•Poly(ether ether ketone ketone) isomers having rigid backbones were synthesized.•They had a good combination of proton conductivity and dimensional stability.•Their H2/O2 performance were similar or moderately improved over Nafion 115.•Me-p-SPEEKK had a maximum power density of 85 mW cm−2 at 2.0 M and 80 °C.Meta- and para-linked homopolymers bearing 3-methylphenyl (Me) pendent groups were postsulfonated to create sulfonated poly(ether ether ketone ketone) (SPEEKK) backbone isomers, which are referred to as Me-p-SPEEKK and Me-m-SPEEKK. Their thermal and oxidative stability, mechanical properties, dimensional stability, methanol permeability, and proton conductivity are characterized. Me-p-SPEEKK and Me-m-SPEEKK proton conductivities at 100 °C are 116 and 173 mS cm−1, respectively. Their methanol permeabilities are 3.3–3.9 × 10−7 cm2 s−1, and dimensional swelling at 100 °C is 16.4–17.5%. Me-p-SPEEKK and Me-m-SPEEKK were fabricated into membrane electrode assemblies (MEAs), and electrochemical properties were evaluated within a direct methanol fuel cell (DMFC) and proton-exchange membrane fuel cell (PEMFC). When O2 is used as the oxidant at 80 °C and 100% RH, the maximum power density of Me-m-SPEEKK reaches 657 mW cm−2, which is higher than those of Nafion 115 (552 mW cm−2). DMFC performance is 85 mW cm−2 at 80 °C with 2.0 M methanol using Me-p-SPEEKK due to its low MeOH crossover. In general, these electrochemical results are comparable to Nafion. These ionomer properties, combined with a potentially less expensive and scalable polymer manufacturing process, may broaden their potential for many practical applications.Download high-res image (348KB)Download full-size image

•Nanocrystal cellulose (NCC) reinforced SFPAEKs composite proton exchange membranes presented better performances than SFPAEKs, such as proton conductivity and mechanical properties.•Nanocomposites were obtained with modified NCC and sulfonated fluorenyl-containing polyaryletherketones (SFPAEKs) for proton exchange membrane application via solution casting method.•NCC could be uniformly dispersed in the SFPAEKs matrix by controlling the NCC ratio.Sulfonated fluorenyl-containing polyaryletherketones (SFPAEKs) were synthesized through a postsulfonation approach under a mild reaction condition. The composite proton exchange membranes based on SFPAEKs and various amounts of the modified nanocrystalline cellulose (NCC) were prepared by solution casting method. The existence of the multiple hydroxyl and sulfonic acid groups on the chemically modified nanocrystalline cellulose was supposed to benefit the formation of hydrogen-bond network and proton-conducting channels, which would improve the proton conducting ability of the composite membranes. Furthermore, the properties, such as mechanical properties, thermal stability, water uptake, swelling ratio and so on, were thoroughly investigated. In comparison to the pristine SFPAEK, the composite membranes containing a “performance enhanced” NCC component presented the higher proton conductivity and better mechanical properties. It was found that the proton conductivity of the composite membrane with 4 wt% of NCC could reach 0.234 S cm− 1 at 100 °C, and this value was higher than that of most of the reported membranes. The results showed that the modified nanocrystalline cellulose reinforced SFPAEK composite membrane would be promising for the application as middle-temperature proton exchange membranes in fuel cells.

A novel high temperature proton exchange membrane (HT-PEM) with a high phosphoric acid (PA) doping level of 24.6, high proton conductivity of 0.217 S cm−1 at 200 °C, as well as excellent mechanical-dimensional stability was prepared based on a structure-designed polybenzimidazole (PBI).

•Three sulfonated polynaphthalimides were successfully synthesized.•Acid functionalized POSS was introduced to yield some novel hybrid membranes.•It was found that isomeric structure could affect the properties of the membranes.•Morphology was studied by SEM and EDX.Three sulfonated polyimides, including a couple of isomeric polymers, were synthesized through a typical “one pot” polymerization reaction. Hybrid membranes were constructed by incorporating a multiple-acid functionalized polysilsesquioxane into the above polymers via a sol–gel process. The properties, including thermal stability, mechanical properties, water uptake, swelling ratio, methanol permeability and proton conductivity were evaluated. The proton conductivities of the membranes were above 0.11 S cm− 1 at 100 °C. Hybrid membranes exhibited the enhanced ability of water absorption and proton conducting. The methanol permeabilities of these membranes were 3.8–6.94 × 10− 7 cm2 s− 1, which were more competitive than Nafion 117. It was found that isomeric structure could affect the properties of both the pristine and hybrid membranes. The microstructures featured with phase-separation morphology could be observed in the hybrid membranes.

Naphthalene-based poly(arylene ether ketone)s were obtained through a three-step process involving polymerization of methylated polymers, followed by bromination and derivatization with a diquaternary-ammonium group. The ionic conductivities of the anion exchange membranes were above 10−2 S cm−1 at room temperature and the membrane with an IEC = 1.46 mequiv. g−1 attained an ion conductivity of 7.4 × 10−2 S cm−1 at 100 °C, which is higher than many reported results. The membrane series had low water uptake and excellent dimensional stability, even at the highest IEC values. In addition, the membranes were insoluble in organic solvents and concentrated alkaline solutions for many days, even under heating, suggesting their excellent stability. These combined data suggest that the membranes have potential to be used as anion exchange membranes for fuel cells applications.

•Novel multiple cyano-groups containing polyimides were prepared for PEM applications.•The properties of the PEMs were carefully characterized.•The cyano-functionalized SPIs exhibited some attractive properties.•The CN-SPI membranes exhibited high proton conductivity and low swelling at 100 °C.Some multiple cyano groups functionalized sulfonated polyimides (CN-SPIs) are prepared derived from a novel CN-diamine monomer for the first time. Meanwhile, some similar SPIs but without cyano groups (Ph-SPIs) are prepared as counterparts for comparison purposes. Both chemical structure and properties of these SPIs are carefully characterized. At 100 °C, proton conductivities of some membranes could reach 0.138–0.146 S cm−1, which are comparative with Nafion. The methanol diffusion coefficients of the membranes are between 1.74 and 5.82 × 10-7 cm2 s−1, which are much more competitive than Nafion 117. It is of interest to find that cyano-functionalized SPIs could possess an excellent combination of low swelling, high proton conductivity and low methanol permeability.

Naphthalene-containing blend membranes, comprising sulfonated polyaryletherketone (SPAEK) as the primary matrix, and basic component polyazomethine (PAM), which has a chemical structure partially similar with SPAEK, were investigated as proton exchange membranes (PEMs). Further, a ternary-composite membrane was successfully prepared by introducing acid-functionalized polysilsesquioxane (POSS–SO3H) into SPAEK/PAM composite using a sol–gel process. The relevant properties of the PEMs, such as proton conductivity, methanol permeability, water uptake, and morphology were determined, and it was shown that the ternary-composite membrane, SPAEK/PAM/POSS–SO3H, showed a superior combination of properties for proton conductivity and methanol resistance. Its selectivity was 7.5 times higher than Nafion.Highlights▸ Binary blend and ternary composite PEMs were constructed. ▸ A polyazomethine was incorporated as a molecular-enhancement component. ▸ Acid-functionalized polysilsesquioxane was incorporated through a sol–gel process. ▸ Ternary composite membrane exhibited enhanced conductivity and selectivity.

Two series of sulfonated naphthalenic polyimides containing ether and ketone linkages (SPI-KK-X and SPI-K-X) were prepared by a one-pot polymerization reaction of sulfonated diamine monomers, 1,4-bis[3-sodium sulfonate-4-(4-aminophenoxy)benzoyl]benzene or 4,4-bis[3-sodium sulfonate-4-aminophenoxy]benzophenone, with 4,4-diaminodiphenyl ether and 1,4,5,8-naphthalenetetracarboxylic dianhydride. The membranes cast from the resulting polymers had good thermal and oxidative stability, dimensional stability and mechanical properties. At 80 °C, the proton conductivities of several samples, including SPI-KK-1, SPI-K-1 and SPI-K-2 were higher than 0.10 S/cm, which were comparable to that of Nafion. Methanol permeabilities of the obtained polymer electrolyte membranes (PEMs) were in the range of 1.43–2.03 × 10−7 cm2/s, which were several times lower than that of Nafion 117. It is interesting to note that the SPI-KK-X series, having a more rigid phenyl–ketone–phenyl–ketone–phenyl moiety, had a lower dimensional swelling ratio and lower methanol permeability in comparison with the corresponding SPI-K-X series at the same level of ion exchange capacity (IEC).Graphical abstractResearch highlights▶ Two sulfonated diamine monomers were synthesized via SNAr reactions. ▶ Two series of sulfonated polyimides containing ether–ketone linkages were prepared. ▶ SPI-KK-X series having more rigid moieties had lower dimensional swelling. ▶ Several obtained PEMs exhibited high selectivity for DMFC applications.

A new diamine monomer, 1,5-bis[4-(4-aminophenoxy)]benzoyl-2,6-dimethoxynaphthalene, was synthesized via a Friedel–Crafts acylation reaction followed by an aromatic nucleophilic substitution reaction. Six ether–ketone linked polymers, named as poly(ether ketone azomethane)s and poly(ether ketone imide)s, were successfully prepared through the polycondensations of the diamine monomer with dialdehydes and dianhydrides, respectively. These naphthylated polymers exhibited high Tg values (142–288 °C), due to their bulky and rigid chemical structure. Meanwhile, they showed good thermal stability and improved solubility. Typically, some of them were casted into thin flexible film and showed high moduli.

A sulfonated poly(aryl ether ether ketone ketone) (PEEKK) having a well-defined rigid homopolymer-like chemical structure was synthesized from a readily prepared PEEKK by post-sulfonation with concentrated sulfuric acid at room temperature within several hours. The polymer electrolyte membrane (PEM) cast from the resulting polymer exhibited an excellent combination of thermal resistance, oxidative and dimensional stability, low methanol fuel permeability and high proton conductivity. Furthermore, membrane electrode assemblies (MEAs) were successfully fabricated and good direct methanol fuel cell (DMFC) performance was observed. At 2 M MeOH feed, the current density at 0.5 V reached 165 mA/cm, which outperformed our reported similarly structured analogues and MEAs derived from comparative Nafion® membranes.

Monophenylated poly(ether sulfone)s (Ph-PES) and diphenylated poly(ether sulfone)s (DiPh-PES), were synthesized as starting materials for the preparation of sulfonated polymers with well-defined chemical structure. Mild post-polymerization sulfonation conditions led to sulfonated Ph-PES (Ph-SPES) bearing acid groups on both the pendant phenyl group and the backbone, and sulfonated DiPh-PES (DiPh-SPES) bearing acid groups only on the two pendant phenyl groups. Both series of polymers had excellent mechanical properties, high glass transition temperatures, good thermal and oxidative stability, as well as good dimensional stability. It is interesting to note that exclusively pendant-phenyl-sulfonated (bis-sulfophenylated) DiPh-SPES copolymers possessed obviously better thermal and oxidative stability compared with the corresponding pendant-phenyl-sulfonated/main-chain-sulfonated Ph-SPES copolymers. The methanol permeability values of the membranes were in the range of 7.0 × 10−7–9.4 × 10−8 cm2/s at 30 °C, which is several times lower than that of Nafion 117. DiPh-SPES-50 and Ph-SPES-40 also exhibited high proton conductivity (approximately 0.13 S/cm at 100 °C).

Naphthalene-based poly(arylene ether ketone)s were obtained through a three-step process involving polymerization of methylated polymers, followed by bromination and derivatization with a diquaternary-ammonium group. The ionic conductivities of the anion exchange membranes were above 10−2 S cm−1 at room temperature and the membrane with an IEC = 1.46 mequiv. g−1 attained an ion conductivity of 7.4 × 10−2 S cm−1 at 100 °C, which is higher than many reported results. The membrane series had low water uptake and excellent dimensional stability, even at the highest IEC values. In addition, the membranes were insoluble in organic solvents and concentrated alkaline solutions for many days, even under heating, suggesting their excellent stability. These combined data suggest that the membranes have potential to be used as anion exchange membranes for fuel cells applications.