PBI Polymer Research Articles

In-situ glass transition of ZIF-62 based mixed matrix membranes for enhancing H2 fast separation

Mixed matrix membranes (MMMs), combining the advantages of polymer membranes and porous materials, processing the potential to realize large-scale gas separation applications. However, the interfacial defects in MMMs greatly hindered gas separation performance improvement. Therefore, designing an MMM with high loading and good interfacial compatibility remains a critical issue in promoting the application of MMMs. Herein, during in-situ heating process, the melting of liquid ZIF-62 in PBI polymer can largely fill the interfacial defects in MMMs. The microporous transport channels of ZIF-62 glass in MMMs promoted the H2 diffusion and inhibited the CO2 and CH4 diffusion, thus enhancing the H2/CO2 and H2/CH4 separation of MMMs. For mixed gas testing, the 45 wt% ZIF-62 glass/PBI membrane had the maximum H2 permeability of 459 barrer, and its H2/CO2 and H2/CH4 selectivities were 23 and 57, higher than the gas separation upper bonds. In addition, ZIF-62 glass/PBI membrane exhibited stable separation performance under 1–5 bar pressure. Therefore, the rational combination of MOF glass and polymer matrix could provide promising potential for reducing the interfacial defects of high-loading MMMs, thus enhancing the gas separation performance.

A novel and clean technique for the one-pot production of green chemical γ-valerolactone from furfural using bifunctional H3PW12O4/UiO-66 catalyst: Pervaporation membrane reactor

This study focuses on the synthesis of gamma-valerolactone (GVL) from furfural using a bifunctional H3PW12O4-UiO-66 catalyst. The membrane was prepared using PBI polymer. H3PW12O4-UiO-66 catalysts with different amounts of H3PW12O4 were synthesized. The catalytic activity of these synthesized catalysts was investigated in pervaporation membrane reactor to obtain GVL from furfural and the catalyst containing 2 g of H3PW12O4 was identified as the optimum catalyst. After determining the optimum catalyst, the effect of temperature, molar feed ratio, and catalyst concentration on the reaction and separation performance was investigated. The optimum values were determined as 90 °C, molar feed ratio 10 and 6 g/L catalyst concentration by evaluating both reaction and separation performance. The performance of the pervaporation membrane reactor (PVMR) was compared with a batch reactor operated under the same conditions. In the batch reactor operating at 90°C, molar feed ratio of 10, and 6 g/L catalyst concentration, a 65% furfural conversion and 51% GVL yield were obtained, whereas the PVMR achieved 100% furfural conversion and 94.21% GVL yield. This comparison demonstrates the improved efficiency of the PVMR in increasing conversion and yield compared to the traditional batch reactor. The obtained conversion and yield values under the investigated operating conditions highlight the proposed process as a promising alternative for the production of GVL from furfural.

Metal organic framework enroutes to mechanically stable and high proton conductive polybenzimidazole membranes

Different contents of metal-organic framework (3, 5, 7, 10 and 12 wt % and MOF is HKUST-1) were incorporated into cyclohexane dicarboxylic acid based polybenzimidazole (Cy-PBI). In the composite membranes, the interaction between MOF and PBI polymer resulted in peak broadening as observed in FTIR spectra (2000–3000 cm−1). The recorded proton conductivity of CM-7 at 160 °C (224 mS/cm) was almost two fold to that of pristine PBI membrane (114 mS/cm and surprisingly high mechanical strength was displayed (Tensile modulus: 671 MPa, elongation 69% under doped condition). Minimum swelling behaviour and high doping level gives the evidence that acid molecules (proton carriers) are housed within the MOF cavities those would act as proton hopping centres. The FESEM images of the composite membrane (CM-7) displayed a uniform distribution of MOF within the matrix, complementing the enhanced properties observed. This work exemplifies the mediating role of MOF in improving the conductivity of PBI membranes.

Development and performance analysis of polybenzimidazole/boron nitride composite membranes for high‐temperaturePEMfuel cells

In this research, polybenzimidazole/boron nitride (PBI/BN) based composite membranes have been prepared for high-temperature PEM fuel cell (HT-PEMFC). BN was preferred because of its superior thermal robustness, high chemical stability, non-conductor property, and high plasticizer characteristic. The loading of BN in the composite membrane was studied between 2.5 to 10 wt%. The composite membranes were characterized using TGA, DSC, XRD, SEM, mechanical tests, acid doping/leaching, and proton conductivity measurements. The highest conductivity of 0.260 S/cm was found for PBI/BN-2.5 membrane at 180°C. It has been determined that the PBI/BN-2.5 membrane has higher performance than the PBI membrane according to the HT-PEMFC tests performed with Hydrogen and dry air. The heightened HT-PEMFC performance can be ascribed to interactive effects between BN particles and the PBI polymer matrix. PBI/BN composite membranes show a good perspective in the high-temperature PEMFC applications.

A proton conductor electrolyte based on molten CsH5(PO4)2 for intermediate-temperature fuel cells.

Molten carbonate fuel cells have been commercialized as a mature technology. Due to the liquid electrolyte in molten carbonate fuel cells, gas seal and low contact resistance are easier to achieve than in other fuel cells. Herein, we report an investigation of the viability of a molten oxoacid salt as a novel type of fuel cell electrolyte. In comparison with molten carbonate electrolytes for MCFCs that operate at 500–700 °C, for which a ceramic support matrix is required, the molten proton conductor electrolyte has a lower working temperature range of 150–250 °C. The present study has shown that an electrolyte membrane, in which molten CsH5(PO4)2 is held in a matrix made of PBI polymer and SiO2 powder, has excellent thermal stability, good mechanical properties, and high proton conductivity. In addition, a molten proton conductor fuel cell equipped with such an electrolyte membrane operating at 200 °C showed an open-circuit voltage of 1.08 V, and a stable output voltage during continuous measurement for 150 h at a constant output current density of 100 mA cm−2.

Development of polybenzimidazole/graphene oxide composite membranes for high temperature PEM fuel cells

In this study, phosphoric acid doped Polybenzimidazole/Graphene Oxide (PBI/GO) nanocomposite membranes were prepared by dispersion of various amounts of GO in PBI polymer matrix followed by phosphoric acid doping for high temperature proton exchange membrane fuel cell (HT-PEMFC) application. The structure of the PBI/GO composite membranes was investigated by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and by thermogravimetric analysis (TGA). The introduction of GO into the PBI polymer matrix helps to improve the acid doping, proton conductivity and acid leaching properties. The SEM analyses have proved the uniform and homogeneous distribution of GO in composite membranes. The composite membranes were tested in a single HT-PEMFC with a 5 cm2 active area at 165 °C without humidification. HT- PEMFC tests show that PBI/GO composite membrane with 2 wt. % GO content performed better than bare PBI membrane at non humidified condition. At ambient pressure and 165 °C, the maximum power density of the PBI/GO-1 membrane can reach 0.38 W/cm2, and the current density at 0.6 V is up to 0.252 A/cm2, with H2/air. The results indicate the PBI/GO composite membranes could be utilized as the proton exchange membranes for HT-PEMFC.

Polybenzimidazole based nanocomposite membranes with enhanced proton conductivity for high temperature PEM fuel cells

In this study, phosphoric acid doped PBI nanocomposite membranes were prepared by dispersion of various amounts of inorganic nanoparticles in PBI polymer followed by phosphoric acid (H3PO4) doping for high temperature proton exchange membrane fuel cells (HT-PEMFC). All of the PBI composite membranes were cast from the same PBI polymer with the same molecular weight. Titanium dioxide (TiO2), silicon dioxide (SiO2) and inorganic proton conductor zirconium phosphate (ZrP) were used as inorganic fillers. The PBI based composite membranes were characterized in terms of their acid uptake and acid leaching properties, mechanical properties, chemical stabilities in NN Dimethylacetamide (DMAc) and impedance analyses. Thermal gravimetric analysis confirmed the improved thermal stability of the PBI composite membranes. The existence of inorganic fillers was improved the acid retention capability. Electrochemical Impedance Spectroscopy (EIS) showed that the introduction of 5 wt. % SiO2 or 5 wt. % ZrP helps to increase proton conductivity. The composite membrane with TiO2 retained low conductivity values than pristine PBI and this is a result of its non-uniform membrane structure. The highest proton conductivity of 0.200 S/cm was obtained for PBI/ZrP composite membrane with the highest value of H3PO4 doping level. Nyquist plots are drawn for all the membranes at different temperatures and the plots showed good fit with Randel's circuit. As a result the experimental results suggested that the PBI based composite membranes may be a promising electrolyte used in HT-PEMFC.

Polybenzimidazole/SiO2 hybrid membranes for high temperature proton exchange membrane fuel cells

Polybenzimidazole/Silicon dioxide (PBI/SiO2) hybrid membranes were prepared and characterized as alternative materials for high temperature proton exchange membrane fuel cell (HT-PEMFC). The PBI/SiO2 membranes were cast from a PBI polymer synthesized in the laboratory and contained 5 wt. % SiO2 as inorganic filler. Scanning electron microscopy (SEM) analysis showed that the uniform and homogeneous distribution of SiO2 particles in the hybrid membrane. The existence SiO2 has improved the acid retention and proton conductivity properties. A maximum conductivity of 0.1027 S/cm at 180 °C was obtained for the PBI/SiO2 hybrid membrane. Gas diffusion electrodes (GDE) were fabricated by ultrasonic coating technique with 1 mg Pt/cm2 catalyst loading for both anode and cathode. The membranes were tested in a single HT-PEMFC with a 5 cm2 active area operating at the temperature range of 140 °C–180 °C. Single HT-PEMFC tests indicated that PBI/SiO2 hybrid membrane was more stable and also performed better than pristine PBI membrane. Maximum current density was observed for PBI/SiO2 membrane at 165 °C and cell voltage of 0.6 V as 0.24 A/cm2. The results suggested that PBI/SiO2 hybrid membrane is promising electrolytes for HT-PEMFC with improved fuel cell performance.

Porous poly(benzimidazole) membrane for all vanadium redox flow battery

Porous poly(benzimidazole) (PBI) membranes of low vanadium ions permeability are described for an all vanadium redox flow battery (VRFB). The PBI membrane was prepared by a water vapour induced phase inversion process of a PBI polymer solution. The membrane has a symmetrical cross-sectional morphology. A low water permeability of 16.5 L (m2 h bar)−1 indicates the high hydraulic resistance stemming from a closed cell morphology with nanoporous characteristics. The PBI membrane doped with 2.5 M H2SO4 shows a proton conductivity of 16.6 mS cm−1 and VO2+ permeability as low as 4.5 × 10−8 cm2 min−1. The stability test of dense PBI membrane in VO2+ solution indicates good chemical stability. An all vanadium redox flow battery (VRFB) operated with the porous PBI membrane shows 98% coulombic efficiency and more than 10% higher energy efficiency compared to VRFB operated with Nafion 112 at applied current densities of 20–40 mA cm−2. High in situ stability of the porous PBI membrane was confirmed by about 50 cycles of continuous charge and discharge operation of the battery.

Experimental study and modeling of proton conductivity of phosphoric acid doped PBI-Fe2TiO5 nanocomposite membranes for using in high temperature proton exchange membrane fuel cell (HT-PEMFC)

In this study, phosphoric acid doped PBI-Fe2TiO5 nanocomposite membranes were prepared by dispersion of various amounts of Fe2TiO5 nanoparticles in PBI polymer matrix followed by phosphoric acid doping and they were applied into high temperature proton exchange membrane fuel cells (HT-PEMFCs). Effects of phosphoric acid doping level (PAdop), Fe2TiO5 mass fraction (Wd), and temperature on proton conductivity of the membranes were evaluated. The highest proton conductivity of 0.078 S/cm was obtained for the membranes containing 4 wt% of Fe2TiO5 nanoparticles with the highest value of phosphoric acid doping level (PAdop). Furthermore, a simple semi-empirical model was developed to predict the proton conductivity of the nanocomposite membranes at elevated temperatures (100–180 °C) and dry conditions. The effects of PAdop, Wd, and temperature on proton conductivity of the membranes were accounted in the model. The model was defined based on the volume fraction of free phosphoric acid inside the nanocomposite membrane structure which showed to be a determining factor in proton conduction of the membranes. The obtained proton conductivities by the model at various temperatures and phosphoric acid doping levels were in good agreement with the experimental results (average relative error <4%), indicating the reliability of the model.

On the chemical filler–polymer interaction of nano- and micro-sized ZIF-11 in PBI mixed matrix membranes and their application for H2/CO2separation

A study of the chemical filler–polymer interactions of micro- and nano-sized ZIF-11 in PBI polymer matrix and H2/CO2separation performance.

Novel morpholinium-functionalized anion-exchange PBI–polymer blends

Ionic cross-linking between the SAC component and (a) F6PBI by imidazole group protonation or (b) N-methylmorpholine after quaternization.

Ionic-Liquid-Based Proton Conducting Membranes for Anhydrous H2/Cl2 Fuel-Cell Applications

An ionic-liquid-doped poly(benzimidazole) (PBI) proton-conducting membrane for an anhydrous H2/Cl2 fuel cell has been proposed. Compared with other ionic liquids, such as imidazole-type ionic liquids, diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]) showed better electrode reaction kinetics (H2 oxidation and Cl2 reduction reaction at platinum) and was more suitable for a H2/Cl2 fuel cell. PBI polymer and [dema][TfO] were compatible with each other, and the hybrid membranes exhibited high stability and good ionic conductivity, reaching 20.73 mS cm(-1) at 160 °C. We also analyzed the proton-transfer mechanism in this ionic-liquid-based membrane and considered that both proton-hopping and diffusion mechanisms existed. In addition, this composite electrolyte worked well in a H2/Cl2 fuel cell under non-water conditions. This work would give a good path to study the novel membranes for anhydrous H2/Cl2 fuel-cell application.

Preparation of PBI/H3PO4-PTFE Composite Membranes for High Temperature Fuel Cells

The poly(benzimidazole) (PBI)/ poly(tetrafluoroethylene) (PTFE) composite membrane was prepared by impregnating a porous PTFE thin film in a PBI solution N,N’-dimethyl acetamide (DMAc) solution mixed with LiCl. LiCl was used as a stabilizer to avoid aggregations of PBI molecules in the DMAc solutions. In this paper, we report a 2 mg/ml PBI/ DMAc/ LiCl solution with a [LiCl]/[BI] molar ratio of ~8.0 (i.e. the LiCl/PBI is ~ 1.1 in wt ratio, where [BI] is the concentration of benzimidazole repeat unit in the solution) has a lowest PBI polymer aggregations and thus a lowest solutions viscosity. The PBI membrane and PBI/PTFE composite membrane prepared from the PBI/DMAc/LiCl solution with a [LiCl]/[BI] molar ratio of ~8.0 were used to dop H3PO4 and prepare membrane electrode assemblies (MEA). The unit cell performances of these MEAs were carried out at 150oC. Owing to the high mechanical strength of porous PTFE, the thickness of PBI/H3PO4-PTFE composite membrane is allowed to be lower than that of a PBI/H3PO4 membrane. The lower thickness of PBI/H3PO4-PTFE membrane than that of PBI/H3PO4 membrane results in a lower resistance of PBI/H3PO4-PTFE than PBI/H3PO4. Thus the MEA prepared from PBI/H3PO4-PTFE has a better fuel cell performance than that prepared from PBI.

Trimethoxymethane as an alternative fuel for a direct oxidation PBI polymer electrolyte fuel cell

The oxidation of trimethoxymethane (TMM) (trimethyl orthoformate) in a direct oxidation PBI fuel cell was examined by on-line mass spectroscopy and on-line FTIR spectroscopy. The results show that TMM was almost completely hydrolyzed in a direct oxidation fuel cell which employs an acid doped polymer electrolyte to form a mixture of methylformate, methanol and formic acid. It also found that TMM was hydrolyzed in the presence of water at 120°C even without acidic catalyst. The anode performance improves in the sequence of methanol, TMM, formic acid/methanol, and methylformate solutions. Since formic acid is electrochemically more active than methanol, these results suggest that formic acid is probably a key factor for the improvement of the anode performance by using TMM instead of methanol under these conditions.