Degradation mechanism of polystyrene sulfonic acid membrane and application of its composite membranes in fuel cells

The lifetime behavior of a H-2/O-2 proton exchange membrane (PEM) fuel cell with polystyrene sulfonic acid (PSSA) membrane have been investigated in order to give an insight into the degradation mechanism of the PSSA membrane. The distribution of sulfur concentration in the cross section of the PSSA membrane was measured by energy dispersive analysis of X-ray, and the chemical composition of the PSSA membrane was characterized by infrared spectroscopy before and after the lifetime experiment. The degradation mechanism of the PSSA membrane is postulated as: the oxygen reduction at the cathode proceeds through some peroxide intermediates during the fuel cell operation, and these intermediates have strong oxidative ability and may chemically attack the tertiary hydrogen at the a carbon of the PSSA; the degradation of the PSSA membrane mainly takes place at the cathode side of the cell, and the loss of the aromatic rings and the SO3- groups simultaneously occurs from the PSSA membrane. A new kind of the PSSA-Nafion composite membrane, where the Nafion membrane is bonded with the PSSA membrane and located at the cathode of the cell, was designed to prevent oxidation degradation of the PSSA membrane in fuel cells. The performances of fuel cells with PSSA-Nafion101 and PSSA-recast Nafion composite membranes are demonstrated to be stable after 835 h and 240 h, respectively.

Sulfonated poly(ether ether ketone)/clay-SO3H hybrid proton exchange membranes for direct methanol fuel cells Journal of Power Sources

A new type of sulfonated clay (clay-SO3H) was prepared by the ion exchange method with the sulfanilic acid as the surfactant agent. The grafted amount of sulfanilic acid in clay-SO3H was 51.8 mequiv. (100 g)(-1), which was measured by thermogravimetric analysis (TGA). Sulfonated poly(ether ether ketone) (SPEEK)/clay-SO3H hybrid membranes which composed of SPEEK and different weight contents of clay-SO3H, were prepared by a solution casting and evaporation method. For comparison, the SPEEK/clay hybrid membranes were produced with the same method.

Synthesis and properties of novel polyimides from sulfonated binaphthalene dianhydride for proton exchange membranes

A sulfonated dianhydride monomer, 6,6-disulfonic-4,4'-binaphthyl-1,1',8,8'-tetracarboxylic dianhydride (SBTDA), was successfully synthesized by direct sulfonation of the parent dianhydride, 4,4'-binaphthyl-1,1',8,8'-tetracarboxylic dianhydride (BTDA), using fuming sulfuric acid as the sulfonating reagent. A series of sulfonated homopolyimides were prepared from SBTDA and various common nonsulfonated diamines. The resulting polymer electrolytes, which contain ion conductivity sites on the deactivated positions of the aryl backbone rings, displayed high proton conductivities of 0.25-0.31 S cm(-1) at 80 degrees C. The oxidative stability test indicated that the attachment of the -SO3H groups onto the dianhydride units did not deteriorate the oxidative stability of the SPI membranes.

Synthesis of sulfonated poly(arylene-co-naphthalimide)s as novel polymers for proton exchange membranes

A series of novel sulfonated poly(arylene-co-binaphthalimide)s (SPPIs) were successfully synthesized via Ni(0) catalytic coupling of sodium 3-(2,5-dichlorobenzoyl)benzenesulfonate and bis(chloronaphthalimide)s. Bis(chloronaphthalimide)s were conveniently prepared from 5-chloro-1,8-naphthalic anhydride and various diamines. Tough and transparent SPPI membranes were prepared and the electrolyte properties of the copolymers were intensively investigated as were the effects of different diamine structures on the copolymer characterisitics. The copolymer membrane Ia-80, with an ion exchange capacity (IEC) of 2.50 meq g(-1), displayed a higher proton conductivity, i.e. 0.135 S cm(-1) at 20 degrees C, as compared to Nafion 117 (0.09 S cm(-1), 20 degrees C).

Localization of Na+-K+ ATPases in Quasi-Native Cell Membranes

Na+-K+ ATPases have been observed and located by in situ AFM and single molecule recognition technique, topography and recognition imaging (TREC) that is a unique technique to specifically identify single protein in complex during AFM imaging. Na+-K+ ATPases were well distributed in the inner leaflet of cell membranes with about 10% aggregations in total recognized proteins. The height of Na+-K+ ATPases measured by AFM is in the range of 12-14 nm, which is very consistent with the cryoelectron microscopy result. The unbinding force between Na+-K+ ATPases in the membrane and anti-ATPases on the AFM tip is about 80 pN with the apparent loading rate at 40 nN/s.

Synthesis of Soluble Poly(arylene ether sulfone) Ionomers with Pendant Quaternary Ammonium Groups for Anion Exchange Membranes

A new bisphenol monomer, 2,2'-dimethylaminemetllylene-4,4'-biphenol (DABP), was easily prepared by Mannich reaction of dimethylamine and formaldehyde with 4,4'-biphenol. Novel partially fluorinated poly(arylene ether sulfone)s with pendant quaternary ammonium groups were prepared by copolymerization of DABP, 4,4'-biphenol, and 3,3',4,4'- tetrafluorodiphenylsulfone, followed by reaction with iodomethane. The resulting copolymers PSQNI-x (where x represents the molar fraction of DABP in the feed) with high molecular weight exhibited outstanding solubility in polar aprotic solvents; thus, the flexible and tough membranes of PSQNI-x with varying ionic content could be prepared by casting from the DMAc solution. Novel anion exchange membranes, PSQNOH-x, were obtained by an anion exchange of PSQNI-x with 1 N NaOH.

Dispersions of carbon nanotubes in sulfonated poly[bis(benzimidazobenzisoquinolinones)] and their proton-conducting composite membranes

A sulfonated poly[bis(benzimidazobenzisoquinolinones)] (SPBIBI) possessing a conjugated pyridinone ring was shown to be effective for dispersing multiwalled carbon nanotubes (MWCNTs) in DMSO. The dispersions in which the SPBIBI to MWCNTs mass ratio was 4:1 demonstrated the highest MWCNTs concentrations, i.e., 1.5-2.0 mg mL(-1), and were found to be stable for more than six months at room temperature. Through casting of these dispersions, MWCNTs/SPBIBI composite membranes were successfully fabricated on substrates as proton exchange membranes for fuel cell applications and showed no signs of macroscopic aggregation. The properties of composite membranes were investigated, and it was found that the homogeneous dispersion of the MWCNTs in the SPBIBI matrix altered the morphology structures of the composite membranes, which lead to the formation of more regular and smaller cluster-like ion domains.

Synthesis and properties of novel sulfonated poly(phenylquinoxaline)s as proton exchange membranes

Two series of sulfonated poly(phenylquinoxaline)s (SPPQ-x and SPPQ(O)-x, x refers to molar percentage of sulfonated tetraamine monomer) were first synthesized from a sulfonated tetraamine (4,4'-bis(3,4-diaminophenoxy)biphenyl-3.3'-disulfonic acid) and two aromatic bisbenzils (4-phenylglyoxalylbenzil and p,p'-oxydibenzil) in a mild condition. The structures of SPPQ-x and SPPQ(0)-x were characterized by IR and H-1 NMR spectra. The properties of these polymer films, such as water uptake, water swelling ratio, proton conductivity, thermal properties, methanol permeability, hydrolytic and oxidative stability were also investigated. The resulting polymers generally showed good solubility in DMAc and DMSO. Flexible and tough membranes with high mechanical strength were prepared. They show very high thermal, thermooxidative, hydrolytic stabilities and low methanol permeability. SPPQ-100 with the IEC value (2.41 mmol/g) displays the conductivity of 0.1 S/cm and a swelling ratio of 7.3% at 100 degrees C.

Synthesis and properties of water stable poly[bis(benzimidazobenzisoquinolinone)] ionomers for proton exchange membranes fuel cells

A novel sulfonated tetraamine, di(triethylammonium)-4,4'-bis(3,4-diaminophenoxy)biphenyl-3,3'-disulfonate (BAPBDS), was successfully synthesized by nucleophilic aromatic substitution of 4,4'-dihydroxybiphenyl with 5-chloro-2-nitroaniline, followed by sulfonation and reduction. A high-temperature polycondensation of sulfonated tetraamine, non-sulfonated tetraamine (4,4 -bis(3,4-aminophenoxy)biphenyl) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (a) or 4,4'-binaphthyl-1,1',8,8'-tetracarboxylic dianydride (b) gave the poly[bis(benzimidazobenzisoquinolinones)] ionomers SPBIBI-a(x) or SPBIBI-b(x), where x refers to the molar percentage of the sulfonated tetraamine monomer. Flexible and tough membranes of high mechanical strength were obtained by solution casting and the electrolyte properties of the polymers were intensively investigated. The ionomer membranes displayed excellent dimensional and hydrolytic stabilities.

Implantation of Nafion (R) ionomer into polyvinyl alcohol/chitosan composites to form novel proton-conducting membranes for direct methanol fuel cells

A series of cost-effective, proton-conducting composite membranes, comprising of Nafion (R) ionomer, chitosan (CS). and polyvinyl alcohol (PVA), is successfully prepared. By taking advantage of the strong electrostatic interactions between Nafion (R) ionomer and CS component, Nafion ionomer is effectively implanted into the PVA/CS composite membranes, and improves proton conductivity of the PVA/CS composite membranes. Furthermore, this effect dramatically depends on the composition ratio of PVA/CS, and the optimum conductivity is obtained at the PVA/CS ratio of 1:1. The developed composite membranes exhibit much lower methanol permeability compared with the widely used Nafion (R) membrane, indicating that these novel membranes have great potential for direct methanol fuel cells (DMFCs).

Highly conductive, methanol resistant fuel cell membranes fabricated by layer-by-layer self-assembly of inorganic heteropolyacid

Layer-by-layer (LBL) self-assembly is a simple and elegant method of constructing organic-inorganic composite thin films from environmentally benign aqueous solutions. In this paper, we utilize this method to develop proton-exchange membranes for fuel cells. The multilayer film is constructed onto the surface of sulfonated poly(arylene ether ketone) (SPAEK-COOH) membrane by LBL self-assembly of polycation chitosan (CTS) and negatively charged inorganic particle phosphotungstic acid (VIA). The highly conductive inorganic nanoparticles ensure SPAEK-COOH-(CTS/PTA)(n) membranes to maintain high proton conductivity values up to 0.086 S cm(-1) at 25 degrees C and 0.24S cm(-1) at 80 degrees C, which are superior than previous LBL assembled electrolyte systems.