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.     

Improving the proton conductivity of sulfonated poly (ether ether ketone) membranes by incorporating a crystalline nanoassembly of trimesic acid and melamine

A novel proton exchange membrane was synthesized by embedding a crystalline which was nano-assembled through trimesic acid and melamine (TMA·M) into the matrix of the sulfonated poly (ether ether ketone) (SPEEK) to enhance the proton conductivity of the SPEEK membrane. Fourier transform infrared indicated that hydrogen bonds existed between SPEEK and TMA·M. XRD and SEM indicated that TMA·M was uniformly distributed within the matrix of SPEEK, and no phase separation occurred. Thermogravimetric analysis showed that this membrane could be applied as high temperature proton exchange membrane until 250 °C. The dimensional stability and mechanical properties of the composite membranes showed that the performance of the composite membranes is superior to that of the pristine SPEEK. Since TMA·M had a highly ordered nanostructure, and contained lots of hydrogen bonds and water molecules, the proton conductivity of the SPEEK/TMA·M-20% reached 0.00513 S cm⁻¹ at 25 °C and relative humidity 100%, which was 3 times more than the pristine SPEEK membrane, and achieved 0.00994 S cm⁻¹ at 120 °C.     

Multi-functionalized acid-base double-shell nanotubes are incorporated into the proton exchange membrane to cope with low humidity conditions

Proton exchange membranes (PEM) with high proton conductivity and water retention are critical to the commercial application of proton exchange membrane fuel cells (PEMFC). In this study, acid-base double-shell nanotubes with carboxylate inner shell and an imidazole outer shell (DSNT-A@B) are synthesized via continuous distillation-precipitation polymerization using halloysite nanotubes (HNTs) as seeds. Then, it is incorporated into sulfonated poly (ether ether ketone) matrix to prepare composite membranes. The carboxylic inner shell can increase the content of combined water, thereby giving the composite membrane higher water retention. The imidazole shell acts as basic shell to create acid-base pairs with the membrane and inner shell to promote proton conductivity following the Grotthuss mechanism. The results show that when the blending amount is 5 wt%, the proton conductivity of the composite membrane reaches 0.336 S/cm at 80 °C and 100% relative humidity (RH), which is twice as high as that of the original membrane. In particular, the water loss of SPEEK/DSNT-A@B-10 composite membrane is only 54.55% at 40 °C and 20% RH, which is 32.77% lower than the SPEEK membrane. Therefore, this DSNT-A@B/SPEEK composite membrane can be used as a potential candidate for high temperature and low humidity fuel cells.     

Dielectric behaviour of UV-crosslinked sulfonated poly (ether ether ketone) with methyl cellulose (SPEEK-MC) as proton exchange membrane

Proton exchange membrane materials based on sulfonated poly ether ether ketone (SPEEK) with Methyl Cellulose (MC) are developed by solution cast technique and exposed to UV radiation with Bezoin Ethyl Ether (BEE) as photoinitiator. The addition of MC into SPEEK polymer enhances the conductivity up to 8.7 × 10^?3 Scm^?1 at 30 °C temperature and 80% relative humidity. This new crosslinked hybrid membrane shows good prospect for the use as proton exchange membrane in fuel cell.     

In-situ molecular-level hybridization enabling high-sulfonation-degree sulfonated poly(ether ether ketone) membrane with excellent anti-swelling ability and proton conduction

Sulfonated poly(ether ether ketone) (SPEEK) membrane with high sulfonation degree (SD) is a promising substitute of Nafion as proton exchange membrane (PEM), due to the excellent proton conductivity and low cost. However, its widespread application is limited by the inferior structural stability. Here, we report the fabrication of high SD SPEEK membrane with outstanding structural stability through an in-situ molecular-level hybridization method. Concretely, the ionic nanophase of SPEEK membrane is filled with precursors, which are then in-situ converted into polymer quantum dots (PQDs) by a microwave-assisted polycondensation process. In this manner, the micro-phase separation structure of SPEEK membrane is well maintained. PQDs with abundant hydrophilic functional groups together with the inherent –SO₃H groups impart hybrid membrane highly enhanced proton conductivity of 138.2 mS cm⁻¹ at 80 °C, which is comparable to Nafion. This then offers a 116.3% enhancement in device output power. Meanwhile, PQDs act as cross-linkers via generated electrostatic interactions with SPEEK, affording hybrid membrane with SD of 94.1% an ultralow swelling ratio of 1.35% at 25 °C, about 35 times lower than control membrane. More importantly, the in-situ molecular-level hybridization method is versatile, which can also boost the performances of chitosan (CS)-based membranes.     

Sulfonated poly(ether ether ketone)/poly(ether sulfone) composite membranes as an alternative proton exchange membrane in microbial fuel cells

Custom-made proton exchange membranes (PEM) are synthesized by incorporating sulfonated poly(ether ether ketone) (SPEEK) in poly(ether sulfone) (PES) for electricity generation in microbial fuel cells (MFCs). The composite PES/SPEEK membranes at various composition of SPEEK are prepared by the phase inversion method. The membranes are characterized by measuring roughness, proton conductivity, oxygen diffusion, water crossover and electrochemical impedance. The conductivity of hydrophobic PES membrane increases when a small amount (3–5%) of hydrophilic SPEEK is added. The electrochemical impedance spectra shows that the conductivity and capacitance of PES/SPEEK composite membranes during MFC operation are reduced from 6.15 × 10⁻⁷ to 6.93 × 10⁻⁵ (3197 Ω–162 Ω) and from 3.00 × 10⁻⁷ to 1.56 × 10⁻³ F, respectively when 5% of SPEEK added into PES membrane. The PES/SPEEK 5% membrane has the highest performance compared to other membranes with a maximum power density of 170 mW m⁻² at the maximum current density of 340 mA m⁻². However, the interfacial reaction between the membrane and the cathode with Pt catalyst indicates moderate reaction efficiency compared to other membranes. The COD removal efficiency of MFCs with composite membrane PES/SPEEK 5% is nearly 26-fold and 2-fold higher than that of MFCs with Nafion 112 and Nafion 117 membranes respectively. The results suggest that the PES/SPEEK composite membrane is a promising alternative to the costly perfluorosulfonate membranes presently used as separators in MFC systems.     

An effective strategy to enhance the performance of the proton exchange membranes based on sulfonated poly(ether ether ketone)s

We report an effective and facile approach to enhance the dimensional and chemical stability of sulfonated poly(ether ether ketone) (SPEEK) type proton exchange membranes through simple polymer blending for fuel cell applications, using commercial available materials. The polymeric blends with sulfonated poly(aryl ether sulfone)s (SPAES) were simply fabricated by a three-component system, which contained SPEEK (10–50 wt%, 1.83 mmol/g), and SPAES-40 (1.72 mmol/g)/SPAES-50 (2.04 mmol/g) at 1:1 in weight. The SPAES-40 was selected for mechanical and dimensional stability reinforcing, while SPAES-50 for the good polymer compatibility. The obtained SPEEK/SPAES blend membranes showed depressed water uptake, better dimensional and oxidative stability, together with higher proton conductivity beyond 70 °C than the pristine SPEEK membrane. The apparent improvements in membrane properties were associated with the homogeneous dispersion of SPEEK and both SPAES copolymers inside the membranes as well as the rearrangements of the polymeric chains. The SPEEK content should be properly controlled in the range of 10–40% (B10 to B40). In a H₂/O₂ fuel cell test, B30 showed a maximum power density of 700 mW/cm², which was 1.6 times as high as that of B40 at 80 °C under 100% RH. The further cross-linking treatment produced more ductile and enduring blend membranes, indicating an appreciable prospective for fuel cell applications.     

Crosslinked sulfonated poly(ether ether ketone) proton exchange membranes for direct methanol fuel cell applications

In the present study, a series of the crosslinked sulfonated poly(ether ether ketone) (SPEEK) proton exchange membranes were prepared. The photochemical crosslinking of the SPEEK membranes was carried out by dissolving benzophenone and triethylamine photo-initiator system in the membrane casting solution and then exposing the resulting membranes after solvent evaporation to UV light. The physical and transport properties of crosslinked membranes were investigated. The membrane performance can be controlled by adjusting the photoirradiation time. The experimental results showed that the crosslinked SPEEK membranes with photoirradiation 10 min had the optimum performance for proton exchange membranes (PEMs). Compared with the non-crosslinked SPEEK membranes, the crosslinked SPEEK membranes with photoirradiation 10 min markedly improved thermal stabilities and mechanical properties as well as hydrolytic and oxidative stabilities, greatly reduced water uptake and methanol diffusion coefficients with only slight sacrifice in proton conductivities. Therefore, the crosslinked SPEEK membranes with photoirradiation 10 min were particularly promising as proton exchange membranes for direct methanol fuel cell (DMFC) applications.     

Improved proton conduction of sulfonated poly (ether ether ketone) membrane by sulfonated covalent organic framework nanosheets

A type of sulfonated covalent organic framework nanosheets (TpPa-SO₃H) was synthesized via interfacial polymerization and incorporated into sulfonated poly (ether ether ketone) (SPEEK) matrix to prepare proton exchange membranes (PEMs). The densely and orderly arranged sulfonic acid groups in the rigid skeleton of the TpPa-SO₃H nanosheets, together with their high-aspect-ratio and well-defined porous structure provide proton-conducting highways in the membrane. The doping of TpPa-SO₃H nanosheets led to an increased ion exchange capacity up to 2.34 mmol g^?1 but a 2-folds reduced swelling ratio, remarkably mitigating the trade-off between high IEC and excessive swelling ratio. Based on the high IEC and orderly arranged proton-conducting sites, the SPEEK/TpPa–SO₃H–5 membrane exhibited the maximum proton conductivity of 0.346 S cm^?1 at 80 °C, 1.91-folds higher than the pristine SPEEK membrane. The mechanical strength of the composite membrane was also improved by 2.05-folds–74.5 MPa. The single H₂/O₂ fuel cell using the SPEEK/TpPa–SO₃H–5 membrane presented favorable performance with an open voltage of 1.01 V and a power density of 86.54 mW cm^?2.     

Cross-linked membranes based on sulfonated poly (ether ether ketone) (SPEEK)/Nafion for direct methanol fuel cells (DMFCs)

A series of cross-linked membranes based on SPEEK/Nafion have been prepared to improve methanol resistance and dimension stability of SPEEK membrane for the usage in the direct methanol fuel cells (DMFCs). Sulfonated diamine monomer is synthesized and used as cross-linker to improve the dispersion of Nafion in the composite membranes and decrease the negative effect of cross-linking on proton conductivity of membranes. FT-IR analysis shows that the cross-linking reaction is performed successfully. The effects of different contents of Nafion on the properties of cross-linked membranes are investigated in detail. All the cross-linked membranes show lower methanol permeability and better dimensional stability compared with the pristine SPEEK membrane. SPEEK-N30 with the 30 wt % Nafion shows a methanol permeability of 0.73 × 10⁻⁶ cm² s⁻¹ and a water uptake of 24.4% at 25 °C, which are lower than those of the pristine membrane. Meanwhile, the proton conductivity of SPEEK-N30 still remains at 0.041 S cm⁻¹ at 25 °C, which is comparable to that of the pristine SPEEK membrane. All the results indicate that these cross-linked membranes based on SPEEK/Nafion show good prospect for the use as proton exchange membranes.     

Sulfonated poly(ether ether ketone) as an ionomer for direct methanol fuel cell electrodes

Sulfonated poly(ether ether ketone) has been investigated as an ionomer in the catalyst layer for direct methanol fuel cells (DMFC). The performance in DMFC, electrochemical active area (by cyclic voltammetry), and limiting capacitance (by impedance spectroscopy) have been evaluated as a function of the ion exchange capacity (IEC) and content (wt.%) of the SPEEK ionomer in the catalyst layer. The optimum IEC value and SPEEK ionomer content in the electrodes are found to be, respectively, 1.33 meq. g⁻¹ and 20 wt.%. The membrane-electrode assemblies (MEA) fabricated with SPEEK membrane and SPEEK ionomer in the electrodes are found to exhibit superior performance in DMFC compared to that fabricated with Nafion ionomer due to lower interfacial resistance in the MEA as well as larger electrochemical active area. The MEAs with SPEEK membrane and SPEEK ionomer also exhibit better performance than that with Nafion 115 membrane and Nafion ionomer due to lower methanol crossover and better electrode kinetics.     

Enhanced proton conductivity of poly (arylene ether ketone sulfone) containing uneven sulfonic acid side chains by incorporating imidazole functionalized metal-organic framework

In this study, the side-chain type hybrid proton exchange membranes which based on metal-organic frameworks (MOFs) and organic matrix of sulfonated poly (arylene ether ketone sulfone) containing both long and short sulfonic acid side chains (S-C-SPAEKS) were prepared. MOF-801 was used as a template and then imidazole was encapsulated into MOF-801 as additional proton carriers. In imidazole -MOF-801, imidazole was used as a functional group to coordinate with the zirconium metal site of the functional group. Imidazole-MOF-801 and hybrid membranes were characterized by XRD, ¹H NMR and FT-IR. These hybrid membranes exhibited excellent proton conductivities and good thermal stabilities. Compared to pure S-C-SPAEKS (0.0487 S cm^?1 at 30 °C, 0.0809 S cm^?1 at 80 °C), S-C-SPAEKS/0.5% Im-MOF-801 showed a great improvement (0.1205 S cm^?1 at 30 °C, 0.1992 S cm^?1 at 80 °C), which was about 2.5 times higher than that of pure S-C-SPAEKS and 2 times higher than that of commercial Nafion117 (0.1003 S cm^?1 at 80 °C). The results indicated that imidazole functionalized MOFs and uneven side chain structure synergistically made an important contribution to proton transport. This series of hybrid membranes have the potential to be used as alternative proton exchange membranes.     

Sulfonated poly(ether ether ketone)/clay-SO3H hybrid proton exchange membranes for direct methanol fuel cells

A new type of sulfonated clay (clay-SO₃H) was prepared by the ion exchange method with the sulfanilic acid as the surfactant agent. The grafted amount of sulfanilic acid in clay-SO₃H was 51.8 mequiv. (100 g)⁻¹, which was measured by thermogravimetric analysis (TGA). Sulfonated poly(ether ether ketone) (SPEEK)/clay-SO₃H hybrid membranes which composed of SPEEK and different weight contents of clay-SO₃H, were prepared by a solution casting and evaporation method. For comparison, the SPEEK/clay hybrid membranes were produced with the same method. The performances of hybrid membranes for direct methanol fuel cells (DMFCs) in terms of mechanical and thermal properties, water uptake, water retention, methanol permeability and proton conductivity were investigated. The mechanical and thermal properties of the SPEEK membranes had been improved by introduction of clay and clay-SO₃H, obviously. The water desorption coefficients of the SPEEK and hybrid membranes were studied at 80 °C. The results showed that the addition of the inorganic part into SPEEK membrane enhanced the water retention of the membrane. Both methanol permeability and proton conductivity of the hybrid membranes decreased in comparison to the pristine SPEEK membrane. However, it was worth noting that higher selectivity defined as ratio of proton conductivity to methanol permeability of the SPEEK/clay-SO₃H-1 hybrid membrane with 1 wt.% clay-SO₃H was obtained than that of the pristine SPEEK membrane. These results showed that the SPEEK/clay-SO₃H hybrid membrane with 1 wt.% clay-SO₃H had potential usage of a proton exchange membrane (PEM) for DMFCs.     

Study on improvement of the selectivity of proton exchange membrane via incorporation of silicotungstic acid-doped silica into SPEEK

Nafion based proton exchange membrane (PEM) has long been used as conventional PEM in direct methanol fuel cell (DMFC) industry. However, the high cost of Nafion membrane and other drawbacks like high methanol crossover hinder the advancement of this industry. This study aims to develop a low cost membrane using sulfonated poly ether ether ketone (SPEEK) polymer. Silica and silicotungstic acid (SiWA) were incorporated into the membrane matrix using solution casting method. The optimum loading of the additives was tuned and it is discovered that the SPEEK membrane containing 10 wt% of silica and 5 wt% of SiWA has the best performance due to its high proton conductivity and moderately low methanol permeability. The performance of the membrane can further be enhanced by adding (3-aminopropyl)triethoxysilane (APTES) and carbonyldiimidazole (CDI) as coupling agents. Inclusion of APTES and CDI in SPEEK could not only improve the compatibility between organic SPEEK and inorganic additives, but also improve the homogeneity and dispersity of the additives. As a result, the resultant membrane with a better dimensional stability achieves high selectivity (10.60 × 10⁴ S.s/cm³) up to 6.5 times more than pristine SPEEK membrane and 1.3 times higher than the commercial Nafion 117 membrane.     

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 modification method to prepare crosslinked sulfonated poly(ether ether ketone)/silica hybrid membranes for fuel cells

Crosslinked organic-inorganic hybrid membranes are prepared from hydroxyl-functionalized sulfonated poly(ether ether ketone) (SPEEK) and various amounts of silica with the aims to improve dimensional stability and methanol resistance. The partially hydroxyl-functionalized SPEEK is prepared by the reduction of some benzophenone moieties of SPEEK into the corresponding benzhydrol moieties which is then reacted with (3-isocyanatopropyl)triethoxysilane (ICPTES) to get a side chained polymer bearing triethoxysilyl groups. These groups are subsequently co-hydrolyzed with tetraethoxysilane (TEOS) and allow the membrane to form a crosslinked network via a sol-gel process. The obtained hybrid membranes with covalent bonds between organic and inorganic phases exhibit much lower methanol swelling ratio and water uptake. With the increase of silica content, the methanol permeability coefficient of the hybrid membranes decreases at first and then increased. At silica content of about 6 wt.%, the methanol permeability coefficient reaches a minimum of 7.15 × 10⁻⁷ cm² s⁻¹, a 5-fold decrease compared with that of the pristine SPEEK. Despite the fact that the proton conductivity is decreased to some extent as a result of introduction of the silica, the hybrid membranes with silica content of 4-8 wt.% shows higher selectivity than Nafion117.     

Enhancement of fuel cell properties in polyethersulfone and sulfonated poly (ether ether ketone) membranes using metal oxide nanoparticles for proton exchange membrane fuel cell

The proton exchange membrane (PEM) was synthesized using polyethersulfone (PES), sulfonated poly (ether ether ketone) (SPEEK) and nanoparticles. The metal oxide nanoparticles such as Fe₃O₄, TiO₂ and MoO₃ were added individually to the polymer blend (PES and SPEEK). The polymer composite membranes exhibit excellent features regarding water uptake, ion exchange capacity and proton conductivity than the pristine PES membrane. Since the presence of sulfonic acid groups provides by added SPEEK and the unique properties of inorganic nanoparticles (Fe₃O₄, TiO₂ and MoO₃) helps to interconnect the ionic domain by the absorption of more water molecules thereby enhance the conductivity value. The proton conductivity of PES, SPEEK, PES/SPEEK/Fe₃O₄, PES/SPEEK/TiO₂ and PES/SPEEK/MoO₃ membranes were 0.22 × 10^?4 S/cm, 5.18 × 10^?4 S/cm, 3.57 × 10^?4 S/cm, 4.57 × 10^?4 S/cm and 2.67 × 10^?4 S/cm respectively. Even though the blending of PES with SPEEK has reduced the conductivity value to a lesser extent, hydrophobic PES has vital role in reducing the solvent uptake, swelling ratio and improves hydrolytic stability. Glass transition temperature (T_g) of the membranes were determined from DSC thermogram and it satisfies the operating condition of fuel cell system which guarantees the thermal stability of the membrane for fuel cell application.     

Investigation of the effects of AMPS-modified nanoclay on fuel cell performance of sulfonated aromatic proton exchange membranes

Here we describe preparation and characterization of a series of nanocomposite polyelectrolytes based on partially sulfonated poly (ether ether ketone) (SPEEK) and organically modified montmorillonite (MMT). Optimum degree of sulfonation for SPEEK is selected based on its transport properties. MMT is modified via ion exchange reaction using a 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as a functional modifier. AMPS-MMT at different loadings is introduced into the SPEEK matrices via the solution intercalation technique. Also, the nanocomposite membranes are fabricated using SPEEK and commercially available nanoclays like Cloisite Na (Na-MMT) and Cloisite 15A. Transport properties, proton conductivity and methanol permeability of the fabricated composite membranes are evaluated. Presence of AMPS-MMT significantly decreases the activation energy needed for proton conductivity. A membrane based on SPEEK/AMPS-MMT-3 wt% is selected as an optimum formulation which exhibits a high selectivity and power density at the elevated methanol concentrations. Moreover, it is found that the optimum nanocomposite membrane not only provides higher power output compared to the neat SPEEK and Nafion^®117 membranes, but also exhibits a higher open circuit voltage (OCV) in comparison with pristine SPEEK and commercial Nafion^® 117 membranes. Owing to the desirable transport and electrochemical properties SPEEK/AMPS-MMT nanocomposite can be considered as an alternative membrane for direct methanol fuel cell applications.     

Sulfonated poly(ether ether ketone) membranes with sulfonated graphene oxide fillers for direct methanol fuel cells

Sulfonated organosilane functionalized graphene oxides (SSi-GO) synthesized through the grafting of graphene oxide (GO) with 3-mercaptopropyl trimethoxysilane and subsequent oxidation have been used as a filler in sulfonated poly(ether ether ketone) (SPEEK) membranes. The incorporation of SSi-GOs greatly increases the ion-exchange capacity (IEC), water uptake, and proton conductivity of the membrane. With well-controlled contents of SSi-GOs, the composite membranes exhibit higher proton conductivity and lower methanol permeability than Nafion^® 112 and Nafion^® 115, making them particularly attractive as proton exchange membranes (PEMs) for direct methanol fuel cells (DMFC). The composite membrane with optimal SSi-GOs content exhibit over 38 and 17% higher power densities, respectively, than Nafion^® 112 and Nafion^® 115 membranes in DMFCs, offering the possibilities to reduce the DMFC membrane cost significantly while keeping high-performance.     

Sulfonated titania submicrospheres-doped sulfonated poly(ether ether ketone) hybrid membranes with enhanced proton conductivity and reduced methanol permeability

Sulfonated titania submicrospheres (TiO₂-SO₃H) prepared through a facile chelation method are incorporated into sulfonated poly(ether ether ketone) (SPEEK) to fabricate organic-inorganic hybrid membranes with enhanced proton conductivity and reduced methanol permeability for potential use in direct methanol fuel cells (DMFCs). The pristine titania submicrospheres (TiO₂) with a uniform particle size are synthesized through a modified sol-gel method and sulfonated using 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt as the sulfonation reagent. The sulfonation process is confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectra (XPS). The hybrid membranes are systematically characterized in terms of thermal property, mechanical property, ionic exchange capacity (IEC), swelling behavior, and microstructural features. The methanol barrier property and the proton conductivity of the SPEEK/TiO₂-SO₃H hybrid membranes are evaluated. The presence of the fillers reduces methanol crossover through the membrane. Compared with the unsulfonated TiO₂-doped membranes, the TiO₂-SO₃H-doped ones exhibit higher proton conductivity due to the additional sulfonic acid groups on the surface of TiO₂. The hybrid membrane doped with 15 wt.% TiO₂-SO₃H submicrospheres exhibits an acceptable proton conductivity of 0.053 S cm⁻¹ and a reduced methanol permeability of 4.19 × 10⁻⁷ cm² s⁻¹.