Electrolyte Membrane Fuel Cell Stack Research Articles

Development of Accelerated Durability Test Protocols for Polymer Electrolyte Membrane Fuel Cell Stacks Under Realistic Operating Conditions

ABSTRACTPolymer electrolyte membrane fuel cell durability is still a major challenge. To overcome time‐consuming durability tests, so‐called accelerated durability tests (ADTs) are of urgent need. This work presents our recent results in developing ADT protocols in the context of realistic operating conditions, especially voltage clipping at 0.85 V. A 5500 h long‐term test was carried out as a reference applying a realistic automotive drive cycle. Focusing on different stressors such as temperature, relative humidity (RH), and load profile four different ADT protocols of 1200 h duration were derived. Seven‐cell short stacks with 240 cm2 active area were used. Comparing cell voltage as a key indicator, an acceleration factor of 3–7 could be achieved. In‐situ characterization techniques such as spatially resolved current measurement, cyclic voltammetry, and electrochemical impedance spectra were employed to investigate the influences of individual stressors on specific degradation mechanisms and components. The highest acceleration was observed in the mass transport region of ADTs addressing RH as a stressor, suggesting that RH cycling leads to increased degradation of hydrophobic surfaces. Increased temperature was found to accelerate primarily carbon support degradation. Accelerated catalyst aging seems to be low, demonstrating the effectiveness of voltage‐clipping conditions. Our most promising ADT shows quite a homogeneous acceleration of voltage degradation across all current regions.

Electrochemical impedance spectroscopy analysis and thermal mapping of different cross-sectional cathode channels in open-cathode polymer electrolyte membrane fuel cell stack

The Electrochemical impedance spectroscopy (EIS) of three novel cathode channels designs square, boot, and triangular for open cathode polymer electrolyte cathode fuel cell stacks are analyzed. Fundamental mechanisms such as oxygen reduction reaction, proton conductivity, bulk resistance of stack, capacitance and structure features of the porous carbon electrode etc. are investigated with the help of Nyquist/Bode plots and Randles circuit. Operational parameters including airflow rate, current, H2 gas condition (humidified and dry), and stack temperature are studied focused on understanding the trend of high and low frequency resistance. The minimum resistance and temperature mapping for cross-section designs at different operating conditions is utilized for parametric optimization. Overall, it is recommended to operate the stacks at minimum resistance obtained just before the peak power density and its corresponding temperature ∼40 °C. Finally, a data-driven hybrid model integrating EIS and artificial intelligence is presented with root mean square error of ∼0.98.

Performance evaluation of cathode channels with different cross-sections for open-cathode polymer electrolyte membrane fuel cell stack

This study proposes six different cross-sectional cathode flow field designs such as square, trapezoid, dome, boot, pentagon, and triangular constructing four cells open cathode polymer electrolyte membrane fuel cell stack with various parameters optimization and suitability for system level development. Parameters, including pressure drop, oxygen concentration, airflow rate, blower power, stack temperature, cooling rates, net power output, and stability are investigated with focus on understanding the trend, interconnected dependencies among the parameters, which collectively influence the overall performance of the cross-section designs. Overall, studies show that, boot cross-section design possessing the optimum pressure drop of 23.9 Pa, shows better performance compared to other cross-section designs due to better oxygen gas distribution, water retention/removal, heat removal/retention, and net power output. Conversely, for galvanostatic analysis done at a higher current value of 35 A, dome and square cross-section designs show highest and stable potential, along with balanced stack temperature.

Dynamic transport characteristics and performance response of commercial-size polymer electrolyte membrane fuel cell stack: An experimental study

The stability and durability of polymer electrolyte membrane fuel-cell stacks are closely related to their dynamic performance responses and internal transport characteristics, particularly for commercial-size stacks in automotive applications. In this study, the dynamic behaviors of a 10-cell stack (active area: 310 cm2) are investigated under various loading/unloading processes and cathode stoichiometric ratios; additionally, the joint influence of these two factors is analyzed. Voltage hysteresis is observed, and the dominant roles of dynamic oxygen, membrane water, and liquid transport are elucidated. The results indicate that the electro-osmotic effect dominates and results in anode-membrane dehydration as the loading process proceeds (>1.5 A cm−2). A larger airflow velocity enables faster downstream oxygen delivery, causing the oxygen concentration to reduce initially and then increase gradually with time after loading, thus voltage undershoots appear. Voltage hysteresis is enabled during the continuous loading/unloading/loading process owing to the difference in accumulated liquid water drainage ability after step loading and unloading. Although the synergistic loads and cathode stoichiometric ratio variations enable less cell-performance deterioration than that on contrary strategy, the dynamic characteristics are much more unstable and more likely to induce cell-stack failure and durability problems. This study provides insights into the dynamic transport characteristics in a commercial-size fuel cell stack and presents a guidance for control strategy development.

Fault Detection and Identification for Polymer Electrolyte Membrane Fuel Cell Stack by External Magnetic Field

Many technological locks prevent the deployment of Proton Exchange Membrane Fuel Cell (PEMFC). Particularly for vehicle applications, cost and durability represent two of the most significant challenges to achieve clean, reliable, and cost-effective PEMFC systems. Solving these shortcomings will be a great opportunity for a decisive breakthrough towards mass-diffusion of the current PEMFC technology. The long-term electrical performance losses are associated to either the degradation of the MEA constitutive materials or due to specific operating conditions (flooding, drying, etc.). In perspective, local current density distribution may support stack-level degradation analyzes as well as effective stack control to mitigate the consequences of degradation due to load cycles (electrochemical, thermal, mechanical and humidity effects) or faults.External magnetic field measurement (MFM) shows a high potential in PEMFC non-invasive diagnosis. Thus, 2D and 3D current distributions and their anomalies in the fuel cell can be identified independent of the size of the causing fault.To perform this local characterization, the external magnetic field measurement will enable to model the current density in stationary conditions over the cell surface and for the different cells of the stack. This methodology requires the complementary development of magnetic field techniques and inverse models.In this work, this challenge is tackled by using tailored defective MEAs and specific operating conditions (flooding, drying, ...) to characterize, how local and overall performances of the MEA are affected and to identify the signatures of the various anomalies. Figure 1

Experimental Analysis of Large Active Area Polymer Electrolyte Membrane Fuel Cell Stack for Determining Optimal Operating Conditions

Experimental Analysis of Large Active Area Polymer Electrolyte Membrane Fuel Cell Stack for Determining Optimal Operating Conditions

Channel to rib width ratio effect on thermal performance of cooling plate in polymer electrolyte membrane fuel cell

AbstractEnsuring a homogeneous temperature distribution inside a polymer electrolyte membrane fuel cell stack is crucial to fuel cell performance and durability, and cooling channels are responsible for this. In this study, a three‐dimensional numerical investigation is performed on a channel to rib width ratio (CR) based on serpentine flow field design. The cooling performance of various designs having different CR values is considered and compared according to the temperature uniformity index, the temperature difference between the maximum and minimum temperature, average bottom temperature, and pressure drop between the inlet and outlet of the cooling channels. Results demonstrate that the average temperature, temperature uniformity index, temperature difference, and pressure drop decrease by about 5%, 40%, 37%, and 79%, respectively, when CR is increased from 0.33 to 3.00. More uniform temperature distribution and thus, better cooling performance is achieved for CR = 3.00, especially at low Reynolds numbers and high heat fluxes. Also, the lowest pressure drops are obtained when CR is 3.00 under all considered operating conditions.

Flooding and dehydration diagnosis in a polymer electrolyte membrane fuel cell stack using an experimental adaptive neuro-fuzzy inference system

Today the need for fault diagnosis in polymer electrolyte membrane fuel cells (PEMFCs) is felt more than ever to increase the useful life and durability of the cell. The present study proposes an indirect in-situ experimental-based algorithm for diagnosing the moisture content issues in a three-cell stack. Three adaptive neuro-fuzzy inference systems (ANFIS) approximate the system outputs (cells voltages, cathodic and anodic pressure drop) in normal conditions. The values of Pearson's correlation coefficients (0.998, 0.983, and 0.995 for outputs, respectively) show the high quality of the modeling. In unknown operating conditions, the residuals of experimental and ANFIS values are compared with obtained deviation thresholds (0.0735 V, 0.0092 bar, and 0.0047 bar for the outputs, respectively) to determine the cathode/anode flooding, membrane dehydration, or normal status. This method is helpful in commercial applications for diagnosing more than 50% of PEMFC faults because it uses accessible parameters and has low-processing demands.

Development of self-breathing polymer electrolyte membrane fuel cell stack with cylindrical cells

Self-breathing fuel cells use oxygen directly from the atmosphere and this eliminates the need of air fans and humidifiers, and as such enables applications where a reduction in size and volume of the power systems is important. Herein, we report a novel design and fabrication of a 12 celled cylindrical self-breathing stack made from stainless steel. A cylindrical geometry was implemented to permit higher self-breathing function and means to improve the Membrane Electrode Assembly compaction and thus reduce hydrogen leaks. The stack delivered a maximum voltage of 9.4 V and a maximum power of 1 W cm−2 while operating under ambient condition (25 °C, 20% relative humidity and with dry hydrogen). The stainless steel bipolar plates provided enough compaction to the stack to minimize ohmic resistance and the hydrogen sealing was done with silicon gaskets which facilitated the stacking of the cells. The developed 12 celled stack delivered a volume power density of 29 W per litre which is 80% higher than previously reported self-breathing polymer electrolyte membrane fuel cells.

The role of effectiveness factor on the modeling of methanol steam reforming over CuO/ZnO/Al2O3 catalyst in a multi-tubular reactor

A pseudo-homogeneous model for the methanol steam reforming process was developed based on reaction kinetics over a CuO/ZnO/Al 2 O 3 catalyst and non-adiabatic heat and mass transfer performances in a co-current packed-bed reactor. A Thiele modulus method and an intraparticle distribution method were applied for predicting the effectiveness factors for main reactions and providing insights into the diffusion-reaction process in a cylindrical catalyst pellet. The results of both methods are validated and show good agreements with the experimental data, but the intraparticle distribution method provides better predictions. Results indicate that increases in catalyst size and bulk fluid temperature amplify the impact of intraparticle diffusion limitations, showing a decrease in effectiveness factors. To satisfy the requirements of a high temperature polymer electrolyte membrane fuel cell stack, the optimized operating conditions, which bring the methanol and CO concentrations to less than 1 % vol in the reformate stream, are determined based on the simulation results. • One-dimensional pseudo-homogeneous model of a packed-bed methanol steam reformer. • Two methods to obtain approximate solutions of the catalytic effectiveness factor. • Validation of reaction kinetics and effectiveness factors with experimental data. • Effects of main operating parameters on the intraparticle heat and mass transfer. • Optimized conditions to obtain less than 1% of CH 3 OH and CO in reformate gas.

Characterization of a Commercial Polymer Electrolyte Membrane Fuel Cell Stack by Means of Physics-Based Modeling and Distribution of Relaxation Times

Characterization of a Commercial Polymer Electrolyte Membrane Fuel Cell Stack by Means of Physics-Based Modeling and Distribution of Relaxation Times

Physically Motivated Water Modeling in Control-Oriented Polymer Electrolyte Membrane Fuel Cell Stack Models

Polymer electrolyte membrane fuel cells (PEMFCs) are prone to membrane dehydration and liquid water flooding, negatively impacting their performance and lifetime. Therefore, PEMFCs require appropriate water management, which makes accurate water modeling indispensable. Unfortunately, available control-oriented models only replicate individual water-related aspects or use oversimplistic approximations. This paper resolves this challenge by proposing, for the first time, a control-oriented PEMFC stack model focusing on physically motivated water modeling, which covers phase change, liquid water removal, membrane water uptake, and water flooding effects on the electrochemical reaction. Parametrizing the resulting model with measurement data yielded the fitted model. The parameterized model delivers valuable insight into the water mechanisms, which were thoroughly analyzed. In summary, the proposed model enables the derivation of advanced control strategies for efficient water management and mitigation of the degradation phenomena of PEMFCs. Additionally, the model provides the required accuracy for control applications while maintaining the necessary computational efficiency.

Model-Based Membrane Hydration Studies for Automotive Fuel Cell Systems

Controlling the hydration of the polymer electrolyte membrane (PEM) is critical for reliable and durable operation of automotive fuel cell stacks. Membrane drying can lead to performance losses due to increased ohmic resistance. More importantly, sustained operation under dry conditions threatens the mechanical and chemical integrity of the membrane. Unfortunately, there is no direct control lever in an automotive fuel cell system (FCS) for membrane humidification, which is often achieved by product water resulting from the electrochemical reactions. Passive gas-to-gas humidifiers may be used in either the hydrogen (anode) or air (cathode) subsystems to circulate some of the product water back into the stack [1]. However, even with passive humidifiers, regions near the stream inlets are generally susceptible to dehydration [2], considering the wide range of operating conditions in automotive settings.Given that the membrane hydration in an automotive FCS can only be controlled indirectly via thermal management and flow and pressure regulation of the incoming gas streams [3], an understanding of the intricate coupling between various subsystems is essential. Modeling the entire FCS with all the balance-of-plant components is a vital tool in understanding these system-level interactions and devising an effective water management strategy. Therefore, a complete system model of an automotive FCS was developed to enable detailed membrane hydration studies. Specifically, the model consists of sub-models for the fuel cell stack [4], gas-to-gas humidifier [1], air compressor [5], hydrogen injector and ejector [6], and all system manifolds and valves [6]. This model is then used to analyze the membrane hydration variations in response to the changes in various practical control actions. The spatially distributed stack model allows hydration trade-offs at different locations of the stack to be analyzed. The results confirm that locations near the stream inlets are often drier than the middle of the stack and that coolant and air path control offer opportunities for effective water management. References Ahluwalia, R. K., Wang, X., Johnson, W. B., Berg, F., & Kadylak, D. (2015). Performance of a cross-flow humidifier with a high flux water vapor transport membrane. Journal of Power Sources, 291, 225-238.Tanaka, S., Nagumo, K., Yamamoto, M., Chiba, H., Yoshida, K., & Okano, R. (2020). Fuel cell system for Honda CLARITY fuel cell. eTransportation, 3, 100046.Kitamura, N., Manabe, K., Nonobe, Y., & Kizaki, M. (2010). Development of water content control system for fuel cell hybrid vehicles based on AC impedance (No. 2010-01-1088). SAE Technical Paper.Goshtasbi, A., Pence, B. L., Chen, J., DeBolt, M. A., Wang, C., Waldecker, J. R., ... & Ersal, T. (2020). A mathematical model toward real-time monitoring of automotive PEM fuel cells. Journal of The Electrochemical Society, 167(2), 024518.Moraal, P., & Kolmanovsky, I. (1999). Turbocharger modeling for automotive control applications (No. 1999-01-0908). SAE Technical Paper.He, J., Ahn, J., & Choe, S. Y. (2011). Analysis and control of a fuel delivery system considering a two-phase anode model of the polymer electrolyte membrane fuel cell stack. Journal of Power Sources, 196(10), 4655-4670.

Data-driven parameterization of polymer electrolyte membrane fuel cell models via simultaneous local linear structured state space identification

In order to mitigate the degradation and prolong the lifetime of polymer electrolyte membrane fuel cells, advanced, model-based control strategies are becoming indispensable. Thereby, the availability of accurate yet computationally efficient fuel cell models is of crucial importance. Associated with this is the need to efficiently parameterize a given model to a concise and cost-effective experimental data set. A challenging task due to the large number of unknown parameters and the resulting complex optimization problem. In this work, a parameterization scheme based on the simultaneous estimation of multiple structured state space models, obtained by analytic linearization of a candidate fuel cell stack model, is proposed. These local linear models have the advantage of high computational efficiency, regaining the desired flexibility required for the typically iterative task of model parameterization. Due to the analytic derivation of the local linear models, the relation to the original parameters of the non-linear model is retained. Furthermore, the local linear models enable a straight-forward parameter significance and identifiability analysis with respect to experimental data. The proposed method is demonstrated using experimental data from a 30 kW commercial polymer electrolyte membrane fuel cell stack.

Development, manufacture and validation of an open cathode LT-PEMFC stack at HySA systems

This work presents open cathode low temperature polymer electrolyte membrane fuel cell stack development and validation process project performed at HySA Systems as a part of a long-term programme funded by Department of Science and Innovation in South Africa. A detailed explanation of the stack design, manufacturing, assembly and validation is given as well as detailed analysis of results is presented. Prototype stack has an electrode active area of 50 cm2, bipolar plates made of graphite composite material (Eisenhuth) and membrane electrode assemblies manufactured in South Africa - HyPlat (Pty) Ltd. A short 10-cell stack is validated using FuelCon Evaluator stack test station and custom designed stack control system integrated with complete balance of plant components. The stack maximum current and power densities are 1.2 Acm−2 at 0.5 V and 0.6 Wcm−2, respectively. Performed current hold (300 h) and open circuit voltage (60 h) durability tests resulted in degradation rates of 0.64 mVh−1 and 3.83 mVh−1, respectively.

Continuous durability study of a high temperature polymer electrolyte membrane fuel cell stack

High Temperature Polymer Electrolyte Membrane (HT-PEM) fuel cells are a promising choice for renewable power generation. We present an experimental study that investigates the durability of a full-size fuel cell stack, where membrane electrode assemblies were continuously extracted during operation of the stack, and analysed in detail with electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The evolution of membrane thinning, the loss of phosphoric acid and the changes in the catalyst layer of the electrodes have been investigated as a function of operation time. A correlation between the acid loss and the decrease of cell voltage has been determined to provide detailed insight into durability data of the HT-PEM fuel cell on a commercial sized stack level.

An Energy Consumption Model for Designing an AGV Energy Storage System with a PEMFC Stack

This article presents a methodology for building an AGV (automated guided vehicle) power supply system simulation model with a polymer electrolyte membrane fuel cell stack (PEMFC). The model focuses on selecting the correct parameters for the hybrid energy buffering system to ensure proper operating parameters of the vehicle, i.e., minimizing vehicle downtime. The AGV uses 2 × 1.18 kW electric motors and is a development version of a battery-powered vehicle in which the battery has been replaced with a hybrid power system using a 300 W PEMFC. The research and development of the new power system were initiated by the AGV manufacturer. The model-based design (MBD) methodology is used in the design and construction of a complete simulation model for the system, which consists of the fuel cell system, energy processing, a storage system, and an energy demand models. The energy demand model has been developed based on measurements from the existing AGV, and the remaining parts of the model are based on simulation models tuned to the characteristics obtained for the individual subsystems or from commonly available data. A parametric model is created with the possibility for development and determination by simulation of either the final system or from the parameters of the individual models’ elements (components of the designed system). The presented methodology can be used to develop alternative versions of the system, in particular the selection of the correct size of supercapacitors and batteries which depend on the energy demand profile and the development of the DC/DC converter and controllers. Additionally, the varying topology of the whole system was also analyzed. Minimization of downtime has been presented as one of many possible uses of the presented model.

Parametric study of passive air-cooled polymer electrolyte membrane fuel cell stacks

• A comprehensive parametric study was conducted using a 3D, multiscale, two-phase PEM fuel cell model to obtain a quantitative understanding of the passive air-cooled PEM fuel cell operation in excess dry air supply. • This study provides comprehensive guidelines for the successful design and operation of passive air-cooled PEM fuel cell systems A passive air-cooled polymer electrolyte membrane (PEM) fuel cell stack is considered a promising technology for use in small-scale drones and unmanned aerial vehicles since it facilitates long flight durations and has a short charging time. However, in the passive air-cooling system, outside air drawn through a fan is used as both fuel for the oxygen reduction reaction and coolant for waste heat removal and using the drawn air for the two purposes is a challenging task in terms of water and heat management. A parametric study was conducted using a three-dimensional, multiscale, two-phase PEM fuel cell model to understand key water and heat transport phenomena under excess dry air supply. The effects of key design variables of the membrane electrode assembly and cathode flow-field were investigated. Furthermore, seasonal changes in the operating characteristics of air-cooled PEM fuel cell systems were analyzed. The use of a thin membrane and a high ionomer fraction in the cathode catalyst layer, and a low set-point temperature at the air outlet were found to improve the degree of electrolyte hydration and the overall cell performance. This study provides comprehensive guidelines for the successful design and operation of passive air-cooled PEM fuel cell systems.

An Evolutionary Computation Approach for the Online/On-Board Identification of PEM Fuel Cell Impedance Parameters with A Diagnostic Perspective

Online/on-board diagnosis would help to improve fuel cell system durability and output power. Therefore, it is a feature the manufacturers may wish to provide for final users to increase the attractiveness of their product. This add-on requires suitable stack models, parametric identification tools and diagnostic algorithms to be run on low-cost embedded systems, ensuring a good trade-off between accuracy and computation time. In this paper, a computational approach for the impedance parameter identification of polymer electrolyte membrane fuel cell stack is proposed. The method is based on an evolutionary algorithm including sub-population and migration features, which improves the exploration capability of the search space. The goal of the evolutionary algorithm is to find the set of parameters that minimizes an objective function, representing the mismatch between two impedance plots in a normalized plane. The first plot is associated with experimental impedance and the second is computed on the basis of the identified parameters using a circuit model. Three kinds of impedance models, characterized by increasing computational complexity, are used, depending on the experimental data—a linear model made of resistors and capacitors, the Fouquet model and the Dhirde model. Preliminary analysis of the experimental impedance data may evidence correlations among parameters, which can be exploited to reduce the search space of an evolutionary algorithm. The computational approach is validated with literature data in a simulated environment and with experimental data. The results show good accuracy and a computational performance that fits well with the commercial embedded system hardware resources. The implementation of the approach on a low-cost off-the-shelf device achieves small computation times, confirming the suitability of such an approach to online/on-board applications. From a diagnostic perspective, the paper outlines a diagnostic approach based on the identified impedance parameters, on the basis of a small set of experimental data including fuel cell stack faulty conditions.

Improving the Performance of a Dual Kalman Filter for the Identification of PEM Fuel Cells in Impedance Spectroscopy Experiments

In this paper, the Dual Kalman Filter (DKF) is used for the parametric identification of an RC model of a Polymer Electrolyte Membrane Fuel Cell (FC) stack. The identification is performed for diagnostic purposes, starting from time-domain voltage and current signals in the framework of Electrochemical Impedance Spectroscopy (EIS) tests. Here, the sinusoidal input of the tests makes the identification of DKF parameters challenging. The paper analyzes the filter performance and proposes a possible approach to address the filter tuning to let it work with FC operating either in normal conditions or in the presence of drying and flooding fault conditions, or in fuel starvation mode. The analysis is mainly performed in a simulated environment, where the Fouquet model is used to simulate the FC. Some criteria to tune the filter are derived from the analysis and used also with experimental data produced by some EIS tests, to achieve the best estimate in constrained conditions. The results show that the DKF can be turned into a valuable tool to identify the model parameters even with signals developed for other scopes. The identification results envisage the possibility of assisting the model-based FC diagnosis by means of a very simple tool that can run on a low-cost embedded device. Indeed, the simplicity of the filter approach and a lightweight implementation allow the deployment of the algorithm in embedded solutions.