Strategies to Mitigate Degradation in Fuel Cell Materials

Abstract High-temperature proton exchange membrane fuel cells (HT-PEMFCs) could replace fossil fuel-based technologies for applications which cannot involve bulky/heavy cooling systems, such as aeronautics. However, severe materials degradations upon operation prevent performance retention for acceptable lifetimes. While others have already reported degradations in HT-PEMFC, post mortem characterizations of used HT-PEMFC membrane electrode assemblies (MEAs) remain scarce. Herein, HT-PEMFC performance degradation is studied by applying a startup/shutdown protocol to a short-stack operated at 160°C; one MEA is characterized using complementary physicochemical/electrochemical techniques to identify/understand the degradation mechanisms and their origin. This start/stop operation mode (co-flow gas reactants) leads to substantial degradation inhomogeneity. For the anode, migration, coalescence, and detachment of Pt nanoparticles are witnessed induced by high-surface-area carbon support functionalization and corrosion. The anode electrochemical surface area (ECSA) remains constant at the i... Read More

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Electro-catalyst plays a central role in many clean energy technology applications including water electrolysis for green hydrogen generation, emission free fuel cells for transportation, electrochemical CO 2 reduction and combine heat and power generation. Electro-catalysts degrade via multiple mechanisms, depending on the exact operating conditions in its life cycles. In this presentation, we demonstrate the dependance of the electro-catalyst degradation in polymer electrolyte fuel cell (PEFC) on the specific “paths” that the fuel cell takes to age. Specifically, differently ordered aging protocols with the same total number of accelerated stress tests (ASTs) cycles ( i.e., 31,000 total cycles including 30,000 cycles of square-wave load/unload ASTs and 1000 cycles of triangular-wave carbon corrosion ASTs) were used to degrade membrane electrode assemblies (MEAs). At the end-of-life, performances were distinct, indicating that depending on the specific aging route taken, the fuel cell catalyst layer degrades differently after same number of total AST cycles. The load/unload aging pr... Read More

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Fuel cells hold immense promise as efficient and sustainable power sources for transportation and stationary applications. However, their operation can be severely impacted by air pollutants, particularly sulfur dioxide (SO 2 ) and nitrogen oxides (NOx). These pollutants can adsorb onto the platinum catalyst, leading to a decrease in fuel cell performance and durability. In this study, we investigate the impact of SO 2 and NO 2 on PEM fuel cell performance and durability. The contamination tests were carried out at a constant current density of 0.5 A.cm −2 , and they consisted of four steps: a pre-poisoning step to evaluate initial performance (15-16 h), poisoning step (50 h), self-recovery in a pure air stream (20-21 h) and a driven CV-induced recovery. Electrochemical characterizations were carried out at the end of each step (Polarization curve, Electrochemical Impedance Spectroscopy, Cyclic Voltammetry and H 2 Crossover). Our initial investigation involved contaminating a single fuel cell with a low concentration of 0.1 ppm of sulfur dioxide (SO 2 ). Remarkably, this resulted in ... Read More

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In order to enhance the durability of fuel cell systems in fuel cell hybrid electric vehicles (FCHEVs), researchers have been dedicated to studying the degradation monitoring models of fuel cells under driving conditions. To predict the actual degradation factors and lifespan of fuel cell systems, a semi-empirical and semi-physical degradation model suitable for automotive was proposed and developed. This degradation model is based on reference degradation rates obtained from experiments under known conditions, which are then adjusted using coefficients based on the electrochemical model. By integrating the degradation model into the vehicle simulation model of FCHEVs, the impact of different fuel cell sizes and dynamic limitations on the efficiency and durability of FCHEVs was analyzed. The results indicate that increasing the fuel cell stack power improves durability while reducing hydrogen consumption, but this effect plateaus after a certain point. Increasing the dynamic limitations of the fuel cell leads to higher hydrogen consumption but also improves durability. When consideri... Read More

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Abstract The lifetime of hydroxyl radicals ( ⋅ OH) in the fuel cell catalyst layer remains uncertain, which hampers the comprehension of radical‐induced degradation mechanisms and the development of longevity strategies for proton‐exchange membrane fuel cells (PEMFCs). In this study, we have precisely determined that the lifetime of ⋅ OH radicals can extend up to several seconds in realistic fuel cell catalyst layers. This finding reveals that ⋅ OH radicals are capable of carrying out long‐range attacks spanning at least a few centimeters during PEMFCs operation. Such insights hold great potential for enhancing our understanding of radical‐mediated fuel cell degradation processes and promoting the development of durable fuel cell devices.

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Proton exchange membrane fuel cells (PEMFCs) have the potential to tackle major challenges associated with fossil fuel-sourced energy consumption. Nafion, a perfluorosulfonic acid (PFSA) membrane that has high proton conductivity and good chemical stability, is a standard proton exchange membrane (PEM) used in PEMFCs. However, PEM degradation is one of the significant issues in the long-term operation of PEMFCs. Membrane degradation can lead to a decrease in the performance and the lifespan of PEMFCs. The membrane can degrade through chemical, mechanical, and thermal pathways. This paper reviews the different causes of all three routes of PFSA degradation, underlying mechanisms, their effects, and mitigation strategies. A better understanding of different degradation pathways and mechanisms is valuable in producing robust fuel cell membranes. Hence, the progress in membrane fabrication for PEMFC application is also explored and summarized.

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Abstract A critical challenge to the commercialization of clean and high-efficiency solid oxide fuel cell (SOFC) technology is the insufficient stack lifespan caused by a variety of degradation mechanisms, which are associated with cell components and chemical feedstocks. Cell components related degradation refers to thermal/chemical/electrochemical deterioration of cell materials under operating conditions, whereas the latter regards impurities in feedstocks of oxidant (air) and reductant (fuel). This article provides a thermodynamic perspective on the understanding of the impurities-induced degradation mechanisms in SOFCs. The discussion focuses on using thermodynamic analysis to elucidate poisoning mechanisms in cathodes by impurity species such as Cr, CO 2 , H 2 O, and SO 2 and in the anode by species such as S (or H 2 S), SiO 2 , and P 2 (or PH 3 ). The author hopes the presented fundamental insights can provide a theoretical foundation for searching for better technical solutions to address the critical degradation challenges.

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Cell deterioration over time is one of the most perplexing obstacles to long-term fuel cell performance. In this study, we employed both in situ and ex situ analytical approaches to investigate the deterioration mechanisms of state-of-the-art AEMFCs.

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Due to its zero emissions, high efficiency and low noise, proton exchange membrane fuel cell (PEMFC) is full of potential for the application of vehicle power source. Nonetheless, its lifespan and durability remain multiple obstacles to be solved before widespread commercialization. Frequent exposure to non-rated operating conditions could considerably accelerate the degradation of the PEMFC in various forms, thus reducing its durability. This paper first analyses degradation mechanisms of PEMFCs under typical automotive operating conditions, including idling, startup-shutdown, dynamic loads, and cold start. The corresponding accelerated stress testing methods are also discussed. Then, as the impurities existed in the reaction gas source and generated from the degradation of the PEMFC itself may occur under all automotive conditions, the degradation mechanisms caused by impurity contamination are classified and reviewed in detail. After that, the techniques proposed by researchers to enhance the durability of PEMFCs are presented from four aspects: MEA materials, bipolar plates and f... Read More

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<title>Abstract</title> Polymer electrolyte membrane fuel cells (PEMFCs) have faced challenges in achieve their lifespan goals due to the degradation of the membrane electrode assembly (MEA) during long-term operation. To enhance the durability of PEMFCs, it is necessary to research materials that can improve the durability of the membrane and electrodes, as well as to study operating conditions that can reduce degradation. This paper investigated methods to mitigate the membrane degradation of electrochemically degraded MEAs by controlling humidity and temperature among the operating conditions. MEA was degraded electrochemically by conducting open circuit voltage (OCV) holding, and then the degradation rate according to temperature and humidity changes was observed through fluoride emission rate (FER) change. In a degraded MEA, it is shown that increasing cell humidity accelerates membrane degradation. According to linear sweep voltammetry (LSV) results, this was confirmed to be due to the increase in hydrogen permeability caused by the higher humidity. The decrease in temperature ... Read More

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<title>Abstract</title> The durability of polymer electrolyte fuel cells (PEFCs) in fuel cell electric vehicles (FCEVs) is important for the shift from passenger cars to heavy-duty vehicles. The components of a PEFC, namely the proton exchange membrane (PEM), catalyst layer (CL), and gas diffusion layer (GDL), contribute to the degradation of the fuel cell performance. These degradation studies were conducted independently and focused on PEMs and CLs. The degraded fuel cell stack in FCEVs is completely replaced. Therefore, it is necessary to counteract rapid material degradation in PEFCs. In this paper, we propose a method for simultaneously evaluating the degradation rates of these components by combining electrochemical characterization with operando synchrotron X-ray radiography. The open-circuit voltage, electrochemically active surface area, and water saturation were used as the degradation indicators for the PEMs, CLs, and GDLs, respectively. The results of two accelerated stress tests (loading and start-stop cycles) showed that the increase in water saturation owing to the los... Read More

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Fuel cells are one of the prioritized energy conversion technologies with highly focused research and development. For the whole fuel cell commercial realization on the market, fuel cells must be very affordable. This realization calls for critical developments in addressing the technical hindrance such as the overall fuel cell cost, electrocatalysts stability, and durability. A step towards fuel cell commercialization means well-defined architectural electrocatalysts designs that fully enhance the oxygen reduction reaction and fuel oxidation reaction. The currently pursued electrocatalyst has drawbacks. These include poisoning from methanol and ethanol cross-over, sluggish anodic and cathodic kinetics, air, fuel management, stability, and durability management. This chapter aims to elucidate how the mentioned challenges affect the electrocatalytic activity of the electrocatalysts and expound on some approaches to mitigate the challenges, enhancing adaptability as fuel cells electrocatalysts.

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On their way to their commercialisation, Fuel Cell Heavy Duty Trucks stakeholders need to demonstrate their cost effectiveness against conventional Diesel Trucks. Beyond the economies of scale of all relevant components that are employed in a Fuel Cell Electric Heavy Duty Truck, the durability of the Fuel Cell System and notably that of the Fuel Cell Stack plays an important role in the determination of a competitive cost of ownership. A key factor for durability improvement is the understanding of the degradation mechanisms and their mitigation. Degradation, however, can be very application specific, that is, different degradation mechanisms may be prevalent in heavy duty truck applications compared to passenger cars or stationary use. This is well known to research and industry. The European research project IMMORTAL is exactly aiming at exploring these mechanisms and their mitigation specifically for heavy duty truck application and developing and MEA that meets heavy duty requirements. Within this context, FPT Industrial, a brand of the Iveco Group, assists in defining the specif... Read More

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Recent years have seen a rise in interest in polymer electrolyte membrane fuel cells (PEMFCs) because of its high power density, high energy efficiency, and zero-emission characteristics. PEMFC-powered fuel cell electric vehicles (FCEVs) have the potential to significantly lower the transportation sector's carbon dioxide emissions, paving the way for the global adoption of the hydrogen economy. However, the durability and robustness of fuel cell systems must be increased before a wider commercialization of FCEVs is possible. The hydrogen starvation in anode, occurring during start-up/shutdown or cold start, can cause rapid and significant deterioration of the performance and durability of a PEMFC system through cell reversal. In hydrogen-starved conditions, the cell's performance can deteriorate in just a few minutes, leading to sudden cell failure. Prior studies have been conducted to understand the degradation caused by hydrogen starvation and cell reversal in PEMFCs, with the aim of identifying mitigation solutions that could minimize deterioration of membrane electrode assembly (... Read More

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Professor Anil Virkar has been a pioneer in the development and characterization of high-performance anode-supported solid oxide fuel cells, and in understanding degradation processes in such cells operated in electrolysis mode. This talk reviews methods for improving anode-supported cells, particularly for yielding high performance at reduced operating temperature. The understanding of degradation mechanisms occurring during solid oxide electrolysis cell operation will be discussed.

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This study deals with Polymer Electrolyte Fuel Cells (PEFC), which are used in automobiles and household fuel cells. Currently, there are two main challenges for the practical application of PEFCs: durability and cost reduction. The target value for durability is required to be 40,000 hours or more. However, the current durability is about 10,000 hours. Therefore, there is an urgent need to investigate the causes of deterioration and to take countermeasures. One of the causes of degradation is chemical degradation of the polymer electrolyte membrane. When the byproduct hydrogen peroxide encounters impurities such as iron ions, hydroxyl radicals are generated, which attack and degrade the polymer electrolyte membrane. To prevent this degradation, a substance that inactivates hydroxy radicals (radical scavengers) has been featured. Radical scavengers have been added to the polymer electrolyte membranes to prevent this degradation and are now being used in practical applications. One of the most useful radical scavengers is Ce ion. However, it has been observed experimentally that Ce io... Read More

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Fuel Cells’ scalability and energy density make them excellent candidates for different applications, especially difficult to electrify applications. Their design flexibility can also be applied to low power, long-life applications. LANL has constructed a unique design to provide continuous, low power (&lt; 100 µW) for very long duration (multiple decades). This LANL system operates passively, without active control of cell parameters, such as temperature and humidity. In addition, the system does not require interventions like refueling or maintenance during its operational lifetime. While the application and operational conditions of the systems mentioned here differ greatly from those of light and heavy-duty vehicles (e.g. ambient temperature operation, passive water management, low current densities), many of the modes of degradation are similar, and listed below: Membrane thinning Degraded performance due to loss of electrochemical surface area (ECSA) Loss of water management due to changes in hydrophobicity Increased cell resistance due to corrosion of cell components To better... Read More

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Predicting degradation of polymer electrolyte membrane fuel cells (PEMFCs) is an important issue from the viewpoint of durability and cost. In fact, in technical roadmaps regarding fuel cell of each country, high targets of durability and performance are set for transport applications especially for heavy duty vehicles. One of important degradation process takes place in catalyst layer. PEMFC catalysts are typically platinum or platinum alloys and consist of nanoparticles to increase the electrochemically active surface area (ECSA). However, these particles are not stable in dynamic operating conditions of the transport applications. A typical degradation mechanism of the catalyst is the electrochemical Ostwald ripening mechanism, and it is known that the platinum particle size distribution shifts to larger particle diameter, resulting in lower ECSA and lower performance. Therefore, predicting platinum catalyst degradation is important to enhance durability of the products. Various numerical models for catalyst degradation of PEMFC have been proposed and used to explore degradation m... Read More

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PEMFCs, or Polymer Electrolyte Membrane Fuel Cells, can be used in both stationary power and transportation applications and are promising for use in heavy duty electric vehicles due to their high energy density, ability to be refueled quickly, and extended range, which are key challenges for battery-powered vehicles [1]. Despite these advantages, there are still obstacles preventing the widespread commercialization of PEMFCs, one of which is production cost [2]. To reduce manufacturing costs, it is imperative to ensure that quality control rejects and scraps are minimized. Moreover, enhancing component integration defect detection would ensure the durability of the fuel cell and enhance its operational lifetime. However, robust quality control requires a thorough understanding of potential non-uniformities and their effects on fuel cell performance and operational degradation. Non-uniformities of the membrane electrolyte assembly (MEA) can result in durability issues by damaging the membrane and making it more vulnerable to mechanical and chemical stress during the operation [3]. Se... Read More

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Proton exchange membrane fuel cells (PEMFCs) have been proven to be a promising candidate to replace combustion engines due to their zero-carbon emission and high power densities. Despite the recent success in PEMFC commercialization, a number of challenges such as high cost and difficulty in lifetime estimation still hinder their further development. PEMFC durability tests require a long time to complete; therefore, durability predicting models are increasingly important as a supporting tool for further development and implementation. Fuel cell membranes undergo a variety of dynamic conditions during regular operation such as varying temperature, humidity, current density, and cell potential. The cyclic variations of humidity and temperature (hygrothermal variations) during dynamic operation lead to swelling and contraction of the membrane. The fluctuating stress caused by the continuous expansion and contraction of the membrane when confined within the cell leads to mechanical membrane degradation. The recurring swelling and contraction of the membrane which stem from water content... Read More

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