Porous Polybenzimidazole Membranes Research Articles

Porous Proton Exchange Membrane with High Stability and Low Hydrogen Permeability Realized by Dense Double Skin Layers Constructed with Amino tris (methylene phosphonic acid)

AbstractPorous proton exchange membranes (PEMs) with abundant porous structures show enhanced phosphoric acid (PA) doping levels and proton transport capability. However, the high PA loss rate and serious hydrogen cross‐over lead to poor membrane stability. Enhancing the stability of PA‐doped porous PEMs is therefore crucial for obtaining high‐performance proton exchange membrane fuel cells. Herein, a porous polybenzimidazole membrane with dense double skin layers is reported using amino tris (methylene phosphonic acid) (ATMP) constructed. This membrane effectively alleviates hydrogen permeation and PA loss in a water/anhydrous environment and exhibits enhanced stability. Surprisingly, as an organic proton conductor, ATMP has strong hydrogen bonding with PA, leading to the formation of more continuous proton transport channels. Due to the dense double skin layers protection and the synergistic mass transfer of ATMP and PA, the porous membrane shows excellent proton conductivity (0.112 S cm−1) and a H2‐O2 fuel cell peak power density of 0.98 W cm−2 at 160 °C. Moreover, it presents excellent fuel cell stability, with a voltage decay rate of only 5.46 µV h−1. In addition, the porous membrane surpasses the traditional working temperature range, operating in the range of 80–220 °C. This study provides new insight into developing high‐performance porous PEMs.

Enhancing proton conductivity on polybenzimidazole (PBI) membrane doped acid

Abstract This study provides various condition for acid doped polybenzimidazole (PBI) membrane which giving the best proton conductivity result with respect to the High Temperature-Polymer Electrolyte Membrane Fuel Cell (HT-PEMFC). A highly phosphonated polymer membrane based on acid-base complex membrane system was introduced where phytic acid (PyA) was chosen as an acid doping instead of phosphoric acid (PA) due to its properties of having high phosphate group content and ability to participate in H bonding interactions with the functionalities in PBI matrix. By introducing this PBI/phytic acid membrane helped to overcome the issues arise from PBI/PA membrane system especially on acid leaching problem. In this study, a simple and cost effective technique on porous PBI membrane fabrication and acid doping condition were employed to search an optimum acid-doping level and to further improve the stability and durability of the membrane.

Porous polybenzimidazole membranes with positive charges enable an excellent anti-fouling ability for vanadium-methylene blue flow battery

A cost-effective, high-performance and highly stable membrane has always been in intensively needed in aqueous organic-based flow batteries. Here we present a porous polybenzimidazole (PBI) membrane with positive charges that endow the membrane with a high rejection and an excellent anti-fouling ability for target organic molecule and asymmetric structure that affords a high conductivity for vanadium-methylene blue flow battery (V-MB FB). The morphologies and thickness of separating layer in particular of the porous PBI can be well adjusted by simply altering the polymer concentration in the cast solution and further afford the membrane with a controllable property in terms of both ion selectivity and ion conductivity. As a result, a V-MB FB assembled with a porous PBI membrane delivers a coulombic efficiency (CE) of 99.45% and an energy efficiency (EE) of 86.10% at a current density of 40 mA cm−2, which is 12% higher than that afforded by a Nafion 212 membrane. Most importantly, the V-MB FB demonstrates a methylene blue (MB) utilization of 97.55% at a theoretical capacity of 32.16 Ah L−1 (based on the concentration of MB in the electrolyte) because of the high ion conductivity of the membrane, which favors reducing the cost of a battery. The results suggest that the designed porous PBI membranes exhibit a very promising prospect for methylene blue-vanadium flow battery.

Symmetric sponge-like porous polybenzimidazole membrane for high temperature proton exchange membrane fuel cells

Conductive porous membranes are promising for environmental and energy applications. Here, a novel symmetric sponge-like porous poly[2,2’-(4,4′-oxybis(1,4-phenylene))-5,5′-bibenzimidazoles] (OPBI) membrane used for high temperature proton exchange membrane fuel cells was successfully fabricated by vapor-induced phase separation (VIPS). Typically, the symmetric sponge-like porous OPBI membrane exhibits thousands of micron-sized cells separated by ultra-thin walls, which are characterized by SEM micrographs. Porous membrane exhibits considerably enhanced acid doping level (ADL) of 9.6 and proton conductivity of 70.8 mS cm−2 at 180 °C compared with the corresponding dense membranes (OPBI: ADL = 4.1). Interestingly, with higher ADL, the porous OPBI membrane showed much lower swelling ratio in in-plane direction (50%) and thus higher dimensional stability than dense OPBI (74%) and mPBI (103%). Moreover, the open circuit voltage (OCV) of the fuel cell based on the porous membrane was 0.86 V indicating the low gas crossover and the fuel cell showed excellent peak power density of 485.3 mW/cm2 at 160 °C, higher than m-membrane of 353.1 mW/cm2 and OPBI membrane of 38.7 mW/cm2. Though the single cell durability is poor for porous OPBI membrane than that of m-PBI due to the leach of PA, the combination of the facile fabrication procedure, high performance and easy up-scaling enables the PBI porous membranes to be promising for high temperature proton exchange membrane fuel cells. Further work for us is to adjust the size of the pores and porous structure, thus improving the PA retention of porous membranes.

Asymmetric Porous Polybenzimidazole Membranes with High Conductivity and Selectivity for Vanadium Redox Flow Batteries

Developing functional membrane with high conductivity and excellent stability is critical for improving the performance of vanadium redox flow batteries (VRFBs). Herein, an asymmetric porous polybenzimidazole (PBI) membrane composed of an ultra‐thin dense layer and a sponge‐like porous layer is proposed and prepared. The dense layer takes the main role of inhibiting vanadium crossover, whereas the porous layer provides not only a fast proton conduction channel but also a mechanical support to the dense layer. Hence, the asymmetric PBI membrane exhibits a high proton conductivity (36.4 mS cm−1 at room temperature) and an extremely low vanadium permeability (0.26 × 10−7 cm2 min−1). The VRFB with this membrane achieves an energy efficiency of 83.17% at 400 mA cm−2 and 78.59% at 500 mA cm−2. Furthermore, the battery enables to be continuously cycled for 1600 times without a significant degradation at 400 mA cm−2. All these results prove that the PBI membrane with an asymmetric porous structure is an ideal membrane for redox flow batteries.

Porous polybenzimidazole membranes with high ion selectivity for the vanadium redox flow battery

Development of high ion-selective polymer membranes is of great importance for vanadium redox flow batteries (VRFBs). In this work, porous polybenzimidazole (PBI) membranes are successfully prepared for improved efficiencies and stability in VRFB applications. The porous structure is constructed via a hard templating method using monodispersed SiO2 solid spheres and 3 M NaOH as template and etching solution, respectively. The influence of the adding content of SiO2 on the microstructure of the membrane is illustrated. The properties of porous membranes, including acid doping, swellings, area resistance, mechanical properties, vanadium ion permeation, and single cell and cycling performance, are investigated systematically. Results show that asymmetric porous PBI membranes exhibit increased sulfuric acid (SA) uptake (>35 wt%), remarkably low area resistance (<0.58 Ω cm2), ultralow vanadium ion permeability (<10-9 cm2 min-1) and superior mechanical strength (>20 MPa) simultaneously. At high current densities (80–200 mA cm-2), the cell with the porous PBI-40%SiO2 membrane possesses superior coulombic efficiencies (CE: 99.5–100%) and energy efficiencies (EE: 87.9–71.5%), together with excellent cycling stability at 120 mA cm-2 in the vanadium flow battery. Accordingly, this work not only provides a kind of advanced membranes for the VRFB, but also offers a facile and effective method to design, optimize and fabricate membranes incorporating the features according to needs.

Porous membrane with improved dendrite resistance for high-performance lithium metal-based battery

Lithium metal is one of the most promising anode materials for next-generation power batteries because of its high energy density and low reduction potential. Unfortunately, uncontrolled Li dendrite growth during cycling leads to an unstable interface, a limited cycling life, and a low Coulombic efficiency, further results in severe capacity decay and safety issues. To address these problems, an effective approach is proposed to realize uniform Li nucleation. Herein, we demonstrate a thermally stable polybenzimidazole (PBI) polymer for making porous membranes with a tuneable morphology via a versatile non-solvent treatment method for Lithium-ion battery's (LIBs) application. The final morphology of PBI membranes is controlled by selecting the appropriate non-solvent and an optimized performance could also be obtained. Notably, our functional porous PBI membrane with abundant polar amine functional groups could enable dendrite-free Li deposition, showing stable and low overpotential cycling durability for 400 h at a current density of 1 mA cm−2. With such a membrane, the LiFePO4/Li cell shows superior cycle stability and rate performance, which are higher than those of commercial PE separators. Remarkably, this work offers a simple and facile method to prepare advance porous membranes for lithium-ion batteries with improved dendrite resistance.

KOH-doped Porous Polybenzimidazole Membranes for Solid Alkaline Fuel Cells

In this study the preparation and properties of potassium hydroxide-doped meta-polybenzimidazole membranes with 20–30 μm thickness are reported as anion conducting polymer electrolyte for application in fuel cells. Dibutyl phthalate as porogen forms an asymmetrically porous structure of membranes along thickness direction. One side of the membranes has a dense skin layer surface with 1.5–15 μm and the other side of the membranes has a porous one. It demonstrated that ion conductivity of the potassium hydroxide-doped porous membrane with the porogen content of 47 wt.% (0.090 S cm−1), is 1.4 times higher than the potassium hydroxide-doped dense membrane (0.065 S cm−1). This is because the porous membrane allows 1.4 times higher potassium hydroxide uptake than dense membranes. Tensile strength and elongation studies confirm that doping by simply immersing membranes in potassium hydroxide solutions was sufficient to fill in the inner pores. The membrane-electrode assembly using the asymmetrically porous membrane with 1.4 times higher ionic conductivity than the dense non-doped polybenzimidazole (mPBI) membrane showed 1.25 times higher peak power density.

Advanced Porous Membranes with Tunable Morphology Regulated by Ionic Strength of Nonsolvent for Flow Battery.

A simple salt-induced phase separation method is presented to prepare porous polybenzimidazole (PBI) membranes with tunable morphology for vanadium flow batteries (VFBs). This method is based on the traditional nonsolvent-induced phase separation (NIPS) method where salt is introduced into the coagulation bath to change the ionic strength of the nonsolvent. The change of ionic strength will affect the phase separation rate, and finally, the morphology of porous membranes is well tuned from finger-like voids to sponge-like pores in site. The membrane with sponge-like pores created multiple barriers to the transfer of vanadium ions, offering the membrane with superhigh selectivity; meanwhile, spongy cells filled with sulfuric acid could provide the membrane with high proton conductivity. As a result, the membrane with sponge-like pores demonstrated a much better performance than that with finger-like voids. The resultant sponge-like porous PBI membrane exhibited a very impressive VFB performance with an energy efficiency of 89.9% at a current density of 80 mA cm-2, which was close to the highest values ever reported. The battery kept very stable performance even after continuously running for more than 10000 cycles at 160 mA cm-2, showing excellent stability. This paper provides an easy to scale up and environment-friendly method to fabricate high-performance porous membranes with tunable morphology.

Exploring the Gas-Permeation Properties of Proton-Conducting Membranes Based on Protic Imidazolium Ionic Liquids: Application in Natural Gas Processing

This experimental study explores the potential of supported ionic liquid membranes (SILMs) based on protic imidazolium ionic liquids (ILs) and randomly nanoporous polybenzimidazole (PBI) supports for CH4/N2 separation. In particular, three classes of SILMs have been prepared by the infiltration of porous PBI membranes with different protic moieties: 1-H-3-methylimidazolium bis (trifluoromethane sulfonyl)imide; 1-H-3-vinylimidazolium bis(trifluoromethane sulfonyl)imide followed by in situ ultraviolet (UV) polymerization to poly[1-(3H-imidazolium)ethylene] bis(trifluoromethanesulfonyl)imide. The polymerization process has been monitored by Fourier transform infrared (FTIR) spectroscopy and the concentration of the protic entities in the SILMs has been evaluated by thermogravimetric analysis (TGA). Single gas permeability values of N2 and CH4 at 313 K, 333 K and 363 K were obtained from a series of experiments conducted in a batch gas permeance system. The results obtained were assessed in terms of the preferential cavity formation and favorable solvation of methane in the apolar domains of the protic ionic network. The most attractive behavior exhibited poly[1-(3H-imidazolium)ethylene]bis(trifluoromethanesulfonyl)imide polymeric ionic liquid (PIL) cross-linked with 1% divinylbenzene supported membranes, showing stable performance when increasing the upstream pressure. The CH4/N2 permselectivity value of 2.1 with CH4 permeability of 156 Barrer at 363 K suggests that the transport mechanism of the as-prepared SILMs is solubility-dominated.

Tuning the ion selectivity of porous poly(2,5-benzimidazole) membranes by phase separation for all vanadium redox flow batteries

Porous polybenzimidazole membranes have been suggested by far as the most promising candidate to replace perfluorinated ionomer membranes in all vanadium redox flow batteries (VRFB). These porous membranes can simply be prepared from a phase separation process induced by water vapor. In this work, the influence of the material properties of poly(2,5-benzimidazole) (ABPBI) on the membrane structure formation and ion transport characteristics is systematically investigated. Two batches of ABPBI polymers (intrinsic viscosity 2.0 and 1.4 dL g−1) are used; concentrations of polymer solution, the water vapor activity (temperature and relative humidity), and the exposure time of polymer solution to the water vapor are varied. It is found that high viscosity of ABPBI solution, among other factors, is essential in obtaining membranes with very low interconnectivity between macropores in the membrane bulk, therefore very low vanadium ion permeability suitable for VRFB applications. The porous ABPBI membranes in dry state have a low amount of pores ranging from 1 to ~ 200 nm. Due to the benzimidazole moieties in ABPBI polymers, the acid in vanadium electrolytes has two positive effects on ABPBI membranes: fixed positive charges, and absorption of acid in the membranes. The ion exchange capacity of ABPBI membranes increases with the increase in solution acid concentration, and reaches striking values as high as 8 mequ g−1 in 4.0 M H2SO4. This makes the Donnan exclusion towards positively charged vanadium ions very profound. The macropores in the porous membranes increase the absorption amount of free acid, therefore significantly increase the membrane ionic conductivity. These properties make porous ABPBI membranes very efficient separators for VRFB applications.

Ion transport properties of porous polybenzimidazole membranes for vanadium redox flow batteries obtained via supercritical drying of swollen polymer films

ABSTRACTA novel method of membrane preparation for use in vanadium redox flow batteries by preswelling of poly(2,5‐benzimidazole) films in organic solvent followed by supercritical CO2 assisted solvent removal is proposed. Influence of the organic solvent type on the morphology, proton, and vanadyl ion transport properties is studied. The performance of the obtained membranes inside single cells of vanadium redox flow batteries is compared to pristine dense poly(2,5‐benzimidazole) and Nafion 115 membranes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46262.

Advanced porous PBI membranes with tunable performance induced by the polymer-solvent interaction for flow battery application

The polymer-solvent interaction was utilized to construct porous polybenzimidazole (PBI) membranes with tunable morphology for vanadium flow battery (VFB) application. Solvent treatment was employed to investigate the polymer-solvent interaction experimentally, further to study the membrane formation mechanism. By varying the form and strength of the polymer-solvent interaction, the membrane morphology could be easily controlled and an optimized performance could also be achieved. As a result, a columbic efficiency of 99.29% and an energy efficiency of 81.93% at 200mAcm-2 were realized by using an optimized membrane, which is the highest value ever reported for porous membranes at a so high current density by far. The Flory–Huggins interaction parameter was then utilized to quantify the strength of the polymer-solvent interaction. Based on the experimental investigation and quantitative calculation, the relationship between the polymer-solvent interaction and membrane performance was clearly clarified, and the membrane formation mechanism became more unequivocal as well. This paper thereby supplies an efficient concept to fabricate porous membranes with well controlled morphology and performance.

WITHDRAWN: Porous polybenzimidazole membranes doped with phosphoric acid: Preparation and application in high temperature PEM fuel cells

Abstract Development of thermally stable polymer electrolyte membranes with higher proton conductivity as well as mechanical stability is a key challenge in commercializing PEM fuel cells operating above 100 °C. Polybenzimidazole (PBI) membrane is one of the promising candidates in this category although with limited mechanical stability and moderate proton conductivity. To improve the proton conductivity, porous PBI was an effective way. For the preparation of porous PBI membranes, glucose and saccharose are selected as porogen and added in PBI resin solution before solvent casting. The porous PBI membrane prepared has high contents of acid doping at room temperature, as well high proton conductivity. The acid doping level is up to 15.7 mol H3PO4 per PBI repeat unit, much higher than pure PBI membrane at the same condition. Further, membrane electrode assembly (MEA) is fabricated with porous PBI membranes doped with phosphoric acid and tested at 150 °C with dry hydrogen and oxygen gas at ambient pressure for both anode and cathode feeds. During 200 h stability testing under a constant current discharge of 0.5 A cm −2 , the cell performance remains stable except for the last 50 h. The high-frequency resistance and the charge-transfer resistance were measured to explore the decay mechanism occurring in the last 50 h.

Superior Thermally Stable and Nonflammable Porous Polybenzimidazole Membrane with High Wettability for High-Power Lithium-Ion Batteries.

Separators with high security, reliability, and rate capacity are in urgent need for the advancement of high power lithium ion batteries. The currently used porous polyolefin membranes are critically hindered by their low thermal stability and poor electrolyte wettability, which further lead to low rate capacity. Here we present a novel promising porous polybenzimidazole (PBI) membrane with super high thermal stability and electrolyte wettability. The rigid structure and functional groups in the PBI chain enable membranes to be stable at temperature as high as 400 °C, and the unique flame resistance of PBI could ensure the high security of a battery as well. In particular, the prepared membrane owns 328% electrolyte uptake, which is more than two times higher than commercial Celgard 2325 separator. The unique combination of high thermal stability, high flame resistance and super high electrolyte wettability enable the PBI porous membranes to be highly promising for high power lithium battery.

A simple approach for preparation of porous polybenzimidazole membranes as a promising separator for lithium ion batteries

A simple approach for the preparation of OPBI porous membranes by simply extracting PEG from dry OPBI/PEG blend membranes.

Durability of symmetrically and asymmetrically porous polybenzimidazole membranes for high temperature proton exchange membrane fuel cells

Two types of porous polybenzimidazole (PBI) membranes with symmetric and asymmetric morphologies were fabricated by the template-leaching method and characterized by scanning electron microscope (SEM). Their physicochemical properties were compared in terms of acid-doping level, proton conductivity, mechanical strength, and oxidative stability. The durability of fuel cell operation is one of the most challenging for the PBI based membrane electrode assembly (MEA) used in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). In the present work, we carried out a long-term steady-state fuel cell test to compare the effect of membrane structure on the cell voltage degradation. It has also been demonstrated that the asymmetrically porous PBI could bring some notable improvements on the durability of fuel cell operation, the fuel crossover problem, and the phosphoric acid leakage.

Porous polybenzimidazole membranes with excellent chemical stability and ion conductivity for direct borohydride fuel cells

Porous membranes based on polybenzimidazole (PBI) are firstly introduced in direct borohydride fuel cell application (DBFC). Membranes with different thicknesses and porosity are successfully fabricated via water vapor phase inversion process. The prepared membranes show excellent ion conductivity and chemical stability under DBFC operating condition. Compare with Nafion 115, the prepared membranes show higher ion conductivity, as a result, much higher peak power density. No weight loss is observed after immersing the prepared membranes in a 3 M NaOH solution for 30 days, indicating the excellent chemical stability of porous PBI membranes. And the DBFC cells assembled with prepared membranes could discharge at 200 mA cm−2 for more than 250 h without voltage decay, which is the longest time reported by far. This work provides a totally new idea for fabricating versatile DBFC membranes.

High performance porous polybenzimidazole membrane for alkaline fuel cells

In this study, a highly ion-conductive and durable porous polymer electrolyte membrane based on ion solvating polybenzimidazole (PBI) was developed for anion exchange membrane fuel cells (AEMFCs). The introduction of porosity can increase the attraction of electrolytic solutions (e.g., potassium hydroxide (KOH)) and ion solvation, which results in the enhancement of PBI's ionic conductivity. The morphology, thermo-physico-chemical properties, ionic conductivity, alkaline stability, and the AEMFC performance of KOH-doped PBI membranes with different porosities were characterized. The ionic conductivity and AEMFC performance of 70 wt.% porous PBI was about 2 times higher than that of the commercially available Fumapem® FAA. All KOH-doped porous PBI membranes maintained their ionic conductivity after accelerated alkaline stability testing over a period of 14 days, while the commercial FAA degraded just after 3 h. The excellent performance and good durability of KOH-doped porous PBI membrane makes it a promising candidate for AEMFCs.

Porous polybenzimidazole membranes doped with phosphoric acid: Preparation and application in high-temperature proton-exchange-membrane fuel cells

In this paper, the preparation and characterization of porous polybenzimidazole membranes doped with phosphoric acid were reported. For the preparation of porous polybenzimidazole membranes, glucose and saccharose were selected as porogen and added into PBI resin solution before solvent casting. The prepared porous PBI membranes had high proton conductivity and high content of acid doping at room temperature with 15.7mol H3PO4 per PBI repeat unit, much higher than pure PBI membrane at the same condition. Further, the performance and stability of the porous PBI membrane in high-temperature proton-exchange-membrane fuel cells was tested. It was found that the cell performance remained stable during 200h stability test under a constant current discharge of 0.5Acm−2 except for the last fifty hours. The decay in the last fifty hours was ascribed to the delamination between the catalyst layer and membrane increasing the charge-transfer resistance.