Acid Proton Exchange Membranes Research Articles

(Invited) Overview of Ion-Conducting Polymer Membranes and Membrane Separators for Water Electrolysis

Traditional liquid alkaline electrolyzer uses a porous diaphragm to allow diffusion of hydroxide ion from a feed of concentrated KOH solution while separating anode and cathode and suppressing mixing of produced H2 and O2 gases. Although liquid alkaline electrolyzer is considered as a matured technology, recent renaissance of new electrode separators suggests there is significant potential for improvement in efficiency and cost reduction by lowering area specific resistance and increasing operation current density.Ion-conducting polymers (e.g., proton or hydroxide) are used as a key component of polymer electrolyte membranes, such as acidic proton exchange membrane (PEM) and alkaline anion exchange membrane (AEM), in electrochemical energy conversion and storage technologies including water electrolyzers. For example, the state-of-the-art PEM electrolyzers have used Nafion for a PEM and ionomer catalyst binder for decades, though it is not ideal proton-conducting membrane material for those applications. Recent pressure on perfluoroalkyl substrates (PFASs) from government and environmental activist groups due to their environmental and health hazard has attracted the development of alternative polymer electrolyte membranes based on hydrocarbon polymers within electrochemical society. Compared to perfluorosulfonated Nafion, hydrocarbon ion-conducting polymers (both PEMs and AEMs) can offer advantages of flexible synthetic tunability, lower gas permeability, and importantly lower production cost.In this tutorial, an overview of recent progress in the development of advanced porous membrane separators, PEMs and AEMs, their key membrane properties, and the state-of-the-art performance in applications of water electrolyzers will be discussed. Figure 1

Nanocone-Modified Surface Facilitates Gas Bubble Detachment for High-Rate Alkaline Water Splitting

Alkaline water splitting (AWS) is one of the most attractive technologies for green hydrogen production. In comparison to the acidic proton exchange membrane (PEM), AWS offers greater flexibility in using non-platinum group metal catalysts and could generate higher-purity hydrogen. However, commercial AWS systems are normally operated at a lower current density (~400 mA cm-2) than PEM electrolyzers. To rapidly generate hydrogen at an industrial scale, it is critical to boost the operating current density of AWS to a level of ~1000 mA cm-2. Nevertheless, the significant amount of gas bubbles generated during high-rate AWS could be detrimental to the process. Bubbles can block the catalysts’ active site, hinder electrolyte diffusion, and increase Ohmic resistance, thus deteriorating the reaction rate and restricting the cell voltage efficiency. The detachment of gas bubbles may also damage the catalyst layer. In this study, we demonstrate a general strategy for facilitating bubble detachment by modifying the nickel electrode surface with nickel nanocone nanostructures, which turns the surface into underwater superaerophobic. The simulation and experimental data show that bubbles take a considerably shorter time to detach from the nanocone-modified nickel foil than the unmodified foil. As a result, these bubbles also have a smaller detachment size and less chance for bubble coalescence. The nanocone-modified electrodes, including nickel foil, nickel foam, and 3D-printed nickel lattice, all show substantially reduced overpotentials at 1000 mA cm-2 compared to their pristine counterpart. The electrolyzer assembled with two nanocone-modified nickel lattice electrodes retains >95% of the performance after testing at ~900 mA cm-2 for 100 hours and the surface NC structure is also well preserved, demonstrating its excellent electrochemical and mechanical stability at high current density. Our findings offer an exciting and simple strategy for enhancing the bubble detachment and, thus, the electrode activity for high-rate AWS.

Cyclic Olefin Copolymer-Based Reinforced Anion Exchange Membrane for Fuel Cell

Alkaline exchange membrane (AEM)-based fuel cells have emerged as a promising technology for clean energy conversion. In contrast to acidic proton exchange membrane in fuel cells, AEM fuel cells utilize an alkaline membrane AEM to facilitate the migration of hydroxide ions, offering advantages of economic earth-abundant catalysts and enhanced electrochemical reaction kinetics. However, AEMs that possess all characters of high ion conductivity, good chemical stability under high pH and temperature, robust mechanical properties, scalable synthesis, and low manufacturing costs are rare until now.Herein, we present quaternary ammonium-functionalized cyclic olefin copolymers (COCs) as a new class of alkaline stable and low-cost AEMs. Furthermore, we developed reinforced composite AEM by impregnating the quaternary ammonium-functionalized COC into a mechanically robust matrix. The prepared COC-reinforced membrane exhibits outstanding hydroxide conductivity of 127 mS/cm at 80°C and low swelling ratio in liquid water, and excellent mechanical properties with a tensile strength > 50 MPa, and elongation at break > 248%. The H2-O2 fuel cell test exhibited a maximum peak power density of >1.2 W cm-2 at 80°C with a low high-frequency resistance (HFR) under 0.1 Ohm cm2.

Covalently attached phosphonic acid‐Si2O3‐PEO polymer membranes for PEMFC applications

AbstractIn the context of growing interest in phosphonic acid proton exchange membranes (PEMs) for fuel cell applications, we report on new PEMs containing low‐cost polyethylene oxide (PEO) covalently linked by siloxane bonds, SiOSi, to phosphonic acid (PA). Key chemistry in the formation of these membranes involves hydrolysis and condensation reactions of triethoxysilyl propyl capped PEO and pre‐hydrolyzed dimethyl phosphonatoethyltrimethoxysilane (DMPTMS) giving PEO‐Si2O3‐PA and cross‐linked chain PEO‐Si2O3‐PEO organosilsesquioxane components. The Si2O3 can enhance membrane thermal and mechanical properties. The membrane formulations were varied by (a) reagent ratios (b) PEO molecular weights or using polypropylene oxide (PPO) (c) incorporating chain extending groups methylene diphenyl diisocyanate (MDI) or hexamethylene diisocyanate (HDI). These variations provided five membrane families, one of which afforded a complete group of robust membranes with weight% x of PA, PAx in range PA0–PA33. These were studied using ATR‐FTIR, dry membrane water uptake capacity, ion exchange capacity (IEC), and conductivity from room temperature to 120°C at 100% relative humidity. Conductivity increased with PAx reaching 15 mS cm−1 at 120°C, activation energy 0.1 eV, for membrane PA33 for which thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and energy dispersive X‐ray analysis (EDAX) are reported. A comparative performance of the five membrane families is presented.

Ion-Exchange Strategy Enabling Direct Reformation of Unreliable Perfluorinated Cationic Polymer for Robust Proton Exchange Membrane towards Hydrogen Fuel Cells

Perfluorosulfonated anionic ionomers are known for their robust ion conductivity and chemical and mechanical stability. However, the structure and transport property degradation of perfluorinated cationic polymers (PfCPs) are not well understood. Herein, we propose an ion-exchange strategy to identify the structural degradation, ion transport mechanisms, and architectural reformation of PfCPs. Particularly, we demonstrate that the utility of a –SO2–N+ strategy employing the Menshutkin reaction cannot yield reliable PfCPs and anion-exchange membranes, but can yield an unreliable zwitterionic intermediate (cations–anions molar ratio is approximately 7.6%). Moreover, the degradation products were efficiently reformed as proton exchange membranes (PEMs), and the as-reformed PEMs achieved an ion-exchange capacity (IEC) value (0.89 mmol g−1), meanwhile retaining more than 94.7% of their initial capacity. Furthermore, the fuel cell assembled with reformed PEMs displayed a power density of 0.91 Wcm−2 at 2.32 A cm−2, which was 90.1% of that of the robust perfluorosulfonic acid PEMs. Our combined findings shed some fresh light on the state of understanding of the structure–property relationship in PfCPs.

Tuning Stainless Steel Oxide Layers through Potential Cycling─AEM Water Electrolysis Free of Critical Raw Materials.

Anion exchange membrane water electrolyzers (AEMWEs) have an intrinsic advantage over acidic proton exchange membrane water electrolyzers through their ability to use inexpensive, stable materials such as stainless steel (SS) to catalyze the sluggish oxygen evolution reaction (OER). As such, the study of active oxide layers on SS has garnered great interest. Potential cycling is a means to create such active oxide layers in situ as they are readily formed in alkaline solutions when exposed to elevated potentials. Cycling conditions in the literature are rife with unexplained variations, and a complete account of how these variations affect the activity and constitution of SS oxide layers remains unreported, along with their influence on AEMWE performance. In this paper, we seek to fill this gap in the literature by strategically cycling SS felt (SSF) electrodes under different scan rates and ranges. The SSF anodes were rapidly activated within the first 50 cycles, as shown by the 10-fold decline in charge transfer resistance, and the subsequent 1000 cycles tuned the metal oxide surface composition. Cycling the Ni redox couple (RC) increases Ni content, which is further enhanced by lowering the cycling rate, while cycling the Fe RC increases Cr content. Fair OER activity was uncovered through cycling the Ni RC, while Fe cycling produced SSF electrodes active toward both the OER and the hydrogen evolution reaction (HER). This indicates that inert SSF electrodes can be activated to become efficient OER and HER electrodes. To this effect, a single-cell AEMWE without any traditional catalyst or ionomer generated 1.0 A cm-2 at 1.94 V ± 13.3 mV with an SSF anode, showing a fair performance for a cell free of critical raw materials.

Highly durable perfluorosulfonic acid proton exchange membrane by combining inorganic free radical scavengers and organic antioxidants

In this work, a new type of complex was constructed by coordinating quercetin (QC) with cerium (Ce) ions. This complex was introduced into perfluorosulfonic acid resin (PFSA) to fabricate a proton exchange membrane. The coordination process prevented the formation of ion cross-links between cerium and sulfonic acid groups in PFSA, thereby keeping proton conductivity and fuel cell performance of membrane samples at a high level. Due to the insolubility of quercetin in water, its coordination with cerium minimized cerium migration, providing long-lasting resistance to free radicals. The effects of additives on PFSA membrane properties were investigated by measuring IEC, water uptake, swelling ratio, and proton conductivity. Fenton degradation experiments and membrane electrode assembly performance tests was conducted simultaneously. The results demonstrated that compared to the addition of quercetin or cerium alone, the use of QC-Ce increased the proton conductivity by 23.70% after 24-h Fenton degradation and lowered fluoride release by 58.29%. Meanwhile, the PFSA/QC-Ce composite membrane samples maintained an open circuit voltage of 0.935 V and a maximum power density of 668.15 mW cm−2 after 96 h of open circuit voltage hold testing.

Proton exchange membranes with functionalized sulfonimide and phosphonic acid groups for next-generation fuel cells operating at 120 °C

Proton exchange membrane fuel cells (PEMFCs) face a significant challenge when operating in high-temperature and low-humidity environments, the hydrocarbon-based polymers that are sulfonated or phosphonated can’t meet the demand for achieving high performance. Modifying perfluorosulfonyl fluoride (PFSF) through meticulous design of side-chain chemical structures and introducing functionalized sulfonimide and phosphonic acid groups. Membranes derived from a perfluorocarbon backbone and polyacid side chain structures exhibit distinct microphase separation. The sulfonimide group exhibits hyper-acidic properties, whereas the phosphonic acid group functions as proton acceptor and donor. These two groups work synergistically to establish a distinct proton transport channel. The robust adsorption between acidic functional groups and water molecules enhances the diffusion of water molecules, resulting in an increase in proton conductivity. Moreover, Density Functional Theory (DFT) calculations reveal that the phosphonic acid group of the side chain has difficulty forming anhydrides. The prepared perfluorosulfonimide-phosphonic acid (PFSNPA) proton exchange membrane demonstrates an impressive conductivity of 263 mS·cm−1 at 120 °C. In H2/Air fuel cell tests, PFSNPA achieves an outstanding output power of 1076.1 mW·cm−2 at 120 °C and 40 % RH. This study introduces a new approach for designing and fabricating proton exchange membrane materials for high-temperature fuel cells.

Design and Synthesis of Comb‐Like Bisulfonic Acid Proton Exchange Membrane with Regulated Microstructure

AbstractThe design and synthesis of proton exchange membranes (PEMs) with controllable microstructure and sulfonation degree play a crucial role in enhancing their performance and expanding their application. In this study, the disulfonic acid monomer is designed and prepared to synthesize the comb‐like disulfonic PEMs with controllable ion exchange capacity. The results show that the side chain structure and more concentrated sulfonic acid groups facilitate the aggregation of sulfonic acid groups in the polymer, improve the microphase separation morphology of PEMs, and increase the ionic conductivity. The proton conductivity of the DS‐PXIDI‐60 membrane is approximately 300 mS cm−1. The PEMs with controllable microstructure are prepared by introducing comonomers, including 9,9‐dimethylxanthrene, biphenyl, and p‐terphenyl, with different reactivity, spatial structure, and solubility. Biphenyl is copolymerized to form a copolymer with an alternating structure, and 9, 9‐dimethylxanthrene is copolymerized to form a random copolymer. In addition, it is worth noting that p‐terphenyl is copolymerized to form a microblock structure of the copolymer, with more excellent comprehensive properties. DS‐PXITp‐60 exhibits better performance than Nafion 212 in redox­flow batteries and fuel cells. Therefore, such molecular design and synthesis strategies provide a reference guide for the development of high‐performance PEMs.

Self-Enhancement of Perfluorinated Sulfonic Acid Proton Exchange Membrane with Its Own Nanofibers.

High-performance proton exchange membrane (PEM) is crucial for the proton exchange membrane fuel cell (PEMFC). Herein, a novel "self-enhanced" PEM is fabricated for the first time, which is composed of perfluorinated sulfonic acid (PFSA) resin and its own nanofibers as reinforcement. With this strategy, the interfacial compatibility issue of conventional fiber-reinforced membranes is fully addressed and up to 80 wt% loading of PFSA nanofibers can be incorporated. Furthermore, on account of chain orientation within the PFSA nanofiber, single fiber exhibits super-high conductivity of 1.45 S cm-1, leading to state-of-the-art proton conductivity (1.1 S cm-1) of the as-prepared "self-enhanced" PEM so far, which is an order of magnitude increase compared with the bulk PFSA membrane (0.29 S cm-1). It surpasses any commercial PEM including the popular GORE-SELECT and Nafion HP membranes and is the only PEM with conductivity at 100 S cm-1 level. In addition, the mechanical strength and swelling ratio of membranes are both substantially improved simultaneously. Based on the high-performance "self-enhanced" PEM, high peak power densities of up to 3.6W cm-2 and 1.7W cm-2 are achieved in H2-O2 and H2-Air fuel cells, respectively. This strategy can be applied in any polymeric electrolyte membrane.

Structural Characterization and Physicochemical Properties of Functionally Porous Proton-Exchange Membrane Based on PVDF-SPA Graft Copolymers.

Fluorinated proton-exchange membranes (PEMs) based on graft copolymers of dehydrofluorinated polyvinylidene fluoride (D-PVDF), 3-sulfopropyl acrylate (SPA), and 1H, 1H, 2H-perfluoro-1-hexene (PFH) were prepared via free radical copolymerization and characterized for fuel cell application. The membrane morphology and physical properties were studied via small-(SAXS) and wide-angle X-ray scattering (WAXS), SEM, and DSC. It was found that the crystallinity degree is 17% for PEM-RCF (co-polymer with SPA) and 16% for PEM-RCF-2 (copolymer with SPA and PFH). The designed membranes possess crystallite grains of 5-6 nm in diameter. SEM images reveal a structure with open pores on the surface of diameters from 20 to 140 nm. Their transport and electrochemical characterization shows that the lowest membrane area resistance (0.9 Ωcm2) is comparable to perfluorosulfonic acid PEMs (such as Nafion®) and polyvinylidene fluoride (PVDF) based CJMC cation-exchange membranes (ChemJoy Polymer Materials, China). Key transport and physicochemical properties of new and commercial membranes were compared. The PEM-RCF permeability to NaCl diffusion is rather high, which is due to a relatively low concentration of fixed sulfonate groups. Voltammetry confers that the electrochemical behavior of new PEM correlates to that of commercial cation-exchange membranes, while the ionic conductivity reveals an impact of the extended pores, as in track-etched membranes.

Recent advances in non-perfluorinated sulfonic acid proton exchange membranes in the energy field

Introduce the latest progress of non-perfluorinated sulfonic acid proton exchange membranes from the aspects of crosslinking methods, properties and applications.

Enabling high-temperature application of Nafion membrane via imitating ionic clusters in proton conduction channels

Nafion membranes, representative of perfluorosulfonic acid (PFSA) proton exchange membranes are not effective in dehydrated state and high-temperature condition (>100 oC). The traditional hybrid modification would lower the mechanical strength of the membrane due to the large-scale phase separation. In this work, a hyperbranched polyamide (HBM) featuring high sulfonate concentration and nanoparticle morphology is synthesized and non-destructively filled into Nafion matrix to imitate the “ionic cluster” to accelerate the proton conduction at elevated temperature. During the non-destructively membrane modification, the Nafion PFSA membrane is swelled in the solution and the main chain structure is expanded, the HBM macromolecules is simultaneously filled into the membrane together with the solvent. After the removal of solvent, HBM end-capped with –COOH forms strong hydrogen bonds with the sulfonate groups in Nafion matrix. As a result, proton conductivity of the composite membrane can reach 0.047 S/cm, which is 1.9 times higher than that of the pristine Nafion membrane, at 110 oC and 60% RH. Given the excellent overall stability, fuel cell performance of the HBM-modified Nafion membrane is studied and a 30% increase in power density is observed, suggesting a viable strategy to expand the operation temperature of PFSA-based fuel cells.

(Invited) Molecular Insights into Water Structure and Proton Transfer at the Interfaces in Bipolar AEM/PEM Membranes

Bipolar membranes (BPMs) are polymeric membranes composed of an acidic proton exchange membrane (PEM) and an alkaline anion exchange membrane (AEM). Bipolar membranes are operated in two different configurations, forward bias and reverse bias, based on the orientation of membranes and electrodes, when the cathode faces the PEM, it is operated in a reverse bias configuration. In reverse bias BPMs facilitates the dissociation of water at the interface of its junction. This unique feature makes it attractive to many industrial applications, including chemical industries, energy conversion and storage, environmental protection, and food processing. It was determined that the rate of water dissociation at the interface of a bipolar membrane increases with the addition of a weak acidic head group material, which acts as the catalyst for the water dissociation reaction and thus referred as the catalyst layer. BPMs have a better ion transport framework because of the amphiphilic nature of all three layers, resulting in well-connected water channels. Hence it is crucial to understand the interaction of water molecules with the functional groups at the molecular level and the morphology at mesoscale to understand the water aggregation and phase separation which helps in the asymmetric transport of proton and hydroxide ions through PEM and AEM respectively.This talk will communicate our efforts to undertake a multiscale approach involving both electronic structure calculations and mesoscale simulations to elucidate: (1) water interaction of water with the headgroups; proton transfer, and (2) connectivity of a TMA AEM, a PFSA PEM, and a phosphonic acid-based catalyst.

Non-destructively incorporating ceria in Nafion membrane as hydroxyl radical scavenging agent for long-term PEMFC application

Aiming at enhancing the long-term operation of proton exchange membrane fuel cell (PEMFC), Nafion as a typical example of perfluorosulfonic acid proton exchange membrane is non-destructively modified by sulfonated ceria (CeO2-DS) nanoparticles via a swelling-filling strategy. CeO2-DS nanoparticles in Nafion matrix can not only act as radical scavenging agent to improve the durability of Nafion, but also assist the re-construction of the efficient proton conduction channel in the composite Nafion membrane. Both oxidative stability and proton conductivity of the Nafion membrane are therefore remarkably improved with the great mechanical and thermal stability of Nafion maintained. PEMFC equipped with the modified Nafion membrane therefore outperforms that with the pristine Nafion membrane in terms of both power output and durability. Specifically, the maximum power density of the PEMFC equipped with modified Nafion after Fenton accelerated degradation test was significantly improved by ca. 25 % compared with that of the pristine Nafion membrane. This work hence provides a facile way to improve the durability of the PEMFC for practical applications.

Na Substitution Steering RuO6 Unit in Ruthenium Pyrochlores for Enhanced Oxygen Evolution in Acid.

Although Ruthenium-based pyrochlore oxides can function as promising catalysts for acidic water oxidation, their limitations in terms of stability and activity still need to be addressed for further application in practical conditions. In this work, the possibility to enhance both oxygen evolution reaction activity and durability of Gd2Ru2O7- δ through partial replacement with Na+ in Gd3+ sites is first offered, leading to the electronic and geometric regulation of active center RuO6. Na+ triggers the emergence of Ru<4+ and the electron rearrangement of active-centered RuO6. Specifically, Ru ions with a negative d-band center after Na+ doping exhibit weaker adsorption energies of *O and result in the conversion of the rate-limiting step from *O/*OOH to *OH/O*, reducing energy barriers for boosting activities. Therefore, the NaxGd2- xRu2O7- δ requires a low overpotential of 260mV at 10mA cm-2 in 0.1m HClO4 electrolyte. Moreover, the higher formation energy of Ru vacancy and less distorted RuO6 enable the as-prepared NaxGd2- xRu2O7- δ to operate steadily at 10 mA cm-2 for 300 h and multi-current chronopotentiometry with current densities from 20 to 100 mA cm-2 for 60 h in acidic proton exchange membrane electrolyzer, respectively.

The Promising Seesaw Relationship Between Activity and Stability of Ru-Based Electrocatalysts for Acid Oxygen Evolution and Proton Exchange Membrane Water Electrolysis.

The development of electrocatalysts that are not reliant on iridium for efficient acid-oxygen evolution is a critical step towards the proton exchange membrane water electrolysis (PEMWE) and green hydrogen industry. Ruthenium-based electrocatalysts have garnered widespread attention due to their remarkable catalytic activity and lower commercial price. However, the challenge lies in balancing the seesaw relationship between activity and stability of these electrocatalysts during the acid-oxygen evolution reaction (OER). This review delves into the progress made in Ru-based electrocatalysts with regards to acid OER and PEMWE applications. It highlights the significance of customizing the acidic OER mechanism of Ru-based electrocatalysts through the coordination of adsorption evolution mechanism (AEM) and lattice oxygen oxidation mechanism (LOM) to attain the ideal activity and stability relationship. The promising tradeoffs between the activity and stability of different Ru-based electrocatalysts, including Ru metals and alloys, Ru single-atomic materials, Ru oxides, and derived complexes, and Ru-based heterojunctions, as well as their applicability to PEMWE systems, are discussed in detail. Furthermore, this paper offers insights on in situ control of Ru active sites, dynamic catalytic mechanism, and commercial application of PEMWE. Based on three-way relationship between cost, activity, and stability, the perspectives and development are provided.

Perfluorosulfonic acid proton exchange membrane with double proton site side chain for high-performance fuel cells at low humidity

Structural optimization of ionomers is an effective strategy for achieving high-performance proton exchange membranes (PEMs) under low relative humidity (RH) conditions. In this study, sulfonimide group and trifluoromethanesulfonate acid (TFSA) ionic liquids were introduced to the perfluorosulfonic acid (PFSA) side chain, resulting in polymer membranes with varying chain lengths (i.e., PFC2-TF-SI, PFC4-TF-SI, and PFC5-TF-SI). This dual proton-conducting structure extended the length of the hydrophilic side chain and enhanced the hydrophobic-hydrophilic phase separation, aiding in the formation of proton transport channels. Notably, the proton conductivity of PFC5-TF-SI and PFC2-TF-SI membranes reached 7.1 and 10.6 mS/cm at 30% RH and 80 °C, respectively, which were approximately 29.1% and 92.7% higher than that of the pristine PFC5-SA membrane (5.5 mS/cm). Furthermore, the maximum power density of the PFC5-TF-SI and PFC2-TF-SI membranes from the built single fuel cell achieved 649 and 763 mW/cm2 at 30% RH and 80 °C, respectively, which were higher than that of the pristine PFC5-SA membrane (567 mW/cm2) by about 14.5% and 34.6%, respectively. Thus, this study provides a strategy for PEM design under low RH conditions.

High-temperature low-humidity proton exchange membrane with "stream-reservoir" ionic channels for high-power-density fuel cells.

The perfluorosulfonic acid (PFSA) proton exchange membrane (PEM) is the key component for hydrogen fuel cells (FCs). We used in situ synchrotron scattering to investigate the PEM morphology evolution and found a "stream-reservoir" morphology, which enables efficient proton transport. The short-side-chain (SSC) PFSA PEM is fabricated under the guidance of morphology optimization, which delivered a proton conductivity of 193 milliSiemens per centimeter [95% relativity humidity (RH)] and 40 milliSiemens per centimeter (40% RH) at 80°C. The improved glass transition temperature, water permeability, and mechanical strength enable high-temperature low-humidity FC applications. Performance improvement by 82.3% at 110°C and 25% RH is obtained for SSC-PFSA PEM FCs compared to Nafion polymer PEM devices. The insights in chain conformation, packing mechanism, crystallization, and phase separation of PFSAs build up the structure-property relationship. In addition, SSC-PFSA PEM is ideal for high-temperature low-humidity FCs that are needed urgently for high-power-density and heavy-duty applications.

Self-healable Nafion-poly(vinyl alcohol)/phosphotungstic acid proton exchange membrane prepared by freezing–thawing method for direct methanol fuel cell

Self-healable Nafion-poly(vinyl alcohol)/phosphotungstic acid proton exchange membrane prepared by freezing–thawing method for direct methanol fuel cell