Canada Foundation For Innovation Research Articles

A4 DNA HYPOMETHYLATION INHIBITS COLITIS-ASSOCIATED CANCER

Abstract Background Colorectal cancer is the second leading cause of cancer death in Canada. A major risk factor for the development of colorectal cancer is chronic inflammation leading to colitis-associated cancer (CAC). We previously described a CAC mouse model in which tumors arise from DCLK1+ cells following loss of the tumor suppressor adenomatous polyposis coli (APC) and induction of colitis. Interestingly, both colitis and CAC are associated with DNA methylation changes that lead to altered gene expression. Moreover, inhibition of DNA methylation has recently been shown to lead to a viral mimicry response. The effects of DNA methylation on colonic tumorigenesis, however, is not known. Aims Thus, we aim to investigate whether inhibition of DNA methylation leads to a viral mimicry response that inhibits colitis-associated tumorigenesis. Methods We first examined the effects of DNA hypomethylation on CAC, by crossing Dclk1-CreERT2/Apcf/f mice to Dnmt1f/f mice which allowed for knock-out of the DNA methyltransferase enzyme DNMT1 in DCLK1+ cells. Dclk1/Apcf/f/Dnmt1f/f and Dclk1/Apcf/f (control group) mice were administered three doses of tamoxifen followed by 2.5% dextran sodium sulfate (DSS) for five days to induce colitis. Fourteen weeks later, we assessed colonic tumor number and size. In a separate cohort of Dclk1/Apcf/f mice treated with DSS, we compared colonic tumor number in mice treated with six doses of 5-AZA-2’-deoxycytidine (5-AZA) versus vehicle. The effects of 5-AZA and DSS on DNA methylation were assessed using the Infinium Mouse Methylation BeadChip Array on colonic epithelial cells isolated from mice treated with vehicle versus 5-AZA in the presence or absence of colitis. RNA expression of viral transposable elements and type I interferon response related genes were measured as a readout of a viral mimicry response. Lastly, we investigated the mechanism by which DNA hypomethylation affects tumorigenesis by crossing Dclk1/Apcf/f/Dnmt1f/f mice to MAVS knockout mice and examining tumor number following tamoxifen and DSS administration as above. Results Deletion of DNMT1 in DCLK1+ cells or treatment with 5-AZA significantly decreased colonic tumor number and size. Treatment with 5-AZA or DNMT1 loss led to DNA hypomethylation and subsequent upregulation of endogenous retroviral expression. Both 5-AZA treatment and DNMT1 knockout in DCLK1+ cells led to increased expression of type I interferon response genes. Knockout of the type I interferon response related gene, MAVS, reversed the anti-tumor effect observed with DNMT1 loss. Conclusions Our findings demonstrate that DNA hypomethylation by 5-AZA or loss of DNMT1 reduces colitis-associated tumorigenesis through activation of a viral mimicry response. Funding Agencies CAG, CIHRCancer Research Society, Canada Foundation for Innovation, Lawson Health Research Institute

Systematic Assessment of Electrode Wettability for Vanadium Redox Flow Batteries

Vanadium redox flow batteries (VRFBs) are a promising energy storage technology due to their advantages such as long-life cycle and scalability. In these systems, porous electrodes such as carbon paper and carbon felts have been used because of their desirable properties such as good acid resistance and low cost. However, these materials may have poor reversibility and wettability, which can negatively affect the system performance. Recently, different activation methods have been proposed to enhance physico-chemical properties and overcome these limitations. Among different methods, surface treatments have been commonly used in the literature [1-5] since they can introduce desirable functional groups (e.g., oxygen, nitrogen) and enhance electrochemically active surface area (ECSA), which is believed to be the main mechanisms for electrode performance improvement. Although it is suggested that higher electrode performance can be achieved by enhancing wetted or active surface area [6], there is still a disparity in how to assess relevant wetting properties, since wettability assessment is often neglected and performance assessment is usually done based on VRFB cycling test results, which is costly and time consuming.Static contact angle (CA) is commonly used to characterize electrode wettability and evaluate the effect of different treatments on the electrode surface. However, this technique offers a limited understanding and superficial analysis, since samples are either classified as hydrophobic or hydrophilic, showing no correlation to electrochemical performance. Moreover, CA measurements are not adequate for porous electrodes, since porosity and surface roughness can impact on contact angle results. In the present work, we propose to use the method of standard porosimetry (MSP) and cyclic voltammetry (CV) to evaluate the impact of surface treatments on electrode wettability from a complete physical (pore size distribution), chemical (functional group density), and electrochemical (electrochemically active surface area) perspective. These tools offer richer information than basic CA measurements and only take a few hours to be performed, thus reducing the assessment time and cost compared to VRFB assembly and cycling tests.Preliminary results show that both MSP and CV techniques can provide useful information regarding physical and chemical properties that can correlate electrode wettability to electrochemical performance. While MSP results can provide electrode morphology (pore size distribution, porosity, specific and wetted surface area), CV measurements can provide surface chemistry information (functional groups density) and electrochemically active surface area (capacitance). Thus, both tools can be used synergistically to investigate how different treatments impact both physical and chemical properties and how wetting properties impact electrode performance. Achieving high performance is essential to increase system energy density and decrease both capital and operational cost, making VRFBs more competitive and suitable for grid-scale storage of renewable energy, having positive environmental impacts and facilitating sustainable transition. Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), Canada Foundation for Innovation (CFI), British Columbia Knowledge Development Fund (BCKDF), Western Economic Diversification Canada (WD), Canada Research Chairs (CRC), and the National Research Council of Canada (NRC). Technical support from Elizabeth Fisher and Jonas Stoll is also acknowledged.

High Durability of Pemion® Proton Exchange Membranes in Cross-Pressure Accelerated Mechanical Stress Tests

Polymer electrolyte membrane fuel cells (PEMFC) are the dominant technology for hydrogen-powered fuel cell electric vehicles in clean transportation systems. To be suitable for commercialization and applicability in real-world use-cases, light and heavy-duty fuel cell vehicles require lifetimes of over 8,000 and 30,000 hours, respectively [1]. Hence, enhancing the durability of all fuel cell components, particularly the proton exchange membrane (PEM), is of great importance.Recently, fuel cell membranes based on hydrocarbon (HC) chemistries have become increasingly common in the literature [2]. Materials with polyaromatic backbones, tunable electrochemical properties, and low reactant permeability are increasingly seen as potential alternatives to incumbent perfluorosulfonic acid (PFSA) materials [2]. Additionally, as restrictions on the use of fluorinated materials in various industries continue to grow, the importance of HC chemistries will as well. Sulfo-phenylated polyphenylenes (sPPPs) are a particular class of HC materials that show promise [3]. However, the phase separation between hydrophilic and hydrophobic domains within sPPPs may not be as discrete as in PFSAs [3], requiring higher ion exchange capacity (IEC) values than PFSAs to achieve similar protonic conductivity. High IEC typically results in greater material hydrophilicity, which can render membranes dimensionally unstable in a fuel cell [4].State-of-the-art commercial PEMs are now manufactured as thin films (≤ 18 µm), offering small ohmic loss and therefore high fuel cell performance. To improve dimensional stability and eliminate the risks of electrical shorting, PEMs are commonly mechanically reinforced using a porous, inert, and non-ionic substrate, such as expanded polytetrafluoroethylene (ePTFE). In a work by Miyake et al. [5], sulfonated polyphenylene-based ionomer membranes with flexible polyethylene mechanical reinforcement were prepared and the results indicated promising mechanical properties and improved longevity in RH cycling tests. However, there is still a lack of data about the fatigue durability of HC membranes in the literature, and evaluating and comparing the mechanical durability of numerous PEMs with a mechanical reinforcement layer in a traditional wet-dry cycling accelerated stress test would be a time-consuming and thus costly process [6].In our previous work, [7] we combined constant pressure differential across an ePTFE-reinforced perfluorosulfonic acid (PFSA) ionomer membrane with in-situ RH cycles (ΔP-AMST) to simulate the actual mechanical stresses in the fuel cell environment, while accelerating the durability testing for reinforced PEMs. In this study, ΔP-AMST is used to benchmark the fatigue lifetime curves for Pemion® membranes and compare it with a commercial reinforced PFSA-based PEM. The test temperature was set to 90 °C, and dry and wet (90% RH) phases were 60s and 30s, respectively. The hardware and semi-MEA specifications used for the test are shown in Figure 1a-c. A semitransparent polycarbonate spacer plate with 20 mm thickness and a circular aperture (25.4 mm) in the middle was used to allow free expansion of the membrane (Figure 1d). The cathode side was pressurized to create a cross pressure between the two sides and intensify the stress on the membrane during the RH cycling process. The ultimate failure of the membrane is shown in Figure 1e. The radial stress at the center of the deformed membrane is estimated by Hencky’s solution, as reported in our previous work [7]. Figure 1f demonstrates the estimated nominal stress on the membranes as a function of their lifetimes in terms of RH cycles. According to the fatigue S-N curves, reinforced Pemion® membranes afford longer lifetime than incumbent PFSA materials if the membrane edges are well protected. In addition, the impact of IEC on the fatigue durability of Pemion® membranes is investigated and the results are evaluated against stress of dehydration and dynamic mechanical analysis measurements. Acknowledgements This project was financially supported by Natural Sciences and Engineering Research Council of Canada (NSERC), Ionomr Innovations Inc, Canada Foundation for Innovation (CFI), British Columbia Knowledge Development Fund (BCKDF), Western Economic Diversification Canada (WD), and Canada Research Chairs (CRC).

Thermo-Mechanical Stability of Hydrocarbon-Based Pemion® Proton Exchange Membranes

Considering the environmental concerns about the disposal of perfluorosulfonic acid (PFSA) membranes as well as the growing interest in higher temperature operability of polymer electrolyte membrane fuel cells (PEMFCs), non-fluorinated hydrocarbon-based proton exchange membranes (PEMs) with aromatic backbones have become an increasingly active area of research. Low reactant cross-over, tunable electrochemical properties, and differentiated chemistries and potentially safer and cost-reducing synthesis procedures, are additional favourable features of hydrocarbon-based PEMs for prospective use in PEMFCs [1]. Vulnerable linking units, however, are known to be the main disadvantages of these polymers in the oxidative environment of fuel cells. During PEMFC operation, destructive radical species such as hydroxyl (HO•) are produced, causing polymer degradation and thinning in the membrane [2]. Recently, sulfo-phenylated polyphenylenes (sPPPs) have shown outstanding oxidative stability due to a polymer backbone comprising only aryl-aryl bonds, with mitigated chemical degradation in ex-situ and in-situ durability studies [3, 4]. Another concern is regarding the thermo-mechanical stability of PEMs. Thus, a systematic thermo-mechanical stability study is required to confirm the potential of sPPP-based PEMs to replace conventional PFSAs, especially for high temperature PEMFC, i.e., 110-120 °C.The present research objective is to assess the thermo-mechanical stability of a commercial reinforced hydrocarbon-based PEM, Pemion® (PF1-HLF8-15-X, 15 µm thick, reinforced), as well as a mechanically-reinforced PFSA-based reference membrane, across a wide range of temperature (30-120 °C) and relative humidity (RH) (10-90%) conditions that includes the crucial high temperature window of interest for future PEMFCs [6]. To this end, a comprehensive design of experiment yielded 19 tensile tests at various hygrothermal conditions with dynamic mechanical analyzer (DMA 850; TA Instruments) equipped with an external environmental chamber accessory (TA Instruments, RH Accessory). Important mechanical properties such as Young’s modulus, ultimate tensile stress, yield stress, maximum elongation at break, strain hardening, and modulus of resilience were extracted and discussed as well. Datapoints were fitted for empirical model development and mechanical properties were estimated for high temperature and RH conditions beyond the capability of the instrument. This method can be employed to assess if the mechanical properties of membrane materials can be retained at higher temperatures, regardless of polymer chemistry and type. Storage modulus and loss modulus were separately measured in a dynamic mode to observe the impact of temperature on the mechanical response of the hydrophobic backbone and hydrophilic ionic clusters, respectively.Overall, Pemion® demonstrates tough tensile properties in the stress-strain tests due to its sterically encumbered polyphenylene backbone (Figure 1a), whereas the reference PFSA (Figure 1b) shows elastomer-like behavior with much lower Young’s modulus, yield stress, and strain hardening (slope of the curve in the plastic deformation region). Figure 1c-f show the main viscoelastic properties extracted from the tensile tests at room (30 °C, 50% RH) and high temperature fuel cell conditions (110 °C, 50% RH). The modulus of elasticity and strain hardening of Pemion® membrane are almost temperature-independent, whereas these properties for the reinforced PFSA material undergo a significant decay at high-temperature ambience. Pemion® maintains good yielding strength even at high temperature and RH conditions (110-120 °C and 80% RH). Nevertheless, small mechanical stress values as low as 1 MPa can cause spontaneous yielding in the PFSA reference material above 110 °C. The modulus of resilience for the reinforced PFSA is also predicted to be zero at elevated hygrothermal conditions (i.e., 90 °C and 70% RH). This is interpreted as an approach to the material’s glass transition condition, where it loses its mechanical integrity and therefore, is potentially unsuitable for higher temperature PEMFC operation. Moreover, the dynamic mechanical thermal analysis revealed that Pemion® retains its robustness at hygrothermal ambience close to high-temperature PEMFCs, i.e., 110-120 °C and 40-50% RH, whereas the backbone of the PFSA material gradually loses its strength. Acknowledgements This project was financially supported by Natural Sciences and Engineering Research Council of Canada (NSERC), Ionomr Innovations Inc, Canada Foundation for Innovation (CFI), British Columbia Knowledge Development Fund (BCKDF), Western Economic Diversification Canada (WD), and Canada Research Chairs (CRC).

Chemo-Mechanical Durability of Reinforced Fuel Cell Membranes in the Presence of Metallic Foreign Particles

High-throughput production is vital to achieve cost-effective proton exchange membrane fuel cells (PEMFCs) at scale1. The high-volume mass production of PEMFCs using industrial manufacturing machinery may however introduce unwanted material in the final product due to the wear and tear of the machinery. As an example, roll-to-roll processes applied to the manufacture of catalyst coated membrane (CCM) generally use Fe alloys such as stainless steel2 components that could release fine metallic particles or related debris that may affect the product quality3,4. Therefore, it is important to understand the fundamental impact of such non-uniformities on PEMFC performance and durability.This work focusses on the impact of slightly oxidized iron (Fe) and stainless steel 316L (SS316L) micro-particles entrapped between the cathode catalyst layer (CCL) and a GORE-SELECT® Membrane A. Fe cations are considered as Fenton’s catalyst/reagent which enhance harmful radical generation and ionomer attack, known to weaken its mechanical strength and ionic conductivity5. Therefore, membrane electrode assemblies (MEAs) containing solid Fe and SS316L particles were prepared to conduct in-situ PEMFC experiments and identify their impact on membrane degradation and durability. The chosen particles were placed carefully on the bare membrane at selected locations based on the flow field design of the graphite bipolar plates. Later, the assembled MEAs were tested using a small-scale fixture (SSF) fuel cell in a combined chemical and mechanical AST after beginning-of-life (BOL) conditioning and diagnostics6.X-ray computed tomography (XCT) has been shown to be a powerful and non-invasive 3D characterization tool for analyzing membrane degradation7,8. Thus, periodic same-location XCT visualization of the CCL-membrane interface was performed after every 10 AST cycles. According to the Fe Pourbaix diagram9, Fe oxidizes to Fe2+ at 0.77 V and indeed, in this work, complete dissolution of the Fe-50µm particles was observed leaving cavities at the CCL-membrane interface. This dissolution manifested as a distinct black spot in CT imaging, as highlighted by the enclosed red circle in Figure 1. In contrast, corrosion of SS316L particles is usually prevented by a native oxide layer formation during fuel cell operational conditions10. The Fe particle laden AST reached membrane failure within 30 cycles and indicates an escalation of degradation by global membrane thinning. This is substantially lower than the baseline AST without particles. The XCT images for Fe-50µm AST seen in Figure 1 show that severe global membrane thinning occurred in the Fe-50µm MEA, which contributed to a high electrochemical leak detection (ELDT) signal exceeding test failure criteria. In contrast, the SS316L MEA did not reach the threshold failure criteria for the AST duration, however, the average OCV remained lower as compared to the baseline MEA AST. XCT imaging showed that the SS316L- 50µm particles did not dissolve throughout the AST duration and the membrane thinning was more pronounced near the particle rather than globally. Additionally, we have evaluated whether chemically and mechanically mitigated GORE-SELECT Membrane® B could enable more robustness and minimize impact of multiple metallic particles. Analysis of combined chemo-mechanical AST with a larger dimension SS316L-500µm present on mitigated GORE-SELECT® Membrane B suggest that chemical and mechanical mitigation can reduce impact of large particles and enable lifetime response at the level close to baseline. In conclusion, the membrane lifetime and failure mode were found to be strongly dependent on the particle chemical composition and membrane degradation mitigation strategies, which are therefore should be considered at PEM design stages to reduce risks and improve CCM and MEA production quality. Keywords: PEM durability, quality control, cost reduction, XCT Acknowledgments This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, Ballard Power Systems, and W.L. Gore & Associates. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program. References H. Tsuchiya and O. Kobayashi, Int. J. Hydrogen Energy, 29, 985–990 (2004).J. Chen, H. Liu, Y. A. Huang, and Z. Yin, J. Manuf. Process., 23, 175–182 (2016).A. Phillips et al., Fuel Cells, 20, 60–69 (2020).A. Phillips, M. Ulsh, K. C. Neyerlin, J. Porter, and G. Bender, Int. J. Hydrogen Energy, 43, 6390–6399.J. G. Goodwin, K. Hongsirikarn, S. Greenway, and S. Creager, J. Power Sources, 195, 7213–7220 (2010).Y. Chen et al., J. Power Sources, 520, 230673 (2022).Y. Chen et al., J. Power Sources, 520, 230674 (2022).Y. Singh et al., J. Power Sources, 412, 224–237 (2019).R. Tolouei et al., Phys. Chem. Chem. Phys., 18, 19637–19646 (2016).N. Kumar et al., Int. J. Energy Res., 44, 6804–6818 (2020). Figure 1

The Role of Thermal Conductivity on Liquid Water Distribution in GDLs

Operating polymer electrolyte fuel cells (PEFCs) at increasingly higher current density and efficiency necessitates overall improvements in fuel cell water management [1]. A crucial role facilitating these improvements is played by the gas diffusion layer (GDL) within the membrane electrode assembly (MEA) [2]. The GDL is responsible for distributing the reactant gases from the flow field towards the catalyst layer as well as removing reaction products from the catalyst layer to the flow fields. For example, at the cathode, the electrochemical reaction of oxygen ions with protons and excess electrons yields water and heat, which must be removed through the GDL to the flow field. The removal of water through the GDL can lead to blocked pores in the GDL [2], thereby restricting the reactants’ gas flow towards the catalyst layer causing mass transport losses. GDL design is crucial towards improving the performance of PEFCs, especially at high current densities, such that it minimizes these transport losses. Additionally, removal of the excess heat generated at the cathode catalyst layer through the GDL indicates that the GDL thermal conductivity (k) plays a crucial role affecting the temperature distribution within the MEA [3].In this work, two GDLs varying in thermal conductivity were selected and assembled in MEAs which were then imaged in-operando using X-ray tomographic microscopy [4]. In-Operando imaging allowed the evaluation of the liquid water distribution at steady state over a range of operational conditions such as temperature and current density. Water distribution results for a range of current densities will be presented for selected cell temperatures between 40 and 70 °C. For GDL I with the lower thermal conductivity, the channels are completely dry at 40 °C. For GDL II with the higher thermal conductivity, a wet-dry transition was observed in between 50 and 70°C. High saturations were observed in both the channel and the land regions at 50 °C, while at 70 °C the channels appear to be dry with liquid water only being present under the lands (see Figure 1). These results provide experimental evidence of a major influence of GDL thermal conductivity on liquid water distribution and overall water management in fuel cells. Keywords – operando, X-ray tomographic microscopy, GDL, water visualization Acknowledgement Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada, Ballard Power Systems, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, and Canada Research Chairs.

Impact of GDL Hole on Chemo-Mechanical Membrane Degradation Investigated by 4D in-Situ Visualization

Membrane electrode assembly (MEA) is the core unit of a fuel cell system, which is composed of proton exchange membrane (PEM), sandwiched on both sides by catalyst layers (CLs) and gas diffusion layers (GDLs). The membrane is subjected to various chemical and mechanical stresses during fuel cell operation, and these stresses will cause membrane degradation over time. Also, the interaction between membrane and other fuel cell components such as CLs and GDLs contributes uncertainty to the membrane degradation process. Previous morphological studies [1] on CLs and GDLs discovered common non-uniform features in these materials such as clusters, sags, cracks, and holes. In addition, such features could also appear during the MEAs assembly [1] process. Previous membrane degradation study discovered buckling driven membrane failure [2], which is strongly related to CL or GDL sags, cracks, and holes. Additionally, impinging driven membrane failure was also reported [2], which is caused by clusters and peaks on CL or GDL surfaces. Models were also developed to understand the mechanism of mechanical membrane degradation related to buckling. For instance, Ramani et al. [2] created a model to simulate membrane buckling into GDL surface pores, and identified stress concentration at the buckling center as the root cause of crack formation. Comparing MEAs made with high and low surface roughness GDLs, it was confirmed that GDL with low surface roughness has significant mitigatory impact on mechanical membrane durability. However, to the authors’ best knowledge, the level of impact of such non-uniform features under combined chemo-mechanical degradation, which is the most common form of membrane degradation during regular fuel cell operation, has not yet been reported.In this work, the objective is to understand the specific impacts of GDL holes as they relate or contribute to the combined chemo-mechanical membrane degradation mechanism and associated membrane durability in polymer electrolyte fuel cells. The study was carried out using a four dimensional (three spatial dimensions plus one temporal dimension) in-situ methodology achieved through X-ray computed tomography (XCT) visualization [3], and the MEAs were made of GORE-SELECT® membrane, Pt based CLs, and AvCarb® GDLs with smooth and crack free microporous layer (MPL). Through-thickness circular GDL holes were introduced with multiple controlled sizes at multiple strategic locations, on anode or cathode GDL. The MEAs were custom designed small scale MEAs with 0.39 cm2 active area for in-situ XCT visualization, and the cells were subjected to a custom accelerated stress test (AST) protocol imparting combined chemo-mechanical stresses in an alternating pattern [3]. The graphite endplates had narrower flow field compared to previously used ones [3], which can reduce membrane degradation rate and better deliver compressive stress to the MEA. A baseline MEA without GDL hole was first tested, with only minor membrane thinning observed. For the GDL hole MEAs, it was discovered that smaller holes were more impactful on membrane durability than larger holes. Among the three selected hole sizes (2.0, 0.5, and 0.2 mm2), through-plane membrane cracks were only observed under the smallest holes, both at the hole center and edge, which are the two stress concentration locations. On the CL surface, cracks were observed at the GDL hole center as a crack network, and along the hole edge, as indicated in the figure. Although the GDL holes are expected to mainly alter mechanical membrane degradation, it was discovered that MEAs with through-plane membrane cracks also had higher membrane thinning rate compared to the baseline. However, the non-uniformity MEAs without through-plane membrane cracks had similar membrane thinning rate as the baseline test. Therefore, the through-plane membrane cracks likely elevated chemical stressors as well; hypothetically, through increased gas crossover. The AST results suggest that GDL holes can be harmful to membrane chemo-mechanical degradation and the level of severity depends on their size and location. Keywords: fuel cell; membrane durability; gas diffusion layer defect; mechanical degradation; chemical degradation; X-ray computed tomography Acknowledgements: This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, Ballard Power Systems, and W.L. Gore & Associates. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program.

Impact of Reinforced Polymer Electrolyte Membrane Scratch on Fuel Cell Durability Using 4D X-Ray Computed Tomography Technique

PEMFCs, or Polymer Electrolyte Membrane Fuel Cells, can be used in both stationary power and transportation applications and are promising for use in heavy duty electric vehicles due to their high energy density, ability to be refueled quickly, and extended range, which are key challenges for battery-powered vehicles [1]. Despite these advantages, there are still obstacles preventing the widespread commercialization of PEMFCs, one of which is production cost [2]. To reduce manufacturing costs, it is imperative to ensure that quality control rejects and scraps are minimized. Moreover, enhancing component integration defect detection would ensure the durability of the fuel cell and enhance its operational lifetime. However, robust quality control requires a thorough understanding of potential non-uniformities and their effects on fuel cell performance and operational degradation.Non-uniformities of the membrane electrolyte assembly (MEA) can result in durability issues by damaging the membrane and making it more vulnerable to mechanical and chemical stress during the operation [3]. Several studies have been done on cation contamination and membrane pinholes and their effect on fuel cell performance and durability [4,5] but little attention has been paid to other types of non-uniformities such as membrane scratches and foreign particles, which may also conceivably affect durability [6]. By implementing 4D in-situ X-ray computed tomography (XCT) [7,8], the current work aims to track the evolution of scratches that appear on a reinforced membrane surface during fabrication and its specific objective is to determine the impacts of membrane scratches on membrane durability in fuel cells.The study was conducted by using small-scale fuel cells with GORE-SELECT® membranes that were intentionally scratched with a razor blade, subjecting them to combined chemomechanical membrane accelerated stress test (AST), and monitoring the membrane degradation and evolution of the scratches using 4D-XCT throughout the AST. During the fabrication step, the depth of scratches was regulated by a weak bond between the reinforcement layer and the perfluorosulfonic acid (PFSA) layer, i.e., the scratches did not tear through the reinforcement. Furthermore, the scratches did not adversely impact the initial cell performance. However, during AST operation the evolution of the scratched region was affected by several factors, including the friction between the layers of the membrane electrode assembly, the width of the scratch (Figure 1), the presence of membrane debris, and the extent of membrane strain. Additionally, it was observed that changes in the quality of catalyst layer transfer onto the scratched region can alter the degradation pattern and potentially create a self-mitigating mechanism. These findings may be used to develop more optimized quality control measures for membrane scratches in fuel cell production. Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, Ballard Power Systems, and W.L. Gore & Associates. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program. Keywords: fuel cell; membrane durability; X-ray computed tomography; membrane scratch; manufacturing References [1] Cullen DA, Neyerlin KC, Ahluwalia RK, Mukundan R, More KL, Borup RL, et al. New roads and challenges for fuel cells in heavy-duty transportation. Nat Energy 2021;6:462–74. https://doi.org/10.1038/s41560-021-00775-z.[2] Whiston MM, Azevedo IL, Litster S, Whitefoot KS, Samaras C, Whitacre JF. Expert assessments of the cost and expected future performance of proton exchange membrane fuel cells for vehicles. Proc Natl Acad Sci U S A 2019;116:4899–904.[3] De Bruijn FA, Dam VAT, Janssen GJM. Review: Durability and degradation issues of PEM fuel cell components. Fuel Cells 2008;8:3–22.[4] Tavassoli A, Lim C, Kolodziej J, Lauritzen M, Knights S, Wang GG, et al. Effect of catalyst layer defects on local membrane degradation in polymer electrolyte fuel cells. J Power Sources 2016;322:17–25.[5] Lü W, Liu Z, Wang C, Mao Z, Zhang M. The effects of pinholes on proton exchange membrane fuel cell performance. Int J Energy Res 2011;35:24–30.[6] Kundu S, Fowler MW, Simon LC, Grot S. Morphological features (defects) in fuel cell membrane electrode assemblies. J Power Sources 2006;157:650–6.[7] Ramani D, Singh Y, White RT, Wegener M, Orfino FP, Dutta M, et al. 4D in situ visualization of mechanical degradation evolution in reinforced fuel cell membranes. Int J Hydrogen Energy 2020;45:10089–103.[8] White RT, Eberhardt SH, Singh Y, Haddow T, Dutta M, Orfino FP, et al. Four-dimensional joint visualization of electrode degradation and liquid water distribution inside operating polymer electrolyte fuel cells. Sci Rep 2019;9:1–12. Figure 1

Interactions between Catalyst Layer Degradation and Liquid Water Distribution in Polymer Electrolyte Fuel Cells

Managing liquid water distribution in PEFCs is critical to desirable high power density operation and cell durability [1–3]. Degradation modes such as carbon corrosion in the cathode catalyst layer (CCL) are believed to depend on local humidification [2,4], while the distribution of liquid water may also be influenced by performance drop associated with such degradation [3]. Although some studies have shown the influence of carbon corrosion on liquid water distribution [2,3], the possible reverse effect of liquid water distribution on the CCL degradation requires further investigation.The objective of the present work is to establish a deeper understanding of the cause-and-effect interactions between CCL degradation and liquid water distribution. This is achieved experimentally by carrying out voltage-cycling accelerated stress tests (ASTs) on fuel cells which differ only in the constituent gas diffusion layers (GDLs); namely, SGL 22 BB and a proprietary Avcarb. Three-dimensional X-ray microscopy is used to observe both degradation effects and liquid water distribution at different stages of the ASTs. A relatively rapid operando two-dimensional visualization technique [5] was also used to investigate the differences in liquid water distribution between the two GDLs. The fuel cells imaged are analyzed and exhibit different liquid water distributions, whereby the Avcarb exhibits a higher liquid water condensation close to the CCL, compared to the SGL. Supported by model results, this difference in liquid water distribution is shown to be attributable to the different transport properties of the GDLs. The degradation results, such as the CCL thickness (Fig. 1) show that the Avcarb cell experiences a faster CCL degradation than the SGL cell. Furthermore, the Avcarb liquid water distribution is seen to change with increasing AST cycles in a manner indicating higher vapour phase removal. These results provide insights for GDL design consideration, showing that GDL transport properties may influence liquid water distribution at the electrode with important implications for CCL durability. Acknowledgement Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada,Ballard Power Systems, Canada Foundation for Innovation, British Columbia Knowledge Development Fund,and Canada Research Chairs.

Fast Continuous and Integer L-Shaped Heuristics Through Supervised Learning

We propose a methodology at the nexus of operations research and machine learning (ML) leveraging generic approximators available from ML to accelerate the solution of mixed-integer linear two-stage stochastic programs. We aim at solving problems where the second stage is demanding. Our core idea is to gain large reductions in online solution time, while incurring small reductions in first-stage solution accuracy by substituting the exact second-stage solutions with fast, yet accurate, supervised ML predictions. This upfront investment in ML would be justified when similar problems are solved repeatedly over time—for example, in transport planning related to fleet management, routing, and container yard management. Our numerical results focus on the problem class seminally addressed with the integer and continuous L-shaped cuts. Our extensive empirical analysis is grounded in standardized families of problems derived from stochastic server location (SSLP) and stochastic multi-knapsack (SMKP) problems available in the literature. The proposed method can solve the hardest instances of SSLP in less than 9% of the time it takes the state-of-the-art exact method, and in the case of SMKP, the same figure is 20%. Average optimality gaps are, in most cases, less than 0.1%. History: Accepted by Alice Smith, Area Editor (for this paper) for Design and Analysis of Algorithms–Discrete. Funding: Financial support from the Institut de Valorisation des Données (IVADO) Fundamental Research Project Grants [project entitled “Machine Learning for (Discrete) Optimization”]; Canada Research Chairs; the Natural Sciences and Engineering Research Council of Canada [Collaborative Research and Development Grant CRD-477938-14]; and the Canadian National Railway Company Chair in Optimization of Railway Operations at Université de Montréal is gratefully acknowledged. E. Frejinger holds a Canada Research Chair. Computations were made on the supercomputer Béluga, managed by Calcul Québec and Digital Research Alliance of Canada. The operation of this supercomputer is funded by the Canada Foundation for Innovation; the Ministère de l’Économie, de la Science et de l’Innovation du Québec; and the Fonds de Recherche du Québec – Nature et Technologies.

246-LB: Stimulation of Hepatic Lipid Secretion by Glucocorticoid Action in the Nucleus of the Solitary Tract

Dysregulated lipid metabolism is a characteristic of diabetes, insulin resistance, and obesity. Increased glucocorticoid (GC) levels and/or action is associated with elevated levels of circulating triglyceride (TG)-rich very low-density lipoproteins (VLDL-TGs). Lipid metabolism is heavily affected by GCs via its direct actions on peripheral organs, e.g. liver, adipose tissue. However, how GCs modulate hepatic VLDL-TG secretion via their actions in the brain is less known. The nucleus of the solitary tract (NTS) in the hindbrain is responsive to various hormones and is an important region involved in whole-body metabolism. Here, we aimed to assess how GC action in the NTS affects hepatic TG secretion and hypothesized that GC receptor (GR) agonism in the NTS stimulates hepatic TG secretion. Sprague-Dawley rats underwent stereotaxic NTS bilateral cannulation and vascular catheterizations to enable simultaneous direct NTS infusions, intravenous injections, and blood sampling. Hepatic TG secretion rates were measured in 10h-fasted rats after intravenous poloxamer injection with concurrent NTS infusions. NTS GC infusion stimulated TG secretion compared to NTS vehicle controls, but this effect was negated with pharmacological and genetic GR antagonism, suggesting that NTS GCs are mediated via its receptor. The NTS GC-induced increase in VLDL-TG was not associated with changes in liver lipogenic gene expression and protein levels or plasma ApoB48/100. However, plasma FFAs were increased in NTS GC infused rats, and this was associated with increased pHSL:HSL protein levels in white adipose tissue. We herein provide evidence that acute GC action in the NTS stimulates hepatic VLDL-TG secretion and affects adipose tissue lipid metabolism. Increased circulating FFA availability may contribute to the hyperlipidemic effects of NTS GCs. Future studies to assess the role of NTS GC action in diabetic and obesity-related metabolic disease dyslipidemic models are warranted. Disclosure B. Vasilev: None. M. S. Grewal: None. B. Lum: None. J. T. Yue: None. Funding Natural Sciences and Engineering Research Council of Canada (RGPIN-2016-06657); Canada Foundation for Innovation (37267); Canada Research Chairs Tier 2 in Brain Regulation of Metabolism

245-LB: Glucagon Infusion into the Mediobasal Hypothalamus Lowers Hepatic Triglyceride Secretion

Diabetes and obesity are associated with dysregulated liver lipid metabolism. Glucagon has an essential role in lipid metabolism, in addition to regulating glucose homeostasis. The brain is a key coordinator of whole-body metabolism. Glucagon signalling in the mediobasal hypothalamus (MBH), a forebrain region that senses hormones and nutrients to regulate metabolism, lowers hepatic glucose production and appetite. However, whether glucagon action in the MBH affects lipid homeostasis in healthy and high-fat diet (HFD)-fed animals remains unknown. We assessed glucagon signaling in the MBH in regulating hepatic TG secretion in chow-fed normolipidemic and HFD-induced hyperlipidemic rats. Stereotaxic MBH cannulation and vascular catheterizations in Sprague-Dawley rats allowed for direct MBH infusions, intravenous (IV) injections, and blood sampling. Plasma TGs were measured in 10h-fasted rats after IV poloxamer injection with concurrent MBH infusions. MBH glucagon decreased TG secretion compared to MBH vehicle control animals. This hypothalamic effect of glucagon was blocked by a simultaneous MBH co-infusion of an antagonist to the glucagon receptor (GCGR) and by protein kinase A (PKA) inhibition in the MBH in chow-fed rats. Direct MBH infusion of a PKA activator recapitulated the TG-lowering effects of MBH glucagon. Together, this suggests that MBH glucagon signals via a MBH GCGR-PKA pathway. Interestingly, both MBH glucagon and MBH PKA activation lowered TG secretion and plasma FFAs in HFD-induced hyperlipidemic animals. However, MBH glucagon did not affect hepatic TG content or liver lipogenic protein levels of MTP, FAS, or pACC:ACC of RC and HFD rats compared to their MBH vehicle controls. We demonstrate that hypothalamic glucagon modulates hepatic TG secretion via a MBH GCGR-PKA signalling pathway, and activating MBH glucagon signalling improves lipid metabolism in hyperlipidemic rats. These findings may provide therapeutic insight on lowering lipids in hyperlipidemia. Disclosure M. S. Grewal: None. B. Vasilev: None. C. M. Soltys: None. B. Lum: None. J. T. Yue: None. Funding Canadian Institutes of Health Research (PJT-378765); Canada Foundation for Innovation (37267); Canada Research Chairs Tier 2 in Brain Regulation of Metabolism

Whole Genome Sequencing to Resolve the Genomic Architecture of Cerebral Palsy in a Canadian Cohort (P13-9.003)

Whole Genome Sequencing to Resolve the Genomic Architecture of Cerebral Palsy in a Canadian Cohort (P13-9.003)

Network Migration Problem: A Hybrid Logic-Based Benders Decomposition Approach

Telecommunication networks frequently face technological advancements and need to upgrade their infrastructure. Adapting legacy networks to the latest technology requires synchronized technicians responsible for migrating the equipment. The goal of the network migration problem is to find an optimal plan for this process. This is a defining step in the customer acquisition of telecommunications service suppliers, and its outcome directly impacts the network owners’ purchasing behavior. We propose the first exact method for the network migration problem, a logic-based Benders decomposition approach that benefits from a hybrid constraint programming–based column generation in its master problem and a constraint programming model in its subproblem. This integrated solution technique is applicable to any integer programming problem with similar structure, most notably the vehicle routing problem with node synchronization constraints. Comprehensive evaluation of our method over instances based on six real networks demonstrates the computational efficiency of the algorithm in obtaining quality solutions. We also show the merit of each incorporated optimization paradigm in achieving this performance. History: Accepted by David Alderson, Area Editor for Network Optimization: Algorithms & Applications. Funding: This work was supported by Mitacs. SciNet is funded by the Canada Foundation for Innovation, the Government of Ontario, Ontario Research Fund–Research Excellence, and the University of Toronto. Supplemental Material: The e-companion is available at https://doi.org/10.1287/ijoc.2023.1280 .

Quality Implications of Foreign Metallic Particles in the Membrane Electrode Assembly of a Fuel Cell

Hydrogen-based polymer electrolyte membrane fuel cells (PEMFCs) are advantageous in terms of high efficiency, zero emissions, and low-temperature operation in both stationary and transportation sectors. Recently, efforts to reduce the cost by developing novel materials used in the membrane electrode assembly (MEA) and its design are underway. Besides the materials, the other factor that could contribute to cost reduction is the high volume production of MEA components with a high yield1. Additionally, during MEA assembly, certain abnormal process conditions or external contaminants may negatively affect the quality of the MEA and its compatibility with scalable high-volume manufacturing. The durability of the perfluorosulfonic acid (PFSA) ion exchange membrane is a major concern for the fuel cell industry, especially under Fenton’s cations such as Fe2+ 2–5.Stainless steel instruments used during the production of catalyst coated membranes (CCMs) may be considered as a possible source contributor of contamination. Micron sized metallic particles of SS316L (or Fe) could attach themselves on to the membrane during fabrication; thus, potentially cause MEA structural damage by perforation, rupture, or electrode delamination. Additionally to structural damage, there is also a possibility that Fe2+ cations leaching from metal corrosion would reduce the membrane proton conductivity, cause backbone chain scission, etc2,6. Whereas the presence of cations has been studied extensively in ex-situ Fenton’s reagent testing of ion-exchanged membranes, controlling, and understanding the role of such cations in the in-situ fuel cell environment is much more challenging. In such an instance, membrane thinning and degradation are anticipated due to the presence of cations which act as a catalyst for radical generation during fuel cell operation6; therefore, it is essential to understand the effect of such metallic particles on the membrane and by extension, improving the fundamental understanding of the effects of various irregular features and foreign contaminants is desirable7,8. The present work focuses on understanding the effect of unintended solid metallic particles in the MEA during and after the conditioning phase of a fuel cell. Stainless steel 316L (SS316L) and pure iron (Fe) particles are located conveniently at the interface of the cathode catalyst layer (CCL) and membrane (M) inside an MEA using a robust and controlled method. During the conditioning phase, the MEA is subjected to a sequential order of air starves, cyclic voltammetry, and constant current hold procedures. After each conditioning procedure, cell imaging is performed using the X-ray computed tomography (XCT) method, which has been proven to provide relevant information without damaging the integrity of the fuel cell9,10. Figure 1(a) &(c) shows the position of SS316L and Fe 50µm particles, respectively located at the CCL/M interface before conditioning, as originally planned. Initializing the air starve cycles, the MEAs containing particles indicates that the SS316L-50µm remains intact, as seen in Figure 1(c), and the Fe-50µm tends to dissolve and leave behind a void directly exposing the membrane as shown in Figure 1(d). The dissolution of Fe particles also leaves behind an ion concentration of more than 50 ppm in the active area. It is believed that Fe2+ leaches from SS316L corrosion as well; however, the process is delayed by the native oxide layer formation on its surface and the concentration of Fe2+ is lower. Therefore, it is important to know the response of such particles when conditioning an MEA so that better quality control processes can be identified prior to fuel cell assembly. Acknowledgments This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, Ballard Power Systems, and W.L. Gore & Associates. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program. References G. Bender, W. Felt, and M. Ulsh, J. Power Sources, 253, 224–229 (2014) http://dx.doi.org/10.1016/j.jpowsour.2013.12.045.J. G. Goodwin, K. Hongsirikarn, S. Greenway, and S. Creager, J. Power Sources, 195, 7213–7220 (2010) http://dx.doi.org/10.1016/j.jpowsour.2010.05.005.J. Qi et al., J. Power Sources, 286, 18–24 (2015) http://dx.doi.org/10.1016/j.jpowsour.2015.03.142.A. Tavassoli et al., J. Power Sources, 322, 17–25 (2016) http://dx.doi.org/10.1016/j.jpowsour.2016.05.016.N. Kumar et al., Int. J. Energy Res., 44, 6804–6818 (2020).S. Kundu, L. C. Simon, and M. W. Fowler, Polym. Degrad. Stab., 93, 214–224 (2008).S. Komini Babu et al., J. Electrochem. Soc., 168, 024501 (2021).A. Phillips, M. Ulsh, K. C. Neyerlin, J. Porter, and G. Bender, Int. J. Hydrogen Energy, 43, 6390–6399 (2018) https://doi.org/10.1016/j.ijhydene.2018.02.050.D. Ramani et al., Int. J. Hydrogen Energy, 45, 10089–10103 (2020) https://doi.org/10.1016/j.ijhydene.2020.02.013.Y. Singh et al., J. Power Sources, 412, 224–237 (2019). Figure 1

Visualization of Water Distribution in Fuel Cell Microporous and Catalyst Layers with 3D Nanoscale X-Ray Imaging

As an efficient green energy technology, polymer electrolyte membrane fuel cells (PEMFCs) are rapidly growing in a wide range of applications. Development of high power-density PEMFCs is under investigation to further reduce the overall cost and footprint. However, in such operational conditions, excessive water production could restrict the transport of reactants due to flooding, and subsequently degrade the performance of the PEMFC. This makes the water management a major challenge and necessitates a good understanding of water distribution and transport within the porous layers of the PEMFC [1, 2].3D X-ray computed tomography (XCT) is a strong tool for visualizing the water distribution within porous media. Micro-scale XCT has shown great promise in understanding and visualizing the water behavior within the gas diffusion layer (GDL) substrate region possessing ~10-100 µm pores [3–6]. This resolution, however, is not sufficient to capture water distribution in microporous and catalyst layers (MPL and CL), which are predominantly composed of nano-scale pores. This work aims to explore a method of water capture and visualization within the MPL and CL of a PEMFC using a lab-based nano-resolution XCT (NXCT) with a spatial resolution as high as 50 nm. Benefitting from the non-invasive NXCT imaging technique, the same spot of a dry/wet material has been studied in Zernike phase contrast mode using a custom-built enclosed fixture with high X-ray throughput to maintain a constant humidity (100% RH) over the tomographic acquisition period. Water domains have been identified after alignment of wet and dry image data sets followed by subtraction of dry from wet data set. Figure 1a shows a 2D projection of the MPL on AvCarb GDL after vacuum-assisted water infiltration. A gold microsphere is fixed on the sample within a thin layer of epoxy to allow for accurate identification of the region of interest. Figure 1b shows a selected segmented 2D projection of wet MPL illustrating how liquid water clusters are distributed within the pores and the 3D volume rendering of structural features is displayed in Figure 1c. Using the above-described method, 18% and ~7% volume fraction of liquid water has been identified within the wetted MPL and CL, respectively. The methodology discussed here is a step toward deep understanding of water transport phenomena in CL and MPL materials dictating the strategies for materials design to prevent flooding under high current densities. Moreover, the set-up and methodology can be further optimized to visualize water domains under controlled temperature and relative humidity, to simulate the real operating conditions. Figure 1. XCT imaging of a wet MPL: (a) A radiograph of MPL on AvCarb GDL after vacuum-assisted water infiltration; (b) a selected 2D projection of MPL showing the segmented solid (green), liquid water (blue), and unoccupied pores (black) domains; and (c) 3D volume rendering of a subdomain in the MPL showing the distribution of liquid water within the pores of the structure (voxel size 32 nm in b and c). Acknowledgement Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada, Ballard Power Systems, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, and Canada Research Chairs.

Effect of Test Conditions on Combined Chemo-Mechanical Membrane Degradation in Polymer Electrolyte Membrane Fuel Cells

In dynamic automotive operation, the fuel cell membrane is subjected to various chemical and mechanical stresses [1,2] that cause degradation. Lab scale membrane durability study typically uses accelerated stress testing (AST) [3], which simulates the stresses experienced by the membrane during dynamic automotive operation, but at elevated stress level to generate representative degradation modes in a shorter timeframe. Membrane visualization is important in degradation studies to identify the root cause of failure. Recently, four-dimensional (4D) in-situ visualization by X-ray computed tomography (XCT) [4–8] has facilitated more insight through non-invasive 3D imaging of the MEA. Previous 4D in-situ visualization studies on small scale MEAs have successfully tracked the membrane degradation process under pure chemical [6], pure mechanical [4], and combined chemo-mechanical ASTs [7]. However, the results of such ASTs are sensitive to a variety of parameters related to fuel cell design and operating conditions. For instance, when combined chemo-mechanical membrane stresses were imposed on a small scale MEA [7], the major failure mode observed through 4D in-situ XCT visualization was wide membrane cracks, mainly driven by mechanical stresses, but membrane thinning [9,10], which indicates chemical degradation, was not clearly observed. This failure mode was comparable to field tested or OCV RH cycled cells [11], where membrane cracks appeared without major membrane thinning, but differed substantially from the original AST findings under combined chemical and mechanical stresses where major membrane thinning and fluoride release was observed [9,10]. Therefore, the reasons behind such differences in membrane failure mode warrant further investigation.The objective of this work is to improve the understanding of the effect of various operating conditions on the combined chemo-mechanical membrane degradation mechanism and associated membrane durability in polymer electrolyte fuel cells. Small-scale fuel cells were subjected to a variable AST with alternating chemical and mechanical stress cycles and 4D in-situ XCT visualization [8]. Firstly, the root cause of mechanical stress dominating chemical stress in the previous work [7] was identified as RH being higher than the set point during the chemical phase due to heat loss, which reduced chemical stresses. Consequently, RH was selected as the target variable in the chemical phase to understand its impact on membrane degradation. Subsequent design mitigations were also made on the test hardware so that the cell temperature could be robustly controlled at elevated temperature to support accurate RH control. Meanwhile, the effects of gas flow rate and wet/dry phase duration during the mechanical RH cycling phase were also studied with the assistance of single frequency electrochemical impedance spectroscopy (EIS), which was used to continuously measure high frequency cell resistance (HFR) during RH cycling. Larger HFR swings between wet and dry phases were interpreted to represent larger amplitude of mechanical stress. It was found that reducing the cell RH during the chemical phase and maximizing the HFR swing during the mechanical phase can considerably affect the membrane failure mode and significantly reduce the test lifetime (8 cycles versus 32 cycles) compared to the previous study [7], as indicated in the attached figure. Analysis of selected planar and cross-sectional XCT images indicates that both membrane thinning and cracking were within the field of view investigated at EOL; therefore, the modified AST protocol was more efficient and chemo-mechanically balanced. Again comparing to the published results from Mukundan et al. [11], membrane failure mode in the present work after elevating chemical and mechanical stresses demonstrated combined degradation modes of both pure OCV and pure RH cycling ASTs, where membrane thinning and cracking appeared simultaneously. This result was also more consistent with COCV ASTs done by Lim et al. [9] and Sadeghi et al. [10] using larger scale technical cells. With reduced RH in chemical phase, membrane thinning became more significant. Although the membrane cracks were narrower and fewer in quantity compared to the previous work, they were formed much earlier. Future testing using this more robust and efficient chemo-mechanical degradation AST protocol on selected reinforced membranes is planned. Keywords: fuel cell; membrane durability; accelerated stress test; mechanical degradation; chemical degradation; X-ray computed tomography Acknowledgements: This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, Ballard Power Systems, and W.L. Gore & Associates. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program. Figure 1

Optimized Decal Transfer Method for the Mitigation of Incidental Particle Deposition at the Interface of Proton Exchange Membranes and Catalyst Layers

The membrane electrolyte assembly (MEA) is the key component of a proton exchange membrane fuel cell (PEMFC). The MEA usually consists of gas diffusion layers as outer layers to the inner catalyst coated membrane (CCM). There are various methods to prepare CCMs and decal transfer is currently a common method which was first introduced by Wilson and Gottesfeld [1] and further developed by other researchers [2]–[4]. The initial step of this method is that the catalyst ink is coated onto an intermediate substrate material creating a catalyst coated film (CCF). This step is followed by a transfer of the active layer onto the membrane by hot pressing the membrane and CCF between heated press platens maintained at a specific high temperature for an optimized time and pressure to ensure bonding.Extensive studies on the procedure of decal transfer, substrate material and its preparation, catalyst solvents, etc. have increased the transfer yield of decal transfer to more than 95% [5]. Additionally, in the last decade, industrial development has reduced its cost; however, the total cost for fuel cell manufacturing is still relatively high. One reason for this high production cost is the contamination sensitivity of the CCMs by external particles that can potentially be detrimental to fuel cell operation [6]. This requirement necessitates the use of cleanrooms and quality control equipment to prevent contaminants entering the manufactured components, thus increasing the overall costs. The purpose of the present research is to improve the understanding of the interactions between foreign contaminants and the manufacturing process in the context of MEA production quality. The specific objectives are to i) understand the impact of external particles on the catalyst layer decal transfer process and ii) improve the robustness of the decal transfer method in the presence of external particles.This research investigates the impact of incidental external particles that may be found on the membrane surface or the CCF prior to hot pressing. 60µm Silica microspheres (Si-M) were selected as a representative of solid particles and CCMs with purposely introduced Si-Ms were fabricated and several decal transfer methods and support materials were tested and imaged using the X-ray computed tomography (XCT) technique to analyze the impact on the fuel cell integrity and operation at the presence of the Si-M. While regular decal transfer protocols result in excessive membrane thinning in the presence of these particles, it was observed that by changing the rate of applied pressure and using alternative support materials when transferring the cathode catalyst onto a half-coated membrane, it was possible to reduce membrane thinning under the particles by more than 20% while maintaining transfer quality and cell performance (Fig. 1). In addition, it was observed that although anisotropic mechanical properties of the membrane can adversely affect the CCM topography after the decal transfer, a tuned protocol is able to prevent unwanted deformations and potential stress concentrations. Overall, it is envisioned that the outcomes of this work may enable relaxed quality control measures and manufacturing site cleanroom standards by reducing the potential effects of external particles on MEA production quality. Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, Ballard Power Systems, and W.L. Gore & Associates. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program. Keywords: fuel cell; membrane durability; X-ray computed tomography; decal transfer; manufacturing References Wilson, M. S. & Gottesfeld, S. Thin-film catalyst layers for polymer electrolyte fuel cell electrodes. J. Appl. Electrochem. 22, 1–7 (1992).Shahgaldi, S., Alaefour, I. & Li, X. Impact of manufacturing processes on proton exchange membrane fuel cell performance. Appl. Energy 225, 1022–1032 (2018).Cho, H. J. et al. Development of a novel decal transfer process for fabrication of high-performance and reliable membrane electrode assemblies for PEMFCs. Int. J. Hydrogen Energy 36, 12465–12473 (2011).Thanasilp, S. & Hunsom, M. Effect of MEA fabrication techniques on the cell performance of Pt-Pd/C electrocatalyst for oxygen reduction in PEM fuel cell. Fuel 89, 3847–3852 (2010).Liang, X., Pan, G., Xu, L. & Wang, J. A modified decal method for preparing the membrane electrode assembly of proton exchange membrane fuel cells. Fuel 139, 393–400 (2015).James, B. D., Moton, J. M. & Colella, W. G. Mass Production Cost Estimation of Direct H2 PEM Fuel Cell Systems for Transportation Applications: 2018 Update. ASME 2014 12th Int. Conf. Fuel Cell Sci. Eng. Technol. collocated with ASME 2014 8th Int. Conf. Energy Sustain. V001T07A002–V001T07A002 (2018). Figure 1

Pore-Scale Saturation and Liquid Water Pathways in PEFCs: Insights from Correlative 2D and 3D X-Ray Imaging

Improving the efficiency of polymer electrolyte fuel cells (PEFCs) through high power density operation necessitates liquid water management in the cathode gas diffusion layer (GDL), where liquid water saturation inhibits oxygen diffusivity. To this end, there have been numerous efforts aimed at understanding liquid water transport behaviour to guide GDL design improvements. X-ray imaging of representative in-operando miniaturized PEFC samples has been instrumental to much of recent progress [1–4] in understanding liquid water distribution patterns. Radiographic two-dimensional (2D) images have enabled visualization of liquid water dynamics [3] while three-dimensional (3D) computed tomography images have provided pore-scale information of liquid water saturation states in the GDL [2] and of its transport mechanism [4]. However, how liquid water pathways are formed and the likelihood for preferential pathways remain unclear.In this work, we investigate factors that influence liquid water distribution and pathway definition using correlative rapid 2D and long duration 3D operando X-ray datasets which enable a visualization of liquid water breakthrough dynamics and the corresponding pore-scale interactions in the GDL. The correlated images together with GDL pore structure visualization are used to identify three characteristic pore-scale saturation behaviour with sample regions highlighted in Fig. 1. These regions include locations with restricted liquid water breakthrough, locations with apparent large breakthrough porous pathways where breakthrough liquid water is observable at least in the 2D images, and similarly porous regions where no liquid water breakthrough is observed. It is found that the behaviour shown in the identified regions are strongly linked to local pore-scale structural characteristics and capillary pressure distribution in the GDL. Investigating the 3D virtual GDL from around the microporous layer through to the channel interface, it is shown that liquid water pathways get increasingly defined with a decrease in spatial uniformity towards the flow channels. Pore-scale analysis and observed flow mechanisms show that the defined pathways are locally accessible paths of least capillary resistance dictated by pore radius and associated hydrophobicity. These findings highlight the important role that pore scale topology plays in addition to pore size distribution for future GDL design aimed at improving water management. Keywords— operando, fuel cell, water, pore structure, X-ray imaging Acknowledgments Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada, Ballard Power Systems, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, and Canada Research Chairs.

Effects of Wet Film Application Parameters on the Structure and Performance of Fuel Cell Catalyst Layers Prepared Using Scalable Methods

The use of high-volume manufacturing processes for polymer electrolyte fuel cells is obligatory to bring the manufacturing cost closer to 80USD/kW fuel cell system cost target for long-Haul Trucks [1] and thereby make this technology an economical competitor in the carbon neutral transportation sector. For the membrane electrode assembly, thin film roll good materials are therefore the norm in the industry. On the lab scale however, catalyst layers and catalyst coated membranes (CCMs) are commonly prepared with low throughput multi-sub-layer coating application techniques, such as ultrasonic spray coating. Overall, each catalyst sub-layer is dried before the next sub-layer is applied via another spraying pass, until the desired catalyst loading and therewith the overall catalyst layer is created. This multi-sub-layer coating approach is therefore time consuming.However, to simulate high volume manufacturing at the lab scale, direct layer coating techniques such as film applicator or Mayer bar coating can be utilized. These coating methods are designed to form a one pass final catalyst wet film thickness, similar to what transpires in a continuous high throughput roll to roll (R-2-R) manufacturing process. As opposed to the multi-layer coating techniques, the entire wet thickness of the catalyst layer is dried in one step, which allows greater throughput, but also influences the catalyst layer formation. Because when a catalyst wet film dries, there are forces related to evaporation, diffusion, and sedimentation which influence the distribution of materials and the ultimate catalyst layer structure [2]. Furthermore, catalyst inks used for Mayer-rod, film applicator, and R-2-R coating methods generally have higher solids content than the inks used in spray coating. With the one pass techniques, CCMs are typically fabricated by coating catalyst ink on a decal film, such as polytetrafluoroethylene (PTFE), followed by a hot lamination process, such as decal transfer, of the catalyst layer to the membrane [3]. Due to the interaction of the catalyst ink with the coating substrate and drying process, there are many factors that may influence the quality of the catalyst layer obtained with direct layer coating, considering both ink formulation and coating parameters.To understand the interaction of these influences, we investigate the effects of wet film application parameters on the structure and performance of fuel cell catalyst layers, prepared using scalable methods. The same drying technique of hot air drying is used to obtain a closer representation of the direct layer R-2-R process. In more detail, we are determining the influence of the following factors on the catalyst layer formation, when coated on a PTFE substrate: drying temperature, ionomer-to-carbon support ratio, ink water-to-alcohol ratio, and wet film thickness for each of the two-lab scale direct layer coating methods. Finally, we will discuss the influence of these factors on the catalyst structure via microscopy. As well as performance and electrochemical analysis data, of selected catalyst layers, after being decal transferred onto a membrane and tested.Figure 1 shows an example of the variance of dried catalyst layers coated via two direct coating methods on PTFE substrates from the alterations of Ink Water-to-Alcohol (2-Propanol, 1-Propanol, Ethanol) ratio and coating wet thicknesses. As can be seen the dried catalyst layer structure vary depending on the Ink Water-to-Alcohol ratio, wet thickness and application method used. Acknowledgments This research was supported by the Simon Fraser University Community Trust Endowment Fund, Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, and Canada Research Chairs. Reference [1] Menezes, Mark W., et al. “"US Department of Energy Hydrogen Program Plan” https://www.hydrogen.energy.gov/roadmaps_vision.html (2020)[2] C.M. Cardinal, Y.D. Jung, K.H. Ahn, L.F. Francis, Drying regime maps for particulate coatings, AIChE J. 56 (2010) 2769–2780, https://doi.org/10.1002/ aic.12190.[3] Wei, Zhaoxu, et al., High performance polymer electrolyte membrane fuel cells (PEMFCs) with gradient Pt nanowire cathodes prepared by decal transfer method. International Journal of Hydrogen Energy 40.7 (2015): 3068-3074. Figure 1