Proton Exchange Membrane Water Research Articles

Impact of Schroeder's paradox on cold start-up failure of proton exchange membrane fuel cells: Three-dimension simulation based on OpenFOAM

In the cold environment, the increase in mass transfer resistance enhances non-equilibrium thermodynamic phenomena of the membrane water in proton exchange membrane fuel cells, such as Schroeder's paradox, but these phenomena were ignored in the classic model. In this study, the impacts of Schroeder's paradox on cold start-up failure, especially ice distributions at different temperatures, were discussed. The transfer procedure from the equilibrium to non-equilibrium between membrane water and vapor was described. A non-equilibrium boundedness model was developed and was run in OpenFOAM, and this model was compared to equilibrium unboundedness models previously and equilibrium boundedness models. Results show that non-equilibrium characteristics cannot be neglected at −20 °C. If the boundedness is considered, output voltages of the equilibrium assumption (frozen membrane water) decrease faster than the non-equilibrium assumption. Icing deteriorates the reabsorption capacity of the membrane and enhances the non-equilibrium between the membrane and the environment.

Nature-inspired hybrid wettability surface to enhance water management on bipolar plates of PEMFC

Proton exchange membrane fuel cell (PEMFC) requires both sufficient water in proton exchange membrane (PEM) and fast water drainage in flow channel to achieve a desirable performance, which creates a dilemma for water management. Herein, we have fabricated a nature-inspired bionic multifunctional surface (BMS) consisting of superhydrophobic coating and superhydrophilic groove. The characterizations of water contact angle, morphology and chemical composition have verified the successful preparation of hybrid wettability surface. The effects of groove width on droplet capture, storage and drainage have been investigated, which yields an optimal width of 600 μm. More importantly, BMS has been fabricated inside the flow channel of graphite bipolar plate (BMS@BP). The peak power density of BMS@BP cell is 26.3% higher than that of the cell without BMS. Under a drought-inclined condition of low current and humidity, BMS@BP mitigates the increase of internal resistance caused by PEM dry-out, whereas under a condition prone to flooding (high current and humidity), BMS@BP can reduce the voltage fluctuation and pressure drop variation incurred by flooding. Hence, BMS has demonstrated a capacity to balance the opposite needs of moisturizing PEM and draining channel water. Our work may afford an innovative hybrid-wettability-based approach to enhance water management for PEMFC.

Hydrogen production technology by electrolysis of water and its application in renewable energy consumption

In order to deal with the energy crisis and environmental pollution, renewable energy power generation in the world has been rapid development. At present, the most widely used is solar energy and wind energy, but also caused a serious problem of abandoning light and wind. Hydrogen energy has become an ideal carrier of electric energy storage due to its high efficiency, clean and renewable characteristics. Electrolytic water hydrogen production technology with renewable energy as power source is one of the most promising energy conversion methods. This paper briefly analyzes the current situation of power generation and consumption of renewable energy in China in recent years, and then expounds the characteristics, principles, development status and improvement methods of alkaline, proton exchange membrane and high temperature solid oxide electrolytic water hydrogen production technology, and demonstrates its application prospect in the field of renewable energy power generation and energy storage with examples.

Adoption of novel porous inserts in the flow channel of pem fuel cell for the mitigation of cathodic flooding

Accumulation of excess water in Proton exchange membrane fuel cell (PEMFC) is one of the significant technical challenges that needs great attention, since it makes the performance of the fuel cell highly unpredictable and unreliable. To address this formidable task, herein by inserting porous inserts in inline and staggered arrangements on the provisions of landing surface of serpentine flow field, we minimize water clogging in gas diffusion layer. Two types of porous inserts namely porous carbon inserts (PCI), porous sponge inserts (PSI) of sizes 2 mm × 2 mm x 2 mm (2 mm porous inserts) and 4 mm × 2 mm x 2 mm (4 mm porous inserts) are tested for water management of PEMFC, and their respective performances are analyzed. The results showed that power density produced by MSI flow field is 9.5% and 11.57% higher than serpentine flow field for 2 mm and 4 mm PCI respectively while the MSS flow field produced 31.81% and 42.56% higher performance in terms of power density compared with serpentine flow field for 2 mm and 4 mm PCI respectively. The MSS flow field with 4 mm PCI produced 27.77% higher power density compared with 2 mm PCI. Using porous sponge insert instead of porous carbon insert increases the power density by 23.33% for 2 mm porous insert and the power density increases 21.73% for 4 mm PSI in MSS flow field. Increasing the size of PSI from 2 mm to 4 mm increases the power density by 26.12% in MSS flow field.

Comparative performance analysis of a grid connected PV system for hydrogen production using PEM water, methanol and hybrid sulfur electrolysis

This paper presents comparative performance analysis of photovoltaic (PV) hydrogen production using water, methanol and hybrid sulfur (SO2) electrolysis processes. Proton exchange membrane (PEM) electrolysers are powered by grid connected PV system. In this system design, electrical grid is considered as a virtual energy storage system (VESS) where the surplus of PV production can be injected and subsequently taken to support the electrolyser. Methanol (ME) and hybrid sulfur (HSE) electrolysis are compared to the conventional water electrolysis (WE) in term of operating cell voltage. Based on the experimental results reported in the literature, semi-empirical models describing the relationship between the hydrogen production rate and the electrolyser cell power input are proposed. Furthermore, power and hydrogen management strategy (PHMS) is developed. Case study is carried out to show the impact of each type of electrolysis on the system component sizes and evaluate the hydrogen production potentialities. Results show that the use of ME allows to produce 65% more hydrogen than with using WE. Moreover, the amount of hydrogen produced is almost double in the case of HSE. At Algiers city, based on a grid connected PV/Electrolyser system, it is possible to produce about 25 g/m2 d and 29 g/m2 d of hydrogen, respectively, through ME and HSE compared to 15 g/m2 d of hydrogen when using WE.

States of water in proton exchange membranes: Part A - Influence of chemical structure and composition

Disulfonated poly(arylene ether) and polyimide copolymers can phase separate to form nanoscale hydrophilic and hydrophobic domain morphology. Water in these domains has been assigned to three different states, tightly bound, loosely bound and free water. The states of water were characterized using DSC, NMR relaxation and TGA. The chemical structures of the proton exchange membranes were varied in chemical composition, microstructure (random and block) and also regarding functional sulfonic acid groups fixed to the polymer backbones. A strong dependence of the types of water on the ion content and morphology was observed. For the random copolymers, the formation of free water in the system occurs after reaching a certain ion content. For the multi-blocks, in addition to the ion content, free water also develops with increasing block lengths. The formation of continuous morphology in the copolymers was correlated to the onset of free water. Influences of the states of water on PEM transport properties will be reported separately.

Toward a Predictive Understanding of Water and Charge Transport in Proton Exchange Membranes

An analytical model for water and charge transport in highly acidic and highly confined systems such as proton exchange membranes of fuel cells is developed and compared to available experimental data. The model is based on observations from both experiment and multiscale simulation. The model accounts for three factors in the system including acidity, confinement, and connectivity. This model has its basis in the molecular-level mechanisms of water transport but has been coarse-grained to the extent that it can be expressed in an analytical form. The model uses the concentration of H(3)O(+) ion to characterize acidity, interfacial surface area per water molecule to characterize confinement, and percolation theory to describe connectivity. Several important results are presented. First, an integrated multiscale simulation approach including both molecular dynamics simulation and confined random walk theory is capable of quantitatively reproducing experimentally measured self-diffusivities of water in the perfluorinated sulfonic acid proton exchange membrane material, Nafion. The simulations, across a range of hydration conditions from minimally hydrated to fully saturated, have an average error for the self-diffusivity of water of 16% relative to experiment. Second, accounting for three factors-acidity, confinement, and connectivity-is necessary and sufficient to understand the self-diffusivity of water in proton exchange membranes. Third, an analytical model based on percolation theory is capable of quantitatively reproducing experimentally measured self-diffusivities of both water and charge in Nafion across a full range of hydration.

Determination of effective water vapor diffusion coefficient in pemfc gas diffusion layers

The primary removal of product water in proton exchange membrane (PEM) fuel cells is through the cathode gas diffusion layer (GDL) which necessitates the understanding of vapor and liquid transport of water through porous media. In this investigation, the effect of microporous layer (MPL) coatings, GDL thickness, and polytetrafluorethylene (PTFE) loading on the effective water vapor diffusion coefficient is studied. MRC Grafil, SGL Sigracet, and Toray TGP-H GDL samples are tested experimentally with and without MPL coatings and varying PTFE loadings. A dynamic diffusion test cell is developed to produce a water vapor concentration gradient across the GDL and induce diffusion mass transfer. Tests are conducted at ambient temperature and flow rates of 500, 625, and 750 sccm. MPL coatings and increasing levels of PTFE content introduce significant resistance to diffusion while thickness has negligible effects.

Applications of a general random-walk theory for confined diffusion

A general random walk theory for diffusion in the presence of nanoscale confinement is developed and applied. The random-walk theory contains two parameters describing confinement: a cage size and a cage-to-cage hopping probability. The theory captures the correct nonlinear dependence of the mean square displacement (MSD) on observation time for intermediate times. Because of its simplicity, the theory also requires modest computational requirements and is thus able to simulate systems with very low diffusivities for sufficiently long time to reach the infinite-time-limit regime where the Einstein relation can be used to extract the self-diffusivity. The theory is applied to three practical cases in which the degree of order in confinement varies. The three systems include diffusion of (i) polyatomic molecules in metal organic frameworks, (ii) water in proton exchange membranes, and (iii) liquid and glassy iron. For all three cases, the comparison between theory and the results of molecular dynamics (MD) simulations indicates that the theory can describe the observed diffusion behavior with a small fraction of the computational expense. The confined-random-walk theory fit to the MSDs of very short MD simulations is capable of accurately reproducing the MSDs of much longer MD simulations. Furthermore, the values of the parameter for cage size correspond to the physical dimensions of the systems and the cage-to-cage hopping probability corresponds to the activation barrier for diffusion, indicating that the two parameters in the theory are not simply fitted values but correspond to real properties of the physical system.

States of Water in Proton Exchange Membranes

not Available.

Influence of Degradations of Catalyst Layer and Gas Diffusion Layer on Flooding in PEFC

Regarding a polymer electrolyte fuel cell (PEFC), the influence of degradations of a catalyst layer and a gas diffusion layer which are parts of membrane electrode assembly (MEA) on electrode flooding was investigated. On a PEFC, high humidity operation is desired for high performance because it is necessary to contain much water in proton exchange membrane and ionomer at catalyst layer. Additionally, high gas utilization is required for high system efficiency. However, under these conditions, significant degradation in a cell performance is caused by water-flooding of electrodes. The purpose of this study is to investigate how the degradation of a catalyst layer and a gas diffusion layer give the influence to occur flooding on electrode. The single cell was generated at 0.3A/cm2 under high humidity operation for 10000 hours. And the cell performance was evaluated as cell voltage, cell resistance, IV curves, gas crossover rate, electrochemical surface area and Oxygen gain in order to find which part of the cell dominates such cell degradation. Consequently, it is found that the gas diffusivity degradation finally dominates the decay of the cell performance and it is mainly caused not in the gas diffusion layer but in the catalyst layer.

Numerical simulation of three-dimensional gas/liquid two-phase flow in a proton exchange membrane fuel cell

Investigation into the formation and transport of liquid water in proton exchange membrane fuel cells (PEMFCs) is the key to fuel cell water management. A three-dimensional gas/liquid two-phase flow and heat transfer model is developed based on the multiphase mixture theory. The reactant gas flow, diffusion, and chemical reaction as well as the liquid water transport and phase change process are modeled. Numerical simulations on liquid water distribution and its effects on the performance of a PEMFC are conducted. Results show that liquid water distributes mostly in the cathode, and predicted cell performance decreases quickly at high current density due to the obstruction of liquid water to oxygen diffusion. The simulation results agree well with experimental data.

Rigorous 3-D Mathematical Modeling of PEM Fuel Cells: II. Model Predictions with Liquid Water Transport

In this part of the paper, we present a model to treat formation and transport of liquid water in proton exchange membrane (PEM) fuel cells (FCs) in three-dimensional (3-D) geometry. The performance of modern-day PEM FCs at high current density are largely dictated by the effective management of liquid water. In the first part of this paper, a rigorous model was presented to model PEM FCs using a computational fluid dynamic technique. It was found that under the assumption of no liquid water formation, the model consistently overpredicted measured polarization behavior. In the model presented here, the phase change process is modeled as an equilibrium process, while the transport of liquid water is governed by pressure, surface tension, gravity and electro-osmotic drag. Results show that the inclusion of liquid water transport greatly enhances the predictive capability of the model and is necessary to match experimental data at high current density. © 2003 The Electrochemical Society. All rights reserved.

The state of water in styrene‐grafted and sulfonated poly(vinylidene fluoride) membranes

AbstractThe state of water in proton exchange membranes prepared by pre‐irradiation (electron beam, 100 kGy) grafting of styrene onto poly(vinylidene fluoride) films (PVDF‐g‐PS), followed by sulfonation (PVDF‐g‐PSSA), has been studied with thermal analysis, Raman spectroscopy and small angle X‐ray diffraction (SAXS). Raman spectra show that, in addition to free liquid water in the membranes, single water molecules are weakly bound to the polymer backbone. Thermal analysis shows that there are three types of water molecules in the membrane; non‐freezable water associated with the ionic sites, freezable free water, and freezable bound water. The amount of non‐freezable water is around 10 H2O/SO3H (mol/mol), and is independent of the degree of grafting (d.o.g.). The amount of freezable water is strongly dependent on the d.o.g. as long as the grafting has not penetrated the whole of the film, and reaches a value of around 40 H2O/SO3H (mol/mol) above a d.o.g. of 50%. The conductivity of membranes containing only the non‐freezable water is low, i. e. the ionically bound water alone does not form the domains necessary for proton and water transport. SAXS measurements show that water/sulfonic acid clusters in hydrated PVDF‐g‐PSSA membranes with a Bragg distance of 25 Å are formed; these form the ion conducting channels in the membrane.

Proton exchange membranes by radiation grafting of styrene onto FEP films. IV. Evaluation of the states of water

AbstractThe nature of water in proton exchange membranes, obtained by radiation grafting of styrene onto poly(tetrafluoroethylene‐co‐hexafluoropropylene) (FEP) films and subsequent sulfonation, was investigated by differential scanning calorimetry. It was found that the membranes contained three different types of water, which were categorized as freezing‐free, freezing‐bound, and nonfreezing water. The degree of grafting had a considerable influence on the relative ratios of these three types of water molecules. The nonfreezing water per ion‐exchange site ratio was found to be independent of the degree of grafting. However, freezing‐free and freezing‐bound water per ionic site ratios increased with increasing graft levels. A correlation between the water uptake and the structural changes occurring in the membrane as a function of the degree of grafting was established. © 1995 John Wiley & Sons, Inc.