Physicochemical properties of alkaline doped polybenzimidazole membranes for anion exchange membrane fuel cells

Separators and Membranes for Advanced Alkaline Water Electrolysis

Traditionally, alkaline water electrolysis (AWE) uses diaphragms to separate anode and cathode and is operated with 5-7 M KOH feed solutions. The ban of asbestos diaphragms led to the development of polymeric diaphragms, which are now the state of the art material. A promising alternative is the ion solvating membrane. Recent developments show that high conductivities can also be obtained in 1 M KOH. A third technology is based on anion exchange membranes (AEM); because these systems use 0-1 M KOH feed solutions to balance the trade-off between conductivity and the AEM's lifetime in alkaline environment, it makes sense to treat them separately as AEM WE. However, the lifetime of AEM increased strongly over the last 10 years, and some electrode-related issues like oxidation of the ionomer binder at the anode can be mitigated by using KOH feed solutions. Therefore, AWE and AEM WE may get more similar in the future, and this review focuses on the developments in polymeric diaphragms, ion solvating membranes, and AEM.

Effect of Water Absorption on Electric Properties of Temperature-Resistant Polymers

The effects of water absorption on the electric resistivity and dielectric constant of polyimide (PI) and poly(ethylene terephthalate) (PET) were investigated, and the mechanism of deterioration in electrical insulation properties was discussed. The polyimides are poly(oxydianiline pyromellitimide) (PMDA-ODA) and poly(para-phenylene diamine biphenyltetracarboxydiimide) (BPDA-PDA). These polymer films were immersed in pure water for various immersion times at room temperature, and the water absorption ratio was evaluated. The electric resistance for these films was measured at room temperature using a high-resistance meter, and the dielectric constant at room temperature was measured using an LCR meter in a frequency range of 200 kHz to 2 MHz. The absorption ratios at equilibrium absorption for PMDA-ODA, BPDA-PDA, and PET were 2.7, 2.5, and 0.5%, respectively. The critical volume fraction of the percolation threshold of electric conductivity due to water absorption was 0.034 for both PMDA-ODA and BPDA-PDA. On the other hand, PET did not show a significant decrease in the resistivity. For both PIs and PET, the dielectric constant observed could be explained by a series model of the respective capacitances of pure water and polymer. Actually, the resistivity of samples cut from the edges of the film after water absorption was almost the same value as that in the dry state. These results suggest that the absorbed water molecules are not uniformly dispersed in the film but are localized at the edges of the film even after the absorption equilibrium has been reached.

High performance chitosan/nanocellulose-based composite membrane for alkaline direct ethanol fuel cells

Polysaccharide anion exchange membranes (AEMs) containing chitosan (CS), cellulose nanofibrils (CNFs) and CNFs quaternized with poly(diallyldimethylammonium chloride) (CNF(P)s) were developed for use in alkaline direct ethanol fuel cells (ADEFCs). The resulting composite membranes prepared by the solvent casting process based on an experimental design were comprehensively assessed for morphology, KOH uptake, swelling ratio, EtOH permeability, mechanical properties, ionic conductivity, and cell performance. The fabricated CS-based composite membranes with CNF(P) fillers were superior to the commercial Fumatech FAA-3-50 membrane in terms of Young's modulus and tensile strength (69 % and 85 % higher, respectively), ion exchange capacity (169 % higher), and ionic conductivity (228 % higher). Single fuel cell tests have shown excellent performance of the CS-based membranes with CNF and CNF(P) fillers, as they exhibited up to 86 % improvement in power density at 80 °C compared to the commercial membrane (65.1 mW/cm2 vs. 35.1 mW/cm2) and higher maximum power density at all test conditions.

Preparation and Characterization of QPVA/PDDA Electrospun Nanofiber Anion Exchange Membranes for Alkaline Fuel Cells

In recent years, there has been considerable interest in anion exchange membrane fuel cells (AEMFCs) as part of fuel cell technology. Anion exchange membranes (AEMs) provide a significant contribution to the development of fuel cells, particularly in terms of performance and efficiency. Polymer composite membranes composed of quaternary ammonium poly(vinyl alcohol) (QPVA) as electrospun nanofiber mats and a combination of QPVA and poly(diallyldimethylammonium chloride) (PDDA) as interfiber voids matrix filler were prepared and characterized. The influence of various QPVA/PDDA mass ratios as matrix fillers on anion exchange membranes and alkaline fuel cells was evaluated. The structural, morphological, mechanical, and thermal properties of AEMs were characterized. To evaluate the AEMs' performances, several measurements comprise swelling properties, ion exchange capacity (IEC), hydroxide conductivity (σ), alkaline stability, and single-cell test in fuel cells. The eQP-PDD_0.5 acquired the highest hydroxide conductivity of 43.67 ms cm^-1 at 80 °C. The tensile strength of the membranes rose with the incorporation of the filler matrix, with TS ranging from 23.18 to 24.95 Mpa. The peak power density and current density of 24 mW cm^-2 and 131 mA cm^-2 were achieved with single cells comprising eQP-PDD_0.5 membrane at 57 °C.

A Brief Review of Poly(Vinyl Alcohol)-Based Anion Exchange Membranes for Alkaline Fuel Cells

Anion exchange membrane fuel cells have unique advantages and are thus gaining increasing attention. Poly(vinyl alcohol) (PVA) is one of the potential polymers for the development of anion exchange membranes. This review provides recent studies on PVA-based membranes as alternative anion exchange membranes for alkaline fuel cells. The development of anion exchange membranes in general, including the types, materials, and preparation of anion exchange membranes in the last years, are discussed. The performances and characteristics of recently reported PVA-based membranes are highlighted, including hydroxide conductivity, water uptake, swelling degree, tensile strength, and fuel permeabilities. Finally, some challenging issues and perspectives for the future study of anion exchange membranes are discussed.

Alcohol Diffusion in Alkali-Metal-Doped Polymeric Membranes for Using in Alkaline Direct Alcohol Fuel Cells

The alcohol permeability of anion exchange membranes is a crucial property when they are used as a solid electrolyte in alkaline direct alcohol fuel cells and electrolyzers. The membrane is the core component to impede the fuel crossover and allows the ionic transport, and it strongly affects the fuel cell performance. The aim of this work is to compare different anion exchange membranes to be used as an electrolyte in alkaline direct alcohol fuels cells. The alcohol permeability of four commercial anion exchange membranes with different structure were analyzed in several hydro-organic media. The membranes were doped using different types of alkaline doping agents (LiOH, NaOH, and KOH) and different conditions to analyze the effect of the treatment on the membrane behavior. Methanol, ethanol, and 1-propanol were analyzed. The study was focused on the diffusive contribution to the alcohol crossover that affects the fuel cell performance. To this purpose, alcohol permeability was determined for various membrane systems. The results show that membrane alcohol permeability is affected by the doping conditions, depending on the effect on the type of membrane and alcohol nature. In general, heterogeneous membranes presented a positive correlation between alcohol permeability and doping capacity, with a lower effect for larger-size alcohols. A definite trend was not observed for homogeneous membranes.

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.

Cationic ether-free poly(bis-alkylimidazolium) ionene blend polybenzimidazole as anion exchange membranes

A new simple route towards ether-free AEM design and fabrication with a wide potential structural scope.

Hydroxide Conduction Enhancement of Chitosan Membranes by Functionalized MXene

In this study, imidazolium brushes tethered by –NH₂-containing ligands were grafted onto the surface of a 2D material, MXene, using precipitation polymerization followed by quaternization. Functionalized MXene was embedded into chitosan matrix to prepare a hybrid alkaline anion exchange membrane. Due to high interfacial compatibility, functionalized MXene was homogeneously dispersed in chitosan matrix, generating continuous ion conduction channels and then greatly enhancing OH⁻ conduction property (up to 172%). The ability and mechanism of OH⁻ conduction in the membrane were elaborated based on systematic tests. The mechanical-thermal stability and swelling resistance of the membrane were evidently augmented. Therefore, it is a promising anion exchange membrane for alkaline fuel cell application.

Adsorption of benzotriazole and benzimidazole from water over a Co-based metal azolate framework MAF-5(Co)

Benzotriazole (BTA) and benzimidazole (BZI) are regarded as water pollutants because of their extensive uses in industry and appreciable water solubility. The adsorption of both BTA and BZI from water over a newly synthesized metal-organic framework, MAF-5(Co), was investigated and compared with zeolitic imidazole frameworks (ZIFs), such as ZIF-8(Zn) and ZIF-67(Co), as well as commercial activated carbon. MAF-5(Co) had the highest adsorption capacities for both BTA and BZI. The maximum adsorption capacities of MAF-5(Co) for BTA and BZI were 389 and 175mgg^-1, respectively. Hydrophobic and π-π interactions between the aromatic adsorbate BTA and MAF-5(Co) were suggested as a plausible mechanism. Based on the zeta potential of MAF-5(Co) and effects of pH on the BTA adsorption, electrostatic interactions between the MAF-5(Co) and BTA species might also affect the adsorption of BTA over MAF-5(Co). MAF-5(Co) can be recycled for adsorptive removal of BTA by simple ethanol washing. Therefore, MAF-5(Co) is suggested as a promising adsorbent for the removal of BTA and BZI from water.