Showing papers on "Phosphotungstic acid published in 2010"

HPW/MCM‐41 Phosphotungstic Acid/Mesoporous Silica Composites as Novel Proton‐Exchange Membranes for Elevated‐Temperature Fuel Cells

Abstract: Proton-exchange membrane and direct methanol fuel cells (PEMFCs and DMFCs) have attracted much attention as clean energy sources for various applications, such as electric vehicles, portable electronics, and domestic power generation, because of their high power density, high efficiency, and low greenhouse gas emission. Especially, the operation of PEMFCs and DMFCs at temperatures above 100 8C is considered to have many advantages, such as the elimination of CO poisoning of the platinum electrocatalyst, faster electrode reaction kinetics, simplified water and heat management, higher energy efficiency, and reduced usage of precious Pt and Pt alloy catalyst. However, the state-of-the-art proton-exchange membranes (PEMs) based on perfluorosulfonic acid (PFSA), such as Nafion, are unstable at elevated temperatures ( 100 8C) and proton conductivity decreases significantly due to the loss of water from the membrane under conditions of high temperatures or low humidities. Therefore, development of PEMs with high proton conductivity and stability at elevated temperatures is a major challenge. Great efforts have been dedicated to developing PEMs for operation at elevated temperatures based on mesoporous or nanoporous inorganic materials. Mesoporous inorganic materials have a pore size range of 2–50 nm and are characterized by high specific surface area, nanometer-sized channels or frameworks with an ordered or disordered interconnected internal structure, and high structural stability, which make feasible potential applications as proton-exchange membranes operating at elevated temperatures. Lu and co-workers reported sol–gel-derived mesostructured zirconium phosphates with proton conductivities of about 10 –10 6 S cm . Colomer et al. synthesized nanoporous anatase thin films with conductivity values from 10 5 to 10 3 S cm 1 in the range of 33%–81% relative humidity (RH) at room temperature. Li and Nogami prepared proton-conducting mesoporous silica films with conductivity ranging from 10 6 to 10 4 S cm 1 under 40%–90% humidity. However, the proton conductivity of the pure mesoporous materials depends significantly on their textural characteristics. For instance, Colomer et al. also reported a proton conductivity of 2.0 10 2 S cm 1 on mesoporous acid-free silica xerogels and 3.78 10 2 S cm 1 on a nanoporous anatase thin film at 80 8C and 81% RH. Yamada et al. reported a TiO2-P2O5 mesoporous nanocomposite with a proton conductivity value of 2 10 2 S cm 1 at 160 8C. Halla et al. synthesized meso-SiO2-C12EO10OH-CF3SO3H as a new protonconducting electrolyte and reported a conductivity of 1 10 3 S cm 1 at room temperature and 90% RH. Although the conductivity values of mesoporous acid-free silica xerogels, meso-SiO2-C12EO10OHCF3SO3H or anatase thin films are adequate for fuel cell applications, their performance as an electrolyte in a PEMFC has not been evaluated yet. Yamada and Honma synthesized a H3PW12O40 (abbreviated as HPW) and polystyrene sulfonic acid (PSS) composite by self-assembly of –SO3H onto the HPW surface, achieving a proton conductivity of 1 10 2 S cm 1 at 180 8C. Nevertheless, the power density of the cell based on a PSS with 10wt% HPW composite membrane is very low, ca. 3mW cm 2 at 160 8C in H2/O2 with no external humidity. Uma and Nogami synthesized an inorganic glass composite membrane consisting of a mixture of phosphotungstic acid (HPW) and phosphomolybdic acid (HPM), and reported very high conductivity values, 1.014 S cm 1 at 30 8C and 85% RH for a mesoporous-structured HPW/HPM-P2O5-SiO2 glass, [24] and 1.01 10 1 S cm 1 at 85 8C under 85% RH for a mesoporousstructured HPW-P2O5-SiO2 glass. [17] The cell performance based on these inorganic PEMs was 35–42mW cm 2 in H2/O2 at ca. 30 8C under 30% RH. However, there is little information on the performance of HPWand HPM-incorporated P2O5-SiO2 glass electrolyte cells at elevated high temperatures or in methanol fuels. Here, we present a novel inorganic PEM based on highly ordered mesoporous MCM-41 silica with assembled HPW nanoparticles by the vacuum-assisted impregnation method (VIM). The proton conductivity of the HPW/MCM-41 mesoporous silica inorganic PEM is 0.018 and 0.045 S cm 1 at 25 and 150 8C, respectively. Most significantly, the PEMFCs based on the HPW/MCM-41 mesoporous-silica membrane showed a very impressive performance, achieving a maximum power density of 95mWcm 2 in H2/O2 at 100 8C and 100% RH, and 90mWcm 2 in methanol/O2 at 150 8C and 0.67% RH of the cathode. Highly orderedmesoporous silica MCM-41 can be synthesized according to the procedure given in the literature. Thus, the key issue is to anchor and assemble HPW into the mesopores or channels of MCM-41 host. We have derived a VIM to assemble HPW molecules into the mesoporous silica. In this process, the impurities or trapped air inside the mesopores are removed under vacuum, and the vacuum-treated mesoporous silica

Sodium-alginate-based proton-exchange membranes as electrolytes for DMFCs

Abstract: Novel mixed-matrix membranes prepared by blending sodium alginate (NaAlg) with polyvinyl alcohol (PVA) and certain heteropolyacids (HPAs), such as phosphomolybdic acid (PMoA), phosphotungstic acid (PWA) and silicotungstic acid (SWA), followed by ex-situ cross-linking with glutaraldehyde (GA) to achieve the desired mechanical and chemical stability, are reported for use as electrolytes in direct methanol fuel cells (DMFCs). NaAlg-PVA-HPA mixed matrices possess a polymeric network with micro-domains that restrict methanol cross-over. The mixed-matrix membranes are characterised for their mechanical and thermal properties. Methanol cross-over rates across NaAlg-PVA and NaAlg-PVA-HPA mixed-matrix membranes are studied by measuring the mass balance of methanol using a density meter. The DMFC using NaAlg-PVA-SWA exhibits a peak power-density of 68 mW cm(-2) at a load current-density of 225 mA cm(-2), while operating at 343 K. The rheological properties of NaAlg and NaAlg-PVA-SWA viscous solutions are studied and their behaviour validated by a non-Newtonian power-law.

A Polypyrrole/Phosphomolybdic Acid ∣ Poly ( 3 , 4-ethylenedioxythiophene ) /Phosphotungstic Acid Asymmetric Supercapacitor

Abstract: An asymmetric conducting polymer/polyoxometalate (POM) supercapacitor was designed using polypyrrole/phosphomolybdic acid and poly(3,4-ethylenedioxythiophene)/phosphotongstic acid as electrode materials. Performance characteristics were measured by cyclic voltammetry and constant current discharge. Energy density and power density were increased by a factor of 3 and 50, respectively, over symmetric conducting polymer/POM systems.

Development of high-temperature PEMFC based on heteropolyacids and polybenzimidazole

Abstract: Inorganic/organic composite membranes have been prepared from polybenzimidazole and two different heteropolyacids; namely phosphotungstic acid and silicotungstic acid. The membranes were characterized using SEM, XRD, and proton conductivity. The conductivity of the composite membrane was relatively high when compared to PBI membrane. The fuel cell performance with the composite membranes doped with phosphoric acid was investigated using hydrogen. It was found that pre-treatment of PWA and SiWA influenced the fuel cell performance and that the performance was enhanced with the use of the composite membrane. However, from the electrode polarization and crossover current data it was revealed that the expected high performance of the fuel cell was not achieved because of voltage losses associated with contact resistance and poor ionic conductivity in the catalyst layer. The best performance of the fuel cell was achieved with a 40% SiWA/PBI composite membrane.

Phosphotungstic Acid: An Efficient Catalyst for the Aqueous Phase Synthesis of Bis-(4-hydroxycoumarin-3-yl)methanes

Abstract: In this present work, we report that phosphotungstic acid provides a simple, efficient and environmentally benign route is a two-component one-pot domino Knoevenagel-type condensation/Michael reaction between 4-coumarin derivative and an aldehyde in water as a solvent in shorter duration with high yields.

Fabrication and application of a novel plant hormone sensor for the determination of methyl jasmonate based on self-assembling of phosphotungstic acid–graphene oxide nanohybrid on graphite electrode

Abstract: A novel methyl jasmonate (MeJA) sensor based on phosphotungstic acid/graphene oxide (PTA/GO) nanohybrid was developed by layer-by-layer assembling on a pre-anodized graphite electrode. Owing to the synergistic effect of the good conductivity, high surface area of GO and the solid super-acidity of PTA, the MeJA electrochemical sensor exhibited excellent electrocatalytic activity for the oxidation of alkylene group in MeJA, displaying as a wide linear response from 5.0 × 10 −7 to 8.0 × 10 −5 M and a low detection limit of 2.0 × 10 −7 M in 0.1 M HClO 4 solution.

Thermotropic Liquid Crystals of a Non-Mesogenic Group Bearing Surfactant-Encapsulated Polyoxometalate Complexes

Abstract: A tri(ethylene oxide)octadecyldimethylammonium p-toluenesulfonate (C18NEO3·Ts) amphiphile was employed to encapsulate Keggin-type polyoxometalates by ion metathesis reactions with phosphotungstic acid, silicotungstic acid, pentapotassium dodecatungstoborate(III), and phosphomolybdic acid, giving the surfactant-encapsulated polyoxometalates (SEPs) in SEP-P, SEP-Si, SEP-B, and SEP-PMo, respectively. Meanwhile, a C18NEO3·PF6 amphiphile was prepared by substituting the p-toluenesulfonate of C18NEO3·Ts with hexafluorophosphate. The chemical composition of all SEPs and amphiphiles was characterized through 1H NMR, infrared spectroscopy, mass spectroscopy, elemental analysis, and thermogravimetric analysis. The thermal properties of the SEPs and the amphiphiles were investigated by differential scanning calorimetry, polarized optical microscopy, and variable-temperature X-ray diffraction. The types of anions have a remarkable influence on the thermal properties of the prepared compounds or complexes. C18NEO3·Ts ...

Surface modification of heteropoly acid/SPEEK membranes by polypyrrole with a sandwich structure for direct methanol fuel cells

Abstract: A series of SPEEK/HPW/Ppy-n composite membranes with a sandwich structure were successfully prepared by surface modification with polypyrrole (Ppy) in order to stabilize phosphotungstic acid (HPW) in poly(ether ether ketone)s (SPEEKs) and reduce the methanol crossover. Ppy coatings with a large number of secondary ammonium groups (NH2+) interact with anions of HPW to decrease HPW leaching from the membrane. In addition, the hydrophobic Ppy layers allow for little methanol transport, which leads to a significant decline in methanol crossover with reasonable levels of proton conductivity. The properties of the membranes were investigated in detail by UV, SEM, ac impedance, and TGA. As observed, Ppy-modified membranes were better at immobilizing HPW and exhibited higher selectivities than previously reported SPEEK/HPW composite membranes. All the results indicate that the SPEEK/HPW/Ppy-n composite membranes are excellent candidates for direct methanol fuel cells.

A process for the dehydration of ethanol to produce ethene

Abstract: The present invention relates to a process for the production of ethylene, from a feedstock comprising ethanol, in the presence of a phosphotungstic acid catalyst.

Preparation of poly(vinylidene fluoride)/phosphotungstic acid composite nanofiber membranes by electrospinning for proton conductivity

Abstract: A composite nanofiber containing poly(vinylidene fluoride) (PVDF) and phosphotungstic acid (PWA) is prepared by electrospinning of their mixtures. The nanofibers are characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction spectroscopy (XRD). The spun nanofibers are in the β phase of PVDF and are bead-free in structure. Membranes prepared from the nanofibers can be used as a proton conductivity membrane for fuel cell applications.

Photocatalytic Degradation of Organic Dye Methyl Orange with Phosphotungstic Acid

Abstract: Silicotungstic acid and phosphotungstic acid were prepared and characterized by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD). The results showed that the prepared catalysts possess classical Keggin structure. The factors on the degradation of methyl orange, such as the kind of catalyst, the amount of catalyst, the original concentration of dye and illumination time were investigated under metal halide lamp. The degradation of methyl orange is up to 93.6% with phosphotungstic acid at the best reaction conditions at 8.89 g/L concentration of phosphotungstic acid, 5.56 mg/L concentration of methyl orange and 80 min illumination time.

Poly(vinyl alcohol)–polyacrylamide blends with cesium salts of heteropolyacid as a polymer electrolyte for direct methanol fuel cell applications

Abstract: A class of inorganic–organic hybrid membranes with low methanol permeability characteristics for possible direct methanol fuel cell (DMFC) applications was architected, formulated, and fabricated through the blending of poly(vinyl alcohol) (PVA) and polyacrylamide (PAM) followed by crosslinking with glutaraldehyde (Glu). Cesium salts of different heteropolyacids, including phosphomolybdic acid (PMA), phosphotungstic acid (PWA), and silicotungstic acid (SWA), were incorporated into the polymer network to form corresponding hybrid membrane materials, namely, PVA–PAM–CsPMA–Glu, PVA–PAM–CsPWA–Glu, and PVA–PAM–CsSWA–Glu, respectively (where “Cs” together with a heteropolyacid abbreviation indicates the cesium salt of that acid). All the three hybrid polymer membranes fabricated exhibited excellent swelling, thermal, oxidative, and additive stability properties with desired proton conductivities in the range 10−2 S/cm at 50% relative humidity. A dense network formation was achieved through the blending of PVA and PAM and by crosslinking with Glu, which led to an order of magnitude decrease in the methanol permeability compared to the state-of-the-art commercial Nafion 115 membrane. The hybrid membrane containing CsSWA exhibited a very low methanol permeability (1.4 × 10−8 cm2/s) compared to other membranes containing cesium salt of heteropolyacids such as PMA and PWA. The feasibility of these hybrid membranes as proton-conducting electrolytes in DMFC was investigated, and the preliminary results were compared with those of Nafion 115. The results illustrate the attractive features and suitability of the fabricated hybrid membranes as an electrolyte for DMFC applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Third phase formation in the extraction of phosphotungstic acid by TBP in n-octane.

Abstract: The solvent extraction of 12-phosphotungstic acid, also known as 12-tungstophosphoric acid—H3PW12O40, the so-called Keggin heteropolyacid—by 0.73 M (20%v/v) tri-n-butyl phosphate (TBP) in n-octane under conditions comparable to those used previously for the extraction of conventional inorganic mineral acids is described. A simplified phase diagram for the pentanary system comprised of H3PW12O40, HNO3, H2O, TBP, and n-octane reveals an extremely low initial concentration of H3PW12O40 (1.1 mM) at the LOC (limiting organic concentration) condition, far lower than the most effective third-phase-forming inorganic acid, namely HClO4. The results from small-angle neutron scattering (SANS) indicate that the interparticle attraction energy—U(r) calculated through application of the Baxter sticky sphere model to the SANS data at the LOC condition—does not approach the −2 k B T value associated with phase splitting in previous studies of TBP third-phase formation. The third-phase formation model based on attractive ...

Noncovalent immobilization of chiral cyclopropanation catalysts on mesoporous TUD-1: Comparison of liquid-phase and gas-phase ion-exchange

Abstract: TUD-1 has been used as Bronsted acidic mesoporous support for the immobilization of a chiral cyclopropanation catalyst. Bronsted acid sites were introduced by supporting phosphotungstic acid on all alumina TUD-1 matrix (PW-TUD-Al 2 O 3 ) or by substitution of Si by Al in all silica TUD-1 matrix (Al-TUD-1). The chiral cyclopropanation catalyst Cu(I)- 2,2′-methylenebis [(4 R ,5 S )-4,5-diphenyl-4,5-dihydro-1,3-oxazole] was immobilized by different noncovalent immobilization techniques; ion-exchange in solution and solid–gas ion-exchange. The chiral cyclopropanation catalyst was adsorbed on PW-TUD-Al 2 O 3 during ion-exchange in solution. This catalyst system displayed high leaching of copper reaching values of 21%. While using Al-TUD-1 as support copper was introduced as CuCl at temperatures from 550 to 850 °C subsequently followed by introduction of the ligand. Noncovalent immobilization by solid–gas ion-exchange of CuCl on Al-TUD-1 resulted in heterogenous catalyst with only 1% leaching of copper but also moderate results in the cyclopropanation of styrene in terms of yield (33%) and enantioselectivities.

PVA–SSA–HPA Mixed-Matrix-Membrane Electrolytes for DMFCs

Abstract: Stabilized forms of heteropolyacids (HPAs), namely phosphomolybdic acid (PMA), phosphotungstic acid (PTA), and silicotungstic acid (STA), are incorporated into poly (vinyl alcohol) (PVA) cross-linked with sulfosuccinic acid (SSA) to form mixed-matrix membranes for application in direct methanol fuel cells (DMFCs). Bridging SSA between PVA molecules not only strengthens the network but also facilitates proton conduction in HPAs. The mixed-matrix membranes are characterized for their mechanical stability, sorption capability, ion-exchange capacity, and wetting in conjunction with their proton conductivity, methanol permeability, and DMFC performance. Methanol-release kinetics is studied ex situ by volume-localized NMR spectroscopy (employing point-resolved spectroscopy'') with the results clearly demonstrating that the incorporation of certain inorganic fillers in PVA-SSA viz., STA and PTA, retards the methanol-release kinetics under osmotic drag compared to Nafion, although PVA-SSA itself exhibits a still lower methanol permeability. The methanol crossover rate for PVA-SSA-HPA-bridged-mixed-matrix membranes decreases dramatically with increasing current density rendering higher DMFC performance in relation to a DMFC using a pristine PVA-SSA membrane. A peak power density of 150 mW/cm(2) at a load current density of 500 mA/cm(2) is achieved for the DMFC using a PVA-SSA-STA-bridged-mixed-matrix-membrane electrolyte. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3465653] All rights reserved.

Composite electrolytes composed of Cs-substituted phosphotungstic acid and sulfonated poly(ether–ether ketone) for fuel cell systems

Abstract: Composite electrolytes composed of cesium hydrogen sulfate containing phosphotungstic acids (CsHSO 4 –H 3 PW 12 O 40 ) and sulfonated poly(ether–ether ketone) (SPEEK) were prepared by casting the corresponding precursor for application in fuel cells. Partially Cs-substituted phosphotungstic acids (Cs x H 3− x PW 12 O 40 ) were formed in the CsHSO 4 –H 3 PW 12 O 40 system by mechanochemical treatment. SPEEK was prepared from PEEK by sulfonation using concentrated sulfuric acid. Flexible composite electrolytes were obtained and their electrochemical properties were markedly improved with the addition of Cs x H 3− x PW 12 O 40 , into the SPEEK matrix. A maximum power density of 213 mW cm −2 was obtained from the single cell test for 50H 3 PW 12 O 40 –50CsHSO 4 in SPEEK (1/5 by weight) composite electrolyte at 80 °C and at 80 RH%. Electrochemical properties and transmission electron microscopy (TEM) results suggest that three-dimensional cluster particles were formed and homogeneously distributed in the SPEEK matrix. The mechanochemically synthesized Cs x H 3− x PW 12 O 40 incorporated into the SPEEK matrix increased the number of protonate sites in the electrolyte. The composite electrolytes were successfully formed with Cs x H 3− x PW 12 O 40 , which consist of hydrogen bonding between surface of inorganic solid acids and not only –HSO 4 − dissociated from CsHSO 4 but also –SO 3 H groups in the SPEEK.

Crosslinked hybrid membranes based on sulfonated poly(ether ether ketone)/γ-methacryloxypropyltrimethoxysilane/phosphotungstic acid by an in situ sol–gel process for direct methanol fuel cells

Abstract: Proton exchange membranes with high dimensional stabilities and low water uptakes were constructed by incorporating phosphotungstic acid (PWA) into a cross-linked network composed of a crosslinkable sulfonated poly(ether ether ketone) containing dipropenyl groups (SDPEEK) and γ-methacryloxypropyltrimethoxysilane (KH570). The chemical structures of the hybrid membranes were confirmed by FT-IR spectroscopy and scanning electron microscopy (SEM). The results indicated that PWA particles were well dispersed in these membranes. The influences of the dispersed PWA on the properties of membranes such as thermal stability, water uptake, swelling ratio, proton conductivity, methanol permeability and mechanical property were researched. The addition of KH570-5/PWA in the hybrid membranes contributed to the improvement of the dimensional stabilities. And the hybrid membranes with 10–40wt% PWA showed higher proton conductivities than Nafion 117 at 80 °C, while the methanol permeabilities of these membranes were much lower than that of Nafion 117. The membranes also exhibited excellent mechanical properties. These results imply that the SDPEEK/KH570-5/PWA-x membranes are promising materials in the direct methanol fuel cells (DMFC) applications.

Composite Polymer Electrolyte Membranes Based on Stabilized Phosphotungstic Acid and Sulfonated Poly(etheretherketone) for Fuel Cell Applications

Abstract: Sulfonated poly(etheretherketone) (SPEEK), with 577 g per equivalent proton, was made by the direct sulfonation method using sulfuric acid Composite membranes were prepared by the addition of 0, 5, 15, 30, and 40 wt % phosphotungstic acid (PTA) to the nonwater soluble SPEEK After Cs + stabilization of the solid acid-containing composites was done, the membranes' conductivities were tested as alternatives to Nafion in proton exchange membrane fuel cells The presence of Cs―PTA in the membranes had little effect on conductivity at low relative humidity (RH), although a 30-40% loading did enable σ = 012 S/cm at 80°C and 100% RH A characterization of Cs―PTA and composite membranes via thermogravimetric and differential thermal analysis, X-ray photoelectron spectroscopy, Fourier transform infrared, and water uptake measurements revealed that stabilization of the PTA with a Cs + ion also resulted in a sharply curtailed ability to uptake and hold water, a necessary attribute of a significant protonic mobility Even so, the presence of Cs―PTA in SPEEK membranes enabled improved current-voltage curves in a fuel cell configuration by reducing the interfacial resistance between SPEEK and the Nafion-based catalyst particle binder

Photocatalytic degradation of nitrobenzene wastewater with H 3 PW 12 O 40 /TiO 2

Abstract: In order to treat a mass of industrial wastewater nitrobenzene, a photocatalytic degradation method was studied in this paper. Phosphotungstic acid(H 3 PW 12 O 40 ) and titanium dioxide(TiO 2 ) were prepared, and a new-style catalyst H 3 PW 12 O 40 supported on TiO 2 (H 3 PW 12 O 40 /TiO 2 ) was prepared by the method of impregnation. We characterized them using X-Ray and FT-IR. The results proved that H 3 PW 12 O 40 possessed classical Keggin structure, TiO 2 was anatase and H 3 PW 12 O 40 can keep the Keggin structure on the TiO 2 . The effects of photocatalytic degradation of nitrobenzene wastewater under visible light in the presence of H 3 PW 12 O 40 /TiO 2 were investigated in detail. The research results revealed that reaction time, catalyst dosage, nitrobenzene original concentration were the main effects, and the biggest degradation of nitrobenzene wastewater was 94.1% at the optimum condition. The exhibited photocatalytic activity of the novel photocatalyst provided a promising solution for the degradation of nitrobenzene water contaminants.

A biocompatible chitosan composite containing phosphotungstic acid modified single-walled carbon nanotubes.

Abstract: Surface modification of carbon nanotubes is crucial for the dispersion and interfacial adhesion of carbon nanotubes in polymer composites. Here we present a novel method to construct single-walled carbon nanotube/chitosan composites using phosphotungstic acid as an anchor reagent to modify single-walled carbon nanotubes. The most direct benefit from this method is that this modification is mild but effective: the induced defects on single-walled carbon nanotubes are negligible based on Raman and transmission electron microscopy observations; and homogeneous dispersion of single-walled carbon nanotubes in chitosan matrices and strong binding between single-walled carbon nanotubes and chitosan are achieved. Moreover, according to the results of tetrazolium-based colorimetric assays in vitro, we demonstrate that the produced phosphotungstic-acid-modified single-walled carbon nanotube/chitosan composites have good biocompatibility. Thus, our study provides a feasible route to fabricate biocompatible composites containing single-walled carbon nanotubes for potential application in bone tissue engineering.