This work investigates the effects of flow field channel/land width (C/L) ratio on the durability of sulfophenylated poly (phenylene) (sPPP) hydrocarbon-based membranes under chemo-mechanical accelerated stress tests (CM-ASTs). Miniaturized fuel cells with C/L ratios of 4.0, 1.75, and 0.625 are evaluated, supported by electrochemical diagnostics, in-situ single-frequency electrochemical impedance spectroscopy, X-ray computed tomography visualization, and finite element modeling (FEM) to understand degradation mechanisms. At high C/L ratio of 4.0, localized membrane creep under the land limits the longevity of sPPP membranes to 25-50 h. Reducing the C/L ratio to 1.75 and 0.625 extends durability to 310-330 and beyond 600 h, respectively, with the latter cell showing no failure within the test duration. FEM simulations show that lower C/L ratios produce a more uniform stress distribution and reduce the predicted in-plane tensile stresses during RH cycling. Experimentally, lower C/L ratios result in lower membrane dehydration during the prolonged dry phase, mitigating dehydration-stress-driven degradation. A reinforced PFSA membrane tested at C/L ratio of 4.0 exhibits minimal degradation after 600 h due to its lower swelling and sensitivity to hydration changes, and better plate electrode-membrane compatibility. The insights gained herein highlight the importance of flow field design for advancing next-generation fluorine-free fuel cell membranes.

Fuel cells and electrolyzers are often discussed as cornerstones of a future hydrogen economy, yet their long-term sustainability depends on much more than deployment alone. Across material recovery, fluoropolymer recycling, catalyst design, policy, and supply chains, researchers and industry leaders are confronting what true circularity could mean for hydrogen technologies, which is the focus of this Voices piece.

Green hydrogen, produced through water electrolysis, is a key enabler of a low-carbon energy future, and anion exchange membrane electrolyzers (AEMELs) have emerged as a promising technology due to their potential for ultra-low-cost operation. However, achieving low cell voltage at high current densities and maintaining long-term durability remain key AEMEL challenges. To address these issues, most research efforts to date have focused on developing advanced catalysts and membranes. In contrast, the influence of non-material factors, such as cell assembly parameters and operating conditions, remains underexplored, even though they can significantly impact performance. This study investigates how such variables affect AEMEL cell voltage and durability, using commercially available Aemion+(R) membranes and ionomers. Cell assembly parameters, including electrode pre-treatment, membrane thickness, cell hardware, and membrane-electrode assembly (MEA) compression, were evaluated alongside key operating conditions such as flow configuration and heating mode. These parameters are shown to have a significant influence on in-cell phenomena, including electrochemical reactions, water and gas transport, and thermal distribution, as well as critical in-cell properties such as electrode-membrane adhesion, interfacial resistance, electrical conductivity, porosity of the catalyst layer, and polymer swelling or shrinkage. A systematic investigation of these factors showed that their careful optimization can lead to substantial reductions in operating voltage, up to 360 mV at 1.0 A cm-2, without any changes to the catalyst or membrane chemistry. These findings offer new insights into practical strategies for improving AEM electrolyzer performance and highlight the importance of considering engineering and operational design parameters alongside material innovations for commercial viability. Systematic optimization of AEM electrolyzer cell assembly and operating conditions360 mV reduction in operating voltage at 1.0 A cm-2 without changing the catalyst or membranePractical design guidance is provided for scalable AEM electrolyzer performance improvementStrategies can be adopted to create standardized testing conditions for research environments

Although fuel cell operation at intermediate temperatures (e.g., 100-120 degrees C) could potentially reduce cost in heavy-duty transportation, the associated durability challenges need systematic investigation. This work employs ex-situ dynamic mechanical analysis and pressure differential accelerated mechanical stress test together with in-situ fuel cell stability and durability tests to evaluate a sulfo-phenylated poly(phenylene)-based composite membrane for intermediate temperature operation. Compared to wet/dry cycling at 80 degrees C, the membrane shows similar to 50 % lower stress of dehydration and 10x slower crack propagation at 110 degrees C, albeit the risks of creep failure are higher. Fuel cell testing at fixed current density (1.5 A cm(-2)) demonstrates stable performance at 110 degrees C and 34 % RH for 100 h, with no indication of irreversible degradation over longer durations. However, single-frequency electrochemical impedance spectroscopy shows that RH cycling at such temperatures increases the rate and depth of membrane drying. In-situ RH cycling durability tests combined with electrochemical diagnostics and 4D X-ray computed tomography visualization reveals membrane-electrode incompatibility and localized thinning near the edges as failure modes. Hence, fully hydrocarbon-based designs with proper stress concentration management are believed to enhance the durability of next generation fuel cell membranes at intermediate temperatures.

Ionomer-catalyst interactions in polymer electrolyte membrane fuel cells (PEMFCs) are studied for sulfo-phenylated polyphenylene (sPPP) ionomers using CO displacement/stripping and oxygen (O2) transport resistance. We find that sPPP ionomers demonstrate low sulfonic acid group adsorption on platinum (similar to 2%) at both dry and super-saturated humidities. This low ionomer adsorption appears to be driven by the ionomer's strong swelling character with hydration, leading to ionomer detachment from the catalyst surface under these conditions. We also report that O2 transport resistance is lower for electrodes containing sPPP ionomers by a factor of three compared to standard perfluorosulfonic acid (PFSA) ionomers. While PFSA thin films have been shown to rearrange over platinum sites, this effect may be limited in sPPP electrodes due to the rigidity of the backbone.

Ionomr Innovations is a venture-backed, post-revenue startup with major operations in Vancouver, BC, Canada and Boston, MA, USA. Ionomr has commercialized and is manufacturing two families of fully hydrocarbon or ‘PFAS-free’ ion-exchange materials developed by Professor Steven Holdcroft and the Holdcroft Group at Simon Fraser University, and licensed from the university together with closing an initial investment round in 2017. Present production volumes are in the multi-tonne scale, >15 GW equivalent internal coating capability, leading capabilities in both advanced anion-exchange materials and hydrocarbon proton- or cation-exchange materials. Ionomr’s membranes and ionomers materials are broadly applicable to electrochemistry but exhibit the greatest benefit to industry in difficult operational conditions, in particular for the replacement of or enablement of alternative applications to the use of polymeric perfluorosulfonic acids (PFSAs). Initially foci include hydrogen production via water electrolysis, hydrogen fuel cells, CO2 electrolysis, and various applications in hydrometallurgy applicable to the processing of critical minerals and process water treatment / renewal of process fluid. Essential aspects of materials commercialization including proving scalability, scaling up, finding product-market fit, pilots, and success within OEM product design-cycles will be discussed. Electrochemical technologies are notably both essential to effect the clean energy transition and immature as an industrial ecosystem compared to other essential elements (e.g. wind & solar, electronics), and perspectives will be shared regarding the necessary maturation of development and manufacturing.

Proton exchange membrane water electrolysis (PEMWE) is a promising route towards green hydrogen production due to the "zero-gap" cell configuration, leading to higher operational current densities, and nearly instantaneous response to fluctuating power output, making it ideal for coupling with renewable energy sources. The major shortcoming of PEMWE, however, is that it requires the use of expensive components, made from critical raw materials (CRM), to ensure sufficiently low interfacial contact resistance, inhibit passivation/corrosion under highly oxidative potentials at the anode, and meet stringent gas-crossover requirements. Today's commercial PEMWE systems all rely on noble metal catalysts and protective coatings, titanium-based bipolar plates, and perfluorinated sulfonic acid (PFSA)-based membranes. These materials lead to increased costs and have been identified as either critical raw materials (e.g., platinum group metals and titanium) or materials with sustainability/environmental concerns (e.g., PFSAs). Developing low cost, non-toxic, safe-by-design PEMWE stacks is therefore crucial to ensure the future of electrolysis remains affordable, circular, and sustainable. This talk will highlight three novel concepts that address the aforementioned shortcomings of PEMWE: i) using humidified air as the anode feedstock, ii) developing carbon-coated stainless steel bipolar plates, and iii) developing hydrocarbon proton exchange membranes. Conventional PEM electrolyzers typically employ thick PFSA membranes (>125 μm) to minimize hydrogen crossover, however, the thick membrane is a significant source of efficiency loss in PEMWE, limiting high current density operations. The unique operational mode developed at SINTEF, where the anode is supplied with humidified air, allows for the use of membranes as thin as 15 µm. The drastically reduced Ohmic resistance afforded by the thin membrane allows for high-current operation while supplying the anode with humidified air effectively dilutes hydrogen crossover to levels well below the lower explosive limit. Coated stainless steel bipolar plates (BPPs) are a promising alternative to the current generation of Pt-coated Ti BPPs due to their low-cost, favourable mechanical properties, and well-established high throughput manufacturing techniques. Alleima, in collaboration with the National Physical Laboratory (NPL), have demonstrated that carbon-coated 316L stainless steel BPPs may be a promising candidate owing to the so-called 'ionic decoupling' effect where the magnitude of the local potential drop from the catalyst layer towards the BPP is dependent on the ionic conductivity of the electrolyte.[1] When the ionic decoupling effect is sufficiently strong, by ensuring the use of highly resistive Type I water feed and an appropriate porous transport layer, the BPP experiences a constant potential of ~1 V during electrolyser operation. This is within the stability window of the carbon coating. Hydrocarbon-based membranes have been considered as alternatives to the current PFSA-based membranes in PEMWE as they alleviate environmental concerns; can be synthesized using inexpensive, readily available precursors; and have inherently lower gas crossover properties. Ionomr Innovation’s hydrocarbon membrane, Pemion ® , has shown excellent stability after being subjected to the DOE’s mechanical, and combined chemical/mechanical accelerated stress tests.[2] Pemion ® exhibited lifetimes of >40,000 cycles in both, exceeding the DOE target of 20,000 cycles and highlighting its potential as an alternative to PFSA-based membranes in electrochemical energy conversion devices. Combining these innovative concepts, i.e., employing carbon-coated stainless steel bipolar plates and hydrocarbon membranes in the unique air-fed PEMWE cell design, has allowed us to demonstrate high performance PEMWE with reduced critical raw materials. The performance and stability of these innovative PEMWE components have been evaluated using advanced in-situ characterization to deconvolute the specific contributions of each component to the overall degradation. Post-mortem analysis was also used to assess the durability of the carbon-coated BPPs and hydrocarbon membranes. Initial technoeconomic analysis estimates that total stack costs can be reduced by up to 35 % through the implementation of carbon-coated bipolar plates and thin hydrocarbon proton exchange membranes. [1] Becker, H.; Dickinson, E. J. F.; Lu, X.; Bexell, U.; Proch, S.; Moffat, C.; Stenström, M.; Smith, G.; Hinds, G. Energy Environ. Sci. 2022 , 15 , 2508. [2] https://ionomr.com/wp-content/uploads/2023/01/Pemion-Durability-Data_News-Release-and-Technical-Backgrounder_For-Release-Jan19.pdf

Water electrolysis for the production of green hydrogen is a critical technology for the renewable energy transition, representing the most economic and scalable technology for multi-day energy and inter-regional energy storage, and in pure or in derivative forms is essential to the decarbonization of ammonia, steel, ‘heavy duty’ transportation, and other ‘difficult to abate’ sectors. Commercial electrochemical systems overwhelmingly rely on perfluorosulfonic acids (PFSAs). With respect to electrodes, balancing high conductivity with mechanical properties when fully hydrated provides a key design challenge, especially with desired operating conditions increasing beyond 80 °C, as is small molecule perfluoroalkyl acid effluent in operation and end-of-life catalyst recovery. Hydrocarbon (i.e. non-fluorinated / non-PFAS) ionomers based on sulfonated polyphenylene (sPP) chemistries offer high chemical stability in fuel cell conditions, providing some indication of suitability for electrolysis [1] and a relative invariance of critical properties as a function of operating temperature, especially providing the desired tolerance to high temperatures, i.e. ≥90 °C [2] and potentially up to 180 °C. Hydrocarbon ionomers prevalently require high-boiling solvents, which even in minute quantities strongly affects ionomer morphology in electrode deposition and significantly challenges reproducibility [3], but high ion-exchange capacity materials such as Pemion ® provide solubility in desired low-boiling, green solvents. Hydrocarbon electrodes with high ion-exchange capacities must balance conductivity and swelling behaviour with the concomitant reduction in mechanical properties as a function of hydration. While a challenge to decal-tranfer, high Tg/Tα ionomers enable the rational, reproducible structuring of layers within electrodes to address these challenges [4]. Specific to fuel cells, recent in-situ results from sPP suggest the ‘agglomerate model’ for triple-phase boundary may be effected with by a combination of polymer properties and electrode design & deposition. Mechanically sound and electrochemically efficient catalyst layers based on the hydrocarbon ionomer properties will be discussed, with evaluation of ion-exchange capacities, molecular volumes, and swelling properties in addition to interactions with the supported electrocatalyst and porous transport layers and gas-diffusion layers. Alkaline anion-exchange membrane water electrolyzers are also a critical technology for the cost reduction of this green hydrogen, as has been suggested by the European Union’s Clean Hydrogen Joint Undertaking multi-annual work plan cost targets for this technology representing a >35% stack cost reduction at volume. This target is substantiated by the elimination of iridium, titanium, and precious metals-coated components c.f. proton-exchange membrane water electrolysis. Compared to alkaline systems, these can achieve markedly smaller stack sizes and use long-lived nickel coatings for pressurized operation. The presence of a membrane allows for the development of full-area electrodes based on porous transport layers (PTLs) rather than mesh electrodes with majority open area. The requirements for ionomer operating in electrolyte have only recently been due to the development of commercial caustic-stable ionomers such as Aemion ® [5]. Recent guidance in system design suggests a larger role of cathode design in safe and effective operation than previously thought [6]. A comparison of strategies for PTL-based electrode design will be discussed across a range of ionomer properties and deposition strategies, with comparison to ionomer-free designs. [1] M. Adamski, N. Peressin, S. Holdcroft, “On the evolution of sulfonated polyphenylenes as proton exchange membranes for fuel cells,” Mater. Adv. , 2, 4966-5005 (2021). [2] S.H. Mirfarsi, A. Kumar, J. Jeong, M. Adamski, S. McDermid, B. Britton, E. Kjeang, “High-temperature stability of hydrocarbon-based Pemion® proton exchange membranes: A thermo-mechanical stability study,” Int. J. Hydrogen Energy , 50 B, 1507-1522 (2024). [3] A. Strong, B. Britton, D. Edwards, T.J. Peckham, H.F. Lee, W.Y. Huang, S. Holdcroft, “Alcohol-Soluble, Sulfonated Poly(arylene ether)s: Investigation of Hydrocarbon Ionomers for Proton Exchange Membrane Fuel Cell Catalyst Layers,” J. Electrochem. Soc., 162, F513ff. (2015). [4] H. Nguyen, D. Sultanova, P.A. Heizmann, S. Vierrath, M. Breitwieser, “Improving the efficiency of fully hydrocarbonbased proton-exchange membrane fuel cells by ionomer content gradients in cathode catalyst layers,” Mater. Adv., 3, 8460ff (2022). [5] M. Moreno-González, P. Mardle, S. Zhu, B. Gholamkhass, S. Jones, N. Chen, B. Britton, S. Holdcroft, “One year operation of an anion exchange membrane water electrolyzer utilizing Aemion+® membrane: Minimal degradation, low H2 crossover and high efficiency”, J. Power Sources Adv. , 19, 100109 (2023). [6] A. Klinger, O. Strobl, H. Michaels, M. Kress, N. Martic, A. Maltenberger, B. Britton, A. Belletti, R. Eichel, G. Schmid, “Transport of Hydrogen Through Anion Exchange Membranes in Water Electrolysis,” Adv. Mater. Interfaces , In press (2024).

While material innovations in membranes, ionomers, and catalysts have dominated recent research on anion exchange membrane electrolyzers (AEMELs), practical system performance has also been strongly governed by how these materials are integrated and operated in AEMELs. This study explored how other variables, such as porous transport layer structure, electrode pretreatment, membrane thickness, cell hardware, MEA compression, heating mode, and flow configuration, affected AEMEL performance and stability using a commercial Aemion +® AF3 membrane and IrOx/PtNi catalysts. The experiments were conducted under alkaline conditions using 1.0 M KOH feed and focused on isolating the effects of each parameter within a zero-gap electrolyzer setup. Key findings revealed that the selection of the porous transport layer had a significant effect on cell performance and durability. Electrode pretreatment duration and hardware conductivity significantly influenced cell voltage and ohmic resistance. Systematic tuning of MEA compression revealed an optimal range for minimizing voltage decay without inducing gas transport limitations. Operational parameters, such as heating mode (hot plate vs. heating pad) and shifting from dual-feed to anode-only feed configuration, resulted in notable reductions in cell voltage. Combined, these changes enabled a drop of up to 300 mV at 1.0 A/cm² at 60 °C relative to the baseline case. This work demonstrated that carefully selecting and optimizing cell assembly and operational variables lead to substantial performance improvement, offering a pathway to improve AEMEL efficiency in real-world systems.

Proton exchange membrane fuel cells (PEMFCs) in heavy duty vehicles (HDVs) are suitable candidates for carbon-free transportations due to their fast refueling speed and high energy density. Despite the considerable progress in their performance and durability, meeting the cost metrics is still a challenge. One strategy to meet the target cost could be increasing the operating temperature of the fuel cell, which is sought after by both U.S. Department of Energy (DOE) and the New Energy and Industrial Technology Development Organization (NEDO) of Japan [1]. This can significantly reduce the heat exchanger size due to a larger temperature gradient between the system and ambiance, thereby minimizing the total cost and weight. Furthermore, operation at higher temperature facilitates the water management in the system, lowers the risks of electrode poisoning, and enhances the kinetics of the electrochemical reactions which can yield a higher efficiency. The targeted lifetime in normal driving cycles for fuel cell HDVs is 30,000 hr, which is about 4 times of the figure for light duty application. This can be even harder to achieve by increasing the temperature in the heavy-duty application as the degradation mechanisms for the fuel cell components, especially the membrane-electrode assembly (MEA) can be more severe in the temperature range of 100-120 °C compared to the typical PEMFC operating temperatures. In particular, proton exchange membrane (PEM) dehydration at the higher temperatures and lower relative humidity (RH) can increase the Ohmic resistance of the PEM and negatively affect the performance. Furthermore, PEMs exhibit higher gas permeability by increasing the temperature [2], leading to a mixed potential at the electrodes and perhaps exponentially faster rate of hydrogen peroxide and radical species production in the MEA. Conventional perfluorosulfonic acid (PFSA) ionomer PEMs are not designed for temperatures above 100 °C; thus, hydrocarbon-based chemistries such as sulfo-phenylated poly(phenylene) (sPPP) membranes with sterically hindered structures are promising candidates given their superior thermo-mechanical stability [3]. This emerging class of PEMs have also shown favorable performance at such conditions [4]. In this study, a series of ex-situ and in-situ experiments are conducted to design a suitable accelerated stress test (AST) for the emerging hydrocarbon-based fuel cell membranes operating at above 110 °C. To this end, the thermo-mechanical stability of reinforced sPPP-based Pemion ® membrane at both steady-state and dynamic fuel cell operations is analyzed. The stress/strain responses of the membrane during RH cycling at 110 °C and 50% RH was determined by dynamic mechanical analysis, and the hydration/dehydration behavior of the membrane at such condition was studied using the single frequency electrochemical impedance spectroscopy. The 4D X-ray computed tomography (XCT) visualization is also leveraged to elucidate the underlying membrane degradation factors in this study. Figure 1a shows the voltage data under a high current density hold (1.5 A cm -2 ) for the cell operating with catalyst coated Pemion ® membrane at 110 °C and 34% RH. A voltage decay rate of 0.8 µV h -1 is observed during the 100 h of testing, which is likely due to gradual membrane dehydration. An identical trend is shown in the polarization curves ( Figure 1b ) , suggesting a minimal impact of high temperature exposure to membrane stability. Then, the MEAs were subjected to in-situ RH cycling at 110 °C, which is a harsh environment for the membrane given the 4-5 MPa of dehydration stress together with a progressive shrinkage and excessive dehydration of the membrane at 110 °C. As shown in Figure 1c a gradual decay in the performance was observed during the 100 hr (1500 cycles) of testing. Figure 1d also depicts a typical through-plane crack formation in the membrane and electrodes after conducting the AST. Overall, the proposed RH cycling at 110 °C is shown to be an efficient method to investigate the durability of hydrocarbon-based membranes and the new findings obtained from the diagnostics and 4D in-situ visualization of the degradation at this condition are deemed vital to understand and therefore mitigate the present failure modes for the next generation fluorine-free fuel cell membranes. References [1] T. Suzuki, A. Iiyama, N. Kubo, N. Saito, K. Shinohara, S. Shimotori, Y. Sugawara, K. Yamada, ECS Transactions, 92 (2019) 3. [2] M. Giacinti Baschetti, M. Minelli, J. Catalano, G.C. Sarti, International Journal of Hydrogen Energy, 38 (2013) 11973-11982. [3] S.H. Mirfarsi, A. Kumar, J. Jeong, M. Adamski, S. McDermid, B. Britton, E. Kjeang, International Journal of Hydrogen Energy, 50 (2024) 1507-1522. [4] H. Nguyen, F. Lombeck, C. Schwarz, P.A. Heizmann, M. Adamski, H.-F. Lee, B. Britton, S. Holdcroft, S. Vierrath, M. Breitwieser, Sustainable Energy & Fuels, 5 (2021) 3687-3699. Figure 1

The transport of hydrogen through an anion-exchange membrane (AEM) is analyzed by in-line product gas analysis in a large dynamic range (0.1-2 Acm-2) at ambient pressure and correlated to ex situ membrane properties, including volumetric electrolyte uptake, dimensional swelling and diffusivities. A commercial AF3-HWK9-75-X membrane from Ionomr Innovations Inc. is characterized and employed in a 25 cm2 electrolyzer cell, which is operated for 56 h at 60 degrees C in 1 M KOH solution. A model of the membrane is developed, based on a combination of existing theoretical knowledge regarding liquid electrolytes and measured properties of the membrane. The model is employed to quantify the transport parameters through the membrane and the porous electrode. The hydrogen transport through the membrane is 770 times slower than through the electrode. The anion-exchange membrane permits a low degree of gas crossover, with a hydrogen-in-oxygen concentration of 0.37%$0.37\,\%$ at 2 Acm-2. The model indicates that modifying the membrane's microstructure has a more pronounced effect on the gas crossover than altering the swollen thickness. A correlation is derived to estimate the polymer diffusivity from the derived effective diffusivity through the membrane, which allows the determination of preferred membrane properties to lower hydrogen crossover.

In recent years, hydrocarbon ionomers, particularly sulfo-phenylated polyphenylenes (sPPP), have emerged as a potential competitor to established per-fluorinated sulfonic acid (PFSA) ionomers for both membrane and electrode applications. Compared to PFSA materials, sPPP ionomers exhibit much lower equivalent weights (EW), higher resistance to gas diffusion in bulk media, and significantly higher water uptake. Despite the promise of these materials, critical gaps in understanding of ionomer thin film properties and the ionomer-catalyst interface remain a barrier to wider deployment. Our group investigated thin film oxygen diffusion and sulfonic acid group adsorption for both sPPP and Nafion electrodes using oxygen transport resistance and CO displacement and stripping experiments. We report that for sPPP electrodes, local oxygen transport resistance, taken at 80% relative humidity (RH), is approximately one-third that corresponding to Nafion. We hypothesize that this difference is attributable to the bulky ionomer backbone, which may prevent preferential rearrangement over catalyst sites, similar to HOPI ionomers for PFSA. We also report that sPPP ionomers demonstrate a starkly different sulfonic acid group adsorption behavior than Nafion. While Nafion electrodes exhibit increased adsorption as relative humidity decreases, sPPP electrodes instead show a bell-shaped adsorption curve, with very low adsorption (~2%) at both dry and super-saturated conditions. This change in behavior between the ionomers is driven by the displacement charge, which is a result of the adsorbed sulfonic acid moieties being removed from the surface by adsorbing CO. Nafion electrodes exhibit a relatively flat displacement response while sPPP ionomers exhibit a bell-like shape with a maximum at 100% RH. We hypothesize that the cause of this difference for sPPP electrodes is driven by ionomer detachment from the surface of the catalyst at extreme hydration states. This is likely caused by a combination of higher dimensional swelling/shrinking with changing humidity as well as weaker attachment to the surface of the platinum due to the absence of fluorine on the polymer backbone. Further work, including computational studies, will be needed to investigate the ionomer configuration close to the catalyst surface.

Water electrolysis for the production of green hydrogen is a critical technology for the renewable energy transition, representing the most economic and scalable technology for multi-day energy and inter-regional energy storage, and in pure or in derivative forms is essential to the decarbonization of ammonia, steel, ‘heavy duty’ transportation such as commercial trucking, aviation, shipping, remote operations, the replacement of diesel generators, and other ‘difficult to abate’ sectors. Where practical, hydrogen fuel cells represent the most efficient use of hydrogen. Commercial electrochemical systems overwhelmingly rely on perfluorosulfonic acids (PFSAs). With respect to electrodes, balancing high conductivity with mechanical properties when fully hydrated provides a key design challenge, especially with desired operating conditions increasing beyond 80 °C, as is small molecule perfluoroalkyl acid effluent in operation and end-of-life catalyst recovery. Hydrocarbon (i.e. non-fluorinated / non-PFAS) ionomers based on sulfonated polyphenylene (sPP) chemistries offer a potential replacement for both membrane and ionomer in the catalyst layers of PEM systems. Exhibiting high chemical stability in fuel cell conditions provides an indication of suitability for electrolysis [1], as does a relative invariance of critical properties as a function of operating temperature, especially >80 °C [2]. Hydrocarbon ionomers prevalently require high-boiling solvents, which even in minute quantities strongly affect electrode morphology and reproducibility [3], but high ion-exchange capacity materials such as Pemion ® provide solubility in desired low-boiling, green solvents. Hydrocarbon electrodes with high ion-exchange capacities must balance conductivity and swelling behaviour with the concomitant reduction in mechanical properties as a function of hydration. While a challenge to decal-tranfer, high Tg/Tα ionomers enable the rational, reproducible structuring of layers within electrodes to address these challenges [4]. Specific to fuel cells, recent in-situ results from sPP suggest the ‘agglomerate model’ for triple-phase boundary may be effected with by a combination of polymer properties and electrode design & deposition. Mechanically sound and electrochemically efficient catalyst layers based on the hydrocarbon ionomer properties will be discussed, with evaluation of ion-exchange capacities, molecular volumes, and swelling properties in addition to interactions with the supported electrocatalyst and porous transport layers and gas-diffusion layers. Alkaline anion-exchange membrane water electrolyzers are also a critical technology for the cost reduction of this green hydrogen, as has been suggested by the European Union’s Clean Hydrogen Joint Undertaking multi-annual work plan cost targets for this technology representing a >35% stack cost reduction at volume. This target is substantiated by the elimination of iridium, titanium, and precious metals-coated components c.f. proton-exchange membrane water electrolysis. Compared to alkaline systems, these can achieve markedly smaller stack sizes and use long-lived nickel coatings for pressurized operation. The presence of a membrane allows for the development of full-area electrodes based on porous transport layers (PTLs) rather than mesh electrodes. The requirements for ionomer operating in electrolyte have only recently been due to the development of commercial caustic-stable ionomers such as Aemion ® [5], and in particular to the anode suggest balancing electrode cohesion and free volume. Recent guidance in system design suggests a larger role of cathode design in safe and effective operation than previously thought [6]. A comparison of strategies for PTL-based electrode design will be discussed across a range of ionomer properties, catalyst ink processing, and electrode deposition strategies, with comparison to ionomer-free designs. [1] M. Adamski, N. Peressin, S. Holdcroft, “On the evolution of sulfonated polyphenylenes as proton exchange membranes for fuel cells,” Mater. Adv. , 2, 4966-5005 (2021). [2] S.H. Mirfarsi, A. Kumar, J. Jeong, M. Adamski, S. McDermid, B. Britton, E. Kjeang, “High-temperature stability of hydrocarbon-based Pemion ® proton exchange membranes: A thermo-mechanical stability study,” Int. J. Hydrogen Energy , 50 B, 1507-1522 (2024). [3] A. Strong, B. Britton, D. Edwards, T.J. Peckham, H.F. Lee, W.Y. Huang, S. Holdcroft, “Alcohol-Soluble, Sulfonated Poly(arylene ether)s: Investigation of Hydrocarbon Ionomers for Proton Exchange Membrane Fuel Cell Catalyst Layers,” J. Electrochem. Soc., 162, F513ff. (2015). [4] H. Nguyen, D. Sultanova, P.A. Heizmann, S. Vierrath, M. Breitwieser, “Improving the efficiency of fully hydrocarbonbased proton-exchange membrane fuel cells by ionomer content gradients in cathode catalyst layers,” Mater. Adv., 3, 8460ff (2022). [5] M. Moreno-González, P. Mardle, S. Zhu, B. Gholamkhass, S. Jones, N. Chen, B. Britton, S. Holdcroft, “One year operation of an anion exchange membrane water electrolyzer utilizing Aemion+® membrane: Minimal degradation, low H2 crossover and high efficiency”, J. Power Sources Adv. , 19, 100109 (2023). [6] A. Klinger, O. Strobl, H. Michaels, M. Kress, N. Martic, A. Maltenberger, B. Britton, A. Belletti, R. Eichel, G. Schmid, “Transport of Hydrogen Through Anion Exchange Membranes in Water Electrolysis,” Adv. Mater. Interfaces , In press (2024).

This work explores the impacts of ion exchange capacity (IEC) and reinforcement thickness on the mechanical durability of reinforced sulfo-phenylated poly(phenylene)-based Pemion (R) fuel cell membranes. Pressure differential accelerated mechanical stress testing (XP-AMST) is leveraged to rapidly investigate the mechanical durability of reinforced Pemion (R) and a reference reinforced perfluorosulfonic acid (r-PFSA) ionomer membrane. The fatigue lifetime curves obtained from XP-AMST are explained by in-situ fuel cell performance diagnostics and ex-situ tensile, hygral expansion, stress of dehydration, and crack propagation rate measurements. The rigid-rod poly(phenylene) backbone in Pemion (R) membranes yields a high stress of dehydration during the dehydration phase, yet superior mechanical fatigue strength in XP-AMST compared to r-PFSA. The XP-AMST results show that reducing the IEC in Pemion (R) by only 0.3 mmol g(-1) can afford three times longer mechanical durability, similar to 20 % lower stress of dehydration and hygral swelling, and higher flexibility and dimensional stability in the dry and wet phases, respectively. Furthermore, 2 mu m thicker reinforcement yields tougher membranes with suppressed swelling, dehydration stress, and crack propagation rate, improving fatigue longevity. Herein, the importance of tuned IEC and membrane design in the mechanical durability of hydrocarbon-based membranes is highlighted for a viable replacement of incumbent PFSA materials in fuel cells.

The alkaline water electrolyzer (AWE) and proton exchange membrane water electrolyzer (PEMWE) are the two dominant commercial platforms to produce hydrogen through electrolysis. Recent efforts have focused on combining the benefits of the two technologies, leading to the creation of the anion exchange membrane water electrolyzer (AEMWE). AEMWEs operate under high pH conditions, like AWEs, enabling the use of cost-effective materials as cell components and non-noble electrocatalysts. AEMWEs also utilize the same high-performance zero-gap design PEMWEs and also have the ability to operate at high differential pressures. Therefore, AEMWEs offer the opportunity to optimize both cost and performance, out-pacing both incumbent technologies after further development. As the “active” materials in AEMWEs, the anion exchange membranes and ionomers and the catalysts have been widely studied and a number of materials have been proposed and reported on in the literature and throughout the last several ECS meetings. However, such materials are only one piece of the overall puzzle when it comes to the operation of AEMWEs. There are several aspects of cell assembly and operation that go a long way to dictating the performance of an operating cell. Therefore, the overarching goal of this study was to investigate several operational variables for AEMWEs with a known high-quality set of anion-exchange materials, known commercially as Aemion+™ paired with commercially available catalysts – PtNi/C at the cathode and either IrOx or NiFeOx at the anode. For cell assembly, representative variables that were changed were the type of membrane and electrode pre-treatment, gasket thickness, cell torque and membrane thickness. Operationally, temperature, current density and break-in procedure were adjusted. This talk will link each of these variables to the polarization performance and galvanostatic durability

Hydrogen fuel cells are a critical technology for the renewable energy transition, pairing with green hydrogen to represent the most economic and scalable power generation for many applications, in particular ‘heavy duty’ systems such as commercial trucking, aviation, shipping, remote operations such as mining, and the replacement of diesel generators. Perfluorosulfonic acid (PFSA) polymers as membrane and ionomer in the catalyst layer today represent the fundamental building blocks of proton-exchange membrane fuel cells (PEMFCs) and a broad range of electrochemical systems including PEM water electrolyzers (PEMWE). However, potential regulation and liabilities related to the production of environmentally mobile fluorinated materials represent a potential bottleneck to the scaling of these critical systems for the renewable energy economy. Acid-functionalized small molecules that are used as process aides and expelled as degradation products are particularly concerning and warrant direct or indirect replacement by non-fluorinated or ‘hydrocarbon’ chemistries. Sulfonated poly(arylene) ionomers exhibit exemplary stability and a the only presently commercialized material of this category, Pemion®, promises to enable to a long-sought step-change in system-level temperature hitherto limited by the physical properties of PFSAs as well as increase durability due to preferential chemical properties. This presentation highlights the similarities and major divergences of the properties of hydrocarbon PEM Pemion®, comparing the physical and electrochemical properties of an ePTFE-reinforced product PF1-HLF8-15-X with those of hydrocarbon-reinforced membranes of various chemistries and production methods, as well as comparing PFSA- and hydrocarbon-based ionomers. Preliminary sub-scale work determining the structure-property relationships within Pemion® ‘fully hydrocarbon’ systems preliminarily demonstrate industrially relevant performances (i.e. sub-scale peak power densities >1 W/cm²) even in ‘hot and dry’ conditions, with a substantial (>50%) reduction in measured hydrogen permeability. The potential for system impacts of higher operational temperatures, increased liquid permeation, non-annealable electrode structures, and reduced gas permeation will be discussed, and preliminary data including multi-day comparisons with PFSA-based systems at operational temperatures ≥110 °C presented.

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). References [1] S.H. Mirfarsi, M.J. Parnian, S. Rowshanzamir, E. Kjeang, International Journal of Hydrogen Energy, 47 (2022) 13460-13489. [2] R. Singh, P. Sui, K. Wong, E. Kjeang, S. Knights, N. Djilali, Journal of The Electrochemical Society, 165 (2018) F3328. [3] M. Adamski, N. Peressin, S. Holdcroft, Materials Advances, 2 (2021) 4966-5005. [4] M. Adamski, T.J. Skalski, B. Britton, T.J. Peckham, L. Metzler, S. Holdcroft, Angewandte Chemie, 129 (2017) 9186-9189. [5] U.S. Department of Energy, Fuel Cell Technical Team Roadmap U.S. Department of Energy, Fuel Cell Technical Team Roadmap (2017). Figure 1

The rate-limiting factors of intermittent renewable energy deployment are grid interconnection amounts and timelines, and the storage of this energy. Hydrogen offers a solution to both issues, to the former offering the ability to produce a valuable and presently subsidized resource with direct connection before the interconnect to utilize overcapacity or even replacing an interconnect, and to the latter offering the unique ability to cost-effectively be stored geologically, transported between regions, and repurpose natural gas infrastructure. Global electrolysis capacity is projected to increase to >500 GW in 2030 and in excess of 2500 GW in 2050 (IEA Net Zero 2050). Buffering capacity with batteries holds some promise but the simplest and most preferred mode of operation would be for electrolysis to follow energy production directly. However, the two established electrolysis technologies suitable to full direct intermittent renewable pairing have limitations to their effectiveness. Proton-Exchange Membrane Water Electrolysis (PEMWE) are known to exhibits non-linear increases to iridium dissolution while operating greater than 1.6 V, in part due to corrosive environment and in part due to a concentrated volumetric current density resulting in a trade-off of performance and lifetime that limits the economic utility of highly dynamic operation. Alkaline water electrolyzers do not exhibit the same voltage limitations due to the alkaline environment and the whole-electrode activation of the KOH electrolyte, but the nature of the porous separator itself reduces the ability for fully dynamic operation, in particular managing hydrogen flux in ramp-down. Alkaline Anion-Exchange Membrane Water Electrolysis (alkaline AEMWE) offers the potential to combine the ability for highly dynamic operation of PEMWE with the larger potential window for electrode stability of AWE to synergistic effect. In essence, the full use of produced energy, lower capital cost of the technology, and ability to trade efficiency for markedly higher production rate results in a lower levelized cost of hydrogen than is achievable with the other technologies. Technology cost-models associated with both direct connection and ‘peaker’ operation will be presented, towards a fuller understanding of the most economically beneficial renewables pairings and operational modes in advance of the expected gigawatt scaling of this technology later this decade. Further, Alkaline AEMWE Aemion® AF2-HWK8-75-X has been demonstrated in excess of 1 year of operation with some intermittency resulting in no apparent membrane degradation, presenting a baseline for the break-in of commercial electrodes with standard conditions relevant to commercial stacks of 1 M KOH and 70 °C. In this presentation, 1.5 years of data with Aemion® AF3-HWK9-75-X, a next-generation material, and large-area (50 cm²) single-cell data with long-term operation with both NiFeOx and commercial electrodes employing representative modes of intermittency will be shown.

The degradation of proton exchange membrane fuel cells (PEMFCs) stands as a critical determinant in evaluating the robustness of fuel cell systems, crucial for the commercial-scale transition to sustainable energy. For zero-emission vehicles, fuel cell stacks need to demonstrate lifespans exceeding 8,000 (light-duty vehicles) and 30,000 hours (heavy-duty vehicles)[1]. For achieving robust PEMFC systems at commercial scale, it is crucial to precisely understand the degradation pathways to effectively pinpoint and mitigate degradation issues. To achieve this, customized small-scale fuel cell fixtures are utilized for accelerated stress testing (AST) and X-ray computed tomography (XCT) in-situ and ex-situ visualization [2,3]. This approach enables comprehensive analysis of membrane electrode assembly (MEA) aging processes. Our group previously employed this approach to identify chemical, mechanical, and chemo-mechanical degradation mechanisms in commonly used perfluorosulfonic acid (PFSA) ionomer membranes[4,5]. In recent years, transitioning from PFSA membranes to hydrocarbon-based (HC) membranes in PEMFCs has gained significant attention. This shift eliminates fluorinated compounds typically found in PFSA membranes, aligning with sustainability goals, and reducing environmental impact. This transition signifies both technological advancement and innovation, driving forward the quest for efficient, cost-effective, and environmentally friendly energy solutions. Despite their promising characteristics, HC membranes are more susceptible to mechanical degradation than PFSA ones[6], presenting unique compatibility challenges due to their distinct chemical composition. Historically, PEMFC systems intentionally developed and optimized for PFSA may face performance issues and premature failure with HC membranes. This research therefore investigates the unique aspects of HC membrane degradation within a conventional fuel cell design with PFSA ionomer catalyst layers, using 4D in-situ XCT to understand chemo-mechanical degradation, enhancing fuel cell technology. Herein, ZEISS Xradia® 520 Versa micro XCT system was used to visualize samples. Repetitive scans were taken at room temperature in a dry state of the MEA. The first set of MEAs consisted of reinforced HC membranes (Pemion-PF1-HLF8-15-X) of 15 µm thickness, spray-coated with PFSA catalyst ink to form catalyst-coated membranes (CCMs), and assembled with gas diffusion layers (Freudenberg H14C15, 190 µm) featuring smooth and crack-free microporous layer. The AST protocol was custom-designed for chemo-mechanical membrane degradation and included open circuit voltage hold for chemical degradation and relative humidity cycling for mechanical degradation, which were applied consecutively. It has been demonstrated that MEAs undergo dimensional changes during wet-dry AST cycles due to alternating conditions of hydration and dehydration[5,7]. It is apparent from the degraded XCT image (Figures 1a-d) that cracks were initiated and propagated between the membrane and catalyst layers, with cracks prominently visible near agglomerated electrode particles. Differential swelling between the membrane and catalyst layer, compounded by varying rates of expansion or contraction, resulted in magnified mechanical stresses at the membrane-catalyst layer interfaces. The second set of cells consisted of the same reinforced HC membrane assembled with commercial gas diffusion electrodes (GDEs; 0.5 mg/cm² 60% Pt on Vulcan, Sigracet 22 BB, 215 µm). The existence of interfacial voids (Figure 1e) was observed in the pristine sample at both anode and cathode membrane-GDE interfaces, likely due to interfacial adhesion fatigue (IAF)[8]. Uneven compression and interfacial incompatibility during fuel cell assembly results in IAF. When these GDE based MEAs were subjected to wet-dry AST cycles, mechanical stress was induced at the membrane-GDE interfaces[9, 10]. The uneven mechanical stress can aggravate creep propagation in the membrane. Due to creep propagation, membrane thinning at the edges was evident from the XCT images, and resulted in electrode shorting, as shown in Figure 1(f and g). It is believed that constraints during creep failure hindered membrane's return to original thickness after swelling, causing permanent dimensional changes. The combined effects of cyclic dimensional changes and membrane thinning due to the creep mechanism contributed to performance degradation and reduced durability of GDE-based MEAs. Acknowledgements This work was supported by the Natural Sciences and Engineering Research Council of Canada, Ionomr Innovations Inc., Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Pacific Economic Development Canada, and Canada Research Chairs. References C.S. Gittleman et al., Joule, 5 (2021) 1660–1677. Y. Singh et al., J Power Sources, 412 (2019) 224–237. D. Ramani et al., Electrochim Acta, 380 (2021) 138194. Y. Chen et al., J Power Sources, 520 (2022) 230674. Y. Chen et al., J Electrochem Soc, 170 (2023) 114526. S.H. Mirfarsi et al., Int J Hydrogen Energy, 47 (2022) 13460–13489. A. Sadeghi Alavijeh et al., J Power Sources, 427 (2019) 207–214. X. Huang et al., J Polym Sci B Polym Phys, 44 (2006) 2346–2357. V.A. Sethuraman et al., J Electrochem Soc, 155 (2008) B50. S.H. Mirfarsi et al., Int J Hydrogen Energy, 50 (2024) 1507–1522. Figure 1

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). References [1] C.S. Gittleman, H. Jia, E.S. De Castro, C.R. Chisholm, Y.S. Kim, Joule, 5 (2021) 1660-1677. [2] D.W. Shin, M.D. Guiver, Y.M. Lee, Chemical reviews, 117 (2017) 4759-4805. [3] M. Adamski, N. Peressin, S. Holdcroft, Materials Advances, 2 (2021) 4966-5005. [4] S.H. Mirfarsi, A. Karimi, S. Rowshanzamir, M.J. Parnian, Journal of Power Sources, 401 (2018) 73-84. [5] J. Miyake, T. Watanabe, H. Shintani, Y. Sugawara, M. Uchida, K. Miyatake, ACS Materials Au, 1 (2021) 81-88. [6] R. Mukundan, A.M. Baker, A. Kusoglu, P. Beattie, S. Knights, A.Z. Weber, R.L. Borup, Journal of The Electrochemical Society, 165 (2018) F3085. [7] A. Sadeghi Alavijeh, S. Bhattacharya, O. Thomas, C. Chuy, E. Kjeang, Journal of Power Sources Advances, 2 (2020) 100010. Figure 1