Membrane Water Content Research Articles

Consortium Application of Endophytic Bacteria and Fungi Improves Grain Yield and Physiological Attributes in Advanced Lines of Bread Wheat

Increasing human population places pressure on agriculture. To feed this population, two time increase in the current wheat production is needed. Today agriculture is becoming input intensive with more reliance on synthetic fertilizers and agrochemicals to fulfil the feed demand of the growing numbers. Use of synthetic fertilizer since last few years is impacting the soil quality. In this scenario, the use of beneficial endophytic microbes is an attractive strategy to overcome the use of synthetic products. To investigate the effect of consortium application of endophytic bacteria and fungus on plant growth, grain yield moisture status, a pot experiment was conducted in different wheat lines. It comprised four treatments like control, application of bacterial strain Bacillus sp. MN54, fungal strain Trichoderma sp. MN6, and their consortium (Bacillus sp. MN54 + Trichoderma sp. MN6). The effect of consortium application was more prominent and significantly different from the sole application of bacteria and fungus. The results showed that with a consortium application of endophytic bacteria and fungus, there was 28.6, 4.3, -6.3 and -3.7% increases in flag leaf area, chlorophyll content, relative membrane permeability and water content respectively. Consortia of endophytic microbes also resulted in the yield enhancement through the betterment of various yield attributes like number of spikelet’s, grains per spike and grain yield per plant (32.2, 25.8 and 30.8%, respectively). So, consortia of endophytic microbes can greatly promote the progress of plants in dry land agriculture and increase the yield in an environmentally sustainable way.

Improvement of Performance of Selective CO2 Facilitated Transport Membrane in Hydrogen Station

The cost reduction of hydrogen stations is a must in order to spread fuel cell vehicles. Generally, the PSA device in the hydrogen station occupies 30% of the construction cost. We have already proposed the cost reduction by replacing the PSA and CO shift converter with a membrane reactor to which CO2 selective facilitated transport membrane is built in 2011. Although the CO2 facilitated transport membrane achieved the CO2/H2 selectivity of 100 or more even if the operation temperature was 160°C, the durability was poor. Therefore, it is necessary to improve the heat resistance and the rate of reaction between carrier and CO2 furthermore so that it can be adopted for the membrane reactor. In order to improve the membrane performance at 160°C by keeping high water content of membrane, graphite rubbish was added to the membrane as it was expected to function as grain for water absorption. As a result, the CO2 selectivity of the membrane improved more than that of the previous membrane by 3 times.

The Effect of Membrane Properties on Performance and Transports inside Polymer Electrolyte Membrane Fuel Cells

The primary focus of this work is evaluation, modeling, and comparison of fuel cell properties for a sulfonated aromatic hydrocarbon polymer membrane under fuel cell operations against the standard commercial Nafion membrane. Membrane characterization of transport properties were reported. The fuel cell performance, current distribution mapping, and water balance measurements of both membrane were also examined at different humidity conditions. The studies show that at high RH, the hydrocarbon membrane gives better performance with less water flooding when compared with standard Nafion. However at low RH, where the membrane needs more hydration and conducting of the proton, the standard Nafion membrane shows higher performance than hydrocarbon membrane. Local distributions of current density, water content and liquid water in hydrocarbon membranes were simulated and compared with a Nafion 212 membrane. Both experimental data and model predictions show that the hydrocarbon membrane gives more uniform current distributions than that of the Nafion membrane. The computational model can predict water transport across the membrane and can be used to observe flooding in PEMFC.

Model-Based Analysis of PFSA Membrane Mechanical Response to Relative Humidity and Load Cycling in PEM Fuel Cells

The hydration/dehydration cycling of the membrane during the fuel cell operation and the resulting mechanical stress are in part responsible for the mechanical failures of a polymer electrolyte membrane. To thoroughly investigate the mechanical behaviors of the membrane under in-situ cyclic conditions, in this paper, we have interfaced a comprehensive two-dimensional transient fuel cell transport model with a viscoelastic-plastic membrane mechanical model. The transport model is used to produce the spatiotemporal profiles of membrane water content and temperature in an operating cell, which are then sent to the membrane mechanical model to calculate the mechanical parameters of interest. This provides the extended capability of studying the membrane mechanical response under in-situ conditions, which was not possible with the original mechanical model. The effects of cycling relative humidity and voltage and current at different temperatures on the membrane stresses are studied using the coupled model. It is found that the location of maximum in-plane tensile stress can vary significantly with the operating temperature during voltage cycling, whereas the highest in-plane compressive stress occurs under the land for all cases, particularly near the cathode. The simulation results confirm the need for coupling the two models to capture comprehensive transport phenomena in studying the membrane mechanical behaviors, and represent an important step toward improved understanding of various synergistic mechanical failure mechanisms that affect the membrane in an operating fuel cell.

To Produce or to Survive: How Plastic Is Your Crop Stress Physiology?

Abiotic stress causes major crop losses and is considered a greater challenge than biotic stress. Comparisons of the number of published articles and patents regarding these different types of stresses, and the number of commercially released crops designed to tolerate different types of stresses, revealed a huge gap in the bench-to-field transfer rate of abiotic stress-tolerant crops, as compared to crops designed to tolerate biotic stress. These differences underscore the complexity of abiotic stress-response mechanisms. Here, we suggest that breeding programs favoring yield-related quantitative physiological traits (QPTs; e.g., photosynthesis rate or stomatal conductance) have canalized those QPTs at their highest levels. This has affected the sensitivity of those QPTs to changing environmental conditions and those traits have become less plastic. We also suggest that breeding pressure has had an asymmetric impact on different QPTs, depending on their sensitivity to environmental conditions and their interactions with other QPTs. We demonstrate this asymmetric impact on the regulation of whole-plant water balance, showing how plastic membrane water content, stomatal conductance and leaf hydraulic conductance interact to canalize whole-organ water content. We suggest that a QPT’s plasticity is itself an important trait and that understanding this plasticity may help us to develop yield-optimized crops.

Asymptotic analysis for the inlet relative humidity effects on the performance of proton exchange membrane fuel cell

In order to study the inlet relative humidity (RH) effects on the performance of proton exchange membrane fuel cell (PEMFC), the inlet humidification efficiency (IHE) model is proposed. The total water content of PEMFC is consisted of two parts including the internal electro-migration water content and the external water content of the humidified gas. The dynamic inlet humidification efficiency is derived. The current density of PEMFC is calculated by the incorporating parameters including inlet humidification efficiency and water content of the humidified gas in the IHE model. Firstly, the schedule diagram of calculation is given and the geometric model is established according to actual size of PEMFC. The computational meshes are partitioned by using the software (Gambit). The IHE model is imported into the computational fluid dynamics software (Fluent). Secondly, the experimental system is established and experiments have been done at the operating temperature of 70 °C and at 40% RH, 55% RH, 70% RH, 85% RH and 100% RH, respectively. Finally, the contours of H2O molar concentrations (both in anode channels and cathode channels), membrane water content (MWC) and polarization curves of the IHE model, the Fluent model and experimental are compared and analyzed at above experimental conditions. The results show that the species distribution uniformities of the IHE model such as H2O molar concentrations (both in anode channels and cathode channels) and MWC are the best when the PEMFC at 100% RH. When the operating temperature is 70 °C (40% RH and 350mA/cm2), the accuracy of the IHE model is improved by 79% compared with the Fluent model. When the operating temperature is 70 °C (40% RH and 350mA/cm2), the inlet humidification efficiency reaches 57%.

Three‐dimensional Modeling of Gas Purge in a Polymer Electrolyte Membrane Fuel Cell with Co‐flow and Counter‐flow Pattern

AbstractGas purge is commonly utilized to minimize residual water after shutdown of proton exchange membrane fuel cell (PEMFC) in cold weather, aiming to reduce damage of ice formation on cell performance and durability. In this paper, a three‐dimensional multiphase gas purge model of proton exchange membrane fuel cell with co‐flow and counter‐flow pattern is established to investigate water removal characteristics using two‐fluid model. The present model mainly includes water transport in membrane, mass transfer between dissolved water and water vapor in catalyst layer (CL), phase change between liquid water and water vapor in porous media. Several cases with co‐flow and counter‐flow pattern have been investigated numerically. In the last, gas purge time comparison between a fresh cell and degraded cell is conducted. The numerical results show that counter‐flow pattern is better in keeping even water content distribution and avoiding over‐drying of membrane. Time constant for gas purge is different in terms of different final target value: water vapor, liquid water saturation, membrane water content. Degraded cells have 2 more seconds than fresh cells when cell temperature is 80 °C and velocity of purge gas 1m s−1.

Real time monitoring of water distribution in an operando fuel cell during transient states

The water distribution of an operating proton exchange membrane fuel cell (PEMFC) was monitored in real time by using Small Angle Neutron Scattering (SANS). The formation of liquid water was obtained simultaneously with the evolution of the water content inside the membrane. Measurements were performed when changing current with a time resolution of 10 s, providing insights on the kinetics of water management prior to the stationary phase. We confirmed that water distribution is strongly heterogeneous at the scale at of the whole Membrane Electrode Assembly. As already reported, at the local scale there is no straightforward link between the amounts of water present inside and outside the membrane. However, we show that the temporal evolutions of these two parameters are strongly correlated. In particular, the local membrane water content is nearly instantaneously correlated to the total liquid water content, whether it is located at the anode or cathode side. These results can help in optimizing 3D stationary diphasic models used to predict PEMFC water distribution.

Ca2+ Effects on a Pt/C Catalyst for the Oxygen Reduction Reaction

The proton exchange membrane fuel cell (PEMFC) is one of the most promising renewable energy sources due to benign exhaust emissions and high energy efficiency. Pt/C is currently the primary catalyst for the slow oxygen reduction reaction (ORR) kinetics at the cathode of a PEMFC. The ORR, O2 + 4H+ + 4e- → 2H2O, indicates that this process preferentially occurs at a triple phase boundary where reactant, electrolyte, and catalyst are in contact [1, 2]. The depletion of O2, H+ or e- would significantly affect reaction kinetics. The Nafion® perfluorosulfonic acid (PFSA) ionomer, composed of a carbon-fluorine backbone and side chains ending with sulfonic acid groups, is conventionally used to prepare catalyst layers by exploiting its binding, proton-conducting and O2 transport properties. Foreign cations replace ionomer protons and occupy sulfonic acid sites by ion exchange [3-6]. The replacement of H+ by foreign cations in the ionomer decreases not only the proton conductivity but also O2 permeability. Uddin et al. [6] model results showed that the presence of Na+ in the ionomer of the cathode catalyst layer, which decreases the O2 permeability, causes a decrease in dissolved O2 concentration. Durst et al. [7] found that the diffusion coefficient and the concentration of O2 in the H2SO4 electrolyte, and the kinematic viscosity of the electrolyte decrease in the presence of Co2+. Cationic impurities decrease the membrane water content in turn shrinking the ionomer and lowering the active catalyst surface area. Also, foreign cations promote the generation of H2O2, a side product of the ORR, which exerts an undetermined influence on the performance and durability of PEMFCs. Literature and our group studies indicated that foreign cations have severe effects on the performance and durability of the PEMFC. Among all cations, Ca2+ deserves special attention because it is one of the most abundant elements within the earth’s crust. Prior efforts have focused on the effects of Ca2+ on PEMFC operation [8-10] and membrane transport properties [11]. However, the effects of Ca2+ on the ORR kinetics have hardly been studied. Okada et al. [12] studied the effects of Ca2+ on the O2 reduction kinetics at a Nafion® film covered Pt rotating disk electrode. Their results showed that impurity ions, even in small amounts, significantly hinder the rate of the O2 reduction charge transfer step. However, the Nafion® film covered Pt electrode is different from the supported catalyst layer for a PEMFC. The O2 transport properties in a Ca2+ form ionomer are poorly understood. In addition, the H2O2 yield has not been measured. In this presentation, detailed analyses of the changes in the Pt/C electrochemical surface area, ORR diffusion-limited and kinetic currents, Tafel slope, H2O2 yield, O2 permeability and ionomer sulfonate site occupation will be presented and discussed. Acknowledgments Authors are grateful to the United States Department of Energy (award DE-EE0000467), the Office of Naval Research (award N00014-12-1-0496), and the Hawaiian Electric Company.

Numerical Simulation and Experimental Comparison of Single, Double and Triple Serpentine Flow Channel Configuration on Performance of a PEM Fuel Cell

In this study, the effect of single (1-S), double (2-S) and triple (3-S) serpentine flow field configuration on the performance of PEM fuel cell (PEMFC) was investigated both numerically and experimentally. First, a complete 3-D PEMFC model was developed, and simulations were carried out to examine the effect of 1-S, 2-S and 3-S flow field configuration on the performance of PEMFC using commercial CFD code ANSYS FLUENT. Along with the cell performance, important parameters such as pressure distribution, mass fraction of hydrogen, oxygen, liquid water activity, current flux density distribution and the membrane water content have been presented. Next, an experimental study is carried out with a PEMFC by changing 1-S, 2-S and 3-S flow field configurations to verify the numerical predictions. Finally numerically and experimentally obtained performance curves have been compared, and 1-S flow channel fuel cell is found to exhibit the best electrochemical performance compared with the 2-S and 3-S flow channel fuel cells.

Influence of preparation procedure and ferric oxide nanoparticles addition on transport properties of homogeneous cation-exchange SPPO/SPVC membrane

Homogeneous cation-exchange membranes were prepared through evaporation and phase inversion methods using sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) and sulfonated polyvinylchloride as binders. The effect of polymers blend’s ratio and preparation method on structure and electrochemical properties of the prepared membranes were evaluated. The microstructures of the membranes were investigated by scanning electron microscopy (SEM) and the sulfonation of polyvinylchloride was confirmed by elemental analyses. Moreover, the membranes performance was evaluated by ion-exchange capacity (IEC), fixed ion concentration, membrane potential, transport number, permselectivity, areal resistance, ionic permeability, flux of ions, current efficiency, membrane oxidative stability, mechanical properties and water content tests. The results indicated that IEC and water content were affected by the SPPO content and microstructures of the membranes. The results showed increased efficiency and suitable electrochemical properties for membranes prepared by the evaporation method in comparison with others. Also, \(\hbox {Fe}_{2}\hbox {O}_{3}\) nanoparticles were synthesized at room temperature by a simple sonochemical reaction between ferric chloride and NaOH. The results revealed that the addition of different amounts of \(\hbox {Fe}_{2}\hbox {O}_{3}\) nanoparticles to the polymeric matrix could affect the hydrophilicity and transport properties of ion-exchange membranes.

Maximum power point tracking of a proton exchange membrane fuel cell system using PSO-PID controller

Fuel cells output power depends on the operating conditions, including cell temperature, oxygen partial pressure, hydrogen partial pressure, and membrane water content. In each particular condition, there is only one unique operating point for a fuel cell system with the maximum output. Thus, a maximum power point tracking (MPPT) controller is needed to increase the efficiency of the fuel cell systems. In this paper an efficient method based on the particle swarm optimization (PSO) and PID controller (PSO-PID) is proposed for MPPT of the proton exchange membrane (PEM) fuel cells. The closed loop system includes the PEM fuel cell, boost converter, battery and PSO-PID controller. PSO-PID controller adjusts the operating point of the PEM fuel cell to the maximum power by tuning of the boost converter duty cycle. To demonstrate the performance of the proposed algorithm, simulation results are compared with perturb and observe (P&O) and sliding mode (SM) algorithms under different operating conditions. PSO algorithm with fast convergence, high accuracy and very low power fluctuations tracks the maximum power point of the fuel cell system.

Investigation of Antibacterial and Fouling Resistance of Silver and Multi-Walled Carbon Nanotubes Doped Poly(Vinylidene Fluoride-co-Hexafluoropropylene) Composite Membrane.

Composite membranes were successfully prepared using a phase-inversion method. The X-ray powder diffraction (XRD) and energy dispersive X-ray (EDX) profiles has confirmed formation of 4.8 wt % Ag/poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP), 3 wt % Ag-MWCNTs/PVDF-HFP (EDX surface composition of Ag nanoparticles) and 1.5 wt % MWCNTs/PVDF-HFP composite membranes. The MWCNTs crystallites are mainly encapsulated by a layer of PVDF-HFP, as evidenced by disappearance of graphitic peak. The scanning electron microscopy (SEM) images have depicted the formation of microporous structure, with few MWCNTs on the surface and strongly interacting with PVDF-HFP as demonstrated by thermogravimetric analysis (TGA), XRD and Fourier transform infrared (FTIR) data. The data indicated an increase in porosity, swellability and water content of the PVDF-HFP membrane with the addition of MWCNTs and/or Ag nanoparticles, showing an improved hydrophilicity. The 1.5 wt % MWCNTs/PVDF-HFP composite membrane showed good desalination and fouling resistance rates, which correlates with a low water contact angle. The combined effects of Ag nanoparticles and MWCNTs do not promote fouling resistance of PVDF-HFP membranes, as shown during NaCl microfiltration (this is linked with high water contact angle as compared to that of MWCNTs/PVDF-HFP composite). Both 1.5 wt % MWCNTs/PVDF-HFP and 3 wt % Ag-MWCNTs/PVDF-HFP composite membranes prevented the bacteria passing through the membrane (100% bacterial load reduction). The surface of 3 wt % Ag-MWCNTs/PVDF-HFP showed good bactericidal and non-leaching properties of the dopant materials (MWCNTs and Ag), as evidenced by bacterial growth on the edges of the membranes.

Adapting the ionic transfer behavior of cation exchange membrane incorporated with SiO2/PAA composite nanoparticles

In this study, silicon dioxide nanoparticles (SiO2 NPs) were functionalized by polyacrylic acid (PAA) then used as the modifier agent in polyvinyl chloride (PVC)-based heterogeneous cation exchange membranes (CEMs). FTIR technique and SEM images were employed to characterize the synthesized SiO2/PAA. All the experiments were carried out at ambient condition. According to the experiments, CEMs modified by SiO2/PAA have more hydrophilic and smoother surface. Membrane water content reduced from 32.2% for the base membrane to 20.1% for modified membrane containing 4.0%wt SiO2/PAA. Modified CEMs showed an improved potential, transport number, selectivity, and electrical conductivity. The selectivity of modified membrane (containing 0.5%wt SiO2/PAA) is 87.3%, and its electrical conductivity is about 37% less than the base membrane. The mechanical stability of prepared membranes was also improved about 25.4%. Moreover, sodium flux increased sharply (21%) loading 0.5%wt NPs in the structure and then reduced by more SiO2/PAA concentration. In addition, membrane ionic flux decreased obviously for bivalent ions by using SiO2/PAA nanoparticles. The prepared membranes showed higher permeability/flux for monovalent ions compared to bivalent type.

Operando μ -Raman study of the actual water content of perfluorosulfonic acid membranes in the fuel cell

Abstract Operando μ-Raman spectroscopy is used to probe the water distribution across Nafion® and Aquivion™ membranes in the operating fuel cell. The through-plane water concentration profile is obtained with μm resolution at the middle of the active surface, both at the gas distribution channel and at the under-lands areas. Depth-resolved measurements carried out at room temperature show that the water content of both membranes increases with the increase of the feed gas relative humidity and decreases with the increase of stoichiometry. At given relative humidity and stoichiometry conditions, the water content first increases at the fuel cell start-up and, then, decreases progressively with the increase of the current density delivered by the cell. The water loss is due to the concomitant rise of pressure drops and of the cell inner temperature, the latter giving the larger contribution. Pressure drops are related to the increase of the feed gases fluxes while temperature rise is due to increasing ohmic losses and heat from the electrochemical reaction. Compared to Nafion, Aquivion exhibits larger water content, but similar dehydration rate as a function of ohmic losses, and larger water accumulation at the under-lands area compared to channel.

Understanding the Role of the Micro-Porous Layer on Fuel Cell Performance Using a Non-Isothermal, Two-Phase Model

Water management is a critical factor in improving fuel cell performance at high current densities [1]. Under dry conditions, keeping the ionomer phase in polymer electrolyte membrane (PEM) and catalyst layers (CLs) sufficiently hydrated is critical to maintaining high protonic conductivity and reducing the ohimc losses. When the cell is operating at high relative humidity, removing the excessive water generated in the electrodes is of importance in order to avoid liquid water accumulation and achieve high performance. An efficient membrane electrode assembly (MEA) design therefore requires an extensive understanding of water management in fuel cells. The use of a micro-porous layer (MPL) in fuel cells is known to improve water and heat management resulting in a better performance. Experimental evidence has shown that remarkable fuel cell performance improvements are still possible by modifying the MPL composition [2] and micro-structure, for instance, by milling holes [3]. In situ heat and water flux measurements conducted by Thomas et al. [4] showed that by inserting an MPL between CL and gas diffusion layer (GDL), the temperature in the electrodes increased by at least 1° C at high current density. The warmer electrode therefore, results in a higher evaporation which also facilitates the diffusive transport of water vapour by creating a higher concentration gradient. Based on experimental observations from the ex situ diffusive vapour flux and liquid permeation flux measurements as well as in situ electrochemical performance with varying MPLs, Owejan et al. [5] hypothesized the role of MPL is to prevent the condensed water in the GDL from forming a liquid film at the GDL/CL interface and creating an in-plane diffusive path for reactant. In their study, the thermal conductivity in porous layers demonstrated a significant impact on improving the performance by creating a higher temperature driven diffusive flux. In order to understand the effects of MPL on capillary-driven flow and phase change induced flow, a multi-dimensional, non-isothermal, two-phase numerical model is developed in OpenFCST [6]. The porous media transport properties for two-phase flow are estimated using a micro-scale mathematical pore size distribution model [1] which is capable of accounting for the layer mixed wettabilities and micro-structure. Experimental validation of two-phase flow models is rarely performed even though it is of importance. In this study, the electrochemical performance of an MEA with a SGL 24BA and SGL 24BC is measured in our laboratory at varying operating conditions and also predicted using the numerical two-phase model. Membrane water transport, water fluxes in liquid and vapour form at cathode boundary, and the phase change induced flow are analyzed for studies with and without an MPL. The performance analysis under hot/dry condition indicates that adding an MPL in the dry condition results in an excessive protonic transport loss in the membrane, especially at high current density. Under hot/wet condition, the additional heat preserved on the electrodes by adding the MPL leads to a substantial reduction in water accumulation. Simulation results at the cold/wet condition highlight that adding an MPL not only leads to a decrease in water accumulation in the electrode but also creates an in-plane diffusion pathway for gas transport in the cathode. The increase in temperature in the electrode also results in a decrease in relative humidity, especially at the anode. This leads to a higher membrane water content gradient between the fully saturated cathode and the anode which results in a higher back diffusion. A parametric study of MPL thermal conductivity suggests that the excessive water in the cathode can be removed as water vapour by decreasing the MPL thermal conductivity under fully humidified conditions. However, an extremely low MPL thermal conductivity can lead to a significant deterioration of performance even at high relative humidity due to the membrane dehydration. The paramteric study highlights the optimal MPL conducivity for our cell. An optimal MPL design requires a comprehensive water balance between membrane hydration and sufficient electrode water evaporation.

Monovalent and divalent ion sorption in a cation exchange membrane based on cross-linked poly (p-styrene sulfonate-co-divinylbenzene)

Many fundamentals of ion sorption in ion exchange membranes (IEMs) are not fully understood, and few modern studies focus on multivalent ion sorption, despite the importance of divalent ion transport properties in water purification applications. Here, MgCl2 and CaCl2 sorption in a commercial cross-linked, styrene-divinylbenzene cation exchange membrane (CEM) with fixed sulfonate groups was measured and compared with NaCl, LiCl and KCl sorption in the same material. The data were correlated with counter-ion size and valence, as well as membrane water content. Divalent salts had higher sorption coefficients than monovalent salts, even though membrane water content significantly decreased in the presence of divalent counter-ions. The Donnan potential is weaker in the presence of multivalent counter-ions, which increases co-ion sorption, contributing to the observed increase in salt sorption coefficients for divalent salts. Ion activity coefficients in the membrane were calculated and compared to predictions of the recently proposed Manning-Donnan model. This model showed much better agreement with the experimental data than the ideal Donnan model, suggesting that ion non-ideality in the membrane is important when analyzing ion sorption and transport in IEMs.

Developing thin film heterogeneous ion exchange membrane modified by 2-acrylamido-2-methylpropanesulfonic acid hydrogel-co-super activated carbon nanoparticles coating layer

Highly selective cation exchange membranes were prepared by coating a thin 2-acrylamido-2-methylpropanesulfonic acid based hydrogel layer and super activated carbon nanoparticles-co-hydrogel layer on polyvinyl chloride based cation exchange membranes. FTIR analysis proved hydrogel formation on membrane surface successfully. Scanning electron microscopy images and swelling ratio measurement were used to study the effect of super activated carbon nanoparticles on properties of formed hydrogel. The surface morphology, surface hydrophilicity and roughness analysis were also used in membrane characterization. Membrane water content was increased by formation of modified layer on the membranes surface. Modified membranes showed a remarkable improvement in potential, permselectivity and transport number compared to pristine type. Membrane ionic flux and permeability were improved initially by using modifier layer on membrane surface, and then showed decreasing trend at high nanoparticles loading ratios in hydrogel layer. Modified membranes showed lower electrical resistance compared to unmodified membrane.

Dynamic Phenomena Coupling Analysis and Modeling of Proton Exchange Membrane Fuel Cells

Dynamic variable coupling analysis is an important method to properly design a control structure for complex multivariable and multi-physical dynamic systems, such as fuel cells. The fuel cell is an electrochemical energy conversion device which includes different inter-coupled dynamic phenomena in electrical, fluidic, and thermal domains. In order to achieve optimized fuel cell performance, different operation variables, such as fuel cell temperature, inlet air flow rate, hydrogen pressure, and membrane water content, need to be properly controlled. In this paper, variable coupling analyses of fuel cell dynamic behaviors are presented and discussed based on a proton exchange membrane fuel cell (PEMFC) dynamic model, which considers in particular the transient phenomena in both fluidic and thermal domain. The analyses of dynamic phenomena step responses are conducted using the relative gain array for various control input variables. Quantitative analyses of coupling effects in different physical domains are shown and discussed. The analysis results can be used to optimize the controller design for fuel cell system.

Electrochemical Reduction of Dissolved Oxygen in Alkaline, Solid Polymer Electrolyte Films.

Mass transport of oxygen through an ionomer contained within the cathode catalyst layer in an anion exchange membrane fuel cell is critical for a functioning fuel cell, yet is relatively unexplored. Moreover, because water is a reactant in the oxygen reduction reaction (ORR) in alkaline media, an adequate supply of water is required. In this work, ORR mass transport behavior is reported for methylated hexamethyl-p-terphenyl polymethylbenzimidazoles (HMT-PMBI), charge balanced by hydroxide ions (IEC from 2.1 to 2.5 mequiv/g), and commercial Fumatec FAA-3 membranes. Electrochemical mass transport parameters are determined by potential step chronoamperometry using a Pt microdisk solid-state electrochemical cell, in air at 60 °C, with relative humidity controlled between 70% and 98%. The oxygen diffusion coefficient (DbO2), oxygen concentration (cbO2), and oxygen permeability (DbO2·cbO2) were obtained by nonlinear curve fitting of the current transients using the Shoup-Szabo equation. Mass transport parameters are correlated to water content of the ionomer membrane. It is found that the oxygen diffusion coefficients decreased by 2 orders of magnitude upon reducing the water content of the ionomer membrane by lowering the relative humidity. The limitation of the Shoup-Szabo equation for extracting ORR mass transport parameters using thin ionomer films was evaluated by numerical modeling of the current transients, which revealed that a significant discrepancy (up to 29% under present conditions) was evident for highly hydrated membranes for which the oxygen diffusion coefficient was largest, and in which the oxygen depletion region reached the ionomer/gas interface during the chronoamperometric analysis.