Novel branched sulfonated polyimide membrane with remarkable vanadium permeability resistance and proton selectivity for vanadium redox flow battery application

A series of novel branched sulfonated polyimide (bSPI-x) membranes with 8% branched degree are developed for application in vanadium redox flow battery (VRFB). The sulfonation degrees of bSPI-x membranes are precisely regulated for obtaining excellent comprehensive performance. Among all bSPI-x membranes, the bSPI-50 membrane shows strong vanadium permeability resistance, which is as 8 times as that of commercial Nafion 212 membrane. At the same time, the bSPI-50 membrane has remarkable proton selectivity, which is four times as high as that of Nafion 212 membrane. The bSPI-50 membrane possesses slower self-discharge speed than Nafion 212 membrane. Furthermore, the bSPI-50 membrane achieves stable VRFB efficiencies during 200-time charge-discharge cycles at 120–180 mA cm^?2. Simultaneously, the bSPI-50 membrane exhibits excellent capacity retention compared with Nafion 212 membrane. All results imply that the bSPI-50 membrane possesses good application prospect as a promising alternative separator of VRFB.     

A novel long-side-chain sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) membrane for vanadium redox flow battery

A novel long-side-chain sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (S-L-PPO) membrane was successfully prepared for VRFB applications. The long side chains were introduced onto the PPO backbones by a simple and controllable acylation with 4-fluorobenzoyl chloride and a subsequent condensation with sodium 4-hydroxybenzenesulfonate. The introduction of long side chains drives the formation of a good hydrophilic/hydrophobic micro-phase separation structure, which is evidenced by AFM. The S-L-PPO membrane with a degree of sulfonation (DS) of 51% showed an ultralow vanadium permeability (4.3 × 10^?9 cm² s^?1) and a decent proton conductivity (44 mS cm^?1). As a result, the energy efficiency of VRFB with S-L-PPO-51% membrane was up to 81.8% that was higher than that with Nafion 212 (78.0%) at a current density of 120 mA cm^?2. In addition, the self-discharge duration of the cell with S-L-PPO-51% membrane was 222 h that was nine times longer than that of Nafion 212 (23 h). All these indicate that the membrane prepared here is promising for the application in VRFB.     

Proton exchange membranes containing densely alkyl sulfide sulfonated side chains for vanadium redox flow battery

Due to further increase the performance of aromatic sulfonated proton exchange membrane (PEM) and make it play a better role in vanadium redox flow battery (VRFB), a series of poly(aryl ether sulfone)s containing eight alkyl sulfide sulfonated side chains (8SPAES-xx) are designed and synthesized. Their molecular structure, phase morphology and some selective properties were investigated in detail, respectively. It is confirmed that 8SPAES-xx membranes have clear hydrophilic/hydrophobic phase separation morphology. These membranes with the ion exchange capacity values of 1.08–1.61 mmol/g exhibit excellent ionic conductivity as well as moderate water uptake and good dimensional stability, and their values are in the range of 25–96 mS/cm, 8–28% and 5–17% at 30 °C, respectively. Among them, the proton conductivity of 8SPAES-12 membrane is 82 mS/cm at 30 °C, which exceeds the ionic conductivity of Nafion 117 (79 mS/cm). The membrane also shows high ion selectivity and excellent battery performance. At current density of 60 mA/cm², the highest energy efficiency of VRFB with 8SPAES-12 membrane is 87.3%, which is higher than that of Nafion 117 (83.8%). Furthermore, the efficiency of VRFB with 8SPAES-12 membrane remains good cycle stability.     

Proton exchange membranes with ultra-low vanadium ions permeability improved by sulfated zirconia for all vanadium redox flow battery

Suppressing vanadium ions crossover is a top priority in the development of membranes for vanadium redox flow battery (VRFB). One method is to dope inorganic fillers into polymer matrix, which usually decreases membrane's ion conductivity. In this work, sulfated zirconia (SZrO₂) is synthesized as a novel additive doped in sulfated poly (ether sulfone) (SPES) to simultaneously enhance the proton conduction and inhibit vanadium migration of the membranes. Membrane characterizations including battery test are carried out to reveal the effects of SZrO₂ on the membrane performance. The SPES/SZrO₂ composite membranes show vanadium permeability one order of magnitude lower than that of Nafion 212 and enhanced proton conductivity, which lead to superior cell performance. The columbic efficiency and energy efficiency of the VRFB reach 98.89% and 86.78%, respectively, at 100 mA cm⁻². Cycling test is carried out to evaluate the chemical and electrochemical stability of the membrane. Energy efficiency above 86% is maintained after70 charge-discharge cycles at 100 mA cm⁻².     

Branched sulfonated polyimide/s-MWCNTs composite membranes for vanadium redox flow battery application

A novel sulfonated multi-wall carbon nanotubes (s-MWCNTs) filler is synthesized by ring-opening reaction. And then, a series of branched sulfonated polyimide (bSPI)/s-MWCNTs composite membranes are also prepared for application in vanadium redox flow batteries (VRFBs). The optimized bSPI/s-MWCNTs-2% composite membrane has lower vanadium ion permeability (2.01 × 10⁻⁷ cm² min⁻¹) and higher proton selectivity (1.06 × 10⁵ S min cm⁻³) compared to those of commercial Nafion 212 membrane. Moreover, the VRFB with bSPI/s-MWCNTs-2% composite membrane exhibits higher coulombic efficiencies (CEs: 96.0–98.2%) and energy efficiencies (EEs: 79.7–69.5%) than that with Nafion 212 membrane (CEs: 86.5–92.5% and EEs: 78.5–67.6%) at 80–160 mA cm⁻². The VRFB with bSPI/s-MWCNTs-2% composite membrane has stable battery performance over 400 cycles at 100 mA cm⁻², whose EE value is in the top level among previously reported SPI-based composite membranes. The results show that the bSPI/s-MWCNTs-2% composite membrane has a great prospect in VRFB application.     

Highly stable graphene oxide composite proton exchange membrane for electro-chemical energy application

Proton exchange membrane is a basic element for any redox flow battery. Nafion is the only commercial available proton exchange membrane used in different electro-chemical energy systems. High cost restrict it's used for energy generation devices. In present work, we synthesised styrene divinylbenzene based composite proton exchange membranes (PEMs) with varying sulfonated graphene oxide (sGO) content for redox flow battery (RFB). Synthesized copolymer PEMs were analyzed in terms of their chemical structure with the help of FT-IR spectroscopy to confirm desired functional groups at appropriate position. Electrochemical characterization was performed in terms proton-exchange capacity, protonic conductivity and water uptake. Membrane shows adequate proton exchange capacity with good proton conductivity. Vanadium ion permeability was also tested for the prepared membrane to assess capability for vanadium redox flow battery (VRFB) in contrast with commercially available Nafion 117 PEM. Higher VO⁺² ion cross-over resistance was found for CEM-4 with 7.17 × 10⁻⁷ cm² min⁻¹ permeability, which is about half of the CEM-1. Further CEM-4 was also evaluated for charging-discharging phenomenon for single cell VRFB. The values of columbic, voltage and energy efficiency for VRFB confirms prepared membrane as a good candidate for redox flow battery. Composite PEM also shows better mechanical and thermal stability. Results indicates that synthesized composite membrane can be used in vanadium redox flow battery.     

Nafion/SiO2 hybrid membrane for vanadium redox flow battery

Sol–gel derived Nafion/SiO₂ hybrid membrane is prepared and employed as the separator for vanadium redox flow battery (VRB) to evaluate the vanadium ions permeability and cell performance. Nafion/SiO₂ hybrid membrane shows nearly the same ion exchange capacity (IEC) and proton conductivity as pristine Nafion 117 membrane. ICP-AES analysis reveals that Nafion/SiO₂ hybrid membrane exhibits dramatically lower vanadium ions permeability compared with Nafion membrane. The VRB with Nafion/SiO₂ hybrid membrane presents a higher coulombic and energy efficiencies over the entire range of current densities (10–80 mA cm⁻²), especially at relative lower current densities (<30 mA cm⁻²), and a lower self-discharge rate compared with the Nafion system. The performance of VRB with Nafion/SiO₂ hybrid membrane can be maintained after more than 100 cycles at a charge–discharge current density of 60 mA cm⁻². The experimental results suggest that the Nafion/SiO₂ hybrid membrane approach is a promising strategy to overcome the vanadium ions crossover in VRB.     

Sulfonated resorcinol-formaldehyde polymer gels synthesized in Nafion ion clusters as nanoscale reactors for a filler of hybrid proton exchange membranes

Nafion ion clusters are used as nanoscale polymerization reactors to synthesize sulfonated resorcinol-formaldehyde (RF) polymer gels to be used as fillers of a hybrid membrane. Because these ion clusters are distributed well over the entire Nafion structure, the polymer gels are also well dispersed in this unique organic–organic hybrid membrane compared with inorganic–organic hybrid membranes prepared by common recasting process that usually show serious aggregation of the fillers. The obtained organic–organic hybrid membranes show increased water uptake capability and the higher proton conductivity relative to pristine Nafion membrane under low-humidity conditions. In single-cell proton exchange membrane fuel cell operation without external humidifying system, the maximum power density of 289 mW/cm² is observed for the membrane electrode assembly (MEA) fabricated with 2 wt% sulfonated RF polymer gels/Nafion hybrid membrane, which is ca. 63% higher than that of the MEA fabricated with pristine Nafion membrane. However, pristine Nafion membrane showed similar or better performance to that of hybrid membranes when reactant gases are fully humidified.     

Novel Nafion composite membranes with mesoporous silica nanospheres as inorganic fillers

Novel Nafion composite proton exchange membranes are prepared using mesoporous MCM-41 silica nanospheres as inorganic fillers. The novelty of this study lies in the structural design of inorganic silica fillers: the nanosized and monodisperse spherical morphology of fillers facilitates the preparation of homogenous composite membranes, whilst the superior water adsorption of the mesostructure in fillers consigns enhanced water retention properties to the polymer membranes. Scanning electron microscopy images of the composite membranes indicate that well-dispersed silica nanospheres are embedded in the Nafion matrix, but a large amount of added fillers (3 wt.%) causes some agglomeration of the nanospheres. Compared with the Nafion cast membrane, the composite membranes offer improved thermal stability, enhanced water retention properties, and reduced methanol crossover. Despite the enhancement of water retention, the composite membranes still exhibit a proton conductivity reduction of 10–40% compared with pristine Nafion. This is likely due to the incorporation of much less conductive silica fillers than Nafion. The composite membrane containing 1 wt.% of fillers displays the best cell performance in direct methanol fuel cell tests; it gives a maximum power density of 21.8 mW cm⁻², i.e., ∼20% higher than the Nafion cast membrane. This is attributed to its similar conductivity to Nafion, and its markedly reduced methanol crossover, namely, ∼1.2 times lower.     

Robust proton exchange membrane for vanadium redox flow batteries reinforced by silica-encapsulated nanocellulose

High ion selectivity and mechanical strength are critical properties for proton exchange membranes in vanadium redox flow batteries. In this work, a novel sulfonated poly(ether sulfone) hybrid membrane reinforced by core-shell structured nanocellulose (CNC-SPES) is prepared to obtain a robust and high-performance proton exchange membrane for vanadium redox flow batteries. Membrane morphology, proton conductivity, vanadium permeability and tensile strength are investigated. Single cell tests at a range of 40–140 mA cm⁻² are carried out. The performance of the sulfonated poly(ether sulfone) membrane reinforced by pristine nanocellulose (NC-SPES) and Nafion® 212 membranes are also studied for comparison. The results show that, with the incorporation of silica-encapsulated nanocellulose, the membrane exhibits outstanding mechanical strength of 54.5 MPa and high energy efficiency above 82% at 100 mA cm⁻², which is stable during 200 charge-discharge cycles.     

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 graphene oxide as an inorganic filler in promoting the properties of a polybenzimidazole membrane as a high temperature proton exchange membrane

A commercial perfluorinated sulfonic acid (PFSA) membrane, Nafion, shows outstanding conductivity under conditions of a fully humidified surrounding. Nevertheless, the use of Nafion membranes that operate only at low temperature (<100 °C) can lead to some disadvantages in PEMFC systems, such as a low impurity tolerance and slow kinetics. To overcome the above problems, this study introduces a highly durable composite membrane with an inorganic filler for a high-temperature proton exchange membrane fuel cell (HT-PEMFC) applications under anhydrous conditions. In this work, polybenzimidazole (PBI) is used as a polymer electrolyte membrane with the addition of a sulfonated graphene oxide (SGO) inorganic filler. The amount of SGO filler was varied (0.5–6 wt.%) to study its influence on proton conductivity at elevated temperature, mechanical stability as well as phosphoric acid doping level. In particular, PBI-SGO composite membranes exhibited higher the level of acid dopant and proton conductivities than those of the pure PBI membranes. The PBI-SGO 2 wt.% composite membrane displayed the highest proton conductivity, with a value of 9.142 mS cm⁻¹ at 25 °C, and it increased to 29.30 mS cm⁻¹ at 150 °C. The PBI-SGO 2 wt.% also displayed the maximum values in the acid doping level (11.63 mol of PA/PBI repeat unit) and mechanical stability (48.86 MPa) analyses. In the HT-PEMFC test, compared with a pristine PBI membrane, the maximum power density was increased by 40% with the use of a PBI composite membrane with 2 wt.% SGO. These results show that the PBI-SGO membrane has a great potential to be applied as an alternative membrane in HT-PEMFC applications, offering the possibility of improving impurity tolerance and kinetic reactions.     

Role of UV irradiated Nafion in power enhancement of hydrogen fuel cells

The influence of optimum UV ray exposure of pristine Nafion polymer membranes on the improvement of proton conductivity and hydrogen fuel cell performance has been examined. Nafion membranes with thickness 183  μm (117), 90  μm (1035), 50  μm (212) and 25  μm (211) were irradiated with ultraviolet rays with doses in the range 0–250 mJ cm^?2 and their proton conductivities have been measured with standard method. The Nafion membranes have also been studied by measuring their water uptake, swelling-ratios and porosity using standard procedures. Hydrogen fuel cells with dual serpentine microchannels with active area 1.9 x 1.6 cm^-2 were assembled with anode gas diffusion layer, Nafion membrane, cathode gas diffusion layer and other components. An external humidifier was used to humidify hydrogen for the fuel cell. The experimental Results have shown an increase in the value of Nafion proton conductivity with an optimum UV irradiation which depends on the thickness of Nafion membrane: the optimum doses for peak proton conductivity were 196mJ/cm^?2 for Nafion 117, 190mJ/cm^?2for Nafion 1035, 180mJ/cm^?2 for Nafion 212 and 160mJ/cm^?2 for Nafion 211. This enhancement of proton conductivity is because of the optimal photo-crosslinking of –SO₃H groups in Nafion. This causes optimum pore-size in Nafion thereby facilitating increased proton-hopping between –SO₃H sites in Nafion. Hydrogen fuel cells were developed with pristine as well as with optimal UV irradiated Nafion with thicknesses of 90 and 50  μm. The polarization plots obtained for these devices showed an increase in power densities approximately by a factor of 1.8–2.0 for devices with optimally UV irradiated Nafion. These results indicate that optimal UV irradiation of Nafion is an excellent technique for enhancing power output of hydrogen fuel cells.     

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.     

Analysis of mechanism of Nafion® conductivity change due to hot pressing treatment

In previous work, the authors observed that multiple hot-pressing cycles of Nafion 212 prior to Proton Exchange Membrane Fuel Cell (PEMFC) operation was found to result in significant performance gains. In order to further explore this effect, Nafion 212 samples were subjected to various thermal treatments and then to various analytical techniques in order to probe whether changes to the membrane contributed to these performance gains in a substantial way. Electrochemical Impedance Spectroscopy (EIS) measurement sought to validate that the treatment caused a proton conductivity change. Thermogravimetric Analysis (TGA) and Fourier Transform Infrared Spectroscopy (FTIR) measurements were implemented to determine whether chemical changes in the membrane occurred. Results suggest that the hot pressing treatment causes a significant effect in the electrical properties of Nafion 212, however the physical change that occurs in the polymer is not chemical in nature. Further analysis attempts to support the idea that the change in proton conductivity is due to water channel reconfiguration in the membrane, activated by elevated temperature and compressive stress at the glass transition temperature of the Nafion 212.     

Phosphonic acid-grafted mesostructured silica/Nafion hybrid membranes for fuel cell applications

Highly conductive and hydration retentive mesoporous silica/Nafion and organically modified mesoporous silica/Nafion membranes are prepared by a surfactant templated sol-gel process involving Nafion solution and silica precursors. Spectroscopic analyses reveal that the in situ generation of a well-condensed silica network and organic (-PO₃H₂) functionalization of the inorganic segment are effectively achieved in the prepared membranes. The homogeneous dispersion of silica nanoparticles in the polymer matrix is apparent in electron micrographs. Structural analyses using small-angle X-ray scattering confirms the periodic short range structural order associated with these mesostructured hybrid membranes. These hybrid membranes exhibit an increased water uptake and an associated conductivity enhancement at 100% RH, compared to unmodified Nafion. More significantly, the functionalized silica/Nafion membranes show high proton conductivities at 80 °C and 50% RH, which is more than 6 times higher than that of Nafion. Thermogravimetric analysis, low temperature DSC studies and a comparison of activation energies (E_a) obtained from temperature-dependent conductivity plots of the membranes at different humidities, provide evidence for the better retention of water in the hybrid membranes compared to Nafion; thereby demonstrating the promising potential of these membranes to tolerate the variations in humidity at elevated temperatures.     

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 hybrid polymer electrolyte membranes with high proton conductivity prepared by a silane-crosslinking technique for direct methanol fuel cells

In order to prepare a hybrid proton exchange membrane with low methanol permeability and high proton conductivity, two silane monomers, namely 3-glycidoxypropyl-trimethoxysilane (GPTMS) and 3-mercaptopropyl-trimethoxysilane (MPTMS) are first blended with a sulfonated poly(arylene ether ketone) (SPAEK). Then the blended membrane is heated to induce the grafting of GPTMS onto SPAEK. Finally, a hydrolysis-condensation is performed on the grafted membrane to induce cross-linking. The -SH groups of MPTMS are oxidized to sulfonic acid groups, which are attributed to enhance the proton conductivity of hybrid membranes. Fourier transform infrared spectroscopy is used to characterize and confirm the structures of SPAEK and these cross-linked hybrid membranes. The proton conductivity of a cross-linked hybrid membrane G50M50 reaches up to 0.20 S cm⁻¹ at 80 °C, which is comparable to that of SPAEK and much higher than that of Nafion. Meanwhile, the methanol permeability is nearly three times lower than that of Nafion and two times lower than that of SPAEK. The ion-exchange capacity, water uptake, membrane swelling and thermal stability are also investigated to confirm their applicability in fuel cells.     

Synthesis and characterization of new proton conducting hybrid membranes for PEM fuel cells based on poly(vinyl alcohol) and nanoporous silica containing phenyl sulfonic acid

Organic-inorganic hybrid proton exchange membranes were prepared from poly(vinyl alcohol) (PVA) and various amounts of nanoporous silica containing phenyl sulfonic acid groups. These hybrid membranes were prepared via co-condensation of functionalized nanoporous SBA-15 (SBA-ph-SO₃H) as hydrophilic inorganic modifier, glutaraldehyde (GLA) as cross-linking agent in a PVA matrix. These membranes were characterized for their morphology, thermal stability, electrochemical and physicochemical properties using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and water uptake studies. The SBA-ph-SO₃H/PVA composite membranes have a higher water retention and thermal stability than that of Nafion 117, perhaps because of responsibility of both acidic groups and nanoporous structure of silica additive. This work demonstrates the promising potential of new composite membranes for the development of high-performance and high-stability PEM fuel cells with improved proton conductivity.     

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.