Composite membranes based on a sulfonated poly(arylene ether sulfone) and proton-conducting hybrid silica particles for high temperature PEMFCs

The organic-inorganic composite membranes are prepared by inserting poly(styrene sulfonate)-grafted silica particles into a polymer matrix of sulfonated poly(arylene ether sulfone) copolymer. The first step consisted in using atom transfer radical polymerization method to prepare surface-modified silica particles grafted with sodium 4-styrenesulfonate, referred to as PSS-g-SiO₂. Ion exchange capacities up to 2.4 meq/g are obtained for these modified silica particles. In a second step, a sulfonated poly(arylene ether sulfone) copolymer is synthesized via nucleophilic step polymerization of sulfonated 4,4′-dichlorodiphenyl sulfone, 4,4′-dichlorodiphenyl sulfone and phenolphthalin monomers in the presence of potassium carbonate. The copolymer is blended with various amounts of silica particles to form organic-inorganic composite membranes. Esterification reaction is carried out between silica particles and the sulfonated polymer chains by thermal treatment in the presence of sodium hypophosphite, which catalyzed the esterification reaction. The water uptake, proton conductivity, and thermal decomposition temperature of the membranes are measured. All composite membranes show better water uptake and proton conductivity than the unmodified membrane. Moreover, the membranes are tested in a commercial single cell at 80 °C and 120 °C in humidified H₂/air under different relative humidity conditions. The composite membrane containing 10%(w/w) of PSS-g-SiO₂ particles, which have ester bonds between polymer chains and silica particles, showed the best performance of 690 mA cm⁻² at 0.6 V, 120 °C and 30 %RH, even higher than the commercial Nafion^® 112 membrane.     

The effective methanol-blocking and proton conductivity membranes based on sulfonated poly (ether ether ketone ketone) and polyorganosilicon with functional groups

To solve the conflict between high proton conductivity and low methanol crossover of pristine sulfonated aromatic polymer membranes, the polyorganosilicon doped sulfonated poly (ether ether ketone ketone) (SPEEKK) composite membranes were prepared by introducing polyorganosilicon additive with various functional groups into SPEEKK in this study. Scanning electron microcopy (SEM) images showed the obtained membranes were compact. No apparent agglomerations, cracks and pinholes were observed in the SEM images of composite membranes. The good compatibility between polymer and additive led to the interconnection, thus producing new materials with great characteristics and enhanced performance. Besides, the dual crosslinked structure could be formed in composite membranes through the condensation of silanols and the strong interaction between matrix and additive. The formation of dual crosslinked structure optimized the water absorption, enhanced the hydrolytic stability and oxidative stability of membranes. Especially, the incorporation of additive improved the strength and flexibility of composite membranes at the same time, meaning that the life of the composite membranes might be extended during the fuel cell operation. Meanwhile, the proton conductivity improved with increasing additive content due to the loading of more available acidic groups. It is noteworthy that at 25% additive loading, the proton conductivity reached a maximum value of 5.4 × 10⁻² S cm⁻¹ at 25 °C, which exceeded the corresponding value of Nafion^@ 117 (5.0 × 10⁻² S cm⁻¹) under same experimental conditions. The composite membrane with 20 wt% additive was found to produce the highest selectivity (1.22 × 10⁵ S cm⁻³) with proton conductivity of 4.70 × 10⁻² S cm⁻¹ and methanol diffusion coefficient of 3.85 × 10⁻⁷ cm² s⁻¹, suggesting its best potential as proton exchange membrane for direct methanol fuel cell application. The main novelty of our work is providing a feasible and environment-friendly way to prepare the self-made polyorganosilicon with various functional groups and introducing it into SPEEKK to fabricate the dual crosslinked membranes. This design produces new materials with outstanding performance.     

Long-term durable solid state electrolyte membranes based on a metal–organic framework with phosphotungstic acid confined in the mesoporous cages

In this study, phosphotungstic acid-encapsulated MIL-101 (Fe) (HPW@MIL-100 (Fe)) was synthesized by the in-situ direct hydrothermal method. Due to the large mesoporous cages and small microporous windows of MIL-100 (Fe), HPW could be well loaded and confined in the cages of MIL-100 (Fe). Furthermore, novel hybrid proton exchange membranes were fabricated by incorporating HPW@MIL-100 (Fe) into sulfonated poly (arylene ether ketone sulfone) containing carboxyl groups (C-SPAEKS) matrix. The structures of MIL-100 (Fe), HPW@MIL-100 (Fe), C-SPAEKS, and hybrid membranes were characterized by XRD and FT-IR. The HPW@MIL-100 (Fe), with a large amount of phosphotungstic acid in cages, could enhance the proton conductivities of hybrid membranes. The hybrid membrane with 4% content of HPW@MIL-100 (Fe) achieved a high proton conductivity of 0.072 S cm⁻¹ at 80 °C and 100% relative humidity, which was 1.8 times higher than that of pure C-SPAEKS (0.040 S cm⁻¹) at the same conditions. Meanwhile, the introduced HPW@MIL-100 (Fe) fillers improved the dimensional stability of hybrid membranes. These results indicate that introduction of MIL-100 (Fe) materials loaded with HPW plays an important role in improving the comprehensive performance and this series of hybrid membranes have potential as proton exchange membranes.     

Synthesis and properties of sulfonated poly(arylene ether ketone sulfone) containing amino groups/functional titania inorganic particles hybrid membranes for fuel cells

In this work, the organic-inorganic hybrid membranes were prepared. The synthesis and properties of the hybrid membranes were investigated. The sulfonated poly(arylene ether ketone sulfone) containing amino groups (Am-SPAEKS) was synthesized by nucleophilic polycondensation. The sol-gel method was used to prepared functional titania inorganic particles (L-TiO₂). The ¹H NMR and FT-IR were performed to verified the structure of Am-SPAEKS and L-TiO₂. The organic-inorganic hybrid membranes showed both good thermal stabilities and mechanical properties than that of Am-SPAEKS. The L-Am-15% membrane exhibited the highest Young's modulus (2262.71 MPa) and Yield stress (62.09 MPa). The distribution of L-TiO₂ particles was revealed by SEM. Compared to Am-SPAEKS, the hybrid membranes showed higher proton conductivities. The L-Am-15% exhibited the highest proton conductivity of 0.0879 S cm⁻¹ at 90 °C. The results indicate that the organic-inorganic hybrid membranes have potential for application in proton exchange membrane fuel cells.     

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.     

Crosslinked sulfonated poly(arylene ether sulfone)/silica hybrid membranes for high temperature proton exchange membrane fuel cells

Sulfonated poly(arylene ether sulfone) copolymer is synthesized via nucleophilic step polymerization of sulfonated 4,4′-dichlorodiphenyl sulfone, 4,4′-dichlorodiphenyl sulfone and phenolphthalin monomers in the presence of potassium carbonate. The copolymer is blended with various amounts of silica particles to form organic–inorganic composite membranes. Esterification reaction is carried out between silica particles and the sulfonated polymer chains by thermal treatment in the presence of sodium hypophosphite, which catalyzed the esterification reaction. The composition and incorporation of the sulfonated repeat unit are confirmed by ¹H NMR. The water uptake, proton conductivity, and thermal decomposition temperature of the membranes are measured. The silica content in the polymer matrix and the effect of esterification are evaluated. All composite membranes show better water uptake and proton conductivity than the unmodified membrane. Moreover, the membranes are tested in a commercial single cell at 80 °C and 120 °C in humidified H₂/air under different relative humidity conditions. The composite membrane containing 10% (w/w) silica shows the best performance among the prepared membranes especially under high temperature and low humidity conditions.     

PEMs with high proton conductivity and excellent methanol resistance based on sulfonated poly (aryl ether ketone sulfone) containing comb-shaped structures for DMFCs applications

Sulfonated poly (aryl ether ketone sulfone) polymers (SPAEKS-PSA X) with the comb-shaped structure were prepared by grafting with 1, 3-propanesultone (PSA). The successful synthesis of SPAEKS-PSA X was confirmed by the FT-IR spectra. The morphology of the membrane was investigated by the small angle X-ray scattering and the transmission electron microscopy. The nanophase separation was brought in a comb-shaped structure between the main chains and the propyl sulfonic acid groups. The SPAEKS-PSA 15 membrane exhibited the highest conductivity of 101 mS cm⁻¹ under 80 °C and 100% relative humidity conditions (100% RH). In addition, the methanol permeability coefficients of SPAEKS-PSA X membranes (7.56 × 10⁻⁷ to 9.44 × 10⁻⁷ cm² s⁻¹) were much lower compared to Nafion®117 (22.37 × 10⁻⁷ cm² s⁻¹). Meanwhile, the SPAEKS-PSA X membranes also displayed excellent mechanical properties (tensile modulus >30 MPa), thermal, oxidative stabilities and fuel cell performance. Considering the parameters above, especially the elevated proton conductivities as well as high methanol resistance, the comb-shaped structure is a promising design for DMFCs applications.     

Fabrication of a highly efficient polymer electrolyte membrane by embedding nanofibrous metal oxide in cell components

In this work, a high-performance polymer electrolyte membrane based on sulfonated polyether ether ketone (SPEEK) loaded with zirconium oxide nanofibres (ZrN) was fabricated. ZrN with an average diameter of 182 nm were prepared by pyrolysing electrospun polyacrylonitrile fibres embedded with a zirconium precursor. The weight percentage of added ZrN and the relevant performance of the hybrid membrane (e.g., proton conductivity, methanol permeability and fuel cell performance) were experimentally determined and verified. It was found that the SPEEK-ZrN hybrid membrane exhibited sufficient proton conductivity (25.9 mS cm⁻¹), low methanol permeability (1.64 × 10⁻⁷ cm² s⁻¹) and superior selectivity (15.8 × 10⁴ S s cm⁻³) at room temperature. Compared to a pure SPEEK membrane, the SPEEK-ZrNT-1.5 membrane showed 1.3 and 1.7 times higher current density and power density, respectively.     

Fluorene-containing poly(arylene ether sulfone)s with imidazolium on flexible side chains for anion exchange membranes

Anion exchange membranes with high ionic conductivity and dimensional stability attract a lot of research interests. In present study, a series of fluorene-containing poly(arylene ether sulfone)s containing imidazolium on the flexible long side-chain are synthesized via copolycondensation, Friedel-Crafts reaction, ketone reduction, and Menshutkin reaction sequentially. The membranes used for characterization and membrane electrode assembly are obtained by solution casting and ion exchange thereafter. The morphology of the membranes is studied via transmission electron microscopy, and the microphase separation is observed. The long side-chain structure is responsible for the distinct hydrophilic-hydrophobic microphase separation, which facilitates the transport of hydroxide ions in the membranes. The incorporation of imidazolium on the flexible long side-chain is favorable for the ionic aggregation and transport in the membranes. The resulted membranes exhibit high hydroxide conductivities in the range of 48.5–83.1 mS cm⁻¹ at 80 °C. All these membranes show good dimensional stability and thermal stability. The single cell performance shows a power density of 102.3 mW cm⁻² at 60 °C using membrane electrode assembly based-on one of the synthesized polymers.     

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.     

Construction of a new continuous proton transport channel through a covalent crosslinking reaction between carboxyl and amino groups

Sulfonated poly(arylene ether ketone sulfone) bearing pendant carboxylic acid groups (C-SPAEKS) and sulfonated poly(arylene ether ketone sulfone) containing amino groups (Am-SPAEKS) were used to prepare C-SPAEKS/Am-SPAEKS crosslinked membranes. ¹H NMR and Fourier transform infrared spectra proved that C-SPAEKS and Am-SPAEKS copolymers, as well as C-SPAEKS/Am-SPAEKS crosslinked membrane, were successfully synthesized. TEM images showed that a continuous proton transport channel formed after crosslinking. Thermogravimetric analysis curves demonstrated that the thermal property of the crosslinked membranes improved. The crosslinked membranes exhibited suitable mechanical properties at 25 and 80 °C. The methanol permeability of C-SPAEKS/Am-SPAEKS-40 was 2.35 × 10⁻⁷ cm² s⁻¹ at 60 °C, which was lower than that of C-SPAEKS (24.12 × 10⁻⁷ cm² s⁻¹) and Am-SPAEKS (17.91 × 10⁻⁷ cm² s⁻¹). The proton conductivity of C-SPAEKS/Am-SPAEKS-40 was 0.089 S cm⁻¹, which was higher than that of C-SPAEKS and Am-SPAEKS at 80 °C. The results proved that C-SPAEKS/Am-SPAEKS crosslinked membranes were potential proton exchange membranes for direct methanol fuel cell applications.     

Enhanced ion conductivity of sulfonated poly(arylene ether sulfone) block copolymers linked by aliphatic chains constructing wide-range ion cluster for proton conducting electrolytes

A series of sulfonated poly(arylene ether sulfone) block copolymers with aliphatic chains (SPAES-LA) to lend structural flexibility in the polymer backbone have been synthesized to prepare proton exchange membranes (PEMs) showing improved electrochemical performance and dimensional/oxidative stabilities. The SPAES-LAs, bearing different hydrophilic/hydrophobic segment lengths, are prepared via polycondensation and sulfonation reactions. The sulfonation reaction occurs in specific fluorenylidene units by using chlorosulfonic acid. The SPAES-LA membrane, fabricated by solvent casting method, exhibits remarkable dimensional/thermal stabilities. Moreover, proton conductivity of as-prepared SPAES-LA membranes demonstrates significant improvement with expansion of ion clusters which is due to the increased hydrophilic volume ratio. In particular, the SPAES-LA-X12Y28 membrane exhibited heightened proton conductivity of 158.4 mS cm⁻¹ as well as suitable dimensional stability and durability towards radical oxidation, due to an effective well-defined hydrophilic-hydrophobic interface. Furthermore, H₂/O₂ fuel cell performance using SPAES-LA-X12Y28 membrane achieves a maximum power density of 232.02 mW cm⁻², a result which points out that SPAES-LA membranes show great potential for applications of polymer electrolyte membrane.     

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.     

Robust proton exchange membrane for vanadium redox flow batteries reinforced by silica-encapsulated nanocellulose

High ion selectivity and mechanical strength are critical properties for proton exchange membranes in vanadium redox flow batteries. In this work, a novel sulfonated poly(ether sulfone) hybrid membrane reinforced by core-shell structured nanocellulose (CNC-SPES) is prepared to obtain a robust and high-performance proton exchange membrane for vanadium redox flow batteries. Membrane morphology, proton conductivity, vanadium permeability and tensile strength are investigated. Single cell tests at a range of 40–140 mA cm⁻² are carried out. The performance of the sulfonated poly(ether sulfone) membrane reinforced by pristine nanocellulose (NC-SPES) and Nafion® 212 membranes are also studied for comparison. The results show that, with the incorporation of silica-encapsulated nanocellulose, the membrane exhibits outstanding mechanical strength of 54.5 MPa and high energy efficiency above 82% at 100 mA cm⁻², which is stable during 200 charge-discharge cycles.     

Synthesizing spindle-shaped anion exchange membranes to improve conductivity and stability

High ionic conductivity and excellent alkaline stability are very important for solid electrolyte. Therefore, spindle-shaped anion exchange membranes (AEMs) based on poly (arylene ether ketone) and 1-Bromo-N,N,N-trimethylhexane-6-aminium bromide (Br-QA) have been prepared. The obtained Br-QA can be grafted with poly (arylene ether ketone) main chains to form micro-phase separation structure enhancing the ionic conductivity. Especially, the grafting quaternary ammonium (QA) cation groups are separated by alkyl bromine endows the AEMs with alkaline stability features. Simultaneously, the OH⁻ conductivity of the QA-PAEK-0.6 obtained membranes is 0.046 S/cm under fully hydrated conditions at 60 °C. After immersing into 1 M NaOH alkaline solution for 15 days at 60 °C, the anionic conductivity still high to 0.03 S/cm. Meanwhile, the poly (arylene ether ketone) backbones provide excellent mechanical properties and the Br-QA cation groups also possess good thermal stability, which satisfy the requirement of wide applications.     

Novel proton exchange membranes based on proton conductive sulfonated PAMPS/PSSA-TiO2 hybrid nanoparticles and sulfonated poly (ether ether ketone) for PEMFC

Nanocomposite membranes based on sulfonated poly (ether ether ketone) (SPEEK) and sulfonated core-shell TiO₂ nanoparticles were prepared. TiO₂ nanoparticles were sulfonated by redox polymerization method by using sodium styrene sulfonate (SSA) and 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) monomers. The resultant hybrid nanoparticles (PAMPS-gTiO₂ and PSSA-g-TiO₂) were introduced to SPEEK with a sulfonation degree of 68%. Grafting of sulfonated polymers onto TiO₂ nanoparticles enhanced the content of proton transport sites in the membrane, leading to an increase in proton conductivity and power density. Besides, the mechanical and dimensional stabilities of the nanocomposite membranes were also improved compared with pure SPEEK membrane. The maximum power density for membranes containing 7.5 wt% of PAMPS-gTiO₂ and PSSA-g-TiO₂ nanoparticles at 80 °C obtained 283 mW cm⁻² and 245 mW cm⁻², respectively.     

Novel cross-linked sulfonated poly (arylene ether ketone) membranes for direct methanol fuel cell

To prepare a cross-linked proton exchange membrane with low methanol permeability and high proton conductivity, poly (vinyl alcohol) is first blended with sulfonated poly (arylene ether ketone) bearing carboxylic acid groups (SPAEK-C) and then heated to induce a cross-linking reaction between the carboxyl groups in SPAEK-C and the hydroxyl groups in PVA. Fourier transform infrared spectroscopy is used to characterize and confirm the structure of SPAEK-C and the cross-linked membranes. The proton conductivity of the cross-linked membrane with 15% PVA in weight reaches up to 0.18 S cm⁻¹ at 80 °C (100% relative humidity), which is higher than that of Nafion membrane, while the methanol permeability is nearly five times lower than Nafion. The ion-exchange capacity, water uptake and thermal stability are investigated to confirm their applicability in fuel cells.     

Quinoxaline-based crosslinked membranes of sulfonated poly(arylene ether sulfone)s for fuel cell applications

A series of crosslinkable sulfonated poly(arylene ether sulfone)s (SPAESs) were synthesized by copolymerization of 4,4′-biphenol with 2,6-difluorobenzil and 3,3′-disulfonated-4,4′-difluorodiphenyl sulfone disodium salt. Quinoxaline-based crosslinked SPAESs were prepared via the cyclocondensation reaction of benzil moieties in polymer chain with 3,3′-diaminobenzidine to form quinoxaline groups acting as covalent and acid-base ionic crosslinking. The uncrosslinked and crosslinked SPAES membranes showed high mechanical properties and the isotropic membrane swelling, while the later became insoluble in tested polar aprotic solvents. The crosslinking significantly improved the membrane performance, i.e., the crosslinked membranes had the lower membrane dimensional change, lower methanol permeability and higher oxidative stability than the corresponding precursor membranes, with keeping the reasonably high proton conductivity. The crosslinked membrane (CS1-2) with measured ion exchange capacity of 1.53 mequiv. g⁻¹ showed a reasonably high proton conductivity of 107 mS/cm with water uptake of 48 wt.% at 80 °C, and exhibited a low methanol permeability of 2.3 × 10⁻⁷ cm² s⁻¹ for 32 wt.% methanol solution at 25 °C. The crosslinked SPAES membranes have potential for PEFC and DMFCs.     

Preparation and characterization of sulfonated PEEK-WC membranes for fuel cell applications: A comparison between polymeric and composite membranes

Sulfonated poly(etheretherketone) with a cardo group (SPEEK-WC) exhibiting a wide range of degree of sulfonation (DS) was used to prepare polymeric membranes and composite membranes obtained by incorporation of an amorphous zirconium phosphate sulfophenylenphosphonate (Zr(HPO₄)(O₃PC₆H₄SO₃H), hereafter Zr(SPP)) in a SPEEK-WC matrix. The nominal composition of the composite membranes was fixed at 20 wt% of Zr(SPP). Both types of membrane were characterized for their proton conductivity, methanol permeability, water and/or methanol uptake, morphology by SEM and mechanical properties. For comparison, a commercial Nafion 117 membrane was characterized under the same operative conditions. The composite membranes exhibited a reduced water uptake in comparison with the polymeric membranes especially at high DS values and temperature higher than 50 °C. As a result, the water uptake into composite membranes remained about constant in the range 20–70 °C. The methanol permeability (P) of both polymeric and composite membranes was always lower than that of a commercial Nafion 117 membrane. At 22 °C and 100% relative humidity (RH), the proton conductivities (σ) of the polymeric membranes increased from 6 × 10⁻⁴ to 1 × 10⁻² S cm⁻¹ with the increase of DS from 0.1 to 1.04. The higher conductivity value was comparable with that of Nafion 117 membrane (3 × 10⁻² S cm⁻¹) measured under the same operative conditions. The conductivities of the composite membranes are close to that of the corresponding polymeric membranes, but they are affected to a lesser extent by the polymer DS. The maximum value of the σ/P ratio (about 7 × 10⁴ at 25 °C) was found for the composite membrane with DS = 0.2 and was 2.5 times higher than the corresponding value of the Nafion membrane.     

Nanocomposite membrane based on SPEEK as a perspectives application in electrochemical hydrogen compressor

Achieving favourable proton exchange membrane characteristics such as proton conduction, mechanical properties and hydrogen crossover is one of the main challenges in development of Electrochemical Hydrogen Compressor (EHC) systems for improving energy consumption. This work demonstrates three different in-house fabricated membranes based on Sulphonated poly (ether-ether ketone, SPEEK). The first membrane is an unmodified membrane ([S70]), second membrane ([S70/HNT15], 15 % wt/wt) was modified with a nanoclay (Halloysite Nanotubes, HNT), and last membrane is Halloysite nanotubes impregnated with Phosphotungstic Acid ([S70/(PWA/HNT30)15]). These membranes show different hydrogen crossover rate, with the [S70] membrane exhibiting 3.873 × 10⁻⁰⁸ mol bar⁻¹s⁻¹cm⁻² whereas the [S70/HNT15] and [S70/(PWA/HNT30)15] nanocomposite membranes show rates of 7.296 × 10⁻¹⁰ and 9.103 × 10⁻¹⁰ mol bar⁻¹ s⁻¹ cm⁻², respectively. Furthermore, unmodified membrane presented quadratic behaviours with increased pressure in cathodic compartment, whereas nanocomposite membranes exhibit a logarithmic behaviour. For another hand, extrapolation data show that unconventional nanocomposites membranes present a low energy consumption at high pressures, which is promising for potential candidates for use in EHC systems.