Enhancement in proton conductivity and methanol resistance of Nafion membrane induced by blending sulfonated poly(arylene ether ketones) for direct methanol fuel cells

Evaluation and optimization of polycarbonate track-etched (PCTE) membranes for direct methanol fuel cells

Direct methanol fuel cells (DMFCs) offer a promising power source by utilizing liquid-state methanol as fuel, providing easy storage and transportability. Currently, DMFCs commonly employ perfluorosulfonic acid membranes, such as the well-known Nafion membrane, as proton exchange membranes. However, perfluorosulfonic acid membranes have significant drawbacks in DMFCs, including a high crossover rate, substantial swelling, poor thermal stability, and elevated costs. The crossover of methanol fuel to the cathode side is particularly detrimental as it can poison the precious Pt catalyst, leading to damage in the fuel cell system. In this manuscript, we propose a non-ionic proton exchange membrane based on the polycarbonate track etched (PCTE) membrane. The aligned nanopores in pristine PCTE, with a regular diameter, facilitate proton passage while mitigating the crossover of methanol molecules. This results in satisfactory proton conductivity and selectivity comparable to that of the commercial Gore membrane. By adding a layer of graphene treated with oxygen plasma for 10 seconds, methanol permeation can be reduced by 16.44%, while achieving a 42.11% increase in proton conductivity compared to the commercial Gore membrane. Furthermore, PCTE material offers a more cost-effective alternative to Gore membrane, with a 18.37% lower swelling ratio and significantly higher stability. These characteristics make PCTE a promising choice for DMFCs, offering potential improvements in performance and cost-effectiveness.

A High-Methanol-Permeation Resistivity Polyamide-Based Proton Exchange Membrane Fabricated via a Hyperbranching Design

Four non-fluorinated sulfonimide polyamides (s-PAs) were successfully synthesized and a series of membranes were prepared by blending s-PA with polyvinylidene fluoride (PVDF) to achieve high-methanol-permeation resistivity for direct methanol fuel cell (DMFC) applications. Four membranes were fabricated by blending 50 wt% PVDF with s-PA, named BPD-101, BPD-102, BPD-111 and BPD-211, respectively. The s-PA/PVDF membranes exhibit high methanol resistivity, especially for the BPD-111 membrane with methanol resistivity of 8.13 × 10-7 cm2/s, which is one order of magnitude smaller than that of the Nafion 117 membrane. The tensile strength of the BPD-111 membrane is 15 MPa, comparable to that of the Nafion 117 membrane. Moreover, the four membranes also show good thermal stability up to 230 °C. The BPD-x membrane exhibits good oxidative stability, and the measured residual weights of the BPD-111 membrane are 97% and 93% after treating in Fenton's reagent (80 °C) for 1 h and 24 h, respectively. By considering the mechanical, thermal and dimensional properties, the polyamide proton-exchange membrane exhibits promising application potential for direct methanol fuel cells.

Prominent Intrinsic Proton Conduction in Two Robust Zr/Hf Metal-Organic Frameworks Assembled by Bithiophene Dicarboxylate

To date, developing crystalline proton-conductive metal-organic frameworks (MOFs) with an inherent excellent proton-conducting ability and structural stability has been a critical priority in addressing the technologies required for sustainable development and energy storage. Bearing this in mind, a multifunctional organic ligand, 3,4-dimethylthiophene[2,3-b]thiophene-2,5-dicarboxylic acid (H2DTD), was employed to generate two exceptionally stable three-dimensional porous Zr/Hf MOFs, [Zr6O4(OH)4(DTD)6]·5DMF·H2O (Zr-DTD) and [Hf6O4(OH)4(DTD)6]·4DMF·H2O (Hf-DTD), using solvothermal means. The presence of Zr6 or Hf6 nodes, strong Zr/Hf-O bonds, the electrical influence of the methyl group, and the steric effect of the thiophene unit all contribute to their structural stability throughout a wide pH range as well as in water. Their proton conductivity was fully examined at various relative humidities (RHs) and temperatures. Creating intricate and rich H-bonded networks between the guest water molecules, coordination solvent molecules, thiophene-S, -COOH, and -OH units within the framework assisted proton transfer. As a result, both MOFs manifest the maximum proton conductivity of 0.67 × 10-2 and 4.85 × 10-3 S·cm-1 under 98% RH/100 °C, making them the top-performing proton-conductive Zr/Hf-MOFs. Finally, by combining structural characteristics and activation energies, potential proton conduction pathways for the two MOFs were identified.

Morphology and Transport Study of Acid-Base Blend Proton Exchange Membranes by Molecular Simulations: Case of Chitosan/Nafion

Blending a basic polymer (e.g., chitosan) with Nafion can modify some membrane properties in direct methanol fuel cell applications, e.g., controlling methanol crossover, by regulating the morphology of hydrophilic channels. Unraveling the mechanisms by which the channel morphology is modified is essential to formulate design strategies for acid-base blend membrane development. Thus, we use molecular simulations to analyze the morphological features of a blend membrane (at 75/25 chitosan/Nafion wt %), i.e., (i) water/polymer phase organizations, (ii) number and size of water clusters, and (iii) quantitative morphological measures of hydrophilic channels, and compare them to the pure Nafion in a wide range of water contents. It is found that the affinity of water to different hydrophilic groups in the blend membrane can result in more distorted and dispersed hydrophilic phase and fewer bulk water-like features compared to pure Nafion. Also, the width of the hydrophilic network bottleneck, i.e., pore limiting diameter (PLD), is found to be almost five times smaller for the blend membrane compared to Nafion at their maximum water contents. Moreover, by changing the chitosan/Nafion weight ratio from 75/25 to 0/100, we show that as Nafion content increases, all channel morphological characteristics alter monotonically except PLD. This is mainly due to the strong acid-base interactions between Nafion and chitosan, which hinder the monotonic growth of PLD. Interestingly, water and methanol diffusion coefficients are strongly correlated with PLD, suggesting that PLD can be used as a single parameter for tailoring the blending ratio for achieving the desired diffusion properties of acid-base membranes.

A simple MOF constructed using Pb(II) with strong polarizing force: a filler of Nafion membrane to increase proton conductivity

Metal-organic frameworks (MOFs) are promising competitive candidates as fillers for Nafion proton exchange membrane (PEM). Increasing efforts have been made to explore methods for synthesizing MOF fillers and the mechanism by which MOF doping improves the proton conductivity (σH+) values of composite membranes. In this study, a Pb(II) cation with strong polarizing force was selected for the hydrothermal reaction with a simple sulfoterephthalate ligand (H3L). Pb-MOF [Pb2L(OH)]n was obtained, which was constructed using Pb-O layers and deprotonated sulfoterephthalate L3- and exhibited good thermal and water stability. Different amounts of Pb-MOF particles were doped into Nafion to fabricate Pb-MOF/Nafion-x composite membranes, which were characterized using SEM, PXRD, IR spectroscopy, TGA, and other methods. It was found that doping Pb-MOF can apparently improve the water absorbability and thermal stability of the composite membrane. The σH+ of the Pb-MOF/Nafion-7 composite membrane was the highest and 2.14 times that of the pure Nafion membrane at 353 K. The higher proton conduction properties may be explained by the strong polarization force, and Pb(II) cations on the surface of Pb-MOF can decrease the bond energy of the O-H bond of absorbed water molecules and increase the acidity of the composite membrane. The phenomena in this study and our previous study confirm that acidity is the most important factor in favor of proton conductivity.

Efficient Proton Conductor Based on Bismuth Oxide Clusters and Polyoxometalates

Developing new solid-state electrolyte materials for improving the proton conductivity remains an important challenge. Herein, a novel two-dimensional layered solid-state proton conductor Bi2O2-SiW12 nanocomposite, based on silicotungstic acid (H4SiW12O40) and Bi(NO3)3·5H2O, was synthesized and characterized. The composite consists of a layered cation framework [Bi2O2]2+ and interlayer-embedded counteranionic [SiW12O40]4-, which forms continuous hydrogen bond (O-H···O) networks through the interaction of adjacent oxygen atoms on the surface of the [Bi2O2]2+ and oxygen atoms of the H4SiW12O40. Facile proton transfer along these pathways endows the Bi2O2-SiW12 (30:1) nanocomposite with an excellent proton conductivity of 3.61 mS cm-1 at 90 °C and 95% relative humidity, indicating that the nanocomposite has good prospects as a highly efficient proton conductor.

Efficiency Analysis of Fuel Cell Components with Ionic Poly-Arylether Composite Membrane

We use polyethylene glycol as an additive to explore how the hydrogen bonding of this additive changes the properties of SA8 blended sulfonated polyetheretherketone (SPEEK) composite films. We mixed a 5%wt polyethylene glycol solution into a 12.5%wt SA8 solution, and then prepared a film with a total weight of 40 g at a ratio of 1:99. The SA8 (PEG) solution was prepared and then mixed with 5%wt SPEEK solution, and a film-forming solution with a total weight of 8g in different mixing ratios was created. Polyethylene glycol (PEG) was mixed into the sulfonated polyarylether polymer SA8 to form physical cross-linking. Therefore, the sulfonated polyether ether ketone SPEEK was mixed in, and it exhibited good thermal stability and dimensional stability. However, there was some decrease in proton conductivity as the proportion of SPEEK increased. Although SPEEK mixed with sulfonated polymer reduces the proton conductivity, the physical cross-linking of PEG can improve the proton conductivity of the composite membrane, and adding SPEEK can not only solve the problem of the high sulfonation film swelling phenomenon, it can also improve the dimensional stability of the film through the hydrogen bonding force of PEG and obtain a composite film with excellent properties.

Nanocomposite Membranes Based on Fluoropolymers for Electrochemical Energy Sources

The physicochemical and transport properties (ion-exchange capacity, water content, diffusion permeability, conductivity, and current-voltage characteristic) of a series of perfluorinated membranes with an inert fluoropolymer content from 0 to 40%, obtained by polymer solution casting, were studied. Based on the analysis of the parameters of the extended three-wire model, the effect of an inert component on the path of electric current flow in the membrane and its selectivity were estimated. The mechanical characteristics of the membranes, such as Young's modulus, yield strength, tensile strength, and relative elongation, were determined from the dynamometric curves. The optimal amount of the inert polymer in the perfluorinated membrane was found to be 20%, which does not significantly affect its structure and electrotransport properties but increases the elasticity of the obtained samples. Therefore, the perfluorinated membrane with 20% of inert fluoropolymer is promising for its application in redox flow batteries and direct methanol fuel cells.

Synthesis, Characterization and Fabrication of Copper Nanoparticles Embedded Non-Perfluorintaed Kraton Based Ionic Polymer Metal Composite (IPMC) Actuator

Recently, cost-effective ionic polymer metal composite (IPMC) membranes coated with novel metals (viz., Ag, Au, or Pt) have exhibited excellent bending actuation performance, which was electrically stimulated. Herein, we have developed an IPMC membrane of highly cost-effective Kraton (KR) fabricated by incorporating Copper nanoparticles (CuNPs). It was then coated with Pt-metal using a solution casting process. The developed IPMC membrane (KR-CuNPs-Pt) was characterized using Fourier-transform infrared (FTIR) spectroscopy, Transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques. Further, ionic exchange capacity (IEC), the proton conductivity (PC), and water uptake/loss studies have also been performed. Actuation performance was measured using the electromechanical techniques. The actuation force of ca. 0.343 mN and displacement of ca. 18 mm at 4 VDC indicate that the developed membrane may serve as an alternative to the highly expensive commercialized IPMC actuators based on perfluorinated polymers. A soft bending actuator in the form of a micro-gripper was also developed.

Development of a Soft Robotic Bending Actuator Based on a Novel Sulfonated Polyvinyl Chloride–Phosphotungstic Acid Ionic Polymer–Metal Composite (IPMC) Membrane

This work presents the development of a cost-effective electric-stimulus-responsive bending actuator based on a sulfonated polyvinyl chloride (SPVC)–phosphotungstic acid (PTA) ionic polymer–metal composite (IPMC), using a simple solution-casting method followed by chemical reduction of platinum (Pt) ions as an electrode. The characterizations of the prepared IPMC were performed using Fourier-transform infrared (FTIR) spectroscopy, Scanning electron microscopy (SEM), X-ray diffraction (XRD) techniques, Thermogravimetric analysis (TGA), and Energy-dispersive X-ray (EDX) analysis. Excellent ion-exchange capacity (IEC) and proton conductivity (PC), with values of ca. 1.98 meq·g⁻¹ and ca. 1.6 mS·cm⁻¹, respectively, were observed. The water uptake (WU) and water loss (WL) capacities of the IPMC membranes were measured at 25 °C, and found to have maxima of ca. 48% for 10 h, and ca. 36% at 6 V DC for almost 9 min, respectively. To analyze the actuation performance of the developed membrane, tip displacement and actuation force measurements were conducted. Tip displacement was found to be ca. 15.1 mm, whereas bending actuation was found to be 0.242 mN at 4 V DC. The moderate water loss, good proton conductivity (PC), high thermal stability, and good electrochemical properties of the developed IPMC membrane actuator position it as a cost-effective alternative to highly expensive conventional perfluorinated polymer-based actuators.

A State-of-Art on the Development of Nafion-Based Membrane for Performance Improvement in Direct Methanol Fuel Cells

Nafion, a perfluorosulfonic acid proton exchange membrane (PEM), has been widely used in direct methanol fuel cells (DMFCs) to serve as a proton carrier, methanol barrier, and separator for the anode and cathode. A significant drawback of Nafion in DMFC applications is the high anode-to-cathode methanol fuel permeability that results in over 40% fuel waste. Therefore, the development of a new membrane with lower permeability while retaining the high proton conductivity and other inherent properties of Nafion is greatly desired. In light of these considerations, this paper discusses the research findings on developing Nafion-based membranes for DMFC. Several aspects of the DMFC membrane are also presented, including functional requirements, transport mechanisms, and preparation strategies. More importantly, the effect of the various modification approaches on the performance of the Nafion membrane is highlighted. These include the incorporation of inorganic fillers, carbon nanomaterials, ionic liquids, polymers, or other techniques. The feasibility of these membranes for DMFC applications is discussed critically in terms of transport phenomena-related characteristics such as proton conductivity and methanol permeability. Moreover, the current challenges and future prospects of Nafion-based membranes for DMFC are presented. This paper will serve as a resource for the DMFC research community, with the goal of improving the cost-effectiveness and performance of DMFC membranes.

Nafion Composite Membranes Impregnated with Polydopamine and Poly(Sulfonated Dopamine) for High-Performance Proton Exchange Membranes

We prepared Nafion composite membranes by impregnating Nafion-212 with polydopamine, poly(sulfonated dopamine), and poly(dopamine-co-sulfonated dopamine) using the swelling-filling method to generate nanopores in the Nafion framework that were filled with these polymers. Compared to the pristine Nafion-212 membrane, these composite membranes showed improved thermal and mechanical stabilities due to the strong interactions between the catecholamine of the polydopamine derivatives and the Nafion matrix. For the composite membrane filled with poly(sulfonated dopamine) (N-PSDA), further interactions were induced between the Nafion and the sulfonic acid side chain, resulting in enhanced water uptake and ion conductivity. In addition, filling the nanopores in the Nafion matrix with polymer fillers containing aromatic hydrocarbon-based dopamine units led to an increase in the degree of crystallinity and resulted in a significant decrease in the hydrogen permeability of the composite membranes compared to Nafion-212. Hydrogen crossovers 26.8% lower than Nafion-212 at 95% relative humidity (RH) (fuel cell operating conditions) and 27.3% lower at 100% RH (water electrolysis operating conditions) were obtained. When applied to proton exchange membrane-based fuel cells, N-PSDA exhibited a peak power density of 966 mW cm^-2, whereas N-PSDA showed a current density of 4785 mA cm^-2, which is 12.4% higher than Nafion-212 at 2.0 V and 80 °C.

Highly selective sulfonated Poly (arylene ether nitrile) composite membranes containing copper phthalocyanine grafted graphene oxide for direct methanol fuel cell

To improve the performances of sulfonated poly (arylene ether nitrile) (SPEN)–based proton exchange membranes (PEMs) in direct methanol fuel cells (DMFCs), the copper phthalocyanine grafted graphene oxide (CP-GO) was successfully prepared via in situ polymerization and subsequently incorporated into SPEN as filler to fabricate a series of SPEN/CP-GO-X (X represents for the mass ratio of CP-GO) composite membranes. The water absorption, swelling ratio, mechanical properties, proton conductivity, and methanol permeability of the membranes were systematically studied. CP-GO possesses good dispersion and compatibility with SPEN matrix, which is propitious to the formation of strong interfacial interactions with the SPEN, so as to provide more efficient transport channels for proton transfer in the composite membranes and significantly improve the proton conductivity of the membranes. Besides, the strong π–π conjugation interactions between CP-GO and SPEN matrix can make the composite membranes more compact, blocking the methanol transfer in the membranes, and significantly reducing the methanol permeability. Consequently, the SPEN/CP-GO-1 composite membrane displayed outstanding tensile strength (58 MPa at 100% RH and 25°C), excellent proton conductivity (0.178 S cm−1 at 60°C), and superior selectivity (5.552 × 105 S·cm−3·s). This study proposed a new method and strategy for the preparation of high performance PEMs.

Catalytic C-C Cleavage/Alkyne-Carbonyl Metathesis Sequence of Cyclobutanones

A ring-opening/alkyne-carbonyl metathesis sequence of alkyne-tethered cyclobutanones catalyzed by AgSbF₆ is realized for the first time to furnish multisubstituted naphthyl ketones under mild conditions. A range of substrates decorated with various substituents at different positions were all well accommodated. Preliminary mechanistic studies show that silver salt acted as a Lewis acid to facilitate both C-C cleavage of the cyclobutanone moiety and the subsequent metathesis between C═O and C≡C bonds.

Composite Polymers Development and Application for Polymer Electrolyte Membrane Technologies-A Review

Nafion membranes are still the dominating material used in the polymer electrolyte membrane (PEM) technologies. They are widely used in several applications thanks to their excellent properties: high proton conductivity and high chemical stability in both oxidation and reduction environment. However, they have several technical challenges: reactants permeability, which results in reduced performance, dependence on water content to perform preventing the operation at higher temperatures or low humidity levels, and chemical degradation. This paper reviews novel composite membranes that have been developed for PEM applications, including direct methanol fuel cells (DMFCs), hydrogen PEM fuel cells (PEMFCs), and water electrolysers (PEMWEs), aiming at overcoming the drawbacks of the commercial Nafion membranes. It provides a broad overview of the Nafion-based membranes, with organic and inorganic fillers, and non-fluorinated membranes available in the literature for which various main properties (proton conductivity, crossover, maximum power density, and thermal stability) are reported. The studies on composite membranes demonstrate that they are suitable for PEM applications and can potentially compete with Nafion membranes in terms of performance and lifetime.

Performance enhancement of direct methanol fuel cells using a methanol barrier boron nitride–Nafion hybrid membrane

Sulfonated hexagonal boron nitride is explored as a potential filler to prepare Nafion hybrid membranes for direct methanol fuel cell (DMFC) applications.

Effect of Crosslinking Degree on Sulfonated Poly(aryl ether nitrile)s As Candidates for Proton Exchange Membranes

In order to investigate the effect of crosslinking degree on the water uptake, swelling ratio, and methanol permeability of sulfonated poly(aryl ether nitrile)s (SPENs), the molar content of sulfonated group in bisphenol monomer is fixed at 60% in this work. The properties of sulfonated poly (aryl ether nitrile) with different crosslinking degrees are studied by changing the content of propenyl group in sulfonated poly (aryl ether nitrile)s. The cross-linking reaction of the propenyl groups in the SPENs is cured at 230 °C. All the results show that this method is an effective way to improve the water uptake, swelling ratio, and methanol permeability to meet the application requirements of the SPENs membranes as proton exchange membranes in fuel cells.