Platinum (Pt) is the most active catalyst for oxygen reduction reaction; however, its activity still requires a significant increase to meet the demands of practical applications. To enhance the catalytic activity, alloy catalysts like platinum-cobalt (Pt-Co), are being extensively investigated. However, Co leaching from the Pt-Co alloy remains a significant concern. Evaluating the durability of Pt-Co alloy catalyst is further complicated by variations in Co leaching, which affects both the observed performance and durability. This variability often arises from an overlooked factor: choice of the inactive area of the membrane electrode assembly (MEA) used during the evaluation. This study examines the critical role of membrane inactive area on the performance loss observed during durability testing of Pt-Co alloys. Our findings indicate that a large membrane inactive area reduces the impact of Co leaching on performance and durability, up to 200 mA/cm^2 difference in performance is observed between large and small inactive area MEA at 0.7 V for dry conditions, and more Co is retained in the active area of MEA for smaller inactive areas which is responsible for larger performance losses.

The development of non-fluorinated hydrocarbon ionomer binders for electrochemical devices has garnered significant attention due to growing regulatory restrictions on polyfluoroalkyl substances. However, hydrocarbon binders generally exhibit inferior performance compared to perfluorosulfonic acid binders. This study investigates the key factors limiting the performance of hydrocarbon binders in fuel cells and electrolyzers. Using half-cell experiments with hydrocarbon ionomers and aqueous hydrocarbon sulfonic acids, three primary performance-limiting factors are identified: undesirable adsorption, electrochemical oxidation, and low gas permeability. The study also demonstrates that competitive sulfate adsorption effectively mitigates the negative impacts of ionomer adsorption and electrochemical oxidation. These findings from half-cell experiments align with the single-cell performance of fuel cells employing sulfonated poly(phenylene) and poly(norbornene) ionomers. Ultimately, this study provides critical insights into the design of advanced hydrocarbon ionomers for fuel cells and other electrochemical applications.

Fuel cells are especially attractive as a decarbonization strategy for heavy duty transportation sector. However, the durability and cost of the fuel cell components remains a major barrier for market penetration. Expensive platinum based catalysts, represent a significant portion of this challenge. Therefore, effort to enhance their durability and performance, without increasing the loading, could make a significant advancement towards commercial viability. In this study, we investigated the incorporation of dihydroxyl additive, ellagic acid (EA), in cathode catalyst layers to improve the performance and durability of the catalysts. Our observation revealed that incorporation of EA into cathode catalyst layer led to an increase in mass activity when used with a Pt catalyst supported on either vulcan and high surface area (HSC) carbon support. Increase in the overall conductivity of the catalyst layers due to the hydrophilic nature of the additive could be responsible for improved performance. Decrease in the catalyst activity inhibition by the ionomer adsorption of the platinum surfaces could also result in improved catalytic activity. Further increase in mass activity with the HSC can be achieved by the optimizing the solvent used for ink preparation for enhanced interaction of EA with the platinum inside the pores and not just the surface platinum particles. We also find enhanced durability of both Pt/Vulcan and Pt/HSC catalyst with the chosen additive in accelerated stress tests. The probable reasons for this behavior will be discussed. Acknowledgement This research was supported by the Hydrogen and Fuel Cell Technologies Office (HFTO), Office of Energy Efficiency and Renewable Energy, US Department of Energy (DOE) through the Million Mile Fuel Cell Truck (M2FCT) consortia, technology managers G. Kleen and D. Papageorgopoulos.

Significant effort has been invested previously to understand the effect of temperature and humidity on water uptake, water transport, structure, and proton conductivity of perfluorosulfonic acid (PFSA) ionomer membranes. One of the significant factors influencing the performance and durability of Nafion is its ability to retain and transport water. Water transport in Nafion is a strong function of sorption, ion exchange capacity, and transport properties of the membrane, which in turn, are functions of its structure and morphology. In addition to the operating conditions, pre-treatment conditions, additives, and the presence of cations significantly affect Nafion's morphology. Infrared spectroscopy (IR) is a powerful tool to gain insight into the properties of Nafion structure and properties. FTIR can monitor real-time changes in chemical interactions, molecular motions, and connectivity of ionic channels under varying operating conditions. FTIR has also been used to validate models developed to explain the dynamic behavior of polymer electrolyte membrane fuel cells. The potential of infrared spectroscopy to understand the impact of environmental changes on Nafion structure is immense but remains underutilized. This review provides a comprehensive summary of the assignment of vibrational modes of Nafion in various regions of the spectrum and sheds light on discrepancies concerning the allocation of vibrational modes to specific interactions. Fourier Transform Infrared Spectroscopy is a valuable low-cost easy to use tool that has helped in understanding the structure and properties of Nafion as a function of environmental changes by closely monitoring the changes in vibrational modes of various functional groups in Nafion.

Core-shell nanoparticles in cathode catalyst layers of Polymer Electrolyte Fuel Cells (PEFCs) are a promising class of electrocatalysts that have received considerable attention owing to their high mass activity compared to their single metal counterparts. The nature of its bimetallic design offers a potential range of tunable parameters to improve its stability mediated by the long-range interactions arising from the strain effect. In this work, we reveal the emergence of thermodynamic metastability in the surface energetics at a critical design limit of large core diameter and shell thickness when the elastic strain energy of the electrocatalyst exceeds the energy to form dislocations. The progression of degradation events induces a transition in the metastability front in the catalyst layer which can be attributed to the heterogeneous nature of particle aging. We performed a screening of key candidate core materials and found that negative misfit scenarios such as Nickel (Ni), Copper (Cu), Cobalt (Co), and Palladium (Pd) impart durability against the primary mode of electrochemical dissolution. The positively mismatched structures however exhibit a disparate trend where the strain ramp at high lattice misfits is suppressed mechanistically by exerting a pseudo-compressive force field. Consequently, the critical onset of the nanocatalysts to reach a limiting diameter is governed by the property mismatch between the core and the shell, in terms of the bulk moduli and molar volume. The contrariety in the metastability-durability characteristics stemming from a variation in the initial thickness of the protective Pt skin is further delineated.

Polymer electrolyte membrane fuel cells (PEMFCs) are a zero emission replacement for heavy duty applications due to their range, energy density and fast refueling times.[1] In 2020, the U.S. Department of Energy (DOE) lunched the Million Mile Fuel Cell Truck (M2FCT) consortium to fund fuel cell R&D to meet heavy duty truck standards.[2] Durability studies focusing on heavy-duty applications for advanced materials testing under the M2FCT consortium have been extensively explored and continue to be analyzed to standardize the evaluation of next generation fuel cell materials. This study combines in situ electrochemical characterization with ex situ analysis of single cell PEMFCs membrane electrode assemblies (MEAs) to predict long-term durability for heavy-duty applications. Various accelerated stress test (AST) parameters were analyzed to determine the stressors affecting the long-term durability. Local degradation resulting from repeated high voltage to low current cycles was analyzed by testing state-of-the-art materials. High potential holds at various conditions were analyzed to determine membrane chemical degradation. Repeated wet and dry cycles were performed to test the membrane mechanical durability. In situ electrochemical analysis include mass activity, electrochemical surface area, hydrogen crossover, and polarization curves were collected and compared among the MEAs. Ex situ analysis includes quantification of membrane thinning at end of life and fluoride emission rate measurement for water effluent throughout the test was conducted to study the membrane degradation. Acknowledgement: This work was supported by the Hydrogen and Fuel Cell Technologies Office (HFTO), Office of Energy Efficiency and Renewable Energy (EERE), US DOE through the Million Mile Fuel Cell Truck (M2FCT) consortium, technology managers G. Kleen and D. Papageorgopoulos. References: David A. Cullen, K. C. Neyerlin, Rajesh K. Ahluwalia, Rangachary Mukundan, Karren L. More, Rodney L. Borup, Adam Z. Weber, Deborah J. Myers, and Ahmet Kusoglu, New roads and challenges for fuel cells in heavy-duty transportation. Nat. Energy, 2021. 6(5): 462-474. DOE Launches Two Consortia to Advance Fuel Cell Truck and Electrolyzer R&D. 2020; Available from: https://www.energy.gov/eere/articles/doe-launches-two-consortia-advance-fuel-cell-truck-and-electrolyzer-rd.

Correction for ‘Infrared spectroscopy for understanding the structure of Nafion and its associated properties’ by Tanya Agarwal et al. , J. Mater. Chem. A , 2024, https://doi.org/10.1039/D3TA05653H.

The performance and long-term durability of polymer electrolyte membrane fuel cells (PEMFCs) are subject to different factors ––material properties, defects, assembly, maintenance and operational procedures.1 Among all the possible failure modes in a fuel cell, membrane electrode assembly (MEA) degradation is a determining factor for performance and lifetime.2 In the past few years, several studies have been developed to understand the degradation of membranes and electrocatalysts, and the corrosion of the carbon support; with a focus on the chemical aspects, rather than the physical features that could promote degradation. More studies are needed to evaluate physical factors that can compromise the MEA structure, especially the aspects that affect the membrane.3 The physical degradation of membranes can be effected by membrane intrinsic factors such as membrane creep, microcracks, and morphological changes.4 Furthermore, it is necessary to study the influence of membrane extrinsic factors ––such as roughness and imperfections at the interfaces between MEA components–– on the processes of membrane degradation. Whether morphological defects are generated before or during the assembly procedure or are intentionally introduced as strategy to improved water management, remains unclear if a defect can act as a precursor pit where membrane could start its degradation. In this sense, more efforts are needed to evaluate the influence of defects on potential and progressive membrane etching and pinholes formation. Our work is focused on understanding the influence of defects, specifically cracks present on gas diffusion layers (GDLs), on the performance and durability of PEMFCs. To control experimental variables associated with different production lots and suppliers, we designed a method to create artificial cracks on the mesoporous layers (MPLs) of commercial GDLs. This technique allows us to compare the cracked GDLs with the pristine GDL, ensuring our “network or pattern of cracks” as the only external variable introduced into the MEA environment. Also, we utilized other commercially available intentionally cracked GDLs as comparative elements. Accelerated stress test (ASTs) were performed and durability results were obtained from long-term (500 hours) fuel cell operation at elevated cell temperature (90 oC). Scanning electron microscopy (SEM) and laser profilometry, were used to characterize all the samples, before and after performance/durability tests. Mechanical and chemical durability of membranes are evaluated based on fluoride emission rates (FERs). This work enables a starting approach to understand the influence of cracks, existing on GDLs, on the membrane degradation processes. Results will give us insights for improving the membrane and GDLs technologies that we are developing in the Million Mile Fuel Cell Truck Consortium (M2FCT). Acknowledgement: This work was supported by the Hydrogen and Fuel Cell Technologies Office (HFTO), Office of Energy Efficiency and Renewable Energy, US Department of Energy (DOE) through the Million Mile Fuel Cell Truck (M2FCT) consortia, technology managers G. Kleen and D. Papageorgopoulos. References: (1) Kundu, S.; Fowler, M. W.; Simon, L. C.; Grot, S. Morphological features (defects) in fuel cell membrane electrode assemblies. Journal of Power Sources 2006, 157 (2), 650-656. DOI: https://doi.org/10.1016/j.jpowsour.2005.12.027. (2) Liu, M.; Wang, C.; Zhang, J.; Wang, J.; Hou, Z.; Mao, Z. Diagnosis of membrane electrode assembly degradation with drive cycle test technique. International Journal of Hydrogen Energy 2014, 39 (26), 14370-14375. DOI: https://doi.org/10.1016/j.ijhydene.2014.02.161. (3) Qiu, D.; Peng, L.; Lai, X.; Ni, M.; Lehnert, W. Mechanical failure and mitigation strategies for the membrane in a proton exchange membrane fuel cell. Renewable and Sustainable Energy Reviews 2019, 113, 109289. DOI: https://doi.org/10.1016/j.rser.2019.109289. (4) Borup, R.; Meyers, J.; Pivovar, B.; Kim, Y. S.; Mukundan, R.; Garland, N.; Myers, D.; Wilson, M.; Garzon, F.; Wood, D.; et al. Scientific Aspects of Polymer Electrolyte Fuel Cell Durability and Degradation. Chemical Reviews 2007, 107 (10), 3904-3951. DOI: 10.1021/cr050182l.

Proton exchange membrane fuel cells (PEMFCs) are expected to play a pivotal role in decarbonizing the transportation sector, and particularly heavy-duty vehicles (HDVs). However, improvements in durability are needed for PEMFCs to compete with state-of-the-art power sources for HDVs. Here, we examine how catalyst layer (CL) cracks that are engineered affect the CL durability by using patterned silicon templates to control the CL crack density at the micrometer scale. Electrochemical analyses show that the initial PEMFC performance is relatively unaffected by crack density, but the performance after durability testing was strongly affected. Specifically, CLs with high crack density showed higher performance relative to CLs without cracks after application of a carbon corrosion accelerated stress test. Electrochemical analyses coupled with X-ray computed tomography and scanning transmission electron microscopy with energy dispersive X-ray spectroscopy showed that the cracks provide shorter oxygen diffusion pathways to reaction sites, leading to decreased oxygen transport resistance. Additionally, we observed that the catalyst durability is unaffected by cracks. Our results provide a mechanistic explanation of the role of cracks in CL durability.

The operation and viability of an air-breathing fuel cell stack will heavily depend on the cleanest available local air, unless its cathode is tolerant to impurities. Previous research on the impact of air impurities showed deleterious impacts on overall performance utilizing platinum catalysts. To date, fuel cell research findings using air impurities employing non-platinum catalysts, platinum group metal-free (PGM-free), is scarce. To test the viability of a PGM-free stack, a miniature four-cell stack with PGM-free catalyst was assembled to compare with results from a standard eight-cell stack Pt-based catalyst, in both H2/Air and H2/O2. A promising open current voltage was obtained, offering a comparable statistic to what would be expected from a platinum-based stack of the same size. Prior research has shown higher performance for PGM-free membrane-electrode assemblies in terms of current density at the desired operating voltage, but significant performance loss after testing indicates poor stability. Repeated testing of the PGM-free stack showed such a decrease in current density performance at designated voltages after initial testing, followed by stability in results. Further testing with exposure to impurities is expected to demonstrate tolerance and reversibility in a PGM-free stack once initial stability is obtained. The purpose of this project is to develop a fuel-cell stack to meet specific power output requirements utilizing PGM-free cathode catalyst.

The electrochemical impedance spectroscopy (EIS) diagnostics using H2/N2 operation condition developed for fuel cell is useful tools to estimate the catalyst layer (CL) proton resistance. Currently, the resistance is estimated by fitting the measured EIS data to an equivalent circuit model. However, it is challenging to correctly determine the transmission line circuit and accurately estimate the proton resistance [1]. Moreover, the capacitive and resistance elements in the transmission line model are assumed similar throughout the CL even if there is nonhomogeneous distribution of ionomer. To understand the EIS response in CL, we present a physics-based model. Utilizing the model, we are able to investigate the H2/N2 cell impedance response under various operating conditions. The continuum scale model will be combined with agglomerate scale model to provide a detail study of the electrode parameters like ionomer loading and ionomer coverage The hybrid theoretical model allows us to study the effect of nonhomogeneous CL and its corresponding EIS response. Acknowledgement This research is supported by U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office, through the Million Mile Fuel Cell Truck Consortium (M2FCT). References: [1] Malevich, D., Jayasankar, B. R., Halliop, E., Pharoah, J. G., Peppley, B. A., & Karan, K. (2012). On the determination of PEM fuel cell catalyst layer resistance from impedance measurement in H2/N2 cells. Journal of the Electrochemical Society, 159(12), F888. [2] Liu, Y., Murphy, M. W., Baker, D. R., Gu, W., Ji, C., Jorne, J., & Gasteiger, H. A. (2009). Proton conduction and oxygen reduction kinetics in PEM fuel cell cathodes: effects of ionomer-to-carbon ratio and relative humidity. Journal of The Electrochemical Society, 156(8), B970.

The chemical durability of perfluorosulfonic acid (PFSA) membranes is a topic of growing interest to meet Department of Energy (DOE) durability targets for heavy‐duty vehicle (HDV) applications. State‐of‐the‐art membranes like Nafion, rely on the use of cerium, heteropolyacids, and other inorganic additives to increase PFSA chemical durability. A less explored avenue for the oxidative stabilization of PFSA and hydrocarbon membranes is the use of organic antioxidants. No reversible organic antioxidant has been demonstrated to date which can enhance membrane lifetime by factors comparable to cerium. Here, ellagic acid (EA) is demonstrated as a promising radical scavenger for PFSA's. It is found that the incorporation of EA enhances the chemical durability of Nafion by 160%. EA, when incorporated with cerium as an electron donorenhances Nafion durability by at least 80% compared to a membrane incorporated with just cerium in DOE‐defined durability tests. EA is found to be reversible in acidic conditions like those of fuel cells and its reversibility could be further enhanced by the use of suitable co‐antioxidants.

Radical species generated during proton exchange membrane fuel cell operation considerably limit the achievable durability, particularly for heavy duty vehicle applications. A promising solution to the problem is the incorporation of radical scavenger additives such as cerium which mitigates chemical attacks on the membrane by such radicals. However, these additives migrate during fuel cell operation causing loss in durability and performance due to detrimental interaction with various components of the fuel cell. Here, we study size selective agents as a means to stabilize cerium within perfluorosulfonic acid (PFSA) membranes, and thereby enhance membrane durability. We synthesized an organometallic complex of cerium with 15-Crown-5 and investigated the effectiveness of this complex to immobilize cerium. Over 1000% increase in cerium retention and 80% increase in chemical durability was observed owing to the stabilization effect of crown ethers on cerium. Migration under potential gradient could be eliminated while the complex also contributed to the enhancement in cerium radical scavenging activity.

The chemical durability of perfluorosulfonic acid (PFSA) membranes is becoming an increasingly investigated subject to meet the Department of Energy (DOE) durability targets for Heavy Duty Applications (HDVs). State-of-the-art membranes like Nafion TM , rely on the use of cerium, heteropolyacids, and other inorganic additives for increasing PFSA chemical durability. A less explored avenue for the oxidative stabilization of PFSA and hydrocarbon membranes is the use of organic antioxidants. No reversible organic antioxidant has so far been demonstrated which can enhance membrane lifetime by factors similar or higher to cerium. Herein, we demonstrate ellagic acid as a promising radical scavenger for PFSAs. We found that the incorporation of EA enhanced the chemical durability of Nafion by 160%. EA when incorporated with cerium as an electron donor could surpass Nafion durability enhancement by 80% compared to a membrane incorporated with just cerium in DOE-defined durability tests. EA was found reversible in acidic conditions like that of fuel cells and its reversibility could be further enhanced by the use of suitable co-antioxidants. We discuss the present challenges with the system and highlight future areas of research. Figure 1

The interaction between the catalyst and the carbon support is crucial to both the performance and durability of the membrane electrode assembly (MEA) in a polymer electrolyte membrane fuel cell. Local oxygen transport resistance (RO2) has shown to be a significant contributor to the overpotential loss in the catalyst layer.1 Utilizing mesoporous carbon supports has shown to reduce RO2 compared to high surface area carbon and prevent ionomer poisoning of Pt inside the pores.2 Engineered catalyst supports (ECS) synthesized through templated organic precursor provides improved control of resulting carbon morphology.3 This work presents a detailed study of the performance and durability of the ECS supported catalyst. Effect of Pt weight percentage on the carbon support, ionomer loading, and the ionomer type on the catalyst performance and durability is presented. Figure 1 shows the performance at beginning of life (BOL) and end of life (EOL) after 90000 cycles, using US DOE’s electrocatalyst protocol, for MEAs with different ionomer loadings. Polarization curve, Pt accessibility through CO stripping, and RO2 from limiting current will be presented are measured at different intervals between BOL and EOL. Characterization of the Pt particle and catalyst layer structure performed at BOL and EOL will also be presented. This study highlights the value of the morphological and electrochemical evaluation to provide detailed insights into the catalyst and mesoporous carbon support interaction. Acknowledgement This research is supported by Technology Readiness Gross Receipts Tax Credit through New Mexico Legislature. This research is supported by U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office, through the Million Mile Fuel Cell Truck Consortium (M2FCT). References 1 Kongkanand, A. et al. Journal of Physical Chemistry Letters, 7, (7), 1127-1137, 2016. 2 Ramaswamy, N. et al. Journal of The Electrochemical Society, 167, (6), 064515, 2020. 3 Ramaswamy, N. US DOE Hydrogen and Fuel Cells Program: 2020 Annual Merit Review and Peer Evaluation Report, 2020. Figure 1

The gas diffusion layer (GDL) is a critical component of proton exchange membrane fuel cells. GDL manufacture is dominated by the use of polyacrylonitrile (PAN) fibers, resulting in high production costs. Those costs contribute to the high cost of fuel cell stacks. Thus, reducing GDL manufacturing costs without sacrificing performance, should help reduce the overall cost of the fuel cell stack. Using inexpensive, natural fiber-based papers and fabric as substrates, we examine the inherent performance these materials as GDLs, and the improvements enabled by the addition of a microporous layer, gas-phase hydrophobic treatment, and densification. The resulting GDLs achieve equivalent performance the commercial baseline GDL and demonstrate the potential of lower cost GDLs.