Masamichi Nishihara

Hydrogen production through polymer electrolyte membrane water electrolysis (PEMWE) offers high efficiency, compact design, and compatibility with renewable energy. However, hydrogen crossover presents safety and durability challenges. This study develops a multilayer polymer electrolyte membrane (PEM) incorporating an ultrathin poly(vinyl alcohol) and poly(vinyl sulfonic acid) (PVA/PVS) gas-barrier interlayer to suppress hydrogen crossover while maintaining electrochemical performance. Performance was evaluated using polarization curves and overvoltage separation, while hydrogen crossover was quantified by linear sweep voltammetry (LSV). Cross-sectional SEM and EDS characterized interlayer morphology. A gas barrier membrane containing PVA/PVS interlayer with 2 µm thickness exhibited the lowest hydrogen crossover current density of 0.21 mA cm⁻², representing reductions of 36.1% and 15.6% compared with Nafion 212 Double Layer (0.33 mA cm⁻²) and Nafion 115 (0.25 mA cm⁻²), respectively. In case of a 1 µm interlayer, hydrogen crossover current density was achieved a 27.3% reduction relative to Nafion 212 Double Layer. These results demonstrate that the proposed PVA/PVS gas-barrier interlayer effectively suppresses hydrogen crossover despite the reduced membrane thickness while maintaining electrolysis performance comparable to that of commercially available Nafion 115. The proposed membrane architecture therefore offers a promising design strategy for developing safer and more energy-efficient PEMWE systems.

Polymer electrolyte fuel cells (PEFCs) are an important contributor to the hydrogen economy, yet their limited lifetime remains a critical barrier to widespread adoption. A primary mode of cell failure is thinning of the polymer electrolyte membrane (PEM), eventually leading to pinhole formation. This is caused by peroxide radicals which arise due to gas crossover. Here we report a simple strategy to double the lifetime of PEFCs by embedding an atomically thin graphene interlayer within a 10 µm thick PEM. The resulting Nafion-Graphene-Nafion (N|G|N) architecture decreases hydrogen crossover current density by ~35%, without compromising ionic conductivity or maximum power density. Accelerated open circuit voltage (OCV) holding tests show that this leads to a doubling of PEFC lifetime, whilst post-mortem analysis confirms that the rate of membrane thinning is dramatically reduced. This work establishes graphene-based barriers as a transformative approach to extend the lifetime of electrochemical devices by suppressing chemical degradation, enabling the development of thinner and more durable membranes whilst advancing the development of cost-effective electrochemical systems.

Engineering the pore structure of biomass‐derived activated carbons is critical for optimizing their performance in adsorption‐based applications. This study demonstrates for the first time that washing hydrochars in solvents of different polarity before activation is a simple yet powerful strategy to tailor pore size distribution. Hydrochar is produced from spent coffee grounds via hydrothermal carbonization, followed by washing in various solvents and activation in KOH. This results in carbons with a very large surface area (∼2700 m ² /g), and washing is demonstrated to significantly increase product yield. Furthermore, washing in non‐polar or mixed‐polarity solvents removes long‐chain carboxylic acids and esters from the hydrochar, promoting the development of narrow micropores while suppressing mesopore formation. To illustrate the impact of this structural control of porous carbons, post‐combustion CO ₂ capture is investigated as a case study. Narrower pore size distribution enhances CO ₂ uptake, significantly improving capacity from 2.8 mmol/g for unwashed samples to 3.8 mmol/g for acetone‐washed samples. Interestingly, moderate pore size (9–12 Å) is shown to be optimal for CO ₂ :N ₂ selectivity, while smaller pores result in lower selectivity due to stronger interactions between N ₂ and the pore walls. These findings highlight the potential role of solvent washing in directing pore architecture of hydrochars for adsorption‐based carbon capture technologies and beyond.

Polymer electrolyte fuel cells (PEFCs) as a power device are highly promising and hold a key factor for the decarbonization of the transportation sector through their implementation into heavy-duty vehicles (HDVs). However, to achieve this, two major challenges must be overcome: (1) improving power generation performance and (2) enhancing durability. One critical factor affecting both power generation and durability is gas crossover between the electrodes. Gas crossover leads to membrane degradation due to oxygen permeation and a decrease in power generation due to hydrogen permeation. A potential solution to these issues is the introduction of interlayer with high gas barrier properties in a polymer electrolyte membrane (PEM). For example, Yang et al. reported that by adding an interlayer with suitable gas barrier properties, the generation of reactive oxygen species could be suppressed, slowing the rate of membrane thinning, and extending the lifetime of the fuel cell [1]. In this study, a new approach is proposed to address the issue of gas crossover between electrodes. A degasser layer, composed of carbon coated with ionomer without catalyst, is introduced between the PEM and the catalyst layer. This layer is designed to release permeated gases into the gas phase, thereby mitigating the factors contributing to performance and durability degradation. The study evaluates whether this approach leads to improvements in power generation performance and other beneficial effects (Fig. 1). In this work, the effects of the degas layer thickness, ionomer/carbon (I/C) ratio, and gas permeability are evaluated and optimized. According to the collected preliminary data, depending on the combination of these factors, a reduction of hydrogen crossover can be observed in samples with an I/C ratio of 0.7 and thicknesses below 5 μm. Without sacrificing IV performance and showing a slight increase in OCV, while maintaining similar ECSA values with a margin error of less than 10 percent when compared to standard membrane electrode assembly (MEA) measurements. This method provides a simple, low-cost and practical solution for improving the power generation performance and durability of PEFCs, potentially contributing to the further application of PEFC for HDVs. References [1] I Yang, Z. A. (2025). Improved chemical durability in polymer electrolyte membranes with nanocellulose-based gas barrier interlayers. Journal of Power Sources , 235833. [2] Zulfi Al Rasyid Gautama, Y. A. (2022). Suppression of radical attack in polymer electrolyte membranes using a vinyl polymer blend interlayer with low oxygen permeability. Journal of Membrane Science , 120734. Fig 1. Concept and a schematic image of the degasser layer. Figure 1

Introduction The reliance on platinum group metal materials in polymer electrolyte membrane (PEM) water electrolysis remains a significant barrier to its large-scale commercialization ¹ . In particular, the reduction of iridium (Ir) catalysts at the anode and platinum (Pt) coatings on the porous transport layer (PTL) is crucial for decreasing the overall system cost. Addressing these challenges is essential for enabling cost-effective and scalable hydrogen production through PEM water electrolysis. Our research group has developed a catalyst-integrated porous transport layer (Ir-PTL) by modifying the surface of Ti-PTL to increase its surface area, followed by the coating of iridium ^2,3,4 . In this electrode design, iridium serves two functions: as a catalyst for the oxygen evolution reaction (OER) and as a conductive coating on PTL. This approach offers the potential to eliminate the need for Pt coating on the PTL. In this presentation, we evaluate how the structural characteristics of the PTL affect the electrochemical performance of the Ir-PTL. Experimental Titanium sheets, serving as both catalyst supports and PTLs, were prepared using Ti fiber sheets or Ti powder sheets, as shown in Fig. 1. The Ti fiber sheet consisted of Ti microfibers with a diameter of approximately 20 μm, and samples with porosities of 70%, 60%, and 50% were used. The Ti powder sheet was composed of Ti powders sintered with diameters of approximately 10-20 μm and had a porosity of 40%.Chemical etching with NaOH solution was performed to increase the surface area of the titanium PTL. First, titanium sheets were etched in an aqueous 1 M NaOH solution at 60 °C for 1 h. After that, the etched titanium sheets were washed under ultrasonication in 0.01M HNO ₃ solution for 30 min and then washed in deionized water at room temperature for 10 min. Heat treatment was then performed at 400 °C in 5% H ₂ -N ₂ gas for 30 min. The Ir-PTL was prepared by depositing the Ir catalyst onto the NaOH-etched titanium sheets at room temperature via arc plasma deposition (APD-S, Advanced RIKO, Inc., Yokohama, Japan). The Iridium catalyst loading was fixed at 0.172 mg cm ^-2 . The PTEs deposited with the Ir catalysts were applied as anodes. MEAs were prepared by hot-pressing the PTLs with the cathode catalyst-coated electrolyte membranes (Nafion 212, Chemours, USA). Results and discussion When PTLs with relatively high porosity were used, the I-V performance was lower. In contrast, employing PTLs with lower porosity improved the I-V characteristics. The Ti powder PTL, which had the lowest porosity of 40%, exhibited the best performance. The differences in I-V characteristics between PTLs were particularly pronounced in the high current density region. While the activation overpotentials were nearly identical for all PTLs, both mass transport and ohmic overpotentials tended to increase with increasing porosity. This increase in overpotential is believed to result from hindered water supply to the catalyst and electrolyte membrane due to intense oxygen gas formation at high current densities, leading to reactant depletion and a decrease in membrane hydration. References The International Renewable Energy Agency, Green Hydrogen Cost Reduction (2020). M. Yasutake, D. Kawachino, Z. Noda, J. Matsuda, S. M. Lyth, K. Ito, A. Hayashi, and K. Sasaki, J. Electrochem. Soc. , 167 , 124523 (2020). M. Yasutake, Z. Noda, J. Matsuda, S. M. Lyth, M. Nishihara, K. Ito, A. Hayashi, and K. Sasaki, Int. J. Hydrogen Energy , 49 , 169 (2024). M. Yasutake, Z. Noda, J. Matsuda, S. M. Lyth, M. Nishihara, K. Ito, A. Hayashi, and K. Sasaki, J. Electrochem. Soc., 170 , 124507 (2023). Acknowledgments This study was supported by the Iwatani Naoji Foundation. The authors gratefully acknowledge the financial support. Figure 1

Introduction One of the key components of polymer electrolyte fuel cells (PEFCs) is the polymer electrolyte membrane (PEM). The PEM facilitates proton transport, acts as an electronic insulator to prevent short circuits, and prevents the direct reaction between hydrogen gas and oxygen in the air. A major technical issue with PEMs is the decomposition of their molecular structure due to chemical degradation. This leads to decreased proton conductivity, increased hydrogen and oxygen crossover, and reduced mechanical strength, all of which significantly impact the performance and durability of the PEMs (1). Previous studies have suggested that Fe impurities in the carbon support mainly exist on the surface, and the amount of these impurities may affect membrane degradation (2). Therefore, this study aims to investigate whether the removal of Fe from the surface of the carbon support can suppress PEM degradation. Experimental In the experiments, Ketjen Black (denoted as KB, EC600JD, Lion Specialty Chemicals Co., Ltd., Japan) was used as the carbon support. Acid treatment was performed to remove Fe impurities from the surface of the KB (Figure 1). KB was added to 2 mmol/L or 200 mmol/L HNO₃ and stirred for 2 h. Then, ultrapure water was added to the catalyst dispersion, followed by vacuum filtration to separate the solid carbon support and the liquid solvent. The carbon support powder was dried overnight in a thermostatic oven set at 100°C. These samples were labeled as KB-AT-2 and KB-AT-200, respectively. To measure the Fe content in each carbon support, the powder was dispersed in 1 mol/L HNO₃ to dissolve the surface impurities, and quantitative analysis was conducted using the resulting solvent. Catalysts were prepared by loading Pt on KB, KB-AT-2, and KB-AT-200. For the anode catalyst, Pt/KB (TEC10E50E, Tanaka Kikinzoku Kogyo, Japan) was used. For the cathode catalyst, the following were used: (i) Pt/KB, (ii) Pt/KB-AT-2, and (iii) Pt/KB-AT-200. Using the prepared MEAs, a 100-hour open circuit voltage (OCV) holding durability test was conducted. After the test, the thickness of the PEMs was measured by cross-sectional observations of the MEAs using focused-ion-beam scanning electron microscope (FIB-SEM). Results and discussion Figure 2 shows cross-sectional images of MEAs using Pt/KB and Pt/KB-AT-200 as the cathode catalyst after 100-h OCV holding test. These results clearly indicate that acid treatment of the carbon support surface to remove Fe impurities can suppress the chemical degradation of PEM. In this presentation, the effectiveness of removing Fe impurities from the surface of carbon supports as a method for suppressing chemical degradation of the PEM will be presented. 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 JST SPRING, Grant Number JPMJSP2136, and the Miyamoto Jun-ichi Hydrogen Research Award of Kyushu University. References M. Zatoń, J. Rozière, and D. J. Jones, Sustain. Energy Fuels , 1 , 409 (2017). S. Nakamura, K. Sanami, Z. Gautama, Z. Noda, M. Yasutake, S. M. Lyth, M. Nishihara, and K. Sasaki, ECS Trans. , 114 (5), 183 (2024). Figure 1

Introduction Research and development of polymer electrolyte fuel cells (PEFCs) has been conducted to increase their power density. The gas diffusion layer (GDL) and microporous layer (MPL) used in PEFCs are much thicker than the electrocatalyst layer and electrolyte membrane. Down-thinning GDL and MPL is expected to reduce gas diffusion resistance and increase the power density per volume of the cell stack. However, while the electrocatalyst layer and electrolyte membrane have been thinned to about 10 µm each, the MPL/GDL is still thick at about 150 µm. Thinner layers have been shown to reduce the molecular diffusion resistance of oxygen, resulting in a lower concentration overvoltage ¹ . The application of highly conductive MPL can also reduce ohmic overvoltage by reducing contact resistance and electrical resistance. In addition, MPLs with appropriate hydrophilic and hydrophobic properties can prevent flooding in a high current density range ² . Previous studies have investigated the possibilities and technical challenges of using porous metals as GDLs, which can be a thin layer with high strength ³ . In addition, a composite MPL with both hydrophobic and hydrophilic channels was developed and its effect on molecular diffusion resistance was investigated ⁴ . Based on these findings, in this study, we try to reduce contact resistance and electrical resistance by printing MPL layer onto carbon mesh, which is relatively stable and thinner than carbon paper, an existing material, as GDL, and to reduce molecular diffusion resistance by thinning the carbon mesh. We also add polytetrafluoroethylene, a hydrophobic material, and tin oxide, a hydrophilic material, to control hydrophobicity and hydrophilicity of MPLs. The objective of this study is to develop a self-supporting thin-layer MPL/GDL for improved power density. Experimental In this study, the MPL/GDL was fabricated by printing a MPL onto a carbon mesh (50 µm thick, Cosmotech, Japan) as a GDL using a screen-printing method. Cells were fabricated by using these materials. Current-voltage characteristics measurements, microstructure observation, and gas diffusion resistance measurements were conducted. The MPLs were initially composed of carbon black, carbon nanotubes (CNT), polytetrafluoroethylene (PTFE), hydrophilic tin oxide (SnO ₂ ), and solvent (a mixture of polyethylene glycol 600, and water). The MPL/GDL preparation was completed by heat treatment at 300°C for 30 min to remove solvent. A standard Pt/C electrocatalyst (TEC10E50E, Tanaka Kikinzoku, Japan) was used for preparing membrane-electrode assemblies (MEAs). As the electrochemical characterization in this study, current-voltage characteristics were evaluated using an electrochemical impedance analyzer (SAS SP-240, Bio-Logic Science Instruments, France), various overvoltages were separated, and molecular resistance of oxygen was measured. Microstructural observations were conducted using a focused ion beam scanning electron microscope (FIB-SEM). Results and discussion Figure 1 (a) shows the current-voltage characteristics of the cell using various MPL/GDLs. The thickness of the MPL/GDLs fabricated was about 80 µm. For comparison, the characteristics of a cell using a standard, commercially-available MPL/GDL (22BB, SGL Carbon, Germany) are also shown. These results show that the use of MPL significantly improves cell performance even with thin GDLs. Using a highly conductive material for the MPL and applying it to carbon-based fibrous materials reduced electrical resistance, and down-thinning MPL/GDLs layers reduced the molecular diffusion resistance of oxygen (Figure 1 (b)). However, the electrical resistance of the GDL substrate is relatively high, and contact resistance is still an issue due to the roughness of the MPL surface in contact with the electrocatalyst layer. If these technical issues can be solved, further improvement in cell performance could be achieved. MPLs with SnO ₂ showed high performance at a low humidity. This may be due to improved dry-up resistance by the addition of hydrophilic material, whereas flooding was noticeable at high humidity. It is suggested that an appropriate mixture of hydrophobic and hydrophilic channels can enhance the dry-up and flooding resistance of MPLs, resulting in improved cell performance. 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) as a part of Adopting Sustainable Partnerships for Innovative Research Ecosystem (ASPIRE), Grant Number JPMJAP2307. References N. Nonoyama, S. Okazaki, A.Z. Weber, Y. Ikogi, T. Yoshida, J. Electrochem. Soc. 158 ,B416 (2011). T. Kitahara, T. Konomi, H. Nakajima, and J. Shiraishi, Kikai B , 76 (761), 101 (2010). K. Yamamoto, M. Yasutake, Z. Noda, S. M. Lyth, J. Matsuda, M. Nishihara, A. Hayashi, and K. Sasaki , ECS Trans., 109 (9),265 (2022). P. Wang, H. Nakajima, and T. Kitahara, J. Electrochem, Soc., 171, 014501 (2024). Figure 1

Introduction Improvement of the durability of polymer electrolyte fuel cells (PEFCs) is important for its application as a clean power source for heavy-duty vehicles. One of the durability issues is the chemical degradation of the polymer electrolyte membrane (PEM) caused by reaction with radical species generated from side reactions in the PEFC system. According to previous studies, one of the radical formation mechanisms is initiated by the reaction of permeated oxygen at the anode side ^1,2 . Consequently, we have developed an alternative mitigation strategy against the chemical degradation by fabricating a multilayer high gas barrier PEM to suppress oxygen permeation. Our multilayer gas barrier PEM consists of a gas barrier layer that is sandwiched between two Nafion layers (Figure 1a). This concept can easily improve the gas barrier property without any compatibility issues with other PEFC components. To evaluate the chemical durability of a PEM material, several accelerated test methods have been established in the literature including the wet Fenton’s test, dry Fenton’s test, and OCV holding test. In our group, the OCV holding test is selected as a representative accelerated test to assess the chemical durability of the PEM because its setup is similar to an actual PEFC operation ¹ . The chemical degradation of the PEM can be monitored through the voltage loss that is linked to the increase of gas crossover due to membrane decomposition. In a previous study, we have shown that a gas barrier layer made of simple hydrocarbon polymers such as polyvinyl alcohol and cellulose nanocrystals could remarkably improve the chemical durability in OCV holding test setup ^3,4 . In this study, we elucidated the degradation mechanism of thin multilayer gas barrier PEMs during the OCV holding test by cross-sectional SEM imaging, electrochemical analysis, and other characterization methods. Our findings show that mechanical degradation has a significant contribution to the voltage loss during the OCV holding test of thin PEMs. Furthermore, chemical degradation, mechanical degradation, and catalyst activity loss have different voltage loss characteristics. Methods Thin multilayer PEMs were prepared for the OCV holding test with a gas barrier loading of 50 µg/cm ² (PVA 50) and 100 µg/cm ² (PVA 100). As a reference, a pristine Nafion sample with comparable thickness was also prepared. The OCV holding test was performed at 90°C and 30% RH under H ₂ (139 ml/min) and air (332 ml/min) flow without any additional back pressure. Electrochemical evaluation is conducted every 24 hours until the hydrogen crossover of each sample reaches 10 times the initial value. After the test, the samples were taken for post-degradation analysis. Results & Discussion The OCV holding test results in Fig. 1b showed that the sample with the slowest voltage drop rate is PVA 100 (~2.3 mV/h), followed by PVA 50 (~2.9 mV/h) and lastly Nafion (~3.3 mV/h). The correlation between voltage drop and chemical degradation is established by monitoring the evolution trend of the hydrogen crossover current density. The PVA 100 showed a very stable hydrogen crossover trend compared to the other samples, which indicated that the membrane thinning happens at a rate much slower than the other two samples. Meanwhile, PVA 50 and Nafion had a similar hydrogen crossover evolution trend with a slightly slower increase rate for PVA 50 close to the end of the test. To confirm this behavior, we use cross-sectional SEM imaging on the degraded samples to measure the PEM thickness after degradation. The thickness of Nafion was much thinner (6 µm) than those of PVA 50 and PVA 100 (15-17 µm), which is within our expectations. However, to our surprise, the thickness of PVA 50 and PVA 100 are almost identical although the PVA 100 showed much longer durability in the OCV holding test. We hypothesized that mechanical degradation around the edge of each sample’s electrodes may significantly affect the lifetime during the OCV holding test. This hypothesis is supported by the sudden voltage drops in the OCV holding test results. Further analysis will be conducted to fully understand the degradation mechanism of these samples in the OCV holding test. References Ohma, A., Suga, S., Yamamoto, S. & Shinohara, K. J. Electrochem. Soc. 154 , B757 (2007). Laconti, A., Liu, H., Mittelsteadt, C. & McDonald, R. ECS Trans. 1 , 199 (2006). Gautama, Z. A. R. et al. Journal of Membrane Science 658 , 120734 (2022). Yang, I. et al. Journal of Power Sources 629 , 235833 (2025). Figure 1

Under high current density operation, water generation at the cathode of polymer electrolyte fuel cells (PEFCs) floods the electrode, resulting in severe mass transport limitation and an associated voltage drop. Water management is thus of crucial importance in improving the overall performance of fuel cell systems. Gas diffusion layers (GDLs) with independent pathways for either gaseous oxygen or liquid water transport present a potential solution to this issue. Here a novel, simple, and scalable method is presented for inducing patterned hydrophobicity into GDLs. Hydrophilic GDLs are prepared by immersion of commercial hydrophobic GDLs in hydrogen peroxide. Circular disks are then punched from these using a precision die‐cutter. Meanwhile, an array of corresponding holes is punched into conventional hydrophobic GDLs. The hydrophilic disks are then pressed into the holes of the hydrophobic GDL and held in place via friction locking, analogous to completing a jigsaw puzzle. This Jigsaw Puzzle Inspired Patterning (JPIP) technique creates precisely patterned hydrophilic domains to act as dedicated water channels, with separate hydrophobic domains for unhindered gas transport. The use of JPIP GDLs dramatically improves fuel cell performance under high current density operation, with important implications for decarbonization via the hydrogen economy.