Chitosan/heteropolyacid composite membranes for direct methanol fuel cell

As inorganic proton conductors. phosphomolybdic acid (PMA), phosphotungstic acid (PWA) and silicotungstic acid (SiWA) are extremely attractive for proton-conducting composite membranes. An interesting phenomenon has been found in our previous experiments that the mixing of chitosan (CS) solution and different heteropolyacids (HPAs) leads to strong electrostatic interaction to form insoluble complexes. These complexes in the form of membrane (CS/PMA, CS/PWA and CS/SiWA composite membranes) have been prepared and evaluated as novel proton-conducting membranes for direct methanol fuel cells. Therefore, HPAs can be immobilized within the membranes through electrostatic interaction, which overcomes the leakage problem from membranes.

Perfectly Hydrophobic Silicone Nanofiber Coatings: Preparation from Methyltrialkoxysilanes and Use as Water-Collecting Substrate

Perfectly hydrophobic (PHO) coatings consisting of silicone nanofibers have been obtained via a solution process using methyltrialkoxysilanes as precursors. On the basis of thermal gravimetry and differential thermal analysis (TG-DTA) and Fourier transform infrared spectroscopy (FTIR) results, the formula of the nanofibers was tentatively given and a possible growth mechanism of the nanofibers was proposed. Because of the low affinity between the coatings and the small water droplet, when using these coatings as substrate for collecting water vapor, the harvesting efficiency could be enhanced as compared with those from bare glass substrate for more than 50% under 25 degrees C and 60-90% relative humidity. By removing the surface methyl group by heat treatment or ultraviolet (UV) irradiation, the as-prepared perfectly hydrophobic surface can be converted into a superhydrophilic surface.

Polyamide thin film composite membranes prepared from 3,4',5-biphenyl triacyl chloride, 3,3',5,5'-biphenyl tetraacyl chloride and m-phenylenediamine

Two novel of tri- and tetra-functional biphenyl acid chloride: 3,4',5-biphenyl triacyl chloride (BTRC) and 3,3',5,5'-biphenyl tetraacyl chloride (BTEC), were synthesized, and used as new monomers for the preparations of the thin film composite (TFC) reverse osmosis (RO) membranes. The TFC RO membranes were prepared on a polysulfone supporting film through interfacial polymerization with the two new monomers and m-phenylenediamine (MPD). The membranes were characterized for the permeation properties, chemical composition, d-space between polymer chains, hydrophilicity, membrane morphology including top surface and cross-section. Permeation experiment was employed to evaluate the membranes performance including salt rejection and water flux. The surface structure and chemical composition of membranes were analyzed by attenuated total reflectance infrared (ATR-IR) and X-ray photoelectronic spectroscopy (XPS). The results revealed that the active layer of membranes was composed of highly cross-linked aromatic polyamide with the functional acylamide (-CONH-) bonds. The TFC membranes prepared from biphenyl acid chloride exhibit higher salt rejection compared with that prepared from trimesoyl chloride (TMC) at the expanse of some flux.

Synthesis and characterization of rigid-rod sulfonated polyimides bearing sulfobenzoyl side groups as proton exchange membranes

A novel wholly aromatic diamine, 2,2 '-bis(3-sulfobenzoyl)benzidine (2,2 '-BSBB), was successfully prepared by the reaction of 2,2 '-dibenzoylbenzidine (2,2 '-DBB) with fuming sulfuric acid. Copolymerization of 1,4,5,8-naphathlenetetracarboxylic dianhydride with 2,2 '-BSBB and 2,2 '-DBB generated a series of rigid-rod sulfonated polyimides. The synthesized copolymers with the -SO3H group on the side chain of polymers possessed high molecular weights revealed by their high viscosity and the formation of tough and flexible membranes. The copolymer membranes exhibited excellent oxidative stability and mechanical properties due to their fully aromatic structure extending through the backbone and pendent groups. They displayed clear anisotropic membrane swelling in water with negligibly small dimensional changes in the plane direction of the membrane. The proton conductivities of copolymer membranes increased with increasing IEC and temperature, reaching value above 1.25 x 10(-1) S/cm at 20 degrees C, which is higher than that of Nafion (R) 117 at the same measurement condition. They displayed reasonably high proton conductivity due to the higher acidity of benzoyl sulfonic acid group, the larger interchain spacing, which is available for water to occupy, taking their lower water uptake (WU) into account. Consequently, these materials proved to be promising as proton exchange membrane.

Sulfonated polyimides bearing benzimidazole groups for proton exchange membranes

A series of sulfonated polymides containing benzimidazole groups were synthesized using 4,4'-binaphthyl-1,1',8,8'-tetracarboxylic dianhydride (BTDA), 4,4'-diaminodiphenyl ether-2,2'-disulfonic acid (ODADS) as the sulfonated diamine, and 2-(3',5-diaminophenyl)benzimidazole (a) or 6,4'-diamino-2-phenylbenzimidazole (b) as the nonsulfortated diamine. The electrolyte properties of the synthesized polyimides Ia-x, Ib-x, x refers to molar percentage of the sulfonated diamine) were investigated and compared with those of polyimides (Ic-x) from BTDA, ODADS, and m-phenylenediamine (c). All synthesized polyimides possessed high molecular weights revealed by their high viscosity, and formation of tough and flexible membranes. Polyintides with benzimidazole groups exhibited much better swelling capacity than those without benzimiclazole groups. This was attributed to the strong interchain interaction through basic benzimidazole functions and sulfonic acid groups. The sulfortated polyimides that are incorporated with 1, 1',8,8'-binaphthalimide exhibited better hydrolytic stability than that with 1,4,5,8-naphthalimide. Polyimide membranes with good water stability as well as high proton conductivity were developed. Polyimide membrane (Ia - 90), for example, did not lose mechanical properties after being soaked in boiling water for tOOO h, while its proton conductivity was still at a high level (compared to that of Nafion 117).

Polyelectrolyte complexes of chitosan and phosphotungstic acid as proton-conducting membranes for direct methanol fuel cells

Polyelectrolyte complexes (PECs) of chitosan and phosphotungstic acid have been prepared and evaluated as novel proton-conducting membranes for direct methanol fuel cells. Phosphotungstic acid can be fixed within PECs membranes through strong electrostatic interactions, which avoids the decrease of conductivity caused by the dissolving of phosphotungstic acid as previously reported. Scanning electron microscopy (SEM) shows that the PECs membranes are homogeneous and dense. Fourier transform infrared spectroscopy (FTIR) demonstrates that hydrogen bonding is formed between chitosan and phosphotungstic acid. Thermogravimetric analysis (TGA) shows that the PECs membranes have good thermal stability up to 210 degrees C. The PECs membranes exhibit good swelling properties and low methanol permeability (P, 3.3 x 10(-7) cm(2) s(-1)). Proton conductivity (sigma) of the PECs membranes increases at elevated temperature, reaching the value of 0.024 S cm(-1) at 80 degrees C.

Synthesis and properties of novel sulfonated polyimides containing binaphthyl groups as proton-exchange membranes for fuel cells

A novel sulfonated diamine monomer, 2,2'-bis(p-aminophenoxy)-1,1'-binaphthyl-6,6'-disulfonic acid (BNDADS), was synthesized. A series of sulfonated polyimide copolymers containing 30-80 mol % BNDADS as a hydrophilic component were prepared. The copolymers showed excellent solubility and good film-forming capability. Atomic force microscopy phase images clearly showed hydrophilic/hydrophobic microphase separation. The relationship between the proton conductivity and degree of sulfonation was examined. The sulfonated polyimide copolymer with 60 mol % BNDADS showed higher proton conductivity (0.0945-0.161 S/cm) at 20-80 degrees C in liquid water. The membranes exhibited methanol permeability from 9 x 10(-8) to 5 X 10(-7) cm(2)/s at 20 degrees C, which was much lower than that of Nafion (2 x 10(-6) cm(2)/s). The copolymers were thermally stable up to 300 degrees C. The sulfonated polyimide copolymers with 30-60 mol % BNDADS showed reasonable mechanical strength; for example, the maximum tensile strength at break of the sulfonated polyimide copolymer with 40 mol % BNDADS was 80.6 MPa under high moisture conditions. The optimum concentration of BNDADS was found to be 60 mol % from the viewpoint of proton conductivity, methanol permeability, and membrane stability.

Water resistant sulfonated polyimides based on 4,4'-binaphthyl-1,1',8,8'-tetracarboxylic dianhydride (BNTDA) for proton exchange membranes

A series of sulfonated polyimides (SPIs) were synthesized in in-cresol from 4,4'-binaphthyl- 1,11,8,8'-tetracarboxylic dianhydride (BNTDA), 4.4'-diaminodiphenylether-2,2-disulfonicacid (ODADS), and 4.4'-diamino-diphenyl ether (ODA) in the presence of triethylamine and benzoic acid. The resulted polyimides showed much better water resistance than the corresponding sulfonated polyimides from 1,4,5,8-naphthatenetetracarboxylic dianhydride (NTDA) and ODADS, which is contributed to the higher electron density in the carbonyl carbon atoms of BNTDA. Copolyimides S-75 and S-50 maintained their mechanical properties and proton conductivities after aging in water at 100 degrees C for 800 h. The proton conductivity of these SPIs was 0.0250-0.3565 S/cm at 20 degrees C and 100% relative humidity (RH), and increased to 0.11490.9470 S/cm at 80 degrees C and 100% RH. The methanol permeability values of these SPIs were in the range of 0.99-2.36 x 10(-7) cm(2)/S, which are much lower than that of Nafion 117 (2 x 10(-6) cm(2)/s).

New proton exchange membranes based on poly (vinyl alcohol) for DMFCs

A series of new composite proton exchange membranes for direct methanol fuel cells (DMFCs) based on poly (vinyl alcohol) (PVA), phosphotungstic acid (PWA) and silica were prepared. The highest proton conductivity (a) of these membranes is 0.017 S/cm at ambient temperature. The methanol permeability (D) of these composite membranes ranges from 10(-7) to 10(-8) cm(2)/S. From the ratios of sigma/D, it was found that the optimal weight composition of the PVA/PWA/SiO2 membrane is PVA/PWA/SiO2=0.40:0.40:0.20 wt. Infrared (IR) spectrographic measurements indicate that the Keggin structure characteristics of the PW12O403- anion is present in the composite membranes. Cyclic voltammetry shows that the electrochemical stability window of the complex membrane is from -0.5 to 1.5 V vs. Ag/AgCl electrode. The results of differential scanning calorimetry (DSC) show that silica can improve the thermal stability of the complexes and the single Tg of the membrane indicates that the membrane is homogeneous. The complexes behave as X-ray amorphous.

Polymeric pH indicators immobilized PVA membranes for optical sensors of high basicity based on a kinetic process

Two kinds of polymeric pH indicators PPF (phenolphthalein-formaldehyde product) and CPF (o-cresolphthalein-formaldehyde product) immobilized cross-linked poly(vinyl alcohol) membranes (PPF-PVA and CPF-PVA) for optical intermittent determination of high basicity ([OH-] = 1-8 M) based on a kinetic process were developed. In our previous work, we had demonstrated that PPF-PVA and CPF-PVA could perform the determination of high pH values from pH 10.0 to 14.0. Here the discoloring kinetic behaviors of PPF-PVA and CPF-PVA were compared with those of free phenolphthalein, o-cresolphthalein and thymolphthalein. Experimental results and theoretical analysis indicated that the response behaviors of the optodes' membranes in concentrated NaOH solutions were diffusion-independent and still complied with the pseudo-first-order kinetics. In addition, two data analysis methods for determination were presented. One was directly based on the reduced absorbance: the other was based on the discoloring kinetic constant. It was found that the latter could perform a rapid (60 s) and reliable (relative standard deviation: 2.6%) determination for high basicity.

Vapor permeation separation of MeOH/MTBE through polyimide/sulfonated poly(ether-sulfone) hollow-fiber membranes

Mixtures of methanol/MTBE were separated with polyimide/sulfonated poly(ether-sulfone) hollow-fiber membranes. The separation was attempted by vapor permeation instead of pervaporation, which had been used by most researchers. The separation properties of the hollow-fiber membranes and operating conditions are discussed. The results showed that separation factors of the blended polyimide/sulfonated poly(ether-sulfone) hollow-fiber membranes were extremely high for the methanol/MTBE mixtures.

Sulfonated poly(arylene-co-naphthalimide)s synthesized by copolymerization of primarily sulfonated monomer and fluorinated naphthalimide dichlorides as novel polymers for proton exchange membranes

A novel sulfonated aromatic dichloride monomer was successfully prepared by the reaction of 2, 5-dichlorobenzophenone with fuming sulfuric acid. Copolymerization of this monomer in the form of sodium salt (1) with N-(4-chloro-2-trifluoromethylphenyl)-5-chloro-1,8-naphthalimide (2) or bis(N-(4-chloro-2-trifluoromethylphenyl)1,4,5,8-naphthalimide (3) generated two series of novel poly(arylene-co-naphthalimide) s I-x and II-x where x represents the content of the sulfonated monomer. The synthesized copolymers with the -SO3H group in the side chains possessed high molecular weights revealed by their high viscosity and the formation of tough and flexible membranes. The copolymers exhibited excellent stability toward water and oxidation due to the introduction of the hydrophobic CF3 groups. The sulfonated copolyimides that incorporated with 1,8-naphthalimide (I-x) exhibited better hydrolytic and oxidative stabilities than those with 1,4,5,8-naphthalimide. Copolymer I-50 membrane endured for more than 83 h in Fenton's reagent at room temperature. The mechanical properties of I-50 membrane kept almost unchanged after immersing membrane in boiling water for 196 h. The proton conductivities of copolymer films increased with increasing IEC and temperature, reaching values above 6.8 x 10(-1) S/cm at 80 degrees C.

The direct synthesis of wholly aromatic poly(p-phenylene)s bearing sulfobenzoyl side groups as proton exchange membranes

Sulfonated poly(p-phenylene)s (SPPs) containing sulfonic acid groups in their side chains had been directly synthesized by Ni(0) catalytic coupling of sodium 3-(2,5-dichlorobenzoyl)benzenesulfonate and 2,5-dichlorobenzophenone. The synthesized copolymers possessed high molecular weights revealed by their high viscosity, and the formation of tough and flexible membranes by casting from DMAc solution. The copolymers exhibited excellent oxidative stability and mechanical properties due to their fully aromatic structure extending through the backbone and pendent groups. Transmission electron microscopic (TEM) analysis revealed that these side-chain type SPP membranes have a microphase-separated structure composed of hydrophilic side-chain domains and hydrophobic polyphenylene main chain domains. The proton conductivities of copolymer membranes increased with the increase of IEC and temperature, reaching values above 3.4 x 10(-1) S/cm at 120 degrees C, which are almost 2-3 times higher than that of Nafion 117 at the same measurement conditions. Consequently, these materials proved to be promising as proton exchange membranes.

Preparation and properties of sulfonated poly(ether ether ketone)s (SPEEK)/polypyrrole composite membranes for direct methanol fuel cells

Polypyrrole (Ppy) was successfully introduced into methyl substituted sulfonated poly(ether ether ketone) (SPEEK) membranes by polymerization in SPEEK solutions to improve their methanol resistance. Uniform polypyrrole (Ppy) distributed composite membranes were formed by this method by the interaction between SPEEK and Ppy. The properties of the composite membranes were characterized in detail. The composite membranes show very good proton conductive capability (25 degrees C: 0.05-0.06s cm(-1)) and good methanol resistance (25 degrees C: 5.3 x 10(-7) 1.1 x 10(-6) cm(2) s(-1)). The methanol diffusion coefficients of composite membranes are much lower than that of pure SPEEK membranes (1.5 x 10(-6) cm(2) s(-1)). The composite membranes show very good potential usage in direct methanol fuel cells (DMFCs).

Defect formation induced by PAMAM dendrimers on Pt-supported bilayer lipid membranes investigated by electrochemistry

The interaction of polyamidoamine (PAMAM) dendrimers (generations 1-7) with supported bilayer lipid membranes was studied by cyclic votammetry and ac impedance. It is shown that the dendrimers (generations 4-6) can induce defects in the Pt-electrode-supported bilayer lipid membrane. The ability of dendrimers to induce defects was dependent on their shapes and surface charge. The results are consistent with a change in the morphology of the dendrimers from an open, branched structure for generations 1-4 to a closed, increasingly compact surface for generations 5-7.