Highly branched poly(arylene ether)/surface functionalized fullerene‐based composite membrane electrolyte for DMFC applications

Sulfonated branched polymer membranes have been gaining immense attention as the separator in energy‐related applications especially in fuel cells and flow batteries. Utilization of this branched polymer membranes in direct methanol fuel cell (DMFC) is limited because of large free volume and high methanol permeation. In the present work, sulfonated fullerene is used to improve the methanol barrier property of the highly branched sulfonated poly(ether ether ketone sulfone)s membrane without sacrificing its high proton conductivity. The existence of sulfonated fullerene with larger size and the usage of small quantity in the branched polymer matrix effectively prevent the methanol transportation channel across the membrane. The composite membrane with an optimized loading of sulfonated fullerene displays the highest proton conductivity of 0.332 S cm^?1 at 80°C. Radical scavenging property of the fullerene improves the oxidative stability of the composite membrane. Composite membrane exhibits the peak power density of 74.38 mW cm^?2 at 60°C, which is 30% larger than the commercial Nafion 212 membrane (51.78 mW cm^?2) at the same condition. From these results, it clearly depicts that sulfonated fullerene‐incorporated branched polymer electrolyte membrane emerges as a promising candidate for DMFC applications.     

Preparation and performance of bisimidazole cationic crosslinked addition-type polynorbornene-based anion exchange membrane

The late transition metal catalyst system (η³-allyl)Pd(PPh₃)Cl/Li[B(C₆F₅)₄]·2.5Et₂O (Li[FABA]) was used to catalyze 5-norbornene-2-methylenehexyl ether (NB-MHE) and 5-norbornene-2-methylene-(6-bromohexyl) ether (NB–O–Br) controllable addition copolymerization to obtain post-functionalized vinyl addition-type block copolymer aP(NB-O-Br-b-NB-MHE). 1,6-Bis(2-methylimidazole)hexane (Bis-MeIm) was used as a crosslinking agent to prepare a series of anion exchange membranes (AEMs) CL-aP(NB-O-Br-b-NB-MHE). The initial thermal decomposition temperature of the obtained addition-type polynorbornene-based AEM was about 250 °C. The AEM had moderate water uptake (WU) and swelling ratio (SR), and obvious micro-phase separation structure that could be observed from the AFM phase diagram. It could maintain high OH^? conductivity (85.07 mS cm^?1, 80 °C) and alkali resistance stability (soaking alkali for more than 500 h at 25 °C). In the single cell test of the H₂/O₂ fuel cell assembled by CL5-aP(NB-O-Br-b-NB-MHE), the peak power density was 177 mW cm^?2.     

An effective strategy to enhance the performance of the proton exchange membranes based on sulfonated poly(ether ether ketone)s

We report an effective and facile approach to enhance the dimensional and chemical stability of sulfonated poly(ether ether ketone) (SPEEK) type proton exchange membranes through simple polymer blending for fuel cell applications, using commercial available materials. The polymeric blends with sulfonated poly(aryl ether sulfone)s (SPAES) were simply fabricated by a three-component system, which contained SPEEK (10–50 wt%, 1.83 mmol/g), and SPAES-40 (1.72 mmol/g)/SPAES-50 (2.04 mmol/g) at 1:1 in weight. The SPAES-40 was selected for mechanical and dimensional stability reinforcing, while SPAES-50 for the good polymer compatibility. The obtained SPEEK/SPAES blend membranes showed depressed water uptake, better dimensional and oxidative stability, together with higher proton conductivity beyond 70 °C than the pristine SPEEK membrane. The apparent improvements in membrane properties were associated with the homogeneous dispersion of SPEEK and both SPAES copolymers inside the membranes as well as the rearrangements of the polymeric chains. The SPEEK content should be properly controlled in the range of 10–40% (B10 to B40). In a H₂/O₂ fuel cell test, B30 showed a maximum power density of 700 mW/cm², which was 1.6 times as high as that of B40 at 80 °C under 100% RH. The further cross-linking treatment produced more ductile and enduring blend membranes, indicating an appreciable prospective for fuel cell applications.     

Sulfonated poly(ether sulfone) for universal polymer electrolyte fuel cell operations

The performances of the proton exchange membrane fuel cell (PEMFC), direct formic acid fuel cell (DFAFC) and direct methanol fuel cell (DMFC) with sulfonated poly(ether sulfone) membrane are reported. Pt/C was coated on the membrane directly to fabricate a MEA for PEMFC operation. A single cell test was carried out using H₂/air as the fuel and oxidant. A current density of 730 mA cm⁻² at 0.60 V was obtained at 70 °C. Pt–Ru (anode) and Pt (cathode) were coated on the membrane for DMFC operations. It produced 83 mW cm⁻² maximum power density. The sulfonated poly(ether sulfone) membrane was also used for DFAFC operation under several different conditions. It showed good cell performances for several different kinds of polymer electrolyte fuel cell applications.     

Crosslinked anion exchange membranes with regional intensive ion clusters prepared from quaternized branched polyethyleneimine/quaternized polysulfone

A series of anion exchange membranes (AEMs) with regionally dense ion clusters are prepared by crosslinking quaternized polysulfone (QPSU) with quaternized branched polyethyleneimine (QBPEI). For the as-prepared QPSU/QBPEI AEMs, the hydrophilic QBPEI forms locally aggregated ion clusters in the QPSU matrix, which can promote the formation of an obvious microphase separation structure in the membrane. The QPSU/QBPEI-3 AEM with an ion exchange capacity of 1.88 meq/g exhibits the best performance, achieving a reasonably high ionic conductivity of 66.14 mS/cm at 80 °C and showing good oxidation stability and alkali resistance. Finally, the maximum power density of a single H₂/O₂ fuel cell with QPSU/QBPEI-3 AEM reaches 75.34 mW/cm² at 80 °C. The above results indicate that QBPEI with a dendritic structure and abundant anionic conductive groups has a good application prospect in the preparation of AEMs with locally aggregated ion clusters and microphase separation structures.     

Increased microbial fuel cell performance using quaternized poly ether ether ketone anionic membrane electrolyte for electricity generation

A high-performance hydroxide exchange membrane was prepared by the chloromethylation and quaternization of Poly ether ether ketone (PEEK) for microbial fuel cell applications. The study reports on the synthesis of a novel quaternized poly ether ether ketone (QPEEK) membrane and subsequent utilization of the ionomer as an anion exchange membrane (AEM). The structural characterization of chloromethylation and quaternization of PEEK was confirmed by FT-IR and ₁H¹ NMR spectroscopy and the morphologies were viewed by scanning electron microscopy. The effects of oxygen crossover and specific substrate crossover on cathode potential were also studied in detail. The investigation of QPEEK with the commercially available AEM (AMI-7001) revealed that the QPEEK shows excellent static properties, i.e. ion-exchange capacity, water uptake, thickness, etc.; and kinetic properties, i.e. diffusion permeability and better durability over 250 days. Power density obtained from an MFC containing the QPEEK-AEM produced higher value (60 W/m³) than the commercial AMI-7001 AEM (52 W/m³). This study shows that QPEEK could be used as an efficient and a cost effective AEM for an MFC.     

A novel strategy for constructing a highly conductive and swelling-resistant semi-flexible aromatic polymer based anion exchange membranes

A novel strategy was proposed to construct a bicontinuous hydrophilic/hydrophobic micro-phase separation structure which is crucial for high hydroxide conductivity and good dimensional stability anion exchange membranes (AEMs). A semi-flexible poly (aryl ether sulfone) containing a flexible aliphatic chain in the polymer backbone with imidazolium cationic group was synthesized by the polycondensation of bis(4-fluorophenyl) sulfone and the self-synthesized 4,4′-[butane-1,4-diylbis(oxy)] diphenol followed by a two-step functionalization. The corresponding membranes were prepared by solution casting. More continuous hydroxide conducting channels were formed in the semi-flexible polymer membranes compared with the rigid based ones as demonstrated by TEM. As a result, given the same swelling ratio, hydroxide conductivity of the semi-flexible polymer membrane was about 2-fold higher than the one of the rigid polymer based membrane (e.g., 45 vs. 22 mS cm^?1 with the same swelling ratio of 24% at 20 °C). The highest achieved conductivity for the semi-flexible polymer membranes at 60 °C was 93 mS cm^?1, which was much higher those of other random poly (aryl ether sulfone) based imidazolium AEMs (27–81 mS cm^?1). The single cell employing the semi-flexible polymer membrane exhibited a maximum power density of 125 mW cm^?2 which was also higher than those for other random poly (aryl ether sulfone) based imidazolium AEMs (16–105.2 mW cm^?2).     

Mechanically robust semi-interpenetrating polymer network via thiol-ene chemistry with enhanced conductivity for anion exchange membranes

Anion exchange membranes (AEMs) have emerged as crucial functional materials in various electrochemical device, such as fuel cell. Both the mechanical property and ionic conductivity play important roles in AEMs. Herein, a series of semi-interpenetrating polymer network AEMs are prepared by introducing flexible polyvinyl alcohol to the rigid photo-crosslinked poly (2,6-dimethyl-1,4-phenylene oxide) network. Such strategy endows AEM with tunable composition and mechanical property. Among these AEMs, membrane with an IEC of 1.46 mmol/g shows the highest mechanical strength of 30.8 MPa and a relatively lower swelling ratio, as well as the highest hydroxide conductivity. Importantly, the alkaline stability of these AEMs has been improved, 66.5% of the hydroxide conductivity is maintained after treatment in 1 M NaOH at 80 °C for 1000 h. Tentative assembly of H₂/O₂ fuel cell at 60 °C with this AEM displays a peak power density of 78 mW/cm². All the results demonstrate that sIPN structure is a promising way to enhance the mechanical property, ionic conductivity, and the alkaline stability of AEMs for the future application in AEMFCs.     

Block copolymer anion exchange membrane containing polymer of intrinsic microporosity for fuel cell application

High hydroxide conductivity and good stability of anion exchange membranes (AEMs) is the guarantee that anion exchange membrane fuel cells (AEMFCs) yield high power output for a long time. Balanced conductivity and stability can be better guaranteed by adopting a relatively low ion exchange capacity (IEC) while reducing the ion transport resistance Herein, a novel block copolymer AEM was designed and synthesized, which contains hydrophobic polymer of intrinsic microporosity (PIM) blocks and hydrophilic, quaternized polysulfone (PSF) blocks. The PIM block imparts high free volume to the membrane so that the resistance of hydroxide ion transport can be reduced; meanwhile, the hydrophilic block can self-assemble more easily to produce a better developed hydrophilic microphase, which may function as efficient channels for hydroxide ion transport. Both transmission electron microscopy images and small-angle X-ray scattering patterns suggested that the resulting AEM possessed a microphase separated morphology. The membrane showed a conductivity of 52.6 mS cm^-l at 80 °C with a relatively low IEC of 0.91 mmol g^?1. It also exhibited a good dimensional stability, swelling ratio maintained almost constant (ca. 17%) at 25 to 80 °C. The assembled H₂/O₂ fuel cell yielded a peak power density of 270 mW cm^?2 at 560 mA cm^?2. Our work demonstrates that incorporation of PIM in an AEM by means of block polymerization is an efficient way of promoting microphase separation and facilitating ion transport.     

Comb-shaped sulfonated poly(aryl ether sulfone) proton exchange membrane for fuel cell applications

Structure design is the primary strategy to acquire suitable ionomers for preparing proton exchange membranes (PEMs) with excellent performance. A series of comb-shaped sulfonated fluorinated poly(aryl ether sulfone) (SPFAES) membranes are prepared from sulfonated fluorinated poly(aryl ether sulfone) polymer (SPFAE) and sulfonated poly(aryl ether sulfone) oligomer (SPAES-Oligomer). Chemical structures of the comb-shaped membranes are verified by ¹H nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectra. The comb-shaped SPFAES membranes display more continuous hydrophilic domains for ion transfer, because the abundant cations and flexible side-chains structure possess higher mobility and hydrophilicity, which show significantly improved proton conductivity, physicochemical stability, mechanical property compared to the linear SPFAE membranes. In a H₂/O₂ single-cell test, the SPFAES-1.77 membrane achieves a higher power density of 699.3 mW/cm² in comparison with Nafion® 112 (618.0 mW/cm²) at 80 °C and 100% relative humidity. This work offers a promising example for the synthesis of highly branched polymers with flexible comb-shaped side chains for high-performance PEMs.     

Branched poly(ether ether ketone) based anion exchange membrane for H2/O2 fuel cell

High-performance anion exchange membranes (AEMs) are in need for practical application of AEM fuel cells. Novel branched poly(ether ether ketone) (BPEEK) based AEMs were prepared by the copolymerization of phloroglucinol, methylhydroquinone and 4,4′-difluorobenzophenone and following functionalization. The effects of the branched polymer structures and functional groups on the membrane's properties were investigated. The swelling ratios of all the membranes were kept below 15% at room temperature and had good dimensional stability at elevated temperatures. The branching degree has almost no effect on the dimensional change, but plays a great role in tuning the nanophase separation structure. The cyclic ammonium functionalized membrane showed a lower conductivity but a much better stability than imidazolium one. The BPEEK-3-Pip-53 membrane with the branching degree of 3% and piperidine functionalization degree of 53% showed the best performances. The ionic conductivity was 43 mS cm⁻¹ at 60 °C. The ionic conductivity in 1 M KOH at 60 °C after 336 h was 75% of its initial value (25% loss of conductivity), and the IEC was 83% of its initial value (17% loss of IEC), suggesting good alkaline stability. The peak energy density (60 °C) of the single H₂/O₂ fuel cell with BPEEK-3-Pip-53 membrane reached 133 mW cm⁻² at 260 mA cm⁻².     

Fabrication and characterization of a PTFE-reinforced integral composite membrane for self-humidifying PEMFC

A novel PTFE-reinforced self-humidifying membrane based on low-cost sulfonated poly (ether ether ketone) (SPEEK) resin was fabricated. In the membrane a base layer and a thin protective layer were bonded by porous polytetrafluoroethylene (PTFE) film. The base layer, which is composed of silicon oxide supported platinum catalyst (abbreviated as Pt-SiO₂) dispersed in SPEEK resin, can suppress reactant crossover and achieve good membrane hydration due to the imbedded hygroscopic Pt-SiO₂ catalysts. The thin protective layer, which constitutes of H₂O₂ decomposition catalyst Pt-SiO₂ and high H₂O₂-tolerant Nafion resin, aims to prevent the SPEEK resin degradation by H₂O₂ produced at the cathode side by incomplete reduction of oxygen. The porous PTFE film tightly bonds with the SPEEK and the Nafion resins to form an integral membrane and accordingly to avoid delamination of the two different resins. The self-humidifying membrane was characterized by TEM, SEM and EDS, etc. The self-humidifying membrane exhibits higher open circuit voltage (OCV) of 0.98 V and maximum power density value of 0.8 W cm⁻² than 0.94 V, 0.33 W cm⁻² of SPEEK/PTFE membrane under dry condition, respectively. The primary 250 h fuel cell durability experiment was conducted and suggested that this low-cost self-humidifying membrane was durable both on fuel cell performance and the membrane structure under fuel cell operation condition with dry H₂/O₂.     

Amelioration in physicochemical properties and single cell performance of sulfonated poly(ether ether ketone) block copolymer composite membrane using sulfonated carbon nanotubes for intermediate humidity fuel cells

A composite membrane composed of a sulfonated diblock copolymer (SDBC) based on poly(ether ether ketone) blocks copolymerized with partially fluorinated poly(arylene ether sulfone) and sulfonated carbon nanotubes (SCNTs) was fabricated by simple solution casting. Addition of the SCNT filler enhanced the water absorption and proton conductivity of membranes because of the increased per‐cluster volume of sulfonic acid groups, at the same time reinforced the membranes' thermal and mechanical properties. The SDBC/SCNT‐1.5 membrane exhibited the most improved physicochemical properties among all materials. It obtained a proton conductivity of 10.1 mS/cm at 120°C under 20% relative humidity (RH) which was 2.6 times more improved than the pristine membrane (3.9 mS/cm). Moreover, the single cell performance of the SDBC/SCNT‐1.5 membrane at 60°C and 60% RH at ambient pressure exhibited a peak power density of 171 mW/cm² at a load current density of 378 mA/cm², while the pristine membrane exhibited 119 mW/cm² at a load current density of 294 mA/cm². Overall, the composite membrane exhibited very promising characteristics to be used as polymer electrolyte membrane in fuel cells operated at intermediate RH.     

Preparation and characterization of imidazolium-functionalized poly (ether sulfone) as anion exchange membrane and ionomer for fuel cell application

Imidazolium-functionalized anion exchange membranes (AEMs) for anion exchange membrane fuel cells (AEMFCs) were synthesized by functionalization of chloromethylated poly (ether sulfone) (PES) with 1-alkylimidazole. The properties of AEMs can be controlled by the degree of chloromethylation of PES. Moreover, with the increment of the alkyl line length on the imidazolium group, the water uptake, swelling ratio and solubility of AEMs increased, whereas the hydroxide conductivity declined. By dissolving AEMs in the mixture of ethanol and water, IM-based anion exchange ionomers (AEIs) can be obtained. Electrochemical studies revealed that the catalytic activities of Pt/C towards oxygen reduction and hydrogen oxidation in the presence of imidazolium-functionalized AEIs were almost the same with that of commercial quaternary ammonium-based ionomers. The fabricated AEM and AEI were utilized to assemble H₂/O₂ AEMFC, yielding a peak power density of ∼30 mW cm⁻² with open circuit potential larger than 1.0 V. The results obtained indicate that imidazolium-functionalized AEMs and AEIs may be candidates which are worth further investigation for the application in the AEMFCs.     

Enhanced properties of SPEEK with incorporating of PFSA and barium strontium titanate nanoparticles for application in DMFCs

Novel blend nanocomposite proton‐exchange membranes were prepared using sulfonated poly (ether ether ketone) (SPEEK), perfluorosulfonic acid (PFSA), and Ba_0.9Sr_0.1TiO₃ (BST) doped‐perovskite nanoparticles. The membranes were evaluated by attenuated total reflection, X‐ray diffraction spectroscopy, water uptake, proton conductivity, methanol permeability, and direct methanol fuel cell test. The effect of two additives, PFSA and BST, were investigated. Results indicated that both proton conductivity and methanol barrier of the blend nanocomposite membranes improved compared with pristine SPEEK and the as‐prepared blend membranes. The methanol permeability and the proton conductivity of the blend membrane containing 6 wt% BST obtained 3.56 × 10^?7 cm² s^?1 (at 25 °C) and 0.110 S cm^?1 (at 80 °C), respectively. The power density value for the optimum blend nanocomposite membrane (15 wt% PFSA and 6 wt% BST) (54.89 mW cm^‐2) was higher than that of pristine SPEEK (31.34 mW cm^‐2) and SPF15 blend membrane (36.12 mW cm^‐2).     

Sulfonated poly(arylene ether sulfone)s membranes with distinct microphase-separated morphology for PEMFCs

Copoly (arylene ether sulfone)s was employed for proton exchange membrane preparation via atom transfer radical polymerization followed by mild sulfonation, enhanced phase-separated morphology and favorable proton conductivity were achieved. The comprehensive ex-situ properties of a range of membranes with different ion exchange capacities were characterized alongside the fuel cell performances investigation. The membranes exhibit higher water uptake, which is beneficial to the proton conduction, compared to Nafion® 211 while maintaining similar swelling ratio. The prepared membranes exhibit reasonably high proton conductivity (0.16 S/cm at 85 °C) benefitting from the well-defined microstructure and high connectivity of the hydrophilic domains. Considering the comprehensive property, membrane with moderate ion exchange capacity (1.39 mmol/g) was employed to fabricate the membrane electrode assembly and peak power density of 0.65 W/cm² at 80 °C, 60% relative humidity was achieved for a H₂/O₂ fuel cell, these hydrocarbon membranes can therefore be implemented in PEMFCs.     

Enhancement of fuel cell properties in polyethersulfone and sulfonated poly (ether ether ketone) membranes using metal oxide nanoparticles for proton exchange membrane fuel cell

The proton exchange membrane (PEM) was synthesized using polyethersulfone (PES), sulfonated poly (ether ether ketone) (SPEEK) and nanoparticles. The metal oxide nanoparticles such as Fe₃O₄, TiO₂ and MoO₃ were added individually to the polymer blend (PES and SPEEK). The polymer composite membranes exhibit excellent features regarding water uptake, ion exchange capacity and proton conductivity than the pristine PES membrane. Since the presence of sulfonic acid groups provides by added SPEEK and the unique properties of inorganic nanoparticles (Fe₃O₄, TiO₂ and MoO₃) helps to interconnect the ionic domain by the absorption of more water molecules thereby enhance the conductivity value. The proton conductivity of PES, SPEEK, PES/SPEEK/Fe₃O₄, PES/SPEEK/TiO₂ and PES/SPEEK/MoO₃ membranes were 0.22 × 10^?4 S/cm, 5.18 × 10^?4 S/cm, 3.57 × 10^?4 S/cm, 4.57 × 10^?4 S/cm and 2.67 × 10^?4 S/cm respectively. Even though the blending of PES with SPEEK has reduced the conductivity value to a lesser extent, hydrophobic PES has vital role in reducing the solvent uptake, swelling ratio and improves hydrolytic stability. Glass transition temperature (T_g) of the membranes were determined from DSC thermogram and it satisfies the operating condition of fuel cell system which guarantees the thermal stability of the membrane for fuel cell application.     

Study of deep oxidation and sulfonation of graphene oxide as low-temperature fuel cell electrolyte

In order improve the fuel cell performance of a free-standing graphene oxide (GO) membrane, the impacts of both the additional oxidation of GO and the modification with vinilsulfonic acid were investigated. The modification with vinilsulfonic acid was conducted with and without adding potassium persulfate, K₂S₂O₈, which is a radical initiator for the polymerization of vinylsulfonate. A total of six types of free-standing GO membranes with and without the oxidation and/or the modification were prepared. The oxidation and the modification additively increased the proton conductivity, and the oxidation significantly improved the durability of the fuel cell performance at 30 °C. The membrane of GOhvsi, of which GO was oxidized and modified with the initiator, showed very high in-plane proton conductivities at 30 °C, i.e., 0.54 S cm^?1 at RH 100%. The H₂–O₂ fuel cell using GOhvsi showed maximum power densities as high as 136 mW cm^?2 and 184 mW cm^?2 at 30 °C and 50 °C, respectively. The performance at 30 °C was stable for more than 20 h. The improved durability by the oxidation was attributed to the increased defects of carbon based on an XPS analysis. The TPD-MS analysis suggested that the oxygenated functional groups at the defects would increase the binding strength.     

Dielectric behaviour of UV-crosslinked sulfonated poly (ether ether ketone) with methyl cellulose (SPEEK-MC) as proton exchange membrane

Proton exchange membrane materials based on sulfonated poly ether ether ketone (SPEEK) with Methyl Cellulose (MC) are developed by solution cast technique and exposed to UV radiation with Bezoin Ethyl Ether (BEE) as photoinitiator. The addition of MC into SPEEK polymer enhances the conductivity up to 8.7 × 10^?3 Scm^?1 at 30 °C temperature and 80% relative humidity. This new crosslinked hybrid membrane shows good prospect for the use as proton exchange membrane in fuel cell.     

Construction of ion transport channels by grafting flexible alkyl imidazolium chain into functional poly(arylene ether ketone sulfone) as anion exchange membranes

A new series of imidazolium-functionalized anion exchange membranes (AEMs), based on poly (arylene ether ketone sulfone) containing pendant amino groups (Am-PAEKS) have been prepared. The structure of the copolymers is characterized by FT-IR and ¹H NMR spectra. The properties of the imidazolium-functionalized Am-PAEKS (Im-Am-PAEKS) including ionic conductivity, dimensional stability, thermal stability, fuel cell performance and mechanical property are investigated thoroughly. The hydroxide conductivities of the prepared membranes are in the range of 1.1 × 10^?2–13.9 × 10^?2 S cm^?1 (20–80 °C). The membranes exhibit excellent alkaline stability including high thermal stability and mechanical property after soaking in 2 M NaOH aqueous solution for 300 h. This study indicates that the imidazolium-functionalized membranes containing pedant amino groups have the potential to be applied in alkaline fuel cells.