Proton Conductivity Research Articles

Advanced Nafion/nanofiller composite proton exchange membranes for fuel cell applications

Proton exchange membrane fuel cells (PEMFCs) exhibit increasing potential in a variety of applications, from automotive to stationary power generation, due to their superior advantages such as high efficiency, quick start-up and low emissions. The cell performance and operation life of PEMFCs are directly affected by the proton exchange membranes (PEMs). Nafion, a well-known perfluorosulfonic acid polymer, represents the state of the art of PEMs. To further improve the performance of Nafion, various nanofillers are incorporated into Nafion matrices, leading to the formation of composite PEMs with enhanced proton conductivity, mechanical strength and chemical stability. This review summarizes the recent advancements in Nafion composite PEMs based on four typical kinds of nanofillers: framework nanomaterials, carbon nanomaterials, polyoxometalate nanoclusters, and inorganic oxide nanoparticles. The preparation strategy, structure-property relationship and fuel cell applications of these membranes are discussed comprehensively, particularly focusing on the synergistic effect between Nafion and nanofillers. This review can provide an instructive insight for designing high-performance PEMs towards emerging energy technologies.

Surface reconstruction of β-Ga2O3 nanorod electrolyte for LT-SOFCs

Solid oxide fuel cell (SOFC) is a promising energy conversion technology, but the high operating temperature caused by electrolytes impedes its widespread application. The development of alternative electrolytes with fast ionic transport plays a vital role in tackling this challenge. In this study, a new electrolyte is proposed based on the wide bandgap semiconductor Ga2O3, by using a facile surface treatment on the nanorods of β-Ga2O3 in hydrogen. The treatment reconstructs the surface of the β-Ga2O3 nanorod to form a core–shell structure with an oxygen vacancy-rich shell. The nanorod sample is applied as the electrolyte in SOFC, delivering a high ionic conductivity of 0.15 S cm−1 and promising power densities of 485 mW cm−2 at 550 °C. Further studies confirm dominated proton conduction in the electrolyte and propose different mechanisms to elucidate the fast proton transport in terms of surface reconstruction. Particular attention is paid to the homo-junction at the core–shell interface by discussing the modulating effect of the junction s built-in field on proton diffusion. This work develops a new electrolyte based on β-Ga2O3 for LT-SOFC and presents an effective method of surface reductive reconstruction to enable fast proton conduction in semiconductor electrolytes.

Highly sulfonated poly ether ether ketone chelated with Cu2+ as a proton exchange membrane at sub-zero temperatures

Improving the proton conductivity (σ) of proton exchange membranes at low temperatures is very important for expanding their application areas. Here, sulfonated poly ether ether ketone (SPEEK) membranes were prepared with different sulfonation degrees, and its maximum ion exchange capacity is 3.15 mmol/g for 10 h at 60 °C. Highly sulfonated SPEEK membrane exhibits ultra-high water uptake and excellent proton conductivity of 0.074 S/cm at −25 °C due to its abundant −SO3H. Nevertheless, its high swelling ratio and low mechanical strength are not conducive to the practical application of the membrane. Luckily, by employing the chelation of Cu2+ with −SO3− on the SPEEK chain, Cu2+-coordinated SPEEK membranes were prepared, and they not only retain high −SO3H content but also possess robust mechanical properties and good dimensional stability compared to pristine SPEEK membrane. Meanwhile, the σ of the SPEEK-Cu membrane reaches 0.054 S/cm at −25 °C, and its fuel cell maximum power (Wmax) reaches 0.42 W/cm2 at −10 °C, demonstrating superior low-temperature performance in comparison to other reported materials. Particularly, water states in the prepared membranes are quantified by low-temperature differential scanning calorimetry. Because much more water bound to the plentiful −SO3H and Cu2+ inside the membrane endows it with anti-freezing performance, the decay of the σ and the Wmax for the SPEEK-Cu membrane is retarded at sub-zero temperatures. It is envisioned that composite membranes comprising metal ions such as Cu2+-SPEEK have a high potential for sub-zero fuel cell applications.

Structural, Functional and Molecular Dynamics Examination of a de novo cloned Otopetrin-like Proton Channel in crayfish.

Proton channels play a crucial role in many biological functions, as they are responsible for the selective transport of protons across cell membranes. Recently, Otopetrins, a family of eukaryotic proton-selective ion channels, have attracted significant attention due to their diverse physiological roles. Despite the importance of Otopetrins, their structural and functional properties remain relatively unexplored. As a model organism, crayfish have been extensively studied to gain insights into the functioning of the nervous system. These studies cover a wide range of aspects, including the properties of individual neurons and behavioral science. However, studying the physiological systems of crayfish poses challenges for molecular research due to limited molecular sequence information available for these organisms. In the present work was identified an originally cloned mRNA, coding an Otopetrin like proton channel in the crayfish. The coded protein was modeled in silico and possible conduction mechanisms and pathways were revealed. A plasmid of the cloned mRNA was heterologously expressed in HEK293T cells. Functional experiments on transfected cells indicated that the expressed mRNA was coupled to proton conduction across the cell membrane.

Hexagonal Mo Bronze: Single Crystal Structures, Electrocatalytic Hydrogen Evolution, and Proton Conductivity.

Molybdenum trioxide (MoO3) is a well-known transition metal oxide that has drawn much attention as a functional material having numerous applications. However, a vast majority of studies have primarily focused on α-MoO3, the thermodynamically stable polymorph of MoO3. This present work encompasses the synthesis of single crystals of two metastable hexagonal MoO3 described by the formulas {Mn0.03Na0.01}@[Mo0.93VIMo0.07VO3] (1) and {Cu0.01Na0.01}@[Mo0.97VIMo0.03VO3] (2), their comprehensive structural characterization by single-crystal X-ray crystallography, and routine spectral and microscopic studies. Interestingly, compound 1 acts as an efficient electrocatalyst for the hydrogen evolution reaction (HER) as well as an effective proton conductor in comparison to the performance of compound 2. The HER activity of compound 1 is characterized by an overpotential of 340 mV@1 mA cm-2 and a low Tafel slope of 75 mV/decade. The catalyst (compound 1) displays a Faradaic efficiency of 88% with a turnover frequency of 2.9 s-1. The proton conductivity value of this compound (1) is determined to be 4.9 × 10-3 S cm-1 at 55 °C under 98% relative humidity; the relevant proton conduction is operated by the Grotthuss mechanism with an activation energy of 0.17 eV.

Exploring the Water Oxidation Catalytic Activity of a Mn-Based Magnetic Metal-Organic Framework: The Role of Proton Conductivity and Oxygen Evolution Reaction Overpotential.

The present work evaluates the water oxidation catalytic activity of a Mn-based metal-organic framework (MOF), which we envisioned to reduce the oxygen evolution reaction (OER) overpotential because of its high electrical conductivity, facilitated by solvent-encapsulated structural features. The presence of Mn centers induces interesting magnetic features in the MOF, which exhibits impressive cryogenic magnetic refrigeration with a ΔSM value of 29.94 J kg-1 K-1 for a field change of ΔH = 5T at 2.3 K. To the best of our knowledge, the ΔSM value of the current system ranked the highest position among the published examples. The crystal structure aligns perfectly with the thematic expectations and features as many as ten metal-coordinated water molecules, forming an extensive web of a hydrogen-bonded network while facing toward the porous channel filled with another set of much-anticipated entrapped lattice water molecules. Such structural features are expected to manifest high proton conductivity, and detailed investigation indeed yields the best value for the system at 1.57 × 10-4 S/cm at 95% humidity and 85 °C. In order to evaluate the thematic notion of a one-to-one relationship between OER and improved electrical conductivity, extensive electrocatalytic water splitting (WS) investigations were carried out. The final results show highly encouraging WS ability of the Mn-MOF, showing the electrocatalytic surface area value of the active species as 0.0686 F/g with a turnover frequency value of 0.043 [(mol. O2) (mol. Mn-MOF)-1 s-1]. Another fascinating aspect of the current communication is the excellent synergy observed between the experimental WS outcomes and the corresponding theoretical data calculated using density functional theory (DFT). Consequently, a plausible mechanism of the overall OER and the role of the Mn-MOF as a water oxidation catalyst, along with the importance of water molecules, have also been derived from the theoretical calculations using DFT.

Oxygen Vacancies Boosted Hydronium Intercalation: A Paradigm Shift in Aluminum‐Based Batteries

AbstractIn aqueous aluminum‐ion batteries (AAIBs), the insertion/extraction chemistry of Al3+ often leads to poor kinetics, whereas the rapid diffusion kinetics of hydronium ions (H3O+) may offer the solution. However, the presence of considerable Al3+ in the electrolyte hinders the insertion reaction of H3O+. Herein, we report how oxygen‐deficient α‐MoO3 nanosheets unlock selective H3O+ insertion in a mild aluminum‐ion electrolyte. The abundant oxygen defects impede the insertion of Al3+ due to excessively strong adsorption, while allowing H3O+ to be inserted/diffused through the Grotthuss proton conduction mechanism. This research advances our understanding of the mechanism behind selective H3O+ insertion in mild electrolytes.

Preparation and study on H–MoS2/SLS modified SPI@SPEEK blend proton exchange membrane with balanced proton conductivity and stability

Proton exchange membranes (PEMs) are the core components of fuel cells, and research has long focused on how to balance their proton conductivity and durability. In this work, a series of homogeneous blend of sulfonated polyimide (SPI) and sulfonated polyether ether ketone (SPEEK) hybrid membranes with were constructed refined with sulfonated MoS2 (H–MoS2) and sodium lignosulfonate (SLS). The results showed that the tensile strength of the films was enhanced by 39.4% (67.84 MPa) compared to the base film. The composite films incorporating 1 wt% H-MoS2 and 2 wt% SLS has excellent proton conductivity, which can reach 50.24 mS/cm at 80°C and 100% humidity. The embed hybrid structure constructed by H–MoS2 and SLS, which not only effectively solves the limitations of the proton transport channel of traditional polymer materials, but also provides abundant proton transport sites, which provides a new strategy for preparing high-performance PEM.

A robust hydrothermal synthesis method of NH4Zr2(PO4)3, a precursor for HZr2(PO4)3 proton conductor

Hydrogen zirconium phosphate (HZP) is a ceramic material with the formula HZr2(PO4)3 that can potentially offer anhydrous protonic conductivity, with thermostability for the intrinsic protons up to 650 °C, and good chemical stability in aqueous environments or acid gases. Despite the attraction of these features for electrolyte applications, such as gas separation, fuel cells or electrolysers, work on this material remains in its infancy. A possible reason for this lack of attention may be related to the complexity to obtain the HZP material as a pure phase. For this reason, the current article examines a new hydrothermal synthesis method to produce the ammonium precursor, NH4Zr2(PO4)3, in its phase pure form, and consequently a refined overall route to produce the desired HZP target material. In the synthesis of the ammonium precursor, we underscore the precise control of reaction conditions that are necessary to obtain the pure NH4Zr2(PO4)3 material, both in its cubic and hexagonal structural polymorphs. For reaction times of 10 h, the cubic phase is obtained by employing a hydrothermal temperature of 150 °C and an aqueous ammonia volume of 2.1 mL, while the hexagonal phase is obtained for a hydrothermal temperature of 200 °C and an aqueous ammonia volume between 2.3 and 2.4 mL. Subsequently, we investigate the required conditions to convert hexagonal NH4Zr2(PO4)3 fully to hexagonal HZr2(PO4)3 via thermal treatment at 600 °C for 5 h, assessed by a combination of X-ray diffraction and infrared spectroscopy.In this way this article aims to open up further research on this interesting HZP material by documenting a robust route for its preparation.

How ozone traces degrade polyimide humidifier membranes for fuel cells

Humidification of polymer electrolyte membranes in fuel cells is essential for high proton conductivity and lifetime, therefore often membrane humidifier modules are used. We report about the degradation of polyimide humidifier membranes under the influence of airborne ozone traces: during operation we tracked the membranes humidifier performance in 5 modules for up to 1000 h with trace levels of ozone (100 ppb) and conducted characterization tests at 200 h intervals. Operating the humidifier with ozone resulted in a linear decrease in the membrane's ability to transfer moisture over time. Moreover, the glass transition temperature of the membrane material decreases linearly with longer exposure to ozone, while the mechanical strength in terms of breaking force and elongation at break decreases too. Infrared spectra of the tested fibers showed no changes. The reduced water vapor flux would limit fuel cell performance, while the reduced mechanical properties of the membrane can lead to rupture.

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.

Breathing Behavior and Superprotonic Conductivity of Two-Dimensional Flexible Metal-Organic Frameworks Tuned with Alkoxy Groups.

Flexible metal-organic frameworks (FMOFs) exhibit reversible structural transitions ("breathing" behaviors), which can regulate the proton transport passageway effectively. This property offers remarkable advantages for improving the proton conductivity. Our objective of this work is to design a single-variable flexibility synergistic strategy for the fabrication of FMOFs with high conductivity. Herein, four two-dimensional FMOFs, {[Co(4-bpdb)(R-ip)]·xsolvents}n (x = rich, 1-4), have been successfully designed and assembled (4-bpdb = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene and R-ip = MeO/EtO/n-PrO/n-BuO-isophthalate). Upon the release and/or absorption of different solvent molecules, they display reversible breathing behaviors, thereby resulting in the formation of the partial and complete solvent-free compounds {[Co(4-bpdb)(R-ip)]·ysolvents}n (y = free or poor, 1A-4A). This breathing behavior involves the synergistic self-adaption of the dynamic torsion of alkoxy groups and reversible structural transformation, leading to remarkable changes in cell parameters and void space, as evidenced by single-crystal X-ray diffraction, powder X-ray diffraction, and N2 and CO2 adsorption analyses. At 363 K and 98% relative humidity, 2A exhibits the best proton conductivity among the FMOFs. Its conductivity reaches 4.08 × 10-2 S cm-1 and is one of the highest conductivities shown by reported unmodified MOF-based proton conductors.

Sulfonated graphene oxide linked with alkali metal ions membranes for proton conductivity in hydrogen production from water electrolysis

Amid technological advances, rising energy demand, and environmental concerns, countries endorse green energy solutions. Prominent among them is hydrogen production via clean water electrolysis, a key strategy for sustainable development. Herein, to address the limitations of expensive and potentially harmful Nafion membranes, we have developed a new graphene oxide (GO) series membranes (hydrophilic sulfonated GO (GO-SO3H) linked with monovalent alkali metal ions were synthesized to fabricate the membranes) to be used in water electrolysis for hydrogen production by introducing the iodide oxidation reaction (IOR) as an alternative to the traditional oxygen evolution reaction (OER). Various modifications by sulfuric acid, methanol, and different alkali metal hydroxides (LiOH, NaOH, KOH) result in membranes with distinct properties. Characterization techniques, including ATR-FTIR, SEM, AFM, XRD, water contact angle (WCA), and electrochemical impedance spectroscopy (EIS), validated the modifications, assessed membrane morphology, interlayer spacing, hydrophilicity, and electrical properties. Among the membranes, GO-SO3K stood out, exhibiting the highest proton conductivity (119.16 mS) and superior potassium ion permeability (20.382 cm/s). Importantly, all GO series membranes demonstrate excellent stability in the electrochemical system. The findings suggested that GO-SO3K holds promise as a potassium ion-conductive membrane for efficient and sustainable hydrogen production, offering a viable alternative to conventional Nafion membranes in water electrolysis applications.

Reactive Magnetron Sputtering for Y-Doped Barium Zirconate Electrolyte Deposition in a Complete Protonic Ceramic Fuel Cell

Yttrium-doped barium zirconate is a commonly used electrolyte material for Protonic Ceramic Fuel Cells (PCFC) due to its high protonic conductivity and high chemical stability. However, it is also known for its poor sinterability and poor grain boundary conductivity. In this work, in response to these issues, reactive magnetron sputtering was strategically chosen as the electrolyte deposition technique. This method allows the creation of a 4 µm tick electrolyte with a dense columnar microstructure. Notably, this technique is not widely utilized in PCFC fabrication. In this study, a complete cell is elaborated without exceeding a sintering temperature of 1350 °C. Tape casting is used for the anode, and spray coating is used for the cathode. The material of interest is yttrium-doped barium zirconate with the formula BaZr0.8Y0.2O3−δ (BZY). The anode consists of a NiO-BZY cermet, while the cathode is composed of BZY and Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSFC) in a 50:50 weight ratio. The electrochemical impedance spectroscopy analysis reveals a global polarization resistance of 0.3 Ω cm2, indicating highly efficient interfaces between electrolytes and electrodes.

Room-Temperature Superprotonic Conductivity beyond 10-1 S cm-1 in a Co(II) Coordination Polymer.

An efficient design of crystalline solid-state proton conductors (SSPCs) is crucial for the progress of clean energy applications. Developing such materials to make them work at room temperature with a conductivity of ≥10-1 S cm-1 is of significant interest in terms of technical and commercial aspects. Utilizing the recently highlighted "coordinated-water-driven proton conduction" approach, herein, we have rationally synthesized two highly stable and scalable 1D Co(II) coordination polymers (CPs) as SSPCs, PCM-2 {[Co(bpy)(H2O)2(NO3)2]·H2O}n and PCM-3 {[Co2(bpy)2(SO4)2(H2O)6].4H2O}n, with distinct alignments in coordinated water and coordinated oxo-anions (nitrate and sulfate, respectively). The acidity of the metal-bound water molecules in PCM-2 is further enhanced through cooperative long-range continuous H bonds with coordinated Brønsted basic nitrates (proton acceptors), leading to ultrahigh superprotonic conductivities even at 25 °C (1.03 × 10-1 S cm-1 under 95% RH), and reached a maximum of 2.99 × 10-1 S cm-1 at 85 °C (95% RH). The conductivity at 25 °C is even higher than that of commercial Nafion 117 (6.74 × 10-2 S cm-1 at 100% RH). The absence of such an H-bonding interaction in PCM-3 (closed loops) resulted in a lesser conductivity of 5.87 × 10-5 S cm-1 (95% RH, 85 °C). PCM-2 represents the first example of SSPC exhibiting conductivity in the order 10-1 S cm-1 at ambient temperature (25 °C) with excellent recyclability.

Efficient Proton Transfer and Charge Separation within Covalent Organic Frameworks via Hydrogen-Bonding Network to Boost H2O2 Photosynthesis.

Photocatalytic synthesis based on the oxygen reduction reaction (ORR) has shown great promise for H2O2 production. However, the low activity and selectivity of 2e- ORR result in a fairly low efficiency of H2O2 production. Herein, we propose a strategy to enhance the proton-coupled electron transfer (PCET) process in covalent organic frameworks (COFs), thereby significantly boosting H2O2 photosynthesis. We demonstrated that the construction of a hydrogen-bonding network, achieved by anchoring the H3PO4 molecular network on COF nanochannels, can greatly improve both proton conductivity and photogenerated charge separation efficiency of COFs. Thus, COF@H3PO4 exhibited superior photocatalytic performance in generating H2O2 without sacrificial agents, with a solar-to-chemical conversion efficiency as high as 0.69%. Results indicated that a much more localized spatial distribution of energy band charge density on COF@H3PO4 led to efficient charge separation, and the small energy barrier of the rate-limiting step from *OOH to H2O2 endowed COF@H3PO4 with higher 2e- ORR selectivity.

Square-planar Tetranuclear Cluster-based Alkaline Earth Metal-organic Frameworks with Enhanced Proton Conductivity.

Alkaline earth (AE) metal complexes have garnered significant interest in various functional fields due to their nontoxicity, low density, and low cost. However, there is a lack of systematic investigation into the structural characteristics and physical properties of AE-metal-organic frameworks (MOFs). In this research, we synthesized isostructural MOFs consisting of AE4(μ4-Cl) clusters bridged by benzo-(1,2;3,4;5,6)-tris(thiophene-2'-carboxylic acid) (BTTC3-) ligands. The resulting structure forms a truncated octahedral cage denoted as [AE4(m4-Cl)]6(BTTC)8, which further linked to a porous three-dimensional framework. Among the investigated AE ions (Ca, Sr, and Ba), the Ca4-MOF demonstrated good chemical stability in water compared to Sr4-MOF and Ba4-MOF. The N2 adsorption and solid-state UV-vis-NIR absorption behaviors were evaluated for all AE4-MOFs, showing similar trends among the different metal ions. Additionally, the proton conduction study revealed that the Ca4-MOF exhibited ultra-high proton conductivity, reaching 3.52×10-2 S cm-1 at 343 K and 98 % RH. Notably, the introduction of LiCl via guest exchange resulted in an improved proton conduction of up to 6.36×10-2 S cm-1 under similar conditions in the modified LiCl@Ca4-MOF. The findings shed light on the regulation of physical properties and proton conductivity of AE-MOFs, providing valuable insights for their potential applications in various fields.

Electrolytic performance of sodium alginate-poly vinyl alcohol matrix with ammonium bromide for proton conduction: Applications in electrochemical systems

Polymer blend electrolytes based on poly(vinyl alcohol) (PVA) and sodium alginate (NaAlg) were prepared using the solution casting method. These electrolytes were doped with varying amounts of ammonium bromide (NH4Br). The compatibility of NH4Br with PVA:NaAlg polymers was examined through X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) studies. The FTIR assessment confirmed the formation of a complex between PVA:NaAlg and the added salt, as evidenced by modifications and reductions in the intensity of FTIR bands related to functional groups. The conductivity and dielectric behavior of the samples were analyzed using AC impedance spectroscopy. The sample with 20 wt% of added salt exhibited a higher ionic conductivity of 1.661×10−5 Scm−1. Activation energy and relaxation time were estimated, and dielectric studies revealed a non-Debye nature. The conduction mechanism was best described by the correlated overlapping large polaron tunneling model (OLPT). The highest conducting sample was found to be suitable for electrochemical devices, as demonstrated by transference number (TNM), cyclic volumetric (CV), and linear sweep voltammetry (LSV) analyses. This high-conductivity sample can be employed in electrochemical devices such as EDLC. The cyclic voltammetry (CV) curve exhibited a nearly rectangular shape with non-faradaic peaks. GCD(Galvanostatic charge-discharge) analysis yielded specific capacitance, power density, and energy density values of 125.01 Fg−1, 1037 WKg−1, and 14.06 WhKg−1 respectively. These results indicate that polymer electrolytes show great promise as electrolytes in proton-conducting electrochemical devices.

Enhancing Performance and Stability of High-Temperature Proton Exchange Membranes through Multiwalled Carbon Nanotube Incorporation into Self-Cross-Linked Fluorenone-Containing Polybenzimidazole.

Addressing critical challenges in enhancing the oxidative stability and proton conductivity of high-temperature proton exchange membranes (HT-PEMs) is pivotal for their commercial viability. This study uncovers the significant capacity of multiwalled carbon nanotubes (MWNTs) to absorb a substantial amount of phosphoric acid (PA). The investigation focuses on incorporating long-range ordered hollow MWNTs into self-cross-linked fluorenone-containing polybenzimidazole (FPBI) membranes. The absorbed PA within MWNTs and FPBI forms dense PA networks within the membrane, effectively enhancing the proton conductivity. Moreover, the exceptional inertness of MWNTs plays a vital role in reinforcing the oxidation resistance of the composite membranes. The proton conductivity of the 1.5% CNT-FPBI membrane is measured at 0.0817 S cm-1 at 160 °C. Under anhydrous conditions at the same temperature, the power density of the 1.5% CNT-FPBI membrane reaches 831.3 mW cm-2. Notably, the power density remains stable even after 200 h of oxidation testing and 250 h of operational stability in a single cell. The achieved power density and long-term stability of the 1.5% CNT-FPBI membrane surpass the recently reported results. This study introduces a straightforward approach for the systematic design of high-performance and robust composite HT-PEMs for fuel cells.

Tailoring porous structure in non-ionic polymer membranes using multiple templates for low-cost iron-lead single-flow batteries

Porous ion-selective membranes are promising alternatives for the expensive perfluorosulfonic acid membranes in redox flow batteries. In this work, novel non-ionic porous polyvinylidene fluoride-hexafluoro propylene membranes are designed for iron-lead single-flow batteries. The membranes are prepared using a multiple template approach, involving simultaneously using polyethylene glycol and dibutyl phthalate (DBP) as pore-forming templates. Their porous structure is finely tuned by adjusting the ratio of the two templates. As a result, dual-porous membranes bearing both macro and micropores are obtained. The H3520 membrane with modified porous structure attains a high proton conductivity of 43.5 mS·cm-1 and a relatively low ferric ion diffusion constant (8.61 × 10-8 cm2·min-1) and demonstrates the best balance between these performance-determining parameters (selectivity 5.04 × 105 S·min·cm-3, higher than that of the N115 membrane). Besides, performance tests of the iron-lead single-flow single cells equipped with the dual-porous membranes show a high energy efficiency, exceeding 87.2% at its rated current density, and outstanding cycling stability over 200 charge-discharge cycles. Altogether, the mixed template method presents a promising strategy to prepare high-performance and low-cost non-ionic membranes for redox flow batteries.