A review of polymer electrolyte membrane fuel cell stack testing

This paper presents an overview of polymer electrolyte membrane fuel cell (PEMFC) stack testing. Stack testing is critical for evaluating and demonstrating the viability and durability required for commercial applications. Single cell performance cannot be employed alone to fully derive the expected performance of PEMFC stacks, due to the non-uniformity in potential, temperature, and reactant and product flow distributions observed in stacks. In this paper, we provide a comprehensive review of the state-of-the art in PEMFC testing. We discuss the main topics of investigation, including single cell vs. stack-level performance, cell voltage uniformity, influence of operating conditions, durability and degradation, dynamic operation, and stack demonstrations. We also present opportunities for future work, including the need to verify the impact of stack size and cell voltage uniformity on performance, determine operating conditions for achieving a balance between electrical efficiency and flooding/dry-out, meet lifetime requirements through endurance testing, and develop a stronger understanding of degradation.     

Parameter optimization for a PEMFC model with a hybrid genetic algorithm

Many steady‐state models of polymer electrolyte membrane fuel cells (PEMFC) have been developed and published in recent years. However, models which are easy to be solved and feasible for engineering applications are few. Moreover, rarely the methods for parameter optimization of PEMFC stack models were discussed. In this paper, an electrochemical‐based fuel cell model suitable for engineering optimization is presented. Parameters of this PEMFC model are determined and optimized by means of a niche hybrid genetic algorithm (HGA) by using stack output‐voltage, stack demand current, anode pressure and cathode pressure as input–output data. This genetic algorithm is a modified method for global optimization. It provides a new architecture of hybrid algorithms, which organically merges the niche techniques and Nelder–Mead's simplex method into genetic algorithms (GAs). Calculation results of this PEMFC model with optimized parameters agreed with experimental data well and show that this model can be used for the study on the PEMFC steady‐state performance, is broader in applicability than the earlier steady‐state models. HGA is an effective and reliable technique for optimizing the model parameters of PEMFC stack. Copyright © 2005 John Wiley & Sons, Ltd.     

Modelling,simulation and control of a proton exchange membrane fuel cell (PEMFC) power system

Fuel cell power systems are emerging as promising means of electrical power generation on account of the associated clean electricity generation process, as well as their suitability for use in a wide range of applications. During the design stage, the development of a computer model for simulating the behaviour of a system under development can facilitate the experimentation and testing of that system's performance. Since the electrical power output of a fuel cell stack is seldom at a suitable fixed voltage, conditioning circuits and their associated controllers must be incorporated in the design of the fuel cell power system. This paper presents a MATLAB/Simulink model that simulates the behaviour of a Proton Exchange Membrane Fuel Cell (PEMFC), conditioning circuits and their controllers. The computer modelling of the PEMFC was based on adopted mathematical models that describe the fuel cell's operational voltage, while accounting for the irreversibilities associated with the fuel cell stack. The conditioning circuits that are included in the Simulink model are a DC–DC converter and DC–AC inverter circuits. These circuits are the commonly utilized power electronics circuits for regulating and conditioning the output voltage from a fuel cell stack. The modelling of the circuits is based on relationships that govern the output voltage behaviour with respect to their input voltages, switching duty cycle and efficiency. In addition, this paper describes a Fuzzy Logic Controller (FLC) design that is aimed at regulating the conditioning circuits to provide and maintain suitable electrical power for a wide range of applications. The model presented demonstrates the use of the FLC in conjunction with the PEMFC Simulink model and that it is the basis for more in-depth analytical models.     

The durability investigation of a 10‐cell metal bipolar plate proton exchange membrane fuel cell stack

The metal bipolar plates (BPs) have replaced the graphite BPs in vehicle‐used proton exchange membrane fuel cell (PEMFC) stack because of their high volume power density. To investigate the durability of metal BP stack, this paper performed a durability test of 2000 hours on a 10‐cell metal BP fuel cell stack. The degradations of the average voltage and individual cell voltage in fuel cell stack were analyzed. To investigate the degradation mechanism, the stack was disassembled and the morphologies and compositions of no. 1, no. 5, and no. 10 cells after 2000 hours were characterized by SEM, TEM, and ASS. The results indicated that at 800 mA/cm², the voltage decay rate is 42.303 μV/hour and the voltage decay percentage of the stack is 14.34% after 2000 hours according to the linearly fitting result. According to the US Department of Energy (DOE) definition of fuel cell stack life, only the voltage decay rate of OCV and the tenth cell is lower than the maximum voltage degradation rates of 10 000 hours. The decreases of homogeneity of stack were the main reason for its performance degradation. Especially for the tenth cell, its performance has almost no drop. The main failure reason of this metal BP stack is structural design rather than metal corrosion. The losses of Pt catalyst and C supporting are the main reason of performance degradation.     

Recent development in design a state-of-art proton exchange membrane fuel cell from stack to system: Theory,integration and prospective

As an efficient energy converter, the proton exchange membrane fuel cell (PEMFC) is developed to couple various applications, including portable applications, transportation, stationary power generation, unmanned underwater vehicles, and air independent propulsion. PEMFC is a complex system consisting of different components that can be influenced by many factors, such as material properties, geometric designs operating conditions, and control strategies. The interaction between components and subsystems could affect the performance, durability, and lifespan of PEMFC system. To design a high performance, long lifespan, high durability PEMFC, it's essential to comprehensively understand the coupling effect of different factors on the overall performance and durability of PEMFCs. This review will present existing research on basis of four aspects, involving fuel cell stack design, subsystems design and management, mass transfer enhancement, and system integration. Firstly, the multi-physics intergradation and component design of PEMFC are reviewed with the designing mechanisms and recent progress. Besides, mass transfer enhancement methods are discussed by bipolar plate design and membrane electrode assembly optimization. Then, water management, thermal management, and fuel management are summarized to provide design guidance for PEMFC. The specifications design and system management for various engineering applications are briefly presented.     

Thermal analysis and management of proton exchange membrane fuel cell stacks for automotive vehicle

The thermal management of a proton exchange membrane fuel cell (PEMFC) is crucial for fuel cell vehicles. This paper presents a new simulation model for the water-cooled PEMFC stacks for automotive vehicles and cooling systems. The cooling system model considers both the cooling of the stack and cooling of the compressed air through the intercooler. Theoretical analysis was carried out to calculate the heat dissipation requirements for the cooling system. The case study results show that more than 99.0% of heat dissipation requirement is for thermal management of the PEMFC stack; more than 98.5% of cooling water will be distributed to the stack cooling loop. It is also demonstrated that controlling cooling water flow rate and stack inlet cooling water temperature could effectively satisfy thermal management constraints. These thermal management constraints are differences in stack inlet and outlet cooling water temperature, stack temperature, fan power consumption, and pump power consumption.     

Experimental study of dynamic performance of defective cell within a PEMFC stack

Defective cell in a PEMFC stack may reduce durability and reliability of the stack and even damage the stack. However, the dynamic performance of defective cell within a PEMFC stack is not clear. In this paper, the dynamic characteristics of the defective cell under different load conditions are analyzed. The results reveal that the defective cell has slower dynamic response rate than other single fuel cells, and the defective cell causes a poor voltage uniformity of the stack. The increased frequency of load change makes the voltage change rate of defective cell higher. The increased amplitude of load change has a more negative impact than the increased frequency of load change, and makes the defective cell more prone to flooding. Furthermore, impedance spectrum shows that these load conditions have greater negative effect for the defective cell than other cells. Finally, according to the experimental results and practical application, recommends related to control strategy of PEMFC stack are proposed to extend lifetime.     

Gas diffusion layers for PEM fuel cells: Materials,properties and manufacturing – A review

The complexity in proton exchange membrane fuel cell (PEMFC) stack stems from the fact that numerous physio-chemical processes as well as multi-functional components are involved in its operation. Among the various components a Gas Diffusion Layer (GDL) being an integral component that plays a significant role in determining the performance, durability, and the dynamic characteristics, when air is used as oxidant. In addition, it serves as an armour to safeguard the membrane (Nafion), which is a delicate as well as one of the most expensive components of the PEMFC stack. A comprehensive insight on the GDL can help us to assess the fuel cell stack performance and durability. Apparently, the gas (hydrogen and air/oxygen) being converted to the energy in a PEM fuel cell needs to be diffused uniformly for which surface attributes and porosity must also be well interpreted. This review is a comprehensive assessment made on the fundamental mechanism of the diffusion process along with the various materials involved and evaluating their pros and cons. Eventually, the various manufacturing techniques involved in the GDL fabrication process are also reviewed holistically. It is envisaged that the additive manufacturing process can be a potential option to fabricate a GDL in a cost-effective and simple manufacturing approach.     

Application of thermal imaging to validate a heat transfer model for polymer electrolyte fuel cells

Heat management in polymer electrolyte membrane fuel cells (PEMFCs) plays a vital role in stack performance and durability, and overall system efficiency. A computational model assembled by the authors has been used to study the heat generated and distributed in single-cell and two-cell PEMFC stacks, with a focus on temperature variation on the external surfaces of the stack under different heat loads.     

Gravity effect on the performance of PEM fuel cell stack with different gas manifold positions

The importance of gravity effect on the performance of proton exchange membrane fuel cell (PEMFC) has recently been recognized. In this paper, the effect of gravity on the performance of PEMFC has been investigated associating with different gas intake modes. The polarization curves of the stack with different positions of reaction gas inlet and outlet at varied gravitational angles are addressed in detail. The results indicate that the output power of PEMFC stack can be greatly enhanced at the optimized gravitational angle. Gas intake modes that were realized by varying the gas inlet and outlet positions strongly affect the stack performance as well. The optimized performance can be reached at the tilted angle of 90° when both air and hydrogen inlets are placed at the upper side of the stack, whereas the worst performance occurs at the tilted angle of 90° when air and hydrogen flow into the channel from the bottom side of the stack. These results have important implications for PEM fuel cell design and operational strategies. In order to improve the performance, fuel cells should be designed and operated at the optimized gravitational angle and gas inlet/outlet position. Copyright © 2011 John Wiley & Sons, Ltd.     

Thermodynamic modeling and exergy analysis of proton exchange membrane fuel cell power system

The proton exchange membrane (PEM) fuel cell (PEMFC) is equipped with a series of auxiliary components which consume considerable amount of energy. It is necessary to investigate the design and operation of the PEMFC power system for better system performance. In this study, a typical PEMFC power system is developed, and a thermodynamic model of the system is established. Simulation is carried out, and the power distribution of each auxiliary component in the system, the net power and power efficiency of the system are obtained. This power system uses cooling water for preheating inlet gases, and its energy-saving effect is also verified by the simulation. On this basis, the exergy analysis is applied on the system, and the indexes of the system exergy loss, exergy efficiency and ecological function are proposed to evaluate the system performance. The results show that fuel cell stack and heat exchanger are the two components that cause the most exergy loss. Furthermore, the system performance under various stack inlet temperatures and current densities is also analyzed. It is found that the net power, energy efficiency and exergy efficiency of the system reach the maximum when the stack inlet temperature is about 348.15 K. The ecological function is maintained at a high level when the stack inlet temperature is around 338.15 K. Lower current density increases the system ecological function and the power and exergy efficiencies, and also helps decrease the system exergy loss, but it decreases the system net power.     

Rapid degradation characteristics of an air-cooled PEMFC stack

Durability is one of the obstacles to the large-scale commercialization of proton exchange membrane fuel cell (PEMFC) stacks. Understanding its decay behavior is a prerequisite for improving durability. In this study, rapid degradation characteristics of an air-cooled PEMFC stack are investigated. Due to the simultaneous presence of various degradation sources, the maximum power of the PEMFC stack has been reduced by 39.6% after just 74.6 h of operations. Performance degradation characteristics are sought by analyzing the cell voltage, temperature distribution, ion chromatography, and surface morphology of the gas diffusion layer. The result shows that abnormal cell voltage and temperature distribution can reflect the problematic location. The fluoride ion emission rate is 0.111 mg/day, which proves that the membrane has been seriously degraded. Contact angle reduction and impurities attached to the surface of the gas diffusion layer lead to the water management failure. It is also found that the main factor for performance degradation could be different under different current conditions. And more information can be found under higher current conditions during monitoring the decay of PEMFCs. This study helps to deepen the understanding of performance degradation characteristics.     

Modeling of the Ballard-Mark-V proton exchange membrane fuel cell with power converters for applications in autonomous underwater vehicles

This paper studies the transient response of the output voltages of a Ballard-Mark-V 35-cell 5 kW proton exchange membrane fuel cell (PEMFC) stack with power conversion for applications in autonomous underwater vehicles (AUVs) under load changes. Four types of pulse-width modulated (PWM) dc-dc power converters are employed to connect to the studied fuel cell in series for converting the unregulated fuel cell stack voltage into the desired voltage levels. The fuel cell model in this paper consists of the double-layer charging effect, gases diffusion in the electrodes, and the thermodynamic characteristic; PWM dc-dc converters are assumed to operate in continuous-conduction mode with a voltage-mode control compensator. The models of the study's fuel cell and PWM dc-dc converters have been implemented in a Matlab/SIMULINKTM environment. The results show that the output voltages of the studied PEMFC connected with PWM dc-dc converters during a load change are stable. Moreover, the model can predict the transient response of hydrogen/oxygen out flow rates and cathode and anode channel temperatures/pressures under sudden change in load current.     

A review of unitized regenerative fuel cell stack: Material,design and research achievements

The stack design of a unitized regenerative fuel cell (URFC) can modify the structure of cells that can be used as storage and energy regenerator aside from cells that use other sources such as solar or wind energy. A reversible unitized polymer electrolyte membrane fuel cell (PEMFC) contains a dual-functional single cell that is less expensive and has enhanced performance. The use of URFCs on hydrogen and oxygen is preferred because it is highly efficient, environmentally friendly, and uses power generators. The stack, then, must be made affordable or accessible. The expenses of URFC stack must be reduced by improving its design, materials, and performance. This study referred to recent studies on developing a method to cut the expenses of the URFC stack. The study also aims to determine its main constituents and to look further into its design by observing its performance and electrochemical behaviors. It also presents the issues that are currently encountered in this field.     

Parametric study on geometric and material properties of polymer electrolyte membrane fuel cell with free vibration analysis

The mechanical aspect of understanding the dynamic behaviour is very important in stack assembly of fuel cell configuration. Designing such configuration would be very useful to tune the system accordingly to avoid catastrophic failure due to resonance. The dynamic analysis of a polymer electrolyte membrane fuel cell (PEMFC) is performed to understand its response during complex loading nature. The stack assembly of bipolar plate, gas diffusion electrolyte (GDE) and membrane are modelled and analysed using Mindilin plate element with finite element method (FEM). The parametric study on thickness, density and young's modulus and its influence on dominant modes of natural frequencies are analysed with a 5%–20% range of variations. It is observed that the bipolar plate's thickness plays a vital role in the vibration behaviour of the PEMFC.     

Comparison of the performance and degradation mechanism of PEMFC with Pt/C and Pt black catalyst

Proton exchange membrane fuel cell (PEMFC) has been used in supplying power for Unmanned Underwater Vehicle which operate in a closed environment and dead-ended anode and cathode (DEAC) mode is deemed as an effective way to enhance the fuel utilization rate. Catalyst is an important factor that influences the performance and durability of PEMFC, especially in DEAC mode. In this paper, the degradation characteristics of PEMFCs with Pt black and Pt/C catalyst after 100 h operation have been investigated by electrochemical techniques and morphological characterization methods. It's shown that the degradation of Pt black catalyst layer (CL) was more severe than that of Pt/C CL. The difference of performance degradation is due to the dominant decay mechanism of these two catalysts is different. According to SEM, TEM and XPS results, the decay of Pt black catalyst is mainly caused by Pt agglomeration and oxidation, causing a higher ohmic resistance, higher mass transfer resistance and severer degradation of performance. The degradation of Pt/C catalyst is mainly due to the reduction of electrochemical surface area and carbon corrosion because the larger carbon corrosion makes micropores and the thicker supporting structure, resulting in the performance degradation.     

Multi-scale coupling between two dynamical models for PEMFC aging prediction

In this paper, an approach allowing connecting two numerical models for the simulation of the PEMFC operation and durability at different physical scales is presented. After explaining the interest of coupling them to study the interactions between the fuel cell system and the fuel cell itself, along with lifetime concerns, the feasibility of the task is assessed. Then the numerical approach to achieve this coupling is presented. Finally the response of the coupled models is examined to check its validity, and first results are presented. Predicted fuel cell lifetime trends when changing the stack operation conditions are shown, which highlight the presence of optima concerning temperature, demanded current, pressure and O₂ stoichiometry. Two operation modes are then compared in terms of their impact on the fuel cell performance decay, showing that power cycles are more damaging the fuel cell than nominal operation.     

Real-time AC voltage control and power-following of a combined proton exchange membrane fuel cell,and ultracapacitor bank with nonlinear loads

The nonlinear loads create a wide range of current harmonics in the system. Such loads can make distortions on the output voltage profile, influence on the fuel cell (FC) performance, and endanger safe operation of the FC unit. In this paper, new strategies for power-following and AC voltage control have been developed. The proposed system consists of the ultracapacitor (UC) bank and proton exchange membrane fuel cell (PEMFC) supplying nonlinear AC loads. The power tracking strategy is based on the Fourier analysis of total load demand. The Fourier analysis is used as an effective tool to eliminate destructive effect of current harmonics on the PEMFC output current. To supply the nonlinear AC loads under sinusoidal voltage with the fast response, a dynamic model for the inverter control loop is also presented. This model is used to enhance the input reference tracking and reject input/output disturbances. The simulation outcomes confirm the desirable PEMFC performance against nonlinear load disturbances. In addition, the output AC voltage is kept sinusoidal and has low deviations under nonlinear load variations.     

Degradation analysis of the core components of metal plate proton exchange membrane fuel cell stack under dynamic load cycles

The durability of metal plate proton exchange membrane fuel cell (PEMFC) stack is still an important factor that hinders its large-scale commercial application. In this paper, we have conducted a 1000 h durability test on a 1 kW metal plate PEMFC stack, and explored the degradation of the core components. After 1000 h of dynamic load cycles, the voltage decay percentage of the stack under the current densities of 1000 mA cm^?2 is 5.67%. By analyzing the scanning electron microscopy (SEM) images, the surfaces of the metal plates are contaminated locally by organic matter precipitated from the membrane electrode assembly (MEA). The SEM images of the catalyst coated membrane (CCM) cross section indicate that the MEA has undergone severe degradation, including the agglomeration of the catalyst layer, and the thinning and perforation of the PEM. These are the main factors that cause the rapid increase in hydrogen crossover flow rate and performance decay of the PEMFC stack.     

Adaptive estimation of PEMFC stack model parameters - An experimental verification

The growing popularity of using proton-exchange membrane fuel cells (PEMFCs) stacks in stationary, portable, and transportation applications is driving researchers to develop proper dynamic models for PEMFCs. These models are used to accurately capture the electrical characteristics and runtime performance. This work proposes a well-known equivalent circuit model of a battery, to be modified and used as a model for a PEMFC stacks voltage-current characteristics. This model is modified by finding suitable functions to model the open circuit voltage and the series resistance, required to model the electrical performance of a 200-W PEMFC stack. The paper also shows that the existing adaptive parameters estimation (APE) technique for Li-ion battery parameters estimation is also able to estimate parameters of the PEMFC stack's model. The model parameters are estimated using the APE technique that requires only five experiments. The model is validated experimentally under different load conditions for a 200-W PEMFC stack supplied from a hydrogen cylinder (voltage error ?0.2 V to 0.5 V), and a 30-W PEMFC stack supplied from a fuel stick (voltage error ?0.2 V–0.4 V). The results show that the parameters estimation methodology works well across PEMFC stacks of different sizes with different input fuel intake configurations, with a minimal terminal voltage estimation error in the order of millivolts. Open circuit voltage measurements (OCV) show that the OCV curve starts at a little lower than 31 V, declines slowly to around 30 V for a normalized hydrogen flow rate of 0.6, after which there is a sudden linear decline in OCV was observed. Most of the data has absolute estimation error less than 0.1 V. In fact, the terminal voltage estimation error across all tests, with different current discharge profiles, lies between ?0.2 and 0.2 V only. Also, 95.84% of the error samples lie between ±0.1% error.