Membrane Thickness Research Articles

(Invited) Development of Second Generation New Structure Fuel Cell Stack

Honda and GM have started co-development program for fuel cell system in 2013. In January of 2024, FCSM (Fuel Cell System Manufacturing, LLC), which was established in 2017 at Brownstown in Michigan, USA, as the joint venture company between Honda and GM, has launched new generation fuel cell system in the world. This new system has adopted new generation (GEN2) fuel cell stack, which has achieved 1/3 cost and 2-time durability compared to previous generation (GEN1) stack with satisfied basic performance.GEN2 stack has also achieved equivalent net power to GEN1 stack even though the stacking number of the cells is reduced in terms of cost reduction. Main features of GEN2 cost reduction are below; 1) Elimination of the outer peripheral structure of the rubber for Bipolar Plate (BPP) with the combination of metal bead seal for BPP and the filters for stack case, 2) Reduction of total Pt amount by adopting Pt alloy catalyst and reduction of polymer electrolyte membrane thickness, 3) Complete automated stack assembly line from Unitized Electrode Assembly (UEA ; membrane electrode assembly with subgasket), cell unitization of UEA and BPP to cell stacking.In order to achieve 2-time durability of the stack, the novel coating for BPP is applied for the reduction of Fe elution from the plate material, and cell-by-cell cooling concept is adopted to improve the cooling performance of the stack.New designed BPP has adopted the novel coating, metal bead seal and welding seal structure to achieve both durability improvement and cost reduction. The novel coating is applied to the coil material before stamping. The BPP for GEN1 stack had adopted gold coating, which resulted higher cost for this specific parts. The novel coating can balance good conductivity and durability of the plate against elution. As a result, the new plate can eliminate expensive material for the coating. New metal bead seal and welding seal structure also help cost reduction. Previous BPP design adopted the rubber seal for the outer peripheral by injection molding. This manufacturing method takes longer time for the molding process. By the combination of metal bead seal and filter concept for stack case, that can realize to eliminate the rubber seal structure for BPP. As a result, the tact time for the manufacturing process of BPP is significantly reduced to help total cost reduction of the parts.New designed UEA has adopted Pt alloy catalyst for electrode, thinner polymer electrolyte membrane and general purpose plastic material for the subgasket. Pt alloy catalyst can enhance the electrode activity for the reaction in the cell, and helps to reduce the total amount of Pt. Precise degradation models for electrode performance and membrane degradation have been developed. That also helps to reduce the amount of catalyst down to 1/5 and membrane thickness down to 3/5 compared to GEN1 model by providing appropriate operating condition in terms of total fuel cell system control. For subgasket, GEN1 model had adopted injection molding plastic. That process takes longer tact time for manufacturing as same as that for the previous BPP. New designed BPP flow field helps to adopt simple structure of UEA subgasket. As a result, general purpose plastic material can be applied as subgasket material. That contributes to reduce material cost and significant reduction of tact time for the manufacturing process.New design stack has adopted stack case instead of panel type structure for GEN1 model. By reconsidering functions of BPP and stack structural parts, that contributes to reduce the number of the structural parts of the stack.New designed stack assembly line has achieved highly efficient stack manufacturing process. By redesign of BPP and UEA, complete automated stack assembly line from UEA to cell stacking can be realized. As a result, the new stack assembly line has achieved significant reduction of stack manufacturing tact time.This new generation fuel cell system with GEN2 stack is installed to brand-new CR-V e:FCEV in 2024. Honda will also provide this system to the customers for the various application such like as commercial vehicles, stationary power stations and construction machinery and so on to contribute to achieving carbon neutrality of the world.

Overcoming Challenges in Ion-Pair Membrane Technology: Advancements in Fuel Cells and Electrochemical Hydrogen Pumps

The Membrane Electrode Assembly (MEA) stands as the pivotal element in electrochemical devices such as fuel cells and electrochemical hydrogen pumps (EHP). Notably, ion-pair High-Temperature Proton Exchange Membrane Fuel Cells (HT-PEMFCs) with reduced phosphoric acid concentrations within the MEA have been innovatively designed, allowing for the integration of diverse ion-conducting binders, known as ionomers, into both the cathode and anode electrodes [1]. This study delineates initial distinctions in MEA configurations among different device types (HT-Fuel cell and EHP, conducting a comprehensive analysis of performance disparities between traditional polybenzimidazole-based systems and various ion-pair proton exchange membranes [2].Subsequently, a detailed exploration unfolds, focusing on the utilization of ion-pair membranes and different ionomer types for the three aforementioned devices. This comprehensive examination offers a unified comparative analysis encompassing ionomer type, membrane thickness, catalyst:ionomer ratio, and phosphoric acid doping levels, particularly in the context of performance at intermediate temperatures (160℃). Conclusions are drawn based on results derived from both half-cell and single-cell evaluations. Finally, overarching guidelines are presented to inform the formulation of high-performance MEA configurations tailored for ion-pair HT-PEMFCs and EHPs.

Computational Modeling of Proton Exchange Membrane Electrolyzer

Hydrogen holds great promise to help decarbonize our energy sector. Proton exchange membrane electrolyzers (PEMELs) are undergoing rapid development and deployment for the generation of green hydrogen based on renewable sources of electricity. The inherent capacity of PEMELs to readily respond to fluctuations in electricity input is an added advantage for the generation of hydrogen. PEMEL optimization with regard to materials, component design, and operating conditions is critical for high performance and efficiency. The development of a robust computational model for PEMELs can facilitate not only an improved understanding of the relevant physical and electrochemical phenomena but also help to develop and test effective strategies for performance optimization. The current research is aimed at developing a 3D parallel flowfield channel PEMEL model in COMSOL Multiphysics. To date, results have been obtained for a single-phase model with the baseline operating temperature and relative humidity (RH) of 60°C and 90%, respectively, under the following assumptions: (1) the feed gas (water vapor) is treated as an ideal gas, (2) the flow in the channel is laminar and incompressible, (3) membrane, catalyst layer (CL), and porous transport layer (PTL) microstructures are assumed to be homogeneous and isotropic, and (4) all physical and electrochemical processes are considered to be at steady state. The simulated polarization curve was validated against in-house experimental data for Nafion 115 at 60°C. We then investigated the effect of operating temperature and membrane thickness on current density, overpotentials due to cell resistance, and polarization curves. It was observed that the PEMEL performance improved significantly with temperature, owing primarily to the higher protonic conductivity of the membrane and improved catalyst kinetics. Polarization curves were also obtained for Nafion 212 (50.4 µm) and 117 (178 µm) at 80°C and the thinnest membrane, i.e. Nafion 212, performed better than its thicker counterparts due to reduced ohmic losses. We are currently developing a two-phase flow PEMEL model wherein liquid water is supplied to the anode inlet, and oxygen gas mixed with liquid water emerges from the anode exit. At high current density, oxygen bubbles can obstruct the reactant flow to the anode catalyst layer resulting in suboptimal PEMEL performance. Results will be presented for the dynamics of two-phase flow in a PEMEL system under various operating conditions from which we may draw insights to optimize PEMEL performance.

(Invited) Unravelling Loss Mechanisms in PEM Water Electrolysis Cells Via Elaborated in Situ Techniques

The urge for changes in our energy mix and in finding sustainable solutions for energy provision, pushes towards fast developments in the field of hydrogen technologies. Proton exchange membrane (PEM) water electrolysis is one of the most promising solutions for a green hydrogen production, but developments of this technology are necessary to make it cheap and feasible.To achieve this, it is necessary to have well-established and advanced characterization methods. These methods can help us understand the limitations and identify areas for improvement in cheaper, performing, and alternative materials. They can also assist us in reducing the production and activation effort of its components. By identifying the specific mechanisms or factors that limit performance or stability under certain conditions, our advanced in situ characterization techniques can provide valuable insights on durability aspects.Before utilizing advanced methods for evaluating PEM electrolysis cell, it is fundamental to accurately assess effects and changes during the tests. These changes must exceed the reproducibility error of our tests to be considered as performance variations only. To achieve this, a round robin test is conducted, which provides reproducibility error within our facility and across different institutes[ 1,2 ]. This study also offers a thorough overview of fundamental characterization, such as polarization curves and electrochemical impedance spectra (EIS).When conducting EIS measurements, it is essential to ensure that external influences are not included in the evaluation and that the discussed mechanisms belong only to the electrolysis cell response[ 3 ]. Improving our cell structure and voltage sense connection allows to uncover previously hidden processes occurring in the high frequency region of the impedance spectrum. This helps to develop reliable equivalent circuit models (ECM) that accurately represent the electrochemical, transport and electrical mechanisms taking place within an electrolysis cell.Impedance spectra serve as a valuable tool for assessing various processes occurring during electrolysis. When combined with a reference electrode, it is possible to evaluate the contribution of each electrode. It allows us to determine which electrode undergoes the most significant variations during cell activation or break-in. Additionally, EIS conducted with a reference electrode and distribution of relaxation times (DRT) can firstly provide evidence to the extent of contribution of each electrode to the overall spectra and can also specify the limiting processes associated with each electrode. The former evaluation is achieved via comparison of tests with variating operating condition in the very first hours of operation (activation or break-in). The latter study is approached via tests with different catalyst layer loadings and membrane thicknesses. These half-cell results can be used to drive developments in manufacturing of catalyst coated membrane (CCM) and fine-tuning the improvements of the electrode performance.

Understanding Durability of Polymer Electrolyte Membrane Water Electrolyzers

Hydrogen is positioned to play a pivotal role in the future energy landscape, bolstered by the increasing adoption of renewable energy sources. The U.S. Department of Energy (DOE) has initiated the Hydrogen earth shot, with a goal of achieving a cost target of $1 per kilogram of hydrogen within a decade. Polymer electrolyte membrane water electrolyzers (PEMWE) are at the forefront of enabling hydrogen production from renewable electricity. Yet, achieving the 80000 h operational lifetime remains a critical challenge for the commercial viability of PEMWE.1 An in-depth understanding of the conditions affecting the degradation of critical PEMWE components including the catalyst layer, membrane, and porous transport layers is crucial for achieving the durability target of PEMWE.In this study, we explore the effect of various operating conditions, such as temperature, pressure, and cycling vs. hold of voltage or current, and the membrane electrode assembly composition, including catalyst loading, membrane thickness, and incorporation of gas recombination catalyst (GRC), on degradation in PEMWE. To assess the degradation rate, our protocol involved long duration durability tests, alternating between high and low current density cycles with long holding periods and rapid cycling. Electrochemical characterization including polarization curve, electrochemical impedance spectroscopy, and cyclic voltammetry will be presented. Additionally, electron microscopy and X-ray spectroscopy analysis provides insight into changes in the catalyst layer. The second part of the study focuses on understating membrane degradation in PEMWEs. Through periodic analysis of the cathode and anode effluent water during long duration current density holds, the fluorine emission rate (FER) was estimated, a key metric for assessing membrane and ionomer loss. Preliminary investigation reveals that incorporation of GRC in the membrane reduces hydrogen crossover, thereby lowering the FER and the degradation rate. This study enhances our understanding of PEMWE degradation, offering critical data to develop accelerated stress test (AST) protocols.Acknowledgment:This research is supported by the U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office through the Hydrogen from Next-generation Electrolyzers of Water (H2NEW) consortium.Reference: Tomic, A. Z., Pivac, I., Barbir, F., Journal of Power Sources (2023) 557

In Preparation of Using Confocal Raman Spectroscopy to Study Mass Transport in Bipolar Membranes

As the world produces more renewable energy in the need to transition away from fossil fuels, the use of low-temperature electrochemical reactors is an increasingly important topic of research. An enabling component of electrochemical reactors is an ion exchange membrane, which selectively transports either cations, in a cation exchange membrane (CEM), or anions, in an anion exchange membrane (AEM), from one compartment of a reactor to another. When a CEM and AEM are physically combined they can create a bipolar membrane (BPM), which can generate protons and hydroxide ions from water dissociation at the junction of the AEM and CEM when operated in reverse bias, while also reducing unwanted ion crossover in electrodialysis and electrolysis applications. Maintaining the junction interface is critical to the operation of a BPM, however due to the small size of the junction and the similarities of appearance between the AEM and CEM, it is difficult to obtain spectroscopic information about the BPM junctions. Additionally, in the literature the mechanism behind BPM failures are not well reported. These gaps in knowledge make rational design for improved membranes hard to achieve. Here, we use Confocal Raman Spectroscopy (CRS) to spatially observe spectral data throughout the AEM, CEM and AEM/CEM junction of a novel 3D spun bipolar membrane. CRS uses a monochromatic light to initiate and observe Raman scattering from the polymers in each membrane, showing characteristics of the polymer backbone structure, linkers, and ion exchange functional groups, throughout the membrane thickness. The confocal Raman microscope enables spectrum collection from a micron scale voxel, as opposed to the bulk volume, resulting in a nominally non-destructive technique for making spatiotemporal measurements. Using CRS, we identify the BPM junction thickness and homogeneity through 3-dimensional spatial mapping. We also demonstrate the ability of CRS to analyze the method of BPM failure when used in an electrodialysis reactor by obtaining spectral maps of failed membranes, showing junction delamination, ionic buildup in either the CEM or AEM, and ionic polymer breakdowns of the CEM or AEM due to contaminants. In collaboration with experimental collaborators, 3D BPM fabrication techniques were assessed for their impact on overall BPM performance and durability, while demonstrating the non-destructive usage of the CRS technique.

Modeling Hydrogen Crossover in Proton Exchange Membrane Water Electrolyzers with and without Recombination Catalyst Interlayers

Low-temperature proton exchange membrane water electrolyzers (PEMWEs) are poised to undergo rapid expansion in the coming decades for clean hydrogen production. Hydrogen has been hailed as the ‘Swiss Army knife’ of decarbonization as it can help mitigate carbon dioxide emissions from ammonia production, metal refining, and heavy-duty vehicle transportation. Proliferation of clean hydrogen production necessitates large reductions in iridium loadings in the anode while also operating at higher current density values. The latter goal can be achieved by adopting thinner proton exchange membranes (PEMs), but the use of thinner membranes exacerbates hydrogen crossover – which leads to unacceptable levels of hydrogen in the anode effluent poising safety concerns (i.e., above the lower explosion limit of 4 vol% hydrogen in oxygen). Notably, the hydrogen content in the anode effluent is high when operating the PEMWE at low current density values (0.1 to 0.5 A cm-2). A PEMWE will sometimes throttle down and operate at low current density because of the intermittent nature of renewable energy sources which are used to power the electrolyzer. Recombination catalyst (RC) interlayers, located within the PEM, can consume hydrogen and mitigate the hydrogen concentration in the anode effluent. This Talk presents our continuum-level modeling approach for hydrogen crossover in PEMWEs with membranes containing RC interlayers. The model accurately captures the hydrogen content in the anode effluent as a function of the PEMWE current density, cathode back pressure, membrane thickness, anode backpressure, RC location, and RC loading. The modeling results, as well as experimental observations in the literature, suggest that RC interlayer effectiveness is limited by oxygen availability at the RC interlayer. The low oxygen concentration at the interlayer relative to hydrogen arises from the lower solubility of oxygen in hydrated PEMs and the lower diffusivity of oxygen in hydrated PEMs. The Talk concludes with future directions to improve the model as well as suggestions for future experiments to aid the accuracy of the model.

Effect of Contamination in the Carbon Catalyst Support on Chemical Degradation of Polymer Electrolyte Membranes in Fuel Cells

Introduction One of the key components of polymer electrolyte fuel cells (PEFCs) is the polymer electrolyte membrane (PEM). The PEM facilitates the transport of protons from the anode to the cathode, acts as an electronic insulator to prevent short circuits, and plays a role in preventing the direct reaction of hydrogen gas and oxygen in air. One of the major technical issues with PEMs is their chemical degradation, causing decomposition of their molecular structure. This leads to reduced protonic conductivity, increased hydrogen and oxygen crossover, and reduced mechanical strength, all of which significantly affect the power generation performance and durability of PEFCs (1). In addition, in our laboratory, the use of SnO2 and mesoporous carbon (MC) as cathode catalyst supports has been suggested to suppress membrane degradation (2). However, the relationship between the cathode catalyst materials and the chemical degradation of PEM has not yet been fully understood. Here in this study, we conduct durability tests such as accelerated chemical degradation of PEM in cells using cathode electrocatalysts with different carbon support materials, aiming to clarify the effects of carbon support materials properties (structure, contaminants, and graphitization) on the chemical degradation of electrolyte membranes. Experimental A commercial Pt/KB catalyst (TEC10E50E, Tanaka Kikinzoku Kogyo, Japan) was used as the anode catalyst. Several types of cathode catalysts were applied and compared: the commercial Pt/KB; Pt/MC where Pt was directly deposited on the MC; and various electrocatalysts where Pt was directly deposited on carbon supports such as graphitized AB (acetylene black). The durability test at open circuit voltage (OCV) was performed for 100 h. Before and after the durability test, cell performance, hydrogen crossover current density, and electrochemical surface area (ECSA) were characterized. The degree of membrane degradation was evaluated by measuring fluoride-ion emission rate (FER) by ion chromatography, and membrane thickness by cross-sectional observation with a focused-ion-beam scanning electron microscope (FIB-SEM), as illustrated in Fig.1. Moreover, contaminants and graphitization of the carbon support materials were also analyzed, and their relationship to membrane degradation was considered. Results and discussion The results of OCV holding tests up to 100 h for four different MEAs are shown in Fig. 2. The voltage drop in using Pt/MC as cathode catalysts was smaller than that in using Pt/KB. The FER of Pt/MC as cathode catalysts was lower than that of Pt/KB as shown in Fig. 3, suggesting that the use of MC as carbon supports may suppress PEM degradation. In this presentation, we will show the effects of carbon support materials properties (structure, contaminants, and graphitization) in cathode catalysts on PEM degradation, and discuss possible mechanisms based on the characteristics of various carbon supports. Acknowledgements This paper is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). An educational part for young scientists was supported by the Japan Science and Technology Agency (JST) through the program “Adopting Sustainable Partnerships for Innovative Research Ecosystem” (ASPIRE), Grant Number JPMJAP2307. The presenting author (S. Nakamura) is supported by the Miyamoto Jun-ichi Hydrogen Research Award, and the Kyushu University Q-PIT Support Program for Young Researchers and Doctoral Students. References M. Zatoń, J. Rozière, and D. J. Jones, Sustain. Energy Fuels, 1, 409 (2017).S. Nakamura, T. Ogawa, Z. Gautama, Z. Noda, M. Yasutake, S. M. Lyth, J. Matsuda, A. Hayashi, M. Nishihara, and K. Sasaki, ECS Trans., 112 (4), 315 (2023). Figure 1

Development, Evaluation and Characterization of Hydrophilic Oxide/Polymer Composite Membranes for Polymer Electrolyte Fuel Cells Operating at Temperatures over 80oc

The present transportation system based on the internal combustion engine is a major contributor to the issue of CO2 emission, and a paradigm shift is required toward to electrical motorization based on batteries and polymer electrolyte fuel cells (PEFCs). The motorization of heavy-duty vehicles (HDVs) by PEFCs is one of the essential targets. HDVs will require higher operating temperatures, at least 120oC, versus normal temperatures (60-80oC), for optimal heat management. A commercial perfluorosulfonic acid-based electrolyte (PFSA, e.g., NafionⓇ) shows better proton conductivity with chemical stability over a wide temperature range, although the conductivity decreases under low back pressure at 100~120 oC. In order to improve the proton conductivity in the higher temperature range, a composite membrane of NafionⓇ with a hydrophilic filler of Ta-doped TiO2 (Ta-TiO2) was synthesized. Ta-TiO2 nanoparticles with fused-aggregate network microstructure were synthesized by the flame oxide-synthesis method and were crushed by wet milling (Star Burst, Sugino Machine, Limited Co.). The fillers were mixed with NafionⓇsolution (20 wt.%, D2020 Chemours Co.) by use of a rotary ultrasonic dispersing processor (500 rpm, 60 min., PR-1, THINKY Co.), a planetary ball mill (500 rpm, 30 min., PULVERISETTE 6, FRITSCH Co.), and a defoaming processor (500 rpm、5 min., HM-400W, Kyoritsu Seiki Co.). The dispersion solution was coated in hot air by use of a die coating system (die coater, Taku-Dai Mini-50, Daimon Co., Ltd.), and were hot-pressed (140 ℃, 3 min., TCMD-2.5, TOHO KOGYO Co.) to form composite membranes (9 cm × 9 cm × 25 µmt). The cross-sectional backscattered electron image BSE) of the composite membrane was observed by scanning electron microscopy (SEM, acceleration voltage 2 kV, SU9000, Hitachi High-Tech Co.) and transmission electron microscopy (TEM, H-9500, Hitachi High-Tech Co.). The proton conductivity of the composite membrane was measured at 80 °C and 120 °C by the AC four-probe method. Water uptake of the composite membrane was measured by water vapor adsorption. The current-voltage (I-V) polarization curves of single cells using the prepared composite membrane (membrane thickness, 25 µm) were measured at 80 ℃, 100% RH and 120 ℃, 20% RH, back pressure 50 kPaG.The obtained composite membranes were soft and flexible. The BSE images indicated, based on their high contrast, that the Ta-TiO2 particles were uniformly dispersed in the composite membrane(Fig. 1(a)). The higher magnification of the cross-sectional TEM images also showed that the hydrophilic surface of Ta-TiO2 adhered to the Nafion® without any voids. The proton conductivity of the composite membrane at 80 °C and 80% RH increased with increasing Ta-TiO2 content and showed a maximum value of 0.13 S cm-1at 3 wt% and then decreased. The maximum proton conductivity was 1.3 times higher than that of Nafion®(Fig. 1(b)). The proton conductivity of the composite membrane (3 wt% of Ta-TiO2) at 120 °C, 20% RH reached 0.018 S cm-1, which was 1.8 times higher than that of a commercial Nafion® membrane, 0.01 S cm-1. The water uptake in each composite membrane was nearly independent of the concentration of the hydrophilic oxide at each humidity(Fig. 1(c)). Comparing with literature results, improvements of the proton conductivity by use of various types of additives have been reported, but the improvement of the proton conductivity by such a small percentage of hydrophilic oxide additive without affecting the water uptake in the membrane has not been reported, to our knowledge. We consider that the protonic hopping (proton mobility) might change as a result of adding the hydrophilic Ta-TiO2 in the membrane. The I-V performance of a single cell using a composite membrane preserved the same performance as that of a cell using an unmodified Nafion® membrane at 80 °C and 100% RH, and then improved at 120 °C and 20% RH(Fig. 1(d)).

Exploring the Effects of Recombination Interlayers on Hydrogen and Oxygen Crossover in PEM Water Electrolysis: Insights from 1D Model-Based Investigations

Proton exchange membrane (PEM) water electrolysis presents a promising solution for renewable energy storage and transportation through the production of green hydrogen. A major problem during the operation of PEM electrolysis, regarding both efficiency and safety, is the gas crossover. Small amounts of the produced hydrogen and oxygen gases permeate through the cell membrane to the opposite electrode side. This is problematic because the hydrogen that permeates to the anode is no longer available as product gas, resulting in Faradaic efficiencies less than unity [1]. Furthermore, hydrogen in oxygen mixtures at the anode with hydrogen contents above 4 vol.% are explosive and pose a critical safety issue [2,3]. Hence, several mitigation strategies like thicker membranes, external recombiners, or recombination interlayers (ILs) inside of the membrane have been developed to reduce gas crossover [4].In this study, we focus on ILs that are used to recombine permeating hydrogen with oxygen to water at catalyst particles (e.g., Pt) inside of the membrane, thus lowering the permeating fluxes. The advantages of ILs are that they can be easily integrated into standard cells, no external devices are needed, and previous experimental work has shown that the hydrogen in oxygen content can be lowered substantially. Until today, there are only experimental investigations regarding this topic, which fail to resolve local effects and only show the integral behavior of a PEM electrolysis cell with an IL. In this contribution, we propose the first model-based approach to investigate local potential, temperature, and concentration profiles during the operation of PEM electrolysis cells with a recombination IL. This further facilitates the understanding of the underlying local mechanisms through numerical investigations and enables further optimization of this mitigation strategy. The proposed model is a 1D through-plane stationary model that takes into account the transport of protons, electrons, heat, and gases dissolved in the water. The domain is represented as a series of seven adjacent layers from the anode to the cathode as shown in Figure 1a. A unique feature of the model is the simulation of the local profiles of the gases dissolved in the water of the membrane. These local concentrations allow us to model the reactions taking place in the IL. The proposed model is fully operational and validated with experimental data for different pressure conditions.The model results show that the IL has a major influence on the local concentrations and crossover fluxes (see Figure 1b). When using an IL, the hydrogen crossover flux entering the anode can be reduced compared to operations without an IL. However, the hydrogen crossover flux leaving the cathode, which is the relevant measure for calculating the Faraday efficiency, is increased when using an IL. This is due to a larger concentration gradient from the cathode to the IL compared to the concentration gradient without an IL. Analogous observations can be made for the oxygen crossover. In addition to these investigations, a series of unresolved issues regarding ILs are tackled with the proposed model. These are namely i) the influence of ILs on the operational limits of a PEM electrolysis cell under different pressure configurations, ii) the influence of recombination heat on the cell’s local heat distribution, and lastly iii) the influence of ILs on the Faraday efficiency of the cell. With regard to the latter investigation, the results show that despite having a major influence on the crossover fluxes, the Faraday efficiency stays constant when using ILs. This can be explained by two counter-acting loss processes, which are identified by the proposed model. These numerical results are consistent with experimental observations. Currently, additional experimental work to further elucidate the reaction kinetics inside of the IL and the relevant transport effects to update the model is underway.The authors gratefully acknowledge funding by BMBF in the framework of project evolver, FKZ 03SF0765.

Unraveling a Novel Degradation Mechanism in Industrial Scale PEM Electrolytic Cells by Multimodal Analysis Based on X-Ray Computed Tomography

Proton exchange membrane electrolytic cell (PEMEC) is a key technology in the production of sustainable “green” hydrogen. In such systems, as an electrolyte and physical barrier, a proton exchange membrane (PEM) is applied [1]. Overall, the performance of a PEMEC depends on many factors, such as the catalyst material and its loading, the thickness of electrodes and membrane and the interface roughness for example. While studies have reported changes in PEM microstructures, even in operando [2], there is still limited data regarding process heterogeneity in large industrial-scale cells operating over long periods. However, enhancing the performance and durability of PEMEC is crucial to propel this technology forward, enabling its up-scaling and market introduction on an industrial level.In this study, we investigated the morphology and degradation mechanisms of membrane electrode assemblies (MEAs) in PEMEC using a multimodal analytical approach. The investigated MEAs, which were operated for 5000 hours, consisted of an Ir coated anode and a Pt cathode and were as large as several hundred cm².Firstly, the morphology of post-test MEAs was analyzed by the means of X-ray computed tomography (XCT). Here, a measurement protocol provided imaging data at multiple scales. Furthermore, the field-of-view was greatly increased by rolling the MEA and later unwrapping the reconstructed image. A simple, yet robust segmentation algorithm, allowed to automatically delineate features like agglomerates and cracks inside the electrodes post-test. This thorough XCT study led to the discovery of a novel degradation mechanism in PEMEC, which, to the best of our knowledge, has not yet been discussed in literature. The found morphological anomaly was linked to electrochemical behavior of the cell by analyzing electrochemical impedance spectra (EIS) and measuring the gas permeation through the MEA. Current sensing atomic force microscopy (AFM) was used to analyze the electrical properties in the vicinity of the detected anomalies.Additionally, metallographic techniques such as focused ion beam scanning electron microscopy (FIB/SEM) and transmission electron microscopy (TEM), combined with energy-dispersive X-ray spectroscopy (EDS) and Raman spectroscopy, provided high-resolution local morphology and the chemical composition within the affected regions. Finally, after collecting all this data, we were able to propose physical 1-D and 3-D models for the observed phenomena and their effects on PEMEC.In conclusion, this study on a previously unknown degradation mechanism inside MEAs demonstrates the significance of a multimodal analytical approach when it comes to detecting, understanding and mitigating the degradation in PEMEC. Such an approach will further pave the way for enhanced performance and durability in PEMEC on an industrial scale.[1] B. Han et al., Electrochimica Acta, 2016, 188, 317-326.[2] E. Leonard et al., Sustainable Energy Fuels, 2020, 4, 921-931. Figure 1

Modeling The Hydrogen Crossover Through Membrane With And Without Catalyst Layers

Introduction At elevated temperatures under low humidification, the failure of the Nafion membrane is unavoidable and it leads to fuel/oxidant passing through the membrane yielding loss of fuel, undesired reaction of fuel and oxidant, and further damage to the membrane. The reaction of hydrogen and oxygen possibly results in formation of hydrogen peroxide. That causes degradation and pinhole formation and thus, membrane durability is affected at elevated temperatures. In the current study, the hydrogen crossover rate was measured under wide range of conditions.The hydrogen crossover flux, N H (M) [mol/(m2 s)], is expressed by Eq. (1) as a function of the difference in the partial pressure of hydrogen between the supply and permeate sides, Δp H, and the total pressure difference, ΔP, with the hydrogen permeance, k pH (M) [mol/(Pa m2 s)], and the gas permeation coefficient, k G (M) [mol/(Pa m2 s)], which are both functions of temperature, moisture content, and film thickness. N H (M)=k pH (M)Δp H+y H k G (M)ΔP (1)where y H represents the hydrogen mole fraction on the supply side. Experimental In the experiments, we used Nafion membranes of various thicknesses, NR-211 (25.4 µm), NR-212 (50.8 µm), and N-115 (127 µm), without any pre-treatment. Both the proton exchange membrane (PEM) and the membrane electrode assembly (MEA) samples were used in the testing cell. The catalyst layer thickness was 10 µm with a platinum loading of 0.35 mg/cm2. Our design featured a serpentine gas channel. Hydrogen diluted with nitrogen (H2:N2) and pure N2 were supplied to the supply side and the permeate side, respectively. To measure hydrogen permeation, micro gas chromatograph (Agilent 990 micro GC) connected to the outlet of the permeate side was employed. Results and Discussion Fig. 1(a) shows the N H (M) vs. Δp H profiles measured with NR-212. They displayed a linear tendency at ΔP = 0.5, 25, 50, and 75 kPa. k pH (M) was represented by the slope of N H (M) vs. Δp H. ΔP did not influence the total permeation flux up to 50 kPa as shown in Fig. 1(b). When ΔP increased above 50 kPa, N H (M) increased by approximately 10 %, which resulted from increase in the contribution of the total pressure difference, y H k G (M)ΔP, shown in Fig. 1(c). It means the flux was determined by the partial pressure difference; the total pressure difference did not remarkably contribute to the permeation flux.By modeling the membrane as a bulk layer sandwiched with skin layers, k pH (M) of PEM is expressed by Eq. (2),1/k pH (M)=δ(B)/P H (B)+2δ(S)/P H (S) (2)where the bulk layer thickness and the skin layer thickness are denoted by δ (B) and δ (S), respectively. P H (B) and P H (S) respectively represent the hydrogen permeability through bulk and skin layers. As shown in Fig. 2(a), PEM had the permeation resistance even at zero membrane thickness, which represents the permeation resistance of the thin skin layers. As shown in Fig. 2(b), however, MEA had no skin layers, and the permeation resistance, 1/ k pH (M), of PEM was approximately 1.5 times higher than that of MEA. It suggested the skin layers of PEM were fused with ionomer in catalyst layers (CLs) during hot pressing, which annihilated the skin layers.The slope in Fig. 2(a) gives P H (B) while the intercept gives the H2 permeance of the skin layer, k pH (S) = P H (S)/δ (S). They were found to be power-law functions of the moisture content at each temperature as shown in Figs. 3(a) and 3(b). P H (B) of PEM with and without CLs were substantially equal as shown in Fig. 3(a). The measured P H (B) was formulated as, P H (B) = (1.72×10– 14 mol Pa– 1m– 1 s– 1×λ 0.339) exp[–(22.8 kJ mol– 1/ R){1/T – 1/(353 K)}]Recalculated P H (B) is also shown in Fig. 3(a).The H2 permeance of the skin layer, k pH (S), was formulated as, k pH (S)= (2.71×10– 9 mol Pa– 1 m– 2s– 1×λ 0.858) exp[–(12.3 kJ mol– 1/R (1/T – 1/(353K)}]These equations reproduce the measured data accurately as shown in Figs. 3(a) and 3(b). Conclusions Hydrogen permeance through the bulk layer and the skin layer of PEM was obtained by measuring the permeation flux. The equations estimating them were determined as functions of temperature and moisture content of the membrane. Whereas the bulk layer showed similar behaviors both in PEM and MEA, the skin layer of MEA was not identified. To estimate the H2 crossover in an actual PEFC, the H2 permeance of the PEM should be measured using an MEA instead of a standalone PEM. Figure 1

Stress Corrosion Cracking of Nasicon Pellets in Aqueous Electrolytes

Recent efforts have explored the use of sodium super ionic conductors (NaSICON) in aqueous redox flow batteries (RFBs) because of their ability to selectively conduct sodium ions while effectively preventing the crossover of active species, thereby enhancing the performance and longevity of RFBs. However, despite the potential of NaSICON membranes in enhancing the electrochemical performance of RFBs, the use of dense and thick ceramic membranes results in increased cell resistances. Modak et al. recently suggested that NaSICON membranes with thicknesses below 100 mm may achieve equivalent power densities to RFBs with polymer membrane and meet the resistance criterion.1 Therefore, to realize the commercial application of these thin ceramic films, careful attention must be paid to the membrane’s mechanical properties, especially fracture strength and toughness.Stress-corrosion cracking (SCC) is particularly important for ceramics when they are exposed to water,2 which is defined as the growth of cracks due to the simultaneous action of a stress and a reactive environment. During cell operation, the NaSICON membrane is immersed in corrosive liquid electrolytes and is simultaneously subject to a pressure gradient due to the uneven electrolyte flow. Consequently, understanding the interaction at solid-liquid interface and its impact on NaSICON is crucial as it may affect the fracture toughness of NaSICON and cause unexpected failure.In this study, the toughness of the samples was determined using Vickers indentation. The indentations were imaged using an optical microscope, allowing for measurement of the crack lengths. To assess the evolution of fracture toughness of NaSICON in the presence of typical RFB reactants, the pellets were soaked in selected aqueous solutions. The influence of solution composition, pH value, and molarity are investigated as well as soaking time. Significant crack propagations were observed in all pellets when immersed in solutions, suggesting a decrease in the fracture toughness of the NaSICON pellet after interacting with these liquids. Measurable crack growth was observed to occur mainly within the first 24 hours of immersion, suggesting a equilibrium had been reached between the driving forces for crack propagation (such as stress intensity and corrosive environment) and the resisting material properties (material toughness). To model the influence of SCC during operation of an aqueous RFB, theoretical analysis was conducted to quantify the relationships between the pressure gradient that a NaSICON membrane can withstand under a given geometry, and the evolution of its fracture toughness. These fundamental mechanical studies will provide valuable insights to understand and manage stress corrosion cracking of NaSICON membranes in contact with liquid electrolytes. Modak, S., Valle, J., Tseng, K. T., Sakamoto, J. & Kwabi, D. G. Correlating Stability and Performance of NaSICON Membranes for Aqueous Redox Flow Batteries. ACS Appl Mater Interfaces 14, 19332–19341 (2022).Spearing, S. M., Zok, F. W. & Evans, A. G. Stress Corrosion Cracking in a Unidirectional Ceramic‐Matrix Composite. Journal of the American Ceramic Society 77, 562–570 (1994).

Mechanical Durability of Water Electrolysis Membranes in a Liquid Environment Under Differential Pressure Mode

A perfluorinated sulfonic acid polymer (PFSA) membrane is extensively used in proton exchange membrane（PEM）water electrolyzers for the production of green hydrogen. It is crucial to ensure the membrane’s chemical stability and mechanical durability for long-term performance. PEM is typically assembled with a porous transport layer (PTL), which supports the membrane electrode assembly (MEA), collects current, facilitates water diffusion to catalysts, and must withstand high compressive deformation in a harsh liquid environment over extended periods.It is known that high pressure applied to polymer materials commonly leads to compressive creep. It has been reported that due to such compressive creep deformation, the catalyst layer applied on the PFSA membrane undergoes significant deformation, resulting in the formation of cracks that degrade the performance1-2). Therefore, it is necessary to investigate the creep response of PFSA membranes on PTLs with various diameters and roughness under different pressure modes in order to understand their mechanical durability for long-term performance.In this study, a thermal mechanical analyzer (TMA) was utilized in a hydrated environment with water at 80℃ and 6.2 MPa for over 100 hours. Initially, the PEM was placed on the PTL at 23℃ and immersed in the water chamber. The sample was then heated from 23℃ to 80℃, and once the experimental temperature stabilized at 80℃, a load corresponding to 6.2 MPa was continuously applied to the membrane during measurement. As a result, the membrane thickness rapidly decreased from its initial thickness due to the high pressure, and the membrane deformation gradually slowed down. After over 100 hours of measurement, observations using an optical microscope showed that the membrane in contact with the PTL gradually flowed and penetrated into the pore of the PTL. The relationship between the creep behavior and the penetration of the membrane into the PTL pore, considering various PTLs and membranes, will be presented during the poster session.Reference T, Schuler. et al., J. Electrochem. Soc. 166 (10) F555-F565 (2019)J, Liu. et al., ACS Cent. Sci. DOI: 10.1021/acscentsci.4c00037

Advancements in the Fabrication of Reinforced Proton Exchange Membranes and Exploration of Next-Generation Membrane Technologies

Developing a polymer-electrolyte membrane (PEM) as a water electrolysis (WE) component is crucial for achieving a hydrogen-based economy while reducing CO2 production. Among proton exchange membranes, per-fluorinated sulfonic acid (PFSA) membranes are considered key components due to their high proton conductivity and chemical and thermal stability. Over the next few years, the demand for PFSA membranes in the PEM electrolysis market is expected to rapidly grow, necessitating suppliers to enhance their manufacturing capabilities and membrane quality.Since 1975, AGC has been manufacturing PFSA membranes, contributing significantly to the electrolysis industry, including PEM water electrolysis and chlor-alkali electrolysis, among others. AGC R&D has developed FORBLUETM S-SERIES, a PFSA membrane for PEMWE, using PFSA polymers manufactured in-house from monomers. PFSA membranes possess the following properties: high proton conductivity, high mechanical strength and chemical stability, low gas permeability, and good dimensional stability. PFSA membrane properties can be optimized by adjusting the membrane thickness and the polymer’s ion exchange capacity (IEC). PFSA membrane dimensional stability can be enhanced using reinforcement, which reduces changes in the in-plane dimensions upon the water uptake and facilitates efficient MEA construction. We have developed two reinforced membranes, Sx-0935DH and Sx-1235DH. Sx-0935DH shows high proton conductivity, and Sx-1235DH exhibits low gas permeation ability. For instance, the overpotential of Sx-0935DH was reduced by >80 mV at 3 A/cm2 compared to N115, measured under ambient pressure at 80 °C. Additionally, the hydrogen concentration on the anode side of Sx-1235DH is 20% of that of N115. Currently, we are working on manufacturing the two reinforced PFSA membranes on a large scale via roll-to-roll (RtR) processing.In the water electrolysis industry, there is a demand for thinner membranes to increase proton conductivity and reduce the energy required for hydrogen production. However, thinner membranes tend to have a higher hydrogen permeation ability. Since the lower explosive limit (LEL) for hydrogen in oxygen is only 4 vol%, reducing the hydrogen gas crossover is critical. A gas recombination catalyst (GRC) is used as a membrane component to lower the concentration of hydrogen in oxygen. AGC is developing thinner membranes, incorporating GRC as the next-generation solution.We will present our recent efforts in manufacturing membranes through RtR processing and developing next-generation membranes for water electrolysis.

Fabrication of Alumina Membrane Filters with Framework

Membrane filters are becoming increasingly important because of their wide range of applications. Precise control of the pore size is essential for precise separation using membrane filters. In addition, a high solution permeability is required for efficient filtration. We previously reported that a large alumina membrane filter with a high density of pores and uniform diameter can be obtained by detaching anodic porous alumina from Al substrates by two-layer anodization using concentrated sulfuric acid [1]. Using this method, the pore size and thickness of the resulting alumina membrane can be controlled by adjusting the preparation conditions, making it possible to produce alumina membrane filters suitable for various applications. However, the resulting alumina membrane filters have a nanohole array structure with cylindrical pores, which makes it difficult to achieve efficient filtration because the solution permeability deteriorates as the thickness of the membrane increases. On the other hand, reducing the membrane thickness to improve the solution permeability results in the deterioration of the mechanical durability. Therefore, alumina membrane filters have a problem in that they cannot achieve both solution permeability and mechanical durability. In this report, we describe the preparation of membrane filters with a structure consisting of a thin filter layer formed at the openings of a thick framework that serves as the support layer. The structure of the membrane filter proposed in this study allows the mechanical strength of the membrane to be reinforced by a thick framework and the filter layer to be thin. This allows the membrane filter to achieve a high permeability and mechanical strength, which is a problem with conventional ordered alumina through-pore membranes. Anodic porous alumina, consisting of a thick framework and a thin filter layer, was prepared by selective etching of anodic porous alumina with a resist mask and re-anodization [2]. Finally, an alumina membrane with a framework was fabricated by detaching porous alumina from the Al substrate via two-layer anodization using concentrated sulfuric acid. The framework structure can be controlled by changing the resist pattern formed on the anodic porous alumina. The thicknesses of the filter and framework layers can also be controlled by adjusting the anodization time. The results of the water permeation measurements using the obtained alumina membrane filter confirmed that it exhibited high permeation performance. The membrane filter with the framework obtained in this study is expected to efficiently separate and filter various substances, such as microplastics, viruses, and bacteria.

Nanoscale Proton-Conducting Oxide Membranes for Low Temperature Water Electrolysis

Operating water electrolyzers at higher current densities is an attractive approach to improving the economics of hydrogen production from water electrolysis. Conventional proton exchange membrane (PEM) electrolyzers based on Nafion membranes already operate at relatively high current densities (1.5-2.5 A cm-2), but increasing the current density to 5 A cm-2 or higher would improve the economics even further. Currently, a major limitation of operating low-temperature PEM electrolyzers at such high current densities is the large ohmic drop across the Nafion membrane, which can dramatically lower electrolyzer efficiency. To reduce the membrane resistance and enable efficient operation at high current densities, our team has been exploring the use of nanoscopic proton-conducting silicon oxide (SiOx) membranes. Although the proton conductivity of these oxide membranes is lower than Nafion, we show that their total resistance can be made much lower than conventional Nafion-117 membranes by decreasing their thickness to the nanoscale. The use of sub-micron thick membranes is made possible by the high density of SiOx compared to Nafion, which makes SiOx membranes excellent hydrogen (H2) diffusion barriers for preventing H2 crossover. In this work, we show that the area specific membrane resistance of nanoscale SiOx membranes can be reduced to less than 20% that of Nafion-117 membranes while still maintaining desirable H2 blocking capabilities and avoiding problematic electronic leakage current.

Monitoring ammonia and water transport through anion exchange membranes in direct ammonia fuel cells

Anion exchange membrane direct ammonia fuel cells (AEM-DAFCs) can generate clean electricity with zero carbon emissions. However, their performance are hindered by severe ammonia crossover, which causes a mixed potential at the cathode, thereby reducing the cell voltage. Meanwhile, the produced intermediates, such as Nads species, adsorb onto catalyst, causing poisoning and thus impeding the oxygen reduction reaction (ORR). Another key issue for AEM-DAFCs is to maintain an appropriate water content at the cathode, which is crucial for promoting ORR and avoiding water flooding. In this work, an in-situ observation method is developed to quantitatively characterize the rates of ammonia and water crossover. Besides, a half-cell configuration is designed and developed to evaluate the cathode potential drop caused by ammonia crossover. The effects of operating conditions (such as ammonia concentration and cell temperature) and membrane electrode assembly (MEA) design parameters (such as membrane thickness and cathode wettability) on behaviors of ammonia and water crossover are thoroughly examined. The findings show that ammonia crossover can be substantially reduced by using a low-concentration ammonia solution or a thicker membrane. Moreover, this study offers guidance on developing fuel and water management strategies to enhance the performance of AEM-DAFCs.

Nonsurgical endodontic retreatment of C-shaped maxillary molars: case reports and review of literature

The root canal systems of maxillary first molar (MFM) and maxillary second molar (MSM) variations represent a clinical challenge for endodontists, especially the prevalence of fused C-shaped roots. Having a thorough knowledge of root canal configuration is an extremely important point for a successful root canal treatment to avoid missing extra canals. The aim of this article was to present 2 cases of maxillary molar with an unusual C-shaped configuration diagnosed during root canal retreatment/treatment and conduct a literature review of the MFM and MSM anatomy. Case 1 reports that three separate palatal root canals fused into a C-shaped configuration in the MFM, which with an enamel pearl in the furcation, was classified as Type D and first reported in MFM. Case 2 reflects the fusion of all three buccal canals of the MSM into a C-shaped configuration that finally formed an apical foramen with a supernumerary tooth, and the configuration was Type B. Evaluation at an 18-month and a 9-month recall revealed that two patients were symptom-free after the conduct of a non-surgical retreatment/treatment, and the X-ray revealed normal periapical tissue. In addition, the thickness of the Schneiderian membrane due to odontogenic maxillary sinusitis returns to normal after an effective retreatment in case 1. These reports serve to remind endodontists of the importance and complexity of anatomical variations, which should always be considered when formulating an effective root canal treatment plan. The combined use of cone-beam computerized tomography (CBCT) and a dental operating microscope (DOM) will be profitable to locate and identify extra canals when a periapical radiograph shows signs of an unusual canal morphology.

Membrane thickness dependence of the suspended mini-LED on visible light communication

This study proposes a suspended thin-film blue light emitting diode (LED) device using backside processing to enhance the performance and light extraction efficiency (LEE) of silicon-based GaN LEDs. Photolithography, deep reactive ion etching (DRIE), and inductively coupled plasma (ICP) techniques were used to completely remove the silicon substrate, creating three LEDs with different GaN epitaxial layer thicknesses (5, 4.5, 4 µm). Compared to LEDs without ICP etching, the 5-minute etched LED exhibited superior optoelectronic performance, with current increasing from 75 mA to 99 mA at 3.5 V and peak light intensity 1.3 times higher at 50 mA. The 10-minute etched LED excelled in light-emitting efficiency and visible light communication (VLC), with a clearer eye diagram, highlighting its potential for high-performance VLC applications.