Degradation Of Proton Exchange Membrane Research Articles

Research Progress of Proton Exchange Membrane Failure and Mitigation Strategies.

Proton exchange membrane (PEM) is critical for the efficient, reliable and safe operation of proton exchange membrane fuel cells (PEMFC). The lifetime of PEM is the main factor restricting the commercialization of PEMFC. The complexity of operating conditions, such as open-circuit/idling, dynamic load and startup-shutdown under automotive conditions, on PEMFC will cause the mechanical and chemical degradation of PEM and affect the service life of PEMFC. In order to understand the degradation behavior and durability of PEM, this paper presents an overview of the degradation failure mechanism and mitigation strategies of PEM. The mechanical and chemical degradation behavior of PEM and its causes, as well as the mitigation strategies are discussed in order to give a direction for PEM design and fuel cell system control strategy. It is proposed as a primary principle in order to further develop and promote the durability of PEM, to focus on the material improvement and system engineering.

A novel work-flow to study Ir electrode thinning and dissolution in proton exchange membrane water electrolyzers

In this work, a new workflow to analyze the structural degradation of proton exchange membrane (PEM) water electrolysis catalyst coated membrane (CCM) was developed, utilizing a unique cryo-microtomy sample preparation method, transmission electron microscopy (TEM) imaging, and a semi-automatic image analytics approach. This workflow is used to demonstrate how an iridium based Ir-NanoStructured Thin Film (Ir-NSTF) oxygen evolution reaction (OER) catalyst/electrode degrades over time at various applied currents and show that iridium interpenetrates into the perfluorosulfonic acid (PFSA) PEM, suggestive of degradation mechanism involving iridium dissolution. The utilization of this workflow in future degradation and lifetime measurements is discussed in detail.

Physical Model of Catalyst Dissolution, Platinum Band Formation, Hydrogen Peroxide Production and Chemical Degradation of Proton Exchange Membrane in Low Temperature Fuel Cells

Low temperature fuel cells with perfluorinated proton exchange membrane (LT-PEMFC) are recognized as one of the most promising technologies for clean electricity production in automotive sector. Despite significant progress in their efficiency and reliability, the degradation of fuel cells still remains an important issue, significantly hindering their wider market adoption. Degradation processes can to some extent be avoided by the use of new, more durable materials and components, but also by properly managing the fuel cell operation and thus avoiding the conditions in which the fuel cell degradation is most pronounced. Fast and reliable computational models of fuel cell operation and degradation are crucial for efficient development of such mitigation strategies.The catalyst layer and the membrane are the components recognized as being most susceptible to degradation phenomena. In the catalyst layer, high temperature, electric potential and relative humidity lead to electrochemical corrosion of carbon support and dissolution of the catalyst, most commonly being platinum or platinum-based binary alloy. Dissolved platinum, diffusing into the membrane, plays an important role in its chemical and consequent mechanical degradation. The platinum particles in the membrane serve as the catalyst for hydrogen peroxide formation from crossover fluxes of hydrogen and oxygen, while the presence of transition metal ions, such as copper or cobalt, originating from the binary catalyst dissolution, initiate the decay of hydrogen peroxide into various radical species via Fenton-like reactions [1]. The radical’s attack on the perfluorinated chains and sulphonic groups leads to a reduction of membrane conductivity, thinning of the membrane and consequent increase in its susceptibility to mechanical degradation, caused by the swelling and shrinking of the membrane due to the changes in its humidity, which can result in formation of cracks and pinholes in the membrane.To properly model the entire causal chain of chemical membrane degradation, several individual processes mentioned above need to be coupled into a unified model. To achieve this, we present a physically based spatially and temporally resolved model of fuel cell operation, providing the detailed picture of species concentration and electric potential distribution in the fuel cell [2], coupled with innovative model of hydrogen peroxide formation, diffusion and decay into reactive radicals, causing the chemical degradation of the membrane. The model describes the electrochemical dissolution of binary alloy catalyst, its diffusion into the membrane and the formation of so-called Pt band. The hydrogen peroxide production is modeled by including both its formation in the catalyst layers and inside the Pt band by consistently taking into account the cross-over fluxes of reactants and local electric potential across the membrane [3]. The rate of radical formation (.H, .OH, .OOH) via Fenton-like reactions is modeled by considering the concentration of transition metal ions, originating from electrochemical dissolution of binary alloy catalyst and their diffusion into the membrane. The chemical degradation due to reactive radical’s attack on the membrane is described by recently developed 0-D reactor approach [4].The output of the model is a detailed spatially and temporally resolved profile of chemical groups concentration in the membrane, which enables the calculation of changes in both membrane thickness and proton conductivity. The results, indicating most pronounced membrane degradation in vicinity of Pt band, are compatible with the Raman measurements of chemical group concentrations in the aged membrane [5]. Furthermore, the testing of the model on long-term degradation experiments is used to identify the optimal fuel cell operating conditions in which the durability of the fuel cell membrane is maximized.[1] Strlič M, Kolar J, Šelih VS, Kočar D, Pihlar B. A comparative study of several transition metals in fenton-like reaction systems at circum-neutral pH, Acta Chim Slov 2003;50:619–32.[2] Tavčar G, Katrašnik T. A Real Time Capable Quasi 3D System Level Model of PEM Fuel Cells, Fuel Cells 2020;20:17–32.[3] Burlatsky SF, Gummalla M, Atrazhev V V., Dmitriev D V., Kuzminyh NY, Erikhman NS. The Dynamics of Platinum Precipitation in an Ion Exchange Membrane, J Electrochem Soc 2011;158:B322.[4] Frühwirt P, Kregar A, Törring JT, Katrašnik T, Gescheidt G. Holistic approach to chemical degradation of Nafion membranes in fuel cells: modelling and predictions, Phys Chem Chem Phys 2020;22:5647–66.[5] Ohma A, Yamamoto S, Shinohara K. Membrane degradation mechanism during open-circuit voltage hold test. J Power Sources 2008;182:39–47. Figure 1

Deep learning based prognostic framework towards proton exchange membrane fuel cell for automotive application

Currently, the larger-scaled commercialization of fuel cell technology is considerably impeded by the limited durability of fuel cells. Prognostics and health management (PHM) is one of the most widely researched technologies used to improve the durability of fuel cell devices. More recently, the combination of deep neural network approaches and PHM techniques shows a broad research prospect. Attention mechanisms can enhance their data processing ability, which helps to extract useful features more efficiently. Herein, we propose an attention-based Recurrent neural network (RNN) model to improve the prognostics of PHM, which enables a more accurate prediction of the output voltage degradation of proton exchange membrane fuel cell (PEMFC) based on the original long-term dynamic loading cycle durability test data. In particular, the prediction results with different prediction models, namely, long short-term memory (LSTM), gated recurrent unit (GRU), attention-based LSTM, and attention-based GRU are obtained and compared. For dynamic test data (dataset 1), the root mean square error results for the attention-based LSTM and GRU models are 0.016409 and 0.015518, respectively, whereas for the LSTM and GRU model the corresponding error results are 0.017637 and 0.018206, respectively. The same effects are demonstrated and proved for the pseudo–steady dataset (dataset 2). The attention-based RNN model achieves a high prediction accuracy, proving that it can help improve the prediction accuracy and may further help the implementation of PHM in the fuel cell system.

Alleviating the performance degradation of fuel cells caused by the uneven distribution of internal physical fields

The performance degradation of proton exchange membrane (PEM) fuel cells is inevitable in real-time application. In particular, water management issues are related to the optimization design and the stable operation of the fuel cell system. The investigation of the mass transportation of an open-cathode PEM fuel cell based on a three-dimensional numerical model is emulated using computational fluid mechanics (CFD). The unified finite element analysis for the coupled phenomena of the charge transport, mass transport, and electrochemical reactions is discussed in this work. The simulation results are observed and compared with other experimental observations and various physical fields have shown uneven distributed inside of the fuel cell due to the single-direction gases transfer strategy. Therefore, in this study, a strategy based on interchangeable anode inlet and outlet is proposed to alleviate the uneven distribution of internal physical fields. Moreover, the optimized periods of inlet and outlet exchange are studied by comparing the experimental results.

Mechanical degradation of proton exchange membrane during assembly and running processes in proton exchange membrane fuel cells with metallic bipolar plates

Mechanical degradation of proton exchange membrane during assembly and running processes in proton exchange membrane fuel cells with metallic bipolar plates

Proton Exchange Membrane Fuel Cell Prognostics Using Genetic Algorithm and Extreme Learning Machine

AbstractThe prognostics can predict the degradation of proton exchange membrane fuel cell (PEMFC) to formulate a reasonable maintenance plan for improving its lifetime and performance. In this paper, the voltage degradation for PEMFC at different conditions is predicted, by using a novel prognostics method based on genetic algorithm (GA) and extreme learning machine (ELM). The novel prognostics method considers the effects of the PEMFC load current, relative humidity, hydrogen pressure, and temperature on the degradation for PEMFC. Firstly, the voltage degradation prediction model for PEMFC is built by the ELM. Then, the GA is adopted to determine the optimal parameter of the proposed degradation prediction model. Finally, the voltage degradation prediction of the proposed prognostics method is validated, using data derived from the PEMFC in actual postal fuel cell electric vehicle (PFCEV) at real conditions and PEMFC at dynamic load current. The experimental results show that the proposed prognostics method can obtain good voltage degradation prediction for PEMFC in PFCEV at real conditions. The proposed method achieves better voltage degradation prediction for PEMFC at dynamic load current than other traditional data‐based prognostics methods.

Investigation of three system shut-down strategies alongside optimization suggestion for proton exchange membrane fuel cells via in-situ measurements

ABSTRACTCarbon corrosion caused by H2/O2 interface during the shut-down process is one of the factors that exacerbate the overall degradation of proton exchange membrane fuel cells (PEMFC) in automotive applications. Numerous studies have shown that system strategies are beneficial for reducing the duration of H2/O2 interface and alleviating performance degradation. In this paper, three different shut-down strategies are investigated and compared based on the internal behaviors acquired by in-situ measurements. For the three shut-down strategies, reverse current and high potential are mainly observed in a lower constant current and constant power strategy. Comparatively speaking, the internal uniformity of the cell under constant current and power load is better than that with constant voltage strategy when the shut-down time is about the same. The results suggest that adopting a higher constant power load followed by a larger voltage load during the shut-down process can effectively shorten the shut-down time and relieve carbon corrosion. These results add significant new insights into the shut-down process and will be of practical importance in directing design of combined shut-down strategy that can withstand carbon corrosion.

Study of relative humidity on durability of the reversal tolerant proton exchange membrane fuel cell anode using a segmented cell

Cell voltage reversal resulted from hydrogen starvation at the anode is one of the factors that exacerbate the overall degradation of proton exchange membrane fuel cells (PEMFCs). An effective mitigation strategy is to involve oxygen evolution reaction (OER) catalysts into the anode to facilitate water electrolysis against carbon corrosion. As such, this paper aims to study the influence of relative humidity (RH) on the performance and durability of reversal-tolerant-anodes (RTAs) during hydrogen starvation. An advanced segmented technique is employed to examine the coupling reactions by simultaneously measuring current density, RH and temperature in a fuel cell with a large active area. It is found that the inlet of RTAs undergoes degradation earlier than the outlet and the membrane electrode assembly (MEA) with a RTA has an optimal humidity during cell reversal. Results also show that the failure of the RTA MEA is due to a loss of electron conduction medium rather than the deactivation of the OER catalyst. In addition, this work highlights the importance of plate flow field design and the OER catalyst gradient design of the RTA MEA.

A multi-scale hybrid degradation index for proton exchange membrane fuel cells

An accurate degradation index can help users understand the aging state of proton exchange membrane fuel cells and take appropriate maintenance measures to improve durability. The degradation of membranes and electrodes is one of the most important causes leading to the performance degradation of proton exchange membrane fuel cells. This paper proposes a multi-scale hybrid degradation index that combines the degradation of membranes and electrodes to estimate the aging state of proton exchange membrane fuel cells. Firstly, different degradation models are utilized to estimate the degradation indexes such as average radius of Pt particles, electrochemical surface area, and membrane thickness. A multi-sale hybrid degradation index is then designed to fuse all the previous indexes based on the quantified effects of electrode and membrane degradation. Finally, based on the automatic machine learning algorithm and the aging experimental data of proton exchange membrane fuel cells, the proposed hybrid degradation index is verified. Experimental results show that the proposed hybrid degradation index can accurately predict the future aging states and the remaining useful life of proton exchange membrane fuel cells.

Mechanical degradation of proton exchange membrane along the MEA frame in proton exchange membrane fuel cells

Mechanical degradation, caused by local stress concentration and variation, significantly affects the lifetime of proton exchange membrane fuel cells. This study constitutes the first numerical investigation of stress evolution in the membrane between the frame of the membrane exchange assembly (MEA) and gas diffusion layer (GDL) throughout the processes of assembly, operation and gas filling in fuel cells. A finite element model is outlined to determine mechanical deformation of the membrane by exerting assembly displacement, hygrothermal conditions and gas pressure in turn. It is observed that severe stress concentration and bending deformations occur in the joint-area membrane. The results show that a plastic deformation occurs after the temperature and water content are increased, and would be substantially enhanced by the gas pressure difference between the anode and cathode. The in-plane stress may throw some light on the rapid degradation of the membrane between the frame and GDL. The gas pressure difference, which exceeds 10 kPa, leads to a rapid increase in the in-plane stress and plastic deformation. Decreasing the joint width may not be a good approach for reducing the stress/strain concentration. It is suggested that additional gasket seals or adhesive protection layers are helpful in joining frame and GDL.

Degradation of Proton Exchange Membrane (PEM) Electrolysis: The Influence of Current Density

Hydrogen is expected to play an important role as a crosslinking technology between power generation, transport and industry. It can substitute fossil fuels when generated by water electrolysis using electricity from renewables energies such as solar or wind. Proton exchange membrane electrolysis (PEMEL) technology is very suitable for this purpose due to its flexibility low footprint and wide range of operation. However, questions about degradation mechanisms during overload (high current densities) remain. This work presents a preliminary study on the short-term degradation effects of operating laboratory PEMEL cells at current densities up to 4.5 A cm-2. The resulting high cell voltages (up to 3.75 V) produce an increase of cell Ohmic resistance of about 10 mΩ cm-2. This degradation effect is irreversible and can be associated to the formation of poorly conductive oxides at the interface between the titanium current collector and anode catalyst layer.

Degradation of Proton Exchange Membrane (PEM) Electrolysis: The Influence of Current Density

Hydrogen is expected to play an important role as a crosslinking technology between power generation on one hand and transport and industry on the other hand. It can directly replace fossil fuels in transport and industry when produced by water electrolysis renewable energies such as solar or wind, which are converted with low efficiencies. The relevant technologies are either the mature alkaline electrolysis or the newer proton exchange membrane (PEM) water electrolysis. The main advantage of PEM electrolysis technology is that it provides high efficiency, high power density with low footprint, and flexibility without the need of corrosive chemicals such as KOH (alkaline electrolysis). On the other hand, questions about degradation mechanisms, long-term stability and the high capital costs compared to the alkaline technology hinder the large-scale industrial penetration of this technology in the market. Moreover, these challenges are mutually dependent. Cost reductions of materials and stack components, for example, can have a negative impact on long-term stability. Thus, more information about the degradation mechanisms is necessary to determine an optimum between cost reduction and long-term stability. Furthermore, degradation measurements are expensive and evidently require a lot of time. Consequently, the development of accelerated stress tests (AST) protocols is in the focus of the current research by the academy and industry in particular. This presentation will discuss degradation processes of MEAs under high current density which has been found to accelerate degradation in our laboratory. Degradation was investigated in a HYLYZER™ Hydrogen Generator (HHG) from Hydrogenics under operation at 4 A cm-2 for almost 3000 h. The degradation of the bipolar plates and gas diffusion layers are neglected since these components are well protected against corrosion. The cells were analyzed by electrochemical impedance spectroscopy. Furthermore samples of ion exchange resin, which keeps the water resistivity above 10 MΩ, were collected and analyzed by XPS to quantify the accumulated ions. In addition, post-test investigations of the aged MEAs by conductive and material sensitive AFM, SEM with EDX and XPS were performed to identify degradation mechanisms. An important observation is a decrease of the ohmic resistance during operation at high current densities which is associated to fluoride release into the water. To analyze the time dependence of the cells in the hydrogen generator system a zero-dimensional system model with effective parameters was developed. This model enables quantifying the degradation measurements and the discussion in the context of system behavior. Preventing metal oxidation by corrosion protective layers leads to increased efficiency mainly due to decreasing ohmic resistances. This decrease is assumed to be depending on current density and time. The observed F release rate supports this conclusion. The degradation mechanism is assumed to be an increased permeability for water, oxygen and hydrogen with corresponds to a membrane thinning and ionomer loss in the electrodes. Such an interpretation was backed by the ex-situ post-test analysis. At the anodes a general increase of conductive area fraction evaluated by AFM indicates a loss of ionomer. At the cathodes, a general decrease of conductive area fraction indicates a loss of catalysts. EDX confirmed the loss of Pt and Ir from cathode and anode respectively, and in addition a loss of Ti from the anode was found. Membrane thinning occurred in all cells. It is explained by ionomer decomposition catalyzed by the well distributed Pt content in the membranes detected by XPS. Acknowledgements The research leading to these results has received funding from the European Union’s Seventh Framework Program (FP7/ 2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant n° 621237, “ INSIDE- In -situ Diagnostics in Water Electrolyzers“ and from national projects “LastElSys” and “WESpe” by Federal Ministry for Economic Affairs and Energy. Figure 1

Degradation behavior of a proton exchange membrane fuel cell stack under dynamic cycles between idling and rated condition

The durability of proton exchange membrane (PEM) fuel cells is a key factor which prevents its commercial application on the vehicle. Dynamic current cycle is one of the most common conditions for PEM fuel cells, especially varying the currents between the idling and the rated condition. To investigate the degradation behavior of fuel cells under this kind of dynamic cycles, a PEM fuel cell stack with 330 cm2 active area is operated under 10,000 dynamic cycles with the cycling current density ranging from 25 mAcm−2 to 600 mAcm−2, which simulates common operating conditions in a vehicle cycle from the idling condition to the rated condition. Polarization curves, the high-frequency resistance (HFR), the uniformity of the individual cells, the performance degradation of PEM fuel cell stack at 25 mAcm−2 and 600 mAcm−2 are characterized to investigate the performance degradation over cycling. In addition, scanning electron microscopy (SEM) of the surface and the cross-section of the tested membrane electrode assemblies (MEAs) are compared with different single-cell samples. The results indicate that the degradation rate of the stack is 1.0 μVcycle−1 at 25 mAcm−2 under the idling condition. A more severe performance degradation of about 2.0 μVcycle−1 is detected at 600 mAcm−2 under the rated condition. The individual cell near the coolant outlet of the PEM fuel cell stack shows a more serious degradation caused by the HFR increase, which is also proved by the SEM analysis. The cross-section SEM analysis indicates that the dynamic cycle has a significantly negative effect on the catalyst layer, resulted in an obvious decrease on the thickness of the catalyst layer.

Performance Degradation of PEMFC by Sea Salt Aerosol Contamination

In this study, performance degradation of proton exchange membrane fuel cells (PEMFCs) by 1 μm scale sea salt aerosol was investigated. The regulations of NOx emission control on ships are strengthened year by year. Installation of PEMFCs as electrical power source is one of important choice. In order to investigate the influence of seawater contamination, several studies focus on the effects of sodium chloride (NaCl) [1, 2]. The fuel cell performance degradation by NaCl was investigated by injecting NaCl solution into the cathode side gas inlet, however, fuel cell has a filter and there is no such a situation. On the other hand, conventional filter cannot remove extreme small sea salt particles (1 μm scale sea salt aerosol). Effects of the invaded sea salt aerosol for the fuel cell performance were not elucidated. In this study, artificial sea salt aerosol generator was developed and the effects of sea salt aerosol contamination in the cathode side were investigated. Figure 1 shows experimental setup. Sea salt aerosol generator was consisted by ultrasonic vibrator, NaCl solution tank, and heated pipe. Ultrasonic vibration generates fine droplets of NaCl solution. Water evaporates from the droplet while flowing through the heated pipe and finally, fine NaCl crystals remain in the gas as aerosol. The diameter of sea salt aerosol can be controlled by varying concentration of NaCl solution. Figure 2 shows SEM image of collected sea salt aerosols at the end of cathode gas supply line. With using 3 mol/L NaCl solution, approximately 1 μm scale sea salt particles were stably produced. The cell has an active area of 4 cm2 (2 × 2 cm) with serpentine channels. The channel width and depth were 1.0 and 1.0 mm, respectively, and the rib-to-channel ratio was 1. Fuel cell temperature and relative humidity of anode/cathode gas were set 60°C and 70%, relatively. Flow rate of sea salt aerosol was 1.2 mg/h. Fuel cell was operated with constant current density condition (0.5 A/cm2). Figure 3 shows time variation of cell voltage. When the sea salt aerosol injection was started, the cell voltage clearly dropped, and it suggested cell performance degradation. The cell was disassembled after completing the power generation test. NaCl deposition was not observed in the channel. On the other hand, it was found that NaCl particles existed in the GDL by polarizing microscope imaging. A large number of NaCl particles were present under the channel, whereas almost no particles presented under the rib. The NaCl particles not only adhered to the channel side of the GDL but also invaded into the region close to the catalyst layer and the particle diameter has increased compare to initial one (Figure 4). Similar distribution was observed from inlet to outlet in the serpentine channels. However, NaCl particles did not block the pore in the GDL, and there were still enough gas flow path. Figure 5 shows result of cyclic voltammetry (CV) measurement. Comparing the effective surface area of the platinum catalyst before and after adding the sea salt aerosol, decrease of 22.6% has been occurred. It is considered that poisoning of platinum catalyst was caused by adsorption of chloride ion (Cl-) [1]. These results suggest that 1 μm scale fine sea salt aerosol reaches catalyst layer in the cathode with passing the GDL easily, and finally, cell performance degradation will be caused. Present experiment has been performed under accelerated condition, investigation of degradation process with different flow rate of sea salt aerosol is future task. Investigation of performance recovery by generated liquid water is also important issues. There is a possibility that high humidity cell operation prevent the poisoning.

(Invited) Durability Evaluation of PEM Fuel Cells for Automotive Application

Proton exchange membrane fuel cells (PEMFC) technology is already in commercialization phase for automotive applications. However, the biggest challenges for its successful mass commercialization are cost and durability. Current PEMFC technology can meet the lifetime targets but the cost to achieve it can be very high due to material’s cost and system level mitigation complexities. Understanding of the membrane electrode assemblies (MEA) degradations using relevant durability accelerated tests at early stages of development is essential. PEMFCs for automotive applications goes through thousands of cycles during normal operation of the vehicle over the expected life span of 10 years. These cycles include a combination of load or voltage cycles, start and stop cycles, humidity cycles and temperature cycles. Study have shown that start-stop cycling accounts for 44% of operation mode while load cycling and idling for 28% each (1). Under these cycles, fuel cells suffer from severe degradations of its main components; cathode, anode, membrane and bipolar plates. The PEMFC cathode can degrade during start-stop operation via carbon corrosion (2). Cathode degradation can be mitigated by using stable materials or by applying system mitigations. System mitigation by a voltage limiting control (VLC) can be one of the effective measures (3). The VLC can, however, lead to voltage spikes (high positive potentials) at the anode during fuel cell start-up and shut-down. Moreover, during fuel (H2) starvation conditions, the potential at the anode can give rise to high positive potentials leading to anode catalyst layer degradation. During idling operation mode, PEMFC is at or near open circuit conditions which is known to accelerate proton exchange membrane (PEM) decomposition especially under low humidification (4). Peroxy-radicals originating from hydrogen peroxide produced at the anode catalyst surface cause the PEM degradation (5). Pt band formation in the membrane is also known to promote peroxide formation leading to membrane decomposition (6-7). Several accelerated protocols are currently being used to evaluate the durability of PEMFC. At Nissan, our durability protocols are focused on understanding the material degradation under relevant automotive cycles and correlating single cell durability to the stack level. Start-stop accelerated protocol to evaluate the cathode support durability consist of potential cycling from 1.0 V to 1.5 V using triangular waveform for 1000 cycles with diagnostics conducted intermittently after certain number of cycles. Cathode catalyst durability is evaluated using load cycling accelerated protocol wherein the potential is cycled between 0.6 V to 0.95 V to simulate peak load and OCV/idle using a square wave profile with 3 second hold at each potential. The upper potential is known to have significant impact on catalyst degradation (8). Load cycling is performed for 10,000 cycles with diagnostics conducted intermittently. Anode degradation under cell reversal condition is evaluated using a protocol designed to simulate high voltage spikes at the anode. Cell reversal cycling is performed by applying a load of 0.2 A/cm2 for 1 sec while flowing N2 at the anode and air at the cathode while measuring the cell voltage under the applied load for a total of 200 cycles. Membrane durability is evaluated using humidity cycling (mechanical durability) and potential hold at open circuit (chemical durability). Membrane’s chemical durability is evaluated at 90 °C and 30% RH under hydrogen and oxygen by operating MEA at open circuit. The target of OCV hold test is 500 hrs while maintaining potential above 0.8 V. Mechanical durability of membrane is evaluated by cycling RH to simulate dry condition (0%) and wet condition (100%) for target of 20,000 cycles. All these accelerated tests are performed at ambient pressure and summarized in the Table 1 below. Acknowledgments: The author would like to gratefully acknowledge Nissan Technical Center North America Fuel Cell Research team members (Dr. Amod Kumar, Dr. Ramesh Yadav and Dr. Cenk Gumeci) and Nissan Motor Co. Ltd Japan Fuel Cell research team members (Dr. Atsushi Ohma, Dr. Yoshihisa Furuya) for technical discussions and data.

Degradation prediction of PEM fuel cell using a moving window based hybrid prognostic approach

In this paper, an innovative robust prediction algorithm for performance degradation of proton exchange membrane fuel cell (PEMFC) is proposed based on a combination of model-based and data-driven prognostic method. A novel approach using the moving window method is applied, in order to 1) train the developed models; 2) update the weight factors of each method and 3) further fuse the predicted results iteratively. In the proposed approach, both model-based and data-driven methods are simultaneously used to achieve a better accuracy. During the prediction process, each dataset in the proposed moving window are divided into three sections respectively: training, evaluation and prediction. The training data are used first to identify the models parameters. The evaluation data are then used to measure the weight of each method, which represents the degree of confidence of each method in the actual state. Based on these dynamically adjusting weight factors, the prediction results from different methods are then fused using weighted average methodology to calculate the final prediction results. In order to verify the proposed method, three experimental validations with different aging testing profiles have been performed. The results demonstrate that the proposed hybrid prognostic approach can achieve a higher accuracy than conventional prediction methods. In addition, in order to find the satisfactory trade-off between the prediction accuracy and forecast time for optimizing on-line prognostic, the performance variation of proposed approach with different moving window length is further showed and discussed.

Causal and Fault Trees Analysis of Proton Exchange Membrane Fuel Cell Degradation

This paper presents a reliability approach to analyze the degradation of proton exchange membrane fuel cell. This approach is based on the dependability analysis tools such as the causal and fault trees to establish an analysis of the internal state of the fuel cell energy conversion performance and evaluate its lifetime. The elaboration of causal tree offers powerful tools to a deductive analysis, which consists on seeking the various combinations of events leading to the fuel cell degradation. The parameters of fuel cell model are identified in order to found the degree of degradation. The experimental determination of the variation interval of the parameters is done according to each of degradation modes. A diagnostic method is proposed in order to identify the depth of each aging process of the fuel cell. The diagnosis is done by comparing the experimental output characteristic at beginning of life of the fuel cell with the used fuel cell to qualify and quantify the depth of degradation.

Pulse radiolysis investigation of · OH and · H radicals initiated degradation reaction of sulfonated aromatics as model compounds for proton exchange membrane

In order to predict ·OH and ·H radicals initiated degradation of proton exchange membrane (PEM) based on polymers obtained by radiation-induced grafting of styrene or α-methylstyrene on different polyolefin, isopropyl benzene sulfonic acid (IPBS) and tert-butyl benzene sulfonic acid (TBBS) were taken as model compounds for PEM with and without α-H, respectively. Results indicated that ·OH radicals played a vital role in PEM degradation. Eighty-nine percent of ·OH radicals reacted with IPBS to form benzylic radicals by electron transfer and subsequent deprotonation reactions. Benzylic radicals can react with O2 to form peroxyl radicals, which leads to PEM degradation. TBBS, without α-H, reacted with ·OH or ·H radicals, benzylic radicals would not be generated, and only adducts were formed. Adducts have less influence on the stability of TBBS than benzylic radicals. In this work, we elucidated that PEM, without α-H, with similar structures to TBBS, had a stronger resistance to oxidative degradation than PEM with α-H, with similar structures to IPBS.

A Mechanistic Study of Perfluorosulfonic Acid Membrane Water Permeance Degradation in Air

Chemical degradation of perfluorosulfonic acid (PFSA) membranes of proton exchange membrane (PEM) fuel cells is a well-known process which can limit PEM fuel cell lifetimes (1, 2). Chemical degradation can weaken membranes to the point where they no longer provide an effective barrier to reactant gas permeation or electrical shorting. PEM chemical degradation is the result of a complex interplay between mechanical and chemical degradation processes, both of which are strong functions of operating conditions. In particular, hot and dry operating conditions induce high rates of chemical degradation whereas relative humidity cycling between wet and dry states challenges the mechanical integrity of the membranes. Because chemical degradation of PEMs is accelerated under low humidity operating conditions, membrane lifetimes are significantly enhanced by providing humidified inlet gas streams to the fuel cell stack. In addition, fuel cell performance is improved with the use of humidified input streams. An efficient method of humidifying the cathode inlet stream employs a passive water vapor transfer (WVT) device that delivers water vapor from the wet cathode exhaust to the cathode inlet stream (Figure 1). The key component of a WVT device is a highly water permeable, but gas impermeable membrane. Not surprisingly, ionomeric membranes such as PFSAs function as excellent WVT materials. Ideally, WVT membrane materials will maintain adequate durability and performance characteristics to provide necessary stack humidification throughout the target operational life of an automotive fuel cell system (>10years />8000 operational hours). Several general pathways known to reduce water permeance values include cation contamination, mechanical degradation and chemical degradation. We have observed during in-situ and ex-situ testing of WVT materials in air that the water permeance values of PFSA-based WVT membranes can degrade by 75% over time. This degradation of water permeance is associated with a physical and chemical change of the membrane. The extent of ionomer transformation is readily monitored using transmission FTIR spectroscopy by the appearance of new absorption bands centered at 3200 and 1434 cm-1 and also by the decreases in water stretching and bending bands centered near 2800 and 1700 cm-1, respectively (Figure 2). In addition to water permeance, other membrane properties including proton conductivity and ion exchange capacity decrease as a function of this degradation reaction. The fully reversible, deuterium exchanged FTIR spectrum proves that the degradation product is not the cross-linked sulfonic acid anhydride as previously suggested (3). Through an extensive series of kinetic studies and analytical characterization, we have determined that the membrane degradation product results from a reaction between the ionomer and a trace atmospheric gas. We will demonstrate that the definitive structural assignment is fully consistent with all known properties and behaviors of the degraded membrane. The revelation of the PFSA degradation product and its formation mechanism will aid in development of highly durable fuel cell systems. References R. Borup, J. Meyers, B. Pivovar, Y. Kim, R. Mukundan, N. Garland, D. Meyers, M. Wilson, F. Garzon, D. Wood, P. Zelenay, K. More, K. Stroh, T. Zawodzinski, J. Boncella, J. McGrath, M. Inaba, K. Miyatake, M. Hori, K. Ota, Z. Ogumi, S. Miyata, A. Nishikata, Z. Siroma, Y. Uchimoto, K Yasuda, K. Kimijima, N. Iwashita, Chem. Rev. 107, 3904, (2007)C. S. Gittleman, F. D. Coms, Y-H. Lai, Membrane Durability: Physical and Chemical Degradation, in Polymer Electrolyte Fuel Cell Degradation, pp 15-88, M. M. Mench, E. C. Kumbur, T. N. Veziroglu, eds, Academic Press, 2012F. M. Collette, C. Lorentz, G. Gebel, F. Thominette, J. Mem. Sci. 330, 21-29, (2009) Figure 1