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In this study, polymeric membranes composed of ionic liquid (IL), 1-ethyl-3-methylimidazolium tetrafluoroborate supported sulfonated poly(ether ether ketone) (SPEEK), and chitosan (CS) were prepared as novel promising solid polymer electrolytes (SPEs). First, the SPEEK polymer matrix was obtained by sulfonation of the PEEK polymer backbone. A composite membrane series (SPEEK/CS/IL-(1–4)) was created by adding CS at varying weight ratios according to the SPEEK. Structural, thermal, mechanical, and morphological characterizations were performed by FTIR, TGA, DMA, and SEM, respectively. Proton conductivity and dielectric measurements were performed over a wide temperature range to evaluate electrochemical properties. Composite membranes were stable for electrochemical processes at average temperatures. Storage modules have also improved with the addition of CS. All composite membranes showed ionic conductivities greater than 1 × 10 −4 S.cm −1 , and the maximum conductivity was measured for SPEEK/CS/IL-4 as 9.87 × 10 −3 S.cm −1 . Proton conductivity and dielectric tests showed that the SPEEK/CS/IL membrane series was presented as a novel SPE candidate.

Sulfonated poly (ether ether ketone) (SPEEK) has received substantial attention for its potential to improve the electrochemical behavior and thermomechanical capabilities of direct methanol fuel cells. This study examines how the integration by solution casting of microcrystalline cellulose (MCC) and 2,3-dialdehyde cellulose (DAC) onto highly sulfonated PEEK (with a sulfonation degree of 80%) affects its physicochemical properties and morphological structures. The mechanical attributes and proton conductivity of the polymer matrix are impacted by MCC and DAC inclusion into SPEEK membrane. The maximum proton conductivity was seen in the SPEEK/MCC membranes at 70 °C (up to 0.1 S cm−1). The proton conductivity in methanol vapor was increased by SPEEK/DAC membranes at high temperatures as opposed to pristine SPEEK and SPEEK/MCC membranes.

It is of great importance to improve the proton conductivity of proton exchange membranes by easy-handling and cost-efficient approaches. In this work, we incorporated a commercially obtained surfactant, sodium dodecyl benzene sulfonate (SDBS), into sulfonated poly(ether ether ketone) (SPEEK) through solution casting to prepare SPEEK/SDBS membranes. When no more than 10 wt % SDBS was added, the SDBS was well dissolved into the SPEEK matrix, and the activation energy for the proton transfer in the SPEEK/SDBS membranes was greatly reduced, leading to significant enhancement of the membrane proton conductivity. Compared with the SPEEK control membrane, the SPEEK/SDBS membrane with 10 wt % SDBS showed a 78% increase in proton conductivity, up from 0.051 S cm−1 to 0.091 S cm−1, while the water uptake increased from 38% to 62%. Moreover, the SPEEK/SDBS membrane exhibited constant proton conductivity under a long-term water immersion test.

Sulfonated poly(ether ether ketone) (SPEEK) is one of the most studied ionic polymers for polymer electrolyte membranes (PEMs) in fuel cells (PEMFCs). To improve its proton conductivity, novel SPEEK/praseodymium-doped zinc spinel ferrite composite membranes of 130–170 μm thickness were prepared via ultrasound-assisted dispersion of various proportions of synthesized doped ferrite nanoparticles into the polymer solution, followed by a simple solution-casting method. The morphology (as observed by SEM and confirmed by DMA) and the conducted physical and chemical tests typical for PEMs, such as water uptake (32–44% at 80 °C), ionic exchange capacity (1.67–1.80 mEq/g), chemical (around 1% loss in Fenton reagent after 24 h), thermal stability (up to 190 °C) and tensile strength (39–50 MPa), were proven to depend on the content of inorganic filler in the composite (up to 5%). The proton conductivity of composite membranes (0.21–2.82 × 10−2 S/cm at 80 °C) was assessed by broadband dielectric spectroscopy. The membrane with a content of 0.25 wt.% ZnFe1.96Pr0.04O4 showed the best proton conductivity (3.41 × 10−2 S/cm at 60 °C), as compared to 1.60 × 10−2 S/cm for Nafion117 measured under the same conditions, demonstrating its suitability as a PEM for fuel cell applications.

As a clean energy utilization device, full cell is gaining more and more attention. Proton exchange membrane (PEM) is a key component of the full cell. The commercial-sulfonated, tetrafluoroethylene-based fluoropolymer-copolymer (Nafion) membrane exhibits excellent proton conductivity under a fully humidified environment. However, it also has some disadvantages in practice, such as high fuel permeability, a complex synthesis process, and high cost. To overcome these disadvantages, a low-cost and novel membrane was developed. The sulfonated poly (ether ether ketone) (SPEEK) was selected as the base material of the proton exchange membrane. Sulfonated graphene (SG) was cross-linked with SPEEK through the elimination reaction of hydrogen bonds. It was found that the sulfonic acid groups and hydrophilic oxygen groups increased obviously in the resultant membrane. Compared with the pure SPEEK membrane, the SG-reinforced membrane exhibited better proton conductivity and methanol permeability prevention. The results indicate that the SG/SPEEK could be applied as a new proton exchange membrane in fuel cells.

A low cost cation exchange membrane to be used in a specific bioelectrochemical system has been developed using poly(ether ether ketone) (PEEK). This material is presented as an alternative to current commercial ion exchange membranes that have been primarily designed for fuel cell applications. To increase the hydrophilicity and ion transport of the PEEK material, charged groups are introduced through sulfonation. The effect of sulfonation and casting conditions on membrane performance has been systematically determined by producing a series of membranes synthesized over an array of reaction and casting conditions. Optimal reaction and casting conditions for producing SPEEK ion exchange membranes with appropriate performance characteristics have been established by this uniquely systematic experimental series. Membrane materials were characterized by ion exchange capacity, water uptake, swelling, potential difference and NMR analysis. Testing this extensive membranes series established that the most appropriate sulfonation conditions were 60 °C for 6 h. For mechanical stability and ease of handling, SPEEK membranes cast from solvent casting concentrations of 15%–25% with a resulting thickness of 30–50 µm were also found to be most suitable from the series of tested casting conditions. Drying conditions did not have any apparent impact on the measured parameters in this study. The conductivity of SPEEK membranes was found to be in the range of 10−3 S cm−1, which is suitable for use as a low cost membrane in the intended bioelectrochemical systems.

Proton exchange membranes are widely used in environmentally friendly applications such as fuel cells and electrochemical hydrogen compression. In these applications, an ideal proton exchange membrane should have both excellent proton conductivity and mechanical strength. Polymer proton exchange membranes, such as sulfonated poly(ether ether ketone) (SPEEK) membranes with high ion exchange capacity, can lead to higher proton conductivity. However, the ionic groups may reduce the interaction between polymer segments, lower the membrane’s mechanical strength, and even cause it to dissolve in water as the temperature exceeds 55 °C. The porous graphitic C3N4 (Pg–C3N4) nanosheet is an important two–dimensional polymeric carbon–based material and has a high content of –NH2 and –NH– groups, which can interact with the sulfonic acid groups in the sulfonated SPEEK polymer, form a more continuous proton transfer channel, and inhibit the movement of the polymer segment, leading to higher proton conductivity and mechanical strength. In this study, we found that a SPEEK membrane containing 3% Pg–C3N4 nanosheets achieves the optimized proton conductivity of 138 mS/cm (80 °C and 100% RH) and a mechanical strength of 74.1 MPa, improving both proton conductivity and mechanical strength by over 50% compared to the SPEEK membrane.

Thorium is a weak radioactive element, but the control of its concentration in natural aqueous systems is of great interest for health, because it is a toxic heavy metal. The present paper presents the recovery of thorium from diluted synthetic aqueous systems by nanofiltration. The membranes used for the nanofiltration of systems containing thorium species are composites containing 4′-Aminobenzo-15-crown-5 ether (ABCE) and sulfonated poly–etherether–ketone (sPEEK). The composite membranes (ABCE–sPEEK) were characterized by scanning electron microscopy (SEM), energy-dispersive X–Ray spectroscopy (EDAX), thermal analysis (TG and DSC), and from the perspective of thorium removal performance. To determine the process performance, the variables were the following: the nature of the composite membrane, the concentration of thorium in the aqueous systems, the rotation speed of the stirrer, and the pressure and the pH of the thorium aqueous system. When using pure water, a permeate flux value of 12 L·m−2 h−1 was obtained for the sPEEK membrane, and a permeate flux value of up to 15 L·m−2 h−1 was obtained for the ABCE–sPEEK composite membrane. The use of mechanical stirring, with a propeller stirrer, lead to an increase in the permeate flux value of pure water by about 20% for each of the studied membranes. Depending on the concentration of thorium and the pH of the feed solution, retentions between 84.9% and 98.4% were obtained. An important observation was the retention jump at pH 2 for the ABCE–sPEEK composite membrane. In the paper, a thorium ion retention mechanism is proposed for the sPEEK membrane and the ABCE–sPEEK composite membrane.

In this work, a composite adsorbent coating constituted by high SAPO 34 content and a sulfonated recycled poly (ether ether ketone) was investigated for adsorption heat pump technology. Specifically, the effect of polymer recycling on mechanical and thermal properties, as well as on water vapor adsorption and desorption performance, has been investigated. The degree of sulfonation obtained after 48 h of reaction remained approximately unaltered. The degradation of the polymer due to recycling anticipates the degradation of the C-C bonds of the polymer by about 20 °C without affecting the temperature at which the sulfonic groups degrade. From the mechanical point of view, the coating containing 90% zeolite, due to the use of recycled PEEK, evidenced a worsening of only 11.8% in scratch resistance compared to the virgin one, whereas the adhesive strength exhibited an increase of about 23.2% due to better miscibility of the sulfonated recycled polymer. Adsorption/desorption isobars show an almost similar adsorption capacity of the coating produced with recycled polymer compared to the virgin one, confirming that the water vapor diffusion is not hindered by the polymer matrix during the adsorption/desorption process.

Sulfonated poly(ether ether ketone) (SPEEK) materials are promising candidates for replacing Nafion™ in applications such as proton exchange membrane (PEM) and direct methanol fuel cells. SPEEK membranes have several advantages such as low cost, thermal and radiation stability and controllable physicochemical and mechanical properties, which depend on the degree of sulfonation (DS). Commercial PEEK was homogenously sulfonated up to a DS of 60–90% and the membranes were prepared using a solvent casting method. Part of the samples were irradiated with a 10 MeV electron beam up to a 500 kGy dose to assess the ionizing radiation-induced effects. Both non-irradiated and irradiated membranes were characterized by Fourier Transformation infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), proton nuclear magnetic resonance (1H-NMR) spectroscopy, electrochemical impedance analysis and, for the first time for non-irradiated membranes, by spectrophotometric analysis with Cr(III). The above-mentioned methods for application for DS assessment were compared. The aim of this study is to compare different methods used for the determination of the DS of SPEEK membranes before and after high-dose irradiation. It was observed that irradiated membranes presented a higher value of DS. The appearance of different new signals in 1H-NMR and FT-IR spectra of irradiated membranes indicated that the effects of radiation induced changes in the structure of SPEEK materials. The good correlation of Cr(III) absorption and SPEEK DS up to 80% indicates that the spectrophotometric method is a comparable tool for the characterization of SPEEK membranes.