Ionomer membranes used to separate the electrodes in polymer electrolyte fuel cells are known to degrade both chemically and mechanically during regular fuel cell operation and may ultimately result in lifetime-limiting failure. The objective of the present work is to understand the effects of combined chemical and mechanical stresses on the mesoscale morphology of the membrane and its role in the overall degradation process. The mesoscale effects of sulfonic acid group loss and fluoride release on the phase segregated morphology of the membrane are analyzed using contrast-enhanced transmission electron microscopy and energy dispersive X-ray spectroscopy. The end-of-life ionic domain size of the ionomer is shown to be substantially enlarged compared to the pristine membrane state. Elemental mapping overlayed with the binary ionic and non-ionic morphology reveals mesoscopic void regions in the degraded material that are depleted of ionomer fluorine and carbon and considered susceptible to micro-crack initiation. A larger, severely degraded void region is also identified which contains evidence of hygrothermal stress induced localized ionomer crazing as a potential nucleation site for macroscopic fracture development. The synergetic effects of chemical and mechanical degradation on the progressive changes in the observed mesoscale morphology are discussed. (C) The Author(s) 2016. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. All rights reserved.

Aiming at durability issues of fuel cells, this research is dedicated to a novel experimental approach in the analysis of local membrane degradation phenomena in polymer electrolyte fuel cells, shedding light on the potential effects of manufacturing imperfections on this process. With a comprehensive review on historical failure analysis data from field operated fuel cells, local sources of iron oxide contaminants, catalyst layer cracks, and catalyst layer delamination are considered as potential candidates for initiating or accelerating the local membrane degradation phenomena. Customized membrane electrode assemblies with artificial defects are designed, fabricated, and subjected to membrane accelerated stress tests followed by extensive post-mortem analysis. The results reveal a significant accelerating effect of iron oxide contamination on the global chemical degradation of the membrane, but dismiss local traces of iron oxide as a potential stressor for local membrane degradation. Anode and cathode catalyst layer cracks are observed to have negligible impact on the membrane degradation phenomena. Notably however, distinct evidence is found that anode catalyst layer delamination can accelerate local membrane thinning, while cathode delamination has no apparent effect. Moreover, a substantial mitigating effect for platinum residuals on the site of delamination is observed.

Catalyst coated perfluorosulfonic acid ionomer membranes (CCMs) were subjected to a combined chemical/mechanical accelerated stress test (AST) designed for rapid benchmarking of in situ membrane stability in polymer electrolyte fuel cells. In order to understand the evolution of the ionomer water sorption characteristics during combined chemical/mechanical degradation, CCM samples were periodically extracted from the AST and analyzed for ionomer mass fraction and water sorption properties. In spite of severe fluoride release and membrane thinning, the water uptake per unit mass of the partially degraded CCMs was found to be essentially constant. The mass fraction of ionomer in the CCM samples determined from thermogravimetric analysis (TGA) showed significant material loss throughout the AST process due to ionomer degradation and fluoride release, up to roughly 50% at end-of-life. The effects proceeding at different stages of degradation were therefore more accurately revealed by ionomer mass-normalized data. The water uptake per unit gram of ionomer was shown to increase significantly with degradation, in contrast to the previous results normalized by CCM dry mass. Although increased water sorption may indicate enlarged solvated hydrophilic domains in the membrane, which would be beneficial for enhanced proton mobility, the proton conductivity was found to decrease. This finding suggests that the additional water sorbed in the membrane was not contributing to proton conduction and was therefore likely situated in non-ionic cavities formed through degradation rather than in the ionic clusters.

A CeO2 supported membrane electrode assembly (MEA) was fabricated by hot-pressing CeO2-coated electrodes and a PFSA ionomer membrane. Upon application of a combined chemical and mechanical accelerated stress test (AST), the CeO2 supported MEA showed six times longer lifetime and 40 times lower fluoride emission rate than a baseline MEA without cerium. The membrane in the CeO2 supported MEA effectively retained its original thickness and ductility despite the highly aggressive AST conditions. Most of the cerium applied on the anode migrated into the membrane and provided excellent mitigation of joint chemical and mechanical membrane degradation.

Membrane degradation is a key lifetime limiting factor in polymer electrolyte membrane fuel cells (PEMFCs). Observation of microstructure evolution in aged membrane electrode assemblies using scanning and transmission electron microscopy has shown a non-uniform degradation across the membrane surface [1]. It is known that under typical automotive operating conditions of PEMFCs, the membrane functional properties and stability decrease due to chemical and mechanical degradation mechanisms [2-3]. However, it is largely unknown why some distinct regions of the membrane experience remarkably more severe degradation, resulting in local thinning and pinhole formation and ultimately fuel cell failure due to significant hydrogen leaks. On this account, several studies have been performed on performance and failure analysis of PEMFCs due to pinhole formation [1, 4-5]; however, very limited knowledge is available on possible causes and initiators of this local phenomenon. In the present work, three new hypotheses are introduced, followed by an extensive experimental validation and analysis, with the aim of understanding the fundamental mechanism of this localized process. A comprehensive review of historical membrane failure analysis data from field operated Ballard MEAs was conducted to determine possible causes of localized membrane degradation and correlations with the MEA structure. Based on this review, it was proposed that catalyst layer delamination and cracks may play a significant role in accelerating the membrane degradation in PEMFCs. Therefore, customized MEAs were designed and fabricated in order to artificially create these two catalyst layer related defects. MEAs were tested under two different in-situ accelerated stress test conditions and extensive post mortem analysis was done on the end-of-life samples with the aim of developing an improved understanding of the relationships between pre-existing catalyst layer delamination and cracks and the localized membrane degradation process. Two possible cases of catalyst layer delamination were simulated, with and without a thin coating of Pt particles on the membrane surface. Figure 1 shows a cross sectional SEM image of the customized MEA. Delamination was simulated by precisely placing a small, thin, highly porous and hydrophilic polycarbonate film between the membrane and the catalyst layer. Also, Figure 2 shows the manipulated MEA with cracks in the cathode catalyst layer. The third hypotheses considered in this study was pinhole formation generated by local sources of Fenton’s reagents. In order to investigate this hypothesis, Iron oxide particles (Iron II and III oxides) were inserted at the membrane-catalyst layer interface. Figure 3 shows a cross sectional SEM image of this setup. The observations suggested a significant accelerating effect for iron contamination on the chemical membrane degradation process in a global nature, leading to remarkably shorter lifetimes, but dismissed the local traces of iron oxide as the local initiators or accelerators of this phenomenon. Studying the potential effects of catalyst layer delamination revealed that having this defect on the anode side can lead to an increasingly thinned membrane, while the same anomaly, if placed at the cathode catalyst-membrane interface, has a negligible effect on the rate of membrane thinning under identical operating conditions. Moreover, a substantial mitigating effect for platinum remainders on the site of delamination was observed in both tests. This was in agreement with comparable observations made by the same group [6]. In the case of artificial catalyst layer cracks, it was verified that anode and cathode cracks had no significant impact on local membrane degradation phenomena. In sum, anode delamination was found to be the most significant MEA feature resulting in accelerated local membrane thinning, while Fenton’s reagents were shown to accelerate global membrane thinning. The anode catalyst layer and its interaction with the membrane may warrant further research to elucidate the complex, local membrane degradation phenomena. Acknowledgements This research was supported by Ballard Power Systems and the Natural Sciences and Engineering Research Council of Canada through an Automotive Partnership Canada (APC) grant. Special thanks and appreciations also go to Dr. Lida Ghassemzadeh, for her persistent and generous support during this project. References [1] L. Guétaz et al., Journal of Power Sources, vol. 212, pp. 169-178, 2012. [2] V. O. Mittal et al., Journal of The Electrochemical Society, vol. 154, no. 7, pp. B652-B656, 2007. [3] A. Young et al., Journal of The Electrochemical Society, vol. 157, no. 3, pp. B425-B436, 2010. [4] R. Lin et al., Journal of The Electrochemical Society, vol. 158, no. 1, pp. B11-B17, 2011. [5] A. Z. Weber, Journal of The Electrochemical Society, vol. 155, no. 6, pp. B521-B531, 2008. [6] N. Macauley et al., ECS Electrochemistry Letters 2, F33-F35, 2013.

The mechanical stability of catalyst coated membranes (CCMs) is an important factor for the overall durability and lifetime of polymer electrolyte fuel cells. In this article, the evolution of the mechanical properties of degraded CCMs is comprehensively assessed. A combined chemical and mechanical accelerated stress test (AST) was applied to simulate field operation and rapidly generate partially degraded CCM samples for tensile and expansion experiments under both room and fuel cell conditions. The tensile results indicated significant reductions in ultimate tensile strength, toughness, and fracture strain as a function of AST cycles, accompanied by a mild increase in elastic modulus. The increased brittleness and reduced fracture toughness of the CCM, caused primarily by chemical membrane degradation, is expected to play an important role in the ultimate failure of the fuel cell. The expansion tests revealed a linear decay in hygrothermal expansion, similar in magnitude to the loss of mechanical strength. The decline in CCM sensitivity to environmental changes leads to non‐uniform swelling and contraction that may exacerbate local degradation. Interestingly, the hygrothermal expansion in the late stages of degradation coincided with the fracture strain, which correlates to in situ development of fractures in chemically weakened membranes.

Proton Exchange Membrane (PEM) failure is one of the key criteria in deciding the durability of the PEM fuel cell system. Physical properties such as ionic conductivity and mechanical properties depend on the microstructure. The microstructure is itself strongly dependent on the water content of the membrane (1, 2). It is therefore important to fully understand the effect of degradation stressors on the morphological changes and water-uptake characteristics in order to improve membrane durability. In this work, standard perfluorosulfonic acid (PFSA) ionomer membranes are subjected to a combined chemical and mechanical accelerated stress test (AST) used for rapid benchmarking of in-situ membrane stability. The degradation stressors in the combined chemical/mechanical AST was previously shown by our group to change the molecular structure and lead to membrane material loss (3). The chemical phase of the AST generates hydroxyl radicals that attack both the side chain and main chain of the polymer, while the mechanically generated stresses due to humidity cycling accelerate mechanical failures. The observed structural changes are anticipated to alter the water-uptake properties of the membrane, as shown previously for ex-situ testing (4). The degradation also alters the morphology, ion exchange capacity, mechanical properties, and proton conductivity of the membrane (5). Water-uptake measurements of partially AST degraded catalyst coated membrane (CCM) samples are carried out at room temperature using a dynamic vapor sorption system. In spite of severe fluoride release and membrane thinning, the water-uptake per unit mass of the AST degraded CCMs is found to be relatively constant. Since the test specimens are CCMs which contain a significant amount of catalyst layer material, an attempt is made to measure and separate the mass of the ionomer by thermogravimetric analysis (TGA). The ionomer material loss throughout the AST process is significant due to fluoride release and ionomer degradation, up to roughly 50% at end-of-life (3). The water-uptake per unit mass of ionomer in the CCM is determined by extracting the ionomer weight obtained by heating the CCM in the TGA chamber. In contrast to the previous results normalized by specimen dry weight, the water-uptake increases significantly per unit mass of the ionomer in the CCM, as shown in Fig. 1. Although the increased water-uptake may indicate enlarged solvated hydrophilic domains in the membrane, which is good for enhanced proton mobility, the proton conductivity is found to decrease (Fig. 1). This may be attributed to a decay in proton concentration due to sulfonic acid functional group loss during side chain degradation. The overall effects of the combined chemical/mechanical AST on the membrane morphology and properties are presented and compared to provide additional insight into the complex degradation mechanism. ACKNOWLEDGMENTS Research funding provided by Automotive Partnership Canada (APC), Natural Sciences and Engineering Research Council of Canada (NSERC) and Ballard Power Systems (BPS) is gratefully acknowledged. BPS is also acknowledged for providing access to experimental facilities, material samples and technical support. REFERENCES 1. J.Benziger, A. Bocarsly, M. J. Cheah, P. Majsztrik, B. Satterfield, and Q. Zhao, in Fuel Cells and Hydrogen Storage 141, Bocarly and Mingos, Editors, p. 85 Springer, Berlin Heidelberg 141 (2011). 2. Y. Yang, A. Siu, T. J. Peckham, S. Holdcroft, in Advances in Polymer Sciences 215: Fuel cells 1, G. G. Scherer, Editor p. 55 Springer, Berlin Heidelberg 215 (2008). 3. C. Lim, L. Ghassemzadeh, F. Van Hove, M. Lauritzen, J. Kolodziej, G.G. Wang, S. Holdcroft, E. Kjeang, J. Power Sources 257 102 (2014). 4. L. Ghassemzadeh and S. Holdcroft, J.Am.Chem.Soc. 135 8181 (2013). 5. S. V. Venkatesan and E. Kjeang, 11th International Fuel Cell Science, Engineering and Technology Conference, ASME, Minneapolis, MN (2013).

A cyclic open circuit voltage (COCV) accelerated stress test (AST) is designed to screen the simultaneous effect of chemical and mechanical membrane degradation in polymer electrolyte fuel cells. The AST consists of a steady state OCV phase to accelerate chemical degradation and periodic wet/dry cycles to provide mechanical degradation. The membrane degradation process induced by COCV AST operation is analyzed using a standard MEA with PFSA ionomer membrane. The OCV shows an initially mild decay rate followed by a higher decay rate in the later stages of the experiment. Membrane failure, defined by a threshold convective hydrogen leak rate, is obtained after 160 h of operation. Uniform membrane thinning is observed with pinhole formation being the primary cause of failure. Mechanical tensile tests reveal that the membrane becomes stiffer and more brittle during AST operation, which contributes to mechanical failure upon cyclic humidity induced stress. Solid state F-19 NMR spectroscopy and fluoride emission measurements demonstrate fluorine loss from both side chain and main chain upon membrane exposure to high temperature and low humidity OCV condition. (C) 2014 Elsevier B.V. All rights reserved.

Enhancing the durability of fuel cells for the transportation sector requires a better understanding of the fundamental processes that cause degradation. Field-operated PEMFCs have been shown to develop a thin parallel band of Pt inside the membrane. Reports on the effect of the Pt band on membrane durability are contradictory. Here, we examined the influence of the Pt band by performing in situ and ex situ membrane degradation tests. We report that the Pt band significantly decreases the rate of membrane degradation, thereby enhancing its longevity. (C) 2013 The Electrochemical Society. All rights reserved.

The effect of the dispersion methods for an unsupported Pt-Ru (1:1) black anode catalyst on the power performance of a direct methanol fuel cell has been studied. The anode catalyst inks were fabricated by ultrasonicating or ball-milling the catalyst in two different types of dispersion solvent, namely deionized water (DI) and isopropyl alcohol (IPA). To fabricate an anode, the inks were sprayed onto the gas diffusion backing electrode, consisting of microporous layer (MPL) and carbon paper. Scanning electron microscopy (SEM) of the cross-sectional morphology of the anode catalyst layers revealed that the layers fabricated by ultrasonicating the catalyst in DI or IPA, ball-milling in DI and ball-milling in IPA consisted of granular-shaped, granular+flake-shaped and flake-shaped agglomerates, respectively. The anode catalyst layer fabricated by ball-milling in IPA exhibited the most porous structure and correspondingly represented the best power performance of 0.13Wcm−2 (0.45Acm−2, 0.3V) at 90°C with 1M aqueous methanol and atmospheric air. Control of the morphology and porosity in the catalyst layer by means of the catalyst dispersion method is suggested.

In this paper, we propose a novel fast motion estimation algorithm based on successive elimination algorithm (SEA), which can dramatically reduce complexity of the variable block size motion estimation by removing the unnecessary computation of SAD in H.264 encoder. The proposed method, which accumulates current sum norms and pre-computed SAD for the bigger block sizes than 4×4 drives tighter bound in the inequality than an ordinary SEA depending on the availability of SAD. Experimental results explain that our method reduces computation complexity. In addition, the proposed method is an extended version of the rate constrained block matching for variable block-sized applications. It surely works on variable block-based motion estimation with just a little degradation.

In this paper, we propose a novel fast motion estimation algorithm based on successive elimination algorithm (SEA) which can dramatically reduce complexity of the variable block size motion estimation in H.264 encoder. The proposed method applies the conventional SEA in the hierarchical manner to the seven block modes. That is, the proposed algorithm can remove the unnecessary computation of SAD by means of the process that the previous minimum SAD is compared to a current bound value which is obtained by accumulating current sum norms and reused SAD of 4x4 blocks for the bigger block sizes than 4x4. As a result, we have tighter bound in the inequality between SAD and sum norm than the bound in the ordinary SEA. If the basic size of the block is smaller than 4x4, the bound will become tighter but it also causes to increase computational complexity, especially addition operations for sum norm. Compared with fast full search algorithm of JM of H.264, our algorithm saves 60 to 70% of computation on average for several image sequences.

In this paper, we propose an infrared LED tracking system called IRED Gun, which is designed for the game gun interface. The conventional systems are practically restricted by physical environment and have a lot of problems. We suggest the IRED Gun system to solve these problems. Unlike conventional systems, our tracking system uses three infrared LED lights attached on a monitor, and enables a user to interact with a game. In addition, our system calibrates reliable aim coordinates along the target position of a user by an error correction method based on an aim correction model. Therefore, our infrared LED tracking method allows users freely move in front of a monitor.

Pt–Ru catalysts have been made by a thermal decomposition and electrodeposition method onto a titanium mesh for the electrooxidation of methanol. Galvanostatic polarisations were used to assess and compare the relative activities of the electrodes. SEM and XRD are employed to study the morphology and structure of the catalyst layers. The performance of the anodes in fuel cell assemblies is also discussed. We can see that the mesh perform well in half and full cell tests despite significant apparent physical differences, which are yet to be explored.

Characterisation of a direct methanol fuel cell using an anode fabricated by thermal decomposition from Pt–Ru chloro-complex on Ti mesh is described. The polarisation characteristic of the resultant membrane electrode assembly is compared with that of a conventional MEA with an anode, consisting of a catalyst layer, a microporous layer and a wet-proof-treated carbon paper. Electrode characterisation was carried out using XRD, SEM and EDX analyses. In 1 m methanol solution, the MEA with the catalysed Ti mesh anode gave a power performance comparable with that of the conventional anode at 90 °C. However, in 0.5 m methanol solution the former showed much higher power density than the latter, indicating high utilisation of methanol fuel.

Effects of hydrophobic polymer content within a carbon paper, used as the cathode gas diffusion layer (GDL), on power performance of a H2/air proton exchange membrane fuel cell (PEMFC) have been studied. Electrochemical methods are used in conjunction with morphology and wetting property characterization. Surface contact angle of wet-proof-treated GDL as a function of temperature is measured by a novel capillary rise method. It is shown that the contact angle generally decreases with the temperature, and that there is insignificant difference in contact angle on carbon papers treated with different contents of fluorinated ethylene propylene (FEP) ranging from 10 to 40wt.%. Under all humidification conditions in this study, a membrane-electrode assembly (MEA) consisting of 10wt.% FEP-impregnated GDL shows higher power densities than 30wt.% FEP-impregnated one. Surface morphology of the hydrophobic polymer-treated carbon paper has been analyzed by scanning electron microscopy (SEM) and is identified as playing a crucial role in affecting the power performance of such treated GDL in the PEM fuel cell.

Based upon Nafion 112 membrane, membrane-electrode assemblies for a liquid-feed direct methanol fuel cell (DMFC) were fabricated by using a novel method of modified Nafion solution and tape-casting, with unsupported Pt-Ru as an anode catalyst and carbon supported 40wt.% Pt as a cathode catalyst. The amounts of catalyst loading were controlled to be 4mg/cm2 in the anode and 1.3mg/cm2 in the cathode. Morphological characteristics of anode and cathode were examined by scanning electron microscopy (SEM). A time-delayed activation effect was found in single cell tests and attributed to time-dependent wetting behavior of Nafion polymers within both catalyst layers. A high compression of the single cell leads to a remarkable decrease in diffusion-limiting current density, caused by hydrophilic broken fibers and cleavage-like defects generated during excessive compression of the cell. A maximum power density of 0.21W/cm2 is achieved in 2M CH3OH solution at 90°C under the operating condition of non-pressurized anode side and non-humidified air pressurized to 15psi.