Sulfonated Polybenzimidazole Membranes Research Articles

Elucidating proton conductivity performance of sulfonated polybenzimidazole polymer membranes: Lessons from molecular dynamics simulation

In this research, molecular dynamics (MD) simulation was performed to explore the proton conductivity performance of three different sulfonated polybenzimidazole (SPBI) polymers with the same backbone but different functional groups as proton exchange membranes. To date, there are a few published experimental works on different SPBI polymer membranes. However, those studies were in profound disagreement about the positive effect of pendant functional groups attached to the backbone on PBI performance; therefore, MD simulations were required to resolve the conflicts. By comparisons of the simulated solubility parameter and glass transition temperature with the experimental measurements, it was initially determined that a simulation box made up of three chains of the polybenzimidazole polymer—each comprising of 30 monomers—was an appropriate simulation box for amorphous materials. Additionally, mean square displacement was used to analyze the dynamics of the self-diffusion coefficients. The calculated diffusion coefficients were 2.0 × 10−6, 1.4 × 10−6, and 1.1 × 10−6 cm2/s for PBI-S (SO3H PBI), PBI-PS (propylsulfonate PBI), and PBI-AS (arylsulfonate PBI), respectively. Based on the results, it was understood that the simulated proton conductivities were comparable with the results obtained by some researchers and consequently against other conflicting claims. The calculated proton conductivities are 13.1, 7.8, and 5.7 mS/cm for PBI-S, PBI-PS, and PBI-AS, respectively. Moreover, the examination of the free volume in the SPBI membranes revealed that the hydronium ion transport is compatible with the Cohen-Turnbull model. Ultimately, by analyzing the radial/angular distribution functions and water clusters, a novel assessment of a potential proton conduction pathway completed the investigation. The findings imply that proton hopping via water cluster connections is feasible.

The Influence of Non-Charged Sidechains on the Performance of Meta-Polybenzimidazole Membranes in Vanadium Redox Flow Batteries

The global goal to combat climate change is growing year by year, as for example indicated by the latest climate conference by the United Nations, COP26. Hereby, one of the main goals concerns the transition from fossil fuels to more renewable energy means. In doing so, the importance of highly efficient energy storage technologies, such as supercapacitors, Li-ion batteries and/or redox flow batteries that both store and release energy on a short-, mid- and long-term scale, grows alongside it1. Among storage technologies, redox flow batteries (RFBs) are considered as promising candidates for mid-term storage (daily discharge for 2-12 h) due to their unique characteristic of a decoupled energy storage and power output2. To enable the incorporation of these systems into society further and thus smoothen the transition towards renewable energy technologies, highly efficient and low cost membranes in terms of efficiency and durability are needed, that will simultaneously improve the efficiency and reduce the cost of energy storage.One of the membrane types for vanadium redox flow battery (VRFB) applications that gained the interest of industry and the scientific community are of the polybenzimidazole (PBI) type. Although these materials possess excellent chemical stability and vanadium barrier properties, they suffer from a poor proton conductivity compared to commercial standards such as Nafion® 212. Several strategies were proposed to tackle this issue, ranging from the preparation of composite membranes with a thin PBI skin layer3, alkaline pretreatments that improve the swelling characteristics of the PBI film4 and chemical modifications to attach ionic conducting groups on the polymer backbone, thus directly improving the conductivity5. This latter approach showed that a highly conductive PBI membrane could be obtained by the addition of sidechains containing charged moieties such as sulfonic acid5. However, this improved conductivity comes at a price, specifically, a decrease in its vanadium barrier properties due to a significant crossover of vanadium ions, thus losing one of the main benefits of PBI type membranes5.The work presented herein describes the preparation of multiple PBI derivatives containing small and readily available non-charged sidechains, such as alkylated or benzylated PBI. Herein, it was envisaged that the addition of non-charged sidechains to the PBI backbone could increase the free volume of the membrane and thus enable the incorporation of electrolyte into the film without significantly affecting its repelling effect for vanadium ions. With this in mind, the influence of these non-charged sidechains on the ex-situ properties under VRFB conditions was studied in terms of dimensional swelling, acid uptake, vanadium barrier properties and mechanical strength. Hereby, key differences in the behavior of the membranes were observed between each individual type of functionalization, such as swelling, uptake and composition in acidic media. Subsequently, the correlation between the ex-situ properties of the PBI derivatives and in-situ VRFB cycling performance was studied to further understand their significance. Through this process, valuable knowledge was obtained that showed a clear correlation between the ex-situ properties and the observed in-situ area specific resistance, energy efficiency and capacity fading of the various materials, with the best material outperforming Nafion® 212 in terms of energy efficiency by 1% at a current density of 200 mA∙cm2, a current density regime that is normally dominated by cation exchange membranes due to their low resistance. Thereby proving that even a small modification of the PBI backbone can have a significant influence on the performance in a VRFB cell. Yuan, Z.; Duan, Y.; Zhang, H.; Li, X.; Zhang, H.; Vankelecom, I., Advanced porous membranes with ultra-high selectivity and stability for vanadium flow batteries. Energy & Environmental Science 2016, 9 (2), 441-447. Chae, I. S.; Luo, T.; Moon, G. H.; Ogieglo, W.; Kang, Y. S.; Wessling, M., Ultra-High Proton/Vanadium Selectivity for Hydrophobic Polymer Membranes with Intrinsic Nanopores for Redox Flow Battery. Advanced Energy Materials 2016, 6 (16), 1600517. Gubler, L.; Vonlanthen, D.; Schneider, A.; Oldenburg, F. J., Composite Membranes Containing a Porous Separator and a Polybenzimidazole Thin Film for Vanadium Redox Flow Batteries. Journal of The Electrochemical Society 2020, 167 (10), 100502. Noh, C.; Serhiichuk, D.; Malikah, N.; Kwon, Y.; Henkensmeier, D., Optimizing the performance of meta-polybenzimidazole membranes in vanadium redox flow batteries by adding an alkaline pre-swelling step. Chemical Engineering Journal 2020, 126574. Yan, X.; Dong, Z.; Di, M.; Hu, L.; Zhang, C.; Pan, Y.; Zhang, N.; Jiang, X.; Wu, X.; Wang, J.; He, G., A highly proton-conductive and vanadium-rejected long-side-chain sulfonated polybenzimidazole membrane for redox flow battery. Journal of Membrane Science 2020, 596, 117616.

Molecular dynamics simulation analysis of sulfonated polybenzimidazole/[formula omitted]: A potential polymer electrolyte membrane for high-temperature fuel cells

In this research work, the ionic conductivity performance of a prospective candidate polymer electrolyte membrane, sulfonated polybenzimidazole/[DEMA+][NTf2-], was investigated using the molecular dynamics simulation technique. At first, a unit cell consisting of three chains (each one consisting 30 monomers) of polybenzimidazole polymer was determined as the optimum amorphous unit cell by comparing the simulated solubility parameter and glass transition temperature with available experimental data. Furthermore, the behavior of the ionic self-diffusion coefficients was investigated using the mean square displacement curves. It was found that the diffusion of [DEMA+] and [NTf2-] depends on the degrees of sulfonation (DS) values: with increasing DS, the ionic self-diffusion coefficients enhance, which could be attributed to a reduction in [DEMA+][NTf2-]- polymer chains interactions. The results revealed that the simulated ionic conductivities of this ionic liquid-based membrane is comparable with other electrolyte membranes and would be suitable for high-temperature applications. In addition, the investigation was complemented with analysis of plausible proton conduction pathways by evaluating the radial/angular distribution function and cationic/anionic clusters. The results suggest that proton hopping through very short ionic bridges is possible but could not be dominated. This work would pave the way for further research into the new protic ionic liquid -doped sulfonated polybenzimidazole membranes for proton exchange membrane fuel cells.

A low vanadium permeability sulfonated polybenzimidazole membrane with a metal-organic framework for vanadium redox flow batteries

A proton selective membrane based on a metal-organic framework (MOF) and polybenzimidazole (PBI) with a controllable sulfonation degree is designed for vanadium redox flow battery (VRFB) applications. The size of UiO-66 is between hydrated multivalent vanadium ions and stokes radius of protons, and its suitable pore size can obstruct the penetration of vanadium ions, resulting in a high vanadium resistance rate. Simultaneously, the imidazole groups and sulfonic acid groups in the sulfonated polybenzimidazole compose the acid-base pairs, which block the penetration of vanadium ions. Therefore, sulfonated PBI together with UiO-66 forms a denser network structure for as a vanadium ion barrier. Compare with the Nafion117 film, the vanadium transmittance of prepared composite film is lower (5.15 × 10−7 cm2 min−1 vs. 2.95 × 10−9 cm2 min−1). Compare with the Nafion117 membrane, VRFB with MOF polymer exhibits higher voltage efficiency (94.54%–74.93%) and energy efficiency (84.82%–73.98%) at 40-200 mA•cm−2.

A highly proton-conductive and vanadium-rejected long-side-chain sulfonated polybenzimidazole membrane for redox flow battery

A long-side-chain sulfonated polybenzimidazole (PBI-PS) membrane was successfully prepared by the reaction of PBI with 1, 3-propanesultone for improving the efficiencies of vanadium redox flow battery. The interaction between sulfonic acid and imidazole groups provides the PBI-PS membrane with excellent swelling resistance, leading to a swelling ratio of only 13% for the membrane with IEC of as high as 3.18 mmol g−1. This results in an ultra-low vanadium permeability (6.5 × 10−9 cm2 s−1). The introduction of sulfonic acid-terminated flexible side chain in the membrane also constructs good microphase separation structure, leading to a low area resistance of 0.51 Ω cm2, which is close to Nafion 212 (0.41 Ω cm2). This membrane exhibits excellent cell performance. The voltage and energy efficiencies are up to 90.73% and 89.13% at 80 mA cm−2, respectively. Furthermore, the efficiencies remain constant values for 200 cycles, and no changes in chemical structure and cell efficiencies are observed after 720 h immersion in electrolyte solution.

Thermally crosslinked sulfonated polybenzimidazole membranes and their performance in high temperature polymer electrolyte fuel cells

The degradation pathway of phosphoric acid doped polybenzimidazole membranes in high temperature polymer electrolyte membrane fuel cells depends on the acid contents. If it is high, creep is discussed as the main reason. If it is low (membranes prepared by solvent evaporation and post-doping), the main cause may be loss of acid due to evaporation. The net transport of acid to the anode side at high current densities should also lead to local softening of the membrane, which could be mitigated by crosslinking the membrane.Here we show that sulfonated para-polybenzimidazole membranes can be stabilized by curing at 350 °C. In contrast to meta-polybenzimidazole and sulfonated para-polybenzimidazole, crosslinked sulfonated para-polybenzimidazole is insoluble in dimethylacetamide at room temperature and phosphoric acid at 160 °C. At 160 °C and 5% relative humidity the conductivity of crosslinked sulfonated para-polybenzimidazole and meta-polybenzimidazole is 214 mS cm−1 and 147 mS cm−1, respectively. At 600 mA cm−2, the voltage decay rate is 16 μV h−1, much lower than published for commercial meta-polybenzimidazole (308 μV h−1). Furthermore, the average voltage at 600 mA cm−2 is 523 mV, while a previously published cured meta-polybenzimidazole membrane only reaches 475 mV.

Enhancing proton conductivity of polybenzimidazole membranes by introducing sulfonate for vanadium redox flow batteries applications

Acid doped polybenzimidazole membrane can transport protons and is a potential proton exchange membrane for vanadium redox flow battery applications. But the proton conductivity of polybenzimidazole membranes is just moderate; the vanadium redox flow battery assembled with polybenzimidazole membranes usual cannot achieve satisfactory voltage efficiency. Therefore, the main aim of this study is to prepare high proton conductivity polybenzimidazole membranes. A series of sulfonated polybenzimidazoles with different sulfonation degree are synthesized. The 5-sulfoisophthalic acid monosodium salt is introduced not only to control the sulfonation degree of the polymer but also to enhance the hydrophilicity of polybenzimidazole and further increase the proton conductivity of polybenzimidazole membrane. The physicochemical properties and single cell performance of sulfonated polybenzimidazoles membranes are thoroughly assessed. The results indicate that the water uptake of membranes are enhanced as the sulfonation degree increases and is superior to increase the proton conductivity. But sulfonate can also form hydrogen bonds with the basic groups N= in imidazole rings and block the protons transport. Ultimately, sulfonated polybenzimidazole membrane with the sulfonation degree of 30% exhibites the highest proton conductivity as well as energy efficiency.

Ultrasonic irradiation to modify the functionalized bionanocomposite in sulfonated polybenzimidazole membrane for fuel cells applications and antibacterial activity

In this article the new proton exchange membranes were prepared from sulfonated polybenzimidazole (s-PBI) and various amounts of sulfonated titania/cellulose nanohybrids (titania/cellulose-SO3H) via ultrasonic waves. The ultrasonic irradiation effectively changes the rheology and the glass transition temperature and the crystallinity of the composite polymer. Ultrasonic irradiation has a very strong mixing and dispersion effect, much stronger than conventional stirring, which can improve the dispersion of titania/cellulose-SO3H nanoparticles in the polymer matrix. The strong –SO3H/–SO3H interaction between s-PBI chains and titania/cellulose-SO3H hybrids leads to ionic cross-linking in the membrane structure, which increases both the thermal stability and methanol resistance of the membranes. After acid doping with phosphoric acid, s-PBI/titania/cellulose-SO3H nanocomposite membranes exhibit depressions on methanol permeability and enhancements on proton conductivity comparing to the pristine s-PBI membrane. The chemical structure of the functionlized titania was characterized with FTIR, and energy-dispersive X-ray. Imidazole and sulfonated groups on the surface of modified nanoparticles forming linkages with s-PBI chains, improved the compatibility between s-PBI and nanoparticles, and enhanced the mechanical strength of the prepared nanocomposite membranes. From SEM and TEM analysis could explain the homogeneous dispersion of titania/cellulose-SO3H in nanocomposite membranes. Moreover, the membranes exhibited excellent antibacterial activities against S. aureus and E. coli. A.

Characterizing Voltage Losses in an SO2 Depolarized Electrolyzer Using Sulfonated Polybenzimidazole Membranes

The hybrid sulfur cycle has been investigated as a means to produce CO2-free hydrogen efficiently on a large scale through the decomposition of H2SO4 to SO2, O2, and H2O, and then electrochemically oxidizing SO2 back to H2SO4 with the cogeneration of H2. The net effect is the production of hydrogen and oxygen from water. Recently, sulfonated polybenzimidazoles (s-PBI) have been investigated as a replacement for Nafion due to the ability to offer increased process efficiency through the generation of higher acid concentrations at lower potentials. Here, we measure the acid concentrations and individual potential contributions toward the overall operating voltage seen in the SO2-depolarized-electrolyzer. We then determine model parameters necessary to predict voltage losses in a cell over a wide range of operating temperatures, pressures, currents and reactant flow rates.

Preparation of covalently cross-linked sulfonated polybenzimidazole membranes for vanadium redox flow battery applications

A series of polybenzimidazole copolymers with varied content of pendant amino groups have been synthesized by condensation polymerization of 4,4′-dicarboxydiphenyl ether (DCDPE), 5-aminoisophthalic acid (APTA) and 3,3′-diaminobenzidine (DAB) in polyphosphoric acid at 190°C for 20h. The resulting copolymers undergo post-sulfonatation in fuming sulfuric acid at 100°C yielded the highly sulfonated polybenzimidazoles (SOPBI-NH2(x/y), ‘x/y’ refers to the monomer molar ratio of DCDPE to APTA). A series of covalently cross-linked membranes (CSOPBI-NH2(x/y)) with good mechanical properties are fabricated by solution cast technique using bisphenol A epoxy resin as a cross-linker. The CSOPBI membranes show 3–4 orders of magnitude lower VO2+ permeability and 6–30 times higher ion diffusion selectivity (proton vs. VO2+) than Nafion117. The charge-discharge behaviors of the vanadium redox flow batteries (VRBs) assembled with the CSOPBI-NH2(x/y) membranes and Nafion 117 are investigated and compared. The VRBs assembled with the CSOPBI membranes exhibit significantly higher columbic efficiency and lower self-discharge rate than that assembled with Nafion 117 owing to the extremely lower vanadium cations crossover of the former. The VRB assembled with the CSOPBI-NH2(9/1) membrane exhibits fairly high energy efficiency (~85% at 60mAcm−2) and little decay in performance is observed after 300 charge-discharge cycles.

Ion Dynamics and Mechanical Properties of Sulfonated Polybenzimidazole Membranes for High-Temperature Proton Exchange Membrane Fuel Cells

Polybenzimidazole (PBI)-based membranes are one of the systems of choice for polymer electrolyte fuel cells. Monomer sulphonation is one of the strategies suggested to improve proton transport in these membranes. We report a NMR and dynamic mechanical study aiming to investigate the effect of the sulphonation on the proton dynamics and the mechanical properties of the membranes. The analyses of 1H self-diffusion coefficients and 1H and 31P spectra versus temperature show that sulphonation causes the formation of interchain cross-links, which involve phosphoric acid molecules and the sulfonic groups. This, in turn, reduces the proton mobility and, consequently, the ionic conductivity. The increase of the membrane stiffness with sulphonation is confirmed by dynamic mechanical analysis through the behavior of the storage modulus.

Modeling of high temperature proton exchange membrane fuel cells with novel sulfonated polybenzimidazole membranes

In this study, a three-dimensional, steady-state, non-isothermal numerical model of high temperature proton exchange membrane fuel cells (HT-PEMFCs) operating with novel sulfonated polybenzimidazole (SPBI) membranes is developed. The proton conductivity of the phosphoric acid doped SPBI membranes with different degrees of sulfonation is correlated based on experimental data. The predicted conductivity of SPBI membranes and cell performance agree reasonably with published experimental data. It is shown that a better cell performance is obtained for the SPBI membrane with a higher level of phosphoric acid doping. Higher operating temperature or pressure is also beneficial for the cell performance. Electrochemical reaction rates under the ribs of the bipolar plates are larger than the values under the flow channels, indicating the importance and dominance of the charge transport over the mass transport.

Synthesis and Characterization of Sulfonated Polybenzimidazole (SPBI) Copolymer for Polymer Exchange Membrane Fuel Cell

A diverse sulfonated polybenzimidazole copolymer (SPBI) as proton exchange membrane was synthesiszed via one-step high temperature polymerization method with 3,3-diaminobenzidine (DABD), 5-sulfoisophthalic acid (SIPA), 4,4-sulfonyldibenzoic acid (SDBA) and biphenyl-4,4-dicarboxylic acid (BDCA). The SPBI membrane was prepared through a direct hot-casting and in situ phase inversion technique. Characterization tests were carried out on the membranes including surface morphology, distribution of elements on the membrane, determination of functional groups, thermal stability, ion exchange capacity, water uptake rate and proton conductivity. The as-synthesized SPBI membrane displayed a smooth surface via scanning electron microscopy (SEM) analysis which is thermally stable up to 443 °C. The SPBI membrane showed higher water uptake rate (WUR) and proton conductivity though it had lower ion exchange capacity (IEC) value compared to recast Nafion membrane. The proton conductivity of the SPBI membrane with IEC of 0.60 mmol/g was 4.50 × 10-2 S/cm at 90 °C. This study shows that the SPBI membrane has great potential in polymer exchange membrane fuel cell (PEMFC) applications.

Sulfonated polybenzimidazole membranes for pervaporation dehydration of acetic acid

Abstract In this study, a novel sulfonated polybenzimidazole (SPBI) membrane has been developed and investigated for pervaporation dehydration of acetic acid, via a two-step sulfonation modification technique—sulfonation with sulfuric acid followed by a thermal treatment at 450 °C. Both steps are found indispensible in order to produce a stable SPBI membrane with enhanced acid resistance and superior separation performance. Effects of the sulfuric acid concentration and thermal treatment duration have been investigated and found to have significant impact on the pervaporation performance of the resultant SPBI membranes. Various characterizations (FTIR, XPS, TGA and XRD) are employed to elucidate the physicochemical changes of membranes as a function of chemical and thermal modifications. In addition, effects of pervaporation temperature and feed composition are studied not only in terms of flux and separation factor, but also of membrane intrinsic permeance and selectivity. The best pervaporation performance of the SPBI membrane has a flux of 207 g/m 2 /h and a separation factor of 5461 for dehydration of a 50/50 wt% acetic acid/water feed solution at 60 °C, which not only outperforms the conventional distillation process, but also surpasses most other polymeric pervaporation membranes reported in literature. It is therefore believed that the novel developed SPBI membrane may have great potential for pervaporation dehydration of acidic organics, as well as other applications that demand acid-proof materials.

Sulfonated polybenzimidazole membranes — preparation and physico-chemical characterization

The preparation of sulfonated polybenzimidazole by sulfuric acid treatment on pre-formed polybenzimidazole membranes was investigated. This polymer, which is originally a thermal resistant and insulating material is transformed by the chemical treatment into a proton conductor. The modified material is stable at temperatures close to 400°C. The proton conductivity of the sulfonated membrane at 160°C and 100% r.h. is 7.5×10 −5 S/cm. The low conductivity is explained by protonation of nitrogen in the imidazolium ring, as evidenced by FT-IR analysis, which lowers the proton mobility. Hydrogen bridge bonds are formed between nitrogen in the imidazole and oxygen of sulfonic group creating a more regular structure in the material which becomes insoluble in polar solvent such as dimethyl sulfoxide. These modifications of the material have been observed in the X-ray diffraction patterns, which evidence an incipient crystalline structure of the sulfonated polybenzimidazole.