Polymer Electrolyte Fuel Cell Components Research Articles

Performance enhancement in polymer electrolyte membrane fuel cell with flow traps and field gradients: A Numerical Study

Efficient reactant distribution and water removal are critical during polymer electrolyte fuel cell (PEFC) operation. The bipolar plate and its corresponding flow field design are vital among the PEFC components for enhancing reactant transport and water removal. The issues arising in the PEFC during the high current operation, such as reactant starvation and water removal, can be alleviated by improving the flow channel geometry. In this study, we analyze the variation in overall PEFC performance and corresponding reactant transport phenomenon for two independent design cases. The converging gradient design without channel traps at 0.4 V operating voltage exhibited a current density increment of 6.85% against the conventional design. Moreover, at 0.4 V, including channel traps enhanced the current density, as we observed a current density increment of 7.1% for the converging design with channel traps against the conventional design without channel traps. Likewise, at 0.4 V, the diverging design with channel traps exhibited a current density increment of 5.85% against the diverging design with no channel traps. Further, enhanced reactant distribution is observed in the catalyst layer upon introducing channel traps in the flow field design.

Water in Polymer Electrolyte Fuel Cells (PEFCs): Friend or Foe? Linking Preferential Catalyst Growth with Liquid Water Distribution in PEFCs

With a recent emphasis on heavy-duty vehicle applications over light-duty, the performance targets for polymer electrolyte fuel cells (PEFCs) have become more demanding. For instance, achieving a net power output of 2.5 kW/g-PGM (1.07 A/cm2 current density) at 0.7 V is required after a 25,000-hour equivalent accelerated stress test (AST) [1]. In recent studies with traditional land/channel architecture, it has been demonstrated that Pt particle size growth is non-uniform and greater under flow field lands compared to channels [2]–[5]. It is hypothesized that preferential water accumulation under the lands during ASTs is responsible for such heterogeneity. However, a direct link between water accumulation/storage and particle size growth has not yet been established. In this study, we utilized high-resolution neutron radiography at NEUTRA, PSI, Switzerland to systematically map and quantify through-plane water content; synchrotron micro-XRD measured spatial Pt particle size distributions in fully functional fuel cells compatible with neutron imaging.The membrane electrode assemblies (MEAs) were aged using the U.S. Department of Energy’s (DOE) square-wave AST (0.6 V to 0.95 V vs. reversible hydrogen electrode, RHE) in both air and nitrogen environments at the cathode [5]. Correlations between through-plane water distribution and Pt particle size distribution maps were established for both pristine and aged samples. Understanding the role of architecture is crucial for assessing degradation, particularly in conventional flow fields where channel-land bias influences thermal and mass transport, impacting liquid water distribution. This knowledge can inform the design and engineering of PEFC components to enhance durability and reduce overall costs for vehicle applications.

Single-Layer-Graphene and Electrochemical Exfoliated Graphene Oxide for HT-PEMFC

High-temperature proton exchange membrane fuel cell (HT-PEMFC) is promising with its low demand for hydrogen purity, simple water management, and high waste heat utilization [1][2]. Although polybenzimidazole (PBI), as a typical high-temperature fuel cell membrane, has been developed for a long period, it still has defects such as phosphoric acid leaching and insufficient mechanical properties under high acid doping level [3][4]. With its unique 2D hexagonal grid structure and its electron cloud arrangement, single-layer graphene (SLG) can block the passage of any atoms [5]. However, hydrogen protons can easily penetrate SLG through a unique intermediate state mechanism to make it have excellent proton conductivity [6]. SLG's high proton conductivity combined with its excellent mechanical properties and thermal conductivity make it an ideal material for blocking phosphoric acid leaching. The SLG prepared by the chemical vapor deposition (CVD) method was transferred to the surface of catalyst layer of electrodes by the wet chemical transfer method. Due to the rupture and incompleteness of the SLG during the transfer process, the coverage rate of the SLG on the electrode surface is about 55%. This incomplete coverage facilitates small quantities of phosphoric acid leaching from PBI membrane to electrodes, which increases the three-phase boundary area and improves the performance of the HT-PEMFC. After 70 hours of accelerated stress testing (AST), the peak power density of membrane-electrode-assembly (MEA) with SLG on both sides of the cathode and anode can reach 480 mW cm-2, while the peak power density of MEA based on pure PBI membrane is only 249 mW cm-2. The quantification of phosphoric acid in the electrode by Lab based X-ray micro-computed tomography and the Raman spectroscopic mapping of the MEA cross-section shows that SLG can mitigate the leaching of phosphoric acid in the PBI film and improve the durability of HT-PEMFC. Graphene oxide (GO) is a low-cost application of graphene. Its doping in the PBI membrane can also reduce the leaching of phosphoric acid through enhancing the interaction between phosphoric acid and the PBI membrane [7]. A reactor based on 3D printing was designed so that natural graphite flakes can be used for electrochemical exfoliation to achieve rapid, safe, environmentally friendly, and mass production of GO. The electrochemically exfoliated (E)GO is doped in the PBI membrane. The 0.5%, 1% and 2% EGO loadings in the PBI membrane increased the peak power density by 13.8%, 24.4% and 29.2%, respectively.[1] Y.-L. Ma, J.S. Wainright, M.H. Litt, R.F. Savinell, Conductivity of PBI Membranes for High-Temperature Polymer Electrolyte Fuel Cells, Journal of The Electrochemical Society. 151 (2004) A8. https://doi.org/10.1149/1.1630037/XML.[2] H. Su, S. Pasupathi, B. Bladergroen, V. Linkov, B.G. Pollet, Optimization of gas diffusion electrode for polybenzimidazole-based high temperature proton exchange membrane fuel cell: Evaluation of polymer binders in catalyst layer, International Journal of Hydrogen Energy. 38 (2013) 11370–11378. https://doi.org/10.1016/J.IJHYDENE.2013.06.107.[3] S. Galbiati, A. Baricci, A. Casalegno, R. Marchesi, Degradation in phosphoric acid doped polymer fuel cells : A 6000 h parametric investigation, International Journal of Hydrogen Energy. 38 (2013) 6469–6480. https://doi.org/10.1016/j.ijhydene.2013.03.012.[4] S.H. Eberhardt, F. Marone, M. Stampanoni, F.N. Büchi, T.J. Schmidt, Quantifying phosphoric acid in high-temperature polymer electrolyte fuel cell components by X-ray tomographic microscopy, Journal of Synchrotron Radiation. 21 (2014) 1319–1326. https://doi.org/10.1107/S1600577514016348.[5] S. Hu, M. Lozada-Hidalgo, F.C. Wang, A. Mishchenko, F. Schedin, R.R. Nair, E.W. Hill, D.W. Boukhvalov, M.I. Katsnelson, R.A.W. Dryfe, I. V. Grigorieva, H.A. Wu, A.K. Geim, Proton transport through one-atom-thick crystals, Nature. 516 (2014) 227–230. https://doi.org/10.1038/nature14015.[6] S.M. Holmes, P. Balakrishnan, V.S. Kalangi, X. Zhang, M. Lozada-Hidalgo, P.M. Ajayan, R.R. Nair, 2D Crystals Significantly Enhance the Performance of a Working Fuel Cell, Advanced Energy Materials. 7 (2017) 1–7. https://doi.org/10.1002/aenm.201601216.[7] J. Li, X. Zeng, T. Ren, E. van der Heide, The Preparation of Graphene Oxide and Its Derivatives and Their Application in Bio-Tribological Systems, Lubricants 2014, Vol. 2, Pages 137-161. 2 (2014) 137–161. https://doi.org/10.3390/LUBRICANTS2030137.

Microporous Layer 3D Porosity Distribution in Fuel Cell Gas Diffusion Layers

Modern gas diffusion layers (GDL) of polymer electrolyte fuel cells (PEFCs) are commonly accompanied by a thin (20 – 50 μm) carbonaceous, microporous layer (MPL), whose porosity variations across the diffusion media area are not well known. MPLs have pore size distributions on the nanometer scale, whereas the channel-rib structure is in the millimeter range. The multiscale size range of the components of PEFCs implies that porosity characterization of the MPLs, typically done in a small volume of interest, is not representative of the MPL structure across the length scale of channel-rib structural variation. It results in a widespread practice of approximating MPL porosities by a homogeneous model [1]. Here we introduce a straightforward quantification method using X-ray tomographic microscopy (XTM) to evaluate the MPL porosity over an area that spans across a field of view >>2 mm2, allowing the porosity-related transport description on a length-scale relevant to fuel cell operation [2].The porosity imaging method is demonstrated using a laboratory computed tomography (CT) scanner with polychromatic X-ray radiation. The linearity between the tomographic greyscale values (GSVs) and the MPL-composing materials’ linear attenuation coefficients was experimentally confirmed, and the porosity of the MPL is determined by comparing the GSVs of the dry MPL and the same fully saturated MPL by n-decane, a highly wetting liquid for MPLs. Since the amount of n-decane is directly derived from GSVs and is proportional to the regional porosity of the MPL, porosity maps of (commercially available) MPLs are determined regardless of their pore size distribution.The results show that, even for the smooth MPL of the commercial Freudenberg gas diffusion layers, regional porosity varies by more than 20% across a length scale of a few hundreds of micrometers. For an in-house made MPL with larger pore size, water distribution and saturation are shown to be different from each other owing to the porosity inhomogeneity of the MPL. The results urge that the spatial determination of MPL porosity should precede any accurate saturation determination, whose values closely influence the effective permeability and diffusivity of the MPL structure under PEFC operation conditions.

Four-dimensional joint visualization of electrode degradation and liquid water distribution inside operating polymer electrolyte fuel cells

Understanding of degradation mechanisms present in polymer electrolyte fuel cells (PEFCs) is important to continue the integration of this clean energy technology into everyday life. Further comprehension of the interaction between various components during fuel cell operation is also critical in this context. In this work, a four-dimensional operando X-ray computed tomography method is developed for combined visualization of all PEFC components as well as transient water distribution residing in the cell, which results as a by-product of the electrochemical reaction. Time resolved, identical-location visualization through degradation stages is uniquely enabled by the non-invasive and non-destructive qualities of this method. By applying an accelerated stress test that targets cathode catalyst layer (CCL) corrosion, novel observations resulting from morphological changes of the CCL such as reduction in the water volume in the adjacent gas diffusion layer, CCL crack formation and propagation, membrane swelling, as well as quantification of local carbon loss is achieved. Additionally, insight into features that contribute to reduced fuel cell performance is enabled by the use of this specialized imaging technique, such as increased membrane undulation causing delamination and separation of the CCL from the microporous layer, which greatly affects liquid water pathways and overall device performance.

Changes in the wettability of polymer electrolyte fuel cells components during cationic contamination and mitigation

Foreign cations are shown to cause mass transport losses, in particular due to wettability changes in the micro-porous layers (MPL) and the carbon paper substrate, and have a major impact on the durability and the performance of polymer electrolyte fuel cells. We studied the effects of cationic impurities on fuel cell system performance, especially on the water management by employing in-situ and ex-situ contamination methods. Changes in the wettability of the carbon paper surface following the in-situ contamination injection were quantified using the Wilhelmy plate method. The CaSO4 precipitation on the macro-pores of the carbon paper substrate after the contamination injection causes a higher wettability leading to increased flooding of the carbon paper substrate and consequent mass transport losses. An ex-situ cleaning with an acid solution is shown to be very effective in removing the salt deposits of the carbon paper substrate. During the mitigation, the highly hydrophobic MPL acts as a barrier to the transport of the recovery solution into the membrane-electrode assembly (MEA), therefore isopropanol (IPA) was added to both the contaminant solution and the recovery solution to increase the wettability of the MPL. Wetting force measurements confirm that the added IPA can alter the wettability of the MPL and can render it fully hydrophilic, enabling the transport of the recovery solution into the MEA.

A Rapid Ex-Situ alternative for Mechanical Accelerated Stress Testing of Fuel Cells

The durability of polymer electrolyte fuel cells (PEFCs) is one of the main challenges facing the commercialization of automotive fuel cells. The lifetime of the membrane, a critical structural component of PEFCs, is one of the principal obstacles in achieving the fuel cell industry durability targets [1]. Under dynamic automotive operating conditions and duty cycles, the membrane is subjected to chemical and mechanical degradation, which could cause hydrogen leaks and ultimate cell failure. Chemical degradation is linked to the polymer molecular decomposition caused by radical species formed during the fuel cell operation as by-products of electrochemical reactions [2]. On the other hand, mechanical degradation is attributed to the fracture caused by the induced mechanical and hygrothermal stresses in a constrained cell [2]. The US Department of Energy (DOE) introduced standardized in-situ accelerated stress test (AST) protocols [3]. Following the DOE mechanical AST protocol, the membrane mechanical durability under pure humidity cycling was investigated [4]. In this manner, two customized in-situ mechanical AST protocols were utilized by our group to evaluate the mechanical durability of PEFCs, indicating significant decay in mechanical properties, formation of microstructural cracks, and initiation of failure [5]. Despite the valuable outputs of the in-situ studies, the current protocols are time consuming and costly. As hygrothermal fatigue is expected to dominate the membrane mechanical lifetime, an ex-situ mechanical fatigue-creep based AST was recently developed by our group as a more convenient alternative [6]. The proposed ex-situ tensile fatigue-creep test demonstrated in this work is intended to evaluate the mechanical durability of catalyst coated membranes (CCMs) in a fraction of the time required for the conventional in-situ tests [7]. The proposed ex-situ tensile fatigue-creep accelerated stress test (TFC-AST) was conducted on dog bone shaped [8] CCM samples using a dynamic mechanical analyzer (DMA) equipped with environmental chamber. After equilibration at 80°C and 50% RH, as illustrated in Figure 1, a high frequency sinusoidal cyclic tensile load with stress ratio (R) of 0.2 and 6.1 MPa mean stress was applied on the CCM samples to certain fractions of fatigue lifetime (~140,000 cycles) [7]. When compared to the well-defined standard in-situ mechanical ASTs which last about 8 weeks [5], the proposed TFC-AST results in mechanical failure ~400 times faster than the in-situ tests due to higher frequency and magnitude of fatigue and creep loading. Depending on the total lifetime, TFC-ASTs were interrupted at different fractions of the CCM lifetime, i.e. 20%, 40%, 60%, and 80%, and partially fatigued samples were extracted for analysis. The obtained partially degraded CCMs were further studied through mechanical and microstructural techniques. The mechanical properties of the extracted CCMs were investigated via tensile and hygrothermal expansion experiments in the same manner as reported in [9] using DMA. Tensile tests revealed remarkable increase in the tensile strength of the partially degraded samples indicating the alignment of the polymer molecules along the TFC stress direction. CCM thermal and hygral expansions were evaluated by stepwise increase in temperature and relative humidity, respectively. Interestingly, the CCM was found to contract, which is contradictory to the typical hygrothermal expansion behaviour of these materials [5,9]. This behaviour can be attributed to the exclusively tensile loading of the TFC-AST. In addition to the mechanical testing, morphological evolution of the TFC-AST degraded CCMs was also examined and compared with the analogous in-situ mechanical AST degraded CCMs using transmission electron microscopy (TEM). The TEM micrographs provided supplementary evidence regarding the reorientation of membrane molecules along the TFC stress direction. However, the mechanical failure of the specimens was found to be dominated by fatigue, similarly to the corresponding in-situ tests. Figure 1. Schematic of the proposed tensile fatigue-creep accelerated stress test (TFC-AST) protocol for rapid mechanical durability testing of fuel cells. Acknowledgements: This research was supported by Ballard Power Systems and the Natural Sciences and Engineering Research Council of Canada through an Automotive Partnership Canada grant.

Quantifying phosphoric acid in high-temperature polymer electrolyte fuel cell components by X-ray tomographic microscopy.

Synchrotron-based X-ray tomographic microscopy is investigated for imaging the local distribution and concentration of phosphoric acid in high-temperature polymer electrolyte fuel cells. Phosphoric acid fills the pores of the macro- and microporous fuel cell components. Its concentration in the fuel cell varies over a wide range (40-100 wt% H3PO4). This renders the quantification and concentration determination challenging. The problem is solved by using propagation-based phase contrast imaging and a referencing method. Fuel cell components with known acid concentrations were used to correlate greyscale values and acid concentrations. Thus calibration curves were established for the gas diffusion layer, catalyst layer and membrane in a non-operating fuel cell. The non-destructive imaging methodology was verified by comparing image-based values for acid content and concentration in the gas diffusion layer with those from chemical analysis.

Nature of Proton Transport in Membranes for Fuel Cell Applications

Development of polymer electrolyte fuel cells (PEFCs) is actively ongoing nowadays because of their potential applications in portable and stationary systems. Polymer electrolyte membranes (PEMs) are important component of PEFC, whose role is to facilitate proton conduction and to separate the anode and the cathode. In the present contribution, we report results of first-principles molecular dynamics (FPMD) simulations carried out for various types of hydrocarbon membranes for fuel cell applications with an emphasis on how molecular structure of membranes affect the transport property of proton. Especially, we applied FPMD to sulfonated poly phenoxy benzoyl phenylene (SPPBP) and sulfonated (arylene ether ether nitrile) (m-SPAEEN). The results of FPMD show that various hydrophilic functional groups, such as the carbonyl group, affect the nature of proton transport in the hydrocarbon membranes. Details on the proton transport mechanism are discussed.

Novel cross-linkers for asymmetric poly-AMPS-based proton exchange membranes for fuel cells

Polymer electrolyte fuel cells (PEFCs) are an ideal solution leading to clean energy by directly converting the fuel’s chemical energy to electricity in order to achieve high degree of efficiency. One of the main components of PEFCs is the proton exchange membrane which should conduct protons but no electrons and should also separate the electrodes and limit fuel crossover. In addition to Nafion®, polymers of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) have been used as a proton-conducting ionomer since sulfonic groups are known for their good proton conductivity. Since poly-AMPS excessively swells or even dissolve in water, we investigated several commercial cross-linkers and new multifunctional monomers to decrease swelling by cross-linking. Formulations with different concentrations of these cross-linkers have been tested constrained in porous polypropylene membranes. Although formulations with commercial cross-linkers (polyethylene glycol diacrylates) already exceeded the conductivity of Nafion®, with some of the synthesized cross-linkers we achieved more than 2.5 times the conductivity of Nafion®. Moreover, the novel amide-based cross-linkers show good hydrolytical stability in contrast to the commercial ones. Finally, we used one of the new cross-linkers to prepare asymmetric membranes and could achieve about 8 times the conductivity of Nafion.

A data-driven approach to establishing microstructure–property relationships in porous transport layers of polymer electrolyte fuel cells

The diffusion media (DM) has been shown to be a vital component for performance of polymer electrolyte fuel cells (PEFCs). The DM has a dual-layer structure composed of a macro-substrate referred to as the gas diffusion layer (GDL) coated with a micro-porous layer (MPL). Efficient prediction of the effective transport properties of the DM from its internal structure is essential to optimizing the multifunctional characteristics of this critical component. In this work, a unique data-driven approach to establishing structure–property correlations is introduced and applied to the case of gas diffusion in the GDL and MPL. This new approach provides an automated process to produce unbiased estimators to microstructural variance, in contrast to many process-related (hence biased) parameters employed by prominent correlations in the field. The present approach starts with a rigorous quantification of microstructure in the form of n-point statistics. It is followed by the identification of the key aspects of the internal structure through the use of principle component analysis. A data-driven correlation is established when the principal components are related to effective diffusivity by multivariate linear regression. This data-driven approach is compared to the conventional correlations and shown to achieve a very high accuracy for capturing the diffusive transport in the tested PEFC components.

Quantitative visualization of temporal water evolution in an operating polymer electrolyte fuel cell

Synchrotron X-ray radiography is employed to visualize the temporal evolution of water inside the gas diffusion layer (GDL) of an operating ( in situ) polymer electrolyte fuel cell (PEFC). A single-cell PEFC test kit is specially designed for the convenient capture of X-ray images. X-ray images of water in the PEFC components, such as the polymer membrane, GDL, and end plate, are captured consecutively. The synchrotron X-ray radiography of high-spatial and high-temporal resolution is suitable for observing the transport of a liquid layer and for visualizing water distribution inside the PEFC. As a result, the spatial distribution of water in the PEFC components is clearly and quantitatively visualized. The temporal evolution of water in the anode GDL due to back diffusion effect is clearly observed by adopting the image normalization method. The water-saturation characteristics at the cathode GDL, including saturation time and speed, are quite different from those at the anode GDL.

Characterization of Interfacial Structure in PEFCs: Water Storage and Contact Resistance Model

In this work, an analytical model of the microporous layer (MPL) and the catalyst layer (CL) interface under compression is developed to investigate the effects of the MPL|CL interfacial morphology on the ohmic and mass transport losses at the MPL|CL interface in a polymer electrolyte fuel cell (PEFC). The model utilizes experimentally measured surface profile data as input. Results indicate that the uncompressed surface morphology of mating materials, the elasticity of PEFC components, and the local compression pressure are the key parameters that influence the characteristics of the MPL and CL contact. The model predicts that a 50% drop in the MPL and CL surface roughness may result in nearly a 40% drop in the MPL|CL contact resistance. The model also shows that the void space along the MPL|CL interface can potentially store a significant amount of liquid water , which could result in performance loss and reduced durability. A 50% drop in the MPL and CL surface roughness is expected to yield nearly a 50% drop in the water storage capacity of the MPL|CL interface. The results of this work provide key insights that will enhance our understanding regarding the complex relation between MPL|CL interfacial structure and cell performance.

Model to Predict Temperature and Capillary Pressure Driven Water Transport in PEFCs After Shutdown

To enhance durability and cold-start performance of polymer electrolyte fuel cells (PEFCs), residual water in the fuel cell components must be minimized during operation and after shutdown. A transient two-phase mathematical and computational model is developed to describe water redistribution in the PEFC components after shutdown, which for the first time includes thermo-osmotic flow in the membrane. The model accounts for capillary and phase-change induced flow in the porous media and thermo-osmotic and diffusive flow in the polymer membrane. In the porous media, liquid-water flow is dominated by capillary transport until irreducible saturation is achieved, after which water removal is dominated by phase-change induced flow. In the membrane, thermo-osmotic flow can significantly help or hinder water drainage from the catalyst layer, depending on the situation. During shutdown to the frozen state, residual water at the cathode can be controlled, and freeze damage can be avoided, through balancing the phase-change induced flux in the diffusion media with the net balance of thermo-osmosis and diffusion flux in the membrane.

Investigation of the Impact of Interfacial Delamination on Polymer Electrolyte Fuel Cell Performance

A two-dimensional anisotropic model is developed to investigate the impact of local delamination on polymer electrolyte fuel cell (PEFC) performance. Localized interfacial delamination of the membrane∣catalyst layer and catalyst layer∣diffusion media were found to increase ohmic resistance significantly. As interfacial delamination width and area fraction increases, the ohmic resistance sharply increases in a nonlinear manner. The in-plane resistance and in-plane–to–thru-plane resistance ratio of PEFC components adjacent to the delamination were determined to be the key controlling parameters for increase in ohmic resistance. The membrane is a critical component because of its relatively low conductivity and very thin cross section. Finally, it is shown that under frozen conditions, small interfacial delaminations can result in a greater ohmic loss due to significantly lower membrane conductivity compared to normal operating conditions.

X-ray imaging of water distribution in a polymer electrolyte fuel cell

At present, water management in a polymer electrolyte fuel cell (PEFC) is a major subject of research. In fact, proper water management is vital to achieve maximum performance and durability from a PEFC. Consequently, this study is conducted to visualize quantitatively the water distribution in a PEFC by means of an X-ray imaging technique. The X-ray images of the PEFC components with and without water are clearly distinguished. Reference to the visualized X-ray images, enables quantitative evaluation of the water distribution in the region between the separator and the gas-diffusion layer (GDL). Likewise, the meniscus of water in the channels of the PEFC is clearly observed.

Modeling of two-phase transport in the diffusion media of polymer electrolyte fuel cells

A three-dimensional model of polymer electrolyte fuel cells (PEFCs) is developed to investigate multiphase flows, species transport, and electrochemical processes in fuel cells and their interactions. This two-phase model consists of conservation principles of mass, momentum, species concentration and charges, and elucidates the key physicochemical mechanisms in the constituent components of PEFCs that govern cell performance. Efforts are made to formulate two-phase transport in the anode diffusion media and its coupling with cathode flooding as well as the interaction between single- and two-phase flows. Numerical simulations are carried out to investigate multiphase flow, electrochemical activity, and transport phenomena and the intrinsic couplings of these processes inside a fuel cell at low humidity. The results indicate that multiphase flows may exist in both anode and cathode diffusion media at low-humidity operation, and two-phase flow emerges near the outlet for co-flow configuration while is present in the middle of the fuel cell for counter-flow one. The validated numerical tools can be applied to investigate vital issues related to anode performance and degradation arising from flooding for PEFCs.

A review of performance degradation and failure modes for hydrogen-fuelled polymer electrolyte fuel cells

A qualitative account of the causes and effects of performance degradation and failure in hydrogen-fuelled polymer electrolyte fuel cells (PEFCs) is given in the present review. The purpose of the review is to establish a backbone understanding of the phenomenological processes that occur within the PEFC, how they interact, how they are influenced through elements of design, manufacturing and operation, and ultimately how they result in performance degradation and cell failure. In the current work, 22 common faults are identified which are induced by 48 frequent causes. The major PEFC components considered here that are susceptible to faults are the polymer electrolyte-based membrane, the anode and cathode catalyst layers, gas diffusion and microporous layers, seals and the bipolar plate. Faults pertaining to these components can cause irreversible increases in activation, mass transportation, ohmic and fuel efficiency losses, or indeed cause catastrophic cell failure.

The structural variation of the gas diffusion layer and a performance evaluation of polymer electrolyte fuel cells as a function of clamping pressure

Interfacial contact resistance between gas diffusion layers (GDLs) and bipolar plates (BPs) has a substantial effect on the performance loss of polymer electrolyte fuel cells (PEFCs). Particularly during the final manufacturing process of a fuel cell stack, an externally applied clamping load determines the extent of electrical contact between those two solid components. In order to have the least electrical contact loss, it is highly necessary to keep all PEFC components close each other without causing structural failure of fuel cell stacks. In the present work, we investigated the effect of the clamping pressure on extrinsic properties such as porosity and permeability, which is closely related to mass transfer of reactants. Also, the variance of interfacial electrical resistance was analyzed as a function of the stack clamping pressure or the compressed GDL thickness, which reflects the external clamping load. Then with these experimentally obtained material properties of GDL, computational efforts were made to account for the effect of the clamping pressure on the fuel cell performance.

X선 영상기법을 이용한 고분자 전해질형 연료전지의 수분분포 가시화

Water management in polymer electrolyte fuel cell (PEFC) has been receiving large attention as an important issue in practical applications. Proper water management is vital to achieve high performance and durability of PEFC. In this study, an X-ray imaging technique was employed to visualize the water distribution in a PEFC quantitatively. X-ray images of the PEFC components with and without water were distinguished clearly. From the visualized X-ray images, we could evaluate the water distribution in the region between separator and gas diffusion layer (GDL) quantitatively. In addition, the contact angle of water in the micro-channels was also clearly visualized.