Exchange Membrane Fuel Cell Stack Research Articles

Ex-situ Characterization of Nb-Ti Alloy/Pt Coated Stainless Steel Bipolar Plates for Proton Exchange Membrane Fuel Cells

Metallic bipolar plates are crucial for the development of compact and lightweight proton exchange membrane fuel cell stacks; however, most of them encounter durability and conductivity challenges in the fuel cell environment. In this study, Nb-Ti alloy/Pt coatings are deposited on SS316L plates to enhance corrosion resistance, surface wettability, electrical and thermal conductivity, with reduced interfacial contact resistance. Corrosion resistance is assessed by exposing test samples to a 1M H2SO4 acidic environment at 25 °C and 80 °C, respectively, via potentiostatic and potentiodynamic polarization tests. It is found that Nb-Ti alloy/Pt coatings exhibit exceptional stability, with corrosion potential increased by 2.5 (at 25 °C) and 0.5 (at 80 °C) times and corrosion current density reduced by orders of magnitude; and their anti-corrosion performance far exceeds the technical targets set by the US Department of Energy, with a protective efficiency of 99.98 % at both temperatures tested. The coated samples have reduced water affinity, indicated by significantly larger contact angle values compared to the uncoated samples in both pre-and post-corrosion tests. The incorporation of Nb-Ti alloy/Pt coatings on SS316L increases the in-plane electrical conductivity by 42.6 % and thermal conductivity by 3.5 %; surpassing the US Department of Energy's technical targets in these categories as well. At a compaction force of 140 N/cm2, the interfacial contact resistance for the coated samples is about 2.5 times lower than the Department of Energy's requirements. These results indicate the viability of Nb-Ti alloy/Pt coated SS316L bipolar plates for fuel cell applications.

A one-dimensional model of air-cooled proton exchange membrane fuel cell stack integrating fan arrangement and operational characteristics

Air-cooled proton exchange membrane fuel cell stack’s performance can be greatly affected by the arrangement and operational characteristics of the fans that generate the air flow. However, the influence mechanisms are complex and poorly understood. In this study, a one-dimensional analytical model specifically for air-cooled stacks integrating important fan features is developed to quickly (e.g. within 5 min for a 100-cell stack) and accurately predict the water and thermal states inside stacks and stack performance under various fan arrangements and operational characteristics. The model accuracy was validated against the experimental results of a 95-cell air-cooled stack, including the stack polarization curves, temperature distribution and air flow rates at different fan’s duty cycles. The model results showed that for high air flow resistance stacks, the air flow rate and maximum net power for fans arrangement in series are higher than those in parallel by about 10% and 0.5%, respectively. Moreover, integrating a single large fan can be better than two small fans as the former induces a higher air flow rate and static pressure. On the other hand, altering the air flow channel length or depth changes the air flow resistance in stacks, leading to a shift of the working point for a fixed fan at a certain duty cycle and greatly influencing stack performance. This one-dimensional air-cooled stack model can be a powerful tool to facilitate stack design and optimization.

CO-tolerance behaviors of proton exchange membrane fuel cell stacks with impure hydrogen fuel

Carbon monoxide poisoning poses a significant challenge for proton exchange membrane (PEM) fuel cells operating with CO-containing hydrogen. One established solution involves air bleeding, a process that enhances the oxidation of carbon monoxide at the anode side of the fuel cell by blending a small quantity of air with the impure hydrogen before its introduction into the fuel cell. However, researchers have raised concerns regarding durability issues about catalyst sintering and membrane decomposition induced by air bleeding. The effects and underlying mechanisms of air bleeding on PEM fuel cells have yet to be comprehensively elucidated. To address this, this study conducts a detailed durability test to quantitatively evaluate the effects of air bleeding on the CO-containing hydrogen-fueled PEM fuel cells via the micro-current excitation method. The investigation substantiates that the PtRu/C catalysts significantly enhance both the performance and durability of fuel cells when air bleeding is employed, exhibiting different CO-tolerance and decay behaviors compared to the Pt/C anode catalyst. Furthermore, the evolution of MEA parameters indicates that the advantageous behaviors of PtRu/C catalysts can be attributed to their CO-tolerance capabilities, alleviated anodic catalyst sintering and loss, and decreased chemical carbon support corrosion and membrane decomposition through diminished hydrogen peroxide generation. This study contributes critical insights and empirical evidence for researchers focusing on CO-tolerant catalyst materials, the durability of PEM fuel cells, and the conversion and utilization of impure hydrogen energy derived from fossil fuels.

Recovery characteristics of reversible degradation for proton exchange membrane fuel cell stack under accelerated stress test

The reversible degradation of proton exchange membrane fuel cells (PEMFC) restricts the high efficiency and long-term durability of fuel cells. The reversible loss, restorable only through specific procedures, significantly diminishes both the operational efficiency and the predictability of their remaining service life. Consequently, it is imperative to elucidate the recovery characteristics of reversible loss in high power PEMFC stacks for engineering applications. However, most of the studies focus on small-area single cells or short stacks, researches on the full-size stacks considering the uniformity and consistency differences are scarce. The recovery characteristics of high-power PEMFC stacks remain unclear. Therefore, in this work, an accelerated stress test with the idle and rated currents as the boundary of the cyclic condition was designed for a 100 kW PEMFC stack to investigate the recovery characteristics. The periodic voltage fluctuations along with the shutdown operations indicate that the voltage recovery may be caused by the redistribution of water content within the stack, and the reversible degradation is more pronounced and readily reversible under the high current condition. The impedance results suggest that the redistribution of water within the catalyst layer takes longer compared to that in the membrane. Furthermore, analyses of single cell voltage indicate that the consistency of voltage recovery is more closely related to variations of water content within the catalyst layer. Cells with higher water content exhibit better voltage recovery.

Modelling and operation characteristics of air-cooled PEMFC with metallic bipolar plate used in unmanned aerial vehicle

The air-cooled proton exchange membrane fuel cell stack composed of the metallic bipolar plate with simple system and lightweight characteristics, is regarded as an ideal power source for unmanned aerial vehicles. A lumped parameter model is developed to analyze the operational characteristics at heights in the range of 0–3000 m. The temperature should not exceed 60 °C to ensure safe and effective operation. The peak power decreases by 20% and the stack has good adaptability to altitudes. The performance degradation can be largely attributed to the lower oxygen pressure at high altitudes through normalization analysis. It is more significant at higher currents owing to increased air starvation. The increase of the air stoichiometry is conducive to heat dissipation and reduces mass transfer loss. The voltage initially increases and then decreases as the air stoichiometry increases, and the optimal air stoichiometry corresponding to the maximum voltage is determined. Appropriately increasing the air stoichiometry can improve the consistency of the temperature and voltage distributions.

Integrating full fan morphology and configuration in three-dimensional simulation of air-cooled proton exchange membrane fuel cell stack

The internal water and thermal state and performance of an air-cooled proton exchange membrane (PEM) fuel cell stack are strongly determined by the fan arrangement and operational characteristics. This study presents an innovative method to investigate the influence of fan on stack performance through integration of fan’s full morphology, including the fan blade, grill between the fan and stack, etc. into a three-dimensional (3D) multiphase stack model. The multiple reference frame (MRF) model is implemented to simulate the air flow field caused by the rotation of fan and the multiple transfers coupled with electrochemical reactions is considered in the 3D stack model in detail. Through this integrated model, the influence of the air supply mode, fan number and duty ratio on stack performance and the distribution characteristics are investigated in detail. It is found that the air flowing into each cell in the fan-cooled stack is highly non-uniform, which increases the variations of oxygen concentration, temperature, and voltage in the stack. In comparison with the blowing mode, the suction mode helps to promote the uniformity of air supply with a lower air flow velocity.

Experimental evaluation of flow field design on open-cathode proton exchange membrane fuel cells (PEMFC) short stack consisting of three cells

The promising nature of proton exchange membrane fuel cell stacks in energy conversion has sparked the need to improve the cell components for improved performance, durability, sustainability, and cost competitiveness. This work presents the pros and cons of different flow field designs concluded from an open-cathode short stack, composed of three cells. The flow fields consist of 3D fine mesh, fine wire mesh, metal foam, and conventional straight channels. The results presented in this study show that the fine wire mesh gives better performance, both when integrated, and not integrated with straight channels. It is followed by the 3D fine mesh, straight channels, and metal foam. The different performance improvements are caused by the various flow fields influencing flow rate, current conductivity, and temperature increment. Water management seems to be a significant factor in the performance variation. This is presented by the IV curves, which show a dramatic discrepancy over the concentration loss region. The straight channels integrated with fine wire mesh cell have the highest degradation rate at a constant voltage of 1.7 V, even though it reached a constant value after 1.4 h of operation.

Experimental and Modeling Analyses of the Correlation between Local 3D Heterogeneities and the Macroscopic Observers of a Proton Exchange Membrane Fuel Cell Stack

In this study, we offer a complete investigation of a high-performing Proton Exchange Membrane Fuel Cell stack customized for automotive use. Our approach goes beyond traditional global electrochemical performance metrics such as polarization curves, ohmic resistance. Instead, we utilize specialized segmented high-surface sensors to measure current density and temperature in the active area plane, along with neutron imaging to determine liquid water distributions. Employing a pseudo three-dimensional two-phase flow model that integrates electrochemical and transport phenomena, we gain insight into the intricate relationships among these observables. The model proves particularly valuable in elucidating the operation of the anode and cathode sides, aspects challenging to capture solely through experimental mean. Our findings emphasize the substantial impact of fluid flow directions and current density on the distribution of liquid water. It is noteworthy that despite fluid flow direction, there is a consistent decrease in overall liquid water content with an increase in current density. This results in voltage instability within the cell, attributed to flooding phenomena, especially at low current densities. However, this is not observed in conditions representative of those encountered in on-field systems. We conduct a thorough analysis of this failure scenario to improve the fuel cell system’s control mechanisms.

Multi-Objective Operating Parameters Optimization for the Start Process of Proton Exchange Membrane Fuel Cell Stack with Non-Dominated Sorting Genetic Algorithm II

Proton exchange membrane fuel cell (PEMFC) is one of the most promising energy conversion devices in the world. Performance, durability, and cost are the key issues currently limiting its large-scale commercial application. This paper proposes a non-dominated sorting genetic algorithm II (NSGA-II) for optimizing operating parameters of the start process to improve the output performance of a PEMFC stack. First, a Simulink model of the PEMFC stack including the anode module, cathode module, water transfer module, output voltage module, and output net power module is established, and the accuracy of the stack model is verified through experiments. The three performances are then optimized simultaneously based on NSGA-II. The results show that the optimized operating parameters for the start process results in a PEMFC stack that outperforms the base case in steady-state voltage, percentage of undershoot, and net power these three indicators with the same response time, demonstrating the success of the method in solving multiple optimization problems. This study presents an effective approach for the multi-objective optimization of the PEMFC stack, which is of guidance for engineering practice.

Experimental study and modelling of an air-cooled proton exchange membrane fuel cell stack in the static and dynamic performance

Research on Proton Exchange Membrane fuel cells is an important area in the field of modern energy sources. Such fuel cells are characterized by high efficiency and fast response times, making them a promising solution for sustainable energy production. Fuel cells operate under both static and dynamic conditions. Such varying operating conditions result in achieving different efficiency of fuel cell systems. This study attempts an experimental and modeled efficiency evaluation of a 1.2 kW open-cathode air-cooled fuel cell stack under static and dynamic conditions. A Sankey energy balance and an analysis of the balance components were determined for the fuel cell stack operating in these two operating states. Simultaneous modeling of the fuel cell under both static and dynamic conditions was carried out. The efficiency values of the fuel cell stack were found to be slightly higher under static conditions than under dynamic conditions. Modeling fuel cells in static and dynamic conditions results in slightly different parameters (better conformance was obtained for static models).

Rapid activation of proton exchange membrane fuel cell stack and underlying mechanisms involved

Activation is a crucial procedure to improve the performance of newly fabricated fuel cell stacks to meet the power requirements in actual application scenarios. However, traditional activation procedures generally last for several hours or even days, which greatly increases the cost and limits the production efficiency. In response to this problem, this paper proposes a rapid activation procedure composed of hydrogen pumping (HP) and limiting-current activation with limited air (LCA). The influence of current density for HP and air supply for LCA on activation effect is studied and the best operating conditions are determined. The importance of water supply to the cathode is highlighted during HP. The influence of air supply for LCA on activation effect is limited, which contributes to gas saving. According to the experiments conducted on a single cell and a 10-cell stack, only 40 min are needed with this combined procedure, which is much shorter than that of the traditional step-current activation. Furthermore, nearly 75% of hydrogen is saved due to the short activation time and the control of gas supply, thus significantly reducing the cost during activation. Furthermore, to reveal the underlying mechanisms, membrane electrode assembly parameters before and after activation are obtained by micro-current excitation. A decrease in ohmic resistance and an increase in roughness factor of catalyst are observed, which contribute to performance improvement. According to the characterizations in the microstructure of membrane electrode assembly and platinum catalyst valence state, the electrolyte hydration and oxide reduction are determined as key factors and principles during activation.

Investigation of non-uniform temperature distribution in air-cooled proton exchange membrane fuel cells with multizone temperature measurement

ABSTRACT Open-cathode air-cooled proton exchange membrane fuel cell stack relies on air fans both for fuel supply and stack cooling. Inappropriate stack thermal management and non-uniform temperature distribution can lead to compromised stack performance, reduced lifespan, and even thermal runaway. Thus, temperature distribution measurement, investigation and analysis are essential for air-cooled PEMFC’s optimized operation and performance. This study uses a multi-zone temperature measurement approach to investigate the impact of air supply method, airflow, and output current on stack temperature distributions. The experimental results reveal that the highest stack temperature occurs at the cathode channel outlet, while the lowest temperature is near the hydrogen inlet. At a 75A load, the maximum temperature difference between the inlet and outlet is 17°C. Increasing fan speed from 4500 to 8800 r/min reduces temperature non-uniformity in cell 10, the most uneven among the 19 cells, by 11.2%. Comparing blowing and suction air supply modes, blowing enhances stack output performance by 2.1%, with smaller temperature differences. Specifically, cell 10 experiences a 7.5°C lower difference at 4500 r/min and a 3.6°C lower difference at 8800 r/min airflow. Under blowing air supply, temperature non-uniformity decreases by 36.95% at 4500 r/min and 29.2% at 8800 r/min.

Modeling of Proton Exchange Membrane Fuel Cell Stack and Start Strategy Optimization with a Multi-Objective Genetic Algorithm

This paper proposes a non-dominated ranking genetic algorithm (NSGA-II) method for fast optimizing the loading strategy at the start of a proton exchange membrane fuel cell (PEMFC) stack to optimize the dynamic response capability, power density and system efficiency. First, a Simulink model of the PEMFC stack including anode module, cathode module, water transfer module and output voltage module is established as the base model for optimization, and the accuracy of the stack model is verified through experiments. The power consumption of the air compressor is the main parasitic power considered, and it is modelled using the air compressor map by taking a table look-up method directly. The three performance indicators of dynamic response capability, power density and system efficiency are then optimized simultaneously based on NSGA-II. The results show that the optimized start-up loading strategy results in a PEMFC stack that outperforms the base model in all three indicators, demonstrating the success of the method in solving time-consuming multiple optimization problems. This study presents an effective and rapid approach for the multi-objective optimization of PEMFC stack, which is of guidance for engineering practice.

Study of Fuel Cell Stacks Combining Pseudo-3D Multi-Physics Simulations with Experimental Mappings of Current Density and Liquid Water

In this work, experimental and numerical analyses of Proton Exchange Membrane Fuel Cell stacks for automotive application are proposed. Performance and durability of PEMFC stacks strongly rely on an optimized water management. An adequate balance has to be found between a sufficient membrane hydration enhancing electrical conductivity and a limited liquid water presence avoiding water flooding. This requires investigations at a local scale inside the cells, because the location of water condensation is not distributed homogeneously in the active area, due to spatial variations of temperature, gas composition or current density.Allowing the quantification of liquid water locally inside PEMFCs, neutron imaging is a powerful tool for the analysis of fuel cell operation at a local scale. It is generally used with single cells and not with stacks, due to the complexity of such experiments. A quantification of liquid water over the active area is obtained through neutron imaging of stacks for several operating conditions. Specific segmented high surface sensors are placed inside stacks to map the current density and temperature distribution in the same area. A multi-physics pseudo-3D two-phase flow model coupling all the electrochemical and transport phenomena supports the understanding of the relationship between all these parameters. The comparison with experimental mappings validates the model, which is able to predict both the current density and the amount of liquid water at a local scale. Unlike experimental measurements that gives a total amount of liquid water in the cell, the model allows to distinguish between anode and cathode sides, or between channels and GDLs, providing crucial information regarding flooding phenomena. Moreover, the flowing direction of the fluids inside the stack have a major influence on liquid water distribution. As a general trend, it is observed that the average total water thickness always decreases when current density increases, in all tested stack flow configurations. Furthermore, a clear relationship appears between flooding, cathode pressure drop and cathode liquid water content. Finally, a detailed analysis is proposed to explain the flooding phenomena, in order to improve the fuel cell stack control. Figure 1

Full-scale three-dimensional simulation of air cooling metal bipolar plate proton exchange membrane fuel cell stack considering a non-isothermal multiphase model

Addressing issues such as the mass transfer characteristics and internal performance consistency of the air cooling (AC) proton exchange membrane fuel cell (PEMFC) stack. A full-scale AC metal bipolar plate (BP) stack is proposed in this study, comprising inlet and outlet manifolds, membrane electrode assembly (MEA), reaction flow field (FF) and cooling FF. The coupling of electrochemical reactions and heat and mass transfer processes in the stack is simulated using a non-isothermal multiphase numerical model. The characterization of the mass spatial distribution in the stack is explored by varying the stoichiometric ratio of the cathode gas, the thermal boundary conditions, the flow direction of the reaction gas and the air inlet flow configuration. According to the simulation results, it is found that, initially, the simulation errors in the one-dimensional (1D) AC stack are large and mainly concentrated in the concentration loss region. Subsequently, the increased stoichiometric ratio enhances the proton exchange membrane (PEM) water content, improves the local current density by 1.6% and facilitates the discharge of waste heat from the stack. Furthermore, thermal boundary conditions significantly affect the distribution of temperature uniformity in the stack, with high local temperatures causing significant water vapor generation and resulting in oxygen dilution. The counter-flow of hydrogen and air enhances the electrochemical reaction rates in the cathode catalyst layer (CCL) by 0.353%, with the lowest liquid water content in the seventh cell, influenced by the uneven distribution of manifold flow. Finally, changing the position of the cathode manifold gas inlet indicates that the positive flow of the cathode and AC inlets from the Z axis reduces the maximum stack temperature and water vapor by 1.04% and 0.38% respectively. The CCLs in Case 4 have optimal oxygen distribution and output voltages of approximately 0.66 V per fuel cell (FC).

Characteristics of heat, power generation, and energy efficiency study on a novel air-cooled PEMFC stack based on micro heat pipe arrays

This study introduces a novel kilowatt-scale air-cooled proton exchange membrane fuel cell stack utilizing micro heat pipe arrays (MHPA-PEMFC stack). This innovative stack design addresses issues commonly associated with conventional air-cooled fuel cell stacks, such as low heat transfer efficiency, suboptimal performance, and safety concerns, especially during high-load operations. In addition to the output performance of the stack, this study investigates the heat and power generation performance limits, operational security, and energy utilization efficiency of the MHPA-PEMFC stack under high power output and varying flow rates. The study introduces two novel evaluation indexes, namely, relative load gain (RLG) and relative safety gain (RSG), to provide a comprehensive evaluation. These indexes are utilized to link energy efficiency and exergy efficiency to the performance of the MHPA-PEMFC stack. The results show that the MHPA-PEMFC stack exhibits superior heat dissipation performance, uniform temperature distribution, and enhanced load capacity and safety compared with conventional PEMFC stacks. The maximum RLG and RSG achieved by the MHPA-PEMFC stack are 100% and 7.53, respectively. The energy efficiency of the MHPA-PEMFC stack surpasses 29% while maintaining a guaranteed maximum RLG. Notably, a higher RSG leads to a sacrifice in both energy and exergy efficiency.

Barrel effect in an air-cooled proton exchange membrane fuel cell stack

The performance of a single cell affects the proton exchange membrane fuel cell (PEMFC) stack's overall output performance, and the barrel effect occurs in PEMFC stacks. This research presents strategies to alleviate single-cell performance degradation in an air-cooled PEMFC stack. Results show that the poorest cell performance is caused by location-related issues. By embedding a copper plate in the position of cell-1, a hollow chamber replaces the cell-1 flow field. The stack equipped with an embedded copper plate achieved its peak power at 2151.22 W under a current of 40 A, signifying an 8.6 % enhancement in performance compared to the original stack. The incorporation of carbon paper and copper plates contributes to the establishment of a uniform stress distribution within the stack, consequently resulting in enhanced voltage consistency, characterized by a minimal variance value of approximately 0.033. Furthermore, the output performance of cell-1 increased by 0.101 V in the stack with copper plate compared to the original stack under 30 A current loading. By introducing a copper plate, the hollow gas chamber replaces the low pressure-drop cells position, effectively resolving the barrel effect in the PEMFC stack, and alleviating the single-cell degradation problem.

Endplate effect in an open-cathode proton exchange membrane fuel cell stack: Phenomenon and resolution

Proton exchange membrane fuel cells (PEMFCs) have garnered substantial attention as highly promising devices for energy conversion. The operational lifespan and overall output performance of such stacks are inherently governed by the performance of the weakest fuel cell, a phenomenon often referred to as the “Bucket Effect.” Evidently, cells located proximate to the hydrogen inlet endplate exhibit poor performance in comparison to the remaining cells in a 95 cells open-cathode fuel cell stack. In response to this challenge, an innovative approach involving endplate heating has been proposed to mitigate the observed endplate effects. Experimental validation of this approach has been conducted, yielding pertinent results. Furthermore, the internal temperature distribution across the stack exhibits an asymmetric parabolic profile, largely attributed to the intricate interplay of the endplate effects. Comparative analysis against a counterpart stack without endplate heating indicates that an application of 80 W heating power leads to a prolongation of operational duration by 156 s, while 100 W heating extends the operational period by 333 s. 80 W heating increased stack power by 31.5 W while improving output power efficiency by 1.9%, and 100 W heating increased stack power by 45.6 W while improving output power efficiency by 2.74%.

Optimal parameters estimation of the proton exchange membrane fuel cell stacks using a combined owl search algorithm

ABSTRACT PEMFC (the proton exchange membrane fuel cell) is an extremely effective energy converter system that generates electricity through electrochemical reactions. Optimizing the design of PEMFC stacks is important for their proper utilization and construction. In the current essay, we present a novel strategy for estimating optimal model parameters of proton exchange membrane fuel cell stacks utilizing the COSA (Combined Owl Search Algorithm), an improved metaheuristic algorithm. We compared the performance of COSA against other published methods, comprising COA, TLBO, BH, the original OSA, and BBO by employing them in three different cost functions. The results show that COSA achieved the minimum error values compared to the other algorithms for all case studies, with error values of 0.01, 1.20, and 0.93 for BCS 500W PEMFC, NedStackPS6, and SR-12 500 W PEMFC stack models, respectively. Our proposed approach could be utilized to optimize other kinds of fuel cells and integrated with other optimization strategies to improve its upcoming efficiency. Future work can focus on simplifying the algorithm structure to reduce its complexity during the optimization process. Overall, the COSA algorithm provides an effective tool for achieving more efficient and optimal fuel cell stacks.

Modeling of Proton Exchange Membrane Fuel Cell Stack and Start Strategy Optimization with a Multi-Objective Genetic Algorithm

This paper proposes a non-dominated sorting genetic algorithm II (NSGA-II) for optimizing the startup strategy of a proton exchange membrane fuel cell (PEMFC) stack to improve the dynamic response capability, output voltage, and net power. First, a Simulink model of the PEMFC stack including the anode module, cathode module, water transfer module, output voltage module, and output net power module is established, and the accuracy of the stack model is verified through experiments. The three performances are then optimized simultaneously based on NSGA-II. The results show that the optimized start-up loading strategy results in a PEMFC stack that outperforms the base model in steady-state voltage, undershoot percent, and net power these three indicators with the same response time, demonstrating the success of the method in solving multiple optimization problems. This study presents an effective approach for the multi-objective optimization of the PEMFC stack, which is of guidance for engineering practice.