Stack Durability Research Articles

Improved Understanding of PEMFC Stack Durability Testing through Comprehensive In-Situ and Ex-Situ Characterization Techniques

Durability testing of Proton Exchange Membrane Fuel Cells for mobile applications remains a critical challenge. While most academic studies focus on single-cell testing, there are only few publications on stack testing of technical relevant sizes. This study utilizes comprehensive characterization techniques to enhance understanding of PEMFC stack durability, aiming to meet the currently targeted durability targets. A 5,500-hour long-term test, based on the Auto Stack Industry (ASI) test protocol, was performed on a 7-cell short stack of 240 cm² active area. In-situ techniques, such as spatially resolved current density measurement, cyclic voltammetry, and electrochemical impedance spectroscopy, provided real-time degradation insights, while ex-situ methods, including FIB-SEM analysis, infrared thermography or contact angle measurements provided information on material degradation mechanisms. Membrane degradation was found to be negligible. Slight thinning of the cathode indicates carbon corrosion of the catalyst support. Catalyst aging was observed in the form of Pt band formation and Co leaching. Gas diffusion layers showed hydrophobicity loss, and increased resistance in bipolar plates contributed to reduced performance. Our findings demonstrate that PEMFC stacks operated under automotive drive cycle protocols can meet the actual targeted durability objectives. Moreover, it illustrates the degradation phenomena that occur under realistic operating conditions and modes, and how they evolve over the duration of thousands of hours of operation.

Improved Understanding of PEMFC Stack Durability Testing through Comprehensive In-Situ and Ex-Situ Characterization Techniques

Durability testing of Proton Exchange Membrane Fuel Cells for mobile applications remains a critical challenge. While most academic studies focus on single-cell testing, there are only few publications on stack testing of technical relevant sizes. This study utilizes comprehensive characterization techniques to enhance understanding of PEMFC stack durability, aiming to meet the currently targeted durability targets. A 5,500-hour long-term test, based on the Auto Stack Industry (ASI) test protocol, was performed on a 7-cell short stack of 240 cm² active area. In-situ techniques, such as spatially resolved current density measurement, cyclic voltammetry, and electrochemical impedance spectroscopy, provided real-time degradation insights, while ex-situ methods, including FIB-SEM analysis, infrared thermography or contact angle measurements provided information on material degradation mechanisms. Membrane degradation was found to be negligible. Slight thinning of the cathode indicates carbon corrosion of the catalyst support. Catalyst aging was observed in the form of Pt band formation and Co leaching. Gas diffusion layers showed hydrophobicity loss, and increased resistance in bipolar plates contributed to reduced performance. Our findings demonstrate that PEMFC stacks operated under automotive drive cycle protocols can meet the actual targeted durability objectives. Moreover, it illustrates the degradation phenomena that occur under realistic operating conditions and modes, and how they evolve over the duration of thousands of hours of operation.

Load Variation Removal and Stack Durability Experiments to Improve Lifetime of Fuel Cell Stack for Hydrogen Electric Vehicles

Load Variation Removal and Stack Durability Experiments to Improve Lifetime of Fuel Cell Stack for Hydrogen Electric Vehicles

수소전기차 연료전지 수명 향상을 위한 부하 변동 제거 및 스택 내구성 실험

수소전기차 연료전지 수명 향상을 위한 부하 변동 제거 및 스택 내구성 실험

A comparative analysis of power control strategies for a plug-in extended-range FCHEV with battery and PEMFC durability considerations

ABSTRACT Fuel cell hybrid electric vehicles employ fuel cells along with batteries or ultracapacitors as power sources, and energy management systems can control their power split. This study investigates energy management strategies for lightweight plug-in extended-range fuel cell hybrid electric vehicles to optimise fuel economy, extend component lifespans, and enhance vehicle efficiency. Comparisons between power follower and dynamic programming-based strategies are conducted, focusing on incorporating PEMFC health constraints to prolong stack durability via on-off binary mode operation. Using the New European Driving Cycle, performance evaluation is conducted on a parallel architecture featuring a 16-kW motor, regenerative braking system, eight 420-Wh batteries in series, and six 1-kW fuel cell stacks. Dynamic programming strategies demonstrated potential improvements, with savings in hydrogen consumption of 62–72 L per driving cycle and SOC levels of 3.9%. Moreover, optimised battery lifespan enabled the system to achieve approximately 18,087 -18,745 charge/discharge cycles. Implementing PEMFC health constraints facilitated reductions in average accumulated active time to 205 seconds per driving cycle and startup/shutdown cycle frequency to 36.5 cycles per hour, promoting enhanced system durability and operational efficiency.

Improving fuel efficiency and durability in fuel cell vehicles through component sizing and power distribution management

The proposed study presents a novel approach to determining the optimal component sizes and power distribution for a vehicle, taking into account various power sources in order to prolong the lifespan of the fuel cell stack. Moreover, this technique aims to increase the vehicle's overall fuel economy. The available experimental data of Toyota Mirai has been used to model the vehicle in the MATLAB-SIMULINK software. The validated model is implemented to evaluate the vehicle power request in different standard driving cycles and routes to size the vehicle components. The arithmetic average of the steady power of different driving cycles and routes has been attributed to the fuel cell stack's maximum efficiency point. The battery size should support the requested dynamic power in any situation. Thus, the maximum power of the fuel cell stack, the high voltage battery size, and the electric motor maximum power are assigned as 96 kW, 3.05 kWh, and 59 kW, respectively. The results of fuel consumption of the vehicle is also improved at least by 10% up to 21% in different driving conditions. Economic analysis reveals that adopting this strategy can lead to a substantial reduction in the initial vehicle cost by $1,328. The operational cost has also decreased 691$ annually due to lower fuel consumption of the new strategy implementation. These advancements along with better fuel cell stack durability hold promise for prospective buyers, allowing for greater accessibility and financial flexibility.

Electrochemical Analysis of an Electrolyte-Supported Solid Oxide Cell-Based MK35x Stack during Long-Term Electrolysis Operation

The currently ongoing scale-up of high-temperature solid oxide electrolysis (SOEL) requires an understanding of the underlying dominant degradation mechanisms to enable continuous progress in increasing stack durability. In the present study, the degradation behavior of SOEL stacks of the type “MK35x” with chromium-iron-yttrium (CFY) interconnects and electrolyte-supported cells (ESC) developed at Fraunhofer IKTS was investigated. For this purpose, the initial electrochemical performance of a 10-cell stack was characterized in various operating conditions in both fuel cell and electrolysis mode. Degradation was evaluated during galvanostatic steady-state steam electrolysis operation for more than 3000 h at an oxygen side outlet temperature of 816 °C and a current density of −0.6 A cm−2 and showed an average voltage evolution rate of −0.3%/kh demonstrating high stability. Initial and final characterization at the part load operating point at −0.39 A cm−2 and 800 °C led to the determination of a positive overall degradation rate of 0.4%/kh showing a considerable impact of the operating conditions on the degradation rate. By means of electrochemical impedance spectroscopy analysis it was shown that the stack’s ohmic resistance increased whereas the polarization resistance decreased most likely due to an enhancement in LSMM’/ScSZ oxygen electrode performance.

Lifespan evaluation of two 30-cell electrolyte-supported stacks for hydrogen production by high temperature electrolysis

The levelized cost of electrochemical hydrogen remains significantly affected by stack replacement frequency, and therefore stack durability. Consequently, demonstrating relevant lifespans is paramount towards supporting the accelerating industrialization of solid oxide technology.Thus, two 30-cell electrolyte-supported stacks were tested in thermoneutral conditions, −0.52 A cm−2 and 70% steam conversion. The first stack comprised a variety of cells and over the 4.5 kh test sequence yielded a degradation rate of +22 mΩ cm2 kh−1, or +4.5 K kh−1. The second stack only included the best cell variant, and degraded at a much lower rate of +12 mΩ cm2 kh−1, or 2.5 K kh−1. The test lasted 9.5 kh, a record for full stacks operated in electrolysis mode.The present report details the testing equipment, the experimental conditions and procedures, and compares the performances and degradation rates recorded. In addition, special attention is given to the feed water quality over time.

Manufacturable Microporous Layers on Sintered Titanium for PEM Electrolysis Applications

Renewed interest in green hydrogen has prompted a re-examination of the components of proton-exchange membrane water electrolyzers to improve stack durability and lower net hydrogen cost. A key component identified as a driver of cell performance and durability is the anode porous transport layer (PTL). The PTL dictates electrical resistance between anode and flow field, manages two-phase flow at the anode interface, and sinks heat from the electrolysis reaction.Efforts to optimize the PTL have typically focused on limiting titanium passivation and optimizing delivery of water and discharge of oxygen at the anode. However, recent work has shown another important effect related to the contact area of the PTL with the anode catalyst layer. Multiple investigators have shown that highly flat and smooth PTLs enhance cell durability, particularly in the case of low anode catalyst loadings (< 0.5 mgIr/cm2). In those studies1–5, commercial PTLs were modified to obtain more uniform surfaces. In some cases this is effected by attachment of finely structured microporous layers (MPLs) that improve catalyst utilization and eliminate localized heating.An integrated manufacturing approach is required to enable commercial adoption of advanced PTLs featuring microporous layers. In this contribution, we investigate multiple routes and materials systems for obtaining manufacturable MPLs. We assess the relative merits of each method with respect to feasibility and resultant component characteristics, and validate ex situ characterization with single-cell electrolyzer durability testing using catalyst-coated membranes with low Ir loadings. References (1) Lettenmeier, P.; Kolb, S.; Sata, N.; Fallisch, A.; Zielke, L.; Thiele, S.; Gago, A. S.; Friedrich, K. A. C Energy Environ. Sci. 2017, 10 (12), 2521–2533. https://doi.org/10.1039/C7EE01240C.(2) Kang, Z.; Yang, G.; Mo, J.; Yu, S.; Cullen, D. A.; Retterer, S. T.; Toops, T. J.; Brady, M. P.; Bender, G.; Pivovar, B. S.; Green, J. B.; Zhang, F.-Y. Int. J. Hydrog. Energy 2018, 43 (31), 14618–14628. https://doi.org/10.1016/j.ijhydene.2018.05.139.(3) Lee, J. K.; Lee, C.; Fahy, K. F.; Kim, P. J.; LaManna, J. M.; Baltic, E.; Jacobson, D. L.; Hussey, D. S.; Stiber, S.; Gago, A. S.; Friedrich, K. A.; Bazylak, Energy Convers. Manag. 2020, 226, 113545. https://doi.org/10.1016/j.enconman.2020.113545.(4) Schuler, T.; Ciccone, J. M.; Krentscher, B.; Marone, F.; Peter, C.; Schmidt, T. J.; Büchi, F. N. Adv. Energy Mater. 2020, 10 (2), 1903216. https://doi.org/10.1002/aenm.201903216.(5) Lee, J. K.; Schuler, T.; Bender, G.; Sabharwal, M.; Peng, X.; Weber, A. Z.; Danilovic, N. Appl. Energy 2023, 336, 120853. https://doi.org/10.1016/j.apenergy.2023.120853. Figure 1

Simulation of cathode catalyst durability under fuel cell vehicle operation –Effects of stack size and temperature

In this work, a fundamental cathode catalyst degradation model is developed in order to simulate fuel cell stack durability under realistic vehicle operation. A dynamic platinum degradation model featuring platinum dissolution and redeposition is developed to account for the Ostwald ripening phenomenon. The model is then calibrated for a variety of accelerated stress test data with different upper and lower potential limits and temperatures. Next, a case study of fuel cell transit bus operation in the city of Victoria, B.C., Canada is carried out to investigate the effects of stack size and temperature on the cathode catalyst durability. To this end, the required power density and cell voltage are calculated from the drive cycle considering vehicle dynamics and specifications. Larger stacks are found to experience higher upper potential limits; thus, showing lower lifetimes. The cathode lifetime is predicted to grow 379% at 80°C if the stack nominal power is lowered from 396 to 132 kW while the performance requirement is met. The temperature is also shown to have a tremendous impact on the cathode lifetime. A temperature drop from 80 to 60°C results in 154% cathode lifetime enhancement for a stack nominal power of 264 kW.

Progress of Solid Oxide Electrolysis and Fuel Cells for Hydrogen Generation, Power Generation, Grid Stabilization, and Power-to-X Applications

Over the past 25+ years, Nexceris has been developing solid oxide cell (SOC) technology for power generation, energy storage and hydrogen production applications. Nexceris is vertically integrated SOC technology provider that develops and manufactures solid oxide electrode materials, interconnect coatings, planar electrolyte supported cells, and solid oxide stacks. Nexceris stacks are designed for low-cost manufacture and pressurized operation, and stacks have large repeat unit area for efficient packaging into megawatt-scale systems. Nexceris’ stacks are being tested in fuel cell, electrolysis, and reversible modes, with a focus on optimizing performance, efficiency, and durability. Current work at Nexceris includes long-term electrolysis stack durability testing, breadboard system testing of reversible SOC stacks, third-party stack validation testing, and SOC system design and demonstration testing. Nexceris also is exploring solid oxide co-electrolysis for converting steam and CO2 to syngas and the conversion of this syngas to fuels and chemicals. This presentation will provide an update on Nexceris’ solid oxide cell technology development and commercialization activities.

Progress of the Evaluation and Analysis Methods for Durability of SOFC Stacks

Recent progress in the development of R&D for the evaluation and analytical methods of SOFC stack durability is reported under the NEDO Japanese national project. The goal of this project is the following two points: (1) to develop the advanced evaluation and analytical methods for the cell stacks which show a lifetime over 15 years (130 kh) with high efficiency of over 65% LHV, and (2) to develop the evaluation and analytical methods for dynamic operation mode such as rapid start-stop and load cycling. Three practical stacks were supplied by the stack developers and tested over 10,000 hours with high fuel utilization (Uf~85%). Relatively stable performances were reported for these stacks and degradation factors were considered taking into account the degradation mechanisms at cells and stacks. Under high Uf conditions, some specific degradation mechanisms are now analyzed in the cells. For rapid starts of stacks, evaluation protocols are considered taking into account the mechanical stress arising from the thermal distribution in the cells. Simulation methods are considered for the evaluation of performance after 15 years of operation in the stacks.

Experimental validation of passive and active fault-tolerant controls against sensor faults in a proton exchange membrane fuel cell system

A fuel-cell system is interconnected with subsystems such as the stack, thermal/water management systems, air/fuel supply systems, and inverter; if an abnormality occurs, operational efficiency and availability of the entire system can decrease. However, when faults occur in the system, terminating system operations or replacing faulty parts every time can be expensive and inefficient. Instead, appropriate decision-making is required, with fault-tolerant control considered an appropriate solution. This study presents methods and criteria for fault-tolerant control when a fault occurs in a proton exchange membrane fuel cell (PEMFC) system. By configuring a 1 kW residential PEMFC system, a fault occurring in either the thermocouple or mass flow meters – targets for the system control – is diagnosed, and real-time control change is performed instead of immediately repairing the sensor. This approach enables stable and continuous operation of the PEMFC system. The fault-tolerant control method consists of either the feed-back control method, using the real-time predicted value of each control sensor, or the feed-forward method, using the constant control-signal value learned in the normal state; the advantages and limitations of each method are compared. Futhermore, considering the system efficiency, stack durability, and operating control deterioration, a guideline is suggested for applying fault-tolerant control and improving its corresponding effectiveness. For example, fault-tolerant control can resolve a 4.6% decrease in system efficiency caused by a thermocouple fault. This study contributes to improving the system operation rate and reliability by applying fault-tolerant control, thus facilitating efficient decision-making following fault diagnosis.

Progress of the Evaluation and Analysis Methods for Durability of SOFC Stacks

Recent progress in the development of R&D for the evaluation and analytical methods of SOFC stack durability is reported under the NEDO Japanese national project. The goal of this project is the following two points: (1) to develop the advanced evaluation and analytical methods for the cell stacks which show a lifetime over 15 years (130 kh) with high efficiency of over 65% LHV, and (2) to develop the evaluation and analytical methods for dynamic operation mode such as rapid start-stop and load cycling. Three practical stacks (one flat tube and two types of planar) were supplied by the stack developers and tested over 10,000 hours with high fuel utilization (Uf~85%). It was found that the same evaluation methods can be applied to the stack resistance component determination between normal Uf (=75%) and high Uf (85%) conditions. Relatively stable performances were reported for these stacks and degradation factors were considered taking into account the degradation mechanisms at cells and stacks. Under high Uf conditions, some specific degradation mechanisms are now analyzed in the cells. For rapid starts of stacks, evaluation protocols are considered taking into account the mechanical stress arising from the thermal distribution in the cells. Simulation methods are considered for the evaluation of performance after 15 years of operation in the stacks.

Performance characterization of metal-supported solid-oxide fuel cell stacks at elevated pressure

In this paper, we present results on performance characterization of solid-oxide fuel cell stacks at elevated pressures up to 6 bara. Stacks are designed and built by Ceres Power, Ltd., and are rated at 1- and 5- kWe. Fuel streams include H2/N2 mixtures, synthetic natural-gas reformate, and simulated anode tail-gas recycle. Elevated operating pressure serves to increase stack electrochemical performance, with the most-pronounced gains found up to 4 bara. Pressurized operation reduces the extent of methane conversion, promoting more-uniform internal reforming and cooling within the stack. Such cooling is critical at higher-current conditions. A previously developed one-dimensional computational stack model is used to provide insight into stack operation. Pressurization is found to slightly increase internal thermal gradients, while promoting more-uniform reactant-concentration profiles across the cell, reducing the likelihood of local fuel starvation. The high fuel dilution brought by anode recycle can modestly decrease stack performance; however, this decrease is recovered through elevated-pressure operation at 3 bara. Anode recycle further promotes compositional uniformity across the cell. These results reflect that pressurized operation can promote stack performance, while potentially promoting long-term stack durability through uniformity in stack environmental conditions.

A novel power allocation strategy considering multi-objective comprehensive optimization for hybrid electric vehicles

This research introduces a multi-objective comprehensive optimization power distribution strategy (PDS), specifically designed for a hybrid electric vehicle (HEV) that utilizes a combination of fuel cell (FC) and battery technology. As hybrid power systems face challenges such as high operating costs and limited stack durability, which hinder the widespread adoption of FCs, this study proposes a strategy that focuses on optimizing both the operational cost and service life of the stack. To enhance the longevity of the stack, this research investigates the coupling relationship between the operational lifespan of the fuel cell and its output power. In addition, this study formulates a mathematical formula to depict the relationship between the FC’s output power and the loss of its lifespan. Furthermore, the lifetime loss of the energy storage system, as well as limitations on the fluctuation of its state of charge (SOC), are also taken into account. Additionally, this study aims to enhance fuel efficiency by optimizing the hydrogen consumption of the system. Based on the above considerations, a cost function has been formulated for the purpose of multi-objective optimization. To expedite the convergence speed when solving the cost function, a sequential quadratic programming (SQP) algorithm has been employed. Based on the hardware-in-the-loop (HIL) bench, the effectiveness of the presented multi-objective comprehensive optimization PDS is validated. The results demonstrate that the proposed strategy has advantages over other benchmark PDSs in many aspects, including operating cost, hydrogen consumption, battery SOC fluctuation range, and power sources operating life loss.

Investigation of the reversible performance degradation mechanism of the PEMFC stack during long-term durability test

This paper reports on 3-cell PEMFC stack durability test of 2500 h in dynamic conditions and different recovery procedures. After electrochemical impedance spectroscopy (EIS) analysis, it was determined that the primary cause of the stack performance degradation is the oxidation of platinum (Pt), which is reversible. The air starvation operation reduced the cathode voltage to less than 0.2 V, part of PtO was reduced, and the stack performance loss was partially recovered. However, the recovery of the three cells varies due to defects in the three-cell stack and uneven gas distribution. The fast load-up operation brought the short-term severe air starvation of the three cells to a similar level, the remaining platinum oxide (PtO) was fully reduced, the stack performance improved again, and the voltage consistency of the three cells was restored significantly. With the optimization of operating parameters and combined recovery procedures, the average degradation rate of the stack voltage is 3.08 μV/h within 2500 h. The results indicated that our combined strategy is of huge importance to mitigate the reversible performance degradation and significantly extend the service life of PEMFC stack and be a very appropriate procedure used in laboratories and systems.

Self-Water-Removal and Voltage Behavior Improvement of Dead-Ended Proton Exchange Membrane Fuel Cell Stack at Steady-State and Dynamic Conditions

The proton exchange membrane fuel cell (PEMFC) demonstrates high commercial competitiveness due to its advantages: low operating temperature, high power/mass ratio, fast response, no emission, and low noise. Thermal and water management remains a challenging issue for ensuring the fuel cell’s performance at steady-state and dynamic conditions. The cathode moisture condensation uses a semiconductor cooler to effectively remove excess water from the PEMFCs and reduce the probability of flooding of the stack. The stack’s voltage uniformity is an essential factor that affects the performance and lifetime of PEMFC. This paper investigates the dynamic response characteristics of the voltage uniformity of a PEMFC stack under cathode moisture condensation conditions. The results show that the condensation temperature at 10°C during the steady-state or transient operation of the PEMFC can effectively optimize the stack’s performance. Compared to conventional PEMFC, applying the cathode moisture condensation technology to the PEMFC stack increases the stack voltage by 6% and decreases the voltage uniformity by up to 30%. This self-water-removal technology effectively improves the voltage uniformity of the stack, which then increase the stack durability.

Effect of dynamic and operational restrictions in the energy management strategy on fuel cell range extender electric vehicle performance and durability in driving conditions

Aiming at increasing fuel cell (FC) stack durability in driving conditions, part of the scientific community has focused its efforts on developing energy management strategies (EMS) for fuel cell hybrid vehicles (FCV). Nonetheless, most of these studies do not explicitly explain the effect of constraining the EMS in both degradation and performance when acting on the FC system dynamics or operational space nor consider the FC range-extender (FCREx) architecture for passenger car application. This study evaluates the potential of FCREx architecture to maximize FC stack durability and performance through control strategy dynamic and operational space limitations. For that purpose, a FCV modeling platform was developed and integrated together with an EMS optimizer algorithm and a semi-empirical advanced FC stack degradation model for driving cycle conditions. The resulting modeling platform was then simulated in WLTC 3b driving cycle to predict FC degradation and H2 consumption with different dynamic and operational restrictions. Practical limits for EMS constraining were identified as —di/dt—max = 0.001 A/cm2s or imin = 0.2 A/cm2 since they prevented the EMS from fulfilling the constant state-of-charge constraint in high-dynamic driving condition. In this sense, —di/dt—max = 0.01 A/cm2s and imin = 0.15 A/cm2 were recommended as the combination of constraints that maximizes FC stack durability (+110%) without affecting the FCV operability with only an increase in of 4.7% in H2 consumption. From these results, a set of recommendations and guidelines for FCREx vehicle manufacturers and FC stack developers were elaborated based on the benefits of understanding the dynamics and operational constraints that the FC system is going to be subjected to under real operation.

A modeling framework for predicting the effect of the operating conditions and component sizing on fuel cell degradation and performance for automotive applications

In this study, durability and performance prediction were integrated in the sizing process of the FC stack of a fuel cell range-extender (FCREx) vehicle together with the design of a dynamics-limited control strategy. For that purpose, a FCREx vehicle model integrating a FC stack, balance of plant, battery, H2 tank and vehicle body (C-class SUV) validated in previous studies was used. To predict FC stack degradation rate, a novel semi-empirical multi-layered degradation modeling framework for automotive application is proposed and developed. Degradation rates are calculated based on reference degradation rates measured at reference and known conditions (1st layer) and scaled with the electrochemical phenomena (2nd layer) and the operating conditions (3rd layer) through scaling functions based on physical tendencies. Results show how increasing the FC stack power decreases H2 consumption but increases durability, while increasing the dynamic limitations on the control strategy increases both H2 consumption and durability. The isolated effect of sizing implied a decrease in H2 consumption of ∼3% and an increase in FC stack durability of ∼53% when comparing the 40 kW and 100 kW designs. In contrast, the effect of dynamic limitations was significantly perceived in the 40 kW design which implied an increase in H2 consumption close to 8% and an increase in durability of 294% when comparing the infinite dynamics and the highest dynamically restricted cases. Nevertheless, the effect of sizing is neglected under high dynamic limitation and limiting the current density change rate to 0.001 A/cm2s may prevent the control strategy from fulfilling the charge sustaining mode in aggressive driving. Based on these results, a set of recommendations were elaborated for FC stack and FCV manufacturers aiming to apply FCREx architecture to passenger car vehicles.