Sulfonated Polyimide Membranes Research Articles

A sulfonated polyimide containing imidazole ring with a low vanadium ion permeable for vanadium redox flow battery

A new type of sulfonated polyimide membrane (6f-abSPI) containing benzimidazole group and trifluoromethyl group (-CF3) is synthesized by one-step copolymerization. The 6f-abSPI-60 membrane with the highest ion selectivity is selected and applied to all vanadium redox flow battery (VRFB). Compared with Nafion 212 (N212) membrane and 6f-SPI-60 membrane, the vanadium ion permeability of 6f-abSPI-60 membrane (1.78 × 10−7 cm2 min−1) is 1/13 lower than that of N212 membrane (2.33 × 10−6 cm2 min−1) and 1/2 lower than 6f-SPI-60 membrane (3.60 × 10−7 cm2 min−1). At the same time, the 6f-abSPI-60 membrane (2.69 × 105 S min cm−3) has significant selectivity, which is 5.6 times higher than N212 membrane (0.48 × 105 S min cm−3). In VRFB tests, the coulombic efficiency (CE) of 6f-abSPI-60 membrane (98.88 %) is significantly higher than that of N212 membrane (92.99 %) and 6f-SPI-60 membrane (97.65 %) at 100 mA cm−2, and the energy efficiency (EE) also reaches a higher value (77.29 %). Additionally, the VRFB equipped with the 6f-abSPI-60 membrane exhibits consistent and reliable performance throughout the 100 cycles of charging and discharging at the current densities of 100 mA cm−2. The good stability of 6f-abSPI membranes is explained by calculating C atoms’ natural bond orbital (NBO) charges on different polyimide (PI) rings.

Sulfonated polyimide membranes with branched architecture and unique diamine monomer for implementation in vanadium redox flow battery

In this paper, a new functional diamine monomer 2-methyl-1,4-bis(4-amino-2-trifluoromethyl) benzene (FAPOB) is designed and synthesized for further improving the performance of branched sulfonated polyimide (SPI–B) membrane for implementation in vanadium redox flow battery (VRB). At the same time, the sulfonation levels of SPI-B membranes are accurately regulated by modifying the proportion of FAPOB and 4,4′-diaminobiphenyl-2,2′-disulphonic acid. Among them, the SPI-B-50 membrane with 50 % sulfonation degree exhibits a remarkable proton selectivity of 2.31 × 105 S min/cm3, which is 5.5 times higher than the Nafion 212 (NR212) membrane. Moreover, the SPI-B membrane's stability is significantly improved due to its branched structure and the presence of numerous trifluoromethyl groups. Compared to NR212 membrane, SPI-B-50 membrane demonstrates superior coulomb and energy efficiencies at the same current density. Furthermore, the SPI-B-50 membrane exhibits a higher voltage holding capacity compared to the NR212 membrane. Remarkably, the SPI-B-50 membrane maintains stable efficiencies even after undergoing more than 500 charge-discharge cycles. This research not only involves the innovative synthesis of a novel diamine monomer but also the construction of various SPI-B membranes with a unique molecular structure specifically designed for VRB applications.

Sulfonated Polyimide Membranes Constructed by Main-Chain and Molecular-Network Engineering Strategy for Direct Methanol Fuel Cell.

Excessive swelling is one important factor that leads to high fuel permeability and limited operating concentration of methanol for proton exchange membranes. Herein, a collaborative strategy of main-chain and molecular-network engineering is applied to lower swelling ratio and improve methanol resistance for highly sulfonated polyimide. Two m-phenylenediamine monomers (4-(2,3,5,6-tetrafluoro-4-vinylphenoxy)benzene-1,3-diamine and 4,6-bis(2,3,5,6-tetrafluoro-4-vinylphenoxy)benzene-1,3-diamine) with tetrafluorostyrol groups are designed and synthesized. Two series of cross-linked sulfonated polyimides (CSPI-Ts, CSPI-Bs) are prepared from the two diamines, 4,4'-diaminostilbene-2,2'-disulfonic acid and 1,4,5,8-naphthalenetetracarboxylicdianhydride. The rigid main-chain structure is cornerstone for wet CSPI-Ts and CSPI-Bs remaining stable at elevated temperatures. The introduction of hydrophobic cross-linked network further improves their dimensional stability and methanol resistance. CSPI-Ts and CSPI-Bs show obviously improved performances containing high proton conductivity (121 ± 0.27-158 ± 0.35 S cm-1 ), low swelling ratio (9.6 ± 0.40%-16.1 ± 0.01%) and methanol permeability (4.14-7.69 × 10-7 cm2 s-1 ) at 80°C. The direct methanol fuel cell (DMFC) is assembled from CSPI-T-10 with balanced properties, and it exhibits high maximum power density (PDmax ) of 82.3 and 72.6mW cm-2 in 2 and 10m methanol solution, respectively. The ratio of PDmax in 10m methanol solution to the value in 2m methanol solution is as high as 88%. The CSPI-T-10 is promising proton exchange membrane candidate for DMFC application.

Novel microporous sulfonated polyimide membranes with high energy efficiency under low ion exchange capacity for all vanadium flow battery

High proton conductivity and low vanadium permeation created great challenges in designing of highly efficient membranes for all vanadium redox flow battery. To overcome this trade-off phenomenon, a series of novel microporous sulfonated polyimides (SPI) with gradient sulfonic acid group concentrations (6FTMA-X) were prepared by a simple one-step polymerization. They demonstrated high molecular weight (Mn of 23 to 59 KDa), modest microporosity (SBET = 437.2 - 39.4 m2 g−1) and suitable interchain space (between 3.7 and 5.2 Å), which provided excellent ion sieving for proton and vanadium ions (2.4 and 6.0 Å). Consequently, although the ion exchange capacities (0.38 - 1.47 mmol g−1) of 6FTMA-Xs were low compared with the reported SPIs, they still achieved high energy efficiency (80.4%) under high current density (100 mA cm−2), which was comparable to Nafion 117 (N117, 81.7%) at the same current density. This was because of the acceptable proton conductivity and ultra-low vanadium permeation (0.59 - 3.56 × 10−7 cm2 min−1). We suppose the micropore inside the sulfonated polyimides behaviors as ion channel for proton transport and a vanadium barrier. All these results demonstrate that the 6FTMA-X membranes show great potential for vanadium redox flow battery applications. This polymer design strategy provided new insight for highly efficient membranes for VRFB applications.

Sulfonated polyimide membrane containing poly [bis (4-aminodiphenyl bissulfonate) phosphoronitrile] flexible chains for vanadium redox flow battery

A novel composite membrane containing poly [bis (4-aminodiphenyl bissulfonate) phosphoronitrile] (PDAP) flexible chains and acid-base sulfonated polyimide (abSPI, synthesized by one-pot method) was prepared. The influence of different content of PDAP on the performance of composite membrane was explored systematically. The results showed that the conductivity was significantly improved through main-chain-type and side-chain-type –SO3H of the pristine abSPI and introduced PDAP flexible chains, respectively, and the abSPI/0.5% PDAP membrane with the best performance reached 1.17 × 10−1 S cm−1, exceeding N212 (1.12 × 10−1 S cm−1) at room temperature. Moreover, the selectivity of composite membrane based on the Donnan repulsion effect between the N-protonated in PDAP and VO2+ and acid-base effect between –SO3H and N–H reached 0.69 × 105 S min cm−3 (1.43 times of N212). The VRFB single cell equipped with the abSPI/0.5% PDAP membrane showed the best battery performance, with the coulombic efficiency (CE) reaching 97.50% and the energy efficiency (EE) reaching 78.09% at 100 mA cm−2. The results of 300 charging-discharging cycles test showed that abSPI/0.5% PDAP membrane has good long-term cycle stability and excellent service life. The SEM and FTIR results showed that abSPI/0.5% PDAP membrane still had excellent mechanical properties and chemical stability after the 300 cycles test.

A novel permselective branched sulfonated polyimide membrane containing crown ether with remarkable proton conductance and selectivity for application in vanadium redox flow battery

As a key component of vanadium redox flow battery (VRFB), the ideal membrane with high proton conductance together with high vanadium ions resistance is urgently required. In this work, a permselective monomer di(aminobenzo)-18-crown-6 with proper aperture of 0.26–0.32 nm is synthesized to prepare branched sulfonated polyimide containing crown ether (ce-bSPI-x) membranes. In virtue of the excellent balance between vanadium ions resistance and proton conductance, the ce-bSPI-60 membrane possesses the optimum physico-chemical properties among all ce-bSPI-x membranes. Subsequently, in comparison with commercial Nafion 212 membrane, the ce-bSPI-60 membrane demonstrates higher coulomb efficiencies (CEs) (96.50%–99.39%) and energy efficiencies (EEs) (69.36%–85.45%). Furthermore, the ce-bSPI-60 membrane can achieve 80% of EE at 140 mA cm−2, which is in a superior position compared with other SPI-based membranes reported in recent years. 1000-time cycles at 140 mA cm−2 without obvious structural and morphological changes proves the excellent durability of ce-bSPI-60 membrane. To sum up, the as-prepared ce-bSPI-60 membrane exhibits a great potential to match the demand of application in VRFB.

Controlling the microphase morphology and performance of cross-linked highly sulfonated polyimide membranes by varying the molecular structure and volume of the hydrophobic cross-linkable diamine monomers

Morphological control is essential for tuning the performance of polymer electrolyte membranes (PEMs). Block copolymerization is an effective but complicated way to control the morphology of PEMs. It is urgent to explore a simple alternative method to achieve this target. Herein, the molecular engineering strategy that changes the molecular structure and volume of hydrophobic cross-linkable diamine and introduces a hydrophobic network structure was used to optimize the microphase morphology of sulfonated polyimides (SPIs). Three diamine monomers containing tetrafluorostyrol pendant groups have been synthesized (4-(2,3,5,6-tetrafluoro-4-vinylphenoxy)benzene-1,3-diamine (TFVPDM), 1,3-bis(2-trifluoromethyl-4-amino-phenoxy)-5-(2,3,5,6-tetrafluoro-4-vinylphenoxy)benzene (6FTFPB), 2,2-bis(3-amino-4-(2,3,5,6-tetrafluoro-4-vinylphenoxy)phenyl)hexafluoropropane (6FATFVP)). Based on these monomers, 4,4′-diaminostilbene-2,2′-disulfonic acid (DASDSA) and 1,4,5,8-naphthalenetetracarboxylicdianhydride (NTDA), three cross-linked SPIs (CSPIs: CSPI-T-10, CSPI-TP-10, CSPI-AP-10) with similar ion-exchange capacity (IEC) value of 2.29–2.46 meq. g−1 but different main-chain structures were prepared through polycondensation and thermal cross-linking process. The introduced hydrophobic cross-linked structure improves the oxidative stability and methanol resistance of CSPI membranes. The CSPI membranes prepared from cross-linkable hydrophobic diamine with larger molecular volume and containing hydrophobic structural units in the main chain exhibit more pronounced phase separation morphology and higher proton conductivity. Moreover, the methanol resistance of CSPI membranes is dependent on the combined effect of IEC, degree of crosslinking (DC), and main-chain structure. The higher DC and main-chain containing hydrophobic structure are beneficial for enhancing the methanol resistance. The CSPI-AP-10, which was prepared from the 6FATFVP with the largest molecular volume, more hydrophobic cross-linkable pendant groups and hydrophobic linkages, exhibits the best performance. The CSPI-AP-10 membranes showed high proton conductivity and excellent methanol resistance. The direct methanol fuel cells (DMFCs) assembled from CSPI-AP-10 have a high max power density (PDmax) of 106.2 mW cm−2 in 2 M methanol and 75.1 mW cm−2 in 10 M methanol. The results indicated that the CSPI-AP-10 was a promising candidate as a PEM in DMFC application.

Enhanced proton selectivity and stability of branched sulfonated polyimide membrane by hydrogen bonds construction strategy for vanadium flow battery

Vanadium redox flow battery (VFB) is promising for use as an energy storage/conversion device, however membrane imposes a limitation in enhancing the performance of VFB. Herein, a novel diamine monomer bis(2-trifluoromethyl-4-aminobenzene) amine containing imino groups is synthesized by nucleophilic substitution and reduction reactions. Then, we develop four branched sulfonated polyimide (I-bSPI) membranes with 40%–70% theoretical sulfonation degrees for application in VFB. The trade-off between proton conduction and vanadium ion blocking of I-bSPI membrane is broken, and the stability of I-bSPI membrane is also effectively enhanced owing to hydrogen bonds network and Donnan repulsion effect. Surprisingly, the proton selectivity of I-bSPI-50 membrane is 4.6 times that of commercial Nafion 212 membrane. In addition, I-bSPI-50 membrane exhibits superior coulomb and energy efficiencies to Nafion 212 membrane at 100–300 mA cm−2. And I-bSPI-50 membrane has steady efficiencies and high capacity holding abilities during 600-time cycles. This work illustrates a promising pathway to obtain cost-effective membrane by hydrogen bonds construction strategy for VFB application.

Study on degradation mechanism of fluorine-containing branched sulfonated polyimide membrane for vanadium flow battery by density functional theory and ex situ experiments

Study on degradation mechanism of fluorine-containing branched sulfonated polyimide membrane for vanadium flow battery by density functional theory and ex situ experiments

Photo crosslinked stilbene-containing sulfonated polyimide membranes as proton exchange membranes in fuel cell

Stilbene containing sulfonated polyimide membranes were synthesized from 1, 4, 5, 8-naphthalenetetracarboxylic dianhydride, 2-bis (4-aminophenoxy) phenyl) hexafluoropropane, 2, 2′-benzidinedisulfonic acid and 4,4′-diamino stilbene. Subsequently, they were photo crosslinked and characterized to investigate their suitability for fuel cell applications. The synthesized membranes exhibit water uptake of 24.47–29.78%, proton conductivity of 0.016–0.046 S cm−1 at 30 °C, and the ion exchange capacity of 1.450–1.485 mequiv g−1. The fuel cell performance of stilbene containing sulfonated polyimide membrane showed a power density of 0.24 W/cm2. The hydrolytic stability of uncrosslinked stilbene containing sulfonated polyimide membranes was 47–68 h, but, after the photocrosslinking, it was increased up to 109 h. The uncrosslinked membranes showed tensile strength in the range of 36.74–47.38 MPa, and after photocrosslinking, the tensile strength was increased in the range of 42.34–54.71 MPa. The oxidative stability of uncrosslinked membranes was found to be in the range of 45–48 h whereas the photocrosslinked membranes showed oxidative stability in the range of 51–57 h.

Highly ion-selective sulfonated polyimide membranes with covalent self-crosslinking and branching structures for vanadium redox flow battery

With an innovatively synthesized X-shaped tetramine monomer 4,4',4'',4'''-(1H,3'H-[5,5'-bibenzo[d]imidazole]) tetraaniline with imidazole groups, a series of novel sulfonated polyimide membranes with covalent self-crosslinking and branching structures (sc-bSPI-x) are designed and prepared for application in vanadium redox flow battery (VRFB). The synergistic effects of protonated imidazole and sulfonic acid are supposed to create proton transport channels and Donnan exclusion, leading to break the trade-off between proton conductance and vanadium ion resistance. Among all the prepared sc-bSPI-x membranes, the sc-bSPI-14 membrane with 14% theoretical cross-linking degree shows the highest ion selectivity (2.78 × 105 S min cm−3), which is about 6.5 times of commercial Nafion 212 membrane (0.43 × 105 S min cm−3). The VRFB performances including self-discharge time, coulombic and energy efficiencies at 80–200 mA cm−2 of sc-bSPI-14 membrane are superior to those of Nafion 212 membrane (sc-bSPI-14: self-discharge time 46 h, CE = 97.6–99.2% and EE = 82.9–63.2%; Nafion 212: self-discharge time 11 h, CE = 86.5–94.5% and EE = 78.4–61.4%). Meanwhile, the 1000-time cycling charge–discharge test of sc-bSPI-14 membrane at 140 mA cm−2 is performed, demonstrating its outstanding operational stability. The results indicate that the proposed sc-bSPI-14 membrane is a promising candidate for VRFB application.

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 fluorinated acid-base sulfonated polyimide membrane with sulfoalkyl side-chain for vanadium redox flow battery

A novel fluorinated acid-base sulfonated polyimide membrane (s-f-SPI) with trifluoromethyl (-CF3), side-chain-type-SO3H and benzimidazole groups was synthesized by a 2-step method for vanadium redox flow battery applications. A series of physico-chemical properties of s-f-SPI membrane were researched systematacially. The acid-base pairs between the side-chain-type -SO3H and protonated imidazole groups provided more channels for proton-transport, enhancing the proton conductivity (0.51×10−1 S cm−1 at ∼25 °C), and Donnan effect of the imidazole groups impeded the penetration of vanadium-ion (3.95×10−7 cm2 min−1). In VRFB tests, s-f-SPI membrane exhibited a coulombic efficiency (CE) of 98.1% and an energy efficiency (EE) of 81.2% at a current density of 100 mA cm−2, higher than those of Nafion 212 (CE: 94.1%, EE: 76.5%). Furthermore, the VRFB with s-f-SPI membrane showed a stable performance in the 500 cycles charging-discharging test at 100 mA cm−2, and the morphology and structure remained unchanged after the cycle test. These results demonstrate that the s-f-SPI membrane has great potential for VRFB applications.

Sulfonated Polyimide Membranes Derived from a Novel Sulfonated Diamine with Pendant Benzenesulfonic Acid for Fuel Cells

For improving the hydrolytic stability of sulfonated polyimides consisting of five membered anhydrides, novel sulfonated polyimides (NSPIs) were prepared via polymerization of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), with a novel diamine monomer with a pendant sulfonic acid group and 4,4-oxydianiline. Water uptake of this NSPI with an excellent film-forming ability was almost equal to that of Nafion® 117, while their ion exchange capacity (IEC) was 22% higher than Nafion® 117. The loss in weight decreased by 53% and loss in IEC decreased by 66% compared to that of Nafion® 117; both were used to quantitatively measure hydrolytic stability, and radical oxidative stability also increased by 75% when compared with Nafion® 117. Mechanically, this NSPI was superior, and its proton conductivity was higher than Nafion® 117 at elevated temperatures. All these improvements were due to the introduction of this pendant group. Taken together, we herein report a promising renewable energy source based on SPIs capable of displaying proton conductivity and enhanced hydrophilicity.

Synthesis of clay‐armored coatable sulfonated polyimide nanocomposites as robust polyelectrolyte membranes

AbstractHerein, coatable sulfonated polyimide (SPI) and clay‐reinforced SPI membranes SPI‐clay 3%, SPI‐clay 5%, and SPI‐clay 7% were successfully fabricated by one‐step high temperature via direct imidization method. The membranes were cast as a coatable thin film using a solution casting method and grafted vermiculite clay nanoparticle were incorporated into the neat SPI as reinforcement by the sonication method. Three different formulated nanocomposite membranes were investigated using different characterization techniques such as Fourier transform infrared spectroscopy as peaks at 1166 and 1227 cm−1 confirmed successful sulfonation. In Proton (1H) NMR synthesis of SPI confirmed as aromatic proton at 7.3–8.8 ppm depicts successful sulfonation and X‐ray diffraction results confirmed the crystalline structure of clay, as its content increased (7%) clear diffraction peak arises at 6 and 25°. Scanning electron microscopy (SEM) provides information about surface morphology of clay reinforced SPI membranes, and SEM micrographs shown uniform dispersion of clay nanofillers and developed easy transfer of electron. Thermogravimetric analysis was performed to investigate the thermal stability of synthesized films, results of thermographs shown degradation in the range of 510–600°C. Different physicochemical parameters employed and their results show the effectiveness of synthesized clay reinforced SPI membranes. Water uptake (WU%) about 0.96%, hydrolytic about 98 h and oxidative stability up to 80°C, ions exchange capacity about 3.16 mmol/g for synthesized clay reinforced SPI membranes. Measurement regarding Dimensional changes was also investigated and dimensional changes (1.557 ∆t/∆l). All these results reveal that the clay‐reinforced coatable SPI membranes are a promising material for polymer electrolyte membranes to be used in fuel cell energy applications.

A novel double branched sulfonated polyimide membrane with ultra-high proton selectivity for vanadium redox flow battery

The development of a vanadium redox flow battery (VRFB) urgently requires proton conductive membranes with high proton selectivity. Herein, we synthesized branched anhydride monomer 1,3,5-tris(3,4-anhydride phenoxy)benzene using a three-step method. Furthermore, we prepared successfully novel double branched sulfonated polyimide (dbSPI) membranes with ultra-low vanadium ion permeability (0.4–2.5×10−8 cm2 min−1), one or two orders of magnitude lower than that of the Nafion 212 membrane (7.25×10−7 cm2 min−1). Among all membranes, the dbSPI-50 membrane with the highest proton selectivity (23.25×105 S min cm−3), approximately 68 times higher than that of the Nafion 212 membrane, was chosen for assembling of a VRFB single cell. Because of its ultra-low vanadium ion permeability, the dbSPI-50 membrane exhibited much longer self-discharge time (97 h) and superior capacity retention (82.6–91.3%) compared with the Nafion 212 membrane. Moreover, both coulomb efficiency (99.6–98.5%) and energy efficiency (69.3–80.1%) of the dbSPI-50 membrane are higher than those of the Nafion 212 membrane after 300 times charge-discharge tests at a current density from 200 to 100 mA cm−2. All these results demonstrate that the optimized dbSPI-50 membrane is a promising candidate for applications in VRFBs.

Polyelectrolyte proton exchange membranes: synthesis and characterization of sulfonated polyimide membranes using novel stilbene-containing diamine

A new unsymmetrical diamine, 4-(2-aminophenoxy)-4′-aminostilbene was successfully synthesized and used to synthesize stilbene-containing sulfonated polyimides. 2,2′-Benzidine-disulfonic acid, 1,4,5,8-naphthalene tetracarboxylic dianhydride and different mole ratios of 4-(2-aminophenoxy)-4′-aminostilbene and 2-bis(4-(4-aminophenoxy)phenyl) hexafluoropropane were used for the synthesis of stilbene-containing polyimides with sulfonic acid groups. The synthesized polymers were characterized using various physicochemical characterization techniques such as nuclear magnetic resonance spectroscopy, infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis and electrochemical impedance spectroscopy. Furthermore, the viscosity, water uptake, ion exchange capacity, swelling ratio, hydrolytic stability, oxidative stability, mechanical properties and proton conductivity of the synthesized membranes were also analyzed. Sulfonated polyimide membranes showed a water uptake capacity of 18.93–28.89%, proton conductivity of 0.028–0.039 S cm−1 at 30 °C, ion exchange capacity of 1.469 meq g−1 and hydrolytic stability of 40–44 h at 80 °C. The solubility of the sulfonated polyimide membranes was improved when unsymmetrical diamine was used to prepare sulfonated polyimides.

4-(4-Aminophenoxy)benzene-1,3-diamine-based covalent cross-linked sulfonated polyimide as proton exchange membranes in fuel cell

Hydrolytic and oxidative stabilities of sulfonated polyimide membranes are of significant concern when they are used as fuel cell polyelectrolyte membranes. To increase the hydrolytic and oxidative stabilities of sulfonated polyimide membranes, atriamine crosslinker, 4-(4-aminophenoxy)benzene-1,3-diamine, was synthesized, characterized, and successfully used to synthesize covalently cross-linked sulfonated polyimide membranes. 1,4,5,8-Naphthalenetetracarboxylic dianhydride, 2,2’-benzidine-disulfonic acid, 4-(4-aminophenoxy)benzene-1,3-diamine and 2-bis(4-(4-aminophenoxy)phenyl) hexafluoropropane-based cross-linked sulfonated polyimide membranes have been synthesized and compared with linear sulfonated polyimide membrane in terms of various fuel cell application parameters. Covalent cross-linking is a simple and efficient method to increase the lifetime of the polyelectrolyte membranes. The covalently cross-linked sulfonated polyimidemembranes show an ion exchange capacity of 1.426 1.441 meq.g-1, proton conduction of 0.026 – 0.031 S cm-1, and water uptake capacity 10.7 – 17.07%. As the triamine concentration is increases, both hydrolytic and oxidative stabilities of the membranes also increased. The linear sulfonated polyimide showed hydrolytic stability of 43 h, whereas hydrolytic stability of the cross-linked sulfonated polyimide membranes is increased up to 70 h.

Stable covalent cross-linked polyfluoro sulfonated polyimide membranes with high proton conductance and vanadium resistance for application in vanadium redox flow batteries

Novel covalent cross-linked polyfluoro sulfonated polyimide membranes are developed by designing and synthesizing polyfluoro non-sulfonated diamine and adopting hydrophilic polyacrylic acid as the cross-linking agent for application in VRFBs.

Modification and Optimization of Rice Husk Ash Bio-Filler in Sulfonated Polyimide Membrane for Direct Methanol Fuel Cell

Direct methanol fuel cell (DMFC) is a very high potential renewable and sustainable energy for portable devices as it has very high energy density and more environmentally friendly. Adding filler into the membrane matrix had reported in improved performance of the DMFC. However, addition of filler will lead to the decrease of the ion exchange capacity of the membrane, which will in turn reduce the fuel cell performance. Hence, this work studies the modification of rice husk ash via sulfonation process and the effect of the synthesis parameter of novel sulfonated polyimides/sulfonated rice husk ash (SPI/sRHA) composite membrane towards fuel cell performance where filler sRHA had been synthesized via the mixing reaction between rice husk ash (RHA) with chloroform and chlorosulfonic acid. The composition of filler in membranes was optimized with different synthesis parameters such as different types of filler used, loading of filler in membrane and membrane annealing temperature. Investigation of the effects for these three parameters on the physicochemical properties of the composite membranes produced was carried out using response surface methodology (RSM) approach to optimize the synthesis parameters of the composite membrane. The fillers and composite membranes were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller (BET) analysis and transmission electron microscopy. Different synthesis parameters had shown different influences on the physicochemical properties of the composite membranes and consequently, gave different passive fuel cell performances of DMFCs too. The optimized membrane (S-12-sR) showed enhanced physicochemical performance as well as the passive single cell performance as compared to pure SPI and Nafion 117 membranes. The water uptake, proton conductivity and IEC that had been achieved by the optimized membrane were 90.97%, 0.1891 S cm−1 and 0.2608 mmol g−1 respectively. The maximum power density of the passive DMFC was improved from 8.1 mW cm−2 to 16.4 mW cm−2 under ambient conditions.