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1.
An inorganic/organic self-humidifying composite membranes for proton exchange membrane fuel cell application 总被引:1,自引:0,他引:1
With an aim to operate the proton exchange membrane fuel cells (PEMFCs) with dry reactants, an inorganic/organic self-humidifying membrane based on sulfonated polyether ether ketone (SPEEK) hybrid with Cs2.5H0.5PW12O40 supported Pt catalyst (Pt-Cs2.5 catalyst) has been investigated. The Pt-Cs2.5 catalysts incorporated in the SPEEK matrix provide the site for catalytic recombination of permeable H2 and O2 to form water, and meanwhile avoid short circuit through the whole membrane due to the insulated property of Cs2.5H0.5PW12O40 support. Furthermore, the Pt-Cs2.5 catalyst can adsorb the water and transfer proton inside the membrane for its hygroscopic and proton-conductive properties. The structure of the SPEEK/Pt-Cs2.5 composite membrane was characterized by XRD, FT-IR, SEM and EDS. Comparison of the physicochemical and electrochemical properties, such as ion exchange capacity (IEC), water uptake and proton conductivity between the plain SPEEK and SPEEK/Pt-Cs2.5 composite membrane were investigated. Additive stability measurements indicated that the Pt-Cs2.5 catalyst showed improved stability in the SPEEK matrix compared to the PTA particle in the SPEEK matrix. Single cell tests employing the SPEEK/Pt-Cs2.5 self-humidifying membrane and the plain SPEEK membrane under wet or dry operation conditions and primary 100 h fuel cell stability measurement were also conducted in the present study. 相似文献
2.
We have developed preparation protocol of practically large size self-humidifying polymer electrolyte membranes (PEMs) with highly dispersed nanometer-sized Pt and/or SiO2 for fuel cells. The Pt particles were expected to catalyze the recombination of H2 and O2, leading to a suppression of the chemical short-circuit reaction at the electrodes, while the SiO2 particles were expected to adsorb the water produced at the Pt particles together with that produced at the cathode reaction. Stable SiO2 particles were formed in a commercial PEM (Nafion®112) via in situ sol-gel reactions at 70 °C. It was found by SAXS that the hydrophilic cluster size increased by water adsorbed SiO2, which may contribute to the increase in the proton conductivity once SiO2 adsorbed water. Pt particles were uniformly dispersed in a Na+-form normal-PEM or SiO2-PEM by an ion-exchange reaction with [Pt(NH3)4]Cl2, followed by a reduction with 1-pentanol at 125 °C. The newly prepared Pt-SiO2-PEM was found to perform a self-humidifying operation in a standard-size PEFC (25 cm2 electrode area) with H2 and O2 humidified at 30 °C. The performance of the Pt-SiO2-PEM cell operated with the low humidity reactant gases was as high as the normal-PEM cell fully humidified, because the ohmic resistance of the former cell was as low as the latter cell. 相似文献
3.
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 SO3H group as a proton conductor with inorganic material, SiO2, using the sol-gel process. Electron probe micro analyser (EPMA) was used to show the homogeneous and uniform distribution of SiO2. 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. 相似文献
4.
Jun-Bin Ko Sung Wook Lee Dong Eun Kim Young Un Kim Gang Li Seung Goo Lee Tae-Sun Chang Dojin Kim Yong Lak Joo 《Journal of Porous Materials》2006,13(3):325-330
(1 − x)SiO2-(x)ZrO2 (x = 0.1, 0.2) composite fiber mats were prepared by electrospinning their sol-gel precursors of zirconium acetate and tetraethyl
orthosilicate (TEOS) without using a polymer binder. The electrospun composite fibers were characterized by powder X-ray diffraction
(XRD), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR) and mercury porosimetry. The composite
fibers having a tetragonal crystalline ZrO2 were obtained by calcining the electrospun composite fibers at high temperatures. The results show that the structure and
crystallization of ZrO2 in the composite fibers can be controlled by sintering temperature, while the porosity and morphology of the fiber mats did
not depend on the sintering temperature. 相似文献
5.
6.
Jiansheng Li Yanxia Hao Huijun Li Minya Xia Xiuyun Sun Lianjun Wang 《Microporous and mesoporous materials》2009,120(3):421-425
A series of CeO2/SiO2 mesostructured composite materials was synthesized by sol–gel process using Pluronic P123 as template, tetraethylorthosilicate as silica source and hexahydrated cerium nitrate as precursor under acid condition. The as-synthesized materials with Ce/Si molar ratio ranging from 0.03 to 0.3 were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), laser Raman spectroscopy (LRS), and N2 adsorption. Characterization revealed that all samples possess ordered hexagonal mesoporous structure similar to SBA-15 and possess high surface area, large pore volume and uniform pore size. The fact that cerium species are present as highly dispersed CeO2 nanocrystals in hexagonal matrix was confirmed by XRD combined with high-resolution TEM and selected area electron diffraction (SAED) analysis. Introduction of ceria to silica matrix can cause a distortion of hexagonal ordering structure and decrease pore diameter and increase the wall thickness of mesopores. Moreover, it can be found that this sol–gel route is a feasible, effective and simple method for templating synthesis of CeO2/SiO2 composite materials. 相似文献
7.
Preparation of TiO2/SiO2 multilayer flakes and their application to decorative powders were investigated. In contrast to conventional products prepared through the multicoating of core platelets, the coreless TiO2/SiO2 multilayer flakes were prepared by detaching multilayer films from their substrates. These flakes exhibited structural colors, when the optical path length of both the TiO2 and SiO2 layers are adjusted to be one fourth of the wavelength of visible light. A multicoating of more than five layers resulted in the propagation of cracks, which prevented the preparation of thick flakes. Paint films fabricated using the multilayer flakes and acrylic resins showed reflectance spectra that were comparable with those obtained for multicoatings on substrates. 相似文献
8.
In this work, a novel self-humidifying membrane electrode assembly (MEA) with Pt/SiO2/C as anode catalyst was developed to improve the performance of proton exchange membrane fuel cell (PEMFC) operating at low humidity conditions. The characteristics of the composite catalysts were investigated by XRD, TEM and water uptake measurement. The optimal performance of the MEA was obtained with the 10 wt.% of silica in the composite catalyst by single cell tests under both high and low humidity conditions. The low humidity performance of the novel self-humidifying MEA was evaluated in a H2/air PEMFC at ambient pressure under different relative humidity (RH) and cell temperature conditions. The results show that the MEA performance was hardly changed even if the RHs of both the anode and cathode decreased from 100% to 28%. However, the low humidity performance of the MEA was quite susceptible to the cell temperature, which decreased steeply as the cell temperature increased. At a cell temperature of 50 °C, the MEA shows good stability for low humidity operating: the current density remained at 0.65 A cm−2 at a usual work voltage of 0.6 V without any degradation after 120 h operation under 28% RH for both the anode and cathode. 相似文献
9.
Meldola blue immobilized on a new SiO2/TiO2/graphite composite was applied in the electrocatalytic oxidation of NADH. The materials were prepared by the sol-gel processing method and characterized by several techniques including scanning electronic microscopy coupled to energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electronic microscopy (HRTEM). Si and Ti mapping profiles on the surface showed a homogeneous distribution of the components. Ti2p binding energy peaks indicate that the formation of Si-O-Ti linkage is presumably the responsible for the high rigidity of the matrices. The good electrical conductivity presented by the composites (5 and 11 S cm−1) can be related to a homogeneous distribution of graphite particles observed by TEM. After the materials characterization, a SiO2/TiO2/graphite electrode was prepared and some chemical modifications were performed on its surface to promote the adsorption of meldola blue. The resulting system presented electrocatalytic properties toward the oxidation of NADH, decreasing the oxidation potential to −120 mV. The proposed sensor showed a wide linear response range from 0.018 to 7.29 mmol l−1 and limit of detection of 0.008 mmol l−1. SiO2/TiO2/graphite has shown to be a promising material to be used as a suitable support in the construction of new electrochemical sensors. 相似文献
10.
Poly(vinylidene fluoride) composite membranes filled with different weight fractions of SiO2 nanoparticles have been prepared by a blending method. Cation-exchange groups were introduced by the copolymerization of glycidyl methacrylate with divinylbenzene and subsequent sulfonation. These hybrid membranes have been characterized by Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and water uptake and ion-exchange capacity measurements. Membrane potential and membrane conductivity measurements have been carried out with different counter ions to investigate the relationship between ionic migration and the SiO2 nanoparticle content. The counter-ion transport number and permselectivity of these membranes are found to be highly dependent on the SiO2 content in the membrane phase and the nature of the counter ion. Membrane conductance was analyzed in terms of phenomenological coefficients using non-equilibrium thermodynamic principles. It can be concluded that these hybrid membranes exhibit high thermal stability, improved selectivity, and moderate membrane conductivity, and may be suitable for use in the electro-driven separation processes. 相似文献
11.
The effect of H4SiW12O40 loading on the catalytic performance of the reduced Ni-H4SiW12O40/SiO2 catalysts for hydrocracking of n-decane with or without the presence of thiophene and pyridine is studied. The catalysts were characterized by BET, XRD, Raman, XPS, H2-TPR, H2-TPD, NH3-TPD and FT-IR of pyridine adsorption. It was found that addition of H4SiW12O40 to the system increases the catalytic activity and the promoting effect is a function of the H4SiW12O40 loading. The best result was obtained on 5%Ni-50%H4SiW12O40/SiO2 catalyst which shows the highest activity for hydrocracking of n-decane and excellent tolerance to the sulfur and nitrogen compounds in the feedstock. The results showed that a suitable amount of H4SiW12O40 loading on the 5%Ni/SiO2 catalyst increases the amount of both hydrogen adsorbed and Brønsted acid and Lewis acid sites on the catalyst. The high catalytic performance of the catalyst can be related to the nature of H4SiW12O40 and the proper balance between metal and acid functions. 相似文献
12.
Spherical (Ni0.5Mn0.5)(OH)2 with different secondary particle size (3 μm, 10 μm in diameter) was synthesized by co-precipitation method. Mixture of the prepared hydroxide and lithium hydroxide was calcined at 950 °C for 20 h in air. X-ray diffraction patterns revealed that the prepared material had a typical layered structure with space group. Spherical morphologies with mono-dispersed powders were observed by scanning electron microscopy. It was found that the layered Li[Ni0.5Mn0.5]O2 delivered an initial discharge capacity of 148 mAh g−1 (3.0-4.3 V) though the particle sizes were different. Li[Ni0.5Mn0.5]O2 having smaller particle size (3 μm) showed improved area specific impedance due to the reduced Li+ diffusion path, compared with that of Li[Ni0.5Mn0.5]O2 possessing larger particle size (10 μm). Although the Li[Ni0.5Mn0.5]O2 (3 μm) was electrochemically delithiated to Li0.39[Ni0.5Mn0.5]O2, the resulting exothermic onset temperature was around 295 °C, of which the value is significantly higher than that of highly delithiated Li1−δCoO2 (∼180 °C). 相似文献
13.
Tao Chen Hongli Wang Ting Zhang Guangchang Wang Jifang Zhou Jianwei Zhang Yuhong Liu 《Ceramics International》2014
(Bi0.5Na0.5)0.94Ba0.06TiO3–xHfO2 [BNBT–xHfO2] lead-free ceramics were prepared using the conventional solid-state reaction method. Effects of HfO2 content on their microstructures and electrical properties were systematically studied. A pure perovskite phase was observed in all the ceramics with x=0–0.07 wt%. Adding optimum HfO2 content can induce dense microstructures and improve their piezoelectric properties, and a high depolarization temperature was also obtained. The ceramics with x=0.03 wt% possess optimum electrical properties (i.e., d33~168 pC/N, kp~32.1%, Qm~130, εr~715, tan δ~0.026, and Td~106 °C, showing that HfO2-modified BNBT ceramics are promising materials for piezoelectric applications. 相似文献
14.
A milling process to reduce kaolin to amorphous phase in the presence of KH2PO4 or NH4H2PO4 and allow mechanochemical (MC) reaction for incorporation of KH2PO4 and NH4H2PO4 into the kaolin structure was investigated in this work. Mixtures of kaolin and KH2PO4 and NH4H2PO4 in separate systems were prepared by milling in a planetary ball mill. Tests with kaolin contents ranging from 25 to 75 wt.% and mill rotational speeds from 200 to 700 rpm were performed to evaluate incorporation of KH2PO4 and NH4H2PO4 and release of K+, NH4+ and PO43− ions into solution. Analyses by XRD, DTA and ion chromatography indicated that the MC process was successfully applied to incorporate both KH2PO4 and NH4H2PO4 into the amorphous kaolin structure. Release of K+ and PO43− ions from the system (kaolin-KH2PO4) when dispersed in water for 24 h reached only up to 10%. Under similar conditions for the system (kaolin-NH4H2PO4), release of NH4+ and PO43− ions reached between 25 and 40%. These results indicated that the MC process can be developed to allow amorphous kaolin to act as a carrier of K+, NH4+ and PO43− nutrients to be released slowly for use as fertilizer. 相似文献
15.
Formation of H2O2 from H2 and O2 and decomposition/hydrogenation of H2O2 have been studied in aqueous acidic medium over Pd/SiO2 catalyst in presence of different halide ions (viz. F−, Cl− and Br−). The halide ions were introduced in the catalytic system via incorporating them in the catalyst or by adding into the reaction medium. The nature of the halide ions present in the catalytic system showed profound influence on the H2O2 formation selectivity in the H2 to H2O2 oxidation over the catalyst. The H2O2 destruction via catalytic decomposition and by hydrogenation (in presence of hydrogen) was also found to be strongly dependent upon the nature of the halide ions present in the catalytic system. Among the different halides, Br− was found to selectivity promote the conversion of H2 to H2O2 by significantly reducing the H2O2 decomposition and hydrogenation over the catalyst. The other halides, on the other hand, showed a negative influence on the H2O2 formation by promoting the H2 combustion to water and/or by increasing the rate of decomposition/hydrogenation of H2O2 over the catalyst. An optimum concentration of Br− ions in the reaction medium or in the catalyst was found to be crucial for obtaining the higher H2O2 yield in the direct synthesis. 相似文献
16.
Kinetic and transport parameters of Li ion during its extraction/insertion into thin film LiNi0.5Mn0.5O2 free of binder and conductive additive were provided in this work. LiNi0.5Mn0.5O2 thin film electrodes were grown on Au substrates by pulsed laser deposition (PLD) and post-annealed. The annealed films exhibit a pure layered phase with a high degree of crystallinity. Surface morphology and thin film thickness were investigated by field emission scanning electron microscopy (FESEM). The charge/discharge behavior and rate capability of the thin film electrodes were investigated on Li/LiNi0.5Mn0.5O2 cells at different current densities. The kinetics of Li diffusion in these thin film electrodes were investigated by cyclic voltammetry (CV) and galvanostatic intermittent titration technique (GITT). CV was measured between 2.5 and 4.5 V at different scan rates from 0.1 to 2 mV/s. The apparent chemical diffusion coefficients of Li in the thin film electrode were calculated to be 3.13 × 10−13 cm2/s for Li intercalation and 7.44 × 10−14 cm2/s for Li deintercalation. The chemical diffusion coefficients of Li in the thin film electrode were determined to be in the range of 10−12-10−16 cm2/s at different cell potentials by GITT. It is found that the Li diffusivity is highly dependent on the cell potential. 相似文献
17.
E.I. Santiago R.A. Isidoro M.A. Dresch B.R. Matos M. Linardi F.C. Fonseca 《Electrochimica acta》2009,54(16):4111-8271
The fabrication and characterization of Nafion-TiO2 hybrid electrolytes for proton exchange membrane fuel cell (PEMFC) operating at high temperature are reported. A low temperature sol-gel synthesis, based on the formation of a sol from Ti-peroxy complex, was used to effectively incorporate hydrophilic anatase TiO2 nanoparticles into the Nafion matrix. Fuel cell testing at temperatures up to 130 °C revealed that the hybrid membranes exhibit an increasing ohmic drop with increasing TiO2 content incorporated into the polymer. However, at high temperatures and low relative humidity (RH) the performance of fuel cells using the hybrid electrolytes was found to surpass the one of Nafion. Electrochemical impedance spectroscopy (EIS) measurements suggest that enhancement of the fuel cell performance at high temperature and low RH is related to a reduced polarization resistance, indicating that the hybrid electrolytes contribute for a better water management of the system. In addition, it was found that the inorganic phase confers stability to the polymer, allowing for the operation at high temperature and reduced RH. 相似文献
18.
LiNi0.5Co0.5VO4 nano-crystals were solvothermally prepared using a mixture of LiOH·H2O, Ni(NO3)2·6H2O, Co(NO3)2·6H2O and NH4VO3 in isopropanol at 150–200 °C followed by 300–600 °C calcination to form powders. TGA curves of the solvothermal products show weight losses due to evaporation and decomposition processes. The purified products seem to form at 500 °C and above. The products analyzed by XRD, selected area electron diffraction (SAED), energy dispersive X-ray (EDX) and atomic absorption spectrophotometer (AAS) correspond to LiNi0.5Co0.5VO4. V–O stretching vibrations of VO4 tetrahedrons analyzed using FTIR and Raman spectrometer are in the range of 620–900 cm−1. A solvothermal reaction at 150 °C for 10 h followed by calcination at 600 °C for 6 h yields crystals with lattice parameter of 0.8252 ± 0.0008 nm. Transmission electron microscope (TEM) images clearly show that the solvothermal temperatures play a more important role in the size formation than the reaction times. 相似文献
19.
A new method was proposed to form (Ba0.5Sr0.5)TiO3–Al2O3 composite oxide film on etched aluminum foils. The specimens were covered with (Ba0.5Sr0.5)TiO3 (BST) layer by dip-coating in citrate solution and subsequent heat-treatment under 400–650 °C, finally by anodizing in a hot boracic acid and borate solution. The BST powders heated under different temperatures were characterized by X-ray diffraction (XRD) and the specific capacitance of the coated specimens heat-treated under different temperatures and times was measured. It is found that the specific capacitance increases initially with enhancing the temperature and reaches to maximum at 550 °C, but slightly decreases with the heat-treatment time. The capacitance was increased by about 35% after BST coating. 相似文献
20.
Combined TiO2/SiO2 mesoporous photocatalysts with location and phase controllable TiO2 nanoparticles 总被引:1,自引:0,他引:1
E. Beyers E. Biermans S. Ribbens K. De Witte M. Mertens V. Meynen S. Bals G. Van Tendeloo E.F. Vansant P. Cool 《Applied catalysis. B, Environmental》2009,88(3-4):515-524
Combined TiO2/SiO2 mesoporous materials were prepared by deposition of TiO2 nanoparticles synthesised via the acid-catalysed sol–gel method. In the first synthesis step a titania solution is prepared, by dissolving titaniumtetraisopropoxide in nitric acid. The influences of the initial titaniumtetraisopropoxide concentration and the temperature of dissolving on the final structural properties were investigated. In the second step of the synthesis, the titania nanoparticles were deposited on a silica support. Here, the influence of the temperature during deposition was studied. The depositions were carried out on two different mesoporous silica supports, SBA-15 and MCF, leading to substantial differences in the catalytic and structural properties. The samples were analysed with N2-sorption, X-ray diffraction (XRD), electron probe microanalysis (EPMA) and transmission electron microscopy (TEM) to obtain structural information, determining the amount of titania, the crystal phase and the location of the titania particles on the mesoporous material (inside or outside the mesoporous channels). The structural differences of the support strongly determine the location of the nanoparticles and the subsequent photocatalytic activity towards the degradation of rhodamine 6G in aqueous solution under UV irradiation. 相似文献