Immobilized phosphotungstic acid for the construction of proton exchange nanocomposite membranes with excellent stability and fuel cell performance

Phosphotungstic acid (HPW) has a good potential as nanofillers in nanocomposite proton exchange membrane with the prerequisite of solving the leakage issue. It is immobilized onto mesoporous graphitic carbon nitride (mg-C₃N₄) nanosheets surface, and then incorporated into sulfonated poly (aryl ether sulfone) (SPAES) membrane. Structures of the HPW/mg-C₃N₄ nanocomposites and corresponding SPAES/HPW/mg-C₃N₄ membranes are characterized by spectroscopic techniques. Fundamental properties and fuel cell performance of the fabricated nanocomposite membranes, and the leakage of HPW are investigated. Along with the highly suppressed HPW leakage, the SPAES/HPW/mg-C₃N₄ membranes show improved dimensional stability, water affinity and physicochemical stability, as well as better proton conductivity and fuel cell performance. At 80 °C and 60–100% RH, the SPAES/HPW/mg–C₃N₄–1.5 membrane exhibits 2–3.6 times peak power densities (354.9–584.2 mW/cm²) of the pristine SPAES membrane, and proton conductivity of 203 mS/cm, dimensional change less than 7.5% and weight loss of 1.4% in Fenton oxidation test at 80 °C.     

Enhanced anhydrous proton conductivity of SPEEK/IL composite membrane embedded with amino functionalized mesoporous silica

The novel SP/IL/AMS composite membrane doped with amino-functionalized mesoporous silica (AMS) was successfully prepared. Sulfonated poly ether ether ketone (SPEEK, SP) was used as the polymer matrix and the ionic liquid (IL) was N-ethylimidazolium trifluoromethanesulfonate (EIm[Tfo]). Its properties were compared with SP/IL/NMS composite membrane doped with non-functionalized mesoporous silica (NMS). Fourier transform infrared spectroscopy (FT-IR) analysis indicated that the components in the composite membrane were bound by intermolecular forces. In addition, an acid-base interaction was formed between -NH₂ in AMS and -SO₃H in SPEEK. The acid-base pair is beneficial to proton conduction. The anhydrous proton conductivity of SP/IL/3-AMS-7.5 composite membrane is about 4 times higher than that of the SP/IL/NMS-7.5. In addition, the good interfacial compatibility between AMS and polymer matrix is conducive for creation continuous proton transfer channel. Thermogravimetric analysis (TG) showed that all composite membranes were stable at 270 °C. The leaching of IL data indicated that IL can be effectively retained due to the presence of -OH and -NH₂ on the NMS and AMS surfaces. The SP/IL/AMS composite membrane could be used in proton exchange membrane fuel cells under medium temperature and anhydrous conditions.     

High performance composite membranes with enhanced dimensional stability for use in PEMFC

Sulfonated poly(sulfide sulfone) (SPSSF)/porous polytetrafluoroethylene (PTFE) reinforced composite membranes were prepared from a mixed solvent containing n-butanol and DMSO. To improve their dimensional stability, SPSSF/PTFE membranes were further oxidized to obtain sulfonated poly(phenylene sulfone) (SPSO2)/PTFE composite membranes under an optimized H₂O₂ oxidation procedure in acidic medium. Thin composite membranes with good mechanical stability can be fabricated due to the PTFE reinforcement. SEM and FTIR indicated the sulfonated polymers were fully impregnated into the expanded PTFE. SPSO2/PTFE membranes show better thermal and dimensional stability than SPSSF/PTFE membranes. Both composite membranes exhibited very excellent single cell performance. A maximum power density of 1.34 W cm⁻² for the SPSO2/PTFE membrane was obtained at 80 °C and 100 RH%.     

Improving the proton conductivity of proton exchange membranes via incorporation of HPW-functionalized mesoporous silica nanospheres into SPEEK

A highly stable composite proton exchange membrane (PEM) was developed by loading phosphotungstic acid in mesoporous silica nanospheres (HPW@MSNs) and blending with sulfonated poly (ether ether ketone) (SPEEK). The SPEEK/HPW@MSNs-0.5 membrane exhibits enhanced comprehensive performance, such as improved and stable proton conductivity and increased methanol barrier property. The proton conductivity decreased by 15.10% after 240 h at 60 °C and was 1.9 times lower than that of the SPEEK/HPW membrane. The selectivity of the SPEEK/HPW@MSNs-0.5 membrane was about 2.0 times that of the pure SPEEK membrane and 3.4 times that of the SPEEK/HPW membrane.     

Composite membranes based on sulfonated poly(aryl ether ketone)s containing the hexafluoroisopropylidene diphenyl moiety and poly(amic acid) for proton exchange membrane fuel cell application

Composite membranes based on sulfonated poly(aryl ether ketone)s containing the hexafluoroisopropylidene diphenyl moiety and poly(amic acid) with oligoaniline in the main chain have been prepared and immersed in H₃PO₄ to obtain acid-doped composite films. As expected, the water uptake values and methanol permeability of the composite membranes decrease with the increase of the weight fraction of PAA in the membrane matrix. Notably, the SPEEK-6F/PAA-15 shows a water uptake of 13.2% and a methanol permeability of 0.9 × 10⁻⁷ cm² s⁻¹, which are much lower than those of the Nafion (28.6% and 15.5 × 10⁻⁷ cm² s⁻¹, respectively). Although the proton conductivities decrease after the addition of PAA, higher selectivity values are obtained with the composite membranes. Therefore, the SPEEK-6F/PAA blend membranes, with the improved proton conductivity, methanol resistance and good thermal stability, can be used as a good alternative for proton conductive membranes with potential application in proton exchange membrane fuel cells (PEMFCs).     

Stack performance of phosphotungstic acid functionalized mesoporous silica (HPW-meso-silica) nanocomposite high temperature proton exchange membrane fuel cells

In this paper, a series of short stacks with 2-cell, 6-cell and 10-cell employing phosphotungstic acid functionalized mesoporous silica (HPW-meso-silica) nanocomposite proton exchange membranes (PEMs) have been successfully fabricated, assembled and tested from room temperature to 200 °C. The effective surface area of the membrane was 20 cm² and fabricated by a modified hot-pressing method. With the 2-cell stack, the open circuit voltage was 1.94 V and it was 5.01 V for the 6-cell stack, indicating a low gas permeability of the HPW-meso-silica membranes. With the 10-cell stack, a maximum power density of 74.4 W (equivalent to 372.1 mW cm⁻²) occurs at 150 °C in H₂/O₂, and the stack produces a near-constant power output of 31.6 W in H₂/air at 150 °C without external humidification for 50 h. The short stack also displays good performance and stability during startup and shutdown cycling testing for 8 days at 150 °C in H₂/air. Although the stack test period may be too short to extract definitive conclusions, the results are very promising, demonstrating the feasibility of the new inorganic HPW-meso-silica nanocomposites as PEMs for fuel cell stacks operating at elevated temperatures in the absence of external humidification.     

Influence of mesoporous phosphotungstic acid on the physicochemical properties and performance of sulfonated poly ether ether ketone in proton exchange membrane fuel cell

This study demonstrates the successful development of hybrid mesoporous siliceous phosphotungstic acid (mPTA-Si) and sulfonated poly ether ether ketone (SPEEK) as a proton exchange membrane with a high performance in hydrogen proton exchange membrane fuel cells (PEMFC). SPEEK acts as a polymeric membrane matrix and mPTA-Si acts as the mechanical reinforcer and proton conducting enhancer. Interestingly, incorporating mPTA-Si did not affect the morphological aspect of SPEEK as dense membrane upon loading the amount of mPTA-Si up to 2.5 wt%. The water uptake reduced to 14% from 21.5% when mPTA-Si content increases from 0.5 to 2.5 wt% respectively. Meanwhile, the proton conductivity increased to 0.01 Scm^?1 with 1.0 wt% mPTA-Si and maximum power density of 180.87 mWcm^?2 which is 200% improvement as compared to pristine SPEEK membrane. The systematic study of hybrid SP-mPTA-Si membrane proved a substantial enhancement in the performance together with further improvement on physicochemical properties of parent SPEEK membrane desirable for the PEMFC application.     

Electrospun multifunctional sulfonated carbon nanofibers for design and fabrication of SPEEK composite proton exchange membranes for direct methanol fuel cell application

Microstructural construction of a polymer/inorganic filler interface in organic/inorganic composite proton exchange membranes is a key to design of high performance proton conducting materials. Here, carbon nanofibers (CNFs) prepared through electrospun were successfully sulfonated to improve interfacial compatibility between the sulfonated poly(ether ether ketone) (SPEEK) and the sulfonated CNFs (SCNFs) via hydrogen bonding interaction. In addition, carbon nanofiber mats were successfully sheared into short lengths to facilitate dispersion of the SCNFs in the composite membranes. To demonstrate the effectiveness of the SCNFs on improvement of properties of the composite membranes, key physical quantities, i.e. mechanical strength, proton conductivity and methanol permeation were measured and systematically compared with the results of the neat SPEEK and Nafion 117 membranes. It was found that doping with the SCNFs of various contents could profoundly influence the physical properties of the composite membranes. In particular, mechanical strength, proton conductivity and methanol permeability prevention of the composite membranes were significantly enhanced upon incorporation of the SCNFs as fillers. The study provides useful insight into the investigation of the SCNFs based composite membranes for fuel cell applications.     

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.     

Stabilizing phosphotungstic acid in Nafion membrane via targeted silica fixation for high-temperature fuel cell application

With PWA as proton transfer and silica as water retainer, stable phosphotungstic acid/silica/Nafion (PWA/Si–N) composite membrane is non-destructively fabricated and exhibits excellent stability and high temperature proton conductivity. Compared with pristine Nafion, high temperature proton conductivity is significantly enhanced due to the collaboration between –SO₃H ionic clusters and the in-situ filled silica embedded PWA nanoparticles. PWA is stabilized in the ionic clusters via in-situ catalyzing the hydrolysis silica precursor targeted filled into the –SO₃H ionic clusters. Stable proton conductivity of the PWA/Si–N membrane at 110 °C and 60% RH is high to 0.058 S/cm, which is 2.4 folds of that of Nafion. At the same time, the composite membrane still maintains good mechanical and thermal stability. As a result, high temperature fuel cell performance of the composite membrane is improved by 41% compared with the pristine Nafion membrane. The in-situ coating method proved to be an effective method to solve the stability of PWA in Nafion membrane, especially the inorganic oxide with good hygroscopicity as the modifier.     

Sulfonated SBA-15 mesoporous silica-incorporated sulfonated poly(phenylsulfone) composite membranes for low-humidity proton exchange membrane fuel cells: Anomalous behavior of humidity-dependent proton conductivity

Sulfonated SBA-15 mesoporous silica (SM-SiO₂)-incorporated sulfonated poly(phenylsulfone) (SPPSU) composite membranes are fabricated for potential application in low-humidity proton exchange membrane fuel cells (PEMFCs). The SM-SiO₂ particles are synthesized using tetraethoxy silane (TEOS) as a mechanical framework precursor, Pluronic 123 triblock copolymer as a mesopore-forming template, and mercaptopropyl trimethoxysilane (MPTMS) as a sulfonation agent. A distinctive feature of the SM-SiO₂ particles is the long-range ordered 1-D skeleton of hexagonally aligned mesoporous cylindrical channels bearing sulfonic acid groups. Based on a comprehensive characterization of the SM-SiO₂ particles, the effect of SM-SiO₂ (as a functional filler) addition on the proton conductivity of the SPPSU composite membrane is examined as a function of temperature and relative humidity. An intriguing finding is that the proton conductivity of the SPPSU composite membrane exhibits a strong dependence on the relative humidity of measurement conditions. This anomalous behavior is further discussed with an in-depth consideration of the characteristics and dispersion state of SM-SiO₂ particles, which affect the tortuous path for proton movement, water uptake, and state of water. Notably, at low-humidity conditions, the SM-SiO₂ particles in the SPPSU composite membrane serve as an effective water reservoir to tightly retain water molecules and also as a supplementary proton conductor, whereas they behave as a barrier to proton transport at fully hydrated conditions.     

Sulfonated poly(ether sulfone)-based silica nanocomposite membranes for high temperature polymer electrolyte fuel cell applications

Fuel Cell operation at high temperature (e.g. 120 °C) and low relative humidity (e.g. 50%) remains challenging due to creep (in the case of Nafion^®) and membrane dehydration. We approached this problem by filling PES 70, a sulfonated poly(ether sulfone) with a T_g of 235 ± 5 °C and a theoretical IEC of 1.68 mmol g⁻¹, with 5-20% silica nano particles of 7 nm diameter and 390 ± 40 m² g⁻¹ surface area. While simple stirring of particles and polymer solutions led to hazy, strongly anisotropic (air/glass side) and sometimes irregular shaped membranes, good membranes were obtained by ball milling. SEM analysis showed reduced anisotropy and TEM analysis proved that the nanoparticles are well embedded in the polymer matrix. The separation length between the ion-rich domains was determined by SAXS to be 2.8, 2.9 and 3.0 nm for PES 70, PES 70-S05 and Nafion^® NRE 212, respectively. Tensile strength and Young’s modulus increase with the amount of silica. Ex-situ in-plane proton conductivity showed a maximum for PES 70-S05 (2 mS cm⁻¹). In the fuel cell (H₂/air, 120 °C, <50%), it showed a current density of 173 mA cm⁻² at 0.7 V, which is 3.4 times higher than for PES 70.     

Influence of alkaline 2D carbon nitride nanosheets as fillers for anchoring HPW and improving conductivity of SPEEK nanocomposite membranes

In the present study, novel composite membranes were prepared based on sulfonated poly (ether ether ketone)/phosphotungstic acid/carbon nitride nanosheets (SPEEK/HPW/g-C₃N₄). The alkaline ultrathin g-C₃N₄ nanosheets in the membranes behaved like “double-sided adhesive”, forming hydrogen bonds with the HPW molecules to anchor hydrophilic HPW without leaking. Moreover, the amine groups of nanosheets formed acid–base pairs with –SO₃H of the SPEEK polymer matrix, facilitating the Grotthuss-type transport of proton to improve conductivity. The g-C₃N₄ inorganic particles provided tortuous pathways for methanol transport to suppress the methanol permeability coefficient. The selectivity of the SPEEK/HPW/g-C₃N₄-1.0 was 2.3 times higher than that of SPEEK/HPW and 1.5 times higher than that of pristine SPEEK. SPEEK/HPW/g-C₃N₄ hybrid membranes exhibited stable and durable operation for 240 h under 100% RH at 60 °C. Moreover, membranes exhibited superior mechanical property, with maximum elongation at break of 223.3%.     

Preparation and properties of sulfonated poly(phthalazinone ether sulfone ketone)/zirconium sulfophenylphosphate/PTFE composite membranes

Porous polytetrafluoroethylene (PTFE) membranes were used as support material for sulfonated poly(phthalazinone ether sulfone ketone) (SPPESK)/zirconium sulfophenyl phosphate (ZrSPP)/PTFE composite membranes. The membranes were prepared via a spray painting method. Membranes were characterized by thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM). The composite membranes exhibited good thermal stabilities. SEM micrographs confirmed that the pores of the PTFE were filled entirely with SPPESK and ZrSPP. The resulting composite membranes were mechanically durable, dimensionally stable in alternating wet/dry environments, and had lower methanol permeabilities compared with the unsupported SPPESK/ZrSPP composite membranes reported in our previous work. The water uptake of these membranes was also lower than previous SPPESK/ZrSPP composite membranes. The proton conductivity of PTFE supported SPPESK (DS 81%)/ZrSPP(10 wt%) composite membrane was as high as 0.24 S/cm at 120 °C. Thus, the composite membranes exhibited good thermal stabilities, proton conductivities, and good methanol resistance, indicating that these composite membranes could serve as effective alternative membranes for direct methanol fuel cells (DMFCs).     

Sulfonated poly(ether ether ketone)/polybenzimidazole oligomer/epoxy resin composite membranes in situ polymerization for direct methanol fuel cell usages

A diamine-terminated polybenzimidazole oligomer (o-PBI) has been synthesized for introducing the benzimidazole groups (BI) into sulfonated poly(ether ether ketone) (SPEEK) membranes. SPEEK/o-PBI/4,4′-diglycidyl(3,3′,5,5′-tetramethylbiphenyl) epoxy resin (TMBP) composite membranes in situ polymerization has been prepared for the purpose of improving the performance of SPEEK with high ion-exchange capacities (IEC) for the usage in the direct methanol fuel cells (DMFCs). The composite membranes with three-dimensional network structure are obtained through a cross-linking reaction between PBI oligomer and TMBP and the acid-base interaction between sulfonic acid groups and benzimidazole groups. Resulting membranes show a significantly increasing of all of the properties, such as high proton conductivity (0.14 S cm⁻¹ at 80 °C), low methanol permeability (2.38 × 10⁻⁸ cm² s⁻¹), low water uptake (25.66% at 80 °C) and swelling ratio (4.11% at 80 °C), strong thermal and oxidative stability, and mechanical properties. Higher selectivity has been found for the composite membranes in comparison with SPEEK. Therefore, the SPEEK/o-PBI/TMBP composite membranes show a good potential in DMFCs usages.     

Sulfonated poly(arylene ether)s based proton exchange membranes for fuel cells

During the past decade proton exchange membrane fuel cells (PEMFCs) as one kind of the potential clean energy sources for electric vehicles and portable electronic devices are attracting more and more attentions. Although Nafion® membranes are considered as the benchmark of proton exchange membranes (PEMs), the drawbacks of Nafion® membranes restrict the commercialization in the practical application of PEMFCs. As of today, the attention is to focus on developing both high-performance and low-cost PEMs to replace Nafion® membranes. In all of these PEMs, sulfonated poly(arylene ether ketone)s (SPAEKs) and sulfonated poly(arylene ether sulfone)s (SPAESs) are the most promising candidates due to their excellent performance and low price. In this review, the efforts of SPAEK and SPAES membranes are classified and introduced according to the chemical compositions, the microstructures and configurations, as well as the composites with polymers and/or inorganic fillers. Specifically, several perspectives related to the modification and composition of SPAESs and SPAEKs are proposed, aiming to provide the development progress and the promising research directions in this field.     

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.     

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.     

Sulfonated poly(arylene ether sulfone)/disulfonated silsesquioxane hybrid proton conductors for proton exchange membrane fuel cell application

Fuel cell operating at high temperature and low humidity conditions is in urgent demand. Low glass transition temperature, high cost, and high humidity dependence of commercial membranes such as Nafion, however, are major obstacles to commercialization. Sulfonated poly (arylene ether sulfone) is a promising polymer that may show a breakthrough in this respect as it shows high thermal stability and mechanical strength while maintaining performance and cost competitiveness. Its relatively high dependence on humidity levels, however, is still an obstacle that needs to be tackled. The incorporation of silsesquioxane particles with disulfonated naphthol (NSi) functionalization is designed to increase the number of proton conducting moieties in the polymer matrix thus aiding proton transport. The incorporation of NSi has drastically improved performance especially at lower humidity conditions. Although current density of 5 wt.% NSi hybrid membrane shows a 2.0% increase in performance at 80°C/100 R.H.% that at 120 °C/30 R.H.% shows a 200% rise in current density at 0.7 V compared to that of pristine membranes. In addition, the evenly distributed silsesquioxane particles physically reduce fuel crossover values by 33.4%.     

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.