Highly alkaline stable fully-interpenetrating network poly(styrene-co-4-vinyl pyridine)/polyquaternium-10 anion exchange membrane without aryl ether linkages

To avoid the detrimental effect of aryl ethers on the alkali stability of anion exchange membrane (AEM), elaborately designed and synthesized poly(styrene-co-4-vinyl pyridine) (PS4VP) copolymer without aryl ether linkages is used to prepare AEMs. By introducing commercialized polyquaternium-10 (PQ-10) as the main ion-conducting molecule, the fully-interpenetrating polymer network quaternized PS4VP/PQ-10 (F-IPN QPS4VP/PQ-10) AEMs are prepared by cross-linking PS4VP and PQ-10, respectively. The as-prepared F-IPN QPS4VP/PQ-10 AEMs have obvious nanoscale microphase-separated morphologies, which ensure the membranes have good mechanical properties and dimensional stability. With optimized component ratios, F-IPN QPS4VP/PQ-10 AEM exhibits high ionic conductivity (74.29 mS/cm at 80 °C) and power density (111.83 mW/cm² at 60 °C), as well as excellent chemical stabilities (94.36% retaining of initial mass after immersion in Fenton reagent at 30 °C for 10 days, and 92.28% retaining of original ionic conductivity after immersion in 1 M NaOH solution at 60 °C for 30 days), which are greater than those of semi-interpenetrating polymer network QPS4VP/PQ-10 AEM. In summary, a combination of fully-interpenetrating polymer network and stable polymer chains and ion-conducting moieties is found to effectively overcome the trade-off between high ionic conductivity and good dimensional/chemical stabilities.     

Novel anhydrous composite membranes based on sulfonated poly (ether ketone) and aprotic ionic liquids for high temperature polymer electrolyte membranes for fuel cell applications

Novel composite membranes were prepared using imidazolium type aprotic ionic liquids and sulfonated poly (ether ketone) (SPEK) as polymer matrix by solution casting process. All the prepared membranes were characterized for their thermal stability, mechanical properties, ion exchange capacity, proton conductivity and leaching out of ionic liquids in presence of water. Ionic liquid based membranes were more flexible than neat SPEK membrane due to the plasticization effect of ionic liquids. The interactions and compatibility occurring among components were investigated by vibration spectroscopy (FTIR ATR) and scanning electron microscopy respectively. The thermal stability of composite membranes was higher than unmodified membranes. The ion conductivity of composite membranes under anhydrous conditions was found to be dependent on temperature, type and concentration of ionic liquid in SPEK matrix. Ion conductivities of composite membranes under anhydrous condition were found to be up to two orders (∼100 times) higher than neat SPEK membrane and it was found to be ∼5 mS/cm at 140 °C for SPEK/OTf-70. These composite membranes can be successfully operated at temperatures ranging from 40 °C to 140 °C under anhydrous conditions.     

Poly(ethyl methacrylate) and poly(2-ethoxyethyl methacrylate) based polymer gel electrolytes

New poly(ethyl methacrylate) and poly(2-ethoxyethyl methacrylate) gel electrolytes containing immobilised lithium perchlorate solution in propylene carbonate were prepared by UV radical polymerisation. Materials exhibit high ionic conductivity up to 0.23 mS cm⁻¹ and long-term stability of chemical and mechanical properties. Both materials keep their suitable conductivity above −20 °C. The effect of material composition, temperature, cross-linking agent and salt concentration on the electrochemical and mechanical properties were studied using impedance spectroscopy and cyclic voltammetry. The accessible electrochemical window of both polymer electrolytes was estimated from −2.1 to 1.5 V versus Cd/Cd²⁺. Impedance measurements showed almost one-order increase of conductivity when ethylene dimethacrylate was used as a cross-linking agent in comparison with the polymer electrolyte without agent.     

Crosslinked polymer electrolytes of high pyridine contents for HT-PEM fuel cells

This report evaluates a new family of pyridine containing aromatic polyether sulfones as polymer electrolytes for high temperature polymer electrolyte membrane fuel cells (HTPEM FCs). The polymers are prepared by high temperature polyetherification reactions, yielding highly soluble polymers even with pyridine contents as high as 90%. Along with the pyridine content, crosslinking density is also tuned, leading to the enhancement of membrane properties such as film integrity, dimensional stability and doping ability in acidic media. The completion of the crosslinking reaction is enabled by a short thermal pre-treatment, preceding the doping step in H₃PO₄ 85%. Both the linear and the crosslinked membranes show high thermal and oxidative stability. Membranes before and after crosslinking are integrated in single cells where their conductivity and performance are monitored, revealing conductivities above 7 × 10⁻² S/cm at temperatures higher than 180 °C.     

Benzimidazole-cross-linked proton exchange membranes for direct methanol fuel cells

Sulfonated poly(ether ether ketone)s with pendent amino groups (Am-SPEEKs) have been prepared for direct methanol fuel cells (DMFCs). With the goal of improving the dimensional stability and reducing the methanol permeability of membranes, Benzimidazole trimer is synthesized as a cross-linker. The cross-linking reaction is induced by heating at 120 °C for 6 h and then the effects of different contents of cross-linker on the properties of the cross-linking membranes are investigated in detail. Combining covalent cross-linking with ionic cross-linking, the cross-linking network structure causes significant enhancement in oxidative and mechanical property. Meanwhile, water uptake, swelling ratio and methanol permeability of the membranes substantially decrease with increasing the content of cross-linker. Although the conductivity of the membranes is lower than that of the pristine membrane, the relative selectivity is much higher. All the results indicate that the cross-linked membrane is potential candidate as membrane for applications in fuel cells.     

Experimental Investigation of boron phosphate Incorporated speek/pvdf blend membrane for proton exchange membrane fuel cells

The recent studies focused on the blend membranes to a great extent due to their capability of gathering some important polymer characteristic features. In this survey, boron phosphate (BP) doped sulfonated poly (ether ether ketone)/Poly (vinylidene fluoride) (SPEEK/PVDF) blend membrane having high ionic conduction capability was synthesized. The boron phosphate doping to the membrane matrix enhanced the membrane properties in terms of proton exchange membrane conditions. The sol-gel and casting method was used to synthesise the SPEEK/PVDF blend membrane. The characterization tests to observe the structure of the membrane, such as X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), FT-IR and mechanical/thermal stability tests were conducted. The membrane ionic transportation and water retention were improved directly by the addition of boron phosphate. The highest power density (242 mW cm^?2) and current density (400 mA cm^?2) at 0.6 V were obtained by SPEEK/PVDF/10BP, respectively. Additionally, the proton conductivity value of 39 mS cm^?1 was obtained for SPEEK/PVDF/10BP sample at 80 °C. The authors concluded that both boron phosphate additive and SPEEK/PVDF blend membrane have promising results for fuel cell future operations.     

Fabrication and characterization of poly(vinyl alcohol)/montmorillonite/poly(styrene sulfonic acid) proton-conducting composite membranes for direct methanol fuel cells

A high performance poly(vinyl alcohol)/montmorillonite/poly(styrene sulfonic acid) (PVA/MMT/PSSA) proton-conducting composite membrane was fabricated by a solution casting method. The characteristic properties of these blend composite membranes were investigated by using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, methanol permeability measurement, and the AC impedance method. The ionic conductivities for the composite membranes are in the order of 10⁻³ S cm⁻¹ at ambient temperature. There are two proton sources used on this novel composite membrane: the modified MMT fillers and PSSA polymer, both materials all contain the -SO₃H group. Therefore, the ionic conductivity was greatly enhanced. The methanol permeabilities of PVA/MMT/PSSA composite membranes is of the order of 10⁻⁷ cm² s⁻¹. It is due to the excellent methanol barrier properties of the PVA polymer. The peak power densities of the air-breathing direct methanol fuel cells (DMFCs) with 1M, 2M, 4M CH₃OH fuels were 14.22, 20.00, and 13.09 mW cm⁻², respectively, at ambient conditions. The direct methanol fuel cell with this composite polymer membrane exhibited good electrochemical performance. The proposed PVA/MMT/PSSA composite membrane is therefore a potential candidate for future applications in DMFC.     

New proton conducting polymer blends and their fuel cell performance

Novel polymer blends based on aromatic polyethers with pyridine units have been prepared for their use as electrolytes after being doped with phosphoric acid for high temperature PEM fuel cells. They exhibit very good film-forming properties, mechanical integrity, high modulus up to 230 °C, high glass transition temperatures (up to 260 °C) and high thermal stability up to 400 °C. In addition to the above required properties, these novel materials show high oxidative stability and acid doping ability, enabling proton conductivity in the range of 10⁻² S cm⁻¹ at 130 °C. The preparation and fuel cell testing of membrane electrode assemblies, demonstrated very promising performance, and an initial study has shown the positive effect of humidity on the measured conductivity.     

Direct methanol fuel cell (DMFC) based on PVA/MMT composite polymer membranes

A novel composite polymer electrolyte membrane composed of a PVA polymer host and montmorillonite (MMT) ceramic fillers (2–20 wt.%), was prepared by a solution casting method. The characteristic properties of the PVA/MMT composite polymer membrane were investigated using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), and micro-Raman spectroscopy, and the AC impedance method. The PVA/MMT composite polymer membrane showed good thermal and mechanical properties and high ionic conductivity. The highest ionic conductivity of the PVA/10 wt.%MMT composite polymer membrane was 0.0368 S cm⁻¹ at 30 °C. The methanol permeability (P) values were 3–4 × 10⁻⁶ cm² s⁻¹, which was lower than that of Nafion 117 membrane of 5.8 × 10⁻⁶ cm² s⁻¹. It was revealed that the addition of MMT fillers into the PVA matrix could markedly improve the electrochemical properties of the PVA/MMT composite membranes; which can be accomplished by a simple blend method. The maximum peak power density of the DMFC with the PtRu anode based on Ti-mesh in a 2 M H₂SO₄ + 2 M CH₃OH solution was 6.77 mW cm⁻² at ambient pressure and temperature. As a result, the PVA/MMT composite polymer appears to be a good candidate for the DMFC applications.     

Double cross-linked polyetheretherketone proton exchange membrane for fuel cell

The proton exchange membrane based on polyetheretherketone was prepared via two steps of cross-linking. The properties of the double cross-linked membrane (water uptake, proton conductivity, methanol permeability and thermal stability) have been investigated for fuel cell applications. The prepared membrane exhibited relatively high proton conductivity, 3.2 × 10⁻² S cm⁻¹ at room temperature and 5.8 × 10⁻² S cm⁻¹ at 80 °C. The second cross-linking significantly decreased the water uptake of the membrane. The performance of direct methanol fuel cell was slightly improved as compared to Nafion^® 117 due to its low methanol permeability. The results indicated that the double cross-linked membrane is a promising candidate for the polymer electrolyte membrane fuel cell, especially for the direct methanol fuel cell due to its low methanol permeability and high stability in a methanol solution.     

Novel ultrathin composite membranes of Nafion/PVA for PEMFCs

The electrospinning approach is an easy and useful method to fabricate porous supports with tailored properties for the preparation of impregnated membranes with enhanced characteristics. Therein, this technique was used to obtain polyvinyl alcohol (PVA) nanofiber mats in which Nafion^® polymer was infiltrated. These Nafion/PVA membranes were characterized in their mechanical properties, proton conductivity and fuel cell performance. Conductivity of the composite membranes was below the showed by pristine Nafion^® due to the non-ionic conducting behaviour of the PVA phase, although the incorporation of the PVA nanofibers strongly reinforced the mechanical properties of the membranes. Measurements carried out in a single cell fed with H₂/Air confirmed the high performance exhibited by a 19 μm thick nanofiber reinforced membrane owing to its low ionic resistance. These reasons make ultrathin (<20 μm) Nafion/PVA composite membranes promising candidates as low cost ion-exchange membranes for fuel cell applications.     

Optimal thermal treatment conditions for durability improvement of highly sulfonated poly(ether ether ketone) membrane for polymer electrolyte fuel cell applications

In this study, a series of sulfonated poly(ether ether ketone) (SPEEK) membranes are prepared and thermally treated in different conditions, i.e., temperature (120–180 °C), time (6–42 h), and residual solvent (RS) values (15–45%). Proton conductivity, water uptake, swelling ratio, hydrogen permeability, mechanical properties, and chemical stability of samples are systematically investigated. Also, membranes' characteristics are studied using FTIR, TGA, and AFM. Two stages of “annealing dominated” and “cross-linking dominated” were observed during thermal treatment. Annealing dominated samples exhibited higher flexibility and overall stability with annealing-induced homogenous microstructure while cross-linking dominated samples showed poor mechanical properties and proton conductivity. Results indicate that the treatment of SPEEK membranes with higher RS value facilitates cross-linking at much lower temperatures with a more controlled rate to inhibit excessive cross-linking. Furthermore, response surface methodology suggested that prolonged thermal treatment at low temperatures (<130 °C) with RS of around 30% results in sufficient proton conductivity and improved overall stability.     

KOH modified Nafion112 membrane for high performance alkaline direct ethanol fuel cell

A polymer electrolyte membrane for alkaline direct ethanol fuel cell (ADEFC) was prepared by dipping Nafion112 membrane into KOH solution for some time at room temperature. The obtained membrane (Nafion112/KOH) exhibited higher mechanical properties and thermal stability than Nafion112 membrane. The ionic conductivity of Nafion112/KOH in 1 M, 2 M and 6 M KOH solutions was 0.011 S/cm, 0.026 S/cm, 0.032 S/cm, respectively, depending on internal OH⁻ concentration and the volume fraction of the internal aqueous phase. Single cell performance suggested that active ADEFC with Nafion112/KOH membrane can deliver a peak power density of 58.87 mW/cm² at 90 °C, meanwhile, it can stably run for at least 12 h above 0.2 V. On the other hand, Pt-free air breathing ADEFC with Nafion112/KOH can output a peak power density of 11.5 mW/cm² at 60 °C, and the corresponding lifetime was as long as 473 h above 0.3 V.     

Facile synthesis of poly (arylene ether ketone)s containing flexible sulfoalkyl groups with enhanced oxidative stability for DMFCs

After tethering sodium 2-mercaptoethanesulfonate (MTS) to the bromomethylated poly(arylene ether ketone) precursor, a novel clustered sulfonated poly(arylene ether ketone) containing flexible sulfoalkyl groups (MTSPAEK) was prepared and used as polymer electrolyte membrane for application in DMFCs. The chemical structure and the degree of grafting of MTSPAEK copolymers were identified by ¹H NMR spectra. The resulted MTSPAEK copolymers exhibited excellent thermal stability (T_d5% > 259 °C) and good mechanical properties (tensile strength at break > 52 MPa). Compared to conventional sulfonated aromatic hydrocarbon polymers, MTSPAEK membranes displayed enhanced oxidative stability in Fenton's reagent owing to the elimination of free radicals by the sulfide groups located on the polymer side chains. Especially, MTSPAEK-2.10 with the highest content of flexible sulfoalkyl groups exhibited a highest proton conductivity of 0.181 S cm⁻¹ at 80 °C. It could be attributed to the obvious hydrophilic/hydrophobic phase-separated structure within the membrane, which was confirmed by AFM images. Moreover, MTSPAEK-2.10 membrane performed a peak power density of 70 mW cm⁻² in DMFC when feeding with 2 M methanol at 80 °C, which was comparable to the performance of recast Nafion as reported. Therefore, the combination of good thermal stability and mechanical properties, good oxidative stability, and good methanol barrier performance of MTSPAEK membranes indicated that they have potential to be alternative materials for PEMs in DMFCs.     

A facile,effective thermal crosslinking to balance stability and proton conduction for proton exchange membranes based on blend sulfonated poly(ether ether ketone)/sulfonated poly(arylene ether sulfone)

The development of hydrocarbon polymer electrolyte membranes with high proton conductivities and good stability as alternatives to perfluorosulfonic acid membranes is an ongoing research effort. A facile and effective thermal crosslinking method was carried out on the blended sulfonated poly (ether ether ketone)/poly (aryl ether sulfone) (SPEEK/SPAES) system. Two SPEEK polymers with ion exchange capacities (IECs) of 1.6 and 2.0 mmol g^?1 and one SPAES polymer (2.0 mmol g^?1) were selected to create different blends. The effect of thermal crosslinking on the fundamental properties of the membranes, especially their physicochemical stability and electrochemical performance, were investigated in detail. The homogeneous and flexible thermally-crosslinked SPEEK/SPAES membranes displayed excellent mechanical toughness (27–46 Mpa), suitable water uptake (<60%), high dimensional stability (swelling ratio < 15%) and large proton conductivity (>120 mS cm^?1) at 80 °C. The thermal crosslinking membranes also show significantly enhanced hydrolytic (<2.5%) and oxidative stability (<2%). Fuel cell with t-SPEEK/SPAES (1:2:2) membrane achieves a power density of 665 mW cm^?2 at 80 °C.     

Novel cross-linked anion exchange membranes with diamines as ionic exchange functional groups and crosslinking groups

Two novel cross-linked anion exchange membranes (AEMs) for alkaline fuel cells (AFCs) were synthesized via nucleophilic substitution reactions. Brominated poly(2,5-bis(perfluorophenyl)-1,3,4-oxadiazole-co-allyl bisphenol), called as precursory polymer (PP), was synthesized by reaction of 2,5-bis(2,3,4,5,6-pentafluorophenyl)-1,3,4-oxadiazole (FPOx) and diallyl bisphenol A (DABPA) followed by bromination. Ethanediamine (EDA) and propane diamine (PDA) were introduced to PP to obtain cross-linked polymers EDA-PP and PDA-PP, respectively. The reactions between PP and diamines rolled the crosslinking and functionalizing process in one. The crosslinking process enhanced the thermal and mechanical stabilities of EDA-PP and PDA-PP, which were affected by the length of alkyl chains of diamines. Meanwhile, the conjugated system of PP extended the electron clouds around the amine groups, which improved the thermal stability and alkaline durability of quaternary ammonium (QA) groups. The solution casting membranes of EDA-PP and PDA-PP showed high ionic conductivities. The swelling ratios, TGA and AFM properties of the membranes also demonstrated their good mechanical and thermal stabilities.     

Development of PVA based micro-porous polymer electrolyte by a novel preferential polymer dissolution process

A micro-porous polymer electrolyte based on PVA was obtained from PVA–PVC based polymer blend film by a novel preferential polymer dissolution technique. The ionic conductivity of micro-porous polymer electrolyte increases with increase in the removal of PVC content. Finally, the effect of variation of lithium salt concentration is studied for micro-porous polymer electrolyte of high ionic conductivity composition. The ionic conductivity of the micro-porous polymer electrolyte is measured in the temperature range of 301–351 K. It is observed that a 2 M LiClO₄ solution of micro-porous polymer electrolyte has high ionic conductivity of 1.5055 × 10⁻³ S cm⁻¹ at ambient temperature. Complexation and surface morphology of the micro-porous polymer electrolytes are studied by X-ray diffraction and SEM analysis. TG/DTA analysis informs that the micro-porous polymer electrolyte is thermally stable upto 277.9 °C. Chronoamperommetry and linear sweep voltammetry studies were made to find out lithium transference number and stability of micro-porous polymer electrolyte membrane, respectively. Cyclic voltammetry study was performed for carbon/micro-porous polymer electrolyte/LiMn₂O₄ cell to reveal the compatibility and electrochemical stability between electrode materials.     

4-Aminopyridine grafted sulfonated poly(arylene ether ketone sulfone) proton exchange membrane with high relative selectivity for fuel cells

A series of sulfonated poly(arylene ether ketone sulfone)s polymer having a degree of sulfonation of 80% and a carboxyl group in the side chain (C-SPAEKS) were prepared by polycondensation. The 4-aminopyridine grafted sulfonated poly(arylene ether ketone sulfone)s polymer membranes (SPPs) were prepared by amidation reaction with the carboxyl group to immobilize 4-aminopyridine on the side chain. The ¹H NMR results and Fourier transform infrared of SPP membranes demonstrated the successful grafting of the 4-aminopyridine. Proton conductivity, water absorption, swelling ratio, and thermal stability of different proportions of SPP membranes were investigated under the different conditions. With the increase of pyridine grafting content, the methanol permeability coefficient of the membrane decreased significantly from 8.17 × 10⁻⁷ cm²s⁻¹ to 8.92 × 10⁻⁸ cm²s⁻¹ at 25 °C. And, the proton conductivity and relative selectivity of the membrane were positively correlated with the grafted pyridine content. Among them, the SPP-4 membrane exhibited the highest proton conductivity of 0.088 Scm⁻¹ at 100 °C. The relative selectivity increased from 4.73 × 10⁴ S scm⁻³ to 9.84 × 10⁴ S scm⁻³.     

Synthesis and characterization of a long side-chain double-cation crosslinked anion-exchange membrane based on poly(styrene-b-(ethylene-co-butylene)-b-styrene)

By choosing a triple block polymer, poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS), as the backbone and adopting a long side-chain double-cation crosslinking strategy, a series of SEBS-based anion-exchange membranes (AEMs) was successively synthesized by chloromethylation, quaternization, crosslinking, solution casting, and alkalization. The 70C16-SEBS-TMHDA membrane showed high OH⁻ conductivity (72.13 mS/cm at 80 °C) and excellent alkali stability (only 10.86% degradation in OH⁻ conductivity after soaking in 4-M NaOH for 1700 h at 80 °C). Furthermore, the SR was only 9.3% at 80 °C and the peak power density of the H₂/O₂ single cell was up to 189 mW/cm² at a current density of 350 mA/cm² at 80 °C. By introducing long flexible side chains into a polymer SEBS backbone, the structure of the hydrophilic–hydrophobic microphase separation in the membrane was constructed to improve the ionic conductivity. Additionally, network crosslinked structure improved dimensional stability and mechanical properties.