Nafion-Based Proton-Exchange Membranes Built on Cross-Linked Semi-Interpenetrating Polymer Networks between Poly(acrylic acid) and Poly(vinyl alcohol)

Proton Exchange Membrane with Dual-Active-Center Surpasses the Conventional Temperature Limitations of Fuel Cells

High temperature-proton exchange membrane fuel cells (HT-PEMFC) call for ionomers with low humidity dependence and elevated-temperature resistance. Traditional perfluorosulfonic acid (PFSA) ionomers encounter challenges in meeting these stringent requirements. Herein, this study reports a perfluoroimide multi-acid (PFMA) ionomer with dual active centers achieved through the incorporation of sulfonimide and phosphonic acid groups into the side chain. The fluorocarbon skeleton and multi-acid side chain structure facilitate the segregation of hydrophilic and hydrophobic microphases, augmenting the short-range ordering of hydrophilic nanodomains. Furthermore, the introduction of a rigid segment-benzene ring is employed to decrease side chain flexibility and raise the glass transition temperature. Notably, the prepared membrane exhibits a conductivity of 41 mS cm-1 at 40% relative humidity, showcasing a 1.8 times improvement over that of PFSA. Additionally, the power output of the H2-air fuel cell based on this membrane reaches 1.5 W cm-2 at 105 °C, marking a substantial 2.3 times enhancement compared to the PFSA. This work demonstrates the unique advantages of perfluorinated ionomers with multiple protogenic groups in the development of high-performance high-temperature electrolyte materials.

Polymers in Physics, Chemistry and Biology: Behavior of Linear Polymers in Fractal Structures

We start presenting an overview on recent applications of linear polymers and networks in condensed matter physics, chemistry and biology by briefly discussing selected papers (published within 2022-2024) in some detail. They are organized into three main subsections: polymers in physics (further subdivided into simulations of coarse-grained models and structural properties of materials), chemistry (quantum mechanical calculations, environmental issues and rheological properties of viscoelastic composites) and biology (macromolecules, proteins and biomedical applications). The core of the work is devoted to a review of theoretical aspects of linear polymers, with emphasis on self-avoiding walk (SAW) chains, in regular lattices and in both deterministic and random fractal structures. Values of critical exponents describing the structure of SAWs in different environments are updated whenever available. The case of random fractal structures is modeled by percolation clusters at criticality, and the issue of multifractality, which is typical of these complex systems, is illustrated. Applications of these models are suggested, and references to known results in the literature are provided. A detailed discussion of the reptation method and its many interesting applications are provided. The problem of protein folding and protein evolution are also considered, and the key issues and open questions are highlighted. We include an experimental section on polymers which introduces the most relevant aspects of linear polymers relevant to this work. The last two sections are dedicated to applications, one in materials science, such as fractal features of plasma-treated polymeric materials surfaces and the growth of polymer thin films, and a second one in biology, by considering among others long linear polymers, such as DNA, confined within a finite domain.

A Review of Solid-State Proton-Polymer Batteries: Materials and Characterizations

The ever-increasing global population necessitates a secure and ample energy supply, the majority of which is derived from fossil fuels. However, due to the immense energy demand, the exponential depletion of these non-renewable energy sources is both unavoidable and inevitable in the approaching century. Therefore, exploring the use of polymer electrolytes as alternatives in proton-conducting batteries opens an intriguing research field, as demonstrated by the growing number of publications on the subject. Significant progress has been made in the production of new and more complex polymer-electrolyte materials. Specific characterizations are necessary to optimize these novel materials. This paper provides a detailed overview of these characterizations, as well as recent advancements in characterization methods for proton-conducting polymer electrolytes in solid-state batteries. Each characterization is evaluated based on its objectives, experimental design, a summary of significant results, and a few noteworthy case studies. Finally, we discuss future characterizations and advances.

Alternative to Conventional Solutions in the Development of Membranes and Hydrogen Evolution Electrocatalysts for Application in Proton Exchange Membrane Water Electrolysis: A Review

Proton exchange membrane water electrolysis (PEMWE) represents promising technology for the generation of high-purity hydrogen using electricity generated from renewable energy sources (solar and wind). Currently, benchmark catalysts for hydrogen evolution reactions in PEMWE are highly dispersed carbon-supported Pt-based materials. In order for this technology to be used on a large scale and be market competitive, it is highly desirable to better understand its performance and reduce the production costs associated with the use of expensive noble metal cathodes. The development of non-noble metal cathodes poses a major challenge for scientists, as their electrocatalytic activity still does not exceed the performance of the benchmark carbon-supported Pt. Therefore, many published works deal with the use of platinum group materials, but in reduced quantities (below 0.5 mg cm-2). These Pd-, Ru-, and Rh-based electrodes are highly efficient in hydrogen production and have the potential for large-scale application. Nevertheless, great progress is needed in the field of water electrolysis to improve the activity and stability of the developed catalysts, especially in the context of industrial applications. Therefore, the aim of this review is to present all the process features related to the hydrogen evolution mechanism in water electrolysis, with a focus on PEMWE, and to provide an outlook on recently developed novel electrocatalysts that could be used as cathode materials in PEMWE in the future. Non-noble metal options consisting of transition metal sulfides, phosphides, and carbides, as well as alternatives with reduced noble metals content, will be presented in detail. In addition, the paper provides a brief overview of the application of PEMWE systems at the European level and related initiatives that promote green hydrogen production.

Chitosan-Linked Dual-Sulfonate COF Nanosheet Proton Exchange Membrane with High Robustness and Conductivity

2D materials that can provide long-range ordered channels in thin-film form are highly desirable for proton exchange membranes (PEMs). Covalent organic framework nanosheets (CONs) are promising 2D materials possessing intrinsic porosity and high processability. However, the potential of CONs in PEMs is limited by loose sheet stacking and interfacial grain boundary, which lead to unsatisfied mechanical property and discontinuous conduction pathway. Herein, chitosan (CS), a natural polymer with rich NH2 groups, is designed as the linker of dual-sulfonate CONs (CON-2(SO3 H)) to obtain CON-2(SO3 H)-based membrane. Ultrathin CON-2(SO3 H) with high crystallinity and large lateral size is synthesized at water-octanoic acid interface. The high flexibility of CS chains and their electrostatic interactions with SO3 H groups of CON-2(SO3 H) enable effective connection of CON-2(SO3 H), thus endowing membrane dense structure and exceptional stability. The stacked CON-2(SO3 H) constructs regular hydrophilic nanochannels containing high-density SO3 H groups, and the electrostatic interactions between CON-2(SO3 H) and CS form interfacial acid-base pairs transfer channels. Consequently, CON-2(SO3 H)@CS membrane simultaneously achieves superior proton conductivity of 353 mS cm-1 (under 80 °C hydrated condition) and tensile strength of 95 MPa. This work highlights the advantages of proton-conducting porous CON-2(SO3 H) in advanced PEMs and paves a way in fabricating robust CON-based membranes for various applications.

Development of High-Performance Polymer Electrolyte Membranes through the Application of Quantum Dot Coatings to Nafion Membranes

Proton exchange membrane water electrolysis (PEMWE) generates oxygen and hydrogen at the anode and cathode, respectively, by conducting protons generated at the anode to the cathode through a proton exchange membrane (PEM). The performance of PEMWE can be improved with faster catalytic reactions at each electrode; thus, the development of a PEM with excellent ionic conductivity and physicochemical stability is essential. Nafion, a type of perfluoro-sulfonic acid polymer, is the most widely used PEM material. However, despite its excellent conductivity and chemical stability, it exhibits high hydrogen permeability due to its structural characteristics. Quantum dots (QDs) have a hydrophilic functional group that can act as an ion conductor and are extremely compatible with the hydrophilic cluster of Nafion due to their characteristic nanosized structure. In this study, various compositions of N-doped carbon quantum dots (CQDs) containing hydrophilic functional groups were coated on a Nafion-212 membrane. The resulting series of CQD-coated Nafion membranes exhibited improvements in morphology and ionic conductivity as well as reductions in hydrogen permeability. In particular, the Nafion membrane coated with 0.75 wt % of N-doped CQD (CQD-cNafion-0.75) exhibited improved mechanical properties and higher oxidation stability compared to Nafion-212. It also displayed higher ionic conductivity of 240.3 mS cm^-1 at 80 °C and reduced hydrogen permeability (about 10% reduction) compared to Nafion-212. In addition, the performance of single-cell PEMWE using the CQD-cNafion-0.75 membrane was found to be approximately 1.2 times higher than Nafion-212.

Nanocomposite Membranes for PEM-FCs: Effect of LDH Introduction on the Physic-Chemical Performance of Various Polymer Matrices

This is a comparative study to clarify the effect of the introduction of layered double hydroxide (LDH) into various polymer matrices. One perfluorosulfonic acid polymer, i.e., Nafion, and two polyaromatic polymers such as sulfonated polyether ether ketone (sPEEK) and sulfonated polysulfone (sPSU), were used for the preparation of nanocomposite membranes at 3 wt.% of LDH loading. Thereafter, the PEMs were characterized by X-ray diffraction (XRD) and dynamic mechanical analysis (DMA) for their microstructural and thermomechanical features, whereas water dynamics and proton conductivity were investigated by nuclear magnetic resonance (PFG and T1) and EIS spectroscopies, respectively. Depending on the hosting matrix, the LDHs can simply provide additional hydrophilic sites or act as physical crosslinkers. In the latter case, an impressive enhancement of both dimensional stability and electrochemical performance was observed. While pristine sPSU exhibited the lowest proton conductivity, the sPSU/LDH nanocomposite was able to compete with Nafion, yielding a conductivity of 122 mS cm-1 at 120 °C and 90% RH with an activation energy of only 8.7 kJ mol-1. The outcome must be ascribed to the mutual and beneficial interaction of the LDH nanoplatelets with the functional groups of sPSU, therefore the choice of the appropriate filler is pivotal for the preparation of highly-performing composites.

Cross-Linked Sulfonated Poly(arylene ether sulfone) Membrane Using Polymeric Cross-Linkers for Polymer Electrolyte Membrane Fuel Cell Applications

Cross-linked membranes for polymer electrolyte membrane fuel cell application are prepared using highly sulfonated poly(arylene ether sulfone) (SPAES) and polymeric cross-linkers having different hydrophilicities by facile in-situ casting and heating processes. From the advantage of the cross-linked structures made with the use of polymeric cross-linkers, a stable membrane can be obtained even though the polymer matrix with a very high degree of sulfonation was used. In particular, hydrophilic cross-linker is found to be effective in improving physicochemical properties of the cross-linked membranes and at the same time showing reasonable proton conductivity. Accordingly, membrane electrode assembly made from the cross-linked membrane prepared by using hydrophilic polymeric cross-linker exhibits outstanding cell performance under high temperature and low relative humidity conditions (e.g., maximum power density of 176.4 mW cm^-2 at 120 °C and 40% RH).

Acrylate and Methacrylate Polymers' Applications: Second Life with Inexpensive and Sustainable Recycling Approaches

Polymers are widely employed in several fields thanks to their wide versatility and the easy derivatization routes. However, a wide range of commercial polymers suffer from limited use on a large scale due to their inert nature. Nowadays, acrylate and methacrylate polymers, which are respectively derivatives of acrylic or methacrylic acid, are among the most proposed materials for their useful characteristics like good biocompatibility, capping ability toward metal clusters, low price, potentially recyclability and reusability. Here, we discuss the advantages and challenges of this class of smart polymers focusing our attention on their current technological applications in medical, electronic, food packaging and environmental remediation fields. Furthermore, we deal with the main issue of their recyclability, considering that the current commercial bioplastics are not yet able to meet the global needs as much as to totally replace fossil-fuel-based products. Finally, the most accredited strategies to reach recyclable composites based on acrylic polymers are described.