SpatiallyResolved Differentiation of Functional Degradationand Perforating Structural Defects in Membrane Electrode AssembliesUsing Diffusion-Cell Coupled DC-SECM

The mass production of polymer electrolyte membrane fuel cells (PEMFCs) requires a reduction in the materials cost. The most costly component of a PEMFC is the membrane electrode assembly (MEA), which contains the precious metal catalyst, platinum. Most related research is focused on cost-reduction of the catalysts, or cost-reduction of the proton exchange membranes (PEMs), and little fundamental research has focused on alternative MEA manufacturing routes as a means of cost-reduction. The MEAs are generally manufactured by decal transfer method. The decal transfer method necessitates coating wider catalyst layers to address alignment tolerance stack up and membrane shrinkage issues at lamination. The costs of existing processes are too high and not scalable and the film quality can be too low for long life. In order to support large scale manufacturing, alternative methods for MEA fabrication are imperative. Available fabrication techniques, such as direct coating by brushing, screen printing, spraying and reactive spray deposition. The direct coating method is more simple and efficient than indirect coating process, decal transfer method and has no risk of uneven and incomplete transfer of catalyst in the catalyst layer (CL). Furthermore, it also produces a higher MEA performance than the conventional decal transfer method due to an easier controllability of the CL thickness as well as a better ionic connection between the CLs and the membrane resulted from a strong attachment of the solvent on the membrane. However, the direct coating of electrode slurry onto the membrane has a critical problem that the membrane has a high tendency to swell or wrinkle with a contact of many solvents in the electrode slurries, which could give rise to the deformation of the CL by fast volume changes of the membrane. Therefore, the optimization of electrode slurry and control of dry process is very important in the direct coating method for the high quality MEA fabrication. Additionally, the effects of direct roll-to-roll coating conditions on the electrode structure and PEMFC performance are poorly understood in many systems. This provides a detailed protocol and materials for the fabrication of reproducible, high-performance, mass-production-scale catalyst coated membranes (CCMs) through implementation of an advance slot-die coating approach of the CLs directly onto PEMs. And this work is to investigate the influence of direct coating parameters on CCM structure and performance, with a particular focus on the slot-die system because of its ability to produce very high performance CCMs at low initial capital cost, particularly at mass-production-scale. The CCMs were analyzed by scanning electron microscopy (SEM) to assess surface morphology, as well as cross-section thickness and porosity. The performance of these CCMs was tested in PEMFCs with standard protocols and their resistance during PEMFC testing was studied by electrochemical impedance spectroscopy. Figure 1. (a) Procedure of direct roll-to-roll coating process, and (b) catalysts coated membrane. Figure 1

An asymmetric membrane electrode assembly for high-performance proton exchange membrane fuel cells

Proton exchange membrane fuel cells (PEMFCs), an electrical device with high energy conversion efficiency and zero-carbon emission, has attracted more attention. The membrane electrode assembly (MEA) is the core component of PEMFCs, mainly including proton exchange membrane (PEM), catalyst layer (CL), microporous layer (MPL) and carbon fiber gas diffusion layer (GDL), which has different structures and significantly affects its power density and durability [1].Generally, MEA is fabricated by catalyst coated electrodes (CCE) and catalyst coated membrane (CCM) methods, which often results in a huge interface resistance between electrode and membrane, the weak adhesion and poor proton and electron transfer, limiting the electrochemical surface area (ECSA) and the power density of PEMFCs [2].To solve this problem, many approaches have been adopted, such as improving sintering temperature for MEA, incorporating a guided cracked layer between cathode and membrane, double-layered catalyst and direct deposition method. Zhao et al prepared an integrated membrane electrode assembly structure to reduce the contact resistance between proton exchange membrane and catalyst layer, which significantly improves the efficiency and stability of water electrolysis [4]. At the same time, Klingele and Breitwieser developed a direct deposition of proton exchange membrane technology to improve high performance and long-term stability of PEMFCs. However, these methods are complex and almost impossible to industrialize [5].In this study, integrated membrane electrode assembly (I-MEA) was prepared by combining casting and doctor blade method techniques. The results show that the casting method is more suitable for fabricating I-MEALT in low-temperature proton exchange membrane fuel cells. The power density of the I-MEALT cell is increased by 18% compared with that of the conventional MEALT (Fig. 1). The doctor blade method is more suitable for preparing I-MEAHT in high-temperature proton exchange membrane fuel cells. The maximum power density of I-MEAHT is increased by about 57% compared with that of the conventional MEAHT. The electrochemical impedance shows that this is mainly attributed to the reduced interface resistance between the electrode and the membrane, which facilitates the proton transfer.

In proton exchange membrane fuel cells (PEMFCs), appropriate water management is critical to achieve high power density operation with increased robustness. Proton exchange membranes (PEMs) require sufficient hydration to fulfill its function as proton conductor, while flooding at the cathode side can hamper the transport of reactant, resulting in deterioration of cell operation. Liquid water transport and accumulation should be affected by materials impregnated in membrane electrode assemblies (MEAs) and this causes variation of cell performance. This motivated us to investigate effects of impregnated materials in MEAs on liquid water accumulation behaviors and resultant cell performance. For this purpose, soft X-ray radiography has been proof it is a powerful incitement for observing liquid water in PEMFCs because of the high spatial and temporal resolution. [1-5]In this study, we focused our attention on micro porous layers (MPLs) with vapor growth carbon fiber (VGCF, Unitetek international co. LTD, Taiwan) impregnated in MEA, because VGCF-modified MPLs have been shown for better cell performance especially in high current density operation, suggesting an improvement on liquid water transport [6]. We first examined polarization curves of two types of MEAs with or without VGCF in MPL. In Fig.1, we observed better cell performance with a MEA with VGCF-modified MPL than those with a conventional MEA without VGCF. In the experiment, we fabricated VGCF MPL coated on gas diffusion substrate (SIGRACET® 24BA). We also used commercial gas diffusion layer (SIGRACET® 24BC) for comparison. In both MEAs, we fabricated catalyst coated membranes (CCMs) by decal transfer method. Nafion® 212 had been selected as the membrane and the same batch of catalyst layer with 0.27mgPt cm-2 loading had been used. The hydrogen and air were fed at 200mL min-1 and 500mL min-1 for a 5cm-2 (23 mm x 23 mm) active area normal cell, respectively. The channel width and depth were 1.0 and 1.0 mm. The rib-to-channel ratio was 1 for normal cell. For a X-ray cell (0.03cm-2, 1 mm x 3 mm), hydrogen and air were both fed at 15mL min-1. The channel width and depth were 0.5 and 0.5 mm. The rib-to-channel ratio was 1 for X-ray cell. Cell operating temperature was set at 80°C and relative humidity of the reactants was kept at 92%. In situ visualization of liquid water distribution in both MEAs by soft X-ray radiography clearly shows their difference as shown in Fig.2. Form the original image Fig.2 (a) and (b), we can found VGCF sample (Fig.2(b)) was difficult to recognize the MPL. The one of the reason is the MPL infiltrate into gas diffusion substrate and another reason is the VGCF MPL maybe has high porosity thus it didn’t absorb much soft X-ray cause to similar intensity of GDL and VGCF-MPL. In both cases (Fig.2(c) and (d)), liquid water was observed under the rib, however, for VGCF-modified MPL at 0.7A cm-2 (Fig.2(d)), less spatially-dispersed liquid water was observed under the rib, while liquid water closed to the catalyst layer was identified in the conventional MEA (Fig.2(c)). At high current density operation (1.2A cm-2), liquid water in the MEA with VGCF was still accumulated closed to the rib. These observations by soft X-ray radiography indicate that VGCF-MPL plays a role to guide liquid water removal in MEAs, which resulted in better cell performance, although physicochemical properties of VGCF-MPL should be unveiled in the future.This work has been supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

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

Polymer electrolyte membrane fuel cells (PEMFCs) show great promise for their applications in electric vehicles. Most studies on PEMFCs typically use catalyst-coated membranes (CCMs); however, gas-diffusion-electrodes (GDEs) offer advantages for large-scale manufacturing with roll-to-roll coating systems. Additional procedures including hot-pressing and coating a thin ionomer overlayer are necessary in the fabrication process of GDE-based membrane electrode assemblies (MEAs) to improve the otherwise poor catalyst layer/membrane interface.1,2 However, these procedures may also introduce potential irregularities and/or defects, especially when thin membranes are used. Limited understanding exists regarding if and to what extent such irregularities impact PEMFC performance and lifetime.In this study, NREL’s custom fuel cell hardware that enables quasi in-situ infrared (IR) thermography studies3 was utilized to visualize spatial hydrogen crossover in GDE-based MEAs to identify and locate Nafion membrane irregularities. The MEA cross-sectional structure of the membrane irregularity was investigated by scanning electron microscopy (SEM) imaging. The impact of membrane irregularities on open-circuit voltage (OCV), hydrogen crossover and PEMFC initial H2/air performance was systematically studied. The effect of micro-porous layer (MPL) surface roughness of gas diffusion media (GDM) on the membrane irregularity formation mechanism was investigated. By employing GDM with a smoother MPL surface and fine tuning the MEA fabrication process, including compression force and hot-pressing temperature, membrane irregularities were successfully mitigated. Furthermore, IR assisted accelerated stress testing (IR-AST) of MEAs containing different amounts of beginning-of-test membrane irregularities was investigated. These membrane irregularities were demonstrated to be seeds of failure points and dramatically shorten the MEA lifetime. Reference: (1) Wang, M.; Medina, S.; Pfeilsticker, J. R.; Pylypenko, S.; Ulsh, M.; Mauger, S. A. Impact of Microporous Layer Roughness on Gas-Diffusion-Electrode-Based Polymer Electrolyte Membrane Fuel Cell Performance. ACS Appl. Energy Mater. 2019, 2 (11), 7757–7761. https://doi.org/10.1021/acsaem.9b01871.(2) Mauger, S. A.; Pfeilsticker, J. R.; Wang, M.; Medina, S.; Yang-Neyerlin, A. C.; Neyerlin, K. C.; Stetson, C.; Pylypenko, S.; Ulsh, M. Fabrication of High-Performance Gas-Diffusion-Electrode Based Membrane-Electrode Assemblies. J. Power Sources 2020, 450, 227581. https://doi.org/https://doi.org/10.1016/j.jpowsour.2019.227581.(3) Phillips, A.; Ulsh, M.; Neyerlin, K. C.; Porter, J.; Bender, G. Impacts of Electrode Coating Irregularities on Polymer Electrolyte Membrane Fuel Cell Lifetime Using Quasi In-Situ Infrared Thermography and Accelerated Stress Testing. Int. J. Hydrogen Energy 2018, 43 (12), 6390–6399. https://doi.org/https://doi.org/10.1016/j.ijhydene.2018.02.050. Figure 1

Introduction: The transport sector is still responsible for a large part (~8Gt/a) of worldwide carbon emission [1]. Polymer Electrolyte Membrane (PEM) Fuel Cells (FCs) are an important emission-free alternative for transport application. Increased commercialization will lead to a large demand of PEM-FCs. As the catalyst coated membrane (CCM) is the heart of every FC, there is need of a lean and cost-effective way to produce CCMs. During CCM production inhomogeneities in the catalyst layer can occur. Several groups worked on understanding the impact of such irregularities on performance and durability [2-6]. In this work we present the results of a systematic experiment investigating the impact of missing CL (anode and cathode) produced via screen printing on the performance and the durability under accelerated stress tests (ASTs). Microscopic and elemental analysis reveal an understanding of the effects observed during the electrochemical characterization. Production of CLs and CCMs: CLs are produced in house. Catalyst ink is prepared to target an ionomer to carbon I/C ratio of 0.8 with a Pt/C ratio of 50 wt%/20 wt% for cathode/anode respectively. The ink is printed on a glass fibre reinforced PTFE (Decal) substrate via screen-printing. Screens are designed such that certain pre-defined geometries and areas of missing CLs are obtained (see attached image). Ten redundant sets of samples are produced featuring the following missing area/geometry variations. Geometries: centre circle, edge circle, line along flow field, line perpendicular to flow field. Missing areas: 4 mm², 16 mm², 64 mm² plus 1 pristine for each set. Each for anode and cathode. For each cathode with missing area a pristine counter electrode is produced and vice versa. Hence all in all around 500 CLs are printed. Cathode/anode target Pt-loadings are 0.25 mg/cm² and 0.04 mg/cm² respectively. After printing on decal substrate six sample sets of CLs are transferred to membranes to produce CCMs. Membrane thickness is 8 µm. Transfer is done by hot-pressing with subsequent subgasket application. Ex-Situ analysis begin of test (BoT): Optical imaging with reproduceable illumination is applied to each CL. X-Ray Fluorescence (XRF) scans of chosen CLs are made to obtain maps of catalyst loading. µXRF-Scans of higher resolution are obtained around the missing areas. Laser scanning microscopy is used to visualize the topology around the missing catalyst areas and the actual missing catalyst area. Scanning electron microscopy (SEM) is applied before and after transfer to visualize CL and CCM cross sections. Attention is paid to layer thicknesses, bending and porosities around missing catalyst area positions. In-situ analysis and aging: In-situ tests are carried out on an in-house developed test bench using Baltic HighAmp zero gradient test cells with 12 cm² active area with H2 at anode and air at cathode side. The produced CCMs are clamped between commercially available gas diffusion layers (GDLs). BoT protocol features Break-In, Cyclovoltammetry (CV), Linear Sweep Voltammetry (LSV), Polarization Curves (U-I) and Electrochemical Impedance Spectroscopy (EIS) at 100 %, 70 % and 40 % relative humidity (RH). A combined mechanical and chemical AST is applied containing both voltage and RH cycling with a total cycling time of 120 h. The AST is chosen such that effects of membrane and electrode degradation become visible. End of Test (EoT) protocol is applied equal to BoT. Ex-situ analysis (EoT): After AST the CCMs are removed from the test bench. Special attention is paid to appearance of CLs and membranes at the position of missing catalyst layers. Resin embedded SEM cross sections are investigated, and cross sections are cut with a focused ion beam (FIB) at the corresponding positions. Highly resolved XRF-maps are obtained at the missing area positions.The results of this study will enable research and industry to make more reliable decisions on inhomogeneities in the catalyst layer, reducing the amount of waste during production.[1] https://www.iea.org/data-and-statistics/charts/global-co2-emissions-by-sector-2019-2022[2] A. Phillips et al. Utilizing a Segmented Fuel Cell to Study the Effects of Electrode Coating Irregularities on PEM Fuel Cell Initial Performance (2017)[3] A. Phillips et al. Impacts of electrode coating irregularities on polymer electrolyte membrane fuel cell lifetime using quasi in-situ infrared thermography and accelerated stress testing (2018)[4] M. Wang et al. Impact of electrode thick spot irregularities on polymer electrolyte membrane fuel cell initial performance (2020)[5] M. Wang et al. Visualization, understanding, and mitigation of process-induced-membrane irregularities in gas diffusion electrode-based polymer electrolyte membrane fuel cells (2021)[6] J. Stoll et al. Impacts of cathode catalyst layer defects on performance and durability in PEM fuel cells (2023) Figure 1

In polymer electrolyte membrane fuel cells (PEMFCs), the membrane electrode assembly (MEA) is the critical component for power production as it is responsible for the electrochemical reactions that convert the fuel to power. The two most common MEA architectures are the catalyst-coated membrane (CCM) and the gas-diffusion electrode (GDE), also referred to as catalyst-coated diffusion media (CCDM). GDEs are of interest for MEA fabrication because under some fabrication and/or operating conditions GDE MEAs have shown improved performance over CCM MEAs.[1] GDEs may also have advantages for roll-to-roll manufacturing due to more robust mechanical properties of the diffusion media and avoidance of membrane swelling during catalyst layer coating. However, the challenge with GDEs is that the catalyst layer/membrane interface is usually inferior to that of CCMs, leading to inferior performance. It has been previously demonstrated that adding a layer of ionomer on top of the GDE catalyst layer can improve the performance of GDE-based MEAs [2], though most studies still show performance inferior to that of CCM-based MEAs. Building on this foundation, our work comprehensively investigated and optimized the fabrication and processing conditions (ionomer overlayer thickness, hot pressing) required to produce high performance GDE-based MEAs with performance comparable to CCM-based MEAs. It was demonstrated that coating a thin ionomer overlayer and then hot pressing the GDEs to the membrane could achieve comparable catalyst activity and air performance to CCM MEAs. Atomic force microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) combined with Energy Dispersive X-Ray spectroscopy( EDS) were employed to investigate the MEA structure including the ionomer overlayer, and interfaces of GDL/catalyst and catalyst/membrane. In situ performance testing was used to assess the impact of MEA fabrication conditions on catalyst utilization and air current-voltage performance. Modeling of electrochemical impedance spectroscopy measurements showed lower catalyst layer resistances in the MEAs with the ionomer overlayer, which was in good agreement with the electrode structure observations. The critical amount of ionomer required to achieve maximized performance was defined. The mechanism for improved performance from the ionomer overlayer and hot pressing were proposed and evidenced: 1) adhering the GDE to the membrane to increase the interfacial contact area of catalyst layer/membrane; and 2) creating a smooth GDE surface with a better contact between GDE and membrane. Moreover, the enhancement of the performance by ionomer overlayer was demonstrated to be highly related to the surface roughness of the gas diffusion media (GDM). The GDM with a smoother surface required less amount of the overlayer ionomer than a GDM with a rougher surface to achieve comparable fuel cell performance.

There are different types of fuel cells, but Polymer Electrolyte Membrane (PEM) Fuel Cells are one of the most promising because they are low-temperature fuel cells. The solid polymer electrolyte has to present transport selectivity, besides the ion conductivity; thus in case of using in fuel cells, the membrane must let the hydrogen ions pass easily and block the passage of fuel (methanol or hydrogen) as well as oxidant molecules (oxygen) which have to be kept separated from each other. In addition to these properties, list other important properties that PEMs must show for high performance: low electronic conductivity, low water transport through diffusion and electro-osmosis, oxidative and hydrolytic stability, good mechanical stability in both dry and hydrated states, low cost, and capability for fabrication into membrane electrode assembly (MEA). This chapter is divided into seven sections. The first section presents some statistical data of publications concerning fuel cell, PEM fuel cells (PEMFC) and PEMFC with zeolites. The second section exhibits some concepts about zeolites types, structure, properties and industrials applications. The third section presents the role of the zeolite properties on the performance of the PEMFC. The fourth section describes the main technique used for producing zeolite/polymer nanocomposite membrane for PEMFCs. The two following sections outline the state of the art of using the zeolite for PEMFC applications, being the fifth and sixth sections dedicated to the synthetic and natural polymers, respectively.

Platinum group metal (PGM) catalysts are the major electrocatalysts for oxygen reduction reaction (ORR) in the polymer electrolyte membrane fuel cells (PEMFCs). However, the cost of PGM catalysts is very high. Particular, the cost becomes unaffordable if the PEMFC is in massive application. In order to remove this cost obstacle of fuel cell commercialization, PGM-free catalysts have been considered as the replacement of PGM catalysts for ORR because of the low cost and the reasonable performance. Fe-C-N complex is the one of the most active centers in PGM-Free catalyst groups. This type of catalyst shows very promising activity in rotation disk electrode (RDE) testing. The half wave potential could reach 0.91 V versus standard hydrogen electrode (SHE). However, in a membrane electrode assembly (MEA), the performance of PGM-Free catalysts is not good enough to replace the PGM catalysts. Since the PGM-free catalysts are so different from the PGM catalysts in terms of catalytic activity, stability, surface conditions, particle size etc, the fabrication of PGM-Free catalyst MEA cannot simply copy the method of making PGM MEA. In addition, the thicknesses of catalyst layers of PFM-free are significantly thicker than that of PGM, for example, 10 times. We proposed a novel method of fabricating PGM-Free catalyst MEA, so that the intrinsic catalyst activity from RDE can be translated into MEA performance. The method is based on the catalyst coated membrane (CCM) method using optimized ionomer to carbon (I/C) ratio and solvent mixture of catalyst ink. Using this method, the PGM-free catalyst MEA achieved the current density 44.9 mA cm-2 at 0.9 ViR-free in H2/O2 and 150 mA cm-2 at 0.8 V in H2/air, which surpassed the performance targets of US Department of Energy (DOE) for PGM-Free catalyst MEA. The property (solvent composition, dispersion of catalyst and ionomer in an ink), structure (pore structure) and the MEA performance have been characterized using ultra-small angle x-ray scattering (USAXS), cyro-TEM, mercury intrusion porosimetry (MIP), SEM/EDAX, RDE and MEA testing. A property-structure-performance relationship has been established.

Platinum group metal (PGM) catalysts are the major electrocatalysts for oxygen reduction reaction (ORR) in the polymer electrolyte membrane fuel cells (PEMFCs). The cost becomes unaffordable if the PEMFC is in massive application. The PGM-Free catalyst shows very promising activity in rotation disk electrode (RDE) testing. The half-wave potential could reach 0.91 V versus standard hydrogen electrode (SHE). However, in a membrane electrode assembly (MEA), the performance of PGM-Free catalysts is not good enough to replace the PGM catalysts. Since the PGM-free catalysts are so different from the PGM catalysts in terms of catalytic activity, stability, surface conditions, particle size, etc., the fabrication of PGM-Free catalyst MEA cannot simply copy the method of making PGM MEA. We proposed a novel method of fabricating PGM-Free catalyst MEA, so that the intrinsic catalyst activity from RDE can be translated into MEA performance. The method is based on the catalyst coated membrane (CCM) method using optimized ionomer to carbon (I/C) ratio and solvent mixture of catalyst ink. Using this method, the PGM-free catalyst MEA achieved the current density 44.9 mA cm-2 at 0.9 V iR-free in H2/O2 and 150 mA cm-2 at 0.8 V in H2/air, which surpassed the performance targets of US Department of Energy (DOE)for PGM-Free catalyst MEA. The property (solvent composition, dispersion of catalyst and ionomer in an ink), structure (pore structure) and the MEA performance have been characterized using, mercury intrusion porosimetry (MIP), MEA testing. A property-structure-performance relationship has been established.

Hydrogen seems to be the most promising energetic vector in order to diversify the sources of energy production. To use this fuel, the Proton-Exchange Membrane Fuel Cell (PEMFC) appears to be one of the most viable and cost effective solution. The materials commonly used in this technology of energy conversion are well known, thus the solid electrolyte is a perfluorinated membrane composed of sulfonic acid groups (-SO3H) in order to permit proton migration through the membrane from one electrode side to the other and the electrodes are composed of platinum-based nanoparticles (NPs) dispersed on a high surface electron conductive substrates. Gas diffusion layer (GDL) is used to support electrode materials and allows the diffusion of the active gas species until the electroactive sites as well as the outlet flux of the generated species. Moreover, to improve the mechanical contacts and the proton migrations between the different elements of the PEMFC, a proton conducting ionomer is added. All these components are assembled in order to obtain Membrane Electrodes Assemblies (MEAs). Strong improvements of PEMFC performances and durability have been achieved with the emergence of new electrode and membrane materials, however due to the characteristics of these innovative components, MEAs conception have still to be improve or adapt in order to deliver the highest performances. In this context, the CEA develops innovative materials for PEMFC application. Thus, low cost membranes based on a hybrid nanocomposite material have been developed. This concept consists on the association of PVDF matrix and hybrid filler composed by silica nanoparticles grafted by sulfonic1 or phosphonic2 acid polymer. The matrix provides electrical insulation, chemical stability and mechanical strength, whereas the proton conductivity properties and the hydration of the membrane are associated to the acid functions. Similar composite material is also developed in order to be used as proton conducting ionomer in the MEA. Other works focus on the elaboration of novel cathodic electrocatalysts by grafting of ionic conducting polymer to the surface of platinum nanoparticles3. The architecture brought by the polymer conducts to an improvement of the proton conduction in the catalyst layer. The work here presented consisted in characterizing the influence of each innovative component of the MEA on the PEMFC performances. The final aim is to elaborate a MEA without Nafion® which is the actual reference as membrane and ionomer. In function of the material properties, MEA conception will be adapted from the most described techniques which are the catalyst-coated membranes (CCM), catalyst-coated backing (CCB) or “Decal method” which is a transfer of the catalytic layer on the membrane by hot pressing. Established MEA will permit to determine the performances brought by the innovative materials under PEMFC conditions as well as the benefit effects of the conception and the impact of the interfaces membrane/electrodes through cyclic voltammetry, electrochemical impedance spectroscopy and polarization measurements. Keywords: Electrochemical characterization, Fuel cell test, Membrane, Catalyst, Ionomer Acknowledgement: The research leading to these results has received funding from the ADEME (French Environment and Energy Management Agency) for its financial support through the MHYEL project. Niepceron F. et al., J. Memb. Science, 338, (2009), 100-110.Souquet-Grumey J. et al., J. Memb. Science, 466, (2014), 200-210.Dru D. et al., ACS Catal., 6, (2016), 6993-7001

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

Introduction Extensive research activities have been carried out on fuel cells worldwide during recent decades, with particular interest and focus on proton-exchange membrane fuel cell (PEMFC) systems.PEMFC is highly relevant for environmental friendly (clean, zero CO2-emission) transport1. This fuel cell type is the most promising candidate for transportation applications due to its relative low operating temperature and fast start-up2, 3. However, the main drawback with PEM fuel cell is a scarcity of platinum (catalyst) and issues related to the durability of the components. Kjelstrup et al.4 introduced a systematic membrane electrode assembly (MEA) design procedure by combining it with an entropy production minimization procedure to optimize the energy efficiency and the catalyst utilization in PEMFC. It was proposed that the concentration polarization that dominates the PEMFC performance at high current density operation can be minimized by cleverly designing the gas and water distribution in the catalyst layer.In this work, two different techniques (template-assisted indentation and pore formers) were employed to fabricate the catalyst layers with uniform pore sizes and homogeneous distribution. Experimental In the former method, the templates with cylindrical pillars depending on the requirement of pore sizes were prepared through photolithography on Si substrates. The Si substrate that holds the template was then hot pressed (at 130 °C, 80 kg cm-2 for 3 minutes) against the cathode side of the catalyst–coated membranes (CCM) (Gore PRIMEA) to obtain uniform channels in the layer.In the second method, monodispersed (synthesized in-house) polystyrene particles with the particle size of 1 µm was used as a pore forming agent. Cathodes were spray coated on Nafion 212 with the catalyst ink containing 70 wt% polystyrene particles, 60 wt% Pt/C (0.12 mg cm-2 Pt) and 17 wt% Nafion. The polystyrenes from the dry catalyst layer were then selectively dissolved in ethyl acetate to form uniform pores.Fuel cell testings were carried out with the catalyst layers formed through these two methods. MEAs with a geometrical area of 5 cm2 were fabricated by sandwiching the CCM between two gas diffusion layers (GDL). The GDLs of type H2315 I2 C6 used in this work were from Freudenberg FCCT. The fuel cells were operated at 60 oC with pure hudrogen and synthetic air. All gases were pre-humidified to 100% RH on the cathode side and 80% RH on the anode side. The flow rates of 1.5/2.0 stoic on the fuel side and 2 stoic on the oxidant side were used. The MEAs were conditioned by pulsing between 0.6 and 0.25 A cm-2 for 24 hours before recording the polarization curve. Results Fig. 1 shows the morphology of Gore MEA after indentation with 4 µm template. It is observed that the formation of the channels is uniform through out the catalyst layer with some debris from the broken template. The polarization curve for the indented MEA is shown in Fig. 2. As expected a noticeable, although minor, difference in the fuel cell performance at high current densities is obtained.Similar differences in the polarization curves are also seen in Fig. 3 where a comparison between a normal and porous MEA is made. Furthermore, the differences in the fuel cell performance are more pronounced here. This could be due to differences in the size of the pores generated in these two catalyst layers (4 µm vs 1 µm); smaller the pore size better the performance. But, these are only preliminary conclusions as the CCMs were made through different methods. Nevertheless, it is identified that the presence of macro pores in the catalyst layers have a positive effect on the fuel cell performance. Further studies such as porosity, pore size distributions, influence of catalyst layer thickness and fuel cell testings are being carried out for better understanding. This work is supported by The Research Council of Norway.

Membrane electrode assemblies (MEAs) are critical components in influencing the electrochemical performance of high-temperature proton exchange membrane fuel cells (HT-PEMFCs). MEA manufacturing processes are mainly divided into the catalyst-coated membrane (CCM) and the catalyst-coated substrate (CCS) methods. For conventional HT-PEMFCs based on phosphoric acid-doped polybenzimidazole (PBI) membranes, the wetting surface and extreme swelling of the PA-doped PBI membranes make the CCM method difficult to apply to the fabrication of MEAs. In this study, by taking advantage of the dry surface and low swelling of a CsH5(PO4)2-doped PBI membrane, an MEA fabricated by the CCM method was compared with an MEA made by the CCS method. Under each temperature condition, the peak power density of the CCM-MEA was higher than that of the CCS-MEA. Furthermore, under humidified gas conditions, an enhancement in the peak power densities was observed for both MEAs, which was attributed to the increase in the conductivity of the electrolyte membrane. The CCM-MEA exhibited a peak power density of 647 mW cm-2 at 200 °C, which was ~16% higher than that of the CCS-MEA. Electrochemical impedance spectroscopy results showed that the CCM-MEA had lower ohmic resistance, which implied that it had better contact between the membrane and catalyst layer.