جستجوی مقالات مرتبط با کلیدواژه « pem fuel cell » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

Due to the needs of industries for clean and environmentally friendly fuels today, new energy sources such as fuel cells are at the center of attention. Polymer fuel cells, meanwhile, require a short start-up time due to low operating temperature, high power density, no emission and very low noise, making them the best option for vehicles as an alternative to internal combustion engines. One of the most important reasons for fuel cell loss is the uneven distribution of reactants on the active area, which causes non-uniform reactions. Therefore, the use of an optimal flow field to improve the durability and performance of PEM fuel cells seems necessary. Although different studies introduced novel designs, a study comparing different patterns comprehensively to introduce the best ones is not performed yet. In this study, first, a numerical validation was performed with an experimental test that showed good accuracy. Then, to achieve efficient patterns, several flow field designs were inspired by previous effective designs and others were selected as superior designs from the literature. The effects of presented geometries on the performance of a PEMFC were investigated to improve its performance. In addition, efficient evaluation criteria from the literature were employed to better analyze the performance of such systems, and the ones consistent with the I-V performance were introduced. By surveying the criteria, a novel performance factor was introduced that showed the best agreement with the I-V performance. The results were obtained in single-phase and two-phase approaches, which lead to remarkable findings. The two-phase study revealed that the waved serpentine case has the highest electrical performance with the highest mass fraction of oxygen.

Among the various fuel cells, Proton Exchange Membrane Fuel Cells (PEMFC) offer many advantages, such as low temperature operation, quick starting, and high energy density. Therefore, the PEMFC can be extensively applied to power generation, portable electric equipment and hybrid vehicles. Heat treatable aluminum alloys such as 7075, because of high strength low density and corrosion resistance, are used widely in industry and PEMFC. In this industry, besides of mechanical properties, corrosion resistance is very important to work at that environment. T6 heat treatment has recommended for this regard, but this temper treatment is sensitive to corrosion induced and Stress Corrosion Cracking (SCC). In this work 5% Pre- Stretching after solution applied to this alloy in order to investigate its resistance to SCC. The results show that by this treatment, the precipitates immigrate from grain boundary into the grains inside and improve Stress Crack Corrosion (SCC) properties which is very important for using in PEMFC. Moreover, the results show that 5% Pre- Stretching after solution improves both tensile strength and elongation and 463MPa Tensile strength with 12% Elongation can be obtained by this heat treatment.

Water management is essential because of its effect on the performance and durability of the polymer electrolyte membrane (PEM) fuel cells. This paper studies the flow in the cathode gas diffusion layer (GDL) of a PEM fuel cell using a non-isothermal two-phase model. For this purpose, the conservation equations of mass, momentum, energy, and other auxiliary equations have been solved numerically and validated with data available in the papers. The results show that the pressure variation of the gas mixture (P_g) along the cathode GDL is negligible, while the capillary pressure (P_c) is significant. An increase in the pressure of the cathode channel as well as the porosity of GDL leads to an increase in the concentration of oxygen in the cathode catalyst layer, but by increasing the porosity coefficient of the electrodes from 0.4 to 0.7, the effective thermal conductivity of the fuel cell decreases and the maximum temperature of the fuel cell increases by about 1K. The flow of liquid water and the consequent saturation are higher in the vicinity of the cathode catalyst layer, but due to evaporation, their amount decreases as approach the channel. In the current density range of 0.6< j< 1A/cm^2, the α parameter (which is defined as the ratio of the water entering from the membrane to the catalyst to the water produced due to the reaction) is nearly equal to 1.2, as a result, the water entering the cathode GDL increases proportionally to the current density.

In this study, the fracture method is used to numerically and experimentally investigate the bending load of graphite-based composite bipolar plates of polymer electrolyte membrane fuel cells. First, simple and perforated composite bipolar plates were tested and simulated to determine flexural stability under static load. Then, mechanical simulation using the finite element method and Abaqus software was used for the numerical analysis. Next, an experimental three-point bending test was performed on the manufactured samples to validate the simulation results. Finally, the results of the numerical and experimental analyzes of the flexural behavior of composite bipolar plates were compared. The results demonstrated that the numerical results acceptably agreed with the experimental data. In addition, the presence of a high percentage of graphite and high fragility weakened the body due to the molecular bond of graphite, which caused the graphite to slip.

One of the most important components of a polymer electrolyte membrane fuel cell is the endplate, which must exert uniform contact pressure distribution on the membrane electrode assembly. Since the endplates must be highly rigid, it is essential to consider the flexural modulus parameter when designing these plates. In this study, the production of lighter-weight endplates with a higher flexural modulus is significantly improved by replacing heavy metallic plates with polymer composite plates. The vacuum bag manufacturing technique was used to create these composite plates from epoxy resin, carbon fibers, and glass fibers, making them compatible with the environment of the fuel cell. The flexural modulus and heat deflection temperature of each sample were evaluated before and after a simulated environment test of the fuel cell. Then, the amount of water absorption for each specimen was calculated. Finally, the composite endplates were fabricated using the two different laminations of fibers to find the optimum fiber lamination to maximize the endplate flexural rigidity. The optimum sample contained carbon fibers with an epoxy resin with 0 degrees arrangement. This specimen has a flexural modulus of about 93.17 GPa, heat deflection temperature of about 261 °C, and water absorption of about 0.86%, which are ideal for fuel cell endplates.

Sealants are one of the most important components of the proton exchange membrane fuel cells (PEMFCs). It has significant roles in issues like safety, energy density, durability and performance of the fuel cells. Thus choosing the proper kind of the sealant which is suitable for PEMFCs may cause to develop the performance of the fuel cells. Sealants must be chemically and physically stable in order to have good performance during the defined lifetime for the fuel cell. The durability of the seal means that it has the ability to be placed in the environment of the fuel cell for a long time, and its physical and chemical properties changes should be small, and performs the sealing function correctly. In this paper, mechanical properties of three different types of materials that are frequently used for fuel cell sealing are assessed in an environment similar to the fuel cells ones. These three materials are silicone, EPDM (ethylene propylene dyne monomer) sheet, and molded EPDM. Mechanical properties of the materials are obtained after being used in environment resembling a fuel cell at specific time and temperature. The mechanical and chemical properties of the specimens such as are hardness, weight changes, tensile strengths, compression set and spectrometry are carried out in accelerated durability test of simulated PEMFC environment. These tests are gathered in the period of 100 days. The results revealed that the molded EPDM is the best sealant from others based on the obtained properties in fuel cell working conditions.

Nowadays, study on alternative sources of fossil fuels for power generation has attracted great attention. Polymer electrolyte membrane fuel cells (PEMFCs) have higher energy densities and lower power densities than the conventional batteries. PEMFCs should be hybridized with battery to increase the stability without decreasing the maximum power. Typically, DC-DC converters are utilized to combine these systems leading to significant increase in cost, size and weight of system; however, using these converters reduces system efficiency. In this paper, a circuit is implemented for PEMFC and battery hybridization system with a power path controller. The experimental investigations covers the main challenges in the PEM fuel cell power system implementation concerning current ripple and electric power changes dynamics. This circuit implementation leads to increasing system efficiency over 95 percent and decreasing the cost by at least 50 percent. The hybridization circuit is verified by simulation and experimental results.Keywords: PEM Fuel Cell, Lead-Acid Battery, Hybridization Circuit, DC/DC Converter, Switch.

Today, for enhancing the trend of energy demand in the world, the use of energy by the approach of maximizing the efficiency of energy systems is inevitable. On the other hand, the high growth rate of unmanned aerial vehicles (UAV), governments investment to develop the necessary infrastructures for the progress of this technology, the variety of applications, and the advantages, indicate its special role in the future. In the present study, an integrated system consisting of PEM electrolyzer, PEM fuel cell, photovoltaic panel, and hydrogen and oxygen storage tanks is developed as a UAV propulsion system so that it can provide the required power. The power required by the UAV was supplied by the PEM fuel cell of the system. The intended hydrogen and oxygen are provided through a hydrogen and oxygen storage tank. In this condition, the capacity of the tanks is known as the limiting factor during the UAV flight time. For more flight continuity, part of the consumable hydrogen and oxygen during the flight is regenerated by installing a photovoltaic panel, using solar renewable energy and also PEM electrolyzer. The hydrogen and oxygen generated by the electrolyzer is 49.04% of the PEM fuel cell consumption, indicating that the UAV flight continuity using the integrated structure of the present study can be increased up to approximately 1.5 times. Then, by performing a parametric study and changing the main parameters of the system, including current densities of PEM electrolyzer and PEM fuel cell, as well as temperature and solar radiation level, the integrated system is evaluated in different conditions and the results are reported. Finally, by examining various aspects of the present plan, including the weight conditions, the efficiency of the integrated system developed in the present study as a new propulsion system for UAVs with various purposes has been specified.

In recent decades, fuel cells have been widely used in energy generation. In a PEMFC, considering the specific application, two types of oxidants are used. Durability tests, which are highly costly products,  are of crucial importance in evaluating the lifetime of fuel cells. The purpose of the present paper is to investigate the performance of a fuel cell by changing the type of oxidant from air to pure oxygen. Because of the presence of impurities in the air oxidant, a cell with air oxidant is more sensitive to operating conditions than one with pure oxygen. In this experiment, a single fuel cell was assembled and used for testing. The lifetime test was carried out in constant current, and the voltage decay rate was reported. Effects of various parameters, like air stoichiometry, Dew point Temperature, and Pressure, have been investigated. Increasing the stoichiometry of the oxidant to 3 greatly increased the voltage of the fuel cell, but no significant increase in the fuel cell voltage was observed in stoichiometries above this value. A comparison of inlet gas temperatures demonstrated that the fuel cell had the best performance at 75 °C, but due to the fluctuation of the output voltage at this temperature, the temperature was decreased to 65 °C. Finally, upon performing durability test with pure oxygen for 9 hours and comparing the results with those of air oxidant, the possibility of using a fuel cell with two different oxidants has been confirmed.

This study used the lattice Boltzmann method (LBM) to evaluate water distribution in the gas diffusion layer (GDL) of cathode PEM fuel cells (PEMFCs) with porosity gradient. Due to the LBM’s capability of parallel processing with a GPU and the high volume of computing necessary, especially for small grids, the GPU parallel processing was done on a graphics card with the help of CUDA to speed up computing. The two-phase flow boundary conditions in the GDL are similar to the water transfer in the GDL of the PEMFCs. The results show that capillary force is the main cause of water transfer in the GDL, and gravity has little effect on the water transfer. Also, the use of GPU parallel processing on the graphics card increases the computation speed up to 17 times, which has a significant effect on running time. To investigate the gradient of porosity of GDLs with different porosity gradients, but the same average porosity coefficient and the same particle diameter have been evaluated. The simulation results show that the GDL with a 10% porosity gradient compared to the GDL with uniform porosity results in a 20.2% reduction in the amount of liquid water in the porous layer. Hence, increasing the porosity gradient of the GDL, further decreases the amount of liquid water in the porous layer. So, for the GDL with a porosity gradient of 14% this decrease is 29.8% and for the GDL with porosity gradient 18.5% this decrease is 38.8% compared to the GDL with uniform porosity.

The PEMFC heat generation was utilized to desorb hydrogen from a LaNi5 filled MH–Hydrogen Storage tank. Heat pipes were used to transfer of heat from the FC to the MH- tank. The study was conducted using CFD simulation. Results showed that the increase of initial pressure of the MH tank and the cooling temperature of 303 K led to a rise in the hydrogen adsorption performance. In the desorption stage, after passing 4000 s, the amount of 5.39 g of hydrogen is purged from the hydride tank. Additionally, results demonstrated that the total hydrogen discharge rate of 0.304 slpm was achieved only to the expense of 7.36 W of a total of 23.43 W generated heats in the fuel cell. Furthermore, the hydrogen desorption flow rate has gained 45 % for the presented geometry compared to a similar system. Moreover, a very good agreement was found between the present work simulation results and the literature data

An electrochemical analysis on a single channel PEM fuel cell was carried out by Computational Fuel Cell Dynamics (CFCD). The objective was to assess the latest developments regarding the effects of change in the current collector materials, porosity of electrodes and gas diffusion layer on the fuel cell power density. Graphite, as the most applicable current collector material, was applied followed by Aluminum and Titanium. It was found that titanium enhances the performance of the fuel cell as compared to the graphite and aluminum. Other results obtained were: the total porosity of electrode's layers does not have a significant effect on power density. At higher porosity of gas diffusion layer at voltages higher than 0.5 is favorable in gas diffusion, which leads to better performance. A numerical model, based on the assessment of basic best practice guidelines for CFCD, was developed that led to reasonably good agreement with the experimental results.

In this article a new structure of PEM fuel cell end plate is presented. The new structure is known as a honeycomb sandwich panel. Several properties of the presented structure, such as mechanical and thermal behavior, as well as its advantages and disadvantages are introduced. The aim of this paper is to reduce the weight of the while maintaining a better compression force on the PEM fuel cell components. By considering a honeycomb sandwich panel, this structure has lighter weight and more strength and flexibility. In this regard, some mechanical experiments and electrical simulations have been done on the honeycomb structure end plates to provide a comparisom between this new structure and the old structure usually made of steel. These mechanical experiments include pressure and bending tests. The results were evaluated in two cases: with foam and no foam. After analyzing the experimental results, it has been concluded that the honeycomb sandwich panel structure for end plates has many advantages that makes it a good alternative to the old endplate structure.

Platinum particles were grown directly by an electrodeposition process on electrochemically treated carbon paper (CP) for kinetic study of carbon monoxide (CO) desorption. The treatment on CP was performed by applying −2 V for cathodic oxidation over 5 min. Treated CP was characterized by FTIR to investigate the oxygen groups on its surface. CO surface coverage at each temperature was determined by monitoring changes in Had (adsorbed hydrogen) desorption charge during CO stripping at different desorption times (300 to 1800 s). CO coverage of the cathodic electrode is lower than non-treated one in all temperatures. Desorption rate constants were calculated for cathodic and non-treated electrodes. From 25 to 85 °C, rate constants for cathodic electrode are higher than the non-treated electrode at all temperatures. The activation energies for desorption, estimated from data obtained by the experiments, are 28480 and 18900 J.mol-1 for non-treated and cathodic electrode, respectively. This shows that CO desorption is easier on the surface of the cathodic electrode than non-treated electrode due to the presence of oxygen surface groups.

There are several obstacles to the commercialization of PEM fuel cells. One of the reasons is that the presence of carbon monoxide (CO) in the reformatted fuel, even at a very small scale, decreases the fuel cell performance. The aim of this paper is to investigate the effect of CO in reformatted fuel on PEM fuel cell performance. For this purpose, a steady state, one-dimensional and non-isothermal model is utilized to evaluate the PEM fuel cell performance with and without CO in the fuel stream. The governing equations which includes the conservation of mass, energy and species equations are solved in MATLAB software and validated by the available data in the literatures. The results indicate that when pure hydrogen is used as anode fuel the activation loss of the cathode is very large relative to the anode value; also, the maximum temperature occurs in the cathode catalyst layer. When reformatted fuel is applied as anode gas stream, activation loss and anode temperature increase by increasing the CO concentration in the reformatted fuel. As example, when CO concentration is over 50 ppm in the fuel stream, the activation loss and anode will be higher than the relevant amounts in cathode catalyst layer. Also it is observed that by increasing the fuel cell temperature and anode pressure, the CO effects on fuel cell performance are reduced.

Distribution of contact pressure between the bipolar plate and gas diffusion layer considerably affect the performance of proton exchange membrane fuel cell. In this regard, an adaptive neuro-fuzzy inference system (ANFIS) is developed to predict the contact pressure distribution on the gas diffusion layer due to dimensional errors of the bipolar plate ribs in a proton exchange membrane fuel cell. Firstly, the main data set of input/output vectors for training and testing of the ANFIS is prepared based on a finite element simulation of the contact between bipolar plate and gas diffusion layer. An experimental procedure is used to validate the simulation results. Then, the ANFIS is developed and validated using the randomly selected data series for network testing. The applied ANFIS model has ten inputs made up of the dimensional errors of the bipolar plate ribs (e1 … e10). The standard deviation of contact pressure distribution (Pstd) on the gas diffusion layer is the unique output of the ANFIS model. To select the best ANFIS model, the average errors of various architectures two different data series of training and testing of the main data set are calculated. Results indicated that the developed ANFIS has an acceptable performance in predicting the contact pressure distribution for the cited fuel cell model. The proposed integrated prediction model is feasible and effective for the dimensional tolerances considered. This method can reduce computing time and cost considering the acceptable accuracy of the obtaining results, and can be used to analyze the effects of dimensional errors of bipolar plate on the performance of proton exchange membrane fuel cell.

In this paper, three innovative 3-D geometries for flow fields of cathode and anode have been developed to investigate the comparative impact of increasing the multiplicity of the involved anode-cathode channel surface contact on the efficiency of electrochemical reaction via the same membrane electrode assembly (MEA) active area. In the introduced new models, each anode channel includes two, three and four cathodes while the convectional model include a one to one connection. The governing equations consist of mass, momentum and energy conservation. In addition, the species transport and the electric/ionic fields were solved numerically using the finite volume method under the assumptions of steady state and non-isothermal fluid flow. Simulation results revealed that increasing the multiplicity of the anode-cathode involved surface of reactants channel leads to current and power density enhancement due to the improved opportunity of reactants penetration and less concentration losses. Also, a considerable reduction of mono-cell volume size and costs for the new models in comparison with the base design was achieved.

In order to present a new and high performance structure of PEM fuel cell and study the influence of the flow direction and distribution on the rate of reactants diffusion, three novel models of vertical reactant flow injection into the anode and cathode reaction area field have been introduced. They consist of one inlet and two inlets and also a continuous channel. The governing equations on the steady, three dimensional non-isothermal flow have been discretized using finite volume method. These 3D simulations are going to evaluate the effectiveness of flow direction on the transportation and chemical phenomena inside the PEM fuel cell by applying computational fluid dynamics (CFD) method to the transportation and conservation equations with the suppositions of steady state and one phase flow. The numerical results are validated with experimental ones for available common fuel cells. The results show that the presented geometries have several mechanical and chemical benefits such as extra diffusion of reactants because of flow direction, improvement of species distributions, enhancement in temperature management and more effective water removal due to the number of outlets and uniform current distribution. Furthermore, the continuous channel inlet due to cover more reaction area and high rate of reactants diffusion presents substantial higher performance than others. With regard to the polarization curve along with other advantages, the so-called design can be strongly recommended for obtaining high operating efficiency and can be considered for the manufacturing of new generation of PEM fuel cells in the form of high performance stacks.

The produced liquid water in cathode catalyst layer (CCL) has significant effect on the operation of proton exchange membrane fuel cell (PEMFC). To investigate this effect, the transport of oxygen in CCL in the presence of immiscible liquid water is studied applying a two-dimensional pore scale model. The CCL was reconstructed as an agglomerated system. To explore the wettability effects, different contact angles were considered at the surface of agglomerates. The effective diffusivity of oxygen was calculated under different contact angles at various saturation levels. The same effective diffusivity was obtained for hydrophilic and hydrophobic domains at lower saturations, however, at saturation above 0.4, hydrophobic domain provided higher effective diffusivity values. The effect of water coverage at reaction surface areas was investigated. The results showed that, at the saturation of 0.4, the hydrophobic domain with the contact angle of 150 has about 2 times more available surface area, due to different distribution of water phase compared to the hydrophilic domain with the contact angle of 20.

In this study cross section geometry and material of gasket in proton exchange membrane (PEM) fuel cells have been investigated to achieve optimized fuel cell in terms of energy efficiency. The role of gaskets in fuel cells is sealing of gas flow channels and preventing from combination of them. In a PEM stack, gasket with approved geometry that suffers more stress has better sealing. For this investigation, at first experimental leakage tests have been done and after gaskets manufacturing, stack assembly, putting setup under press and studying leakage values in terms of time and various pressures, results showed that sealing gasket with width of 3mm and thickness of 0.4mm in pressure of 2MPa seals well according to standards, To access to optimal results, width of 3mm and thickness of 0.4mm has been considered for numerical simulation. After leakage test, some materials have been tested and results showed that gasket with hyper elastic properties is the best choice for sealing. After experimental tests 6 shapes of gasket cross section profile in fuel cell stack have been modeled in Abaqus software and with attention to results and analyzing them, the best material and profile shape for gasket in fuel cell has been selected. Results of simulations showed good uniform pressure distribution in stack.