Sulfonated Poly(arylene ether phosphine oxide ketone) Block Copolymers as Oxidatively Stable Proton Conductive Membranes

The introduction of triphenylphosphine oxide moiety into the hydrophilic segments of aromatic multiblock copolymers provided outstanding oxidative stability and high proton conductivity. Our designed multiblock copolymers are composed of highly sulfonated phenylene ether phosphine oxide ketone units as hydrophilic blocks and phenylene ether biphenylene sulfone units as hydrophobic blocks. High molecular weight block copolymers (<i>M</i>_w = 204–309 kDa and <i>M</i>_n = 72–94 kDa) with different copolymer compositions (number of repeat unit in the hydrophobic blocks, <i>X</i> = 30, and that of hydrophilic blocks, <i>Y</i> = 4, 6, or 8) were synthesized, resulting in self-standing, transparent, and bendable membranes by solution-casting. The block copolymer membranes exhibited well-developed hydrophilic/hydrophobic phase separation, high proton conductivity, and excellent oxidative stability due to the highly sulfonated hydrophilic blocks, which contained phenylene rings with sulfonic acid groups and electron-withdrawing phosphine oxide or ketone groups

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 <i>p</i>-phenylene groups and oligo­(arylene ether sulfone ketone)­s, as high-molecular-weight polymers (<i>M</i>_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

Partially Fluorinated Polyphenylene Ionomers as Proton Exchange Membranes for Fuel Cells: Effect of Pendant Multi-Sulfophenylene Groups

The six kinds of sulfonated poly­(arylene perfluoroalkylene) (SPAF) ionomers with pendant multi-sulfophenylene groups were designed and synthesized to apply to fuel cells as proton exchange membranes. The SPAF polymers possessed high ion exchange capacity (IEC) values (2.07–2.15 mequiv g–1), good solubility in organic solvents, and high molecular weight, providing the flexible membranes by solution casting. Compared with our previous SPAF-MM membrane (with no pendant sulfophenylene groups), the introduction of the pendant sulfophenylene groups resulted in the significant improvement of proton conductivity, whereas it did not deteriorate the other favorable membrane properties, such as gas impermeability and mechanical properties. The SPAF-BM, as the chosen membrane, exhibited higher fuel cell performance than that of our previous SPAF-MM membrane under low humidified conditions. During the open circuit voltage (OCV) hold test, the SPAF-BM cell showed the low average decay of 40 μV h–1 and kept high OCV even after 1000 h. Post-test analyses proved that the SPAF-BM membrane after the OCV hold test retained the original fuel cell performance without practical changes in the molecular structure and molecular weight due to the high chemical stability of SPAF-BM

Remarkable Reinforcement Effect in Sulfonated Aromatic Polymers as Fuel Cell Membrane

Fluorine-free aromatic ionomers are next generation materials for proton exchange membrane fuel cells (PEMFCs). In addition to high proton conductivity and chemical durability, a membrane must also have high mechanical durability under practical fuel cell operating conditions, where frequent humidity changes are involved. We herein demonstrate that a fluorine-free reinforced aromatic PEM exhibits much improved mechanical durability compared with the parent aromatic PEM under the humidity cycling test conditions. The parent PEM and the reinforcement material are a sulfonated polybenzophenone derivative (SPK, in house) and a nonwoven fabric (NF, composite of glass and PET fibers), both of which do not contain any fluorine atoms. Because the compatibility between the SPK and the reinforcement materials is high, an almost void-free, dense, homogeneous, and tough reinforced PEM is attainable even with thin membrane thickness (18 μm), leading to a reasonably high fuel cell performance. The reinforcement material improves in-plane dimensional stability and mitigates crack propagation during frequent humidity changes, resulting in high durability (more than 18 000 cycles) in the wet–dry cycling test. The advantages of this fluorine-free reinforced PEM, unlike typical reinforced PEMs (e.g., Gore-SELECT consisting of a perfluorosulfonic acid ionomer and a microporous expanded polytetrafluoroethylene support layer), include versatility in molecular design, enabling further improvement in performance and durability of PEMFCs with lower cost

Highly Luminescent BODIPY-Based Organoboron Polymer Exhibiting Supramolecular Self-Assemble Structure

Highly Luminescent BODIPY-Based Organoboron Polymer Exhibiting Supramolecular Self-Assemble Structur

Sulfonated Phenylene/Quinquephenylene/Perfluoroalkylene Terpolymers as Proton Exchange Membranes for Fuel Cells

A novel series of terpolymers (SQF) containing sulfophenylene, quinquephenylene, and perfluoroalkylene groups in the polymer main chain were designed and synthesized as proton exchange membranes for fuel cells. The terpolymers with high molecular weight (Mw = 179–207 kDa, Mn = 41–50 kDa) and different ion exchange capacity (IEC) values (1.70, 2.56, and 3.34 mequiv g–1) gave flexible self-standing membranes by solution casting. Compared to the two-component (sulfophenylene and quinquephenylene segments) copolymer membranes, the incorporation of the third component, perfluoroalkylene groups, resulted in better water utilization for the proton conduction, while it did not alter the other properties such as gas permeability and mechanical strength. The selected membrane (SQF-3 with IEC = 2.56 mequiv g–1) exhibited high fuel cell performance under high- and low-humidity conditions with maximum power density reaching 0.97 W cm–2 at 100% RH (relative humidity) and 0.82 W cm–2 at 30% RH, respectively, at a current density of 1.51 A cm–2 with oxygen. A good interfacial compatibility between the SQF-3 membrane and catalyst layers resulted in mass activity of the cathode catalyst comparable to that obtained with the Nafion membrane NRE 211. During the open circuit voltage (OCV) hold test with air and hydrogen at 80 °C and 30% RH for 1000 h, the OCV showed a slight decrease from 0.97 to 0.88 V. Post-test analyses revealed that the SQF-3 membrane retained its initial high fuel cell performance due to its high chemical stability as well as low gas permeability

Anion Conductive Aromatic Block Copolymers Containing Diphenyl Ether or Sulfide Groups for Application to Alkaline Fuel Cells

A novel series of aromatic block copolymers composed of fluorinated phenylene and biphenylene groups and diphenyl ether (QPE-<i>bl</i>-5) or diphenyl sulfide (QPE-<i>bl</i>-6) groups as a scaffold for quaternized ammonium groups is reported. The block copolymers were synthesized via aromatic nucleophilic substitution polycondensation, chloromethylation, quaternization, and ion exchange reactions. The block copolymers were soluble in organic solvents and provided thin and bendable membranes by solution casting. The membranes exhibited well-developed phase-separated morphology based on the hydrophilic/hydrophobic block copolymer structure. The membranes exhibited mechanical stability as confirmed by DMA (dynamic mechanical analyses) and low gas and hydrazine permeability. The QPE-<i>bl</i>-5 membrane with the highest ion exchange capacity (IEC = 2.1 mequiv g^–1) exhibited high hydroxide ion conductivity (62 mS cm^–1) in water at 80 °C. A noble metal-free fuel cell was fabricated with the QPE-<i>bl</i>-5 as the membrane and electrode binder. The fuel cell operated with hydrazine as a fuel exhibited a maximum power density of 176 mW cm^–2 at a current density of 451 mA cm^–2

Appearing, Disappearing, and Reappearing Fumed Silica Nanoparticles: Tapping-Mode AFM Evidence in a Condensation Cured Polydimethylsiloxane Hybrid Elastomer

Appearing, Disappearing, and Reappearing Fumed Silica Nanoparticles:  Tapping-Mode AFM Evidence in a Condensation Cured Polydimethylsiloxane Hybrid Elastome

Aromatic Copolymers Containing Ammonium-Functionalized Oligophenylene Moieties as Highly Anion Conductive Membranes

The synthesis and properties of anion conductive aromatic copolymers containing oligophenylene moieties as a scaffold for quaternized ammonium groups are reported. Our new hydrophilic components consist of a chemically robust oligophenylene main chain modified with a high density of ionic groups. A partially fluorinated oligo­(arylene ether) was employed as a hydrophobic block. The targeted copolymers (QPE-<i>bl</i>-9) were synthesized via nickel-mediated coupling polymerization, followed by chloromethylation, quaternization, and ion exchange reactions. QPE-<i>bl</i>-9 provided tough, bendable membranes by solution casting. The resulting membrane with the highest ion exchange capacity (IEC = 2.0 mequiv g^–1) exhibited high hydroxide ion conductivity (138 mS cm^–1) in water at 80 °C. Reasonable alkaline stability of QPE-<i>bl</i>-9 membrane was confirmed in 1 M KOH aqueous solution for 1000 h at 40 °C. A noble metal-free fuel cell with QPE-<i>bl</i>-9 used as the membrane and electrode binder was successfully operated. A maximum power density of 510 mW cm^–2 was achieved at a current density of 1.20 A cm^–2 with hydrazine as the fuel and O₂ as the oxidant