Membranes from Poly(aryl ether)-Based Ionomers Containing Randomly Distributed Nanoclusters of 6 or 12 Sulfonic Acid Groups

Asymmetric Synthesis of α-Arylcyclohexenones Catalyzed by Diphenylprolinol Silyl Ether

A general methodology for the asymmetric synthesis of α-arylcyclohexeneones from arylacetones and α,β-unsaturated aldehydes catalyzed by diphenylprolinol silyl ether followed by p-TSA-mediated cyclization is developed. A variety of arylacetones and α,β-unsaturated aldehydes were successfully converted to α-arylcyclohexeneones in 34-67% yield, 10:1-100:0 dr, and 81-99% ee. The scalability of this methodology by a gram-scale synthesis and their utility by converting the product to the corresponding epoxide, alcohol, and diol are demonstrated.

Atomistic Simulations of Hydrated Sulfonated Polybenzophenone Block Copolymer Membranes

We present a classical molecular dynamics simulations study on the nanostructures of the sulfonated polybenzophenone (SPK) block copolymer membranes at 300 K and 353 K. The results of the radial distribution function (RDF) show that the interactions of the sulfonate groups of the membrane with the hydronium ions are more significant than those of water due to the strong electrostatic attraction over the hydrogen bonding. However, the effect of temperatures on the RDF profile seems insignificant. Furthermore, the spatial distribution function (SDF) portrays that the sulfonate groups of the hydrophilic components are preferential binding sites for hydronium ions against the hydrophobic counterpart of the SPK membrane. The mobility of the H3 O+ ions at 300 K and 353 K is two (or three) times lower than that of Nafion/Aciplex. However, the diffusion coefficients for water molecules closely agree with Nafion/Aciplex. This study suggests that water clusters are more localized around the sulfonate groups in the SPK membranes. Thus, the molecular modeling study of SPK block copolymer membranes is warranted to design better-performing membrane electrolytes.

A Critical Review of Electrolytes for Advanced Low- and High-Temperature Polymer Electrolyte Membrane Fuel Cells

In the 21st century, proton exchange membrane fuel cells (PEMFCs) represent a promising source of power generation due to their high efficiency compared with coal combustion engines and eco-friendly design. Proton exchange membranes (PEMs), being the critical component of PEMFCs, determine their overall performance. Perfluorosulfonic acid (PFSA) based Nafion and nonfluorinated-based polybenzimidazole (PBI) membranes are commonly used for low- and high-temperature PEMFCs, respectively. However, these membranes have some drawbacks such as high cost, fuel crossover, and reduction in proton conductivity at high temperatures for commercialization. Here, we report the requirements of functional properties of PEMs for PEMFCs, the proton conduction mechanism, and the challenges which hinder their commercial adaptation. Recent research efforts have been focused on the modifications of PEMs by composite materials to overcome their drawbacks such as stability and proton conductivity. We discuss some current developments in membranes for PEMFCs with special emphasis on hybrid membranes based on Nafion, PBI, and other nonfluorinated proton conducting membranes prepared through the incorporation of different inorganic, organic, and hybrid fillers.

Branched Poly(arylene ether ketone sulfone)s with Ultradensely Sulfonated Branched Centers for Proton Exchange Membranes: Effect of the Positions of the Sulfonic Acid Groups

Branched sulfonated polymers present considerable potential for application as proton exchange membranes, yet investigation of branched polymers containing sulfonated branched centers remains to be advanced. Herein, we report a series of polymers with ultradensely sulfonated branched centers, namely, B-x-SPAEKS, where x represents the degree of branching. In comparison with the analogous polymers bearing sulfonated branched arms, B-x-SPAEKS showed a reduced water affinity, resulting in less swelling and lower proton conductivity. The water uptake, swelling ratio (in-plane), and proton conductivity of B-10-SPAEKS at 80 °C were 52.2%, 57.7%, and 23.6% lower than their counterparts, respectively. However, further analysis revealed that B-x-SPAEKS featured significantly better proton conduction under the same water content due to the formation of larger hydrophilic clusters (∼10 nm) that promoted efficient proton transportation. B-12.5-SPAEKS exhibited a proton conductivity of 138.8 mS cm^-1 and a swelling ratio (in-plane) of only 11.6% at 80 °C, both of which were superior to Nafion 117. In addition, a decent single-cell performance of B-12.5-SPAEKS was also achieved. Consequently, the decoration of sulfonic acid groups on the branched centers represents a very promising strategy, enabling outstanding proton conductivity and dimensional stability simultaneously even with low water content.

Alkyl bisimidazolium-mediated crosslinked comb-shaped polymers as highly conductive and stable anion exchange membranes

Crosslinked poly(arylene ether sulfone)s (PES) with pendant alkyl bisimidazolium units, which act as both crosslinkage sites and hydroxide conductors, were developed as anion exchange membranes (AEMs).

Effect of the Hydrophilic Component in Aromatic Ionomers: Simple Structure Provides Improved Properties as Fuel Cell Membranes

To elucidate the effect of the hydrophilic component on the properties of aromatic ionomers, we have designed for the first time one of the simplest possible structures, the sulfo-1,4-phenylene unit, as the hydrophilic component. A modified Ni-mediated coupling polymerization produced the title aromatic ionomers composed of sulfonated p-phenylene groups and oligo(arylene ether sulfone ketone)s, as high-molecular-weight polymers (M_w = 202-240 kDa), resulting in the formation of tough, flexible membranes. The aromatic ionomer membranes showed well-developed hydrophilic/hydrophobic phase separation. Comparison with our previous aromatic ionomer membrane containing sulfonated benzophenone groups as a hydrophilic component revealed that the simple sulfophenylene structure (i.e., no polar groups such as ether, ketone, or sulfone groups in the hydrophilic component) was effective for the improvement of the membrane properties, i.e., reduced water uptake and excellent mechanical stability under humidified conditions. Furthermore, because of the high local ion exchange capacity (IEC), the simple structure led to high proton conductivity, especially at low humidity (reaching up to ca. 7.3 mS/cm at 80 °C and 20% RH), which is one of the highest values reported thus far. The improved properties of the membranes were also confirmed in an operating fuel cell.