Synthesis and Membrane Properties of Sulfonated Poly(arylene ether sulfone) Statistical Copolymers for Electrolysis of Water: Influence of Meta- and Para-Substituted Comonomers.

Two series of high molecular weight disulfonated poly(arylene ether sulfone) random copolymers were synthesized as proton exchange membranes for high-temperature water electrolyzers. These copolymers differ based on the position of the ether bonds on the aromatic rings. One series is comprised of fully para-substituted hydroquinone comonomer, and the other series incorporated 25 mol % of a meta-substituted comonomer resorcinol and 75 mol % hydroquinone. The influence of the substitution position on water uptake and electrochemical properties of the membranes were investigated and compared to that of the state-of-the-art membrane Nafion. The mechanical properties of the membranes were measured for the first time in fully hydrated conditions at ambient and elevated temperatures. Submerged in water, these hydrocarbon-based copolymers had moduli an order of magnitude higher than Nafion. Selected copolymers of each series showed dramatically increased proton conductivities at elevated temperature in fully hydrated conditions, while their H2 gas permeabilities were well controlled over a wide range of temperatures. These improved properties were attributed to the high glass transition temperatures of the disulfonated poly(arylene ether sulfone)s.

Controlled disulfonated poly(arylene ether sulfone) multiblock copolymers for direct methanol fuel cells.

Structure-property-performance relationships of disulfonated poly(arylene ether sulfone) multiblock copolymer membranes were investigated for their use in direct methanol fuel cell (DMFC) applications. Multiple series of reactive polysulfone, polyketone, and polynitrile hydrophobic block segments having different block lengths and molecular composition were synthesized and reacted with a disulfonated poly(arylene ether sulfone) hydrophilic block segment by a coupling reaction. Large-scale morphological order of the multiblock copolymers evolved with the increase of block size that gave notable influence on mechanical toughness, water uptake, and proton/methanol transport. Chemical structural changes of the hydrophobic blocks through polar group, fluorination, and bisphenol type allowed further control of the specific properties. DMFC performance was analyzed to elicit the impact of structural variations of the multiblock copolymers. Finally, DMFC performances of selected multiblock copolymers were compared against that of the industrial standard Nafion in the DMFC system.

Solid-state NMR molecular dynamics characterization of a highly chlorine-resistant disulfonated poly(arylene ether sulfone) random copolymer blended with poly(ethylene glycol) oligomers for reverse osmosis applications.

We have investigated the dynamics-transport correlations of a chlorine-resistant polymeric system designed as a next-generation reverse osmosis (RO) membrane material by solid-state NMR spectroscopy. A random disulfonated poly(arylene ether sulfone) copolymer in the potassium salt (-SO(3)(-)K(+)) form (BPS-20K) was blended with poly(ethylene glycol)s (PEGs) for improving water permeability. Blended BPS-20K/PEG membranes maintained the intrinsic chlorine-resistant property of BPS-20K, with a somewhat reduced salt rejection. The dynamic characteristics of BPS-20K/PEG blends studied by the spin-lattice relaxation time (T(1)) and rotating frame spin-lattice relaxation time (T(1)ρ) indicated correlations with the observed water uptake and permeability. (1)H T(1) measured on the polymer's aromatic phenylene rings and (1)H T(1)ρ measured on the oxyethylene (-CH(2)CH(2)O-) units of PEG were sensitive to the morphological changes, due to the blending of PEGs, induced in the mixed matrices. Membranes made of BPS-20K/PEG blends, with a lower molecular weight and higher amount of PEGs, that exhibited higher water permeability also provided shorter (1)H T(1) and T(1)ρ relaxation times. PEGs behaved as a plasticizer in the BPS-20K matrix, providing shorter (1)H T(1) times and therefore shorter motional correlation times in the nanosecond regime. (1)H T(1)ρ data have indicated the formation of networks among different polymeric chains via K(+)-oxyethylene ion-dipole interactions. Other properties that exhibit ad hoc correlations with the observed T(1) and T(1)ρ times include density, glass transition temperature, and salt rejection. Additionally, the ring flip motions measured on the hydrophobic phenylene rings did not reveal any correlations to the molecular weight and amount of PEGs blended, suggesting that the blending of PEG molecules modifies only the ionic domains of the BPS-20K polymer matrix.

Advances in membrane materials: desalination membranes based on directly copolymerized disulfonated poly(arylene ether sulfone) random copolymers.

The water and salt transport properties of chlorine tolerant disulfonated poly(arylene ether sulfone) (BPS) copolymers have been characterized. Cast BPS membranes of both salt form and acid form with sulfonation levels from 20% to 40% were investigated. Water permeability of BPS films increases more than one order of magnitude as sulfonation level increases from 20% to 40%, while the salt permeability of the corresponding membranes increases two orders of magnitude. Moderate salt rejection (98.2%) was achieved by a BPS salt form membrane with a sulfonation level of 20%.

Chemically tuned anode with tailored aqueous hydrocarbon binder for direct methanol fuel cells.

An anode for direct methanol fuel cells was chemically tuned by tailoring an aqueous hydrocarbon catalyst (SPI-BT) binder instead of using a conventional perfluorinated sulfonic acid ionomer (PFSI). SPI-BT designed in triethylamine salt form showed lower proton conductivity than PFSI, but it was stable in the catalyst ink forming the aqueous colloids. The aqueous colloidal particle size of SPI-BT was much smaller than that of PFSI. The small SPI-BT colloidal particles contributed to forming small catalyst agglomerates and simultaneously reducing their pore volume. Consequently, the high filling level of binders in the pores, where Pt-Ru catalysts are mainly located on the wall and physically interconnected, resulted in increased electrochemical active surface area of the anode, leading to high catalyst utilization. In addition, the chemical affinity between the SPI-BT binder and the membrane material derived from their similar chemical structure induced a stable interface on the membrane-electrode assembly (MEA) and showed low electric resistance. Upon adding SPI-BT, the synergistic effect of high catalyst utilization, improved mass transfer behavior to Pt-Ru catalyst, and low interfacial resistance of MEA became greater than the influence of reduced proton conductivity in the electrochemical performance of single cells. The electrochemical performance of MEAs with SPI-BT anode was enhanced to almost the same degree or somewhat higher than that with PFSI at 90 degrees C.

Surface-fluorinated proton-exchange membrane with high electrochemical durability for direct methanol fuel cells.

Random disulfonated poly(arylene ether sulfone)-silica nanocomposite (FSPAES-SiO2) membranes were physicochemically tuned via surface fluorination. Surface fluorination for 30 min converted about 20% of the C-H bonds on the membrane surface into C-F bonds showing hydrophobicity and electronegativity at the same time. The membranes with hydrophobic surface properties showed high dimensional stability and low methanol permeability when hydrated for direct methanol fuel cell applications. In particular, the surface enrichment of fluorine atoms led to anisotropic swelling behavior, associated with a stable electrode interface formation. Interestingly, in spite of the use of a random copolymer as a polymer matrix, the low surface free energy of the C-F bonds induced a well-defined continuous ionic channel structure, similar to those of multiblock copolymers. In addition to the morphological transition, fluorine atoms with high electron-withdrawing capability promoted the dissociation of sulfonic acid (-SO3H) groups. Consequently, FSPAES-SiO2 membranes exhibited improved proton conductivity. Thus, FSPAES-SiO2 membranes exhibited significantly improved single-cell performances (about 200%) at a constant voltage of 0.4 V in comparison with those of Nafion 117 and nonfluorinated membranes. Surprisingly, their good electrochemical performances were maintained with very low nonrecovery loss over the time period of 1400 h and interfacial resistances 380% times lower than those of conventional membrane-electrode assemblies comprising the control hydrocarbon membrane and a Nafion binder for the electrodes.