Analytical and experimental investigations of a proton exchange membrane fuel cell

The high power density and rapid adjustment to power demands make proton exchange membrane fuel cells (PEMFCs) one of the best candidates for a clean alternative energy sources for the 21st century. Analytical and experimental works have been presented in this paper to investigate a single PEMFC. These include a study of PEMFC performance, the effects of operating temperature and pressure on performance, and flow characteristics within the cell. Experimental data show the positive effects of temperature and pressure on performance, which is also analyzed by the two-phase multicomponent flow model validated by test data. The predicted performance curves agree reasonably with the experimental data and demonstrate the increase in cell performance at elevated temperature. In addition, the simulation model proposed in this paper can also reasonably capture the flow characteristics in a PEMFC.     

Effects of the humidity and the land ratio of channel and rib in the serpentine three‐dimensional PEMFC model

The construction of a reliable numerical model and the clarification of its operational conditions are necessary for maximizing fuel cell operation. Numerous operating factors, such as mole fractions of species, pressure distribution, overpotential, and inlet relative humidity, affect the performance of proton exchange membrane fuel cells (PEMFCs). Among these operational parameters, geometrical shape and relative humidity are investigated in this paper. Specifically, the land ratio of the gas channel and rib is an important parameter affecting PEMFC performance because current density distribution is influenced by this geometrical characteristic. Three main variables determine the current density distribution, namely, species concentration, pressure, and overpotential distributions. These distributions are considered simultaneously in assessing fuel cell performance with a given PEMFC cell‐operating voltage. In this paper, three different land ratio models are considered to obtain better PEMFC performance. Similarly, three different inlet relative humidity variations are studied to achieve an enhanced operating condition. A three‐dimensional numerical PEMFC model is developed to illustrate the current density distribution as the determining factor for PEMFC performance. Copyright © 2012 John Wiley & Sons, Ltd.     

Configuration effects of air,fuel, and coolant inlets on the performance of a proton exchange membrane fuel cell for automotive applications

The configuration of fuel, air, and cooling water paths is one of the major factors that influence the performance of a proton exchange membrane fuel cell (PEMFC). In order to investigate the effects of these factors, a quasi-three-dimensional dynamic model of a PEMFC has been developed. For validation, simulation results are compared with experimental data in one-flow configuration case and show good agreement with the experimental cell performance data. Five different flow configurations are then simulated to systematically investigate the effects of fuel, air, and cooling channel configuration on the local current and species distribution. Voltage and power vs. current density for five different configurations are compared. The type 1 configuration, which has a fuel–air counter flow and an air-coolant co-flow, has the highest performance in all ranges of current density because the membrane remains the most hydrated. When the operating current density increases, the effects of temperature on membrane hydration slightly decrease. It is confirmed that fuel cell performance improves with increased humidity until flooding conditions appear. An interesting result shows that it is possible to lower the fuel cell operating temperature to improve fuel cell hydration, which in turn improves cell performance. In addition, the different flow configurations are shown to have an effect on the pressure losses and local current density, membrane hydration, and species mole fractions. These results suggest that the model can be used to optimize the flow configuration of a PEMFC.     

A parametric comparison of three fuel recirculation system in the closed loop fuel supply system of PEM fuel cell

Anodic fuel recirculation system has a significant role on the parasitic power of proton exchange membrane fuel cell (PEMFC). In this paper, different fuel supply systems for a PEMFC including a mechanical compressor, an ejector and an electrochemical pump are evaluated. Furthermore, the performances of ejector and electrochemical pump are studied at different operating conditions including operating temperature of 333 K–353 K, operating pressure of 2 bar–4 bar, relative humidity of 20%–100%, stack cells number from 150 to 400 and PEMFC active area of 0.03 m²–0.1 m². The results reveal that higher temperature of PEMFC leads to lower power consumption of the electrochemical pump, because activation over-potential of electrochemical pump decreases at higher temperatures. Moreover, higher operating temperature and pressure of PEMFC leads to higher stoichiometric ratio and hydrogen recirculation ratio because the motive flow energy in ejector enhances. In addition, the recirculation ratio and hydrogen stoichiometric ratio increase, almost linearly, with increase of anodic relative humidity. Utilization of mechanical compressor leads to lower system efficiency than other fuel recirculating devices due to more power consumption. Utilization of electrochemical pump in anodic recirculation system is a promising alternative to ejector due to lower noise level, better controllability and wide range of operating conditions.     

Modeling and experimental validation of H2 gas bubble humidifier for a 50 kW stationary PEMFC system

Ensuring uniform membrane hydration in a PEMFC (Proton Exchange Membrane Fuel Cell) is important for its performance and durability. In this study, a bubble humidifier for humidifying hydrogen in a 50 kW PEMFC pilot plant was designed, built, and modeled. Initial tests, carried out by humidifying air, show that a dew point temperature of higher than 59 °C is attained when operating the PEMFC plant at nominal power at 65 °C. The model simulation results show good agreement with experimental data and the model is used for studying humidifier performance at other conditions. Steady state simulation results suggest that by increasing the heating water flow rate, the humidifier outlet dew point temperature can be increased by several degrees because of improved heat transfer. Finally, dynamic simulation results suggest that the humidity of the hydrogen can be controlled by manipulating the heat supply to the humidifier.     

Investigation of the effect of humidity at both electrode on the performance of PEMFC using orthogonal test method

Under the vehicle working conditions, operating temperature and relative humidity (RH) of gas supplies have an important influence on the performance and durability of PEMFC. In this paper, the influence of hydrogen RH, air RH, operating temperature and air stoichiometric ratio on the performance of PEMFC was studied with the help of 5 factors and 4 levels orthogonal test table. The fifth factor was set to be empty to carry out the variance analysis. Using variance analysis method, the influence degree of random errors on the experiments was analyzed. The credibility of the experimental results was verified along with the polarization curve and the electrochemical impedances spectroscopy (EIS) results. The experiment results show that the most important factor which affects the performance of PEMFC is air stoichiometric ratio, followed by air RH, and then the operating temperature. The effect of hydrogen RH on PEMFC performance is minimal and negligible. Low hydrogen RH can be used during operation to reduce energy consumption of auxiliary system.     

CFD investigating the effects of different operating conditions on the performance and the characteristics of a high-temperature PEMFC

The effects of different operating conditions on the performance and the characteristics of a high-temperature proton exchange membrane fuel cell (PEMFC) are investigated using a three-dimensional (3-D) computational fluid dynamics (CFD) fuel-cell model. This model consists of the thermal-hydraulic equations and the electrochemical equations. Different operating conditions studied in this paper include the inlet gas temperature, system pressure, and inlet gas flow rate, respectively. Corresponding experiments are also carried out to assess the accuracy of this CFD model. Under the different operating conditions, the PEMFC performance curves predicted by the model correspond well with the experimentally measured ones. The performance of PEMFC is improved as the increase in the inlet temperature, system pressure or flow rate, which is precisely captured by the CFD fuel cell model. In addition, the concentration polarization caused by the insufficient supply of fuel gas can be also simulated as the high-temperature PEMFC is operated at the higher current density. Based on the calculation results, the localized thermal-hydraulic characteristics within a PEMFC can be reasonably captured. These characteristics include the fuel gas distribution, temperature variation, liquid water saturation distribution, and membrane conductivity, etc.     

Performance enhancement in a H2/O2 PEMFC with dual-ejector recirculation

Water management in various components of the proton exchange membrane fuel cell (PEMFC) is a significant and challenging issue affecting output performance. PEMFC utilizing dual ejector-based recirculation has been developed to evaluate and improve the performance and water transport properties. A detailed investigation into the effects of ejector operating conditions, such as primary flow pressure and secondary flow relative humidity, on the performance of PEMFC is conducted. The results show that significant performance improvement of PEMFC can be achieved by increasing the operating pressure. The power density can be increased by 37.8% and 86.5% with ejector primary flow pressures of 300 and 400 kPa, respectively. Furthermore, an optimization strategy integrating PEMFC operating condition is proposed to ensure the stability and lifespan of performance. The water management and integration optimization strategy obtained in this paper can provide valuable insight into options for improving the performance of PEMFC with dead-ended anode and cathode.     

Two dimensional dynamic modeling of a shell-and-tube water-to-gas membrane humidifier for proton exchange membrane fuel cell

Water management is a crucial factor in determining the performance of proton exchange membrane fuel cell (PEMFC) for automotive application. The shell-and-tube water-to-gas membrane humidifier is useful for humidifying the PEMFC due to its good performance. Shell-and-tube water-to-gas membrane humidifiers have liquid water on one side of the tube wall and a dry gas on the other. In order to investigate humidifier performance, a two-dimensional dynamic model of a shell-and-tube water-to-gas membrane humidifier is developed. The model is discretized into three control volumes – shell, tube and membrane – in the cross-sectional direction to resolve the temperature and species concentration of the humidifier. For validation, the dew point temperature of the simulation result is compared with that of experimental data and shows good agreement with only a slight difference. The distribution of humidification characteristics can be captured using the discretization along the air-flow direction. The humidification performance of two different flow configurations, counter and parallel, are compared under various operating conditions and geometric parameters. Finally, the dynamic response of the humidifier at the step-change of various air flow rates is investigated. These results suggest that the model can be used to optimize the inlet flow humidity of a PEMFC.     

Experimentally and numerically investigating cell performance and localized characteristics for a high-temperature proton exchange membrane fuel cell

This paper is to experimentally and numerically investigate the cell performance and the localized characteristics associated with a high-temperature proton exchange membrane fuel cell (PEMFC). Three experiments are carried out in order to study the performance of the PEMFC with different operating conditions and to validate the numerical simulation model. The model proposed herein is a three-dimensional (3-D) computational fluid dynamics (CFD) non-isothermal model that essentially consists of thermal–hydraulic equations and electrochemical model. The performance curves of the PEMFC predicted by the present model agree with the experimental measured data. In addition, both the experiments and the predictions precisely demonstrate the enhanced effects of inlet gas temperature and system pressure on the PEMFC performance. Based on the simulation results, the localized characteristics within a PEMFC can be reasonably captured. These parameters include the fuel gas distribution, liquid water saturation distribution, membrane conductivity distribution, temperature variation, and current density distribution etc. As the PEMFC is operated at the higher current density, the fuel gas would be insufficiently supplied to the catalyst layer, consequently causing the decline in the generation of power density. This phenomenon is so called mass transfer limitation, which can be precisely simulated by the present CFD model.     

Modeling electrochemical performance in large scale proton exchange membrane fuel cell stacks

The processes, losses, and electrical characteristics of a Membrane-Electrode Assembly (MEA) of a Proton Exchange Membrane Fuel Cell (PEMFC) are described. In addition, a technique for numerically modeling the electrochemical performance of a MEA, developed specifically to be implemented as part of a numerical model of a complete fuel cell stack, is presented. The technique of calculating electrochemical performance was demonstrated by modeling the MEA of a 350 cm², 125 cell PEMFC and combining it with a dynamic fuel cell stack model developed by the authors. Results from the demonstration that pertain to the MEA sub-model are given and described. These include plots of the temperature, pressure, humidity, and oxygen partial pressure distributions for the middle MEA of the modeled stack as well as the corresponding; current produced by that MEA. The demonstration showed that models developed using this technique produce results that are reasonable when compared to established performance expectations and experimental results.     

Development of bipolar plates with different flow channel configurations based on plant vein for fuel cell

In this paper, a kind of proton exchange membrane fuel cell (PEMFC) bipolar plate based on plant vein is developed through biomimetic analogy theory. Fluent software is employed to test the performance characteristics of this newly designed bipolar plate. It is found from the numerical simulation results that the PEMFC performance will be influenced by the number and location of the biomimetic flow channel branches. The distribution pattern of branches has great impact on the outlet velocity. The more the branch number is, the more favorable for water removal. Finally, different operating parameters, such as temperature, pressure, relative humidity and stoichiometric ratio, are chosen based on the optimal flow channel configuration to improve PEMFC performance. Copyright © 2013 John Wiley & Sons, Ltd.     

The effect of low humidity on the uniformity and stability of segmented PEM fuel cells

The performance and stability of a PEMFC depends on many operating parameters. The measurement of local currents in PEMFC cells is an important tool for diagnoses and development of fuel cells. In this study, a segmented cell was developed, which could serve as an essential instrument to investigate the different operating conditions in the cells and stacks of technical relevance. In addition, the effects of different feed gas humidity and temperatures were investigated to analyze the steady-state performance, uniformity, and the local stability of PEMFC with the use of eight segmented regions. With this research method, the resistance in each segment could be measured by ac impedance as well as make a comparison between Nafion^® 117 and 112 membranes in PEMFC. In the experiment, by probing into the high frequency internal resistance and performance of this cell, the effects of flow rates of fuels, oxidants, relative humidity, and directional channel flows were investigated for performance and stability of local segmented regions. The results of the experiments demonstrate that the local current distribution is strongly influenced by the relative humidity of fuel, the stoichiometric of the processed air, and the mode of operation. The cell was operated at a cell temperature of 50 °C with low relative humidity of 33% and 0%, causing the drying of the membrane (and increase of its resistance) at the top-stream path. The membrane conductivity was enhanced due to the water product increase by the reaction in the middle- and down-stream paths, because the down-stream has higher current than the top-stream. The relative humidity of the air increased along the path due to the product water, therefore, the current density increased as well. The local segmented cell could maintain stable performance at low hydrogen stoichiometry of 1.05 for low humidity gases. As the counter-flow and inverse gravity direction of hydrogen fuel was operated, the fuel cell showed the much more stable and uniform local performance.     

Simultaneous direct visualisation of liquid water in the cathode and anode serpentine flow channels of proton exchange membrane (PEM) fuel cells

Water flooding is detrimental to the performance of the proton exchange membrane fuel cell (PEMFC) and therefore it has to be addressed. To better understand how liquid water affects the fuel cell performance, direct visualisation of liquid water in the flow channels of a transparent PEMFC is performed under different operating conditions. Two high-resolution digital cameras were simultaneously used for recording and capturing the images at the anode and cathode flow channels. A new parameter extracted from the captured images, namely the wetted bend ratio, has been introduced as an indicator of the amount of liquid water present at the flow channel. This parameter, along with another previously used parameter (wetted area ratio), has been used to explain the variation in the fuel cell performance as the operating conditions of flow rates, operating pressure and relative humidity change. The results have shown that, except for hydrogen flow rate, the wetted bend ratio strongly linked to the operating condition of the fuel cell; namely: the wetted bend ratio was found to increase with decreasing air flow rate, increasing operating pressure and increasing relative humidity. Also, the status of liquid water at the anode was found to be similar to that at the cathode for most of the cases and therefore the water dynamics at the anode side can also be used to explain the relationships between the fuel cell performance and the investigated operating conditions.     

Operating characteristics of an air-cooling PEMFC for portable applications

Optimal design and proper operation is important to get designed output power of a polymer electrolyte membrane fuel cell (PEMFC) stack. The air-cooling fuel cell stack is widely used in sub kW PEMFC systems. The purpose of this study is to analyze the operating conditions affecting the performance of an air-cooling PEMFC which is designed for portable applications. It is difficult to maintain well balanced operating conditions. These parameters are the relative humidity, the temperature of the stack, the utility ratio of the reactant gas and so on. In this study a 500 W rate air-cooling PEMFC was fabricated and tested to evaluate the design performance and to determine optimal operating conditions. Moreover, basic modeling also is carried out. These results can be used as design criteria and optimal operating conditions for portable PEMFCs.     

Experimental and numerical investigations of the effects of PBI loading and operating temperature on a high-temperature PEMFC

In this paper, experimental and numerical investigations of the effects of polybenzimidazole (PBI) loading and operating temperature on a high-temperature proton exchange membrane fuel cell (PEMFC) performance are carried out. Experiments related to a PBI-based PEMFC are performed and a two-dimensional (2-D) simulation model is developed to numerically predict the cell characteristics. Variations of 5–30 wt% in PBI amount in the catalyst layer (CL) and 160–200 °C in cell temperature are considered. On the basis of the experimental and numerical results, the negative effect of PBI content and positive effect of operating temperature on the cell performance can be precisely captured. These effects can also be shown by measurements of the impedance spectrum and predictions of O₂ concentration and current density distributions. In addition, non-uniform distributions in the O₂ concentration and the current density in the cathode compartment are also shown in the model simulation results. Cell performance curves predicted by the present model correspond well with those obtained from experimental measurements, showing the applicability of this model in a PBI-based PEMFC.     

Novel in situ measurements of relative humidity in a polymer electrolyte membrane fuel cell

Miniature temperature/humidity sensors are incorporated into the graphite flowplates of a single cell polymer electrolyte membrane fuel cell (PEMFC) in order to measure the humidity profile along the serpentine channels of both anode and cathode in real time. The sensors show robust performance and importantly are able to recover after saturation. The key observation is a significant increase in relative humidity along the anode gas channel due to back diffusion of water from cathode to anode. Such measurements may be used to determine the water balance in the cell under a range of operating conditions to facilitate model validation and system optimisation.     

Aging prognosis model of proton exchange membrane fuel cell in different operating conditions

The aging prognosis model of Proton Exchange Membrane Fuel Cell (PEMFC) can predict the aging state of PEMFC to develop an effective prognostic maintenance plan. This paper proposes an aging prognosis model of PEMFC in different operating conditions based on the Backpropagation (BP) neural network and evolutionary algorithm. The influence of PEMFC current, hydrogen pressure, temperature, and relative humidity on the aging of PEMFC can be considered by the proposed method. Firstly, the aging prognosis model of PEMFC is built by the BP neural network. Then, the evolutionary algorithm including Mind Evolutionary Algorithm (MEA), Particle Swarm Optimization (PSO), and Genetic Algorithm (GA) is used to optimize the parameters of the established aging prognosis model of PEMFC. Finally, the accuracy of the proposed aging prognosis model is validated by 3 PEMFC aging experiments in different operating conditions. The results show that MEA, GA, and PSO can greatly improve the accuracy of the aging prognosis model of PEMFC. The MEA improves the accuracy by 10 times, while the computing time increases by 0.085s. The proposed MEA-BP that has a very short computing time can be applied to online applications.     

Membrane-hydration-state detection in proton exchange membrane fuel cells using improved ambient-condition-based dynamic model

Proton-exchange-membrane fuel cells (PEMFCs) are a popular source of alternative energy because of their operational reliability and compactness. This paper presents an improved model to represent the semi-empirical voltage of PEMFCs to overcome the limitations of existing models. The proposed model considers variations in ambient conditions, such as the ambient temperature and relative humidity, to obtain the accurate output voltage that corresponds to variations in dynamic and static loads. The proposed model was developed by conducting several experiments on the Horizon PEMFC system under normal, humid, and dry ambient conditions. Subsequently, the model parameters corresponding to each case were optimised using the quantum lightning search algorithm (QLSA). Parameters demonstrating significant variations with ambient conditions were finally represented as a function of the ambient temperature and relative humidity via statistical regression analysis. The voltage obtained using the modified model was verified by conducting experiments on both the Horizon and NEXA PEMFC systems by varying the ambient temperature and relative humidity with root mean square error (RMSE) less than 0.5. As observed, the results we obtained using the modified model closely approximated those obtained using PEMFCs under various operating conditions, and in both cases, the PEMFC voltage was observed to vary with the ambient and load conditions. The inherent advantages of the proposed PEMFC model include its ability to determine the membrane-water content and water pressure inside PEMFCs. The membrane-water content provides clear indications regarding the occurrence of drying and flooding faults. Under normal conditions, this membrane water content ranges from 11 to 7 for both the Horizon and NEXA PEMFC system. The simulation results suggested using the threshold membrane-water-content level as a possible indicator of fault occurrence under extreme ambient conditions. The limits of the said threshold were observed to be useful for fault diagnosis within PEMFC systems.     

Optimization and parametric analysis of PEMFC based on an agglomerate model for catalyst layer

A one-dimensional, non-isothermal, single-phase, steady-state comprehensive model is developed to investigate the effects of different parameters of catalyst layer and operational case as relative humidity on the proton exchange membrane fuel cell (PEMFC) performance, then to optimize the design and operation of PEMFC. The agglomerate model with thin film of polymer and liquid water was employed to describe electrochemical reaction in catalyst layers. The model considers the effect of different production ratio of water vapor and liquid water in the reaction on the fuel cell performance. The effects of operational case as temperature, relative humidity of reactants and catalyst layer structure parameters as Pt loading, agglomerate radius and Pt radius on cell performance are computed and discussed in detail. The results indicate that agglomerate radius, Pt loading and Pt particle radius, operation temperature and pressure have different kinds of effects on performance, and the performance can be improved by suitable operational case and catalyst layer structure. Results can provide good reference for optimization design of the catalyst layer and the whole cell.