Pure Polybenzimidazole Research Articles

A Stable Polymer-Blended Anion-Exchange Membrane for Enhanced Performance in Redox Flow Batteries

Redox flow batteries (RFBs) operate with a membrane, responsible for the separation of cationic active species and allowing the passage of counter-ions, to preserve electroneutrality on each side of RFBs. Commercial cation-exchange membranes (CEMs), such as Nafion®, possess excellent ionic conductivity and chemical stability. However, they face challenges in blocking cationic active species common in RFBs, leading to significant capacity loss over time. Anion-exchange membranes (AEMs) efficiently block active species with the assistance of the Donnan effect. Nevertheless, commercial AEMs lack acid stability and conductivity compared to their cationic counterparts.Polytetrafluoroethylene (PTFE)-reinforced quaternary ammonium cardo poly(ether)ketone (QPEK-C)-based membranes with Al2O3 additives (PQPAM), a heterogeneous AEM developed in our lab1, possess excellent ionic conductivity with low permeability of active species and good mechanical properties. PQPAM has demonstrated better acid stability than commercial AEMs. However, its acidic and oxidative stability require improvement, as evidenced by degradation after 250 hours of in-situ harsh RFB cycling due to the heterogeneous nature of PQPAM and the exposure of the susceptible QPEK-C-rich side to the electrolytes2. To address this issue, we propose a strategy to enhance the chemical stability of QPEK-C-based membranes by inhibiting the exposure of QPEK-C to oxidation agents through blending with a hydrophobic engineering thermoplastic like polybenzimidazole (PBI)3,4. Furthermore, PBI's known ability to protonate in acidic media will reinforce ionic conductivity and the separation of active species, thus improving the Donnan effect, in addition to enhancing chemical and mechanical stability.Elemental analyses and microscopy images confirm a homogeneous blending of PBI and QPEK-C, promising stability improvement. The results of ex-situ tests on ionic conductivity, cation permeability, and chemical stability align with the mentioned hypotheses, showcasing that blend of PBI/QPEK-C outperforms pure PBI and QPEK-C AEMs. Additionally, the mechanical properties of the PBI/QPEK-C blended AEMs are improved compared to pure QPEK-C AEMs and PBI/QPEK-C blended AEMs outperform pure PBI and QPEK-C AEMs in in-situ cycling tests with our patented titanium-cerium RFBs5. Moreover, this work will explore other strategies to improve the blended AEM properties, such as utilizing inorganic fillers or PTFE reinforcement.

Constructing immobilized H3PO4 network in nanosized ZSM-5 zeolitic framework achieves high proton conductivity after acceleration acid leaching test

In the midst of demand for the high and stable anhydrous proton conducting membrane for the high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), phosphoric acid (PA)-doped polybenzimidazole (PBI) is positioned as one of the most promising candidates. The key to develop the PA-PBI is to address the issue of phosphoric acid leaching, which causes significant performance deterioration. Here we introduced the nanosized ZSM-5 zeolite which plays the role of the rigid cage for confining H3PO4 to the PBI, and then evaluated by utilizing the acceleration acid leaching test (ALT) to put long-term operation in perspective. The ZSM-5 not only retain the high degree of PA after ALT, but also constructs the efficient proton conducting channel derived by the chemically-immobilized H3PO4 in pore channel. After ALT, PBI electrolyte membrane with 5 wt% of ZSM-5 exhibited 2.8 × 10−5 S cm−1 of proton conductivity at 150 °C anhydrous condition, which is three orders higher magnitude than pure PBI (1.1 × 10−8 S cm−1). Furthermore, H2/O2 HT-PEMFC single-cell constructed with PBI/5%ZSM-5 displayed an excellent maximum power density of 387 mW cm−2 at 150 °C anhydrous conditions, even after the ALT. The results indicate the possible improvement of the long-term stability of the fuel cell by utilizing readily available ZSM-5.

Poly(phenylene oxide) cross-linked with polybenzimidazole for the applications of high-temperature proton-exchange membrane fuel cells

A series of imidazolium-functionalized poly(phenylene oxide) (QPPO) cross-linked with polybenzimidazole (PBI) (cQPPOx-PBI) membranes were prepared. Compared to the pure PBI membrane without a cross-linked structure nor imidazolium groups, the cQPPOx-PBI membranes showed enhanced toughness, phosphoric acid (PA) retention, and chemical stability. The cQPPOx-PBI membranes showed a enhanced PA uptake than that of PBI membranes, and the cQPPO35-PBI membrane achieves a high conductivity of 139 mS cm−1 at 160 °C, which is much higher than that of PBI membrane under the same conditions (26 mS cm−1). The performance of the single fuel cell assembled with the obtained membranes showed a similar trend as their conductivity, and the cell with cQPPO35-PBI showed a maximum power density of 344 mW cm−2 at 140 °C, while the value for PBI membrane was only 175 mW cm−2 under the same conditions. Herein, a straightforward method was developed for introducing imidazolium groups and cross-linked structures, which can be employed to prepare PEMs with enhanced performance for HT-PEMFCs application.

Cucurbit[6]uril builds a water channel for improving the water/salt selectivity of polybenzimidazole

Polybenzimidazole (PBI) has garnered significant interest in desalination due to its exceptional chemical stability and mechanical strength, but suffers from poor water permeability. In this work, different contents of hydroxylated Cucurbit [6]uril (CB [6] were added to PBI to build a “water transport channel”. The effects of CB [6] addition on the chemical structure and surface morphology were analyzed by FTIR, SEM, and Zeta potential, respectively. Based on the solution-diffusion model, the effect of CB [6] on the water/salt transport properties of PBI membranes was thoroughly investigated. The results show that appropriate CB [6] doping can enhance water sorption of PBI through the special “outer hydrophilic and inner hydrophobic cavity” structure, and boost water diffusion with the channeling effect of the hydrophobic CB [6] cavity. While the complexation between the carbonyl group in CB [6] and Na+ ions slightly increased salt sorption, the specific cavity structure of CB [6] can significantly decrease salt diffusion by blocking salt ions and increasing transport path tortuosity. The cavity effect of CB [6] was further confirmed by hybridizing CB [6] with biphenylsulfonyl-substituted PBI when the cavity can be occupied. Therefore, the introduction of CB [6] improves the water/salt diffusion selectivity and then the permeability selectivity of PBI. Notably, the PBI@CB [6] membrane with a 0.25 wt% CB [6] loading exhibited a 40-fold increase in water permeability coefficient compared to pure PBI, while experiencing only a slight decrease in salt permeability coefficient, water/salt selectivity almost exceeding the empirical upper bound line of polymers. This work provides a theoretical foundation for the development of high-performance desalination membranes based on macrocyclic molecules such as CB [6].

Study of Innovative GO/PBI Composites as Possible Proton Conducting Membranes for Electrochemical Devices.

The appeal of combining polybenzimidazole (PBI) and graphene oxide (GO) for the manufacturing of membranes is increasingly growing, due to their versatility. Nevertheless, GO has always been used only as a filler in the PBI matrix. In such context, this work proposes the design of a simple, safe, and reproducible procedure to prepare self-assembling GO/PBI composite membranes characterized by GO-to-PBI (X:Y) mass ratios of 1:3, 1:2, 1:1, 2:1, and 3:1. SEM and XRD suggested a homogenous reciprocal dispersion of GO and PBI, which established an alternated stacked structure by mutual π-π interactions among the benzimidazole rings of PBI and the aromatic domains of GO. TGA indicated a remarkable thermal stability of the composites. From mechanical tests, improved tensile strengths but worsened maximum strains were observed with respect to pure PBI. The preliminary evaluation of the suitability of the GO/PBI X:Y composites as proton exchange membranes was executed via IEC determination and EIS. GO/PBI 2:1 (IEC: 0.42 meq g-1; proton conductivity at 100 °C: 0.0464 S cm-1) and GO/PBI 3:1 (IEC: 0.80 meq g-1; proton conductivity at 100 °C: 0.0451 S cm-1) provided equivalent or superior performances with respect to similar PBI-based state-of-the-art materials.

Synthesis of phosphonated graphene oxide by electrochemical exfoliation to enhance the performance and durability of high-temperature proton exchange membrane fuel cells

The doping of functionalized graphene oxide (GO) in the membranes becomes a promising method for improving the performance of high-temperature proton exchange membrane fuel cells (HT-PEMFC). Phosphonated graphene oxide (PGO) with a P/O ratio of 8.5% was quickly synthesised by one-step electrochemical exfoliation based on a three-dimensiaonal (3D) printed reactor and natural graphite flakes. Compared with the GO prepared by the two-step electrochemical exfoliation method, the PGO synthesized by the one-step electrochemical exfoliation can better improve the performance of the membrane-electrode-assembly (MEA) based on the polybenzimidazole (PBI) membrane in the HT-PEMFC. The doping of 1.5 wt% GO synthesised by electrochemical exfoliation with the 2-step method or reactor method in PBI increased the peak power density by 17.4% or 35.4% compared to MEA based on pure PBI membrane at 150 °C, respectively. In addition, the doping of PGO in PBI improves its durability under accelerated stress test (AST).

Performance and Durability of HT-PEMFC Enhanced By One-Step Electrochemical Exfoliated Phosphonated Graphene Oxide

The high-temperature proton exchange membrane fuel cell (HT-PEMFC) conducts protons through the hydrogen bond network established by the polymer and phosphoric acid (PA), which reduces the dependence on humidity and allows its operating temperature to be higher than 100°C [1]. A higher operating temperature is conducive to improve catalyst activity, reducing carbon dioxide adsorption on the catalyst thus reducing the requirement for hydrogen purity, and convenient water management [2]. As the most widely commercialized HT-PEMFC proton exchange membrane material, the performance and durability of Polybenzimidazole (PBI) still need to be improved. In particular, it has insufficient proton conductivity, insufficient mechanical properties, and phosphoric acid leaching issues under high acid doping level [3] [4] [5].The doping of functionalized graphene oxide in the PBI membrane can build additional proton transfer channels, promote proton hopping and act as a trap for PA to reduce its leaching by virtue of abundant functional groups of functionalized GO [6] [7] [8]. Among the groups that can be used for functionalization, the phosphoric acid group has become one of the most promising due to its strong hydrogen bonding and water retention ability [9] [10] [11]. Phosphonated graphene oxide (PGO) is usually synthesized by further phosphonation of GO obtained by chemical exfoliation [6] [7]. Chemical exfoliation methods usually require the long-term action of strong acids and strong oxidants [12]. The safety and environmental issues caused by those methods can not be underestimated. And the two-step synthesis method of PGO has a long reaction period.This work achieved the rapid, safe, and large-yield production of electrochemically exfoliated PGO by using a 3D printed reactor, ammonium dihydrogen phosphate as the electrolyte and natural graphite flakes as the raw material. The two-step electrochemical exfoliation method of producing GIC with concentrated sulfuric acid as the first electrolyte is also used to synthesize electrochemical exfoliated (E)GO. 1.5wt% EGO or PGO was doped in the PBI membrane to explore the effect of different GO on the performance and durability of the PBI- membrane-based HT-PEMFC. Compared with pure PBI, the doping of EGO and PGO increases the peak power density of HT-PEMFC by 17.4% and 35.4%, respectively.[1] Y.-L. Ma, J.S. Wainright, M.H. Litt, R.F. Savinell, Journal of The Electrochemical Society 2004, 151, A8.[2] H. Su, S. Pasupathi, B. Bladergroen, V. Linkov, B.G. Pollet, International Journal of Hydrogen Energy 2013, 38, 11370.[3] S. Galbiati, A. Baricci, A. Casalegno, R. Marchesi, International Journal of Hydrogen Energy 2013, 38, 6469.[4] S.H. Eberhardt, F. Marone, M. Stampanoni, F.N. Büchi, T.J. Schmidt, Journal of Synchrotron Radiation 2014, 21, 1319.[5] Q. He, X. Yang, W. Chen, S. Mukerjee, B. Koel, S. Chen, Physical Chemistry Chemical Physics 2010, 12, 12544.[6] J. Yang, C. Liu, L. Gao, J. Wang, Y. Xu, R. He, RSC Advances 2015, 5, 101049.[7] C. Xu, Y. Cao, R. Kumar, X. Wu, X. Wang, K. Scott, Journal of Materials Chemistry 2011, 21, 11359.[8] Y. Cai, Z. Yue, S.X.-J. of A.P. Science, undefined 2017, Wiley Online Library 2017, 134, 44986.[9] E. Abouzari-Lotf, H. Ghassemi, A. Shockravi, T. Zawodzinski, D. Schiraldi, Polymer 2011, 52, 4709.[10] E. Abouzari-Lotf, M. Zakeri, M.M. Nasef, M. Miyake, P. Mozarmnia, N.A. Bazilah, N.F. Emelin, A. Ahmad, Journal of Power Sources 2019, 412, 238.[11] S. Some, I. Shackery, S.J. Kim, S.C. Jun, Chemistry - A European Journal 2015, 21, 15480.[12] C. Xu, Y. Cao, R. Kumar, X. Wu, X. Wang, K. Scott, Journal of Materials Chemistry 2011, 21, 11359.

Single-Layer-Graphene and Electrochemical Exfoliated Graphene Oxide for HT-PEMFC

High-temperature proton exchange membrane fuel cell (HT-PEMFC) is promising with its low demand for hydrogen purity, simple water management, and high waste heat utilization [1][2]. Although polybenzimidazole (PBI), as a typical high-temperature fuel cell membrane, has been developed for a long period, it still has defects such as phosphoric acid leaching and insufficient mechanical properties under high acid doping level [3][4]. With its unique 2D hexagonal grid structure and its electron cloud arrangement, single-layer graphene (SLG) can block the passage of any atoms [5]. However, hydrogen protons can easily penetrate SLG through a unique intermediate state mechanism to make it have excellent proton conductivity [6]. SLG's high proton conductivity combined with its excellent mechanical properties and thermal conductivity make it an ideal material for blocking phosphoric acid leaching. The SLG prepared by the chemical vapor deposition (CVD) method was transferred to the surface of catalyst layer of electrodes by the wet chemical transfer method. Due to the rupture and incompleteness of the SLG during the transfer process, the coverage rate of the SLG on the electrode surface is about 55%. This incomplete coverage facilitates small quantities of phosphoric acid leaching from PBI membrane to electrodes, which increases the three-phase boundary area and improves the performance of the HT-PEMFC. After 70 hours of accelerated stress testing (AST), the peak power density of membrane-electrode-assembly (MEA) with SLG on both sides of the cathode and anode can reach 480 mW cm-2, while the peak power density of MEA based on pure PBI membrane is only 249 mW cm-2. The quantification of phosphoric acid in the electrode by Lab based X-ray micro-computed tomography and the Raman spectroscopic mapping of the MEA cross-section shows that SLG can mitigate the leaching of phosphoric acid in the PBI film and improve the durability of HT-PEMFC. Graphene oxide (GO) is a low-cost application of graphene. Its doping in the PBI membrane can also reduce the leaching of phosphoric acid through enhancing the interaction between phosphoric acid and the PBI membrane [7]. A reactor based on 3D printing was designed so that natural graphite flakes can be used for electrochemical exfoliation to achieve rapid, safe, environmentally friendly, and mass production of GO. The electrochemically exfoliated (E)GO is doped in the PBI membrane. The 0.5%, 1% and 2% EGO loadings in the PBI membrane increased the peak power density by 13.8%, 24.4% and 29.2%, respectively.[1] Y.-L. Ma, J.S. Wainright, M.H. Litt, R.F. Savinell, Conductivity of PBI Membranes for High-Temperature Polymer Electrolyte Fuel Cells, Journal of The Electrochemical Society. 151 (2004) A8. https://doi.org/10.1149/1.1630037/XML.[2] H. Su, S. Pasupathi, B. Bladergroen, V. Linkov, B.G. Pollet, Optimization of gas diffusion electrode for polybenzimidazole-based high temperature proton exchange membrane fuel cell: Evaluation of polymer binders in catalyst layer, International Journal of Hydrogen Energy. 38 (2013) 11370–11378. https://doi.org/10.1016/J.IJHYDENE.2013.06.107.[3] S. Galbiati, A. Baricci, A. Casalegno, R. Marchesi, Degradation in phosphoric acid doped polymer fuel cells : A 6000 h parametric investigation, International Journal of Hydrogen Energy. 38 (2013) 6469–6480. https://doi.org/10.1016/j.ijhydene.2013.03.012.[4] S.H. Eberhardt, F. Marone, M. Stampanoni, F.N. Büchi, T.J. Schmidt, Quantifying phosphoric acid in high-temperature polymer electrolyte fuel cell components by X-ray tomographic microscopy, Journal of Synchrotron Radiation. 21 (2014) 1319–1326. https://doi.org/10.1107/S1600577514016348.[5] S. Hu, M. Lozada-Hidalgo, F.C. Wang, A. Mishchenko, F. Schedin, R.R. Nair, E.W. Hill, D.W. Boukhvalov, M.I. Katsnelson, R.A.W. Dryfe, I. V. Grigorieva, H.A. Wu, A.K. Geim, Proton transport through one-atom-thick crystals, Nature. 516 (2014) 227–230. https://doi.org/10.1038/nature14015.[6] S.M. Holmes, P. Balakrishnan, V.S. Kalangi, X. Zhang, M. Lozada-Hidalgo, P.M. Ajayan, R.R. Nair, 2D Crystals Significantly Enhance the Performance of a Working Fuel Cell, Advanced Energy Materials. 7 (2017) 1–7. https://doi.org/10.1002/aenm.201601216.[7] J. Li, X. Zeng, T. Ren, E. van der Heide, The Preparation of Graphene Oxide and Its Derivatives and Their Application in Bio-Tribological Systems, Lubricants 2014, Vol. 2, Pages 137-161. 2 (2014) 137–161. https://doi.org/10.3390/LUBRICANTS2030137.

Zwitterionic interface engineering enables ultrathin composite membrane for high-rate vanadium flow battery

Thin membranes with high conductivity are of great importance for high power density vanadium flow batteries (VFBs), however, the trade-off between conductivity and ion selectivity limits their further development. Herein, an ultrathin composite membrane (∼10 μm) enabled by a zwitterionic interface between conductive polybenzimidazole (PBI) and porous polyethylene (PE) substrate is proposed to break the trade-off, and greatly enhance the power density of a VFB. The zwitterionic interface is engineered by the covalent reaction between polydopamine and zwitterionic sulfonated 3-dimethylaminopropylamine (DMAPAPS). The as-fabricated composite membrane features excellent mechanical properties and high dimensional stability. Furthermore, the zwitterionic interface facilitates proton transportation while blocking vanadium-ion permeation. More importantly, the ion selectivity of the ultrathin membrane is nearly three times higher than the pure PBI membrane (i.e., 2.71 × 104 vs. 1.09 × 104 S min cm−3). As a result, a VFB assembled with the ultrathin membrane demonstrates a superior energy efficiency of 78.7% at 300 mA cm−2, and achieves an excellent cycle stability over 500 cycles at 300 mA cm−2. Therefore, the engineering of zwitterionic interface provides a promising strategy in the development of ultrathin composite membrane for high power density VFBs.

Probing the Nanoscale Heterogeneous Mixing in a High-Performance Polymer Blend.

The blend of polyetheretherketone (PEEK) and polybenzimidazole (PBI) produces a high-performance blend (PPB) that is a potential replacement material in several industries due to its high temperature stability and desirable tribological properties. Understanding the nanoscale structure and interface of the two domains of the blend is critical for elucidating the origin of these desirable properties. Whilst achieving the physical characterisation of the domain structures is relatively uncomplicated, the elucidation of structures at the interface presents a significant experimental challenge. In this work, we combine atomic force microscopy (AFM) with an IR laser (AFM-IR) and thermal cantilever probes (nanoTA) to gain insights into the chemical heterogeneity and extent of mixing within the blend structure for the first time. The AFM-IR and nanoTA measurements show that domains in the blend are compositionally different from those of the pure PEEK and PBI polymers, with significant variations observed in a transition region several microns wide in proximity to domain boundary. This strongly points to physical mixing of the two components on a molecular scale at the interface. The versatility intrinsic to the combined methodology employed in this work provides nano- and microscale chemical information that can be used to understand the link between properties of different length scales across a wide range of materials.

Preparation of polybenzimidazole/ZIF-8 and polybenzimidazole/UiO-66 composite membranes with enhanced proton conductivity

Metal-organic frameworks (MOFs) are considered emerging materials as they further improve the various properties of polymer membranes used in energy applications, ranging from electrochemical storage and purification of hydrogen to proton exchange membrane fuel cells. Herein, we fabricate composite membranes consisting of polybenzimidazole (PBI) polymer as a matrix and MOFs as filler. Synthesis of ZIF-8 and UiO-66 MOFs are conducted through a typical solvothermal method, and composite membranes are fabricated with different MOF compositions (e.g., 2.5, 5.0, 7.5, and 10.0 wt %). We report a significant improvement in proton conductivity compared with the pristine PBI; for example, more than a three-fold increase in conductivity is observed when the PBI-UiO66 (10.0 wt %) and PBI-ZIF8 (10.0 wt %) membranes are tested at 160 °C. Proton conductivities of the composite membranes vary between 0.225 and 0.316 S cm−1 at 140 and 160 °C. For the comparison, pure PBI exhibits 0.060 S cm−1 at 140 °C and 0.083 S cm−1 at 160 °C. However, we also report a decrease in permeability and mechanical stability with the composite membranes.

Improvement of Performance and Lifetime of Polybenzimidazole Membranes in High Temperature Fuel Cells by Incorporation of Muscovite

Polybenzimidazole (PBI) is a basic aromatic heterocyclic polymer with excellent thermal and chemical stability. The phosphoric acid (PA) doped PBI and its derivative membranes have high proton conductivity, low gas permeability, good fuel impurity tolerance, and excellent oxidative and thermal stability at temperatures up to 200 °C [1], hence, PA doped PBI is a promising candidate for high-temperature proton exchange membrane fuel cells. However, PA doped PBI membranes also has some limitations, including the dehydration of phosphoric acid above 140 °C, PA leaching out of the membranes, and deterioration of membrane mechanical strength especially at high acid doping level.The incorporation of clay minerals into membranes attract a great interest due to their hygroscopicity, high surface area and cheap cost [2]. The hygroscopic properties of clay minerals can increase the humidity inside the membranes, interact with PA molecules and maintain a strong proton conductivity. Here we present work on the incorporation of a cheap muscovite into the PBI membrane. As the muscovite is highly hygroscopic and has hydroxyl groups on the surface, an optimal cell performance was observed when the loading of muscovite is 1 wt.%. The PBI membrane with 1 wt.% muscovite showed the membrane resistance of 189 mohm cm2 and peak power density of 612 mW cm-2 at 150 °C, 26% higher than the pure PBI membrane with the membrane resistance of 235 mohm cm2 and the power density of 485 mW cm-2. Furthermore, the durability of inorganic-organic composite membranes was tested by an accelerated stress test (AST) operating the membrane electrode assembly between 0.6 A cm−2 and 1.0 A cm−2 [3]. After running around 50 h AST, the composite PBI membrane with 1 wt.% muscovite showed much lower degradation (9.3% at 0.6 A cm−2 and 12.8% at 1.0 A cm−2) than the pure PBI membrane (11.2% at 0.6 A cm−2 and 22.6% at 1.0 A cm−2). The improved durability of the composite membranes might be explained by the muscovite forming hydrogen bonding with PA molecules and polymer chains, which alleviates the degradation of polymer chains and PA leaching out of the membranes. The PA distribution and retention properties of the composite membranes were also characterized by energy dispersive X-ray spectroscopy and electron probe micro-analysis.

Insights into the performance and degradation of polybenzimidazole/muscovite composite membranes in high–temperature proton exchange membrane fuel cells

To improve the performance and durability of phosphoric acid (PA) doped polybenzimidazole (PBI) membranes in high–temperature proton exchange membrane fuel cells (HT–PEMFCs), in this work, as–received natural muscovite (Mus), a clay material, was successfully incorporated into PBI matrix as an inorganic filler through the doctor blade method. The amount of Mus was varied (0.5–2 wt%) to explore its impact on the proton conductivity, mechanical and dimensional stability, power density, durability, and acid retention ability of the composite membranes. As the incorporation of Mus into membranes can introduce interactions with polymer chains and PA molecules to afford additional proton transport pathways at the interfaces in Mus–PBI and Mus–PA crosslinks, the membrane with 1 wt% Mus showed highest power density of 586 mW cm−2 at 150 °C without humidification, 24% higher than the pure PBI membrane (474 mW cm−2). Meanwhile, the PA doped composite membrane with 1 wt% Mus also displayed the highest mechanical strength (7.5 MPa) and lowest dimensional swelling (70.99% in area swelling and 202% in volume swelling). Compared with the pristine PBI membrane, the composite membranes had significantly improved durability under accelerated stress test (AST). The decreased ohmic resistance and increased polarization resistance after AST are related to the membrane thinning and the loss of catalyst active area, respectively. Most importantly, it was found that the strong interactions between Mus and PA molecules lead to improved acid retention ability of the composite membranes, thus less leached acid from the composite membrane reduces the negative effects on the catalyst degradation to alleviate degradation on cell performance and durability.

Enhanced electrical, mechanical and thermal properties of chemically modified graphene-reinforced polybenzimidazole nanocomposites

Chemically modified graphene-reinforced polybenzimidazole (PBI) nanocomposites were prepared by liquid-phase exfoliation of graphene oxide (GO) and reduced graphene oxide (rGO) in methanesulphonic acid (CH4O3S), followed by in-situ polymerization using GO–CH4O3S and rGO–CH4O3S suspensions as reaction media. Various reducing agents were used to produce rGOs and their reducing efficiency was examined to attain highly graphitic structure and excellent electrical conductivity of the resulting rGOs. The results of Raman, Fourier transform infrared and X-ray photoelectron spectroscopy indicate higher extent of reduction of GO with hydrazine compared to other reducing agents. The PBI nanocomposite containing 10 wt% rGO derived from hydrazine reduction reaction (rGO–H) exhibits the highest dc conductivity of 2.77 × 10−3 S cm−1 at room temperature, which is 11 orders of magnitude higher than pure PBI. The thermal annealing treatment at 350°C resulted in a substantial increase in dc conductivity of the PBI/GO nanocomposite, whereas the enhancement of conductivity is much less for the PBI/rGO nanocomposites. Compared to pure PBI, both tensile strength and Young’s modulus enhanced by 3.4 times and 6.9 times, respectively, for the PBI nanocomposites with 10 wt% GO content, which is ascribed to strong interfacial interactions and subsequent effective stress transfer between the PBI matrix and GO. The PBI/rGO nanocomposites exhibited relatively lower tensile strength/modulus compared to the GO-reinforced nanocomposite. The thermal stability of PBI was significantly improved upon the incorporation of both GO and rGO nanosheets, whereas higher thermal stability was achieved for rGO-reinforced nanocomposites.

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.

Enhancing electrical, mechanical, and thermal properties of polybenzimidazole by 3D carbon nanotube@graphene oxide hybrid

In the present work, comparison of electrical conductivity , mechanical properties and thermal stability of graphene oxide (GO), multi-walled carbon nanotubes (MWCNTs) and GOMWCNT hybrid reinforced polybenzimidazole (PBI) nanocomposites prepared via one-pot in situ polymerization have been carried out. The influences of the nanofillers content and mass ratio of GOMWCNT hybrid on the tensile performances and dc conductivity of nanocomposite films were evaluated. In contrast to single-phase GO and MWCNTs, the incorporation of GOMWCNT (mass ratio of 1:1) hybrid into PBI matrix endows optimum dispersion of GO nanosheets and MWCNTs together with better synergistic enhancing effects on the resultant performances of nanocomposites. Both tensile strength and dc conductivity of the GOMWCNT/PBI (1:1) nanocomposites enhanced remarkably with addition of 0–5 Wt% GOMWCNT, followed by petty improvement at higher filler content. The highest dc conductivity of 2.43 × 10 −5 S/cm was achieved at 10 Wt% loading of GOMWCNT (1:1) in PBI. The dc conductivity was further enhanced to 1.06 × 10 −3 S/cm upon thermal annealing at 400 °C. The tensile strength showed 3-fold increase and the Young's modulus was enhanced by 12-fold with respect to the pure PBI. The reinforcing efficiency of GOMWCNT was predicted using the modified Halpin-Tsai modeling. This work provides a simple method to prepared GOMWCNT/PBI nanocomposite with high electrical conductivity and mechanical properties, which could be explored in potential applications in aerospace structure and aerospace electronics. • Polybenzimidazole nanocomposites reinforced with GO-MWCNT hybrid. • Nanocomposite with excellent dc conductivity, tensile strength and modulus. • Nanocomposite films could be useful for flexible electronic devices.

Communication—Polyethylene/PBI Pore-Filling Composite Membrane for High Performance Vanadium Redox Flow Battery

A pore-filling proton exchange membrane is fabricated by combining a porous polyethylene (PE) substrate and polybenzimidazole (PBI) resin for vanadium redox flow batteries (VRFB). The PE substrate not only optimized the structure of the composite membrane, but also significantly reduces its cost (< 30$·m−2). Compared with Nafion212 and pure PBI membrane, PE/PBI composite membrane exhibits higher VRFB energy efficiency (88.62%–80.11%) in a current density range of 100–200 mA cm−2. And within 150 cycles at 180 mA cm−2, the composite membrane maintains stable charge-discharge performance with slower capacity decay rate, indicating a promising membrane candidate for VRFBs.

Mechanically strong sulfonated polybenzimidazole PEMs with enhanced proton conductivity

Proton exchange membranes (PEMs) with good proton conductivity and mechanical properties are highly desired for applications in fuel cells. This work immobilized sulfonic acid groups stably into polybenzimidazole (PBI) by a solid phase reaction. The structures of the sulfonated PBI (s-PBI) are characterized by FT-IR spectroscopy. The proton conductivity and mechanical properties of s-PBI are measured. The s-PBI PEMs showed improved proton conductivity as increasing the amount of azides when comparing to the pure PBI PEM. The strength and modulus of s-PBI PEMs are decreased, but still much larger than s-PBI PEMs prepared by acid doping, sulfonation, and blending. Such s-PBI PEMs made by solid phase reaction would be good candidate for fuel cell applications.

Effects of mesoporous fillers on properties of polybenzimidazole composite membranes for high-temperature polymer fuel cells

In this study, we elucidated the effects of the addition of various mesoporous silicates (0–20 wt%) to the membranes used for high-temperature proton exchange membrane fuel cells (HT-PEMFCs) on cell performance. Two types of polybenzimidazole (PBI)-based hybrid membranes were prepared by homogeneously dispersing a predetermined amount of MCM-41 or SBA-15 within the PBI matrix. Compared to the pure PBI membrane, those with MCM-41 and SBA-15 exhibited significantly enhanced phosphoric acid doping and better mechanical properties, leading to improved HT-PEMFC performance and reduced acid migration. However, the membranes with 20 wt% silicate showed inferior performance compared to those with 10 wt% silicate. In addition, the membranes with SBA-15 exhibited noticeable aggregation, lower phosphoric acid doping, and greater phosphoric acid migration during the leaching test than did the membranes with MCM-41. Finally, during the short-term durability test, the PBI/MCM-41 (10 wt%) membrane showed the best performance (maximum power density of 310 mW cm−2).

Fabrication of Polybenzimidazole/Palladium Nanoparticles Hollow Fiber Membranes for Hydrogen Purification

AbstractA novel scheme to fabricate polybenzimidazole (PBI) hollow fiber membranes with a thin skin loaded with fully dispersed palladium nanoparticles is proposed for the first time. Palladium is added to the membrane during the spinning process in the form of ions that coordinate to the imidazole groups of the polymer. This is attractive for membrane production because agglomeration of nanoparticles is minimized and the high‐cost metal is incorporated in only the selective layer—where it is required. Pd‐containing membranes achieve three orders of magnitude higher H2 permeances and a twofold improvement in H2/CO2 selectivity compared to pure PBI hollow fiber membranes.