Gas Barrier Research Articles

Strong and tough bio-based biomimetic-multiphase composite polyesters with superior barrier and chemically closed-loop performances

A full-natural bionics-multiphase composite polyester with mechanical robustness, high gas barrier and chemically closed-loop properties was designed and prepared using bio-based monomers and single-layered mica to achieve a replacement for plastic.

Buckling Resistance and Its Effect on the Gas Barrier of Composite Coating Layers Based on Polyvinyl Alcohol and Montmorillonite

In addition to the mechanical properties and barrier performance, one of the key properties of flexible films used in food packaging is the resistance of their gas barrier layer to buckling and bending. Testing the gas barrier before and after mechanical stress is time-consuming and resource-intensive, but important to assure a certain gas barrier during the whole life time of the package until food consumption. The aim of this study was, on the one hand, to identify the most significant influencing factors of a composite lacquer formulation and coating on its buckling resistance and, on the other hand, to show a fast and efficient method to identify defects occurring during buckling. The influence of mechanical stress was simulated via Gelbo-Flex treatment, and the samples were examined and evaluated before and after using light microscopy. The evaluation was verified with scanning electron microscopy (SEM) and helium barrier measurement. Polyethylene terephthalate (PET) and polyethylene (PE) films were coated with composite barrier lacquers made of polyvinyl alcohol (PVA) and montmorillonite (MMT) and the wet coating layer thickness (20;40;80;130m) and the composition of the coating were changed. It was found that thin coatings are more resistant to buckling than thick coatings. It was also shown that a higher proportion of MMT in the coating layer leads to a better gas barrier, but poorer buckling resistance. Additionally, it was found that soft PE films are already subjected to high stresses during the coating process, which means that barrier coatings do not build up ideally. However, the barrier-coated soft film withstood mechanical stress better and lost less barrier by a lower factor than the counterpart on the basis of PET. To conclude, the evaluation of the buckling resistance with microscopy offers an efficient method during lacquer development; however, the final decision on the right lacquer composition is dependent on many factors.

Recent trends and advancements in the utilization of green composites and polymeric nanocarriers for enhancing food quality and sustainable processing

Abstract Consumers now have access to synthetic natural organic nanofoods with tailored properties. These nanofoods use organic or inorganic nanostructured ingredients to enhance bioavailability, making them more effective than traditional supplements. Common materials include metals like iron, silver, titanium dioxide, magnesium, calcium, selenium, and silicates. Modifying the surface of these nanoparticles can provide unique benefits such as improved preservation, mechanical strength, moisture control, and flavor enhancement. Nanocarriers, such as polymeric, lipid, and dendrimer-based carriers, are used in food production. Common polymers include polyglycolic acid, poly (lactic acid), chitosan, and sodium alginate. Lipid carriers have a hydrophobic outer layer and a hydrophilic core, while dendrimer carriers are made from materials like polyethylene glycol and polyamidoamine. These nanocarriers can encapsulate up to 99% of active ingredients, ensuring precise delivery and stability. The nanocarriers in commercial foods are emulsions, inorganic coatings, and fiber coatings. For instance, cucumbers coated with nano emulsions show up to 99% antimicrobial effectiveness. Inorganic coatings, such as potassium sorbate, calcium caseinate, and titanium dioxide, significantly extend the shelf life of packaged foods. Lipid and protein-encapsulated nanosystems offer complete gas barrier protection. This review highlights the exclusive use of nanoparticles in food processing and packaging to enhance quality, safety, and shelf life.

Advances in Valorization of Biomass-Derived Glycolic Acid Toward Polyglycolic Acid Production

Glycolic acid (GA) is a versatile two-carbon organic chemical with multiple applications in industry and daily life. Currently, GA production depends heavily on the coal chemical industry. In this context, the sustainable production of GA from renewable resources has garnered significant attention. With the design and development of various catalytic systems, the yield of GA from biomass-based feedstocks has been improved observably. Poly(glycolic acid) (PGA) is an aliphatic polyester that exhibits a unique crystalline structure, excellent gas barrier properties, high mechanical strength, superior biocompatibility, and biodegradability. It has a wide range of applications in various fields, such as medical devices, oil extraction, bottle materials, film materials, and textile materials. This article comprehensively elaborates on the methods for the biomass-based synthesis of glycolic acid, the precursor of polyglycolic acid (PGA), as well as the preparation process of PGA. It fills the research gap regarding the sources of biomass raw materials for polyglycolic acid. Additionally, it delves into various modification strategies for PGA and provides an overview of its current applications in multiple fields, including biomedicine, food packaging materials, oil and gas resource development, and agricultural cultivation. The purpose of this article is to provide comprehensive reference information on the synthesis techniques, modification methods, and practical applications of PGA. Furthermore, it offers guidance for research on biodegradable plastics and the biomass-based synthesis of glycolic acid.

High Gas Barrier Elastomer/Boehmite Composites with Mechanical Robustness and Improved Flame Retardance Enabled by Segregated Structure with Interfacial Dynamic Cross-Links

High Gas Barrier Elastomer/Boehmite Composites with Mechanical Robustness and Improved Flame Retardance Enabled by Segregated Structure with Interfacial Dynamic Cross-Links

Zeolite Additives for Flexible Packaging Polymers: Current Status Review and Future Perspectives.

Zeolites are interesting inorganic additives that could be employed for plastic packaging applications. Polyethylene (PE) and polypropylene (PP) are intensively used for packaging as they provide great performance at low cost, even though they have poor environmental sustainability and may be more valorized. Biodegradable polymers may therefore represent a more eco-friendly alternative, but still, they have limited applications due to their generally inferior properties. Therefore, this review focuses on the use of zeolites as additives for flexible packaging applications to mainly improve the mechanical and barrier properties of PE, PP, and some biodegradable polymers, possibly with antimicrobial and scavenging activities, by exploiting zeolites' cation exchange ability and adsorption properties. Film preparation and characterization have been investigated. The obtained enhancements regard generally higher gas barriers, elastic moduli, and strengths, along with thermal stability. Elongation at break decreased for all PE composites and tended to increase for other matrices. The use of zeolites as additives for polymer films is promising (mainly for biodegradable polymers); still, it requires overcoming some limiting drawbacks associated with the additive concentration and dispersion mainly due to matrix-additive incompatibility.

Enhancement of toughness and gas barrier properties of PLA‐based films through bio‐based isosorbide dioctate: Synthesis, characterization, and application

AbstractPolylactic acid (PLA), as a bio‐based biodegradable material, has high tensile strength and modulus, but its low flexibility and poor barrier properties limit its application in packaging. In this study, Pullulan polysaccharide (Pullulan) and chain extenders (ADR4468) were selected to improve the properties of PLA‐based films. The ratio of PLA/Pullulan/ADR4468 was optimized by studying the mechanical and barrier properties of films. Then isosorbide dioctate (SDO), a kind of bio‐based plasticizer, was synthesized and added into PLA/Pullulan (4 wt%)/ADR4468 (0.8 wt%) system to study the effect of SDO content on the properties of films. A film with 15 wt% SDO showed elongation at a break of 79.7% while retaining a tensile strength of 30.6 MPa. With 20 wt% SDO, water vapor permeability and oxygen permeability of PLA/Pullulan/ADR/SDO film were reduced by 12.7% (2.95 × 10−14 kg m/(m2 s Pa)) and by 20.6% (1.95 × 10−3 cm3 m/ (m2 d Pa)), respectively, compared with that of PLA/Pullulan/ADR films. This study fills the research gap between PLA and Pullulan blends, broadens the application scenarios of new bio‐based plasticizers, and provides a method for improving the toughness and barrier properties of PLA. The films prepared in this study have potential applications in the green‐packaging field.Highlights The synthesis and characterization of isosorbide dioctate. The modified compatibility of PLA and Pullulan by ADR 4468. The optimization of the content of PLA/Pullulan/ADR 4468 film. The improvement of toughness and barrier properties of film by SDO.

Toward Sustainable Poly(lactic acid)/Poly(propylene carbonate) Blend Films with Balanced Mechanical Properties, High Optical Transmittance, and Gas Barrier Performance via Reactive Compatibilization and Biaxial Stretching.

Sustainable poly(lactic acid) (PLA)/poly(propylene carbonate) (PPC) blends were compatibilized by the environmentally friendly epoxidized soybean oil (ESO) through the chemical reaction of epoxy functional groups on ESO with the terminated carboxyl and hydroxyl groups of PLA/PPC. The compatibilization effect of ESO was confirmed by Fourier transform infrared spectroscopy, rheological property testing, differential scanning calorimetry, and morphological observations. It was revealed that the molecular chain entanglement between PLA and PPC was significantly enhanced and the dispersed PPC phase size was decreased, which endowed the blend with high viscosity modulus, low tan δ, and great stretchability, especially for the blend containing 1.0 wt % ESO. The compatibilization effect dramatically reinforced the toughening modification of PPC on PLA, resulting in a great ductility with a fracture strain up to 187.3%, more than 20 times that of the pristine PLA, while maintaining a high strength of 44.5 MPa. Compared to the neat PLA and the PLA/PPC blend, the compatibilized blend showed a much larger draw ratio of up to 6.5 × 6.5 during biaxial stretching, producing a uniform film with balanced mechanical properties, high optical transparency, and good oxygen barrier performance. This work will be of vital importance for guiding the preparation of PLA-based films with superior comprehensive properties.

Innovative edible films for food preservation: Combining pectin and flavonoids from citrus peels with soy protein isolates

In this study, sequential extraction technology was employed to extract pectin and flavonoids from citrus peel by-products. Subsequently, citrus flavonoids (CF) were incorporated into a matrix comprising soy protein isolate (SPI) and citrus pectin (CP), resulting in the development of a series of active films (SPI/CP-CFs). The physicochemical properties of these films were evaluated along with their capability in food preservation. The SPI/CP-CFs films exhibited exceptional mechanical properties, thermal stability, and gas barrier properties. Furthermore, the films exhibited enhanced antioxidant and antimicrobial activities due to the sustainable release of CF. In practical applications, these antimicrobial edible films were more effective in extending the shelf life and maintaining freshness of red grapes and pork compared to CF-free counterparts. These findings suggest that the novel edible films based on the formulation of SPI, CP, and CF hold significant potential as versatile active packaging materials for preserving both fruit and meat products.

Performance Improvement of Chemically Durable PVA Gas Barrier PEM by Optimizing the Interlayer Thickness

Polymer electrolyte fuel cell (PEFC) is a portable and clean power source suitable for decarbonizing the transport sector. Recently, PEFC has been developed as a power source for heavy-duty vehicles which requires further improvement on its components, such as the durability of the polymer electrolyte membrane (PEM). One of the challenging issues on PEM is suppression of chemical decomposition of PEM. Several decomposition mechanisms of PEM are proposed like the reactions of crossover oxygen to form hydrogen peroxide (H2O2) at the anode site or deposited platinum in PEM. H2O2 is a starting material of a radical which decomposes the polymer chain of PEM. To mitigate this issue, we have designed a gas barrier PEM which can suppress oxygen penetration through PEM by incorporating a gas barrier polymer layer in between two Nafion layers (Fig. 1a). In a previous study, we loaded 0.5 mg/cm2 of PVA/PVS blend (Fig. 1b) with 100:1 molar ratio as the gas barrier interlayer, which consequently improved the chemical durability by 1.7 times than Nafion under in-situ accelerated stress test (OCV holding test) [1]. However, the fuel cell performance of this gas barrier PEM could only reach 70% of the Nafion’s current density at 0.6 V. To practically use our gas barrier PEM concept as a viable mitigation strategy against chemical decomposition, the fuel cell performance must be improved.To improve the fuel cell performance of the gas barrier PEM, we focused on optimizing the thickness of the gas barrier interlayer. The interlayer majorly affects the resistance of gas barrier PEMs due to its low proton conductivity. On the other hand, an interlayer with enough thickness is also important to achieve high chemical durability by high gas barrier property. Therefore, we developed thinner gas barrier interlayer with enough high gas barrier property and low resistance. After optimizing the interlayer thickness, we optimized the conditioning procedure for the selected gas barrier PEM to achieve similar catalytic activity with the Nafion MEA.In this presentation, the effect of interlayer thickness reduction towards fuel cell performance of gas barrier PEM will be discussed in detail. In addition, we also observed that preparation of the gas barrier PEM affected to the MEA performance. Therefore, we optimized the conditioning procedure of the MEA. In this presentation, we selected PVA 0.1 (interlayer loading: 0.1mg/cm2, interlayer thickness: 1 mm, total PEM thickness: 17 mm, PVA: PVS =100:1 (mol)) to have the best balance between fuel cell performance (90% of Nafion’s current density at 0.6 V) (Fig. 1c) and gas barrier property (30% lower hydrogen crossover at 80°C 95% RH). From several results, we confirmed that the PVA 0.1 demonstrated higher chemical durability than Nafion with the same thickness in OCV holding test (Fig. 1d).

Chemical Durability Enhancement of Gas Barrier Cellulose Nanocrystal Electrolyte Membranes

Polymer electrolyte fuel cells (PEFCs) system for fuel cell vehicle (FCV) application is one of promising technologies to reduce carbon dioxide emission from transportation sector and mitigate the global warming issue. However, durability of the PEFC system is not enough for commercial requirement, especially heavy-duty vehicles. With regards to polymer electrolyte membranes (PEMs) in the PEFCs system, chemical degradation is the important issue of PEM durability and occurs because of radical attacks during fuel cell operation. One of the routes of radical formation is related to oxygen penetration from cathode to anode through PEMs (Fig. 1, a)[1]. Based on this mechanism, suppressing gas penetration is one of the solutions to alleviate radical attacks to PEMs. To realize this concept, we developed a high gas barrier sandwiched PEM by introducing a cellulose nanocrystals (CNC) interlayer (Fig.1, b, c). CNCs are an abundant biomaterial and have high gas barrier property. To use the biomaterial with high gas barrier, we confirmed the fuel cell performance and chemical durability of the gas barrier PEM.A gas barrier CNC interlayer was sandwiched between two Nafion211 outer layers (Fig.1, c), and the total thickness was about 55µm. Fuel cell performance of the CNC gas barrier PEM was evaluated under 80°C and 95% RH. Then, open-circuit voltage (OCV) holding test, accelerated stress test for PEMs, was performed to evaluate the chemical durability of PEMs under 90°C and 30% RH, and the performance of PEMs were also measured after every 72 hours cycle during OCV holding test by following NEDO protocol.CNC gas barrier PEM could exhibit about 4 times higher gas barrier properties than Nafion211 doble layer (N211DL, 50µm) under 80˚C and dry condition. And the CNC gas barrier PEM could show about 1.6 times longer durability than N211DL in the OCV holding test (Fig. 1, d), indicating that good gas barrier CNC interlayer could suppress radical formation. Therefore, we proved our research concept is available for cellulose nanocrystals, promising for durable PEMs and future PEFCs applications.References Gautama, et. al, J. Membrane Science, 2022, 658, 15, 120734. Figure 1

Graphene-Based Electrolyte Membranes with Low Hydrogen Permeability

Electrolyzers and fuel cells are promising candidates for sustainable conversion of electricity to hydrogen and hydrogen to electricity, offering an energy storage solution with high efficiency and low environmental impact. However, the problem of hydrogen crossover in the polymer electrolyte membrane (PEM) presents a particular challenge, limiting the efficiency and ultimately hindering their widespread adoption. Meanwhile, graphene is a well-known nanomaterial that is reportedly practically impermeable to gases. Here, we present innovative approaches to tackle the issue of hydrogen crossover by using graphene in different forms and different cell architectures. First, we will explore pure graphene oxide (GO) as a new electrolyte material in both acid and alkaline configurations. Then we will look at thin films of GO sandwiched in Aquivion membranes as a gas barrier layer. Finally, we will demonstrate that monolayer graphene is an effective gas barrier layer when sandwiched in Nafion membranes.Similar to the case of graphene, GO also exhibits remarkable materials properties including high strength, excellent hydrogen gas barrier properties, hydrophilicity, and proton conduction assisted by acidic functional groups. These factors potentially make GO an attractive material for electrolyte membranes. We demonstrate the preparation of pure GO membranes via vacuum-filtration, and measure hydrogen permeability (2x10-2 barrer) three orders of magnitude lower than conventional Nafion membranes (30 barrer). Furthermore, we observe a significant anisotropy in ionic conductivity, attributed to the lamellar structure of GO. The resulting fuel cell power density was relatively low, due to limited conductivity (0.3 mS cm-1). To compensate for this, extremely thin (3 µm) electrode-supported GO membranes were deposited via spray deposition, resulting in improved fuel cell power density up to 79 mW cm-2. This showcases the potential of GO-based membranes in enhancing fuel cell performance.Furthermore, we present a novel class of anion exchange membrane (AEM) fabricated from KOH-modified multilayer graphene oxide paper. As with the case of acidic electrolyte membranes, these also display high tensile strength and low gas permeability. A hydroxide ion conductivity of 6 mS cm-1 was recorded and confirmed using ion blocking layers, and attributed to a water-mediated reverse Grotthuss-like mechanism. An alkaline fuel cell was assembled but a relatively low proton conductivity of 1 mW cm-2 was obtained, attributed to reaction with CO2 in the oxidant gas supply.The above studies are promising, but the low ionic conductivity of pure graphene limits the ultimate achievable fuel cell power densities. Therefore, we explored the use of ultrathin GO layers (100 nm) sandwiched in Aquivion PEMs to combine the high ionic conductivity of Aquivion with the gas barrier properties of graphene oxide (as well as CeO2 as a radical scavenger). These novel multilayer sandwich PEMs were deposited via spray deposition, resulting in just 10 µm total thickness. This method resulted in extremely high-power densities (1.6 W/cm2) and very low hydrogen crossover current density (1 mA/cm2). As such the concept of adding hydrogen blocking interlayers is shown to be highly effective.Finally, we investigate the potential of monolayer graphene as a barrier to hydrogen crossover in PEMs, since graphene reportedly presents minimal resistance to hydrogen ion transport through the basal plane. Graphene grown via chemical vapor deposition on a copper substrate was coated with Nafion via spray deposition. The copper was removed via etching in acid and then a second layer of Nafion was sprayed onto the freshly exposed graphene surface, forming a sandwich PEM. Again, this resulted in significantly reduced hydrogen crossover current, whilst having minimal impact on the power density.In conclusion, graphene is an ideal material for incorporation into PEMs to minimise hydrogen crossover. This has the potential to enhancing the performance and durability of fuel cells and electrolysers. T. Bayer, S. R. Bishop, M. Nishihara, K. Sasaki, S. M. Lyth, Journal of Power Sources 272 (2014) 239-247T. Bayer, R. Selyanchyn, S. Fujikawa, K. Sasaki, S. M. Lyth, Journal of Membrane Science 541 (2017) 347–357T. Daio, T. Bayer, T. Ikuta, T. Nishiyama, K. Takahashi, Y. Takata, K. Sasaki, S. M. Lyth, Scientific Reports, 5 (2015) 11807T. Bayer, S. R. Bishop, N. H. Perry, K. Sasaki, S. M. Lyth, ACS Applied Materials and Interfaces 8, 18 (2016) 11466–11475T. Bayer, B. V. Cunning, R. Selyanchyn, T. Daio, M. Nishihara, S. Fujikawa, K. Sasaki, S. M. Lyth, Journal of Membrane Science, 508 (2016) 51–61M. Breitwieser, T. Bayer, A. Büchler, R. Zengerle, S. M. Lyth, S. Thiele, Journal of Power Sources, 351 (2017) 145-150

Study on the Distribution of Platinum within Polymer Membrane during MEA Degradation in PEMFC

The Pt/C added to the PEMFC polymer membrane serves as a gas barrier, facilitating the generation of water through the hydrogen and oxygen combustion reactions on the Pt surface within the membrane. As water is produced, Pt acts as an antioxidant, humidifying the membrane and preventing radical generation, thus enhancing performance and durability. Pt needs to be closely spaced between particles to act as a radical scavenger, and it has been reported that under different operating and degradation conditions, the size and distribution of Pt within the membrane vary. Therefore, this experiment aimed to observe the movement and distribution changes of Pt/C within the membrane during accelerated degradation.In this experiment, Pt/C was added to the cathode ionomer layer to manufacture a reinforced membrane with a thickness of 15 μm. The MEA was produced by hot pressing Pt/C electrodes onto the reinforced membrane, with a Pt loading of 0.4 mg/cm2. After assembling the MEA into a cell, chemical durability evaluations of the electrode catalyst, catalyst support, and membrane were conducted. The cross-sections of the MEA before and after degradation were analyzed using SEM and TEM to confirm the distribution of Pt within the membrane.After chemical degradation of the polymer membrane, Pt/C within the membrane remained stationary, but dissolved/deposited Pt within the electrode layer migrated into the membrane, indicating a closer proximity between Pt/C and Pt. During catalyst and catalyst support degradation, movement of Pt/C within the membrane and changes in its distribution were observed.

Additives for Improving Chemical Stability of Polymer Electrolyte Membranes

Polymer electrolyte membrane (PEM) is a key component that affects the performance and durability of various electrochemical devices, including fuel cells and electrolyzers. Despite improvements in PEM performance, durability still needs to be improved. The lifetime of membranes deteriorates under operating conditions due to chemical degradation. This chemical degradation not only reduces electrochemical performance but also its mechanical integrity, ultimately leading to device failure. In recent years, many researches report that durability has been improved by synthesizing chemically stable polymers such as polyphenylenes. In addition, the incorporation of various additives into PEMs has emerged as a promising strategy to enhance chemical stability of membranes. The most commonly used additives to improve the chemical stability of PEMs are antioxidants. Since radicals are mainly generated by hydrogen crossover, additives that can reduce hydrogen crossover can also enhance the chemical stability.In this study, we investigated the gas barrier properties of several additives and their impact on the performance and durability of PEMs. Gas barrier additives (GBA) were dispersed in polymer solution to form a membrane without phase separation or agglomeration. Composite membranes showed similar water uptake and mechanical properties to the pristine membrane. Although GBAs had excellent gas barrier properties, some of them decreased fuel cell performance. GBA effectively reduced the hydrogen permeation. We down selected GBAs that did not deteriorate fuel cell performance and conducted stability test under open circuit voltage (OCV) conditions. While monitoring OCV, hydrogen permeability and fluoride emission concentration were measured to confirm the degradation tendency of membranes. The durability of the composite membranes was improved compared to the pristine membrane. These results show that not only removing radicals using antioxidants, but also slowing down radical generation by blocking hydrogen crossover is effective in improving the chemical stability of the PEM.

(Invited) Self-Recovery of Photodegraded CsPbBr3 Perovskite Nanocrystals and Problems By Irreversible Damage

CsPbBr3 perovskite nanocrystals (NCs) synthesized by a typical hot injection method are adsorbed with surface modifiers. The authors have investigated photodegradation and self-recovery phenomena due to photo-induced desorption by excitation light irradiation and re-adsorption of the surface modifiers in the dark, respectively [1-4]. These phenomena occurred when a dry solid sample of NCs was placed in a sample holder covered with a glass plate to shut out the atmosphere. On the other hand, the dried NCs exposed to the air did not show the self-recovery after photodegradation. This was due to irreversible degradation caused by surface oxidation by atmospheric oxygen. When the dried NCs were covered with a resin film instead of a glass plate, the resin with lower gas barrier properties did not prevent oxidation. However, the use of a resin with higher gas barrier properties confirmed the occurrence of photodegradation and subsequent self-recovery. The authors will present recent results including experiments on nanocomposite films of the NCs dispersed in resin.References K. Kidokoro, Y. Iso, T. Isobe, J. Mater. Chem. C, 7, 8546 (2019).K. Miyashita, K. Kidokoro, Y. Iso, T. Isobe, ACS Appl. Nano Mater., 4, 12600 (2021).I. Enomoto, Y. Iso, T. Isobe, J. Mater. Chem. C, 10, 102 (2021).K. Kano, Y. Iso, T. Isobe, ECS J. Solid State Sci. Technol., 12, 056003 (2023). Figure 1

Hydrocarbon Proton and Anion Exchange Polymers for Water Electrolysis Applications

Renewable energy and water electrolysis (WE) are deemed to be the pillars over which the incoming green hydrogen era and energy transition will stand. Water electrolysis can undergo in both acidic and alkaline conditions. In modern times, solid polymer electrolyte WE has attracted particular interest, due to the advantage of a compact design combined with the possibility to operate at higher pressure and temperatures even using pure water.Still to date, the most used membranes in PEMWE are poly(perfluorosulfonic) acids (PFSAs) (e.g., Nafion™) due to their mechanical strength, strong chemical resistance, and high proton conductivity. However, recent concerns regarding their cost, environmental impact due to fluorine chemistry, mechanical instability above 80 °C, and low gas barrier (especially H2) require urgent development of suitable hydrocarbon alternatives. Sulfonated poly(phenylene sulfones) (sPPS) represent a valuable hydrocarbon alternative to PFSAs as they exhibit lower gas crossover, higher conductivity, better thermal stability and low production cost.[1] [2] This class of polymer is able to outperform Nafion™ in PEMWE thanks to their higher proton conductivity (Fig. 1 b)).[1] To improve long term-stability of these polymers in operative PEMWE conditions (T = 80°C, > 1 Acm-2 ), fluorine-free reinforcement and Ce-based “damage-reparation”[3] strategies have been successfully implemented extending their stability in the range of thousands of hours.A major drawback of PEMWE technology is the reliance on platinum group metals (PGMs) (i.e. Pt and Ir). This stimulated the research of alternative strategies to respond to the demand of green H2 necessary to mitigate global warming reduction. AEMWE is the ideal alternative to PEMWE since it can be performed efficiently with non-PGMs, i.e., iron and nickel. The main shortcoming in AEMWE comes from the need of an alkaline electrolyte, which drastically limited the development of AEM technology in past decades. The harsh alkaline and electrochemical stress present in AEMWE have only recently been overcome by a new class of polyphenylene piperidinium and polynorbornene-based polymers which are also commercially available as Piperion™ and Pention™ respectively. The first are obtained by super-acidic Friedel-Craft addition[4] while the polynorbornene chemistry requires special catalysts.[5] Inspired by these results, in our lab, we have dedicated particular efforts to develop hydrocarbon AEM materials implementing phosphorous superbases as anion conducting functionalities to eliminate the presence of constant charges close to the polymer chain. AEMs based on polynorbornenes are proposed, including stable amino-linkage inspired by previous work.[6] Additionally, anion exchange ionomers (AEI) for catalyst layers with enhanced gas permeability were synthesized based on “canal” polynorbornene and novel crosslinked polyarylpiperidinium. The main synthetic strategies and properties (e.g., IEC, WU, alkaline resistance) of the resulting polymers are presented.

Understanding the Mechanism of Chemical Durability Enhancement through Modeling of Electrolyte Membranes with Improved Oxygen Barriers

In pursuit of a carbon-neutral society, polymer electrolyte fuel cells (PEFCs) are gaining significant attention in commercial applications, particularly for heavy-duty vehicles. The system demands long-term durability to its components, especially for polymer electrolyte membranes (PEMs), which require further thinning in the future[1]. The chemical degradation of PEMs occurs because of the attack by radical species. It is posited that hydrogen peroxide, arising from the crossover of oxygen, contributes to the formation of radical species. We hypothesized that introducing a gas barrier layer (GBL) against oxygen into the PEM could suppress chemical degradation, and confirming this hypothesis through durability tests using a GBL sandwiched between PEMs [2]. In this study, we constructed a model having the GBL to understand the mechanism behind this enhanced durability.According to the scanning electron microscopy (SEM) observations of the fabricated membrane electrode assembly (MEA) with the GBL (Fig. 1a), we constructed a 1D through-plane model of MEA (Fig. 1b). Species conservation equations were solved in each layer to calculate the potential and concentration. Reactions R1– R4 were assumed in the catalyst layers for the source terms of the conservation equations. 2H+ + 2e- → H2 (R1) O2 + 4H+ + 4e- → 2H2O(R2) O2 + 2H+ + 2e- → H2O2 (R3) H2O2 + 2H+ + 2e- → 2H2O(R4) We compared the distribution of hydrogen peroxide concentration in MEAs with and without the GBL by using our model. In MEAs with the GBL, a significant concentration (expressed by an equivalent partial pressure) gradient developed, leading to a reduction in oxygen concentration on the anode side (Fig. 2a) compared to those without the GBL (Fig. 2b). This indicates a lower oxygen flux towards the anode, which resulted in a reduced rate of hydrogen peroxide formation and lower concentrations in the MEA with the GBL. These results suggest that the presence of the GBL prevented degradation and enhanced the durability of the MEA. In the presentation, we will present the details of the model and discuss strategies for further enhancing the durability of MEAs with the GBL by showing various case studies. Figure 1

(Invited) Application of Liquid Metals in Battery Technology

Stretchable devices have many potential applications, including wearable electronics, robotics, and health monitoring. These mechanically adaptable devices and sensors can seamlessly integrate with electronics on curved or soft surfaces. Given that liquids are more deformable than solids, sensors and actuators utilizing liquids encased in soft templates as sensing elements are particularly suited for these applications. Such devices, leveraging ultra-flexible conductive materials, are referred to as stretchable electronics.Liquid metals (LMs) have emerged as one of a leading material in this field. In recent years, interest in liquid metals has surged, notably in flexible and soft electronics. When considering liquid metals, mercury often comes to mind due to its fluid state at room temperature. However, its high toxicity precludes its use in wearable technology. Instead, gallium-based liquid metals are preferred due to their safety in such applications.Gallium alone melts at about 30°C, but an alloy of 75% gallium and 25% indium lowers the melting point to 15°C. Adding 10% tin further reduces it to -19°C. These gallium-based liquid metals, which form low-viscosity eutectic alloys, have extremely low melting points and high biocompatibility. In addition, they rapidly form a thin oxide layer on their surface, which complicates patterning on substrates. To address this, metal nanoparticles like nickel can be blended using ultrasonic probing to create a malleable paste.These materials are still under research to explore additional functionalities. Liquid metals are particularly promising for self-healing materials and advanced wiring technologies for sensors and smart devices in stretchable electronics. More recently, their application in battery technologies in addition to sensors and wiring has been proposed. With ongoing advancements in flexible and stretchable electronics, the flexibility of lithium-ion batteries, essential for powering these devices, is also under investigation. This presentation discusses research on flexible battery electrodes using liquid metal and on materials for stretchable battery packages.In our first study, liquid metal served as a battery electrode, integrating the reaction and current collecting layers into a single process, thus simplifying manufacturing. However, this integration results in lower conductivity compared to traditional two-layer electrodes. By employing materials such as Li4Ti5O12 (LTO) or Li2TiS3 (LTS) with liquid metal, we developed a high-conductivity, printable liquid metal electrode ink that combines both functions.In a second application, liquid metal was used as an package for stretchable batteries. Recent studies on batteries have primarily focused on enhancing their stability and lifespan, with less attention to packaging. Conventionally, aluminum laminate film is used to prevent moisture and gas permeation in highly deformable batteries. Our study introduced a novel approach using a layer-by-layer technique to apply a thin liquid metal coating on a gold-coated thermoplastic polyurethane film, resulting in a stretchable packaging film with excellent gas barrier properties. This innovation not only enhances the battery's operational stability but also allows it to function reliably in atmospheric condition.The applications for liquid metals are extensive and hold promise for further exploration in various fields.

Mechanically Tough Polymer Electrolyte Membranes Prepared By Radiation-Induced Graft Polymerization of Poly (ether ether ketone) Film

The development of state-of-the-art polymer electrolyte membranes is indispensable for solid polymer fuel cells. To make a desired membrane, we have reported the radiation-induced graft polymerization (RGP) method in our previous studies, which is a fascinating technique with great advantages of low-cost fabrication and imparting new functionality via graft polymers to commercially available substrate polymer films, whose excellent mechanical/thermal properties are maintained. Among various substrate polymers, poly (ether ether ketone) (PEEK) is regarded as the most promising aromatic hydrocarbon material for the long life-time operation requirement of fuel cells due to its excellent mechanical stability and high gas barrier property at high temperature. However, graft polymerization on PEEK substrate is rather difficult. To successfully obtain PEEK-based polymer electrolyte membranes with suitably-balanced properties, we have extensively investigated the graft polymerization and irradiation conditions. In this work, we will report the synthesis of both PEEK-based proton- and anion-exchange membranes (PEEK-PEMs and PEEK-AEMs, respectively), and the fuel cell performance using these two types of membranes.1)RGP for making PEEK-PEMs and PEEK-AEMs. The PEEK base films used for RGP was previously immersed in (1, 4-dioxane) DOX at 50°C for 18 hours as a solvent annealing treatment. Ethyl styrene sulfonate (ETSS) and chloromethyl styrene (CMS) are used as precursors for PEMs and AEMs, respectively (Scheme 1).For the synthesis of PEEK-PEMs, the solvent-annealed PEEK films were pre-irradiated with 60Co ϒ-ray at room temperature in argon atmosphere with a total dose 160 kGy. Then the samples were immersed in ETSS/DOX solution (1/1 v/v) at 80°C under the argon atmosphere. The resultant grafted-PEEK membranes has a grafting degree (GD) of 150%. After hydrolysis treatment, the final PEEK-PEM shows an ion-exchange capacity (IEC) of 2.5 mmol/g and a proton conductivity of 0.1 S/cm at 25 °C. For the synthesis of PEEK-AEMs, the same irradiation and polymerization procedures as in the synthesis of PEEK-PEMs were performed, by using CMS as monomers instead of ETSS. The CMS-grafted PEEK with high GD of 66% was obtained in tetraethylenglycol as a solvent. The grafted PEEK was converted to AEM by treating in trimethylamine with a quaternization degree of 76%. The obtained AEM has an IEC of 1.7 mmol/g and an anion conductivity of 0.128 S/cm at 60°C. The mechanical strength and elongation of the resulting PEEK-PEM at 80°C and 100%RH were measured to be 22 MPa and 50%, respectively, which are superior to those of Nafion (10 MPa and 200%, respectively). PEEK-AEM also shows good mechanical strength and elongation of 94 MPa and 18%, respectively, at room temperature and 70% RH.2)Fuel cell performance evaluation. Fuel cell test using PEEK-PEMs and AEMs was carried out according to previous reports [1]. The membrane was sandwiched by anode and cathode electrodes (Pt or Pt/Ru loading 0.5 mg/cm2) and hot-pressed, and then obtained membrane/electrodes assembly (MEA) was then set into a 5 cm2 fuel cell for testing. The cell was fed with pure hydrogen and oxygen gases at a flow rate of 0.05 L/min each to the anode and cathode, respectively, under atmosphere pressure. The cell condition was 80°C and 100%RH.Fuel cell test with an MEA incorporating 16 μm PEEK-PEM shows a good performance of an open circuit of 0.9 V and a power density of 860 mW/cm2 at a current density of 2240 mA/cm2 (Figure 1(a)). Using the PEEK-g-AEM membrane, it shows an open circuit voltage value of more than 0.9 V and a power density of 673 mW/cm2 at a current density of 1199 mA/cm2 (Figure 1(b)). As described above, utilizing radiation-induced graft polymerization, we have for the first time successfully developed two types of polymer electrolyte membranes, PEEK-PEM and PEEK-AEM, using the mechanically tough and chemically stable aromatic hydrocarbon polymer PEEK as the substrate.[1] J. Chen, et al. J.Membr. Sci. 2008, 319, 1-4. Figure 1

Crystallization, Gas Barrier, and Mechanical Properties of Polypropylene Nanocomposites Reinforced by Graphite‐Like Carbon Nitride Nanosheets

ABSTRACTPolypropylene (PP) based nanocomposites with graphitic carbon nitride nanosheets (CNNSs) exfoliated from g‐C3N4 (CN) were fabricated via melt compounding. The detailed structure and morphology of the CNNSs were examined using X‐ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscope (TEM), and atomic force microscopy (AFM) measurements. The effects of CNNSs on the crystalline morphology, oxygen vapor permeability, and mechanical properties of PP based nanocomposites were carefully evaluated. The CNNS not only increased the crystallization peak temperature and crystallinity, but also enhanced gas barrier properties and tensile strength of the PP nanocomposites. For PP/CNNS‐2 nanocomposites, the tensile strength was increased by 10.7%, and oxygen permeability coefficients decreased by 64.5% compared to pure PP. Therefore, PP/CNNS nanocomposite could be a potential candidate for packing application.