This work investigates the use of roll-to-roll coating methods for the production of iridium oxide catalyst layers for proton exchange membrane water electrolyzers. Catalyst layers were produced using two coating methods: slot die and gravure. By varying the solids content of the catalyst ink and coating process variables loadings between 0.08 and 0.64 mgIr cm-2 were prepared with relatively high spatial uniformity. However, at loadings below 0.2 mgIr cm-2 microscopy reveals voids in the catalyst layer due to similar length scales of catalyst agglomerates and overall layer thickness. Electrochemical testing shows that these voids do not impact initial membrane electrode assembly performance but lead to increased performance losses after potential cycling compared to spray coated catalyst layers.

PEM water electrolyzers (PEMWEs) have transitioned from a specialized, low-volume technology into large-scale industrially deployed platform for low-temperature, high-purity hydrogen production. While PEM stacks have been commercially available for decades, the current challenge lies in meeting the high demand for multi-megawatt installations. To achieve this, the industry is shifting from labor-intensive batch processing to high-speed continuous Roll-to-Roll manufacturing of catalyst-coated membranes (CCMs). While these methods enable efficient, large-area manufacturing, factors such as process instabilities, substrate contaminants, clogs, and bubbles can introduce non-uniformities into coated catalyst layers (CL). A wide variety of inhomogeneities have been studied in the PEM fuel cell (PEMFC) literature. 1 For example, it has been shown that catalyst-layer irregularities such as local thickness variations 2,3 , cracks, 4 and non-uniform ionomer distributions 5 lead to spatially localized current constriction, accelerated performance decay, and points of local failure. In particular, voids in CL coatings lead to spatial variations in current density and localized degradation, reducing fuel cell durability even when area-averaged polarization remains largely unchanged 6 . Although these irregularities are well characterized for PEMFCs, less work exists that investigates the effects of irregularities on PEMWE performance. To better understand the impact of streaks on PEMWE performance, this work evaluates CCMs in which streaks were intentionally introduced by adjusting coating parameters, enabling controlled and reproducible fabrication of CLs with streaks with defined dimensions and number. A combination of single-cell and spatially resolved segmented-cell testing were used to probe local variations arising from non-uniform CL structures. Initial performance results show no significant differences in overall electrochemical behavior due to the presence of streaks, but notable variations in hydrogen crossover were observed, where the quantity of hydrogen crossover depended upon both streak size and total amount of missing CL. By linking coating-induced non-uniformities to local electrochemical behavior and gas crossover, this work underscores the importance of tolerance-aware electrode design and precise manufacturing control. References: Yang, G. et al. Advanced Electrode Structures for Proton Exchange Membrane Fuel Cells: Current Status and Path Forward. Electrochem. Energy Rev. 7 , 9 (2024). 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. International Journal of Hydrogen Energy 43 , 6390–6399 (2018). Wang, M. et al. Visualization, understanding, and mitigation of process-induced-membrane irregularities in gas diffusion electrode-based polymer electrolyte membrane fuel cells. International Journal of Hydrogen Energy 46 , 14699–14712 (2021). Taylor, A. K. et al. The influence of electrode crack dimensions on the durability of polymer electrolyte membrane fuel cells. Journal of Power Sources 628 , 235884 (2025). Phillips, A. et al. The Effect of Membrane Casting Irregularities on Initial Fuel Cell Performance. Fuel Cells 20 , 60–69 (2020). Phillips, A., Ulsh, M., Porter, J. & Bender, G. Utilizing a Segmented Fuel Cell to Study the Effects of Electrode Coating Irregularities on PEM Fuel Cell Initial Performance. Fuel Cells 17 , 288–298 (2017).

The dispersion medium in fuel cell catalyst ink formulations is typically a water–alcohol mixture with 20%–75% wt alcohol to enable ink processability, electrode coating uniformity, and device performance targets. However, from a manufacturing perspective, high concentrations of alcohol pose a flammability hazard that increases safety burden and capital cost by requiring the use of explosion-use proof equipment. Thus, in this study, the effect of increasing water content beyond 80% wt in catalyst inks is systematically investigated to reduce ink flammability. Increasing the ink water content in increments of 5% wt results in surprisingly dramatic variations in ink flow properties, ink microstructure, and catalyst layer cracking. We propose that the degree of cracking relates to catalyst particle packing efficiency. Despite these differences, catalyst and ionomer remain uniformly distributed throughout the catalyst layer in all formulations. Importantly, electrochemical testing shows that increasing ink water content beyond 80% wt can minimally impact device performance, demonstrating the feasibility of low VOC fuel cell electrodes for scaled manufacturing.

Proton exchange membrane water electrolysis (PEMWE) shows great potential for producing high-purity hydrogen for industrial applications. However, further improvements in PEMWE, particularly the optimization of the anode catalyst layer, are paramount to commercial deployment. The anode catalyst layer is typically fabricated through liquid coating of the iridium oxide catalyst and ionomer dispersed in a mixture of water and alcohols (e.g., 1-propanol). Due to the presence of alcohols, manufacturing at scale is complicated by cost and safety barriers associated with handling flammable liquids. Here, we target low flammability, water-rich catalyst ink formulations as a pathway to reduce manufacturing costs and safety constraints while maintaining electrochemical performance. In this study, the role of solvent composition is systematically investigated by varying water content to quantify its impact on ink rheology, coating uniformity, and catalyst layer morphology. Analysis of ink properties reveals that as water content is increased, a significant shift in ink rheology occurs, with viscosity increasing from 0.03 Pa·s to approximately 2 Pa·s. Challenges associated with this increased viscosity are mitigated by selecting coating methods such as Mayer rod or blade coating, enabling uniform films even under water-rich conditions. While these bench-scale coating methods can accommodate elevated viscosities, such formulations may pose challenges in roll-to-roll coating processes. To retain desired rheological properties without reintroducing volatile organic solvents, we explore formulation strategies using additives that enable fine-tuning of viscosity, dispersion stability, and coatability. These formulation–processing relationships, paired with single-cell, beginning-of-life electrochemical testing, demonstrate that alcohol content can be reduced by up to ~60% (i.e., relative to a baseline 1:1 w/w water:alcohol mixture) while maintaining competitive PEMWE performance, achieving cell voltages of ~1.7 V at 2 A·cm⁻² under the conditions evaluated. These results demonstrate viable pathways toward non-flammable, water-based catalyst ink systems compatible with scalable manufacturing. Both solvent composition and additive-driven strategies are rationalized in terms of how molecular-level interactions govern catalyst layer microstructure and, ultimately, electrochemical performance. In summary, this work identifies formulation–processing–performance relationships that enable low-VOC catalyst inks and highlights future pathways towards cost-effective PEMWE electrode fabrication compatible with roll-to-roll manufacturing.

X-ray photoelectron spectroscopy (XPS) is a commonly used technique for investigating the surface properties and composition of catalysts used in polymer electrolyte membrane fuel cells and electrolyzers. XPS analysis of catalyst layers (CLs) is becoming increasingly utilized to provide greater understanding of CL properties and relationships between catalyst and support composition and structure, catalyst ink composition, CL fabrication methods and parameters, and their performance and durability. Characterization of Ir-based CLs is challenging due to several factors including interpretation of Ir 4f spectra, deconvolution of catalyst and ionomer species in O 1s spectra, and ionomer susceptibility to X-ray damage that leads to changes at the catalyst-ionomer interface often more significant than differences between samples. This study reports an approach for detailed XPS characterization of Ir-based CLs, establishes quantitative metrics and provides insights into the catalyst-ionomer interface that can be correlated to wide variety of processing and performance metrics. Specifically, we have evaluated surface compositional differences in CLs prepared with several common CL coating methods. We also investigated CLs prepared with different catalyst loadings and selected samples after electrochemical testing. In general, we found good agreements in trends observed from elemental ratios and those derived from detailed analysis of the O 1s spectra. Additionally, O 1s analysis revealed differences in the catalyst composition, addressing some of the challenges and limitations related to the interpretation of the Ir 4f spectra.

Lower anode catalyst loadings and higher current densities are essential to lowering the levelized cost of H2 production via proton exchange membrane water electrolysis (PEMWE). However, these approaches can induce significant durability challenges. Here, we show that cell degradation can include large reversible voltage losses across a variety of conditions, including low loadings and high currents. Although there is limited published discussion of reversible voltage losses in PEMWE, we demonstrate that they are an important consideration in cell efficiency and durability. Understanding the mechanisms of reversible losses and developing mitigation strategies is therefore a key priority for enabling low-cost PEMWE.

Advances toward next-generation polymer electrolyte membrane fuel cells (PEMFCs) are focused to heavy-duty applications with emphasis on durability, efficiency, and long-term performance. State-of-the-art, polymer electrolyte membranes (PEMs) have been developed to mitigate chemical and mechanical degradation pathways using radical scavengers and reinforcement strategies. The efficacy of such material design strategies is, however, reliant on the use of suitable pre-assembly techniques that avoid process-induced membrane irregularities (PIMs).[1]These PIMs are often undetected at beginning of test but result in premature cell failures.[2] In this work, fabrication of irregularity-free MEAs was established as a precursor to assess the influence of electrode crack defects on the durability of the MEA.[3] Electrode-level crack dimensions were systematically tuned using catalyst ink solvent formulations and selection of the diffusion media type. Using these modalities, we accessed electrode crack dimensions on the order of single microns and tens of microns. The crack width areal density (Φ CW ) parameter was developed to quantify the degree of discontinuity in the electrode surfaces. On-line, open circuit voltage (OCV) transient analyses were used to track membrane degradation events signaled by deviations from thermodynamically predicted voltage values. Accelerated stress tests over 50 cm 2 active areas reveal that the void width dimension should be kept to a minimum at membrane interfaces for robust MEA durability. The work herein emphasizes the need for material processing strategies that consider defect tolerances to limit membrane failures in PEMFCs. [1] Taylor, A. K., Smith, C., & Neyerlin, K. C.* “Mitigation and Diagnosis of Pin-hole Formation in Polymer Electrolyte Membrane Fuel Cells” J. Power Sources , 2023. 571, 232971. [2] Wang, M., Taylor, A. K., Ochoa-Lozano, J., Medina, S., Pfeilsticker, J. R., Mauger, S. A., Pylypenko S., Ulsh, M., Bender, G.* “The Impact of Hot-Press Conditions on the Durability of Polymer Electrolyte Membrane Fuel Cells”. Int. J. Hydrog. Energy , 2025, 98, 639-647. [3] Taylor, A. K., Baez-Cotto, C., Hu, L., Smith, C., Rodriguez-Nazario, A., Young, J. L., Mauger, S. A., Neyerlin, K. C.* “The Influence of Electrode Crack Dimensions on the Durability of Polymer Electrolyte Membrane Fuel Cells” J. Power Sources , 628, 2025, 235884.

Understanding water, evolved gas, and ionic transport in membrane-electrode-assemblies (MEAs) is essential for the development of high performance and durable anion exchange membrane water electrolyzers (AEMWEs). This study evaluates the MEA conditioning process, operating conditions, and short-term stability in a 1 M potassium hydroxide (KOH) electrolyte, focusing on the underlying transport phenomena. We observe a significant initial voltage loss in continuous cell operation, which could be associated with gas bubble accumulation, transport layer or flow field passivation, and changes in the catalyst oxidation state. Further, we investigate the effects of materials and operational configurations, including the membrane type and thickness, and the electrolyte flow rate, including KOH being fed to both electrodes as well as to the anode only. Furthermore, the effect of membrane drying temperature on ex situ as well as in situ electrochemical performance is evaluated. Finally, we discuss 700 h of AEMWE operation at 1 A/cm2, highlighting the underlying degradation phenomena.

Fuel cell electrode catalyst layers are typically manufactured using colloidal ink casting and coating techniques such as slot-die coating or spray coating. While ink deposition and drying require careful optimization of their own, a crucial prerequisite is tuning the catalyst ink to have appropriate rheological and microstructural properties like viscosity, particle/cluster dispersion, and aggregate size and size distribution. Despite studies that have elucidated mechanisms for fine-tuning ink properties for subsequent coating and drying process control, formulating brand new inks with specific properties still requires slow trial-and-error studies. The difficulty of discovering new ink formulations lies within three main challenges: 1) fuel cell catalyst inks have many components (ionomer, catalyst, catalyst support, solvent), leading to a large formulation design space; 2) ink properties are determined by complex multi-scale physics that simultaneously involve almost all components; and 3) ink property optimization is multi-objective in nature, requiring one to make calculated property trade-offs. This work leverages uncertainty-aware machine learning (ML) models to correlate carbon-based fuel cell ink formulation parameters with experimentally measured ink properties. Statistical sampling is first used to define a design of experiments for an initial batch of experiments. This initial dataset is used to begin a multi-objective Bayesian Optimization campaign that designs new experiments to improve ML accuracy and obtain target ink properties. After iterations of experiment-ML development, we report our refined ML models with the elucidated ink material-property correlations.

Electrode cracks in polymer electrolyte membrane fuel cells (PEMFCs) are correlated with early onset failures. In this work we investigate the influence of cracked gas diffusion electrodes (GDEs) on the durability of the membrane electrode assembly (MEA) using a combined chemical-mechanical accelerated stress test (AST). Electrode crack dimensions were systematically tuned using ink formulations and material selection strategies. A parameter to describe the crack width areal density (Phi CW) was used to quantify the degree of discontinuity in the electrode surfaces. Open circuit voltage (OCV) transient analyses were used to benchmark and characterize the failure mechanisms in the MEAs as a function of the Phi CW . While smaller electrode-level cracks, on the order of microns, yielded a 28 % decrease in operating lifetime, larger cracks that propagated from a discontinuous, microporous layer (MPL) coating, decreased the operating lifetime by 56 %. This work emphasizes the need for material processing strategies that consider defect tolerances to limit membrane failures in PEMFCs.

This work focuses on porous transport electrodes (PTEs), which integrate the anodic catalyst with the adjacent Ti porous transport layer (PTL). Challenges in catalyst deposition on PTLs, particularly at low loadings, motivated this study to evaluate various fabrication methods and characterization approaches. This work investigated Pttreated PTLs coated with Ir-based catalysts using several common methods, including airbrush coating, rod coating, ultrasonic spray coating, electrodeposition, and sputter deposition, with catalyst loadings ranging from 2.9 to 0.1 mg/cm2, providing the opportunity for comparisons across a large set of samples produced by different methods. Two widely accessible characterization techniques: X-ray computed tomography (XCT) and scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS) were explored. Initial evaluation of selected samples with XCT provided qualitative insights into catalyst distribution, however comprehensive quantitative analysis was limited. SEM-EDS enabled detailed information on the catalyst distribution both qualitatively and quantitatively using two metrics. Atomic and surface area % ratios of Pt:Ir and Ti:Ir revealed trends in catalyst loading and losses into the PTL pores, as well as evaluating the homogeneity of catalyst coatings. The analysis demonstrated that ultrasonic spray coating, electrodeposition, and sputter coating produced the most homogeneous coatings, with minimal catalyst losses observed for electrodeposition and sputter coating. By adapting common techniques with novel, standardized methodologies, this work establishes a universally applicable framework for cross-study comparison of PTEs. The SEM-EDS approach provides a practical, accessible tool for PTE characterization and contributes a reference dataset supporting both research development and rapid quality control.

X-ray photoelectron spectroscopy (XPS) has been widely used to study catalysts and support materials, offering valuable insights about surface composition and contributing to the optimization of their performance. However, investigations of catalyst layers (CLs) using XPS are more limited, due to several challenges—including surface sensitivity of low concentration elements, the ionomer being vulnerable to X-ray damage, and spatial heterogeneity of the CL surface. Our recent studies demonstrated that, although the Nafion ionomer is inherently susceptible to X-ray-induced degradation, XPS can still be effectively employed through a modified acquisition strategy [1]. It has been established that XPS can be used to track ionomer, catalyst and support species which in turn can be utilized to compare both intentional and unintentional variations in ionomer at the catalyst-ionomer interface induced by ink processing, CL fabrication conditions, testing conditions [2, 3]. This talk will present a series of studies focused on the catalyst-ionomer interface under humidified conditions. Initially, a set of Pt/carbon catalyst layers—with variations in support material, Pt loading, and ionomer content—were investigated under ultra-high vacuum (UHV) conditions. The relative amount of ionomer to catalyst and support was quantified using the F/Pt elemental ratio and the C-Fₓ/C-C ratio derived from high-resolution C 1s spectral fitting. The ionomer distribution on the surface was further assessed using the F/S ratio (from elemental analysis) and O 1s-Ionomer/O 1s-Catalyst ratios (from O 1s spectral deconvolution). Selected samples were then evaluated under in situ humidified conditions to detect changes in the catalyst-ionomer interface resulting from water exposure. Following this, the samples were re-analyzed under UHV to assess the reversibility of any observed changes. This study revealed differences in the arrangement and rearrangement of the ionomer as a function of surface ionomer content, Pt nanoparticle loading and dispersion, and the nature of the support material. The parameters and methodology developed here can be applied more broadly to analyze a wide range of catalyst layers and operational conditions relevant to real-world device environments. Dzara, M. J.; Artyushkova, K.; Foster, J.; Eskandari, H.; Chen, Y.; Mauger, S. A.; Atanassov, P.; Karan, K.; Pylypenko, S. X-Ray Photoelectron Spectroscopy Analysis of Nafion-Containing Samples: Pitfalls, Protocols, and Perceptions of Physicochemical Properties. Phys. Chem. C 2024 , 128 (20), 8467–8482. Foster, J.; Lyu, X.; Serov, S.; Mauger, S.; Padgett, E.; Pylypenko, S., X-ray Photoelectron Spectroscopy Analysis of Iridium Oxide Catalyst Layers with a Focus on the Catalyst-Ionomer Interface, Electrochimica Acta. 2025 ,517, 145705. Medina, S.; Foster, J. G.; Dzara, M. J.; Wang, M.; Ulsh, M.; Mauger, S. A.; Pylypenko, S., Multi-technique characterization of spray coated and roll-to-roll coated gas diffusion fuel cell electrodes. Journal of Power Sources 2023 , 560, 232670.

The proton exchange membrane integrity can be compromised during hot-press fabrication of membrane electrode assemblies (MEAs) causing premature cell failures during operation. In this work, infrared (IR) thermography was used as a diagnostic tool to spatially visualize hydrogen (H2) crossover and identify process-induced- membrane irregularities (PIMs). These irregularities were identified as seed locations for MEA failures. Fine tuning of hot-press conditions was used to mitigate premature cell failures informed by accelerated stress testing (AST). The impact of PIMs on the initial performance, high-frequency resistances, open-circuit voltage, and H2 crossover are reported. Nafion XL and 212 membranes, hot-pressed with a force of 16 kg/cm2 and temperature of 120 degrees C, were found to be consistently irregularity-free. Irregularity-free MEAs using Nafion 211, 212, and XL membranes demonstrated AST lifetime improvements of 58, 64 and 400%, respectively, compared to those fabricated with non-optimized conditions. This work highlights the importance of fabrication parameters on premature cell failures.

This work utilizes EIS to elucidate the impact of catalyst-ionomer interactions and cathode hydroxide ion transport resistance (RCL, OH-) on cell voltage and product selectivity for the electrochemical conversion of CO to ethylene. When using the same Cu catalyst and a Nafion ionomer, varying ink dispersion and electrode deposition methods results in a change of 2 orders of magnitude for RCL, OH- and ca. a 25% change in electrode porosity. Decreasing RCL, OH- results in improved ethylene Faradaic efficiency (FE), up to similar to 57%, decrease in hydrogen FE, by similar to 36%, and reduction in cell voltage by up to 1 V at 700 mA/cm2. Through the optimization of electrode fabrication conditions, we achieve a maximum of 48% ethylene with >90% FE for nonhydrogen products in a 25 cm2 membrane electrode assembly at 700 mA/cm2 and <3 V. Additionally, the implications of optimizing RCL, OH- is translated to other material requirements, such as anode porosity. We find that the best performing electrodes use ink dispersion and deposition techniques that project well into roll-to-roll processes, demonstrating the scalability of the optimized process.

Iridium oxide (IrO2) is recognized as a state-of-art catalyst for anodes of low-temperature polymer-electrolyte membrane water electrolyzers (PEMWE), one of the promising clean energy technologies to produce hydrogen, a critical energy carrier for decarbonization. However, typical IrO2 ink formulations are challenging to process in liquid-film coating processes because of their poor stability against gravitational settling and low viscosities. Here we report on time evolution of the microstructure of concentrated IrO2 inks in a water-rich dispersion medium, probed using a combination of rheology and X-ray scattering for up to four days. The inks progressively evolve from a predominantly liquid-like to a gel-like material with increasing aging time that can be leveraged as a formulation strategy to enhance their stability against sedimentation, and processability during electrode fabrication. We also elucidate the aging behavior by investigating the effects of ink formulation composition - ionomer concentration and solvent composition - and using the extended-DLVO theory. The implications of aging on electrode fabrication, including via direct coating onto membranes and porous transport layers, and membrane-electrode-assembly performance has also been examined. Our findings offer not only a facile but also an environmentally benign formulation strategy to enhance ink processibility, expand practical fabrication approaches, and advance PEMWE manufacturing.

The transition of the United States energy infrastructure towards hydrogen energy involves the optimization of proton exchange membrane water electrolyzers (PEMWEs) for reliable hydrogen generation. PEMWE device typically consists of titanium porous transport layer (PTL) and an iridium-based anode catalyst layer. Several directions are being pursued to improve performance and to reduce the costs. To mitigate naturally occurring titanium passivation, protective coatings, typically platinum or other platinum-group metals (PGMs) are commonly applied to the PTLs. The drive to decrease the cost and the use of scarce materials has led to the development of catalyst layers with lower catalyst loadings. Reducing fabrication time and cost as well as increasing efficiency of the anode has led to the investigation of direct application of the iridium-based catalyst onto the Pt-coated Ti PTL. This motivated our investigation of porous-transport electrodes (PTEs) prepared with a variety of deposition methods, using different ink formulations, and targeting different catalyst loadings. There is need to develop a characterization approach that can be used to assess and compare quality of coatings across large parameter space or to monitor quality during production. Several sets of PTEs samples consisting of a titanium porous layer, platinum protective coating and iridium-based catalyst layer were prepared using a wide range of catalyst layer coating methods and parameters, including spray coating, gravure, airbrush and electrodeposition. All samples were characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) to analyze the elemental composition and assess the distribution of elements of interest (Ti, Pt, and Ir). First, the atomic% of each element was used to calculate elemental ratios for quantitative assessment of the amount of deposited catalyst. However, it is crucial to recognize the limitations of relying solely on this information for assessing catalyst coating since it doesn’t account for heterogeneity of the coatings. Although elemental maps provide valuable insights into spatial distribution, they alone do not offer a complete picture. To better understand the catalyst coating distribution, each individual EDS elemental map was used to calculate the surface area, which served as a measure of PTL area covered by the catalyst. Further, surface area ratios (Pt/Ir) were calculated to determine variations in surface coverage. This poster will highlight differences between fabricated samples and will demonstrate that together, at% and surface area ratio values allow for a comprehensive quantitative assessment of the composition and distribution of catalyst surfaces that were produced through a wide range of fabrication variables. The implementation of proper characterization of these PTEs can help aid future decisions on which parameters should be used moving forward. This approach can also be used for quality control, enabling quick screening of commercially produced samples.

Adverse climatic conditions caused by greenhouse gas (GHG) emissions from non-renewables have led to increased focus on utilization of clean alternative fuels such as hydrogen (H 2 ). Clean H 2 can be obtained via electrochemical reaction of water splitting through proton exchange membrane water electrolyzers (PEMWEs). However, challenges to its widespread commercialization lie with the high H 2 production cost, a large portion of which comes from use of expensive anodic catalyst materials. To improve anodic catalyst utilization to attain better performance at reduced cost, a thorough understanding of anodic catalyst layer microstructure is needed. In-depth characterization through scanning transmission electron microscopy with energy dispersive spectroscopy (STEM/EDS) can provide a comprehensive dataset, which can be processed further to extract structural parameters and correlate to electrochemical performance. However, extracting relevant information from these datasets can be very challenging and time-consuming. In this study, an automatic python-based image processing framework is implemented to quantify compositional and microstructural parameters for different IrO 2 based catalyst inks and their corresponding catalyst layers. The code can provide areal density of catalyst materials, pore/agglomerate size distribution, connectivity of phases, coverage of catalyst particles by ionomer, and its content percentage and distribution. Quantified parameters are then correlated with the electrochemical performance of the PEMWEs. The results provide adequate pointers to not only help capturing microstructural details of catalyst layers but also provide a basis to predict electrochemical behavior and performance of the inks and catalyst layers being studied.

Perflourosulfonic acid (PFSA) ionomers are used in many applications including polymer-electrolyte membrane fuel cells and electrolysers owing to their many attractive properties such as excellent ion-conductivity, chemical resistance, mechanical properties, and thermal stability. In polymer-electrolyte membrane fuel cells and electrolysers, they are used as the membrane and as a component in the catalyst layers, to provide proton conductivity and serve as a binder for the catalyst particles, which are two key components of these devices. Understanding the structure and rheological properties of the ionomer dispersions is important for solution-processed fabrication of the membranes and the catalyst layers, and will enable better control their final structure/morphology, and improve the device performance. A water-alcohol solvent mixture is a common dispersion media for ionomer dispersions as well as the catalyst inks. While significant efforts exist on the structure of ionomer dispersions in water-alcohol solvent mixtures, their rheological properties, particularly the effect of solvent composition at non-dilute concentrations remain less explored. In this talk, the effect of water-alcohol (isopropanol) composition of the dispersion media on the rheological properties of ionomer dispersions will be presented. The results of small-angle x-ray scattering characterization of the ionomer dispersions will be also discussed. As a model ionomer, a short sidechain perfluorinated ionomer (PFSA), produced by 3M, was used. In dispersions with low ionomer concentrations, the zero-shear viscosity scaling with concentration was found to be similar for all alcohol fractions in the solvent mixture, following Fuoss’s law for polyelectrolytes. Whereas at higher concentrations, beyond the semi-dilute unentangled regime, their scaling was strongly dependent on alcohol fraction, where the scaling exponent increasing with increasing the alcohol fraction. Furthermore, the dispersions showed dramatic shear-thickening and strain-stiffening behaviors at higher alcohol fractions. The rheological observations suggest water-alcohol composition significantly alters the interactions between ionomer, and consequently their structure, and has strong implications in processing as well as on the morphology/structure of the membranes and the catalyst layers.

Cracks in catalyst layers (CLs) are a potential source of long-term failure in a fuel cell membrane electrode as-sembly (MEA). While modifications to the CL ink formulation can affect the degree of cracking, these changes may lead to lower initial performance than their cracked analogues due to the established link between formulation and performance. In this work, we explored the use of polymeric additives to mitigate CL cracks. Small quantities of poly (acrylic acid), poly (ethylene oxide), poly (methyl methacrylate), or poly (vinyl alcohol) - 5 wt% relative to ionomer mass - were added to the ink prior to its final mixing. Poly (vinyl alcohol) resulted in crack-free CLs, whereas the other polymers resulted in CLs with similar crack percentages as the control CL. Through a combination of transmission electron microscopy, X-ray computed tomography, and infrared spectroscopy, we ascribed the crack-mitigating mechanism of poly (vinyl alcohol) to its ability to hydro-gen-bond with Nafion, the ion conducting polymer binder in the catalyst ink. Initial performance of this non --cracked electrode exhibited nearly identical electrochemical behavior to its cracked counterpart, demonstrating that PVA additives successfully reduce cracks while maintaining cell initial performance.

Proton exchange membrane fuel cell and electrolyzer manufacturing are in the early stages of rapid expansion. Many companies have announced plans for significantly increase their manufacturing capacity through new facilities or expansion of existing facilities. This increase in scale is necessary to achieve system-cost and emission-reduction targets. However, manufacturing speed is not a knob that can simply be turned up to produce high performance, durable systems. Manufacturing processes must be understood and developed to produce fuel cells and electrolyzers that meet the requirements for both throughput and performance. The U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office (HFTO) has launched a new consortium, the Roll-to-Roll (R2R) Consortium, to conduct process science and engineering research for fuel cell and electrolyzer manufacturing. R2R’s mission is to advance efficient, high-throughput, and high-quality manufacturing methods and processes to accelerate domestic manufacturing and reduce the capital cost of durable and high-performing systems. Three major research thrusts in catalyst synthesis process science, MEA fabrication process science, and quality control are set to address challenges associated with high-volume manufacturing, which is supported by additional activities including the development of characterization tools suited for the needs of the manufacturing environment, process modeling, artificial intelligence and machine learning, and technoeconomic analysis (TEA). The objective of these activities is to enable increased production speed, yield, and efficiency to achieve fuel cell and electrolyzer manufacturing rate and cost targets. This talk will provide an overview of the R2R Consortium’s research activities.