Composite Proton Exchange Membranes Research Articles

SCTF nanosheets@sulfonated poly (p-phenylene-co-aryl ether ketone) composite proton exchange membranes for passive direct methanol fuel cells

The development of a simple and efficient methanol-resistant membrane strategy is of great significance for improvement of the performance of fuel cells, making it an attractive and challenging topic. In this work, sulfonated covalent triazine framework (SCTF) nanosheets are prepared by a micro-interface method and post-sulfonation, which show excellent dispersion in polar solutions, such as water and N, N-Dimethylacetamide (DMAc). Then a series of composite proton exchange membranes (SCTF-x@SPP-co-PAEKs) are prepared by blending these SCTF nanosheets with sulfonated micro-block copolymers (SPP-co-PAEKs) resin. The results show that the appropriate addition of SCTF can significantly improve the proton conductivity (PC), methanol resistance and fuel cell performance of the prepared composite membrane, which can be attributed to the good interfacial compatibility between the SCTF nanosheets and the sulfonated micro-block copolymer matrix. The passive direct methanol fuel cells (DMFCs) with SCTF-x@SPP-3 membrane exhibit power density in the range of 28.0–33.3 mW cm−2 at 25 °C, which is superior to the related values of the pristine membrane and the commercial Nafion® series membranes.

Anchoring Water Soluble Phosphotungstic Acid by Hybrid Fillers to Construct Three-Dimensional Proton Transport Networks.

Phosphotungstic acid (HPW)-filled composite proton exchange membranes possess high proton conductivity under low relative humidity (RH). However, the leaching of HPW limits their wide application. Herein, we propose a novel approach for anchoring water soluble phosphotungstic acid (HPW) by polydopamine (PDA) coated graphene oxide and halloysite nanotubes (DGO and DHNTs) in order to construct hybrid three-dimensional proton transport networks in a sulfonated poly(ether ether ketone) (SPEEK) membrane. The introduction of PDA on the surfaces of the hybrid fillers could provide hydroxyl groups and secondary amine groups to anchor HPW, resulting in the uniform dispersion of HPW in the SPEEK matrix. The SPEEK/DGO/DHNTs/HPW (90/5/5/60) composite membrane exhibited higher water uptake and much better conductivity than the SPEEK membrane at low relative humidity. The best conductivity reached wass 0.062 S cm−1 for the composite membrane, which is quite stable during the water immersion test.

Fabrication of water-insoluble phosphotungstic acid-carbon nitride nanohybrids for promoting proton transport of nanocomposite proton exchange membranes

Incorporation of heteropolyacids (HPAs) could greatly improve proton conductivity of composite proton exchange membranes (PEMs). However, HPA leaching, due to their high solubility in water, remains one of the major problems hindering the further development of these composite PEMs. In this work, we have prepared water-insoluble P–C3N4 nanohybrids via the hydrothermal reactions between phosphotungstic acid (HPW) and graphitic carbon nitride (g-C3N4) nanosheets, in which HPW is chemically bonded with g-C3N4. The introduction of P–C3N4 nanohybrids promotes the proton transport by providing the strong acidity of HPW and the continuous 2D proton transport pathways, resulting in the proton conductivity reaching up to 0.086 S cm−1 in liquid water and 0.91 × 10−3 S cm−1 at 45% RH at 20 °C for the sulfonated poly(ether ether ketone) (SPEEK) nanocomposite membrane, which are 50% and 6000% higher than the SPEEK control membrane (0.056 S cm−1 and 1.5 × 10−5 S cm−1), respectively. The fuel cell performance for the MEA based on the SPEEK/P–C3N4 nanocomposite membrane is significantly improved, achieving a 38.1% increase in the peak power density at 80 °C under 92% RH. Therefore, our study demonstrates a facile and promising approach to prepare water-insoluble solid proton conductor with HPW components, which could be further applied to fabricate high performance nanocomposite PEMs.

Electrospun multi-scale nanofiber network: hierarchical proton-conducting channels in Nafion composite proton exchange membranes

Electrospun multi-scale nanofiber network: hierarchical proton-conducting channels in Nafion composite proton exchange membranes

Enhanced proton transport properties of sulfonated polyarylene ether nitrile (SPEN) with moniliform nanostructure UiO-66-NH2/CNT

Metal-organic frameworks (MOFs) have been widely investigated for their porosity and functional diversity. Inspired by the flexible designability of MOFs, UiO-66-NH2/CNT with moniliform nanostructure was designed and synthesized successfully. SPEN@UiO-66-NH2/CNT composite proton exchange membranes were prepared by loaded UiO-66-NH2/CNT into sulfonated polyarylene ether nitrile (SPEN). Due to the addition of UiO-66-NH2/CNT, all the properties of composite proton exchange membranes were improved. The composite membranes exhibit excellent thermal stability and dimensional stability. The tensile strength of the composite membranes was improved about twofold compared to that of recast SPEN membrane, which was contributed by the interlaced property and rigid structure of UiO-66-NH2/CNT. Especially, the proton conductivity of the composite membranes was greatly facilitated by the additional proton acceptors and donors provided by the abundant amino groups and carboxyl groups in UiO-66-NH2/CNT. Furthermore, the methanol permeability of SPEN@UiO-66-NH2/CNT reduced consistently (from 6.13 to 0.96 × 10−7 cm2 s−1), which was much lower than that of Nafion membrane (21.36 × 10−7 cm2 s−1). All the results suggest that the design of multifunctional nanofillers based on the skeleton structure of MOFs could provide a new strategy to enhance the performance of PEMs.

UiO-66-NH2 functionalized cellulose nanofibers embedded in sulfonated polysulfone as proton exchange membrane

Metal–organic frameworks (MOFs) exhibit high proton conductivity, thermal stability, and offer immense flexibility in terms of tailoring their size. Owing to their unique characteristics, they are desirable candidates for proton conductors. Nevertheless, constructing ordered MOF proton channels in proton exchange membranes (PEMs) remains a formidable challenge. Herein, blend nanofibers of cellulose and UiO-66-NH2 (Cell–UiO-66-NH2) obtained via the electrospinning process were embedded in a sulfonated polysulfone matrix to obtain high-performance composite PEMs with an orderly arrangement of UiO-66-NH2. Comprehensive characterization and membrane performance tests reveal that composite membrane with 5 wt% (nominal) UiO-66-NH2 have revealed high proton conductivity of 0.196 S cm−1 at 80 °C and 100% relative humidity. Meantime, the composite membrane exhibits a low methanol permeability coefficient (~5.5 × 10−7 cm2 s−1). Moreover, the composite membrane exhibits a low swelling ratio (17.3%) even at 80 °C. The Cell–UiO-66-NH2 nanofibers exhibit strong potential for use as a proton-conducting nanofiller in fuel-cell PEMs.

Composite proton exchange membrane with balanced proton conductivity and swelling ratio improved by gradient-distributed POSS nanospheres

A proton exchange membrane with high proton conductivity and stability is critical to high power density and durability for proton exchange membrane fuel cells (PEMFC). To balance the“trade-off”effect between proton conductivity and swelling ratio of sulfonated poly (arylene ether sulfone) (SPAES) based PEMs, a series of SPAES composite membranes with the gradient-distribution of polyhedral oligomeric silsesquioxane (POSS) nanospheres were fabricated via UV radiation process. Numerous POSS nanospheres act as reactive interfacial modifiers, and the moieties of hydrophobic POSS are immobilized into SPAES matrix with an ordered manner, which results in extremely low swelling ratio (1.0%) and maintains high proton conductivity (0.09 S/cm) under fully hydrated states at 80 °C for POSS/S50. This work provides a new approach to fabricate large-size composite membranes with a gradient structure for PEMFCs, and a reference for the other functional membranes related researches such as batteries and filtrations.

A Robust Composite Proton Exchange Membrane of Sulfonated Poly (Fluorenyl Ether Ketone) with an Electrospun Polyimide Mat for Direct Methanol Fuel Cells Application.

As a key component of direct methanol fuel cells, proton exchange membranes with suitable thickness and robust mechanical properties have attracted increasing attention. On the one hand, a thinner membrane gives a lower internal resistance, which contributes highly to the overall electrochemical performance of the cell, on the other hand, strong mechanical strength is required for the application of proton exchange membranes. In this work, a sulfonated poly (fluorenyl ether ketone) (SPFEK)-impregnated polyimide nanofiber mat composite membrane (PI@SPFEK) was fabricated. The new composite membrane with a thickness of about 55 μm exhibited a tensile strength of 35.1 MPa in a hydrated state, which is about 65.8% higher than that of the pristine SPFEK membrane. The antioxidant stability test in Fenton’s reagent shows that the reinforced membrane affords better oxidation stability than does the pristine SPFEK membrane. Furthermore, the morphology, proton conductivity, methanol permeability, and fuel cell performance were carefully evaluated and discussed.

Enhanced Proton Selectivity in Ionomer Nanocomposites Containing Hydrophobically Functionalized Silica Nanoparticles

Perfluorosulfonic acid (PFSA) ionomers are ubiquitous as proton-exchange membranes (PEMs) in vanadium redox flow batteries (VRFBs), as they provide high proton conductivity and robust chemical stability. However, traditional PFSA ionomers suffer from high vanadium ion crossover, i.e., low ion selectivity, which reduces the efficiency and lifetime of the battery. Herein, a novel method to fabricate PFSA nanocomposites containing fluorocarbon-decorated silica nanoparticles is presented. These composite ionomers exhibit drastically reduced vanadium ion permeability and an almost two orders of magnitude increase in proton selectivity when compared to the current benchmark commercial ionomer. Small-angle neutron scattering data suggest that the nanostructures of these nanocomposites are drastically different from their pristine counterpart, where the periodic spacing of the hydrophobic domains is significantly reduced, while changes to the ionic structure were seen to be minimal. This work suggests that composite PEMs containing a secondary phase that alters the hydrophobic, nonion-conducting phase of the ionomer may prove to be a fruitful fabrication route to produce ionomer membranes with enhanced performance for use in VRFBs.

Improved performance of sulfonated poly ether ether ketone/three-dimensional hierarchical molybdenum disulfide nanoflower composite proton exchange membrane for fuel cells

As one of the most essential components of fuel cells, the commercialized Nafion-based proton exchange membranes(PEMs) suffer from several drawbacks like high cost and methanol permeability. The aim of this work is to fabricate a high performance PEM with combined low cost and methanol permeability together with high proton conductivity. Three-dimensional hierarchical molybdenum disulfide (MoS2) nanoflower is synthesized via a facile one-pot hydrothermal method, and then was embedd into sulfonated poly ether ether ketone (SPEEK) matrix to prepare composite PEM. The three-dimensional hierarchical architectures of MoS2 nanoflower can not only avoid the aggregation of MoS2 nanosheets but also provide abundant surface area and active sites, which are of benefit to fully take advantage of the intrinsic water absorption and methanol diffusion resistance ability of MoS2 nanosheets. The formed hydrogen bond network with water passway contributes to the improvement in proton conduction of composite membrane. As a consequence, composite membrane with 1 wt% MoS2 nanoflower loading content achieves optimized proton conductivity (0.123 S cm−1, 80 °C) and methanol permeability (21.5 × 10–7 cm2 s−1, 70 °C), which is 59.7% higher and 79.1% lower than that of SPEEK control membrane. Owing to increased proton conductivity and decreased methanol permeability, the maximum power density of the SPEEK/MoS2-1 composite membrane is 82.7 mW cm−2 at 70 °C, which is nearly 64.7% higher than that of pure SPEEK membrane (only 50.2 mW cm−2). Furthermore, the durability test confirms that the SPEEK/MoS2 composite membrane still possesses satisfactory stability even after continuous operation at 70 °C for 100 h.

MXene potassium titanate nanowire/sulfonated polyether ether ketone (SPEEK) hybrid composite proton exchange membrane for photocatalytic water splitting.

A cross-linked sulfonated polyether ether ketone (C-SPEEK) was incorporated with MXene/potassium titanate nanowire (MKT-NW) as a filler and applied as a proton exchange membrane for photocatalytic water splitting. The prepared hybrid composite PEM had proton conductivity of 0.0097 S cm−1 at room temperature with an ion exchange capacity of 1.88 meq g−1. The hybrid composite proton exchange membrane is a reactive membrane which was able to generate hydrogen gas under UV light irradiation. The efficiency of hydrogen gas production was 0.185066 μmol within 5 h for 12% wt of MKT-NW loading. The results indicated that the MKT-NW/C-SPEEK membrane is a promising candidate for ion exchange with hydrogen gas evolution in photocatalytic water splitting and could be applied as a renewable source of energy to use in various fields of applications.

Performance of microbial fuel cell operating with clay-manihot starch composite proton exchange membrane using RSM

This study optimized the performance of a microbial fuel cell (MFC) operating with raw clay sample (RCS)–manihot starch composite functioning as proton exchange membrane for electric power generation and bio-treatment of wastewater using central composite design (CCD) technique of the response surface methodology (RSM). The clay sample was heated at different temperatures ranging from 100 ​°C to 900 ​°C. The responses, power density and biochemical oxygen demand (BOD) removal efficiency were functions of four critical quantitative variables: pH, proton exchange membrane (PEM) preparation temperature (PPT), anolyte concentration and relative mass of clay in the PEM manihot-clay composite. A 24 CCD was employed to model and predict the process parameters. Sanitary wastewater of maximum cell density 4.25 ​× ​104/100 ​mL sustained the cell. Optimal responses of 82.4 ​mW/m2 power density and 72.3% BOD removal efficiency were recorded at clay PPT (RCS – 300 ​°C), 80 v/v wastewater to 10% glucose solution anolyte concentration, pH of 6.5 and clay component of PEM of mass 70 ​g optimum conditions. The study therefore suggests that RSM is an effective tool for evaluating and optimizing the Rsc-manihot composite PEM-MFC device for clean energy recovery and wastewater treatment, thereby providing the necessary leeway to overcoming the challenge of MFC scalability and greater performance.

Effect of Polyhedral Silsesquioxane Functionalized Sulfonic Acid Groups Incorporated Into Highly Sulfonated Polyphenylsulfone as Proton-Conducting Membrane

A Composite proton exchange membrane consists of octaphenyl polyhedral silsesquioxane (POSS) has been incorporated into a highly sulfonated polyphenylsulfone (SPPSU) for potential use in fuel cell applications. The effect of modified POSS by functionalization with sulfonic acid groups (SPOSS) addition on physicochemical properties, mechanical strength, and proton conductivity of the SPPSU is examined. Results revealed that the incorporation of POSS and SPOSS has significantly improved the mechanical strength and conductivity of the SPPSU composite membranes. SPPSU-POSS composite membrane shows tough and ductile features. Meanwhile, the SPPSU-SPOSS composite membrane exhibits mechanically lower strength but greater in flexibility as compared to SPPSU-POSS composite membrane. As per expectation, the proton conductivity of the SPPSU-SPOSS composite membrane is significantly improved compared to SPPSU-POSS composite membrane according to its relatively higher water uptake value. Based on the obtained results, it has been suggested that POSS has enhanced the proton conductivity and mechanical strength of the highly sulfonated PPSU based membrane desirable to be served as a proton exchange membrane in fuel cell application.

Advancements in proton exchange membranes for high-performance high-temperature proton exchange membrane fuel cells (HT-PEMFC)

Abstract The high-temperature proton exchange membrane fuel cell (HT-PEMFC) offers several advantages, such as high proton conductivity, high CO tolerance, good chemical/thermal stability, good mechanical properties, and low cost. The proton exchange membrane (PEM) is the critical component of HT-PEMFC. This work discusses the methods of current PEMs development for HT-PEMFC including modifications of Nafion® membranes and the advancement in composite PEMs based on non-fluorinated polymers. The modified Nafion®-based membranes can be used at temperatures up to 140 °C. Nevertheless, the application of Nafion®-based membranes is limited by their humidification with water molecules acting as proton carriers and, thus, by the operation conditions of membranes under a relative humidity below 20%. To obtain PEMs applied at higher temperatures under non-humidified conditions, phosphoric acid (PA) or ionic liquids (ILs) are used as proton carriers in PEMs based on non-fluorinated polymers. The research discussed in this work provides the approaches to improving the physicochemical properties and performance fuel cell of PEMs. The effects of polymer blending, crosslinking, and the incorporation of inorganic particles on the membrane properties and fuel cell performance have been scrutinized. The incorporation of inorganic particles modified with ILs might be an effective approach to designing high-performance PEMs for HT-PEMFC.

An investigation into polymer blending, plasticization and cross-linking effect on the performance of chitosan-based composite proton exchange membranes for microbial fuel cell applications

Chitosan (Cs) is one of the biopolymers increasingly employed to prepare proton exchange membranes (PEMs) in microbial fuel cells (MFCs). In this work, Cs is blended with three other natural or synthetic biopolymers including alginate (Alg), carboxymethylcellulose (CMC) and polyvinyl alcohol (PVA) followed by cross-linking/ plasticization with phosphoric acid, sulfuric acid, 3-(Trimethoxysilyl)propyl methacrylate (TMSPM), and glycerol (Gly), techniques have been examined as enhancement to neat Cs PEM in MFC system. The obtained membranes were characterized by FTIR, XRD, FESEM, mechanical properties, sorption study, and cation exchange capacity studies. The performance of the cross-linked and plasticized blended Cs membranes was evaluated in bio-power production and COD removal with municipal wastewater as an anolyte in the typical 2-chambered MFCs. The performance of MFC attached Cs PEM with the power density of 237 mW/m3 was increased up to 365 mW/m3 when it installed Cs/Alg. Therefore, after plasticization, power densities were decreased; however, COD removal of 23% for Cs/Alg membrane was increased up to 88% for phosphoric acid cross-linked Cs/Alg. The results confirm that this material could be a promising enhanced alternative to neat Cs, as a PEM in MFCs.

Ordered proton channels constructed from deoxyribonucleic acid-functionalized graphene oxide for proton exchange membranes via electrostatic layer-by-layer deposition

Based on the construction strategy of proton transport channels, we design a high-performance proton exchange membrane (PEM) with ordered deoxyribonucleic acid (DNA)-functionalized graphene oxide (GO) and Nafion matrix via the electrostatic layer-by-layer deposition (ELD) technique, which is a novel method of membrane formation aided by electrostatic force. The effects of different content rations of single-strand DNA (ss-DNA) molecules and GO (ss-DNA@GO) on the proton conductivity, methanol permeability, and single cell performance of composite PEMs are investigated. The composite membrane shows a high proton conductivity of 351.8 mS cm−1 (80 °C, 100%RH) but a low methanol permeability of 1.63 × 10−7 cm2 s−1 at room temperature. Furthermore, the composite membranes are assembled into direct methanol fuel cells at 60 °C, and Nafion/DNA@GO-2/5 exhibits a maximum power density of 255.33 mW cm−2, which is 2.42 times higher than that of pure Nafion. This work explores the application potential of DNA@GO in PEM and provides a bioinspired avenue to designing next-generation high-performance PEM for fuel cells.

Friedel-Crafts self-crosslinking of sulfonated poly(etheretherketone) composite proton exchange membrane doped with phosphotungstic acid and carbon-based nanomaterials for fuel cell applications

In this work, self-crosslinked sulfonated polyether etherketone membrane (C-SPEEK) was synthesized by Friedel-Crafts alkylation at 130 °C with chloromethylated sulfonated polyether etherketone (SPEEK-Cl). The water uptake (WU) of the C-SPEEK was 47.75% with a 8.69% swelling rate (SR) at 60 °C, compared with the sulfonated polyether etherketone membrane (SPEEK) with WU of 110.60% and SR of 57.99%. The contradiction between dimensional stability and proton conductivity under high sulfonation degree was overcome. The self-crosslinking composite membranes were prepared by doping with carbon nanomaterials (Graphite oxide, GO; reduced graphene oxide, rGO and carbon nanotubes, CNTs) and phosphotungstic acid (HPW). Since HPW and carbon nanomaterials incorporated in membrane facilitate protons conduction via both Grotthuss and Vehicle mechanisms, the hybrid membranes demonstrated the improved conductivities. At 80 °C, C-SPEEK/HPW/GO showed proton conductivity as high as 119.04 mS/cm, which was 2.4 folds higher than that of the C-SPEEK. Furthermore, the superior performance of C-SPEEK/HPW/GO was further validated through H2/O2 single cell test. The C-SPEEK/HPW/GO produced a higher power output of 876.80 mW/cm2, whereas only 776.72 mW/cm2 for C-SPEEK was recorded. Thus, C-SPEEK/HPW/GO and C-SPEEK may be promising membrane materials for potential applications in fuel cells.

Synthesis and characterization of a novel poly (vinyl alcohol)-based zinc oxide (PVA-ZnO) composite proton exchange membrane for DMFC

Electrolyte polymeric membranes were synthesized by impregnating zinc oxide (ZnO) nanoparticles (NPs) in a cross-linked PVA matrix for Direct Methanol Fuel Cell (DMFC) applications. The novel membranes consist of PVA as the support while zinc oxide nanoparticles serve as inorganic ion exchangers. The fabricated composite proton exchange membranes exhibit a wide variety of advantages which include good thermal and chemical stability. The synthesized membranes demonstrate a high percentage of water uptake (85%–105%) and a low percentage of methanol uptake (17%–21%). Other important properties such as transport number (0.88) and ion exchange capacity (0.78 meq.g−1) were also determined, and they were found comparable to Nafion®117. Ionic conductivity (3.9 mS/cm) of the composite membranes was determined and found comparable to other PVA based composite membranes reported in literature. Characterization of the membranes was carried out using Fourier-Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Energy-dispersive X-ray Spectroscopy (EDX) and Thermogravimetric analysis (TGA). These characterizations revealed the structural interaction between the support and the ion exchanger, crystalline nature, surface morphology, elemental analysis and the thermal stability (upto 280 °C) of the membranes, respectively. The mechanical characterization of the membranes was also carried out on a Universal Testing Machine (UTM), revealing satisfactory mechanical stability. The results demonstrate the possibility of synthesis of a low-cost proton exchange membrane for DMFC applications.

Sulfonated poly(ether ether ketone) composite membranes based on amino‐modified halloysite nanotubes that effectively immobilize phosphotungstic acid

AbstractIn this work, we prepared amino‐modified halloysite nanotubes (PEI‐DHNTs) via the co‐deposition of self‐polymerized dopamine and polyethylenimine (PEI) on the surface of nanotubes, which was confirmed by X‐ray photoelectron spectroscopy (XPS) and Thermogravimetric analysis (TGA). A series of composite proton exchange membranes (PEMs) were prepared by incorporating PEI‐DHNTs and phosphotungstic acid (HPW) into sulfonated poly(ether ether ketone) (SPEEK). It was found that both PEI‐DHNTs and HPW were well dispersed in the polymer matrix, exhibiting excellent filler‐matrix compatibility. The composite membranes demonstrated enhanced proton conductivity, reaching as high as 0.078 S cm−1 with 33.3 wt.% HPW loading, which was ~90% higher than that of SPEEK control membrane. Such improvement was mainly attributed to the strong acid–base pairs formed by PEI‐DHNT with both SPEEK and HPW, which shortened proton hopping distance and created more continuous proton conduction pathways. Furthermore, the membrane conductivity remained almost constant after 1 year's immersion in liquid water, indicating the successful immobilization of HPW in the composite membranes.

Sulfonated silica coated polyvinylidene fluoride electrospun nanofiber-based composite membranes for direct methanol fuel cells

A sulfonated silica coated polyvinylidene fluoride (S-SiO2@PVDF) nanofiber substrate with high strength and ultrahigh surface concentration of sulfonic acid groups was prepared by a three-step simple surface functionalization process. The S-SiO2@PVDF substrate was then used as both mechanical reinforcement support and inter-connected three-dimensional proton transport network for chitosan (CS) to prepare thin composite proton exchange membranes for direct methanol fuel cells (DMFCs). As the mechanical support for CS matrix, the S-SiO2@PVDF nanofiber framework could significantly improve the dimensional stability, tensile strength, elongation and mechanical damage resistance. Meanwhile, as a proton conduction network, the conductivity of the composite membrane was remarkably enhanced to 21.2 mS cm−1 (about 2.8 times than that of pure CS). Moreover, due to the excellent methanol barrier ability of CS matrix itself as well as the limitation role of the nanofibers, the methanol crossover of the composite membrane was as low as 4.2 × 10−7 cm2 s−1 that was only 26% of commercial Nafion 115. DMFC test showed the composite membrane exhibited the maximum power density of 86.3 mW cm−2 (80 °C), and the power density loss was only 5.4% even after operating at a constant current of 0.35A cm−2 for 100 h.