeling of a Proton Exchange Membrane Fuel Cell: Effect of Electric Double Layer in Cathodic Interface at Different O2 Concentrations

Mathematical models have played an important role for the understanding of proton exchange membrane fuel cells (PEMFCs ) (1), (2), (3), (4). Specifically, multiscale models attempt to take into account the physicochemical phenomena from atomistic to macroscopic scales to reliably reproduce the PEMFCs performance and reducing the number of parameters involved in equations. Through the last years multiscale models have employed different approaches: from non equilibrium thermodynamics, electrodynamics, and transport equations in general (5), (6), (7), (8), (9), (10), (11) to statistical mechanics using kinetic monte carlo method (MC) (11), or quantum physics using density functional theory (DFT) (7), (11), (12). In this work a molecular dynamics (MD) simulation of a platinum / oxygen / water interface is employed to describe the formation of the electric double layer (EDL) and also an electric overpotential associated with different operational concentrations of molecular oxygen. Those overpotentials are included in kinetic equations of the oxygen reduction reaction (ORR) mechanism for the cathode. Finally this ORR kinetics is included in a multiscale model of a PEMFC (13). Such multiscale model also utilizes other three approaches: DFT to calculate activation energies (14), a modified transport model for the membrane (15) and also it uses the transition state theory for the catalyst layer. It is expected that this EDL coupling will generate an improvement of the description capacity of the multiscale model in comparison with the experimental data of the electroosmotic drag coefficients vs current density for different relative humidities of the cathode.References D.M. Bernardi, M.W. Verbrugge. J. Electrochem. Soc. 139, 2477–2491 (1992).M. Yoneda, Y Tago, K Suzuki, M. Takimoto, S. Sukemura. ECS Trans. (1) 1149-1158 (2006)K. Takaya and T. Araki, ECS Trans., 75, 563–572 (2016).T. Berning, M. Odgaard, and S. K. Kær, J. Power Sources, 196, 6305–6317 (2011).54. B. Laoun, 14, 441–448 (2011).A. A. Franco, P. Schott, C. Jallut, and B. Maschke, J. Electrochem. Soc., 153, A1053 (2006).P. Rama et al., Energy and Fuels, 24, 3130–3143 (2010).L. F. L. Oliveira, C. Jallut, and A. A. Franco, Electrochim. Acta, 110, 363–374 (2013).S. Strahl, A. Husar, and A. A. Franco, Int. J. Hydrogen Energy, 39, 9752–9767 (2014).L. Chen et al., Int. J. Heat Mass Transf., 63, 268–283 (2013).C. Robin, M. Gerard, A. A. Franco, and P. Schott, Int. J. Hydrogen Energy, 38, 4675–4688 (2013).M. A. Quiroga and A. A. Franco, J. Electrochem. Soc., 162, E73–E83 (2015) http://jes.ecsdl.org/cgi/doi/10.1149/2.1011506jes.R. F. De Morais, P. Sautet, D. Loffreda, and A. A. Franco, Electrochim. Acta, 56, 10842–10856 (2011).S. Castaneda Ramirez, a. E. Perez Mendoza, and R. E. Ribadeneira Paz, ECS Trans., 66, 19–39 (2015).S. Castañeda Ramírez, A. E. Pérez Mendoza and R. E. Ribadeneira Paz, ECS Transactions, 66 (28) 7-18 (2015).A. Z. Weber, J. Newman, J. Electrochem. Soc. 150 (2003) A1008. doi:10.1149/1.1580822.

Determining Electro-Osmotic Drag of Water in Anion Exchange Membrane Fuel Cells

In an effort to reduce the cost of proton exchange membrane fuel cells (PEMFCs), a significant amount of research into non-precious metal (NPM) oxygen reduction catalysts has been conducted in recent decades. Despite this effort, platinum remains the only material with suitable stability and activity for use in the harsh environment of PEMFCs. Anion exchange membrane fuel cells (AEMFCs) have been gaining increased attention in recent years, providing advantages of higher stability and activity of NPM catalysts in alkaline environments. Unfortunately, the relevant properties, e.g. conductivity and mechanical & chemical stability, of anion exchange membranes (AEMs) are inferior to their proton conducting counterparts. Many studies have been conducted which focus on improving membrane properties such as swelling ratio, conductivity, and stability. In comparison, relatively little attention has been paid to studying ion and water transport in anion exchange membranes. Previous work conducted in our group has indicated that the majority of AEMFC polarization arises from the anode. The performance is relatively insensitive to catalyst loading and initial results indicate that electrode flooding is the primary cause of poor performance. To improve the performance of AEMFCs and better design AEMs, it is therefore important to study the transport of water and ions within AEMs. One key parameter which has received very little attention in the literature is the electro-osmotic transport of water due to the conduction of anions from the cathode to the anode. In this work, we study the electro-osmotic drag (EOD) in anion exchange membranes. The cell design and concept for electro-osmotic drag coefficient (ε) measurements in this work follow from the work of Fuller and Newman as adapted by others1–3. Analysis is conducted on the membranes in pure hydroxide form and carbonate form. The conductivity, water uptake and water mobility of the membranes is also studied over a wide range of relative humidities and temperatures. Better understanding of the transport of water and ions within anion exchange membranes will facilitate the development of models for AEMFC behavior and offer insight for future AEM production. Figure 1: Effect of water activity on the EOD coefficient (ε) and water content (λ) in Tokuyama A201. T. F. Fuller and J. Newman, J. Electrochem. Soc., 139, 1332–1337 (1992).T. A. Zawodzinski, J. Davey, J. A. Valerio, and S. Gottesfeld, Electrochim. Acta, 40, 297–302 (1995).X. Wang, J. P. Mcclure, and P. S. Fedkiw, Electrochim. Acta, 79, 126–132 (2012) http://dx.doi.org/10.1016/j.electacta.2012.06.098. Figure 1