Sulphonated (PVDF-co-HFP)-graphene oxide composite polymer electrolyte membrane for HI decomposition by electrolysis in thermochemical iodine-sulphur cycle for hydrogen production

In overall iodine-sulphur (I-S) cycle (Bunsen reaction), HI decomposition is a serious challenge for improvement in H₂ production efficiency. Herein, we are reporting an electrochemical process for HI decomposition and simultaneous H₂ and I₂ production. Commercial Nafion 117 membrane has been generally utilized as a separator, which also showed huge water transport (electro-osmosis), and deterioration in conductivity due to dehydration. We report sulphonated poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) (SCP) and sulphonated graphene oxide (SGO) composite stable and efficient polymer electrolyte membrane (PEM) for HI electrolysis and H₂ production. Different SCP/SGO composite PEMs were prepared and extensively characterized for water content, ion-exchange capacity (IEC), conductivity, and stabilities (mechanical, chemical, and thermal) in comparison with commercial Nafion117 membrane. Most suitable optimized SCP/SGO-30 composite PEM exhibited 6.78 × 10^?2 S cm^?1 conductivity in comparison with 9.60 × 10^?2 S cm^?1 for Nafion® 117. The electro-osmotic flux ofSCP/SGO-30 composite PEM (2.53 × 10^?4 cm s^?1) was also comparatively lower than Nafion® 117 membrane (2.75 × 10^?4 cm s^?1). For HI electrolysis experiments, SCP/SGO-30 composite PEM showed good performance such as 93.4% current efficiency (η), and 0.043 kWh/mol-H₂ power consumption (Ψ). Further, intelligent architecture of SCP/SGO composite PEM, in which hydrophilic SGO was introduced between fluorinated polymer by strong hydrogen bonding, high efficiency and performance make them suitable candidate for electrochemical HI decomposition, and other diversified electrochemical processes.     

Proton conductivity and performance in fuel cells of grafted membranes based on polymethylpentene with radiation-grafted crosslinked sulfonated polystyrene

In this work, a comparative study was carried out of the transport properties and performance in a hydrogen-air fuel cell of the membranes based on polymethylpentene (PMP) with grafted sulfonated polystyrene and the standard Nafion® 212 membrane. Grafted cation-exchange membranes (GCM) were obtained by radiation graft post-polymerization of styrene onto UV-exposed PMP film followed by sulfonation with chlorosulfonic acid. The proton-conductivity of the GCM membrane with an ion-exchange capacity of 2.9 ± 0.1 meq/g reaches 21 ± 1 mS cm^?1 at room temperature and 95% relative humidity, which is twice higher the conductivity of the Nafion® under the same conditions. The GCM-1 H₂-permeability of 2.06?10^?7 cm² s^?1 even slightly lower than that of the Nafion® 212 (2.14?10^?7 cm² s^?1). A comparison of these membranes in the membrane electrode assemblies (MEA) of hydrogen-air fuel cells (FC) shows that the use of the grafted membranes with the high ion-exchange capacity is highly promising. The maximum performance of FC with grafted and Nafion® 212 membrane are both close to 180 mW/cm² at the current density of 400 mA/cm². At the same time, the high degree of crosslinking of sulfonated polystyrene leads to a decrease in conductivity and does not give an advantage in gas permeability.     

Proton exchange membrane from the blend of poly(vinylidene fluoride) and functional copolymer: Preparation,proton conductivity,methanol permeability,and stability

A polymer electrolyte membrane is considered as the heart of fuel cells. Here we report the preparation of proton exchange membranes (PEMs) of poly (vinylidene fluoride) (PVDF) blend poly (methyl methacrylate)-co-poly (sodium-4-styrene sulfonate) (PMMA-co-PSSNa) by solvent evaporation method. Three different types of PEMs have been prepared by using different ratios of PVDF and PMMA-co-PSSNa copolymer. We have investigated the effect of concentration of PVDF on water uptake, ion exchange capacity, mechanical, thermal, and oxidative stability, proton conductivity (K^m), and methanol permeability (P_M) of the blend membranes. These blend PEMs showed good physicochemical and electrochemical properties along with thermal and oxidative stability. The membrane prepared from PVDF (45% w/w) to PMMA-co-PSSNa (55% w/w) exhibited optimum P_M at room temperature (8.38 × 10^?7 cm²s^?1). This low fuel crossover and high relative selectivity can make our prepared blend membranes a potential candidate in polymer electrolyte membrane fuel cells (PEMFCs) or direct methanol fuel cells (DMFCs).     

Phosphorylated chitosan/poly(vinyl alcohol) based proton exchange membranes modified with propylammonium nitrate ionic liquid and silica filler for fuel cell applications

In our previous work, phosphorylated chitosan was modified through polymer blending with poly(vinyl alcohol) (PVA) polymer to produce N-methylene phosphonic chitosan/poly(vinyl alcohol) (NMPC/PVA) composite membranes. The aim of this work is to further investigate the effects of a propylammonium nitrate (PAN) ionic liquid and/or silicon dioxide (SiO₂) filler on the morphology and physical properties of NMPC/PVA composite membranes. The temperature-dependent ionic conductivity of the composite membranes with various ionic liquid and filler compositions was studied by varying the loading of PAN ionic liquid and SiO₂-PAN filler in the range of 5–20 wt%. As the loading of PAN ionic liquid increased in the NMPC/PVA membrane matrix, the ionic conductivity value also increased with the highest value of 0.53 × 10^?3 S cm^?1 at 25 °C and increased to 1.54 × 10^?3 S cm^?1 at 100 °C with 20 wt% PAN. The NMPC/PVA-PAN (20 wt%) composite membrane also exhibited the highest water uptake and ion exchange capacity, with values of 60.5% and 0.60 mequiv g^?1, respectively. In addition, in the single-cell performance test, the NMPC/PVA-PAN (20 wt%) composite membrane displayed a maximum power density, which was increased by approximately 14% compared to the NMPC/PVA composite membrane with 5 wt% SiO₂-PAN. This work demonstrated that modified NMPC/PVA composite membranes with ionic liquid PAN and/or SiO₂ filler showed enhanced performance compared with unmodified NMPC/PVA composite membranes for proton exchange membrane fuel cells.     

Quantitative analysis of proton exchange membrane prepared by radiation-induced grafting on ultra-thin FEP film

Radiation-induced graft polymerization is introduced to effectively fabricate proton exchange membrane based on 12.5 μm fluorinated ethylene propylene (FEP) film. The graft side chains penetrate FEP film and distribute inside the bulk matrix evenly. The membranes exhibit hydrophilic/hydrophobic microphase-separated morphology as well as good thermal stability. The influences of irradiation parameters on the membrane property are investigated and the resulting membranes (named FEP-g-PSSA) exhibit excellent physicochemical properties. Membrane with 27.48% degree of graft and 130.1 mS cm^?1 proton conductivity is employed for fuel cell performance measurement. Under optimized operate conditions (80 °C, 75% relative humidity), the power density could reach up to 0.896 W cm^?2, inspiring for fuel cell application. The mass-transport-controlled polarization of membrane electrode assembly (MEA) based on FEP-g-PSSA membrane is higher than Nafion® 211 within the whole current density range and the gap is widening with increasing current density. At 2.0 A cm^?2, the mass transfer polarization of FEP-g-PSSA reaches up to 0.204 V, far higher than Nafion® 211 (0.084 V). By promoting the compatibility between the ionomer in the catalyst layer and FEP-g-PSSA membrane and optimizing the membrane/catalyst layer/gas diffusion layer interfaces, the fuel cell performance could be significantly enhanced, making the FEP-g-PSSA membranes promising in fuel cell application.     

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.     

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.     

Polybenzimidazole composite membranes containing imidazole functionalized graphene oxide showing high proton conductivity and improved physicochemical properties

Polymer composite membranes are fabricated using poly[2,2'-(m-phenylene)-5,5′-bibenzimidazole] (PBI) as a polymer matrix and imidazole functionalized graphene oxide (ImGO) as a filler material for high temperature proton exchange membrane fuel cell applications. ImGO is prepared by the reaction of o-phenylenediamine with graphene oxide (GO). The compatibility of ImGO with PBI matrix is found to be better than that of GO, and as a result PBI composite membrane having ImGO exhibits improved physicochemical properties and larger proton conductivity compared with pure PBI and PBI composite membrane having GO. For example, PBI composite membrane having 0.5 wt% of ImGO shows enhanced tensile strength (219.2 MPa) with minimal decrease of elongation at break value (28.8%) compared with PBI composite membrane having 0.5 wt% of GO (215.5 MPa, 15.4%) and pure PBI membrane without any filler (181.0 MPa, 34.8%). The proton conductivity of this membrane, at 150 °C under anhydrous condition, is 77.52 mS cm^?1.     

Macromolecule sulfonated Poly(ether ether ketone) crosslinked poly(4,4′-diphenylether-5,5′-bibenzimidazole) proton exchange membranes: Broaden the temperature application range and enhanced mechanical properties

Proton exchange membranes with a wide application temperature range were fabricated to start high-temperature fuel cells under room temperature. The volume swelling stability, oxidative stability as well as mechanical properties of crosslinked membranes have been improved for covalently crosslinking poly(4,4′-diphenylether-5,5′-bibenzimidazole) (OPBI) with fluorine-terminated sulfonated poly(ether ether ketone) (F-SPEEK) via N-substitution reactions. High proton conductivity was simultaneously realized at both high (80–160 °C) and low (40–80 °C) temperatures by crosslinking and jointly constructing hydrophilic-hydrophobic channels. The crosslinked membranes exhibited the highest proton conductivity of 191 mS cm⁻¹ at 80 °C under 98% relative humidity (RH) and 38 mS cm⁻¹ at 160 °C under anhydrous, respectively. Compared with OPBI membrane, the fuel cell performance of the crosslinked membranes showed higher peak power density at full temperature range (40–160 °C).     

Effects of phosphotungstic acid on performance of phosphoric acid doped polyethersulfone-polyvinylpyrrolidone membranes for high temperature fuel cells

Heteropoly acids have been employed to increase the proton conductivity of phosphoric acid (PA) doped polymer membranes for high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). In this work, we develop a new composite membrane based on phosphotungstic acid (PWA) doped polyethersulfone-polyvinylpyrrolidone (PES-PVP) matrix, forming PWA/PES-PVP composite membrane for HT-PEMFCs. The homogeneous distribution of PWA on the PES-PVP membrane enhances its mechanical strength. In addition, there is a strong interaction between PWA and PA that is confirmed experimentally by the attenuated total reflectance Fourier Transform Infrared spectroscopy and semi-empirical quantum mechanics calculation. This enhances not only the PA uptake but also the proton conductivity of the PWA/PES-PVP composite membrane. ¹H nuclear magnetic resonance spectroscopy results elucidate that the high proton conductivity of the PA doped PWA/PES-PVP membranes is due to their higher proton content and mobility compared to the pristine PA doped PES-PVP membrane. The best results are observed on the PES-PVP composite membrane with addition of 5 wt% PWA, reaching proton conductivity of 1.44 × 10^?1 S cm^?1 and a peak power density of 416 mW cm^?2 at 160 °C and anhydrous conditions. PWA additives increase the proton conductivity and cell performance, demonstrating significantly positive effects on the acid-base composite membranes for high temperature polymer electrolyte membrane fuel cell applications.     

Improved hydrogen permeation through thin Pd/Al2O3 composite membranes with graphene oxide as intermediate layer

Here we proposed the decreasing in the roughness of asymmetric alumina (Al₂O₃) hollow fibers by the deposition of a thin graphene oxide (GO) layer. GO coated substrates were then used for palladium (Pd) depositions and the composite membranes were evaluated for hydrogen permeation and hydrogen/nitrogen selectivity. Dip coating of alumina substrates for 45, 75 and 120 s under vacuum reduced the surface mean roughness from 112.6 to 94.0, 87.1 and 62.9 nm, respectively. However, the thicker GO layer (deposited for 120 s) caused membrane peel off from the substrate after Pd deposition. A single Pd layer was properly deposited on the GO coated substrates for 45 s with superior hydrogen permeance of 24 × 10⁻⁷ mol s⁻¹m⁻² Pa⁻¹ at 450 °C and infinite hydrogen/nitrogen selectivity. Activation energy for hydrogen permeation through the Al₂O₃/GO/Pd composite membrane was of 43 kJ mol⁻¹, evidencing predominance of surface rate-limiting mechanisms in hydrogen transport through the submicron-thick Pd membrane.     

SCTF nanosheets@sulfonated poly (p-phenylene-co-aryl ether ketone) composite proton exchange membranes for passive direct methanol fuel cells

The development of a simple and efficient methanol-resistant membrane strategy is of great significance for improvement of the performance of fuel cells, making it an attractive and challenging topic. In this work, sulfonated covalent triazine framework (SCTF) nanosheets are prepared by a micro-interface method and post-sulfonation, which show excellent dispersion in polar solutions, such as water and N, N-Dimethylacetamide (DMAc). Then a series of composite proton exchange membranes (SCTF-x@SPP-co-PAEKs) are prepared by blending these SCTF nanosheets with sulfonated micro-block copolymers (SPP-co-PAEKs) resin. The results show that the appropriate addition of SCTF can significantly improve the proton conductivity (PC), methanol resistance and fuel cell performance of the prepared composite membrane, which can be attributed to the good interfacial compatibility between the SCTF nanosheets and the sulfonated micro-block copolymer matrix. The passive direct methanol fuel cells (DMFCs) with SCTF-x@SPP-3 membrane exhibit power density in the range of 28.0–33.3 mW cm⁻² at 25 °C, which is superior to the related values of the pristine membrane and the commercial Nafion® series membranes.     

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.     

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.     

Study of deep oxidation and sulfonation of graphene oxide as low-temperature fuel cell electrolyte

In order improve the fuel cell performance of a free-standing graphene oxide (GO) membrane, the impacts of both the additional oxidation of GO and the modification with vinilsulfonic acid were investigated. The modification with vinilsulfonic acid was conducted with and without adding potassium persulfate, K₂S₂O₈, which is a radical initiator for the polymerization of vinylsulfonate. A total of six types of free-standing GO membranes with and without the oxidation and/or the modification were prepared. The oxidation and the modification additively increased the proton conductivity, and the oxidation significantly improved the durability of the fuel cell performance at 30 °C. The membrane of GOhvsi, of which GO was oxidized and modified with the initiator, showed very high in-plane proton conductivities at 30 °C, i.e., 0.54 S cm^?1 at RH 100%. The H₂–O₂ fuel cell using GOhvsi showed maximum power densities as high as 136 mW cm^?2 and 184 mW cm^?2 at 30 °C and 50 °C, respectively. The performance at 30 °C was stable for more than 20 h. The improved durability by the oxidation was attributed to the increased defects of carbon based on an XPS analysis. The TPD-MS analysis suggested that the oxygenated functional groups at the defects would increase the binding strength.     

High-performance SO2-depolarized electrolysis cell using advanced polymer electrolyte membranes

Three different proton conducting polymeric membrane materials (Nafion® 115, Nafion® 212, and sulfonated Diels-Alder polyphenylene [SDAPP]) were evaluated for use in SO₂-depolarized electrolyzers for the production of hydrogen via the hybrid sulfur cycle. Their performance was measured using different water feed strategies to minimize overpotential losses while maintaining high product acid concentration. Both thin membranes (Nafion® 212 and SDAPP) showed performance superior to that of the thicker Nafion® 115. The SDAPP membrane electrode assembly (MEA) performed well at higher acid concentrations, maintaining low ohmic and kinetic overpotentials. Finally, short-term (100-h) stability tests under constant current conditions showed minimal degradation for the SDAPP and Nafion® 212 MEAs. SDAPP MEA performance approached the targets needed to make the hybrid sulfur cycle a competitive process for hydrogen production (product acid concentration ≥65 wt% H₂SO₄ at ≤ 0.6-V cell potential and ≥0.5 A-cm^?2 current density).     

Simple design of PVA-based blend doped with SO4(PO4)-functionalised TiO2 as an effective membrane for direct borohydride fuel cells

Nanocomposite membranes for low-temperature fuel cells, specifically, direct borohydride fuel cells (DBFCs), are formulated from a ternary polymer blend of poly (vinyl alcohol), poly (vinyl pyrrolidone), and poly (ethylene oxide) with the incorporation of (SO₄–TiO₂) nanotubes and (PO₄–TiO₂) as doping agents. The functionalisation of TiO₂ is carried out by impregnation-calcination method. Structural and morphological characterisation by FTIR, TEM, SEM, EDX, ICP, and XRD confirmed the successful preparation of the doping materials and their incorporation into the polymer blend. The influence of SO₄–TiO₂ and PO₄–TiO₂ doping and their content on the physicochemical properties of the composite membranes is assessed. Water uptake and swelling degree gradually reduced to below 20% with increasing the concentration of TiO₂-based doping agent, while the ion exchange capacity raised 3.5 times compared to that of the undoped membrane. The increase of the doping agent content also increased the ionic conductivity, tensile strength and thermal stability of the membrane. DBFC using the composite membrane produced a maximum power density of 75 mW cm⁻², close to that using Nafion®117 membrane (81 mW cm⁻²) but at a significantly lower cost. The promising results obtained in this study pave the way for a simple, green and economic approach for the development of composite membranes for application in DBFCs.     

Enhanced hydrogen permeance through graphene oxide membrane deposited on asymmetric spinel hollow fiber substrate

Membranes of graphene oxide (GO) present suitable application for hydrogen (H₂) purification. The deposition of a selective and high permeable GO membrane on a proper substrate is still a challenge. Here we applied the vacuum-assisted method to deposit a GO layer on asymmetric spinel (MgAl₂O₄) hollow fibers. The synthetized GO showed a nanosheeted morphological structure and a relative high degree of oxidation. The hollow fibers were produced with dolomite and alumina as the ceramic starting material and showed the desired asymmetric pore size distribution, in addition to suitable bending strength, 54.88 ± 4.25 MPa, and average surface roughness, 180 ± 8.2 nm. A continuous GO layer of 1.7 ± 0.2 μm was deposited onto the fiber outer surface. The composite MgAl₂O₄/GO membrane presented H₂ permeance of 8.2 ± 0.0 × 10^?7 mol s^?1 m^?2 Pa^?1 at room temperature (approximately 25 °C) and 0.3 MPa of transmembrane pressure. Ideal hydrogen/nitrogen and hydrogen/carbon dioxide selectivity values were of 3.3 ± 0.0 and 11.4 ± 0.1, respectively.     

Development of crosslinked SEBS-based anion exchange membranes for water electrolysis: Investigation of the crosslinker effect

SEBS (styrene-b-(ethylene-co-butylene)-b-styrene)) is a non-aryl-ether-type tri-block copolymer widely used as an anion exchange membrane (AEM) material due to its excellent alkaline stability and phase separation properties. However, low tensile strength due to the aliphatic chains and the poor physical properties of the SEBS-based membranes limit their practical application for AEM water electrolysis (AEMWE) or AEM fuel cell (AEMFC). In this study, three types of crosslinked AEMs were prepared using bromohexyl pentafluorobenzyl SEBS as a polymer backbone, and three different crosslinkers, dimethyl amine (DMA), tetramethyl diaminohexane (TMHA), and tris(dimethyl aminomethyl) phenol (TDMAP). Once introduced, these crosslinking agents were converted into the corresponding conducting head groups. The thermal, chemical, physical, and electrical properties of the obtained crosslinked membranes were then investigated for use in AEMWE. In particular, the TDMAP-50x-SEBS membrane with 50% degree of crosslinking experienced hydrogen bonding with water and OH⁻ due to the presence of OH groups in the structure of the crosslinking agent (TDMAP). Because of this, the membrane showed an improved morphology and high conductivity (20 °C: 31.8 mS cm⁻¹, 80 °C: 109.9 mS cm⁻¹). In addition, TDMAP induced physical crosslinking by hydrogen bonding between molecules so that the corresponding membrane (TDMAP-50x-SEBS) exhibited high alkaline and oxidative stability and good mechanical properties. This SEBS-based membrane has a tensile strength of 18.0 MPa and Young's modulus of 165.14 MPa. The WE single-cell test (1 M KOH solution at 70 °C) using TDMAP-50x-SEBS also showed a cell performance of 1190 mA cm⁻² at 2.0 V. This is 126% higher than the cell performance measured for FAA-3-50, a commercialized AEM material, under the same conditions.     

Flexibly crosslinked and post-morpholinium-functionalized poly(2,6-dimethyl-1,4-phenylene oxide) anion exchange membranes

Morpholinium-functionalized cross-linked poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) anion exchange membranes were prepared using a crosslinking/post-functionalization method. 4,4'-(oxybis(ethane-2,1-diyl)) dimorpholine (OEDM) having a flexible long chain and hydrophilic ether bond was for the first time used as the crosslinker. The brominated PPO reacted with OEDM, forming a crosslinked structure and accomplishing partial functionalization. Further functionalization was carried out by immersion in N-methylmorpholine aqueous solution. The degree of crosslinking was controlled by varying the proportion of brominated PPO to OEDM because excessive bromomethyl groups ensured the occurrence of crosslinking reaction. The cross-linked structure promoted the formation of micro-phase separation and effectively limited swelling. The crosslinked membrane shows much higher conductivity and lower swelling ratio compared to non-crosslinked one at similar IEC. The highest hydroxide conductivity that the crosslinked membrane achieves is 35 mS cm⁻¹ at 20 °C. The power density for the H₂/O₂ single cell assembled with this membrane is up to 193 mW cm⁻². In addition, the crosslinked PPO-MmOH-Cr membrane exhibits good alkaline stability with conductivity loss of less than 15% after soaking in 1 M KOH for 96 h.