Pure Nafion Membrane Research Articles

Comparative Study on the Proton Conduction Behaviors of Two Acidic Amphiphilic and Hydrophilic Coordination Compounds in Nafion Composite Membranes.

The acidic amphiphilic compound H[Co(H2L1)(HL1)(phen)]·3H2O (H4(Co-L1), H3L1 = 5-(3', 5'-dicarboxylphenyl)-pyridine-2-carboxylic, phen = phenanthroline) and the hydrophilic compound [Ni(HL2)(H2O)5]·H2O (H(Ni-L2), H3L2 = 5-(3',5'-dicarboxylphenyl)-pyridine-3-carboxylic) were synthesized via hydrothermal reactions at acidic conditions. The acidity of H4(Co-L1) is stronger than of H(Ni-L2); while the hydrogen bond continuity in H4(Co-L1) extended monodirectionally, which is smaller compared to the three-directional extension observed in H(Ni-L2). The proton conduction behaviors of these two compounds as fillers of Nafion composite membranes have been investigated. The results indicate that the optimal doping amounts of H4(Co-L1) and H(Ni-L2) are 2 and 1%, respectively; the proton conductivities of H4(Co-L1)/Nafion-2 and H(Ni-L2)/Nafion-1 composite membranes are 0.243 and 0.212 S·cm-1, respectively, which are approximately 50.2 and 30.6% higher than that of pure Nafion membrane, respectively. A higher doping amount of H4(Co-L1) can be attributed to its hydrophobic phen ligand, which promotes compatibility with Nafion membrane and reduces aggregation. Hydrogen bond continuity has a more significant effect on proton conductivity than acidity at relatively low doping amounts; conversely, this relationship reverses at relatively high doping amounts.

Performance of Teflon- reinforced Nafion against microbes and removal of heavy metal ions from aqueous environment

Considering its promising antimicrobial and metal removal capabilities, water filtration systems have not yet widely used ionic polymer membranes. A textile structure made of Nafion polymer reinforced with Teflon (TFRN) was coated with non-precious metals copper and silver using a chemical decomposition technique. Scanning electron microscopy makes it quite evident that a surface coating was formed with evenly distributed metal particles. Water and moisture uptake capacity for Silver (Ag)-Copper (Cu) coated membrane was reduced by 80 and 67 % respectively compared to pure membrane. Inaddition, Ag–Cu coated membrane showed best performance against Escherichia coli (ATCC25922), and Staphylococcus aureus (ATCC 25923) with 2.04 and 1.7 CFU/ml respectively, by considering below level of Quantification as 1.6 CFU/ml. Pure Nafion membrane at pH 6.5, was used to perform the adsorption studies of transition metal ions like Copper, Nickel, Chromium, Barium, Tin and Arsenic at room temperature. The maximum metal ion removal was about 35 % for Copper followed by Nickel (31 %) and the least adsorption was observed for Barium (13.5 %) from multi-heavy metals solution. The study revealed that the potential of TFRN membrane for water purification in terms of metal and microbial removal process.

Synthesis, structure, and small molecule in situ modification effects on proton conduction properties of triazine‐based triscarboxylic acid complexe

In this study, we synthesized and characterized a new Co(II)‐based coordination polymer, denoted as {[Co(HL)(dpa)]·H2O}n (1), derived from the H3L ligand and dpa co‐ligand. Single crystal X‐ray diffraction revealed that 1 forms a two‐dimensional (2D) layer and a three‐dimensional (3D) supramolecular structure via hydrogen bonding interactions. Presence of carboxylic acid groups in 1 was confirmed by X‐ray crystallography, prompting investigation into its proton transport properties. Additionally, electrostatic potential surface and nucleophilic index analyses were conducted to simulate potential proton transfer pathways. Furthermore, we prepared nine modified encapsulated materials using 1 as the base material (SDA@1, APH@1, APY@1, TA@1, BA@1, DIC@1, IDZ@1, SCA@1, and TYD@1), and tested their proton conductivity and activation energy compared to pure Nafion membrane and 1, analyzing the influence of different small molecule structures on proton conductivity. Comparative analysis revealed that only SDA@1 exhibited enhanced proton conductivity and reduced activation energy at 303 K, with an improvement rate of 220.8%. We hope that the methods presented herein can provide valuable insights for the design and development of high‐performance proton‐conducting materials, as well as for the exploration of proton conduction mechanisms.

Interconnected hollow metal–organic framework network towards excellent proton transfer for proton exchange membrane

Interconnected hollow metal–organic framework (MOF) network (GO@HZIF-8) was designed as an efficient proton transfer accelerator in Nafion membrane. GO@HZIF-8 was constructed by in situ synthesis of ZIF-8 onto graphene oxide (GO) and succedent etching with tannic acid (TA). The hollow construction and surface TA functionalization of hollow ZIF-8 (HZIF-8) bestowed composite membrane with superior water retention. This was highly beneficial to the rapid proton transfer. Besides, the hollow construction could effectively reduce the proton transfer resistance onto GO@HZIF-8. More importantly, the interconnective architecture between HZIF-8 by the tethering function of GO and the interfacial hydrogen bond interaction between GO@HZIF-8 and Nafion resulted in connective proton transfer routes at GO@HZIF-8 surfaces and GO@HZIF-8/Nafion interfaces. These dramatically accelerated the proton transfer of GO@HZIF-8/Nafion composite membrane, enabling a considerable proton conductivity (PC) of 0.301 S cm−1 under 90 °C, 95 % RH, ∼1.33-fold greater than that of the pure Nafion membrane (RN). Moreover, the composite membrane exhibited a peak power density of 45.8 mW cm−2, ∼1.22-fold higher than that of RN. These results menifest that constructing hollow MOF network possesses grand prospect in the construction of high performance proton exchange membranes (PEMs).

Mixed-ceria reinforced acid functionalized graphene oxide-Nafion electrolyte membrane with enhanced proton conductivity and chemical durability for PEMFCs

Towards the next-gen energy solutions, Nafion, as a state-of-the-art polymer electrolyte to low temperature fuel cell (LTFC) application has been one of the most demanding hydrogen to clean energy conversion device ever achieved. However, the inherent issue of limiting chemical durability and restricted proton conductivity have always been a topic of concern with pure Nafion membranes. To tackle this, we report a mixed-ceria reinforced phosphorylated graphene oxide (sPGO)/Nafion membrane as a potential electrolyte to simultaneously improve the chemical durability and proton conductivity of bare Nafion by utilizing the redox property of ceria nanoparticles and acidic sites of sPGO for accelerated proton transfer. As a progressive method, the single-step phosphorylation of GO introduced short chain branching along with enhanced number of acidic sites in the Nafion matrix whereas incorporation of mixed-ceria nanoparticles improved the chemical durability of the membrane due to its superior radical scavenging property. As a result, mixed-ceria reinforced sPGO/Nafion (Ce-sPGO/NF) electrolyte membrane showed higher proton conductivity (1.2-times) and chemical durability (8.1-times) than bare Nafion. Furthermore, the polymer electrolyte membrane (PEM) was also showcased high enough thermomechanical and electrochemical stability at 80 °C and 100% relative humidity (RH).

Boosting ion conduction in polymer blends by tailoring polymer phase separation

Polymer blending is a facile method for preparing cost-effective membranes for redox flow batteries with improved properties. It is of great importance to reveal the effects of the polymer chain morphology on the membrane properties and to successfully tailor the performance. Phase separations of various Nafion-based polymer blends are predicted and membranes with well-controlled phase separation are obtained. It is indicated that the domain size of the polymer phase separation significantly influences the ion transport behavior and thus, the battery performance of the redox flow battery. By varying the polymer compatibility, the Nafion/PVDF-HFP blend membrane possesses the highest proton conductivity among the different blend membranes due to the minimized domain of phase separation. Its proton conductivity reaches 53.61 mS/cm, almost 3 folds of that of the Nafion/PVDF membrane with the same Nafion content of 60 wt%. The cell equipped with the Nafion/PVDF-HFP blend membrane (50 wt% Nafion) shows a voltage efficiency of 87.45% and an energy efficiency of 83.83% at 100 mA/cm2, which are comparable to the pure Nafion membrane. The blend membrane shows excellent chemical stability during an 800-cycle charge-discharge test. By fine-tuning polymer phase separation, cost-effective blend membranes with significantly enhanced performance for redox flow batteries can be obtained.

Novel Nafion/Graphitic Carbon Nitride Nanosheets Composite Membrane for Steam Electrolysis at 110 °C.

Hydrogen is expected to have an important role in future energy systems; however, further research is required to ensure the commercial viability of hydrogen generation. Proton exchange membrane steam electrolysis above 100 °C has attracted significant research interest owing to its high electrolytic efficiency and the potential to reduce the use of electrical energy through waste heat utilization. This study developed a novel composite membrane fabricated from graphitic carbon nitride (g-C3N4) and Nafion and applied it to steam electrolysis with excellent results. g-C3N4 is uniformly dispersed among the non-homogeneous functionalized particles of the polymer, and it improves the thermostability of the membranes. The amino and imino active sites on the nanosheet surface enhance the proton conductivity. In ultrapure water at 90 °C, the proton conductivity of the Nafion/0.4 wt.% g-C3N4 membrane is 287.71 mS cm-1. Above 100 °C, the modified membranes still exhibit high conductivity, and no sudden decreases in conductivity were observed. The Nafion/g-C3N4 membranes exhibit excellent performance when utilized as a steam electrolyzer. Compared with that of previous studies, this approach achieves better electrolytic behavior with a relatively low catalyst loading. Steam electrolysis using a Nafion/0.4 wt.% g-C3N4 membranes achieves a current density of 2260 mA cm-2 at 2 V, which is approximately 69% higher than the current density achieved using pure Nafion membranes under the same conditions.

Construction of low-cost and long-time proton exchange membranes by using slow-release radical scavenger

The bottlenecks of commercial application of proton exchange membranes (PEM) fuel cell are cost and oxidation stability of PEM. Hence, we encapsulate Resveratrol (Res, a kind of reductant) in hydroxypropyl-β-cyclodextrins (CDs) to prepare the inclusion complexes of Res and CDs (Res@CDs) under the guidance of theoretical arithmetic. Then the Res@CDs are evenly dispersed in Nafion emulsion, which is subsequently combined with porous polytetrafluoroethylene (PTFE) substrate by emulsion pouring method to form the antioxidative composite membrane (Res@CDs-Nafion/PTFE). The as-prepared Res@CDs-Nafion/PTFE shows the similar performance on proton conductivity (103.9 mS cm−1) and hydrogen-air fuel cell (317.84 mW cm−2) compared to the Nafion/PTFE composite membrane. The content of Nafion in the Res@CDs-Nafion/PTFE is less than 30%, which dramatically reduces the production cost compared to pure Nafion membrane. The weight loss of Res@CDs-Nafion/PTFE and Nafion/PTFE immersed in Fenton's reagent after 36 h is 4.97% and 16.49%, respectively, which demonstrate that Res@CDs can enhance oxidation stability of composite membrane. The Res@CDs-Nafion/PTFE offer huge merits of low cost and enhanced oxidation stability, which greatly promotes the application process of long-lifetime PEM fuel cell.

Using Metal-Organic Framework HKUST-1 for the Preparation of High-Conductive Hybrid Membranes Based on Multiblock Copolymers for Fuel Cells.

Novel proton-conducting hybrid membranes consisting of sulfonated multiblock copolymer of polysulfone and polyphenylsulfone (SPES) reinforced with a HKUST-1 metal-organic framework (MOF) (5, 10, and 20 wt. %) were prepared and characterized for fuel cell applications. The presence of the MOF in the copolymer was confirmed by means of FE-SEM and EDS. The hybrid membranes show a lower contact angle value than the pure SPES, in agreement with the water uptake (WU%), i.e., by adding 5 wt. % of the MOF, this parameter increases by 20% and 40% at 30 °C and 60 °C, respectively. Additionally, the presence of the MOF increases the ion exchange capacity (IEC) from 1.62 to 1.93 mequivH+ g−1. Thermogravimetric analysis reveals that the hybrid membranes demonstrate high thermal stability in the fuel cell operation temperature range (<100 °C). The addition of the MOF maintains the mechanical stability of the membranes (TS > 85 MPa in the Na+ form). Proton conductivity was analyzed using EIS, achieving the highest value with a 5 wt. % load of the HKUST-1. This value is lower than that observed for the HKUST-1/Nafion system. However, polarization and power density curves show a remarkably better performance of the hybrid membranes in comparison to both the pure SPES and the pure Nafion membranes.

Enhancing Proton Conductivity of Nafion Membrane by Incorporating Porous Tb-Metal-Organic Framework Modified with Nitro Groups.

A rigid carboxylate ligand with a nitro functional group was selected to coordinate with Tb(III) cation, and Tb-MOF ({[Tb4(L)4(OH)4(H2O)3]·8H2O}n, H2L = 2-nitroterephthalic acid) with large porous and excellent hydrophilicity was obtained successfully. The obtained Tb-MOF was filled into the Nafion matrix to improve its proton conduction performance. The Tb-MOF/Nafion composite membrane was characterized by PXRD, IR, and thermogravimetry (TG) and for water uptake, area swelling, and proton conductivity. The activity energy, Ea, value of the composite membrane, which is a very important factor affecting the proton conduction performance of the membrane, was fitted and calculated. It was revealed that Tb-MOF can improve the proton conductivities of composite membranes, and the improvement degree and Ea value were both affected by Tb-MOF content. When Tb-MOF content was 5%, the proton conductivity of the composite membrane was 1.53 × 10-2 S·cm-1 at 100% RH and 80 °C, which is 1.81 times that of the pure Nafion membrane. A MOF containing a nitro functional group was first doped into Nafion in this study and exhibited excellent performance for improving composite membrane proton conductivity. This study will provide a valuable reference for designing different functionalized MOFs to promote the proton conductivities of proton exchange membranes.

Comparative Studies on the Proton Conductivities of Hafnium-Based Metal-Organic Frameworks and Related Chitosan or Nafion Composite Membranes.

Hafnium (Hf)-based UiO-66 series metal-organic frameworks (MOFs) have been widely studied on gas storage, gas separation, reduction reaction, and other aspects since they were first prepared in 2012, but there are few studies on proton conductivity. In this work, one Hf-based MOF, Hf-UiO-66-fum showing UiO-66 structure, also known as MOF-801-Hf, was synthesized at room temperature using cheap fumaric acid as the bridging ligand, and then imidazole units were successfully introduced into MOF-801-Hf to obatin a doped product, Im@MOF-801-Hf. Note that both MOF-801-Hf and Im@MOF-801-Hf demonstrate excellent thermal, water, and acid-base stabilities. Expectedly, the maximum proton conductivity (σ) of Im@MOF-801-Hf (1.46 × 10-2 S·cm-1) is nearly 4 times greater than that of MOF-801-Hf (3.98 × 10-3 S·cm-1) under 100 °C and 98% relative humidity (RH). To explore their possible practical application value, we doped them into chitosan (CS) or Nafion membranes as fillers, namely, CS/MOF-801-Hf-X, CS/Im@MOF-801-Hf-Y, and Nafion/MOF-801-Hf-Z (X, Y, and Z are the doping percentages of MOF in the membrane, respectively). Intriguingly, it was found that CS/MOF-801-Hf-6 and CS/Im@MOF-801-Hf-4 indicated the highest σ values of 1.73 × 10-2 and 2.14 × 10-2 S·cm-1, respectively, under 100 °C and 98% RH and Nafion/MOF-801-Hf-9 also revealed a high σ value of 4.87 × 10-2 S·cm-1 under 80 °C and 98% RH, which showed varying degrees of enhancement compared to the original MOFs or pure CS and Nafion membranes. Our study illustrates that these Hf-based MOFs and related composite membranes offer great potential in electrochemical fields.

Proton Conductive Composite Membranes with Stable Anisotropic Though-Plane Conductivity: A New Preparation Approach

In common PEMFCs, a polymer electrolyte membrane selectively conducts protons but blocks passage of electrons and reactants. Nafion, current benchmark membrane material, offers a superior conductivity owing to unique morphology comprising randomly oriented elongated ionic nanochannels within a Teflon-like matrix. Nanochannel orientation is a promising approach to enhance Nafion conductivity, yet there has been no facile method to induce a strong and stable alignment within membranes in the most desired through-plane (TP) direction.Here we report a novel and facile preparation approach based on dual electrospun Nafion-PVDF nanofiber composite that yields a stable TP alignment. The preparation starts from electrospinning of a mixed fiber mat, which is subsequently converted to a solid membrane by plunging the mat into a thin slit. Due to extreme thinness, the electrospun nanofiber readily buckle into a folded structure, thereby a strong inherent microscopic channel orientation within nanofibers is readily converted to macroscopic TP channel alignment. Ultimately, the folded nanofibers fuse, consolidating the membrane.A pronounced TP alignment of ion channels in the membranes, sustaining fusion and annealing, is demonstrated using TEM and SAXS. The analysis also highlights the importance of PVDF fiber as a stabilizing and confining component. Electrospun PVDF fibers within consolidated Nafion-PVDF composite preserve channel orientation upon annealing both in TP and in-plane (IP) aligned membranes, while pure Nafion membranes, similarly prepared from electrospun Nafion fibers, rapidly lose structural anisotropicity. Finally, the impedance measurements demonstrate highly anisotropic conductivity of both TP- and IP-aligned membranes, consistent with their anisotropic structure. Thus, measured TP conductivity of TP-aligned 46% Nafion composite is nearly three times its IP conductivity and about 70% that of Nafion 212, thereby the conductivity normalized to Nafion content exceeds that of pure Nafion. The approach, still leaving much room for optimization, holds potential to advance PEMFC technology by overcoming current limitations and fully utilizing advantageous features of Nafion membranes. Figure 1

Electrospun Ion-Conducting Composite Membrane with Buckling-Induced Anisotropic Through-Plane Conductivity.

Fuel cell (FC) is an attractive green alternative for today's fuel combustion systems. In common FCs, a polymer electrolyte membrane selectively conducts protons but blocks the passage of electrons and fuel. Nafion, the current benchmark membrane material, has a superior conductivity owing to unique morphology comprising randomly oriented elongated ionic nanochannels within its Teflon-like matrix. Channel orientation enhances Nafion conductivity, yet there has been no facile method to induce a stable alignment in the desired through-plane (TP) direction. Here, we report an approach based on dual electrospun Nafion-PVDF nanofiber composites that yields a stable TP alignment. It utilizes extreme thinness and strong inherent orientation within electrospun nanofibers, which is readily converted to TP alignment by plunging an electrospun nanofiber mat into a thin slit, resulting in nanofiber buckling and subsequent consolidation. Using TEM and SAXS, we demonstrate a pronounced and sustained TP ion channel orientation in prepared membranes, yielding a highly anisotropic swelling and conductivity exceeding that of bulk Nafion when normalized to Nafion content. The analysis also highlights the importance of PVDF as a stabilizing component, preserving orientation upon annealing, while a similarly prepared pure Nafion membrane loses anisotropy. The approach holds potential to advance the FC technology by overcoming current limitations of ionomeric membranes.

Proton Conduction of Nafion Hybrid Membranes Promoted by NH3-Modified Zn-MOF with Host–Guest Collaborative Hydrogen Bonds for H2/O2 Fuel Cell Applications

It is of great significance to develop creative proton exchange membrane materials for proton exchange membrane fuel cells (PEMFCs). The strategy of doping metal-organic frameworks (MOFs) with guest molecules into the Nafion matrix is adopted to improve the electrochemical performance of Nafion hybrid membranes. Various and abundant hydrogen bonds can make a tremendous contribution to the proton conduction of hybrid membranes. In this work, we used high proton-conducting Zn-MOFs with the characteristics of host-guest collaborative hydrogen bonds as the filler to prepare Zn-MOF/Nafion hybrid membranes. Alternating current (AC) impedance tests show that when the doping amount of Zn-MOF is 5%, the proton conductivity reaches 7.29 × 10-3 S·cm-1, being 1.87 times that of the pure Nafion membrane at 58% relative humidity (RH) and 80 °C. In an attempt to prove the promotion effect of guest NH3 on proton conductivity of Nafion hybrid membranes, Zn-MOF-NH3 was filled into the Nafion matrix. Under the same conditions, its proton conductivity reaches the maximum value of 2.13 × 10-2 S·cm-1, which is 5.47 times that of the pure Nafion membrane. Zn-MOF-NH3/Nafion-5 was used to fabricate a proton exchange membrane for application in H2/O2 fuel cells. The maximum power density of 212 mW cm-2 and a current density of 630 mA cm-2 reveal a respectable single cell performance. This study provides a promising method for optimizing the structure of MOF proton conductors and inspires the preparation of high-performance Nafion hybrid membranes.

Two acidic coordination polymers containing uncoordinated carboxyl groups: Syntheses, crystal structures and proton conductivities in Nafion composite membranes

Two coordination polymers [Cu(H2L)(bpyBr)]n (1) and [Ni(H2L)(bpy)(H2O)2]n (2) (H4L ​= ​5,5’-(butane-1,4-diylbis (oxy)) diisophthalic acid, bpyBr ​= ​4,4′-dibromo −2, 2′-bipyridyl, bpy ​= ​4, 4′-bipyridyl) were synthesized at lower temperature and weaker acidity condition. Crystal structure studies revealed that both compounds exhibited 2-D coordination layer with uncoordinated protonated –COOH groups, which can promote the acidity of compounds, form hydrogen bonds and benefit to proton conducting behavior. So, their proton conductivities have been evaluated through incorporating with Nafion to form composite membrane. AC impedance spectra studies suggested that compounds 1–2 can promote the proton conductivity of the composite membrane about 15.97% and 24.61% higher than that of pure Nafion membrane, respectively. The higher proton conductivity of 2/Nafion should be attributed to the continuous hydrogen bonding chains in the crystal structure.

Two nonporous MOFs with uncoordinated carboxylate groups: Fillers for enhancing the proton conductivities of nafion membrane

Two nonporous MOFs [Ni(L)0.5 (Mbpy)(H2O)2]2 (1) and [Cd(H2L)(Mbpy)]n (2) (H4L = 5,5’-(butane-1,4-diylbis (oxy)) diisophthalic acid, Mbpy = 5,5′-dimethyl-2,2′-bipyridine) were obtained through hydrothermal reactions under different pH values reaction condition. Structure analyses reveal that there are uncoordinated deprotonated and protonated carboxylate groups in compounds 1 and 2, respectively, which are confirmed by IR spectra. The XRD and TG studies indicate that both of compounds exhibit good water and thermal stability. The proton conductivities of the Nafion membrane doped by compounds 1 and 2 have been studied. It was revealed that compound 2 can enhance the proton conductivity of the composite membrane about 29% higher than that of pure Nafion. The water uptakes of 1/Nafion and 2/Nafion composite membrane are similar and slightly higher than that of pure Nafion membrane. The apparently high proton conductivity of 2/Nafion membrane should be attributed to the high proton density of compound 2 framework, which is resulted by the protonated uncoordinated carboxylate acid groups.

Study on Nafion/Nafion-g-poly (sulfobetaine methacrylate)-blended amphoteric membranes for vanadium redox flow battery

In order to reduce the vanadium ion permeability while still keep its high stability, atom radical polymerization (ATRP) method was used to introduce zwitterionic sulfobetaine methacrylate (SBMA) onto the Nafion matrix in homogenous solution. The Nafion-grafted poly SBMA (N-g-PSBMA) solution was then used to blend with common Nafion solution to prepare Nafion/Nafion-g-PSBMA (N/N-g-PSBMA) amphoteric membranes by solution casting method. The grafted resins and membranes were characterized by attenuated total reflectance Fourier transform infrared spectra (ATR-FTIR), energy dispersive X-Ray spectroscopy (EDX), scanning electron microscopy (SEM), and water-contact angle analysis. The results prove that the SBMA has been successfully grafted onto the Nafion backbones. Furthermore, the N/N-g-PSBMA membranes have shown higher ion selectivity, coulombic efficiency, and energy efficiency than that of pure recast Nafion (r-Nafion) membrane for VRB application. At the current density of 40–80 mA cm−2, the average energy efficiency of the VRB with N/N-g-PSBMA-20% membrane has reached up to 84.9%, which is 4.2% higher than that of the VRB with the r-Nafion membrane at the same current densities. Moreover, the 100-cycles charge-discharge test proves that the N/N-g-PSBMA-20% membrane possesses higher stability and capacity retention ability than that of r-Nafion membrane, confirming the great potential of such membranes for VRB application.

Super-Strong Nafion/PVA/Uhmwpe Membranes for Proton and Hydroxide Ion-Exchange Fuel Cells

Perfluorosulfonic acid (PFSA) ionomers have been used extensively in proton exchange membranes due to their high proton conductivity and strong electrochemical stability. However, proton and anion conductivity through the PFSA membranes are contingent upon water uptake, but high water content in the membrane causes loss of long-term durability of the fuel cell system because of the water swelling-induced reduction in membrane’s mechanical strengths. Large body of literatures are available to address these issues, for example, hydroscopic nanoparticulate fillers have been used for self-hydration of the membrane, and aligned polytetrafluoroethylene (PTFE) has been employed to reinforce the tensile strengths of the PFSA ionomer. Unfortunately, there is yet no report to date that can resolve pareto fronts issues, i.e., simultaneously having high proton conductivity and high tensile property. Besides, the cost of PFSA membranes, e.g., Nafion, is still prohibitively high. Here, we report a new and low-cost hierarchical membrane with high proton/anion conductivity, low moisture/methanol uptake and super-high tensile strengths. The new membrane is a hybridized composite structure consisting of biaxially oriented nanoporous ultrahigh molecular weight polyethylene (UHMWPE) film coated with Nafion and polyvinyl alcohol (PVA) blend. The tensile strength of the composite membrane is at least 10 times higher than that of the pure Nafion membrane when fully humidified, and the proton and alkaline conductivity is comparable to that of the Nafion/PVA blend. The nanoporous UHMWPE simultaneously acted to provide the high tensile strengths, ion-conductivity selectivity and nanoconfinement to limit the water and methanol uptake. Thus the new hierarchical Nafion/PVA/UHMWPE membrane is potentially an ideal ion-exchange membrane for low temperature hydrogen and direct methanol fuel cells. The work is financially supported by the theme-based research project of the university grants committee of Hong Kong, Grant No. T23-601/17-R

Amelioration of PEMFC performance at high temperature by incorporation of nanofiller (sepiolite/layered double hydroxide) in Nafion membrane

Nanoheterostructured material composed of sepiolite clay mineral in which is assembled a MgAl layered double hydroxide (LDH) was used in the preparation of Nafion composite electrolyte membranes and their behavior compared to those of membranes filled with the LDH alone. Both, the neat MgAl LDH and the MgAl LDH-sepiolite hybrid materials were obtained via the co-precipitation method. Sepiolite fibers provide a large external surface area for bonding MgAl LDH particles while maintaining high microporosity and water molecules. The nanocomposite membranes were prepared incorporating different amount of LDH or LDH-sepiolite hybrid. Composite membranes present better water retention, good thermal properties and high proton conductivities at high temperatures than the pure Nafion membrane. The proton conductivity at 100 °C and 100% RH reaches a value of 0.13 S/cm for the LDH-sepiolite Nafion membrane whereas is only 0.010 S/cm in the case of the Nafion membrane. Fuel cell tests using Nafion membranes containing LDH or LDH-sepiolite hybrid as composite electrolytes show a good result for the operation of the PEMFC at 80 °C, 100 °C and 110 °C, with a clear favoring effect of the LDH-sepiolite filler for operation at the highest temperatures.

Novel composite Nafion membranes modified with copper phthalocyanine tetrasulfonic acid tetrasodium salt for fuel cell application

In this paper, Nafion membrane was firstly modified by copper phthalocyanine tetrasulfonic acid tetrasodium salt (CuTSPc) to prepare the Nafion/CuTSPc-x composite membranes. FTIR, XRD and SEM results revealed the successful incorporation of CuTSPc into Nafion and good compatibility between the two composites. The proton conductivities of the Nafion/CuTSPc-x composite membranes were evidently higher than pure cast Nafion membrane, and increased with CuTSPc contents. Among them, the Nafion/CuTSPc-6% membrane with the highest ion exchange capacity (1.14 mequiv•g−1) exhibited the highest proton conductivity of 0.084 S cm−1 at 30 °C and 0.131 S cm−1 at 80 °C, respectively. When fabricated of a membrane electrode assembly (MEA), the Nafion/CuTSPc-4.5% membrane displayed an initial fuel cell performance with a power density of 43.3 mW cm−2 at room temperature, close to that for pure cast Nafion membrane. Benefiting from the compact structure, high proton conductivity and outstanding stability, the Nafion/CuTSPc-x composite membranes show promising potentials for fuel cell applications.