Sulfonated Polyimide Research Articles

A Novel Sulfonated Polyimide Composite Membrane Containing a Sulfonated Porous Material for All-Vanadium Redox Flow Batteries.

To improve the battery efficiency and cycling stability of sulfonated polyimide (SPI), a polyphosphazene with built-in -SO3H moieties (PP-SO3H), which is a porous covalent organic framework (COF) material, is facilely synthesized by the polymeric combination of hexachlorocyclotriphosphazene (HCCP) and p-diaminobenzenesulfonic acid. Due to its tunable pore size and flexible molecular design, the COF material can address the trade-off between the conductivity and the ion permeability of ion exchange membranes well, thereby improving the ion selectivity of membranes. The experimental results show that the SPI/PP-SO3H composite membrane has an excellent conductivity (up to 114.8 mS cm-1); the ion selectivity of the SPI/2% PP-SO3H membrane is 11.69 × 104 S min cm-3, which is 2.18 times higher than that of the SPI base membrane. PP-SO3H also improves the SPI membrane's mechanical strength, and the effect of PP-SO3H on SPI intermolecular interactions is analyzed by surface electrostatic potential (ESP) theoretical calculations. The Coulombic efficiency (CE) of the SPI/2% PP-SO3H membrane is 98.92%, the energy efficiency (EE) is 84.1% at a current density of 100 mA cm-2, and the self-discharge time of the SPI/2% PP-SO3H membrane is 3.5 times compared with the SPI base membrane. To measure the cycling stability of the composite membrane, the SPI/2% PP-SO3H membrane is cycled in the VRFB for more than 400 cycles, which is more stable than that of the SPI base membrane. These results show that SPI/2% PP-SO3H composite membranes are viable for VRFB applications.

Amination modification of graphene oxide for the in-situ synthesis of sulfonated polyimide-based composite proton exchange membranes

To mitigate the severe degradation of mechanical properties and stability of highly sulfonated proton exchange membranes (PEMs) caused by the sulfonic acid groups, amino-functionalized graphene oxide (AGO) was embedded into sulfonated polyimide (SPI) for the in-situ synthesis of a composite proton exchange membrane. The introduction of AGO nanoparticles facilitated the enhancement of the crystallinity of the composite membrane, with the well-constructed interface and dispersion. The resulting AGO-SPI composite membrane exhibited high mechanical strength and stability. The fracture strength of AGO-SPI composite membrane was approximately 61 MPa, which was 1.85 times higher than that of pure SPI. Meanwhile, the weight loss of AGO-SPI composite membrane in Fenton’s reagent was only 2.11 %. Additionally, at 90 °C/98 % RH, the proton conductivity of AGO-SPI composite membrane reached 50.1 mS cm−1, which was 3.53 times higher than that of pristine SPI. The results suggest the promising application prospects of the proton exchange composite membrane.

Construction and Investigation of Novel Cross-Linked Fluorine-Containing Sulfonated Polyimide Membranes for VFB Application.

Membrane with remarkable proton conductance and selectivity plays a key role in obtaining high vanadium flow battery (VFB) performance. In this work, the trade-off effect between proton conductance and vanadium ion blocking was overcome by the introduction of a cross-linking structure to prepare covalent cross-linked fluorine-containing sulfonated polyimide (CFSPI-PVA) membranes. Herein, the CFSPI-PVA-15 membrane possesses excellent comprehensive properties, including acceptable area resistance (0.21 Ω cm2), lower vanadium ion permeability (0.76 × 10-7 cm2 min-1), and remarkable proton selectivity (3.11 × 105 min cm-3) compared with the commercial Nafion 212 membrane. At the same time, the CFSPI-PVA-15 membrane exhibits higher coulomb efficiencies (97.26%-99.34%) and energy efficiencies (68.65%-88.11%) and a longer self-discharge duration (29.2 h) in contrast with the Nafion 212 membrane. Moreover, 500 cycles of the CFSPI-PVA-15 membrane at 160 mA cm-2 are also stably executed. The internal reasons for the improved chemical stability of the CFSPI-PVA-15 membrane are clarified from theoretical calculations with the mean square displacement value and fractional free volume. Therefore, the CFSPI-PVA-15 membrane exhibits great potential for application in VFB.

Investigation of branched sulfonated polyimide membranes containing self-synthesized trianhydride monomer for vanadium flow battery via a combined theoretical-experimental strategy

In this work, a new branched trianhydride monomer 1,3,5-tris(4-naphthyloxy-1,8-diacid) phthalic anhydride is established for improving the chemical/dimensional stability and proton conduction of the branched sulfonated polyimide (BSPI) membrane for application in vanadium flow battery (VFB). Compared with linear SPI-60 membrane containing conventional dianhydride monomer 1,4,5,8-naphthalenetetra-carboxylic dianhydride, BSPI-60 membrane exhibits remarkable resistance to vanadium ions, proton conduction and structural stability. Besides, the challenge of simultaneously improving vanadium ions resistance and proton conductance is tackled. The proton selectivity of BSPI-60 membrane achieves 1.11 × 105 S·min/cm3, which is 2.8 and 2.5 times higher than both SPI-60 (0.39 × 105 S·min/cm3) and commercial Nafion 212 (0.44 × 105 S·min/cm3) membranes, respectively. At the same time, BSPI-60 membrane exhibits higher coulomb efficiencies (97.2 %–99.3 %) and energy efficiencies (85.6 %–69.5 %) compared those of SPI-60 and Nafion 212 membranes at 100–300 mA/cm2. Remarkably, the 500 cycles of BSPI-60 membrane at 140 mA/cm2 are also stably executed. The internal reasons for enhanced chemical/dimensional stabilities and proton conduction of BSPI-60 membrane are clarified from theoretical calculations with mean square displacement value, fractional free volume and natural bond orbital charge via density functional theory and molecular dynamics simulation. Our study encompasses not only the synthesis of a novel branched trianhydride monomer but also the development of a BSPI membrane with a unique molecular structure specifically designed for VFB applications.

Preparation and study on H–MoS2/SLS modified SPI@SPEEK blend proton exchange membrane with balanced proton conductivity and stability

Proton exchange membranes (PEMs) are the core components of fuel cells, and research has long focused on how to balance their proton conductivity and durability. In this work, a series of homogeneous blend of sulfonated polyimide (SPI) and sulfonated polyether ether ketone (SPEEK) hybrid membranes with were constructed refined with sulfonated MoS2 (H–MoS2) and sodium lignosulfonate (SLS). The results showed that the tensile strength of the films was enhanced by 39.4% (67.84 MPa) compared to the base film. The composite films incorporating 1 wt% H-MoS2 and 2 wt% SLS has excellent proton conductivity, which can reach 50.24 mS/cm at 80°C and 100% humidity. The embed hybrid structure constructed by H–MoS2 and SLS, which not only effectively solves the limitations of the proton transport channel of traditional polymer materials, but also provides abundant proton transport sites, which provides a new strategy for preparing high-performance PEM.

Simultaneously improved H+ conductivity and H+/V4+ selectivity for all vanadium flow battery by ZIF-8 induced physical cross-linking

One of the major challenges in all vanadium redox flow battery (VRFB) is the trade-off between proton conductivity and vanadium ion cross-mixing. Here, we simultaneously enhanced proton conductivity and sharply reduced the vanadium crossover by introducing ZIF-8 into a sulfonated polyimide (6FTMA-100) to prepared a high performance VRFB membrane. Compared with the pristine membrane, the proton conductivity increased from 34.6 to 47.4 mS cm−1, and the vanadium ion permeation rates decreased from 3.56 × 10−7 to 0.82–1.88 × 10−7 cm2 min−1 with different ZIF-8 doping concentrations. The ZIF-8 doped membranes also showed increased viscosity, reduced membrane swelling ratio and increased Young's modulus. We propose this is due to the strong hydrogen bonding (−106.68 Kcal/mol) between the N in imidazole group and H in -SO3H. Battery performance confirmed that the optimized MMM-2 (2 % ZIF-8 loading) displayed the energy efficiency of 80 % at 160 mA cm−2 that much higher than its pristine 6FTMA-100, N117, and most of the reported sulfonated polyimides. This idea of creating physical crosslinked network provided an efficient way for achieving highly efficient VRFB membranes.

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.

A sulfonated polyimide containing flexible aliphatic segments with high chemical stability for vanadium redox flow battery application

To improve sulfonated polyimide (SPI) chemical stability, the SPI containing flexible aliphatic segments is successfully designed and synthesized. The highest occupied molecular orbital (HOMO) energy, lowest unoccupied molecular orbital (LUMO) energy and their energy gaps (HOMO-LUMO gap (ΔE)) can quantitatively compare the molecular reactivity, which are calculated and used to compare firstly in the SPIs for vanadium redox flow battery (VRFB) application. Furthermore, the natural bond orbital (NBO) charge of SPIs is also used to calculate and compare, respectively. Theoretical calculation shows SPI(DAD) has higher chemical stability. Obtained by experimental results that the retention time in water of SPI(DAD)-60 membrane is 23.58 h at 80 °C, which is nearly four times than conventional SPI under the same conditions. The SPI(DAD)-60 membrane at a current density of 100 mA cm−2 shows higher columbic efficiency (CE: 96.83%), and energy efficiency (EE: 79.47%) than that of N212 membrane (CE: 93.14%, EE: 74.13%). Besides, the SPI(DAD)-60 membrane has 479.1 mA h more charging capacity after 100 cycles compared to N212 membrane. The theoretical calculation of the LUMO energy, HOMO-LUMO gap may be a potential tool that is used to analyze and evaluate the chemical stability of membranes for VRFB 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.

Lyotropic Liquid Crystalline Property and Organized Structure in High Proton-Conductive Sulfonated Semialicyclic Oligoimide Thin Films.

Fully aromatic sulfonated polyimides with a rigid backbone can form lamellar structures under humidified conditions, thereby facilitating the transmission of protons in ionomers. Herein, we synthesized a new sulfonated semialicyclic oligoimide composed of 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA) and 3,3'-bis-(sulfopropoxy)-4,4'-diaminobiphenyl to investigate the influence of molecular organized structure and proton conductivity with lower molecular weight. The weight-average molecular weight (M w) determined by gel permeation chromatography was 9300. Humidity-controlled grazing incidence X-ray scattering revealed that one scattering was observed in the out-of-plane direction and showed that the scattering position shifted to a lower angle as the humidity increased. A loosely packed lamellar structure was formed by lyotropic liquid crystalline properties. Although the ch-pack aggregation of the present oligomer was reduced by substitution to the semialicyclic CPDA from the aromatic backbone, the formation of a distinct organized structure in the oligomeric form was observed because of the linear conformational backbone. This report is the first-time observation of the lamellar structure in such a low-molecular-weight oligoimide thin film. The thin film exhibited a high conductivity of 0.2 (±0.01) S cm-1 under 298 K and 95% relative humidity, which is the highest value compared to the other reported sulfonated polyimide thin films with comparable molecular weight.

Designing sulfonated polyimide-based fuel cell polymer electrolyte membranes using machine learning approaches

Fuel cells are the efficient electrochemical energy conversion devices with wide-ranging applications. Polymer Electrolyte Membrane (PEM) is the primary component of a PEM fuel cell whose proton conductivity majorly determines the performance of the fuel cells. Due to the high cost and limited range of operating parameters, alternatives of perfluorinated ionomers based commercial PEMs are urgently required. Sulfonated polyimides (SPIs) based hydrocarbon PEMs, have exhibited better proton conductivity even at low hydration levels and high temperatures, making them possible candidates for replacing commercial PEMs. However, finding alternative SPI PEMs is a critical polymer discovery problem that requires enormous experimental efforts where Machine learning (ML) approaches can help to reduce such efforts. To this end, both supervised and unsupervised ML approaches are developed to predict the proton conductivity of SPIs. A hybrid dataset of 81 unique SPIs is generated that consists of collected chemical structure–properties data from reported literature and calculated quantitative structure–property and semi-empirical quantum chemical descriptors. Using simple and interpretable Decision Trees, rules that lead to a low or high class of proton conductivity labels with high accuracy are identified. The trained decision tree model can accurately predict the proton conductivity class labels with a prediction accuracy of 88% and a kappa statistic of 0.77. The random forest regression (RFR) model, on the other hand, identified additional set of features that can predict proton conductivity with reasonable error. Thus, high information-gain features have been identified and their correlation with the proton conductivity class labels have been explored. These findings are key to designing novel SPI PEMs while correlating proton transport at the ionomer level with factors such as the morphology of the microstructure and inter-chain interactions.

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

Advances in polybenzimidazole based membranes for fuel cell applications that overcome Nafion membranes constraints

High-temperature proton exchange membrane fuel cells (PEMFCs) are becoming more appealing to researchers around the world due to several advantages such as high energy conversion efficiency, lightweight due to the use of polymeric materials, low noise due to the lack of mechanical components, zero or low emission of harmful greenhouse gases, simple design, first reaction kinetics, and simple water management. The performance, limitations, and possibilities for the practical implementation of different high-temperature proton exchange membranes (PEMs) utilized in fuel cells are discussed in this review paper. A suitable PEM must be developed to improve the performance of membrane electrode assemblies for high-temperature PEMFCs (working temperature above 100 °C). Various PEMs such as sulfonated poly(ether ether ketone) (SPEEK), sulfonated polystyrene (SPS), sulfonated polyimide (SPI), sulfonated polysulfone (SPSU), phosphoric acid doped polybenzimidazole (PA-PBI), perfluorosulfonic acid (PFSA) polymer-based membranes have been investigated as PEMs for fuel cell applications by several research groups. Among the various PEMs, PA-PBI membranes are the most promising high-temperature PEM for fuel cell applications because of their higher proton conductivity at high temperatures and anhydrous conditions, good chemical and thermal, mechanical stability, and high durability. However, the performance of high-temperature PEMs based on pristine PA-PBI is insufficient to fulfill the need for practical implementation of high-temperature PEMFCs, which needs to be enhanced further before they can be used commercially. Therefore, PA-PBI composite membranes containing various multifunctional inorganic, organic, and hybrid fillers are being actively explored to produce high-temperature PEMs. The PA-PBI composite membranes’ proton conductivity increases with rising temperature and maintains conductivity in anhydrous conditions, as well as chemical, thermal, and oxidative stability under operating conditions and long-term performance stability.

New polyimide ionomers derived from 4,4′-diamino-[1,1′-biphenyl]-2,2′-disulfonic acid for fuel cell applications

The set of important properties of polymers necessary for their use as fuel cell membranes, such as film-forming properties, stability in acidic aqueous media, thermal stability, proton conductivity, is determined by their chemical structure, which provides not only basic and fragmentary mobility of the polymer chain but also complex supramolecular structural features (in particular, phase separation). The effect of the chemical structure of aromatic polyimide sulfonic acids, containing a fragment of 4,4′-diamino[1,1′-biphenyl]-2,2′-disulfonic acid (BDSA), on their membrane-forming properties is discussed, as well as the membrane stability under the conditions of a hydrogen-air fuel cell. The research is aimed at investigating sulfonated polyimides based on the commercially available rigid monomer - BDSA and flexible dianhydrides with an electron donor in their structure. As a model for this study, two aromatic anhydrides with flexible -O- bonds were chosen for investigating the potential of corresponding polyimide films in application to proton exchange membranes. The synthesized sulfonic acid polyimide BDSA-SPI-4(H) is of interest as a proton-conducting membrane polymer for direct energy conversion electrochemical devices and has shown to be a promising material for this group of devices. It is suggested that the presence of the flexible electron donor bonds in the structure of dianhydride should increase the stability of the membranes prepared from BDSA. The properties of polyimide sulfonic acids from the aforementioned diamine and dianhydrides of different fragmentary flexibility implemented in this work could help the understanding of the connection between chemical structure and properties of the material in application to proton exchange membranes development.

A novel sulfonated aromatic polyimide synthesis and characterization: Energy calculations, QTAIM simulation study of the hydrated structure of one unit

AbstractA new type of sulfonated polyimide was synthesized from a one‐step polycondensation reaction with perylene‐3,4,9,10‐tetracarboxylic dianhydride and 4,4′‐diamino‐2,2′‐stilbenedisulfonic. Pure characterization of sulfonated polyimide (SPI) was performed by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, thermogravimetric analysis, differential thermal gravimetric analysis, ultraviolet–visible spectroscopy, and solubility tests. Moreover, the SPI film was prepared by a thermal imidization step heating procedure. Furthermore, quantum chemical calculations of the synthesized SPI were investigated with density functional theory (DFT) and time‐dependent density functional theory. By calculating the frontiers molecular orbital energies of the obtained polyimide, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), and the energy gap (Δ) values were found for the one structural unit and three structural units of SPI, respectively. Also, QTAIM was carried out based on the AIMAll program. With the increase in water molecules, the average electronic energy density (HBCP) value decreased according to the results of QTAIM. The SPI can be used as a potential membrane in fuel cells.

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.