Tensile mechanical properties of sulfonated poly(ether ether ketone) (SPEEK) and BPO4/SPEEK membranes

A study to evaluate the tensile mechanical properties of sulfonated poly(ether ether ketone) (SPEEK) and BPO₄/SPEEK composite membranes has been carried out. It is aimed to give an assessment of these materials for applications in proton exchange membrane fuel cells. The stress–strain response of the membranes was measured as a function of the degree of sulfonation (DS) and the filler–matrix ratio. In addition, the effects of immersion in water at various temperatures were explored in situ by means of a homemade testing chamber fitted to the tensile analyzer. The results indicate that the DS has an important influence on the final mechanical behavior of the membranes. The introduction of the BPO₄ solid filler leads to deterioration in mechanical performance compared to unfilled SPEEK. A general picture of the microstructural features influencing the mechanical properties of SPEEK and BPO₄/SPEEK membranes is proposed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2380–2393, 2005     

Effect of thermal crosslinking process on membrane structure and PEM fuel cell applications performed with SPEEK-PVA blend membranes

One of the promising options in the pursuit of clean and sustainable energy is fuel cell technology. PEM fuel cell stands out among fuel cell technologies due to its high efficiency, compactness, and ability to be used in portable applications. SPEEK (with different sulfonation degrees) and PVA blend membranes, which are thought to create a good synergy for PEM fuel cell, were prepared by using the solution casting method. As a result of the weight loss experiments, it was understood that the membranes dissolve in water regardless of the degree of sulfonation. Thermal crosslinking was carried out to prevent the membrane dissolution in water, which is in continuous contact with water in the fuel cell. Dissolution was mostly prevented by means of the thermal crosslinking process. Changes in the physical, chemical, and mechanical structure of the membrane after thermal crosslinking were comparatively determined by fourier transform infrared (FTIR), thermogravimetric analysis – differential thermal analysis (TGA-DTA), differential scanning calorimetry (DSC), water uptake capacity, swelling property, ion exchange capacity (IEC), dynamic mechanical analysis (DMA), electrochemical impedance analysis and oxidative stability. In addition, single-cell performance tests were performed with the membrane that gave the best results in the characterization analyses. Analysis results showed that thermal crosslinking prevented the dissolution of membranes in water ingreat extent. In addition, it was determined that the thermally crosslinked membranes had a more stable structure.     

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.     

Investigation of self-humidifying membranes based on sulfonated poly(ether ether ketone) hybrid with sulfated zirconia supported Pt catalyst for fuel cell applications

A self-humidifying membrane based on sulfonated poly(ether ether ketone) (SPEEK) hybrid with sulfated zirconia (SO₄²⁻/ZrO₂, SZ) supported platinum catalyst (Pt-SZ catalyst) was synthesized for fuel cell applications. The SZ, a solid state superacid with hygroscopic properties and proton-conductive properties, was employed to synthesize the Pt-SZ catalyst. The self-humidifying membrane (SPEEK/Pt-SZ) was characterized by TEM, FT-IR, TGA and SEM coupled with EDX. The SPEEK/Pt-SZ membrane exhibited higher water uptake and proton conductivity than the plain SPEEK membrane. Consequently, the SPEEK/Pt-SZ self-humidifying membrane under dry operation showed a higher open circuit voltage (OCV) of 1.015 V and a maximum power density of 0.95 W cm⁻², relative to 0.96 V and 0.54 W cm⁻² for the plain SPEEK membrane. The incorporation of the catalytic, hygroscopic and proton-conductive Pt-SZ catalyst in the SPEEK matrix facilitated water balance and proton conduction, accordingly improved the single cell performance under dry operation. In addition, the enhanced OCV and the decreased area ohmic resistance confirmed the effect of Pt-SZ catalyst in the self-humidifying membrane on suppressing reactant crossover and the membrane self-humidification.     

Modified SPEEK membranes for direct ethanol fuel cell

Membranes with low ethanol crossover were prepared aiming their application for direct ethanol fuel cell (DEFC). They were based on (1) sulfonated poly(ether ether ketone) (SPEEK) coated with carbon molecular sieves (CMS) and (2) on SPEEK/PI homogeneous blends. The membranes were characterized concerning their water and ethanol solution uptake, water and ethanol permeability in pervaporation experiments and their performance in DEFC tests. The ethanol permeabilities for the CMS-coated (180 nm and 400 nm thick layers) SPEEK were 8.5 and 3.1 × 10⁻¹⁰ kg m s⁻¹ m⁻² and for the homogeneous SPEEK/PI blends membranes with 10, 20 and 30 wt.% of PI were 4.4, 1.0 and 0.4 × 10⁻¹⁰ kg m s⁻¹ m⁻² respectively, which is 2- to 50-fold lower than that for plain SPEEK (19 × 10⁻¹⁰ kg m s⁻¹ m⁻²). Particularly the SPEEK/PI membranes had substantially better performance than Nafion 117^® membranes in DEFC tests at 60 °C and 90 °C.     

The effect of sulfonic acid groups within a polyhedral oligomeric silsesquioxane containing cross-linked proton exchange membrane

In this study, polyhedral oligomeric silsesquioxane (POSS) moieties were incorporated into sulfonated poly(ether ether ketone) (SPEEK) to form a new cross-linked proton exchange membrane (PEM). The distribution of the POSS containing cross-linkers with or without sulfonic acid groups dictates the water behavior and connectivity of hydrophilic domains of the PEM. A PEM formed by incorporating 17.5 wt% of the cross-linker (containing POSS macromer and sulfonic acid groups) into SPEEK exhibits high proton conductivity (0.0153 S/cm), low methanol permeability (1.34 × 10⁻⁷ cm²/s), and high selectivity (1.14 × 10⁵ Ss/cm³).     

磺化聚醚醚酮磺化度的测定及其对质子交换膜性能的影响

以聚醚醚酮（PEEK）和浓硫酸为原料,采用后磺化法制备不同磺化度的磺化聚醚醚酮（SPEEK）。采用核磁共振法测定SPEEK的磺化度,并研究了磺化度对SPEEK质子交换膜性能的影响。结果表明：磺化度高于80％的SPEEK会发生过度溶胀,而磺化度为48％～65％范围的SPEEK膜表现出较好的质子传导率、阻醇性能及抗吸水性能。     

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.     

SPE water electrolysis with SPEEK/PES blend membrane

Sulfonated poly(ether ether ketone) (SPEEK) was blended with poly(ether sulfone) (PES) to make solid polymer electrolyte (SPE) membranes for hydrogen production via water electrolysis. The blend membranes were characterized in terms of proton conductivity and the swelling degree in water. Membrane electrode assemblies (MEA), with Ir anode and Pt cathode at the two side of the blended membrane, were prepared by a decal method. The effect of hot pressing conditions in fabricating the MEA and the influence of ionomers in the catalyst layers were investigated. The MEA, with an effective area of 4 cm², were tested using a single cell water electrolysis test stand. An electrolytic current of 1655 mA/cm² were obtained at 2 V and 80 °C with the SPEEK based MEA and under suitable fabrication conditions. The experimental results suggest that SPEEK/PES blend membrane could be an alternative to costly perfluorosulfonate membranes in SPE water electrolysis for hydrogen production.