Organic-inorganic Composite Membranes Research Articles

Organic–inorganic composite pervaporation membranes prepared by self-assembly of polyelectrolyte multilayers on macroporous ceramic supports

An organic–inorganic composite membrane was successfully prepared by means of electrostatic self-assembly of polyelectrolytes on silica sol–gel modified macroporous ceramic supports. The integrality of the as-prepared composite membrane was evaluated in pervaporation of ethanol/water mixtures. Membrane separation performance was optimized by studying the modification cycle, polyelectrolyte molecule structure, self-assemble conditions, thermal treatment conditions and operating temperatures. It was found that the polyelectrolyte molecule structure mainly affected the separation performance of the composite membrane after a two-cycle modification and raising pervaporation operating temperature was an efficient way to improve both membrane flux and water selectivity. The composite membrane deposited by 60 layer pairs of polyethylenimine/poly(vinyl sulfate) (PEI/PVS) showed a high flux of 18.4 kg m −2 h −1 and a water concentration enhancement from 6.2 to 35.3 wt.%. Our study demonstrates that the composite membrane prepared on macroporous ceramic support through our route is suitable for separation of liquid species at a molecular level.

Nano Composite Membranes of Branched Sulfonated Poly(Ether Ketone Sulfone) and SiO<sub>2</sub> for Fuel Cell Application

Branched sulfonated poly(ether ketone sulfone) copolymer was prepared from1,1,1- tris(4-hydroxyphenyl) ethane, 4,4-difluorophenylsulfone, 3,3'-disodiumsulfonylbenzophenone (40 mol% of bisphenol A) and bisphenol A by polycondensation with the elimination of water in toluene and NMP at 160) in the presence of anhydrous potassium carbonate. Composite membranes were successfully cast from the control of organic polymer with SiO2 4-10 wt% of polymer in DMSO. The films were converted from the salt to acid forms with dilute hydrochloric acid. Organicinorganic composite membranes for operation in polymer electrolyte membrane fuel cells (PEMFCs) were characterized and cell-tested. The physico-chemical properties of all membranes were investigated their thermal properties, water uptake, DSC and thermogravimetric analyzer (TGA). Branched copolymer and nano composite membranes exhibit proton conductivities from 1.7x10-3 to 8.3x10-3 S/cm2, water uptake from 22 to 26%, IEC from 1.28 to 1.46 meq/g and methanol diffusion coefficients from 1.2x10-7 to 1.7x10-7 cm2/S.

Nano Composite Membranes of Sulfonated Poly (Ether Ketone)/ Poly (Ether Sulfone) Copolymer and SiO<sub>2</sub> for Fuel Cell Application

Novel bisphenol-based wholly aromatic poly(ether ketone)/poly(ether sulfone) copolymers containing pendant sulfonate groups were prepared by direct aromatic nucleophilic substitution polycondensation of 4,4-difluoro-3,3’-disodiumsulfonylbenzophenone (40mol% of bisphenol), difluorophenylsulfone and bisphenol A. Organic-inorganic composite membranes were obtained by mixing organic polymers with hydrophilic SiO2 (ca. 20nm) obtained by sol-gel process. The physic-chemical properties of these composite membranes were studied by thermogravimetry analysis(TGA), differential scanning calorimetry (DSC) and transform infrared(FTIR) spectroscopy. Scanning electron microscopy (SEM) and atomic Force microscopy (AFM) were used to observe the surface of membrances. The proton conductivity as a function of temperature decreased as SiO2 content increased, but water uptake increased. The membranes were shown all requisite properties; IEC (1.5meq./g), thermal stablity (Tg= 185°C), and low affinity towards methanol (1.5x10-7 - 4.3x10-7 cm2/S).

Characterizations and stability of polyimide–phosphotungstic acid composite electrolyte membranes for fuel cell

Organic–inorganic composite membranes from partially aliphatic sulfonated polyimides and heteropolyacids (HPAs) were synthesized. A series of composite membranes with varying amounts of heteropolyacid were prepared by altering the weight ratio of polyimide and HPA. The partially aliphatic sulfonated polyimides are synthesized from 1,4,5,8-naphthalenetetracarboxylic dianhydride, 4,4′-diaminobiphenyl 2,2′-disulfonic acid as the sulfonated diamine, and decamethylenediamine as the aliphatic diamine. The incorporation of HPA is confirmed by FT-IR analyses. When appropriately embedded in a hydrophilic polymer matrix, the hydrated HPAs are expected to endow the composite membrane with their high proton conductivity, while retaining the desirable mechanical properties of the polymer film. These composite membranes were evaluated for thermal stability, ion exchange capacity, water uptake and proton conductivity. Also the extraction of HPA from the polyimide membranes and their stability in water were determined. Though water uptake and IEC decreased with increase in HPA content, the proton conductivity of the composite membranes increased with increase in HPA weight content. This study shows that partially aliphatic sulfonated polyimide composite membranes with HPA can be a viable substitute for Nafion ® for fuel cells which show good conductivity comparable to Nafion ®117 at temperatures nearing 100 °C, keeping in mind that polyimides have good thermal stability and low cost.

Organic-Inorganic Nano Composite Membranes of Sulfonated Poly(ether Sulfone-Ketone) Copolymer and SiO<sub>2</sub> for Fuel Cell Application

Novel bisphenol-based wholly aromatic sulfonated poly(ether sulfone-ketone) copolymer and organic-inorganic composite membranes were prepared for operation 80°C in polymer electrolyte membrane fuel cell (PEMFCs). The copolymer were synthesized by direct aromatic nucleophilic substitution polycondensation of 4,4-difluorobenzophenone, 2,2’-disodiumsulfonyl- 4,4’-fluorophenylsulfone (40mole% of bisphenol A) and bisphenol A. Polymerization proceeded quantitatively to high molecular weight in N-methyl-2-pyrrolidinone at 180°C. Organic-inorganic composite membranes were obtained by mixing organic polymers with hydrophilic SiO2 obtained by sol-gel process. The polymer and a series of composite membranes were studied by FT-IR, 1HNMR, differential scanning calorimetry (DSC) and thermal stability. The proton conductivity as a function of temperature decreased as SiO2 content increased, but methanol permeability decreased. The nano composite membranes were found to poses all requisite properties; Ion exchange capacity (1.2meq./g), glass transition temperatures (164-183), and low affinity towards methanol (4.63-1.08x10-7 cm2/S).

Preparation and Properties of Proton Conducting Composite Membranes from Sulfonated Poly(phthalazinone ether keton) and Phosphotungstic Acid

A novel inorganic-organic composite membrane based on sulfonated poly(phthalazinone ether keton) (SPPEK) with embedded phosphotungstic acid (PWA) was prepared. IR spectra results indicated that both the bridging oxygen and the terminal oxygen of PWA interacted with SPPEK. PWA was well dispersed in the membranes with 20% and 40% PWA in SPPEK of 58% sulfonation degree as shown in SEM pictures. But conglomeration was found in the SEM picture of composite membrane with 60% PWA. After treated in water for four days, less than 10% PWA was extracted from the composite membranes. With the increment of PWA content, the conductivity, water content, and methanol permeability of the PWA/SPPEK composite membranes were all increased. The composite membranes with PWA content higher than 40% and SPPEK of 58% sulfonation degree have conductivity similar or superior to that of Nafion115 membrane at temperature higher than 100 ℃. Methanol permeability of the PWA/SPPEK composite membranes was lower than that of Nafion115 membrane except the composite membrane with 60% PWA in SPPEK of 58% sulfonation degree.

The influence of α-ZrP coat on proton transfer resistance of cation exchange membrane–solution interface

In this work, the effect of surface modification on proton transfer resistance of the membrane and/or membrane surface interface is investigated. Cation exchange membranes, PE01 and Nafion1135, were modified by zirconium phosphate (ZrP) and inorganic–organic composite membranes were prepared. α-ZrP (α-Zr(HPO 4) 2 · H 2O) was deposited on the composite membrane surface as verified by XRD and SEM. Zeta potential of the composite membrane decreases with the increase of immersion time, indicating that the deposition α-ZrP results in a decrease of membrane surface charge density. The proton transfer resistance measured by AC impedance technique in 0.05 mol/L H 2SO 4 solution shows an interesting result: the proton transfer resistance of membrane–solution ( Z e) sharply reduces while proton transfer resistance of membrane ( Z m) increases slightly with the immersion time for both of the membranes. The slight increase of Z m is due to the deposit of ZrP on membrane surface, and the sharp decrease of Z e is attributed to the decrease in the static electrical interaction strength between counterions and the charged groups of the membrane, which is caused by interact of α-ZrP with the ion exchange groups resulting in a reduction of membrane surface charge density. The equivalent circuit models for electrode/solution/membrane/solution/electrode system and electrode/solution system were examined. The results observed in this work seem very interesting in the ion transfer study between phase interfaces.

Montmorillonite functionalized with perfluorinated sulfonic acid for proton-conducting organic–inorganic composite membranes

Organic sultones and a perfluorinated sultone are grafted on the surface of montmorillonite (MMT) to render the organic sulfonic acid (HSO 3–) functionality. Organic–inorganic composite proton-conducting membranes are cast together with Nafion ® using these functionalized MMTs as inorganic fillers. Grafting with the perfluorinated sultone is more efficient on the surface of MMT than with non-fluorine organic sultones. Montmorillonite functionalized with the perfluorinated organic sulfonic acid also shows higher ion exchange capacity and ion conductivity, which are desired attributes to serve as an effective filler for a proton-conducting composite membrane. The composite membrane reduces the relative permeability of methanol in 3 M solution by about 40%, while maintaining comparable ionic conductivity relative to pristine Nafion membrane. This leads to much enhanced performance of a direct methanol fuel cell employing the Nafion ®/sulfonated MMT composite membrane. The current density of a membrane-electrode assembly (MEA) fabricated with a composite membrane containing MMT functionalized with perfluorinated organic sulfonic acid is about 24% higher than that of a MEA fabricated with a composite membrane containing MMT functionalized with non-fluorine organic sulfonic acids, and about 40% higher than that with pristine Nafion ®.

Proton conducting composite membranes from sulfonated polyethersulfone Cardo and phosphotungstic acid for fuel cell application

A new kind of inorganic–organic composite membranes based on sulfonated polyethersulfone Cardo (SPES-C) with embedded phosphotungstic acid (PWA) was prepared. The composite membranes were characterized by using FT-IR, XRD, TGA and SEM techniques. FT-IR and XRD measurements confirmed the presence of PWA particles into the polymer matrix. FT-IR spectra indicated the existence of a specific interaction between PWA particles and SPES-C polymer. TGA results showed that the composite membranes were thermally stable up to approximately about 200 °C. SEM micrographs verified that nano-scale PWA particles were homogeneously distributed into the polymer matrix. By incorporation PWA into SPES-C polymer the proton conductivity of the composite membranes was enhanced. It was 4.5 × 10 −2 S cm −1 at 90 °C and 6.7 × 10 −2 S cm −1 at 110 °C, while the conductivity of Nafion ® 115 membrane was 4.1 × 10 −2 S cm −1 and 4.7 × 10 −2 S cm −1 at 90 °C and 110 °C, respectively.

Low water/methanol permeable Nafion/CHP organic–inorganic composite membrane with high crystallinity

High methanol crossover is one of the main issues of the polyelectrolyte in direct methanol fuel cells (DMFCs). In order to decrease methanol crossover, we introduced a new method that crystallinity control was performed with incorporating CHP (calcium hydroxyphosphate) into Nafion solution. As a result, crystallinity in the composite membranes increased with CHP content compared to cast Nafion accompanying the formation of new crystalline peaks in the original amorphous region of Nafion. On the other hand, water uptake content, methanol sorption/desorption permeability and methanol crossover in the composite membranes remarkably decreased. We conclude that an increase in crystallinity due to the strong interfacial adhesion between Nafion and CHP can suppress the methanol crossover.

Preparation of poly(vinylidene fluoride)(pvdf) ultrafiltration membrane modified by nano-sized alumina (Al 2O 3) and its antifouling research

Organic–inorganic composite membranes are formed by nano-sized alumina particles uniformly dispersed in the poly(vinylidene fluoride) solution (19% polymer weight). Membranes were prepared by phase inversion process and were characterized by ultrafiltration (UF) experiments in terms of water flux, molecular weight cut-off for the wet membranes. Contact angle between water and the membrane surface were measured by contact angle measurement in order to characterize the hydrophilicity changing of the membrane surface. The cross-sectional structures, porous dispersion in membranes surface and nanometer particles distribution in the membrane were examined by scanning electron microscopy (SEM) and transmission microscopy (TEM), respectively. The effect of nanometer Al 2O 3 particles concentration in the polymer dope on the permeation properties, membrane structures and antifouling performances were examined. The experimental results indicate that Al 2O 3–PVDF composite membranes exhibit significant differences in surface and intrinsic properties due to nanometer particles addition.

Performance and efficiency of a DMFC using non-fluorinated composite membranes operating at low/medium temperatures

In order to increase the chemical/thermal stability of the sulfonated poly(ether ether ketone) (sPEEK) polymer for direct methanol fuel cell (DMFC) applications at medium temperatures (up to 130 °C), novel inorganic–organic composite membranes were prepared using sPEEK polymer as organic matrix (sulfonation degree, SD, of 42 and 68%) modified with zirconium phosphate (ZrPh) pretreated with n-propylamine and polybenzimidazole (PBI). The final compositions obtained were: 10.0 wt.% ZrPh and 5.6 wt.% PBI; 20.0 wt.% ZrPh and 11.2 wt.% PBI. These composite membranes were tested in DMFC at several temperatures by evaluating the current–voltage polarization curve, open circuit voltage (OCV) and constant voltage current (CV, 35 mV). The fuel cell ohmic resistance (null phase angle impedance, NPAI) and CO 2 concentration in the cathode outlet were also measured. A method is also proposed to evaluate the fuel cell Faraday and global efficiency considering the CH 3OH, CO 2, H 2O, O 2 and N 2 permeation through the proton exchange membrane (PEM) and parasitic oxidation of the crossover methanol in the cathode. In order to improve the analysis of the composite membrane properties, selected characterization results presented in [V.S. Silva, B. Ruffmann, S. Vetter, A. Mendes, L.M. Madeira, S.P. Nunes, Catal. Today, in press] were also used in the present study. The unmodified sPEEK membrane with SD = 42% (S42) was used as the reference material. In the present study, the composite membrane prepared with sPEEK SD = 68% and inorganic composition of 20.0 wt.% ZrPh and 11.2 wt.% PBI proved to have a good relationship between proton conductivity, aqueous methanol swelling and permeability. DMFC tests results for this membrane showed similar current density output and higher open circuit voltage compared to that of sPEEK with SD = 42%, but with much lower CO 2 concentration in the cathode outlet (thus higher global efficiency) and higher thermal/chemical stability. This membrane was also tested at 130 °C with pure oxygen (cathode inlet) and achieved a maximum power density of 50.1 mW cm −2 at 250 mA cm −2.

Preparation of organic–inorganic composite anion-exchange membranes via aqueous dispersion polymerization and their characterization

Organic–inorganic composite membranes based on poly(vinyl alcohol)/SiO 2 were prepared via an aqueous dispersion polymerization route and anion-exchange groups were introduced in the membrane matrix by the chemical grafting of 4-vinylpyridine with the desired content. These membranes were extensively characterized for their surface morphology, thermal stability, water content, and surface-charge properties using SEM, TEM, FTIR, TGA, water uptake, and ion-exchange capacity measurements. Counterion transport numbers across these membranes were estimated from membrane potential data. Membrane conductance measurements were also performed and these data were used for the estimation of values of counterion diffusion coefficients in the membrane phase. Physicochemical and electrochemical properties of these membranes and equivalent pore radius (estimated from electroosmotic flux measurements) were found to be highly dependent on the 4-vinylpyridine (4-VP) content in the membrane phase. It was also observed that for better selectivity and membrane conductivity of anion-exchange membranes complete optimization of the loading of 4-VP in the membrane phase is necessary. Furthermore, among these, membrane with 25% loading with 4-VP exhibited very good selectivity, water content, and ion-exchange capacity along with moderate membrane conductivity, which may be used for their application in electro-driven separation at elevated temperatures or for other electrochemical processes.

Organic–inorganic composite membranes as addition of SiO 2 for high temperature-operation in polymer electrolyte membrane fuel cells (PEMFCs)

Organic–inorganic composite membranes for operation above 100 °C in polymer electrolyte membrane fuel cells (PEMFCs) were prepared, characterized and cell-tested. Composite membranes were obtained by mixing organic polymers, which have a SO 3H group as a proton conductor with inorganic material, SiO 2, using the sol–gel process. Electron probe micro analyser (EPMA) was used to show the homogeneous and uniform distribution of SiO 2. The physico-chemical properties of all membranes were investigated regarding their tensile strength, water uptake and thermogravimetric analyzer (TGA). Due to a higher water uptake and thermal stability of composite membranes, the cell performances at high temperatures above 100 °C, were improved. In addition, the SiOH group in the composite membrane was shown to play a major role in capturing water strongly and maintaining proton conductivity even at high temperature. Furthermore, the fuel cell performance of organic–inorganic composite membranes was superior to that of the Nafion membrane at high current density over all ranges of temperature.

Sulfonated polyether ether ketone membranes cured with different methods for direct methanol fuel cells

Direct methanol fuel cells (DMFC) have attracted considerable attention, since they offer numerous benefits, such as high efficiency, high power density, low or zero emissions and reliability. The proton exchange membrane (PEM) is one of the most critical components in the direct methanol fuel cell. Generally, PEMs with high proton conductivity and low methanol permeability are desirable for efficient fuel cell operation. Currently Nafion©R membrane, a perfluorosulfonate ionomer, is the major membrane used in polymer electrolyte membrane fuel cells (PEMFC). But Nafion©R membrane is a poor barrier to methanol crossover. In addition, the high cost of perfluorosulfonate membranes prohibits wide commercial application for PEMFC. Therefore it is important to find novel PEMs with low methanol permeability and low cost. Several new types of membranes have been prepared for use in DMFC. Among them are sulfonated polyether ether ketone (SPEEK) [1], sulfonated poly(arylene ether sulfone) (BPSH) copolymer [2], sulfonated or phosphonated polyphosphazenes [3, 4], poly(vinyl alcohol) (PVA)-crosslinked-polystyrene sulfonic acid (PSSA) [5], blend membranes [6, 7] and inorganicorganic composite membrane [8]. Recently, a few researchers found that the proton conductivity of PEMs varies with curing method [9–11]. Bauer et al. [9] reported that the conductivity of SPEEK membranes cured in boiling water for 4 h increased by a factor of ca 7 compared to the blank. McGrath et al. [10] also noted that the post-treatment of BPSH copolymers in boiling water produced higher proton conductivity and water absorption. These initiated our interest to understand the phenomenon and to see if curing affects methanol permeability of PEMs as well. In this paper, we report the influence of curing of the SPEEK membranes on their proton conductivity and methanol permeability. Sulfonated polyether ether ketone (SPEEK) with degree of sulfonation 38% (100% sulfonation corresponds to 1 sulfonic acid group per repeat unit) was prepared as described in [12]. Membranes were prepared by casting a 10 wt% SPEEK in dimethylformamide (DMF) solution on glass plates and then drying them at 60 ◦C for 6 h and 100 ◦C for 4 h. Afterwards, the membranes were cured by two different methods: (1) immersing in 1.0 M sulfuric acid solution at room temperature for 24 h and subsequently rinsing with

Preparation of Organic-Inorganic Composite Electrolyte Membrane for Direct Methanol Fuel Cell

Preparation of Organic-Inorganic Composite Electrolyte Membrane for Direct Methanol Fuel Cell

Inorganic modification of proton conductive polymer membranes for direct methanol fuel cells

New organic–inorganic composite membranes based on sulfonated polyetherketone (SPEK) and sulfonated poly(ether ether ketone) (SPEEK) for application in the direct methanol fuel cell (DMFC) were synthesized. The membranes’ water and methanol permeabilities were evaluated in pervaporation experiments and the conductivity determined by impedance spectroscopy. The permeabilities were decreased by inorganic modification. The first approach was the in situ generation of SiO 2, TiO 2 or ZrO 2. The modification with ZrO 2 led to a 60-fold reduction of the methanol flux. However, a 13-fold reduction of conductivity was also observed. Modification with organically modified silane led to a 40-fold decrease of the water permeability without a large decrease of proton conductivity. A good balance of high conductivity and low water and methanol permeability was possible with a mixture of ZrO 2 and zirconium phosphate. In this case, a 28-fold reduction of water flux was observed with only 10–30% reduction of proton conductivity.

Preparation and properties of novel organic–inorganic porous membranes

This paper deals with the preparation and characterization of novel organic–inorganic composite membranes formed by fine silica particles uniformly dispersed in the porous matrix of poly(vinylidene fluoride). Membranes were prepared by phase inversion process and were characterized by ultrafiltration (UF) experiments, burst pressure tests and scanning electron microscope (SEM) observations. Spectroscopic (FTIR-ATR, FT-Raman) and calorimetric (DSC) measurements were also carried out in order to investigate interactions between membrane components. Supported membranes were finally prepared and their ultrafiltration performance was compared with that of unsupported ones.

A novel pH-sensitive membrane from chitosan — TEOS IPN; preparation and its drug permeation characteristics

A novel organic–inorganic composite membrane was prepared, using tetra ethyl ortho silicate (TEOS) as an inorganic material and chitosan as an organic compound. Equilibrium and oscillatory swelling studies were conducted to investigate swelling behaviors of the membrane according to the pH of the swelling medium. Drug permeation experiments were also performed in phosphate buffer solution of the pH of 2.5 and 7.5, respectively. Lidocaine·HCl, sodium salicylate and 4-acetamidophenol were selected as model drugs to examine the effect of ionic property of drug on the permeation behavior. The effects of membrane composition and the external pH on the swelling and the drug permeation behavior of IPN membrane could be summarized as follows; chitosan incorporated into TEOS IPN swelled at pH 2.5 while shrunk at pH 7.5. This swelling behavior was completely reversible and the membrane responded rapidly to the change in environmental pH condition. According to swelling behavior, an increase in pH from 2.5 to 7.5 yielded an increase in the rate of drug permeation because of the shrinking of the incorporated chitosan in TEOS IPN, while decrease in pH resulted in low permeation rate. The optimal TEOS-chitosan ratio for maximum pH-sensitivity existed and drug permeation was influenced not only with the external pH but also with the ionic interactions between the drug and membrane.

Cobalt(II) Hematoporphyrin IX immobilized in a cellulose acetate niobium(V) oxide composite membrane: preparation and oxygen reduction study

Hematoporphyrin IX [8,13,-bis(1-hydroxyethyl)-3,7,12,17-tetramethyl-21H-porphyrin-2,18-dipropionic acid] was adsorbed on the organic-inorganic composite membrane Cel/Nb2O5 surface. The porphyrin is strongly adhered on the Nb2O5 surface by reaction of the porphyrin CO2H groups with Nb2O5 forming the -COO-Nb chemical bond. Metallation of the porphyrine ring was made very easily by immersing the membrane in Co(II) solution and allowing to rest for a few hours. The electronic absorption bands due to the Q bands indicated the symmetry change from D2h to D4h upon metallation of the porphyrin ring. The chemical analyses of the material confirmed that the metallation yield was practically 100%. Oxygen was reduced on a electrode surface made with the material under a cathodic peak potential of -390 mV, in 1 M KCl solution at pH 1, temperature of 298 K and at ambient pressure. The oxygen reduction was proposed to occur by a two electron transfer mechanism. A linear cathodic peak current response was obtained for dissolved oxygen concentrations between 1.5 and 15 ppm.