Organic/inorganic composite membranes based on polybenzimidazole and nano-SiO2

Polymer Electrolyte Membranes Containing Functionalized Organic/Inorganic Composite for Polymer Electrolyte Membrane Fuel Cell Applications

To mitigate the dependence on fossil fuels and the associated global warming issues, numerous studies have focused on the development of eco-friendly energy conversion devices such as polymer electrolyte membrane fuel cells (PEMFCs) that directly convert chemical energy into electrical energy. As one of the key components in PEMFCs, polymer electrolyte membranes (PEMs) should have high proton conductivity and outstanding physicochemical stability during operation. Although the perfluorinated sulfonic acid (PFSA)-based PEMs and some of the hydrocarbon-based PEMs composed of rationally designed polymer structures are found to meet these criteria, there is an ongoing and pressing need to improve and fine-tune these further, to be useful in practical PEMFC operation. Incorporation of organic/inorganic fillers into the polymer matrix is one of the methods shown to be effective for controlling target PEM properties including thermal stability, mechanical properties, and physical stability, as well as proton conductivity. Functionalization of organic/inorganic fillers is critical to optimize the filler efficiency and dispersion, thus resulting in significant improvements to PEM properties. This review focused on the structural engineering of functionalized carbon and silica-based fillers and comparisons of the resulting PEM properties. Newly constructed composite membranes were compared to composite membrane containing non-functionalized fillers or pure polymer matrix membrane without fillers.

Material and Process Tests of Heterogeneous Membranes Containing ZIF-8, SiO2 and POSS-Ph

Heterogeneous membranes made of a polymer matrix and containing nano-metric fillers in their structure may present improved physicochemical and process properties compared to homogeneous membranes made only of polymer materials. Membranes made of a PEBAX^®2533 block copolymer were tested with fillers such as ZIF-8, SiO₂ and POSS-Ph being dosed to them. The material analysis and process tests indicate that these nanomaterials can be used as fillers for heterogeneous membranes. Chemometric analyses determined the influence of individual fillers on selected physicochemical properties of the materials which were used to produce the membranes. For specific concentrations of these fillers, improvement in the permeability and selectivity of the membranes, or at least in one of these parameters, was achieved. The greatest increase in permeability against the homogeneous membrane was obtained for membranes containing 10 wt% ZIF-8 (for CO₂, an increase of 2.07 times; for CH₄, 2.36 times; for N₂, 3.08 times). In turn, the greatest increase in selectivity was obtained for the CO₂/CH₄ mixture for the membrane containing 5 wt% SiO₂ (1.15 times), and for the CO₂/N₂ mixture for the membrane containing 2 wt% POSS-Ph (1.21 times).

Introducing a new 7-ring fused diindenone-dithieno[3,2-b:2',3'-d]thiophene unit as a promising component for organic semiconductor materials

A novel π-conjugated molecule, EtH-T-DI-DTT is reported, which is fused, rigid, and planar, featuring the electron-rich dithieno[3,2-b:2',3'-d]thiophene (DTT) unit in the core of the structure. Adjacent to the electron-donating DTT core, there are indenone units with electron-withdrawing keto groups. To enable solubility in common organic solvents, the fused system is flanked by ethylhexylthiophene groups. The material is a dark, amorphous solid with an onset of absorption at 638 nm in CH2Cl2 solution, which corresponds to an optical gap of 1.94 eV. In films, the absorption onset wavelength is at 701 nm, which corresponds to 1.77 eV. An ionisation energy of 5.5 eV and an electron affinity of 3.3 eV were estimated by cyclic voltammetry measurements. We have applied this new molecule in organic field effect transistors. The material exhibited a p-type mobility up to 1.33 × 10-4 cm2 V-1 s-1.

Recent Progress on Nanomaterial-Based Membranes for Water Treatment

Nanomaterials have emerged as the new future generation materials for high-performance water treatment membranes with potential for solving the worldwide water pollution issue. The incorporation of nanomaterials in membranes increases water permeability, mechanical strength, separation efficiency, and reduces fouling of the membrane. Thus, the nanomaterials pave a new pathway for ultra-fast and extremely selective water purification membranes. Membrane enhancements after the inclusion of many nanomaterials, including nanoparticles (NPs), two-dimensional (2-D) layer materials, nanofibers, nanosheets, and other nanocomposite structural materials, are discussed in this review. Furthermore, the applications of these membranes with nanomaterials in water treatment applications, that are vast in number, are highlighted. The goal is to demonstrate the significance of nanomaterials in the membrane industry for water treatment applications. It was found that nanomaterials and nanotechnology offer great potential for the advancement of sustainable water and wastewater treatment.

Polybenzimidazole-Based Polymer Electrolyte Membranes for High-Temperature Fuel Cells: Current Status and Prospects

Polymer electrolyte membrane fuel cells (PEMFCs) expect a promising future in addressing the major problems associated with production and consumption of renewable energies and meeting the future societal and environmental needs. Design and fabrication of new proton exchange membranes (PEMs) with high proton conductivity and durability is crucial to overcome the drawbacks of the present PEMs. Acid-doped polybenzimidazoles (PBIs) carry high proton conductivity and long-term thermal, chemical, and structural stabilities are recognized as the suited polymeric materials for next-generation PEMs of high-temperature fuel cells in place of Nafion® membranes. This paper aims to review the recent developments in acid-doped PBI-based PEMs for use in PEMFCs. The structures and proton conductivity of a variety of acid-doped PBI-based PEMs are discussed. More recent development in PBI-based electrospun nanofiber PEMs is also considered. The electrochemical performance of PBI-based PEMs in PEMFCs and new trends in the optimization of acid-doped PBIs are explored.

Recent Progress in the Development of Composite Membranes Based on Polybenzimidazole for High Temperature Proton Exchange Membrane (PEM) Fuel Cell Applications

The rapid increasing of the population in combination with the emergence of new energy-consuming technologies has risen worldwide total energy consumption towards unprecedent values. Furthermore, fossil fuel reserves are running out very quickly and the polluting greenhouse gases emitted during their utilization need to be reduced. In this scenario, a few alternative energy sources have been proposed and, among these, proton exchange membrane (PEM) fuel cells are promising. Recently, polybenzimidazole-based polymers, featuring high chemical and thermal stability, in combination with fillers that can regulate the proton mobility, have attracted tremendous attention for their roles as PEMs in fuel cells. Recent advances in composite membranes based on polybenzimidazole (PBI) for high temperature PEM fuel cell applications are summarized and highlighted in this review. In addition, the challenges, future trends, and prospects of composite membranes based on PBI for solid electrolytes are also discussed.

Phase Inversion-Induced Porous Polybenzimidazole Fuel Cell Membranes: An Efficient Architecture for High-Temperature Water-Free Proton Transport

To cope with the demand for cleaner alternative energy, polymer electrolyte membrane fuel cells (PEMFCs) have received significant research attention owing to their high-power density, high fuel efficiency, and low polluting by-product. However, the water requirement of these cells has necessitated research on systems that do not require water and/or use other mediums with higher boiling points. In this work, a highly porous meta-polybenzimidazole (m-PBI) membrane was fabricated through the non-solvent induced phase inversion technique and thermal cross-linking for high-temperature PEMFC (HT-PEMFC) applications. Standard non-thermally treated porous membranes are susceptible to phosphoric acid (PA) even at low concentrations and are unsuitable as polymer electrolyte membranes (PEMs). With the porous structure of m-PBI membranes, higher PA uptake and minimal swelling, which is controlled via cross-linking, was achieved. In addition, the membranes exhibited partial asymmetrical morphology and are directly applicable to fuel cell systems without any further modifications. Membranes with insufficient cross-linking resulted in an unstable performance in HT-PEMFC environments. By optimizing thermal treatment, a high-performance membrane with limited swelling and improved proton conductivity was achieved. Finally, the m-PBI membrane exhibited enhanced acid retention, proton conductivity, and fuel cell performance.

Fabrication of Novel Avermectin Nanoemulsion Using a Polyurethane Emulsifier with Cleavable Disulfide Bonds

In this study, a polyurethane emulsifer with various functional groups was prepared from isophorone diisocyanate, avermectin, 2,2-dimethylol propionic acid, and bis(2-hydroxyethyl) disulfide. The chemical structure of the polymer was confirmed by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, and element analysis. The polymer exhibited adequate emulsification ability for avermectin after neutralization with triethylamine. A satisfaying nanoemulsion was obtained, in which avermectin was encapsulated in nanoparticles with 50 wt % drug loading, low organic solvent content, and high stability under dilution and centrifuging treatment in addition to low surface tension, high affinity to crop leaf, and improved avermectin photostability. The resulting nanoparticles showed degradability in the presence of dl-dithiothreitol or inside the insect as a result of the disulfide bonds, promoting the release of avermectin. As a result, the avermectin nanoparticles showed higher insecticidal ability compared to both the avermectin nanoparticles without a disulfide group and the avermectin emulsifiable concentrate.

Structural and dielectric properties of cobaltacarborane composite polybenzimidazole membranes as solid polymer electrolytes at high temperature

The conductivity of a series of composite membranes, based on polybenzimidazole (PBI) containing the metallacarborane salt M[Co(C2B9H11)2], M[COSANE] and tetraphenylborate, M[B(C6H5)4], M[TPB] both anions having the same number of atoms and the same negative charge, has been investigated. Different cations (M = H+, Li+ and Na+) have been studied and the composite membranes have been characterized by water uptake, swelling ratios, ATR FT-IR, thermogravimetric analysis and electrochemical impedance spectroscopy to explore the dielectric response and ion dynamics in composite membranes. Our results show that conductivity increases with increasing temperature and it is higher for H+ than for Li+ and Na+ for all temperatures under study. The mobility of Li+ is greater in [COSANE]- than in [TPB]- composite PBI@membranes while for Na+ it is the opposite. The temperature dependence of the conductivity of the composite was followed by a typical Arrhenius behaviour with two different regions: (1) between 20 and 100 °C, and (2) between 100 and 150 °C. Using the analysis of electrode polarization (EP) based on the Thrukhan theory we have calculated the ionic diffusion coefficients and the density of carriers. From the double logarithmic plot of the imaginary part of the conductivity (σ'') versus frequency in the entire range of temperatures studied we have determined for each sample at each temperature, the frequency values of the onset (fON) and full development of electrode polarization (fMAX), respectively, which permit us to calculate static permittivity.

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.

An proton conductor electrolyte membrane, in which molten CsH₅(PO₄)₂ is held in a matrix made of PBI polymer and SiO₂ powder, is prepared for intermediate-temperature fuel cells.

Structure and properties of polybenzimidazole/silica nanocomposite electrolyte membrane: influence of organic/inorganic interface

Although increased number of reports in recent years on proton exchange membrane (PEM) developed from nanocomposites of polybenzimidazole (PBI) with inorganic fillers brought hope to end the saga of contradiction between proton conductivity and variety of stabilities, such as mechanical, thermal,chemical, etc.; it still remains a prime challenge to develop a highly conducting PEM with superior aforementioned stabilities. In fact the very limited understanding of the interactions especially interfacial interaction between PBI and inorganic filler leads to confusion over the choice of inorganic filler type and their surface functionalities. Taking clue from our earlier study based on poly(4,4'-diphenylether-5,5'-bibenzimidazole) (OPBI)/silica nanocomposites, where silica nanoparticles modified with short chain amine showed interfacial interaction-dependent properties, in this work we explored the possibility of enhanced interfacial interaction and control over the interface by optimizing the chemistry of the silica surface. We functionalized the surface of silica nanoparticles with a longer aliphatic chain having multiple amine groups (named as long chain amine modified silica and abbreviated as LAMS). FTIR and (13)C solid-state NMR provided proof of hydrogen bonding interactions between the amine groups of modifier and those of OPBI. LAMS nanoparticles yielded a more distinguished self-assembly extending all over the OPBI matrix with increasing concentrations. The crystalline nature of these self-assembled clusters was probed by wide-angle X-ray diffraction (WAXD) studies and the morphological features were captured by transmission electron microscope (TEM). We demonstrated the changes in storage modulus and glass transition temperature (Tg) of the membranes, the fundamental parameters that are more sensitive to interfacial structure using temperature dependent dynamic mechanical analysis (DMA). All the nanocomposite membranes displayed enhanced mechanical, thermal and chemical stability than neat OPBI. The lower water uptake and swelling ratio and volume in both acid and water reflected the more hydrophobic characteristic of the nanocomposites. All the nanocomposite membranes showed phosphoric acid (PA) values to be higher than OPBI but the levels showed decreasing trend with increasing silica content; the reason attributed to the interparticle interaction. The self-assembled clusters of LAMS nanoparticles in the matrix created more sites for proton hopping as a result of which the proton conductivity of all the nanocomposites displayed an increasing trend.

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.

High-temperature proton-exchange-membrane fuel cells using an ether-containing polybenzimidazole membrane as electrolyte

Herein, poly[2,2'-(p-oxydiphenylene)-5,5'-benzimidazole] (PBI) is synthesized from 3,3'-diaminobenzidine and 4,4'-oxybisbenzoic acid, and the membrane is prepared by solvent casting. The main characteristics of PBI are studied. In the preparation of the PBI/H(3) PO(4) composite membrane, the absorbing temperature of H(3) PO(4) is 120 °C, which leads to a membrane with a high content of H(3) PO(4) . Membrane electrode assemblies (MEAs) are fabricated from PBI/H(3) PO(4) membranes with the catalyst layer made of Pt/C, PBI, and polyvinylidene fluoride (230:12:7 w/w). The fabricated MEA is tested at 150 °C with dry hydrogen and oxygen gas at 0.2 MPa for both anode and cathode feeds. No degradation of voltage is seen during stability testing of the PBI/H(3) PO(4) membrane at a constant current for 100 h. The maximum power density is 1.17 W cm(-2) , and the maximum current density is 6.0 A cm(-2) with a Pt loading of 0.5 mg cm(-2) . The high performance of these membrane materials demonstrates that PBI can be regarded as an alternative membrane material for high-temperature proton-exchange-membrane fuel cells.