Transient computation fluid dynamics modeling of a single proton exchange membrane fuel cell with serpentine channel

The proton exchange membrane fuel cell (PEMFC) has become a promising candidate for the power source of electrical vehicles because of its low pollution, low noise and especially fast startup and transient responses at low temperatures. A transient, three-dimensional, non-isothermal and single-phase mathematical model based on computation fluid dynamics has been developed to describe the transient process and the dynamic characteristics of a PEMFC with a serpentine fluid channel. The effects of water phase change and heat transfer, as well as electrochemical kinetics and multicomponent transport on the cell performance are taken into account simultaneously in this comprehensive model. The developed model was employed to simulate a single laboratory-scale PEMFC with an electrode area about 20 cm². The dynamic behavior of the characteristic parameters such as reactant concentration, pressure loss, temperature on the membrane surface of cathode side and current density during start-up process were computed and are discussed in detail. Furthermore, transient responses of the fuel cell characteristics during step changes and sinusoidal changes in the stoichiometric flow ratio of the cathode inlet stream, cathode inlet stream humidity and cell voltage are also studied and analyzed and interesting undershoot/overshoot behavior of some variables was found. It was also found that the startup and transient response time of a PEM fuel cell is of the order of a second, which is similar to the simulation results predicted by most models. The result is an important guide for the optimization of PEMFC designs and dynamic operation.     

Dynamic models and model validation for PEM fuel cells using electrical circuits

This paper presents the development of dynamic models for proton exchange membrane (PEM) fuel cells using electrical circuits. The models have been implemented in MATLAB/SIMULINK and PSPICE environments. Both the double-layer charging effect and the thermodynamic characteristic inside the fuel cell are included in the models. The model responses obtained at steady-state and transient conditions are validated by experimental data measured from an Avista Labs SR-12 500-W PEM fuel-cell stack. The models could be used in PEM fuel-cell control related studies.     

Numerical investigation of transient responses of a PEM fuel cell using a two-phase non-isothermal mixed-domain model

In this paper, a transient two-phase non-isothermal PEM fuel cell model has been developed based on the previously established two-phase mixed-domain approach. This model is capable of solving two-phase flow and heat transfer processes simultaneously and has been applied herein for two-dimensional time-accurate simulations to fully examine the effects of liquid water transport and heat transfer phenomena on the transient responses of a PEM fuel cell undergoing a step change of cell voltage, with and without condensation/evaporation interfaces. The present numerical results show that under isothermal two-phase conditions, the presence of liquid water in the porous materials increases the current density over-shoot and under-shoot, while under the non-isothermal two-phase conditions, the heat transfer process significantly increases the transient response time. The present studies also indicate that proper consideration of the liquid droplet coverage at the GDL/GC interface results in the increased liquid saturation values inside the porous materials and consequently the drastically increased over-shoot and under-shoot of the current density. In fact, the transient characteristics of the interfacial liquid droplet coverage could exert influences on not only the magnitude but also the time of the transient response process.     

Effects of inlet humidification on PEM fuel cell dynamic behaviors

The dynamic behaviors of a proton exchange membrane (PEM) fuel cell have been studied both experimentally and numerically. The objective of this paper is to investigate the effects of cathode inlet humidification on PEM fuel cell load change operations and the fuel cell performance during a simulated start‐up process. The PEM fuel cell was found to respond quickly and reproducibly to load changes. It was also found that an increase in the cathode inlet humidification significantly influences the start‐up performance of a PEM fuel cell. The cathode inlet relative humidity (RH) under 30% significantly dropped the cell dynamic performance. Extensive numerical simulations, with the transient processes of load jump and gradual changes considered, were performed to characterize dynamic responses of a singe‐channel PEM fuel cell under different inlet humidification levels. The results showed that the response time for a fuel cell to reach steady state depends on water accumulation in the membrane, which is consistent with the experimental results. Copyright © 2010 John Wiley & Sons, Ltd.     

Combined heat and power generation via hybrid data center cooling-polymer electrolyte membrane fuel cell system

Although there has been a lot of waste heat utilization studies for the air-cooled data center (DC) systems, the waste heat utilization has not been studied for the liquid-cooled DC systems, which have been rapidly gaining importance for the high-performance Information and Communication Technology facilities such as cloud computing and big data storage. Compared to the air-cooled systems, higher heat removal capacity of the liquid-cooled DC systems provides better heat transfer performance; and therefore, the waste heat of the liquid-cooled DC systems can be more efficiently utilized in the low-temperature and low-carbon energy systems such as electricity generation via polymer electrolyte membrane (PEM) fuel cells. For this purpose, the current study proposes a novel hybrid system that consists of the PEM fuel cell and the two-phase liquid-immersion DC cooling system. The two-phase liquid immersion DC cooling system is one of the most recent and advanced DC cooling methods and has not been considered in the DC waste heat utilization studies before. The PEM fuel cell unit is operated with the hydrogen and compressed air flows that are pre-heated in the DC cooling unit. Due to its original design, the hybrid system brings its own original design criteria and limitations, which are taken into account in the energetic and exergetic assessments. The power density of the PEM fuel cell reaches up to 0.99 kW/m² with the water production rate of 0.0157 kg/s. In the electricity generation case, the highest energetic efficiency is found as 15.8% whereas the efficiency increases up to 96.16% when different multigeneration cases are considered. The hybrid design deduces that the highest exergetic efficiency and sustainability index are 43.3% and 1.76 and they are 9.4% and 6.6% higher than exergetic and sustainability performances of the stand-alone PEM fuel cell operation, respectively.     

Time delay control for fuel cells with bidirectional DC/DC converter and battery

Transient behavior is a key property in the vehicular application of proton exchange membrane (PEM) fuel cells. A better control technology is constructed to increase the transient performance of PEM fuel cells. A steady-state isothermal analytical fuel cell model is constructed to analyze mass transfer and water transport in the membrane. To prevent the starvation of air in the PEM fuel cell, time delay control is used to regulate the optimum stoichiometric amount of oxygen, although dynamic fluctuations exist in the PEM fuel cell power. A bidirectional DC/DC converter connects the battery to the DC link to manage the power distribution between the fuel cell and the battery. Dynamic evolution control (DEC) allows for adequate pulse-width modulation (PWM) control of the bidirectional DC/DC converter with fast response. Matlab/Simulink/Simpower simulation is performed to validate the proposed methodology, increase the transient performance of the PEM fuel cell system and satisfy the requirement of energy management.     

A new dynamic model for predicting transient phenomena in a PEM fuel cell system

In this paper, a mathematical model is developed to simulate the transient phenomena in a polymer electrolyte membrane fuel cell (PEMFC) system. At present many electrochemical models are available to the fuel cell designers to capture steady state behavior by estimating the equilibrium voltage for a particular set of operating conditions, but models capable of describing transient phenomena are scanty. In practical applications such as powertrains of land-based vehicles or submarines, the output power from the fuel cell system undergoes large variations especially during acceleration and deceleration. During such processes, many transient dynamic mechanisms become significant, while simple empirical models are unable to represent the transient dynamics caused by such as diffusion effect and double layer capacitance at the interface between the electrodes and the electrolyte. Hence, a novel dynamic fuel cell model is developed in this paper which incorporates the effects of charge double layer capacitance, the dynamics of flow and pressure in the anode and cathode channels and mass/heat transfer transient features in the fuel cell body. This dynamic model can predict the transient response of cell voltage, temperature of the cell, hydrogen/oxygen out flow rates and cathode and anode channel temperatures/pressures under sudden change in load current. The proposed model is implemented in SIMULINK environment. The simulation results are analyzed and compared to benchmark results. Lab tests are carried out at Connecticut Global Fuel Cell Center and a good agreement is found between tests and simulations. This model will be very useful for the optimal design and real-time control of PEM fuel cell systems.     

Steady and unsteady 3D non-isothermal modeling of PEM fuel cells with the effect of non-equilibrium phase transfer

A 3D model that fully couples multi-species and multi-phase transport, electrochemical kinetics, and heat transfer processes has been developed. The non-equilibrium membrane water absorption/desorption processes along with non-equilibrium condensation/evaporation processes have been investigated utilizing this comprehensive model. In addition, the fallacious assumption that water is produced in vapor phase during the half cell electrochemical reaction is addressed for the first time. The difference and relationship of the cell output current density among three water production mechanisms are exhibited to show the potential error induced by vapor or liquid production assumptions. The present model is capable of predicting transient phenomena within the cell as well. Our results show that compared to the liquid production modeling the dynamic response of PEM fuel cells in vapor production modeling is significantly overestimated owing to the sluggish condensation process.     

Hydrogen crossover through perfluorosulfonic acid membranes with variable side chains and its influence in fuel cell lifetime

In this study, hydrogen crossover in long side chain Nafion 211 membrane and short side chain Aquivion membrane is studied under different conditions. It is found that both temperature and relative humidity significantly influence the hydrogen crossover in the polymer electrode membranes (PEMs). The difference in hydrogen crossover behavior between Nafion 211 membrane and Aquivion membrane is revealed. The influence of hydrogen crossover on the fuel cell lifetime is also investigated under open circuit voltage (OCV). It is proved hydrogen crossover in the PEM would lead to possible degradation of the PEM and the decrease of electro-chemical surface area in the catalyst of the single cell. Single cell assembled with Aquivion membrane shows slower OCV and ECSA decay compared to the Nafion 211 single cell. Our results suggest that the PEM fuel cell lifetime is closely related to the hydrogen crossover in the PEM. The current study also highlights the possibility of improving the fuel cell durability by rational design of the PEM morphology.     

An experimental study and model validation of a membrane humidifier for PEM fuel cell humidification control

This paper presents an experimental study and model validation of an external membrane humidifier for PEM fuel cell humidification control. Membrane humidification behavior was investigated with steady-state and dynamic tests. Steady-state test results show that the membrane vapor transfer rate increases significantly with water channel temperature, air channel temperature, and air flow rate. Water channel pressure has little effect on the vapor transfer rate and thus can be neglected in the system modeling. Dynamic test results reveal that the membrane humidifier has a non-minimum phase (NMP) behavior, which presents extra challenges for control system design. Based on the test data, a new water vapor transfer coefficient for Nafion membrane was obtained. This coefficient increases exponentially with the membrane temperature. The test results were also used to validate a thermodynamic model for membrane humidification. It is shown that the model prediction agrees well with the experimental results. The validated model provides an important tool for external humidifier design and fuel cell humidification control.     

Morphological characterization of sulfonated graphene and Nafion composite membrane by dynamic mode atomic force microscopy

Maintaining proper hydration in the proton exchange membrane (PEM) is a crucial issue for passive air breathing PEM (ABPEM) fuel cells. The inorganic filler Nafion composite membrane has great potential for replacing commercialized PEM for ABPEM. We synthesize sulfonated graphene and Nafion composite membrane by using functionalized graphene to enhance the water content in the membrane. We analyze morphological variation of a sulfonated graphene–Nafion composite membrane by using dynamic mode atomic force microscopy (DMAFM). The phase map and topography of the sulfonated graphene–Nafion composite membrane were simultaneously studied for systematic characterization. Through characterization, we find that the water content on the composite membrane has increased remarkably and that it is related to the morphological variation after the composition. In the composite membrane, the root‐mean‐squared surface roughness has increased compared with pristine Nafion because of the sulfonated graphene. In the DMAFM study, the composite membrane shows an entirely different phase map than the pristine Nafion. The elliptical domains, which have positive phase lags, are created on the composite membrane surface. The creation of these domains reflects the existence of a repulsive interaction between the tip and sample surface because of an increasing adhesive force between the tip and sample. Copyright © 2015 John Wiley & Sons, Ltd.     

Construction of low-cost and long-time proton exchange membranes by using slow-release radical scavenger

The bottlenecks of commercial application of proton exchange membranes (PEM) fuel cell are cost and oxidation stability of PEM. Hence, we encapsulate Resveratrol (Res, a kind of reductant) in hydroxypropyl-β-cyclodextrins (CDs) to prepare the inclusion complexes of Res and CDs (Res@CDs) under the guidance of theoretical arithmetic. Then the Res@CDs are evenly dispersed in Nafion emulsion, which is subsequently combined with porous polytetrafluoroethylene (PTFE) substrate by emulsion pouring method to form the antioxidative composite membrane (Res@CDs-Nafion/PTFE). The as-prepared Res@CDs-Nafion/PTFE shows the similar performance on proton conductivity (103.9 mS cm⁻¹) and hydrogen-air fuel cell (317.84 mW cm⁻²) compared to the Nafion/PTFE composite membrane. The content of Nafion in the Res@CDs-Nafion/PTFE is less than 30%, which dramatically reduces the production cost compared to pure Nafion membrane. The weight loss of Res@CDs-Nafion/PTFE and Nafion/PTFE immersed in Fenton's reagent after 36 h is 4.97% and 16.49%, respectively, which demonstrate that Res@CDs can enhance oxidation stability of composite membrane. The Res@CDs-Nafion/PTFE offer huge merits of low cost and enhanced oxidation stability, which greatly promotes the application process of long-lifetime PEM fuel cell.     

A review: Exergy analysis of PEM and PEM fuel cell based CHP systems

In recent years, growing attention has been given to new alternative energy sources and exergy analysis since fossil fuels cause emissions that have some negative impacts on earth such as global warming, greenhouse effect etc. New power generation systems have been developed in order to reduce or eliminate these impacts as possible. So that, new alternative energy systems have been taken place instead of fossil fuel based systems with nearly zero emission levels. One of them is solid polymer electrolyte or proton exchange membrane (PEM) fuel cell. Although it has significant advantages, there are some disadvantages such as cost, and hydrogen is not a fuel that can be easily obtained. For these reasons, efficiency of a PEM fuel cell has a great significance. Energy efficiency of a system is the most important parameter for utilization. But, energy analysis does not always show the capacity to do work potential of energy of a system. Exergy analysis must be investigated for a system in order to see available work of the system. Because of disadvantages of the PEM fuel cell, exergy analysis has quite importance. In this paper PEM fuel cell and exergy analysis of PEM fuel cell are combined and investigated. A detailed review of the past and recent research activities has been documented. The review focuses on exergy analysis of both PEM fuel cells and PEM based combined heat and power (CHP) systems at different operating parameters. It is concluded that there are a lot of parameters which effects the exergy efficiencies of systems.     

Numerical simulation for the effect of vaporization intensity in membrane on the performance of PEM fuel cell

The heat and mass transfer characters of proton-exchange membrane (PEM) fuel cell have major impact on the performance of cell system, and suitable moisture content in the membrane is one of the most important enhancing factors of PEM fuel cell systems. In this article, the effect to different vaporization mechanism of water in the membrane is investigated numerically, the results show that the temperature of the fuel cell increases with lessens of the heat transfer coefficient, and the average temperature located in membrane is reduced most significantly by 18.03% compared to no vaporization condition in membrane for cases in which heat transfer coefficient is 50?W/m²?·?K. Furthermore, the current density with evaporation in membrane is much lower than take no account of vaporization, especially on the cathode side; meanwhile, the excess percentage of oxygen and water vapor concentration is more significantly different from the condition without vaporization when the fuel cell temperature reaches the boiling point.     

Mixed-ceria reinforced acid functionalized graphene oxide-Nafion electrolyte membrane with enhanced proton conductivity and chemical durability for PEMFCs

Towards the next-gen energy solutions, Nafion, as a state-of-the-art polymer electrolyte to low temperature fuel cell (LTFC) application has been one of the most demanding hydrogen to clean energy conversion device ever achieved. However, the inherent issue of limiting chemical durability and restricted proton conductivity have always been a topic of concern with pure Nafion membranes. To tackle this, we report a mixed-ceria reinforced phosphorylated graphene oxide (sPGO)/Nafion membrane as a potential electrolyte to simultaneously improve the chemical durability and proton conductivity of bare Nafion by utilizing the redox property of ceria nanoparticles and acidic sites of sPGO for accelerated proton transfer. As a progressive method, the single-step phosphorylation of GO introduced short chain branching along with enhanced number of acidic sites in the Nafion matrix whereas incorporation of mixed-ceria nanoparticles improved the chemical durability of the membrane due to its superior radical scavenging property. As a result, mixed-ceria reinforced sPGO/Nafion (Ce-sPGO/NF) electrolyte membrane showed higher proton conductivity (1.2-times) and chemical durability (8.1-times) than bare Nafion. Furthermore, the polymer electrolyte membrane (PEM) was also showcased high enough thermomechanical and electrochemical stability at 80 °C and 100% relative humidity (RH).     

Effect of design and operating parameters on dynamic response of a micro direct methanol fuel cell

Dynamic response of the micro direct methanol fuel cell (μDMFC) is of significant importance, and has to be considered during cell design as well as operation. In order to explore the effect of design parameter and operating conditions on dynamic behavior, a μDMFC with stainless steel current collectors as well as stainless steel mesh was fabricated. Different load conditions were applied to the cell to test the effect of stainless steel mesh, cell orientation, methanol concentration and methanol flow rate on transient performance of the cell. A variety of physical and electrochemical processes in the cell are coupled and interactive, which determine that factors affecting transient behavior are complex. But experimental results indicate that methanol crossover through proton exchange membrane (PEM), methanol transportation in anode, removal of CO₂ bubbles and heat loss brought away by methanol solution are four crucial causes influencing dynamic behavior of the cell.     

Nafion degradation mechanisms in proton exchange membrane fuel cell (PEMFC) system: A review

Nafion is one of the polymer materials used as polymer electrode membrane (PEM) for fuel cells. However, the electrochemical reaction and water management processes that occur at the catalyst layer affect the performance and degradation of the membrane in the fuel cell resulting in various degradation mechanisms. Understanding the degradation mechanisms of the Nafion membrane in operation, the anhydrous and electrochemical conditions in the fuel cell is highly a necessity as outlined in this review. This review further recommends that further improvement in the Nafion membrane can be made by fabrication and coating the Nafion membrane with materials that can withstand the electrochemical environment in the fuel cell.     

Effect of operating parameters on dynamic response of water-to-gas membrane humidifier for proton exchange membrane fuel cell vehicle

An analytic multi-dimensional dynamic model of a membrane type humidifier has been developed for the study of transient responses of the humidifier under proton exchange membrane fuel cell vehicle operating conditions. The dynamic responses of heat and mass transfer and fluid flow in a membrane humidifier are mathematically formulated and modeled with a newly developed pseudo-multi-dimensional concept. The model is used to analyze the performance of the humidifier under various operating conditions and the dynamic response of the humidifier under transient operating conditions. The simulation results show that, in the case of the water-to-gas type membrane humidifier modeled in this study, the time constant of water diffusion in the membrane is less than 1 s. Thus, the delay of the response of the humidifier induced by the vapor diffusion in the membrane is not significant in vehicle operation. However, it is also found that the dynamic behavior is mainly due to the thermal resistance and heat capacity of the membrane humidifier.     

Effect of flow orientation on thermal-electrochemical transports in a PEM fuel cell

A non-isothermal model of a proton exchange membrane (PEM) fuel cell in contact with interdigitated gas distributors has been performed. The model accounts for the major transports of convective and diffusive heat and mass transfer, electrode kinetics, and potential fields. The effects of flow orientation and total overpotential across a five-layer membrane-electrode assembly on the thermal behaviors in a PEM fuel cell are examined. A unique feature of the model is the implementation of a thermal-electrochemical algorithm to predict the fluid-phase temperature as well as the solid-matrix temperature in a PEM fuel cell. The simulation results reveal both the solid-matrix temperature and the fluid-phase temperature are increased with increasing total overpotential. Moreover, the fluid-phase and solid-matrix temperature distributions are significantly affected by the flow orientation in the PEM fuel cell. Replacing the parallel-flow geometry by the counter-flow geometry has an advantage of reducing the local maximum temperature inside the fuel cell. Thermal effects on the active material degradation and hence fuel cell durability will be incorporated in the future work.     

Effect of the micro porous layer design on the dynamic performance of a proton exchange membrane fuel cell

The mass transport characteristics of a gas diffusion layer (GDL) predominantly affect the performance of a proton exchange membrane (PEM) fuel cell. However, studies examining the transient response related to the GDL are insufficient, although the dynamic behavior of a PEM fuel cell is an important issue. In this study, the effects of the design of a micro porous layer (MPL) on the transient response of a PEM fuel cell are investigated. The MPL slurry density and multiple functional layers are treated as the variable design parameter. The results show that the transient response is determined by the capillary pressure gradient through the GDL. The trade-off relation for the PEM fuel cell performance under low and high humidity conditions due to the hydrophobic GDL is mitigated by designing a reverse capillary pressure gradient in the MPL.