Stack Assembly Research Articles

Model‐Based Exploration of Web Guiding Behavior for a Novel Battery Cell Stacking Process

Innovative production processes are required to meet the rapidly growing demand for batteries and the associated material trends. In particular, the process step of stack assembly using new machine concepts promises a high potential for optimization. However, these concepts are untested in practice. The use of digital models makes it possible to develop corresponding optimization approaches. This article presents the development of a model for the web guiding systems of electrodes and its integration into an overall machine model for a novel machine concept. Finally, optimization approaches are identified by determining appropriate controller parameters for the web guiding systems.

An ultrasensitive flexible force sensor with nature-inspired minimalistic architecture to achieve a detection resolution and threshold of 1 mN for underwater applications

Highly sensitive flexible force sensors enable precise detection of underwater signals for monitoring biological activity, environmental conditions, and vehicle movement. Multilayer stack assembly and micro/nano structure array are often seen in most force/pressure sensors which are toughly hard to control the interlayer spacing and micro/nano structures alignment precisely, resulting in poor consistency and stability. Herein, we first reported a new force sensor with a nature-inspired minimalistic architecture, addressing such issues in an elegant and surprising approach by using a single-layer arched functional membrane with one microgroove. Inspired by the scorpions’ slit sensilla and mantis’ campaniform sensilla, a highly sensitive and waterproof flexible force sensor was fabricated. It is demonstrated that the force sensor has a sensitivity of 27.6 N−1, a high force resolution (1 mN), a fast response time of 70 ms, excellent stability over 5000 cycles and linearity (0.996), and a small force detection limit (≤ 1 mN), showing great potential in underwater environment sensing and motion monitoring of vehicles. This novel but minimalistic architecture provides a new direction in the development of sensors with advanced performance.

Flexible MXene/CuNWs/Tartaric Acid composite fabrics constructed by stacking assembly for Electromagnetic Interference Shielding

With the rapid development of modern communication technology, the exploration of flexible wearable shielding fabrics with exceptional electromagnetic interference (EMI) shielding performance has emerged as an utmost priority to safeguard both human beings and electronic devices from the detrimental effects of electromagnetic radiation. Herein, a scalable multilayer stacking assembly method is proposed to prepare uniform MXene/CuNWs/Tartaric Acid (TA) composites-coated fabrics. MXene, as a new type of material, can achieve higher electron and ion transfer rates. However, it is prone to oxidation in air, leading to poor stability. Benefiting from the synergistic effect of tartaric acid, the MXene/CuNWs/TA-coated fabrics exhibit certain oxidation stability and corrosion resistance, while retaining the inherent flexibility and breathability of natural polymer textiles. Furthermore, the multilayer stacking structure works perfectly with the MXene/CuNWs conductive network, enabling multiple reflections and absorptions of electromagnetic waves internally, thus effectively diminishing energy transmission. The modified fabrics exhibit a low sheet resistance of 3.25 ± 0.12 Ω/sq and a good EMI shielding performance of 41.2 dB at X-band. Therefore, MXene/CuNWs/TA fabrics with high shielding performance are expected to reach their potential in wearable electronic products.

Ion‐Pairing Chromonic Liquid Crystals via Alternately Stacked Assembly of Amphiphilic Charged π‐Electronic Systems

In this study, a new assembly strategy for lyotropic chromonic liquid crystals (LCLCs) is proposed using iπ–iπ interactions, mainly comprising electrostatic and dispersion forces, between charged π‐electronic systems to form stacking structures supported by the hydration of triethylene glycol (TEG) units. Meso‐TEG‐aryl‐substituted porphyrin AuIII complex, an amphiphilic π‐electronic cation, showed diverse states and assembly modes in ion pairs depending on the coexisting counteranions. The PCCp– ion pair formed a hexagonal columnar (Colh) LC phase based on a charge‐by‐charge assembly, suggesting the formation of an ordered arrangement of charged p‐electronic systems through iπ–iπ interactions, with reduced interactions between the TEG chains. Furthermore, in the presence of water, LCLC behaviors in the Colh and nematic columnar phases according to the amount of water were observed for the PCCp– ion pair via iπ–iπ interactions. Magnetic‐field‐induced orientation of the charge‐by‐charge columnar structures upon dehydration was observed. Furthermore, single‐stranded charge‐by‐charge columnar structures, as components of the LCLCs, were observed using transmission electron microscopy (TEM).

Membrane Electrode Assembly Development for Industrial CO2 Electrolysis

Membrane electrode assemblies (MEAs) are the key components of zero-gap CO2 electrolyzers, having various functions in the electrolysis process. The catalyst layers serve as the reaction interface, the porous transport layers ensure reactant and product transport to and from the catalysts, while the membrane is responsible for the ion transport between the two half cells. Thus, the structure of the MEA has a determining role on the electrolyzer operation. Industrial application requires large surface area electrolyzers and / or assembly of stacks. The scale-up, however, imposes different challenges on MEA preparation and on electrolyzer operation, therefore the optimal operating conditions can not necessarily be translated from small-scale (< 10 cm2) experiments.With the aim to scale-up the CO2 electrolysis to an industrially relevant level (>2500 cm2 active area), we thoroughly study the MEA components in a test electrolyzer cell having 100 cm2 active area. Currently we focus mainly on the optimization of the catalyst layers and the porous transport layers. The used electrolyzer size is already large enough that we can draw relevant conclusions for the operation of the large-scale electrolyzer, however, still offers possibility to screen a wide range of parameters.I will present selected results on how the improvement of the quality of the catalyst layers - through the optimization of the catalyst ink and the coating process- results in enhanced CO2 reduction performance. We also focus on the screening of different porous transport layers on the anode side with the long-term goal to reduce the precious metal consumption of the CO2 electrolysis. In the second part of my presentation, I will show how the operational parameters (e.g. cell temperature, humidity) affect the stability of the electrolysis. We have thoroughly investigated one of the biggest issues of the anion exchange membrane CO2 electrolysis: the carbonate precipitate formation and the related flooding phenomenon. We identified the pressure drop at the cathode side as a key test output parameter, which can serve as an early warning for the start of the undesired precipitation. When it is recognized in time, and the adequate preventive measures are applied, the lifetime of the electrolyzers can be greatly improved.

Statistical Investigation of the Reproducibility of Stack Components in a PEM Water Electrolyzer

To achieve homogeneous conditions throughout a single cell of a stack and within a stack and furthermore within several stacks, the components assembled in a stack should be reproducible to achieve a homogeneous performance. To evaluate how reproducible the stack components are, the porous transport layers, the expanded metals sheets, the perforated metal sheets, and the flow field plates from a 5-cell stack were examined.Eight samples were cut out of each of the 450 cm² layers, and a height profile (area: 10 x 10 mm) was recorded using a laser scan. From the height profile, the roughness values Ra (arithmetic average) and Rz (maximum peak to valley height) could be derived as well as the curvature of the samples (see Figure 1). Figure 1a) shows a contour plot of a perforated metal sheet. There is a height difference of up to 20 µm from the edge to the center of the sample. For the stack assembly this means an initial force is required to flatten the sheet before the actual compression of the stack takes place. Figure 1b) shows the roughness values Ra and Rz. The values vary within the sample (Ra: ± 3.8 µm, Rz: ± 5.7 µm) and throughout the samples (Ra: ± 1.4 µm, Rz: ± 2.5 µm). Further, the thickness of the components was measured, and the variation was calculated. In terms of stacking the components, as done in the stack, the best and worst case were calculated. The aim of this study was to determine input parameters for follow-up tests for the mechanical and electrical characterization of the components as especially the roughness of the components may have a significant impact on the contact resistance. Figure 1

Protonic Ceramic Electrochemical Cell Manufacturing at Idaho National Laboratory

Protonic Ceramic Electrochemical Cells (PCECs), operating at intermediate temperatures of 400-600oC, show great potential for hydrogen production and versatile chemical manufacturing. As this technology rapidly evolves, scaling up production in both quantity and size is crucial. This step bridges the gap between fundamental academic research on small button cells (e.g., 10 mm to 1 inch) and higher-technology readiness level development of industry-standard units (> 10x10 cm2) for stack assembly. At Idaho National Laboratory, we've made significant strides in this transition by applying advanced manufacturing technologies and our expertise in materials science and engineering. Our approach integrates materials, structural, and interface engineering research and development into the cell fabrication process, guided by a stringent quality assurance and quality control (QA&QC) system. This ensures the reliable, repeatable, and durable performance of PCECs.

Transitioning Low-Temperature GDC Socs: Lab to Commercialization Scale

Solid oxide fuel cells (SOFCs) electrochemically convert hydrogen and oxygen into electricity, heat, and water with high efficiency (~55%) [1], while in reverse operation, water and electricity are converted to hydrogen and oxygen in solid oxide electrolysis cells (SOECs). Appropriately designed solid oxide cells (SOCs) can operate in both SOFC and SOEC mode.Conventional SOCs typically demand elevated operating temperatures (800-1000°C), resulting in higher cost and accelerated degradation issues. Lowering operating temperatures below 600°C reduces thermal stresses, shortens start-up times, and broadens applications [2].Ce1-xGdxO2-δ (GDC), due to its superior oxygen ion conductivity at reduced temperatures, has lower ohmic losses than competing electrolyte materials. Thus, our 1.2 cm diameter circular anode supported GDC cell with 0.31 cm2 active area exhibits exceptional power densities, reaching approximately 3 watt per square centimeter at 650°C. Through optimal design, these cells exhibit exceptional performances in fuel cell mode, significantly enhancing efficiency and effectiveness when operating as an electrolyzer for fuel generation. This advance in performance is a result of mitigating the leakage current issues typical of ceria-based electrolytes through precise engineering of the cathodic microstructure and surface chemistry modification [3].The transition from lab-scale to large-scale commercialization (with active areas of 16 cm² &; 81 cm²) presents significant challenges such as tailoring material properties for large-cell versus button-cell synthesis while maintaining high performance levels.In this work we explore the challenges encountered during the scaling-up process. We report on fabrication strategies employed to achieve cell flatness, maintain high efficiency, ensure cost-effectiveness, and achieve long-term stability. Specifically, we have fabricated graded anode-supported cells [4] by developing an innovative lamination strategy involving tapes oriented perpendicular to each other. This approach notably contributed to achieving superior electrolyte densification and resulted in significantly flatter (low curvature values) with respect to both horizontal and vertical axes in cartesian coordinate space. When compared to the flatness values of 10x10 cm2 commercially available cells, our cells demonstrated remarkably flatter curvatures as shown in figure 1. This characteristic has proven highly beneficial for stack assembly, minimizing issues such as cell cracking and reducing sealing-related problems. By optimizing the cathode scaffold and infiltration process on larger area cells through a spray-coating machine, scaling up challenges are effectively mitigated compared to the button cell approach, where scaffold preparation and infiltration were performed using blade coating and a hand pipette, respectively. This approach effectively tackles electronic conduction issues in ceria-based electrolytes, leading to higher Open Circuit Voltages (OCVs) in fuel cell mode and increased efficiencies in reversible mode.

Bonded Bipolar Plate-Graphite Felt Components for Redox Flow Batteries Manufactured via Thermal Fusion by Electro-Welding

Bipolar plates and graphite felt electrodes were thermally fused to one single component via a newly developed electro-welding process. A dropwise arrangement of the polymeric binder led to mechanically stable bonding and was documented by X-ray micro-computed tomography. Electrical conductivity of the fused components was achieved without any conductive filler and electro-welded samples show lower resistance values than unbonded ones at the same graphite felt electrode compression of 5% in ex situ electrical conductivity measurements. Applicability was demonstrated in situ in a 2-cell vanadium redox flow battery stack operated at a graphite felt electrode compression rate of 5% only. Obtained energy efficiencies of the battery are at least equal or even higher compared to state of the art vanadium redox flow battery with unbonded components at 20% graphite felt electrode compression. Composite components will simplify stack assembly and their increased electrode porosity during operation is expected to reduce pressure drop and to increase overall system efficiency.

The Integration of Mechanical Energy Absorbers into Rollover Protective Structures to Improve the Safety of Agricultural Tractors in the Event of Rollover

The combination of safety belts and rollover protective structures (ROPSs) is key in improving the safety of agricultural tractors in the event of rollover. However, we also have the opportunity to enhance the security provided by each ROPS; one such example is the combination of this safety device with adequate mechanical energy absorbers (MEAs). Inexpensive disc-shaped MEAs can be included in the anchoring points of a ROPS onto the chassis of a tractor. Three configurations of ROPS combined with MEAs were tested during the application of loads that simulated the effects of side rollover in the vehicle. The tested configurations included a blank MEA as a reference case alongside a single MEA and a stack assembly containing both elements. The results of the tests show that both the deformation of the ROPS itself and the strain energy are larger in the case of blank MEAs; thus, there is also a risk that the clearance zone will be infringed upon and that the protective structure will collapse. We can conclude that the implementation of an appropriate MEA in ROPS reduces the deformation of the ROPS itself and its strain energy in cases of vehicle rollover; hence, the safety provided by such protection systems may be improved at a low cost.

Advancing electrodialysis: Harnessing the potential of spiral-wound membrane stacks for improved desalination-efficiency and cost-efficiency

Membrane separation technology encompasses a variety of processes, of which electrodialysis (ED) has become one of the irreplaceable technologies due to its high concentration factor and energy saving. Currently, the main membrane stacks of ED technology on the market are plate-and-frame membrane (PFM) stacks, while there are almost no spiral-wound membrane (SWM) stacks. The SWM stacks have many advantages, such as higher mass transfer efficiency, higher packing density, etc. Inspired by its advantages, we have designed and assembled a SWM for ED. In this study, the PFM and SWM stacks in the efficacy of the two processes were compared using the Finite Element Method to simulate the distribution of fluid and electric fields within the stacks. The desalination efficiency of SWM has been improved compared with that of PFM. In particular, when the voltage is 36 V, the single path desalination rate is 98.7 %. The effective area of the membrane stack has been increased from 63.6 % to 88.9 % since the components of the SWM stack are more efficient and easy to assemble. Due to its low cost, excellent performance and partial fluid simulation, it is believed that this work can provide an inspiration for the assembly of membrane stacks.

Experimental Study on the Electrochemical Performance of PEMFC under Different Assembly Forces

Proton exchange membrane fuel cell (PEMFC) is of paramount significance to the development of clean energy. The components of PEMFC are assembled using many pairs of nuts and bolts. The assembly champing bolt torque is critical to the electrochemical performance and mechanical stability of PEMFC. In this paper, a PEMFC with the three-channel serpentine flow field was used and studied. The different assembly clamping bolt torques were applied to the PEMFC in three uniform assembly bolt torque and six non-uniform assembly bolt torque conditions, respectively. And then, the electrochemical performance experiments were performed to study the effect of the assembly bolt torque on the electrochemical performance. The test results show that the assembly bolt torque significantly affected the electrochemical performance of the PEMFC. In uniform assembly bolt torque conditions, the maximal power density increased initially as the assembly bolt torque increased, and then decreased on further increasing the assembly torque. It existed the optimum assembly torque which was found to be 3.0 N·m in this work. In non-uniform assembly clamping bolt torque conditions, the optimum electrochemical performance appeared in the condition where the assembly torque of each bolt was closer to be 3.0 N·m. This could be due to the change of the contact resistance between the gas diffusion layer and bipolar plate and mass transport resistance for the hydrogen and oxygen towards the catalyst layers. This work could optimize the assembly force conditions and provide useful information for the practical PEMFC stack assembly.

Differentiating Plasmon-Enhanced Chemical Reactions on AgPd Hollow Nanoplates through Surface-Enhanced Raman Spectroscopy.

Plasmonic photocatalysis demonstrates great potential for efficiently harnessing light energy. However, the underlying mechanisms remain enigmatic due to the transient nature of the reaction processes. Typically, plasmonic photocatalysis relies on the excitation of surface plasmon resonance (SPR) in plasmonic materials, such as metal nanoparticles, leading to the generation of high-energy or "hot electrons", albeit accompanied by photothermal heating or Joule effect. The ability of hot electrons to participate in chemical reactions is one of the key mechanisms, underlying the enhanced photocatalytic activity observed in plasmonic photocatalysis. Interestingly, surface-enhanced Raman scattering (SERS) spectroscopy allows the analysis of chemical reactions driven by hot electrons, as both SERS and hot electrons stem from the decay of SPR and occur at the hot spots. Herein, we propose a highly efficient SERS substrate based on cellulose paper loaded with either Ag nanoplates (Ag NPs) or AgPd hollow nanoplates (AgPd HNPs) for the in situ monitoring of C-C homocoupling reactions. The data analysis allowed us to disentangle the impact of hot electrons and the Joule effect on plasmon-enhanced photocatalysis. Computational simulations revealed an increase in the rate of excitation of hot carriers from single/isolated AgPd HNPs to an in-plane with a vertical stacking assembly, suggesting its promise as a photocatalyst under broadband light. In addition, the results suggest that the incorporation of Pd into an alloy with plasmonic properties may enhance its catalytic performance under light irradiation due to the collection of plasmon-excitation-induced hot electrons. This work has demonstrated the performance-oriented synthesis of hybrid nanostructures, providing a unique route to uncover the mechanism of plasmon-enhanced photocatalysis.

Reinforcement Learning with Task Decomposition and Task-Specific Reward System for Automation of High-Level Tasks.

This paper introduces a reinforcement learning method that leverages task decomposition and a task-specific reward system to address complex high-level tasks, such as door opening, block stacking, and nut assembly. These tasks are decomposed into various subtasks, with the grasping and putting tasks executed through single joint and gripper actions, while other tasks are trained using the SAC algorithm alongside the task-specific reward system. The task-specific reward system aims to increase the learning speed, enhance the success rate, and enable more efficient task execution. The experimental results demonstrate the efficacy of the proposed method, achieving success rates of 99.9% for door opening, 95.25% for block stacking, 80.8% for square-nut assembly, and 90.9% for round-nut assembly. Overall, this method presents a promising solution to address the challenges associated with complex tasks, offering improvements over the traditional end-to-end approach.

Effects of Inhomogeneous Gas Diffusion Layer Properties on the Transportation Phenomenon and Performances of Proton-Exchange Membrane Fuel Cells.

The encapsulation of the proton-exchange membrane fuel cell (PEMFC) is an essential step of fuel cell stack assembly. The selection of the assembly pressure is very important to the stack performance and life. Based on that, this paper presents a method to describe the internal physical deformation of the gas diffusion layer (GDL) after inhomogeneous pressure by using user-defined functions (UDFs). The results show that the transmission difference caused by the nonuniform GDL deformation can be clearly seen by the UDFs method, and there is an obvious transition of GDL at the interface of the channel and the rib. A three-dimensional single-channel PEMFC model is established, and an optimal assembly pressure range is obtained, between 1.5 and 2.0 MPa. The maximum thermal stress inside the cell occurs in the middle of the membrane electrode assembly and decreases as the assembly pressure increases. Furthermore, the influence of rib-channel ratios is discussed. Compared to the fuel cells with ratios of 2:1, 2:3, and 1:2, the one with 1:1 exhibits the maximum current density and the highest power density.

Pyrolysis-Free Covalent Organic Polymers Directly for Oxygen Electrocatalysis.

ConspectusOxygen electrode catalysis is crucial for the efficient operation of clean energy devices, such as proton exchange membrane fuel cells (PEMFCs) and Zn-air batteries (ZABs). However, sluggish oxygen electrocatalysis kinetics in these infrastructures put forward impending requirements toward seeking efficient oxygen-electrode catalytic materials with a clear active-site configuration and geometrical morphology to study in depth the structure-property relationship of materials. Although transition-metal-nitrogen-carbon (M-N-C) electrocatalysts have shown great prospects currently and potential in oxygen electrocatalysis as promising platinum group metal-free catalysts, the universal pyrolysis operation in the preparation process often inevitably brings about randomness and diversity of active sites, for which it is difficult to determine the structure-activity relationship, understand the catalytic mechanism, and further improve facilities performance.Covalent organic polymers (COPs) are a class of molecular geometric constructs linked by irreversible kinetic covalent bonds through reticular chemistry. Unique structural tailorability, diverse design principles, and inherent well-defined construction in pristine COPs naturally provide a great platform to study the structure-property relationship of active sites and exhibit unique features for application. In this Account, we afford an overview of our recent attempts toward the utilization of COP materials as free-pyrolysis oxygen electrode catalysts, enabling accurate construction of oxygen electrodes with clear active site and geometrical morphology characteristics in PEMFC and ZAB devices yet without enduring any high-temperature pyrolysis treatments. Starting from the needs of modern electrocatalysis, we discussed the unique properties for the design and development of pyrolysis-free pristine COPs as high-performance oxygen electrode catalytic materials in terms of intrinsic electronic structure properties and membrane-electrode-assembly (MEA) application distinguished from pyrolysis M-N-C catalysts. First, the pyrolysis-free COP catalysts provide a viable molecular model catalyst platform, which is conducive to mechanism comprehension for the relationship between catalyst activity and structure. Second, the simple and low-energy consumption synthesis process for pyrolysis-free catalysts lays the foundation for the large-scale production of catalysts, oxygen electrodes, and even the entire stack assembly without considering numerous complicated factors as traditional pyrolytic catalysts. Besides, most traditional COPs are difficult to dissolve and solution process due to their cross-linked skeleton. Our newly developed COP materials with solution processability bring about new opportunities to the process and assemble oxygen electrodes into device. These properties are unparalleled and have not been systematically reviewed and analyzed by any research reports so far. Here, we have clarified the specific advantage and potential of pyrolysis-free COP materials as oxygen electrodes applied in PEMFC and ZAB devices in response to the latest progress and requirements of current electrocatalytic research.

Development of an Adaptive Human-centered Work Station for Fuel Cell Stack Assembly

Facing the challenges of modern production, such as increased product variability and individuality, assembly systems must strive for maximum flexibility. Consequently, despite the continuous advancements in automation, the human workforce retains its crucial role in industrial assembly due to its exceptional adaptability and learning capabilities. However, the industry is confronted with the additional challenge of addressing a shortage of skilled workers, managing ongoing demographic changes, and handling an increasingly heterogenous workforce in terms of age, skills, and experience. As a result, there is a growing emphasis on the efficient and ergonomic use of the human workforce. In this context, the concept of human-centered production systems has emerged as an important approach.The objective of this paper is to propose a general concept for the implementation of a human-centered assembly system that can adapt to different human characteristics in terms of anthropometry, functional capabilities, knowledge, and personal needs during the assembly process. This in-process adaptation is based on the tracking of human movements and actions during the assembly process using LiDAR and camera technology. The collected data is utilized to feed a recommender system that serves to suggest possible configuration optimizations in the assembly system dimensions of Working height, Range of vision, gripping area, and handedness, Lighting and Use of information and assistance systems, encompassing a laser projector, spatial augmented reality facilitated by a dynamic beamer, and intelligent tools.Subsequently this general approach is applied to the development of a work station designed for the assembly of fuel cell stack components.

Performance comparison of bio-inspired flow field designs for direct methanol fuel cell and proton exchange membrane fuel cell

Bipolar flow channel plate design, which is a key component and performance qualifier of fuel cells, is an extensively investigated area. Recently, bio-inspired flow fields (FFs) have been designed to increase the overall performance as an alternative to traditional FFs. In the present study, performance evaluation of the various bio-inspired FFs was carried out in PEM fuel cell and direct methanol fuel cell modes. The effects of the main performance characteristics including the clamping force of the short stack assembly, air flow rate, and operating temperature on the cell power were investigated for both PEMFC and DMFC modes. The highest performance output was ensured with the Morus leaf-inspired FF (MLFF) at PEMFC mode at 55 °C with a peak power density of 313 mW/cm2. Besides, the highest performance for DMFC mode was achieved at 35.8 mW/cm2 with the Ficus Carica leaf-inspired FF (FCLFF).

Present and Future Perspectives on Fuel Cell Membrane Chemical Stability

Durability is key to the value proposition of proton exchange membrane (PEM) fuel cells for transportation applications. Ultimately, fuel cell vehicles need to match the lifetimes of diesel powered trucks, and last longer than lithium batteries, for widespread adoption[1]. The burden of reaching these aggressive targets falls on all components of the system, stack, and membrane electrode assembly. Of these, membrane durability remains an important area of research, in particular the chemical stability of the ionomer. The recognition of the ‘simple unzipping’ of the perfluorosulfonic acid (PFSA) backbone by hydroxyl radicals (HO·)[2],[3] and the subsequent introduction of cerium radical scavengers[4],[5] mark significant advancements in fuel cell lifetimes. Yet, even with this technology, it is unclear if this class of membranes can meet the 25,000+ hours required for heavy duty applications without additional improvements. Furthermore, recent proposals to restrict usage of fluorochemicals in many applications[6] presents a risk to the rapidly growing PEM fuel cell and water electrolysis markets. This talk will outline recent work that looks beyond simple peroxide degradation of PFSA ionomers and highlight the role of other reaction mechanisms suspected in accelerated fuel cell durability testing. Analysis of effluent water for ionomer fragments during these tests provides a greater understanding of the degradation mechanisms and suggests additional pathways beyond back-bone unzipping. Not only are these fragments useful in inferring reaction mechanisms, but there is also evidence they adsorb to the platinum surface, ultimately adding to performance decay. In other words, increased membrane durability may also result in increased catalyst stability. Finally, chemical stability of hydrocarbon membranes will be considered in light of the advances over the last two decades in understanding PFSA stability. Similarities and differences will be discussed between these two classes of PEM membrane with suggestions on how the techniques used to understand PFSA stability could be applied to hydrocarbon ionomers and advance the understanding of chemical stability in these systems.[1] Cullen, D. A.; Neyerlin, K. C.; Ahluwalia, R. K.; Mukundan, R.; More, K. L.; Borup, R. L.; Weber, A. Z.; Myers, D. J.; Kusoglu, A. New Roads and Challenges for Fuel Cells in Heavy-Duty Transportation. Nat Energy 2021, 6 (5), 462–474. .[2] Curtin, D. E.; Lousenberg, R. D.; Henry, T. J.; Tangeman, P. C.; Tisack, M. E. Advanced Materials for Improved PEMFC Performance and Life. Journal of Power Sources 2004, 131 (1), 41–48.[3] Coms, F. D. The Chemistry of Fuel Cell Membrane Chemical Degradation. ECS Trans. 2008, 16 (2), 235.[4] Frey, M. H., Pierpont, D. M., Hamrock, S. J., US 8,367,267 and US 9,431,670[5] Coms, F. D.; Liu, H.; Owejan, J. E. Mitigation of Perfluorosulfonic Acid Membrane Chemical Degradation Using Cerium and Manganese Ions. ECS Trans. 2008, 16 (2), 1735.[6] European Chemicals Agency (ECHA) proposal submitted 7th February 2023

Anion Exchange Membrane Using Fused Expanded Pyridinium As Their Cationic Unit

Ion conductivity is expressed as a function of the Faraday constant, ion concentration, and mobility. Thus, an increase in both ion concentration and mobility is crucial for increasing the ion conductivity. Ion mobility reflects ionic motion in the restricted area of ion conduction channels. The general approach to expand ion conduction channels in AEM is to introduce a large number of ionic groups, i.e., to increase ion-exchange capacity (IEC). Because the increase of IEC also increase ion concentration, increase of IEC have been major strategy for increasing ion conductivity. However, this approach causes softening of the AEM because high IEC involves large amount of water uptake (WU).On the other hand, the ion concentration in AEM is also affected by the dissociation constant of the ionic groups. However, conventional ionic groups in AEMs, such as ammonium cations, suffer from a low dissociation constant that leads to low ion conduction in AEM. Previously, we found that a fused expanded pyridinium cation (FEP) having a delocalized positive charge showed high dissociation of OH– owing to the weak interaction between the soft acid (FEP) and the hard base (OH–) which can be explained based on the Pearson Hard Soft Acid Base (HSAB) principle. As the result, AEM with FEP unit exhibited excellent ion conductivity of 123.4 ±13.3 mS cm–1 at 80 °C with very low IEC (0.77 mmol g-1).Recently, we synthesized alkylated fused expanded pyridinium (CxFEP) with alkyl chain lengths (x) of 0, 6, 12, and 18 and introduced into polymers as side chains for AEM applications. FEP is characterized by a large π cation that offers weak electrostatic interactions with anions such as hydroxide (OH–) ions and therefore leads to high OH– conductivity in AEM. CxFEP shows synergetic effect between the π-π interactions of FEP and van der Waals interactions of the alkyl chains and forms a strong assembly, particularly for C6FEP. On the other hand, when CxFEP was introduced into the polymers, C12FEP formed an ordered stacking assembly in the films, whereas the other polymers with shorter (C0 and C6) and longer (C18) alkyl chains exhibited no such ordered structure. For the AEM, all the polymers showed higher ion conductivities than that of commercial ammonium-based AEM, even with their low ion exchange capacities (IEC), probably because of their characteristic weak interactions between the FEP cation and OH–. In particular, the AEM with C12FEP showed the highest ion conductivity of 143.3 ± 27.3 mS cm-1 even with a very low IEC of 0.41 mmol g-1. In addition to the high ion dissociation of FEP, the molecular assembly of FEP provides ionic conduction paths. This study demonstrates the importance of high ion dissociation and formation of a conduction pathway for AEM with high conductivity.