Dihydrogenimidazole modified silica-sulfonated poly(ether ether ketone) hybrid materials as electrolyte membranes for direct ethanol fuel cells

The present study reports on dihydrogenimidazole modified inorganic-organic mixed matrix membranes for possible application as a proton exchange membrane in direct ethanol fuel cells. The polymeric phase consisted mainly of sulfonated poly(ether ether ketone) (sPEEK) with a sulfonation degree of 55%. The inorganic phase was built up from hydrophilic fumed silica particles interconnected with partially hydrolyzed and condensed tetraethoxysilane with a total inorganic loading of 27.3%. This inorganic phase was further modified with N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole (DHIM), which consists of an hydrolyzable inorganic part and a functional organic group. The influence of the modifier on the mixed matrix system was studied by means of various modifier concentrations in various aqueous-ethanolic systems (water, 2 M and 4 M ethanol). Modifier concentration and ethanol concentration of the ethanol-water mixture exhibited significant but opposite effects on the liquid uptake of the mixed matrix membranes. The proton conductivity as well as the proton diffusion coefficient as a function of modifier content showed a linear decrease. The proton conductivity as a function of temperature showed Arrhenius behavior and the activation energy of the mixed matrix membranes was 43.9 ± 2.6 kJ mol⁻¹. High selectivity of proton diffusion coefficient to ethanol permeability coefficient was obtained with high modifier concentrations. At low modifier concentrations, this selectivity was dominated by ethanol permeation and at high modifier concentrations by proton diffusion. The main electrolyte properties can be optimized by setting the DHIM content in mixed matrix membrane. With this approach, tailor-made membranes can be prepared for possible application in direct ethanol fuel cells.     

Structure, growth and magnetic property of hard magnetic CoPtP nanowires synthesized by electrochemical deposition

This paper reports the electrochemical synthesis and characterization of one dimensional hard magnetic CoPtP nanowires. Three electrode potentiostatic electrochemical technique was used to deposit nanowires into a nanoporous track-etched polycarbonate membrane with a nominal pore diameter 50 nm and thickness around 6-9 μm. The room temperature electrolyte used for the deposition of nanowires consists of 60 g/lt CoSO₄7H₂O, 4.1 g/lt H₂PtCl₆, 4.5 g/lt NaHPO₂ and 25 g/lt B(OH)₃. The structural morphology was observed by scanning electron microscope and transmission electron microscope. The magnetic property of the nanowires was measured by vibrating sample magnetometer before removing the template. The coercive fields were measured to be 143 kA m^− 1 and 103 kA m^− 1 for parallel (H_║) and perpendicular to the nanowire axis, respectively. The higher coercivity value for H_║ indicating nanowires' easy magnetization direction lies along the nanowires' axis. The average composition of the CoPtP nanowires was determined by electron dispersive spectroscopy and the crystallinity was measured by X-ray diffractometer.     

Effects of APTEOS content and electron beam irradiation on physical and separation properties of hybrid nylon-66 membranes

Nylon-66 contains functional groups which form hydrogen bonds with inorganic silica networks and allow the creation of hybrid membranes. As a typical semicrystalline polymer, nylon-66 can be crosslinked through electron beam (EB) irradiation to form nanofiltration membranes. The effects of γ-aminopropyltriethoxylsilane (APTEOS) and EB irradiation on the physical and separation properties of nylon-66 membranes were studied in this work. Hybrid nylon-66 membranes were prepared by adding an APTEOS solution (5 wt%, 10 wt% and 20 wt%) into nylon-66 which was dissolved in formic acid. Before air drying, membranes were irradiated at 60 kGy, 70 kGy and 80 kGy. More cellular pores were formed in nylon-66 membranes with the addition of APTEOS. However, increased irradiation dose caused the formation of a dense layer in nylon-66 membranes. Crosslinked silica in nylon-66 membranes was confirmed by FT-IR and DMA, while XRD results showed that there was a high degree of crystallinity in some membranes after irradiation. With improvements in membrane pore size and the ratio of membrane thickness to porosity, nylon-66 membrane with 10 wt% of APTEOS irradiated at 70 kGy exhibited satisfactory permeability, excellent removal of neutral solutes and improved rejection of divalent ions.     

Zeolite-filled regenerated cellulose membranes for pervaporative dehydration of glycerol

Regenerated cellulosic membranes were prepared by dissolving linter pulp in N-methylmorpholine-N-oxide (NMMO) solution with four different cellulose concentrations (3, 5, 8 and 10 wt. % cellulose) at three different coagulation temperatures (5, 25 and 50 °C). Zeolite 13 X with an average particle size of 310 nm and Zeolite 4A with an average particle size of 270 nm were added during dissolution. The resulting composite membranes were characterized by Fourier Transform Infrared (FTIR), Thermogravimetric Analyzer (TGA), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). Pervaporation performances of the zeolite filled and unfilled regenerated cellulose membranes were tested for glycerol/water mixture.Chemically and thermally stable regenerated cellulose membranes could be prepared by using submicron sized zeolite loading maximum of 50%. The SEM pictures showed that the zeolite particles in polymer phase were uniformly distributed. It was concluded that the zeolite filled regenerated cellulose membranes have minimum degradation during membrane preparation obtained from NMMO and could be used as pervaporation membranes. At 30 °C and with the addition of 20 wt. % Zeolite 13 X to the cellulose membrane, the flux and selectivity was obtained 65 gm⁻²h⁻¹ and 1681 for 90 wt% glycerol aqueous solution, respectively.     

The influence of Ni nanoparticles and Ni (II) on the growth of Ag dendrites immobilized on the chelating copolymer membrane

Preparation of Ag dendrites on the surface of chelating copolymer membranes (PBAGI), which was synthesized by using the soap-free emulsion copolymerization of n-butylacrylate (BA) and acrylonitrile (AN), as well as 2-methacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester (GMA-IDA) that was used as a chelating group, is presented in this study. The characteristics of polymer membranes were investigated by Fourier transform infrared (FTIR) spectroscopy and elementary analysis (EA). The weight fraction of GMA-IDA in the polymer was 4.2 wt% as revealed by elemental analysis. The chelating group, –N(CH₂COO⁻Na⁺)₂ on the polymer was used to coordinate different amounts of Ni(II), controlled by different chelating times and subsequently reduced to Ni nanoparticles, as templates for growing Ag nanocrystals from 1.67 wt% AgNO₃ aqueous solution with 55.7 ppm poly(vinyl pyrrolidone) (PVP) added. In addition, the effect of Ni²⁺ concentration on the growth of the Ag dendrites was studied. Crystallinity and morphology of Ag dendrites were examined with X-ray diffraction (XRD) and scanning electronic microscopy (SEM), respectively. Amount of Ag dendrites increased with the increasing of Ni nanoparticles on the PBAGI membrane or the dose of Ni²⁺ present in the aqueous solution. Notable, under higher amount of Ni nanoparticles (over 200 mmol Ni²⁺/g PBAGI membrane), Ag dendrites could be successful grown on the membrane. However, higher dose of Ni²⁺ (over 41.3 ppm) might inhibit the growth of Ag dendrites.     

Enhanced electron emission from titanium coated multiwalled carbon nanotubes

Enhanced field emission properties and improved crystallinity of titanium (Ti) coated multiwalled carbon nanotubes (MWCNTs), prepared by microwave plasma enhanced chemical vapour deposition have been observed. Ti films of extremely low thicknesses (0.5 nm, 1.0 nm and 1.5 nm) were coated over carbon nanotubes (CNTs) and their field emission behaviour was investigated. The turn on field of Ti coated CNTs was found to be low (~ 0.8 V/μm) as compared to pristine CNTs (~ 1.8 V/μm). The field enhancement factor for Ti coated CNTs was quite large (~ 1.14 × 10⁴) as compared to pristine CNTs (~ 6 × 10³). This enhancement in electron emission is attributed to the passivation of defects and improved crystallinity of CNTs. Surface morphological and microstructural studies were carried out to investigate the growth of pristine and Ti coated CNTs. It was observed that Ti nanoclusters adsorb on the edges of MWCNTs and increase their crystallinity. This increase is directly correlated with the thickness of Ti film deposited. Micro Raman spectroscopy confirmed the improved crystallanity of Ti coated CNTs.     

Synthesis of high quality TiO2 membranes on alumina supports and their photocatalytic activity

This study describes the synthesis of TiO₂ membranes on alumina supports by the spin-coating technique using the sol-gel method with water-soluble chitosan (WSC) as an additive. After calcining the sample at 500 °C, the WSC was completely decomposed, and the remaining membrane consisted mainly of anatase. Controlling the amount of WSC in the TiO₂ sol to within a range of 0.1 wt.%-0.3 wt.% resulted in TiO₂ membranes on alumina supports with enhanced structural and catalytic properties. These properties included a high surface area (164 m²/g-116 m²/g) and porosity (47.3%-52.2%), homogeneity without cracks and pinholes, thinness (0.8 μm), as well as high degradation of methyl orange (61.2%-49.2%).     

Cermet-type hydrogen separation membrane obtained from fine particles of high temperature proton-conductive oxide and palladium

A mixed ionic and electronic conducting hydrogen separation membrane, which consisted of proton-conductive oxide and metallic palladium, was fabricated. A porous alumina tube was employed as a support, and proton-conductive oxide particles were introduced into a microporous top layer of the support by an impregnation method. Palladium particles were deposited into the same porous layer by chemical vapor deposition. Hydrogen permeated preferentially via the membrane thus obtained with a hydrogen permeance (PH₂) of 1.2 × 10^− 9 mol·m^− 2·s^− 1·Pa^− 1 at 873 K. Selectivity for hydrogen (PH₂/PN₂) increased with the operating temperature due to an increase in proton conductivity of the membrane, and PH₂/PN₂ = 5.7 was attained at 873 K.     

Hydrogen transport through thin palladium-copper alloy composite membranes at low temperatures

Hydrogen permeation performance of three thin palladium-copper composite membranes with different thicknesses had been studied between 398 K and 753 K. Hydrogen permeance was obtained up to 2.7 × 10^− 6 mol/(m² s Pa) with an ideal selectivity over 1000 at 753 K. The hydrogen permeation exhibited two different activation energies over the temperature range: lower activation energy of about 9.8 kJ/mol above 548 K, while higher activation energy of about 26.4 kJ/mol below 548 K. After permeation tests, the alloy membranes were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis and in situ X-ray diffraction. Palladium segregation on the surface of these palladium-copper alloys may induce changes of hydrogen permeation performance and thus influence the activation energies.     

Effect of hot-filament annealing in a hydrogen atmosphere on the electrical and structural properties of Nb-doped TiO2 sputtered thin films

In this work Nb-doped TiO2 thin films were deposited by d.c.-pulsed reactive magnetron sputtering at 500 °C from a composite target with weight fractions of 96% Ti and 4% Nb, using oxygen as reactive gas. In order to enhance the conductive properties, the as-deposited samples were treated in vacuum with atomic hydrogen at a substrate temperature of 500 °C. The atomic hydrogen flow was generated by a hot filament, inside a high-vacuum chemical vapour deposition reactor, at a temperature of 1750 °C. In order to optimise the hydrogen hot-wire treatments, the H₂ pressure was varied between 1.3 and 67 Pa, the treatment time was monitored between 1 and 5 min and the hot-filament current was changed between 12 and 17 A. Dark conductivity was measured as a function of temperature and its value at room temperature was extrapolated and used to assess the effect of the hydrogen annealing on the charge transport properties. A two-order of magnitude increase in dark conductivity was typically observed for optimised hydrogen treatments (10 Pa), when varying the hydrogen pressure, resulting in a minimum resistivity of ~ 3 × 10^− 3 Ω cm at room temperature. The maximum amount of atomic H incorporation in oxygen vacancies was determined to be ~ 5.7 at.%. Carrier mobility and resistivity were also investigated using Hall effect measurements. Correlations between structural and electrical properties and the hydrogen treatment conditions are discussed. The purpose of these films is to provide a transparent and conductive front contact layer for a-Si based photovoltaics, with a refractive index that better matches that of single and tandem solar cell structures. This can be achieved by an appropriate incorporation of a very small amount of cationic doping (Nb^5 +) into the titanium dioxide lattice.     

Titanium diffusion in gold thin films

In the present study, diffusion phenomena in titanium/gold (Ti/Au) thin films occurring at temperatures ranging between 200 and 400 °C are investigated.The motivation is twofold: the first objective is to characterize Ti diffusion into Au layer as an effect of different heat-treatments. The second goal is to prove that the implementation of a thin titanium nitride (TiN) layer between Ti and Au can remarkably reduce Ti diffusion.It is observed that Ti atoms can fully diffuse through polycrystalline Au thin films (260 nm thick) already at temperatures as a low as 250 °C. Starting from secondary ion mass spectroscopy data, the overall diffusion activation energy ΔE = 0.66 eV and the corresponding pre-exponential factor D₀ = 5 × 10^− 11 cm²/s are determined. As for the grain boundary diffusivity, both the activation energy range 0.54 < ΔE_gb < 0.66 eV and the pre-exponential factor s₀D_gb0 = 1.14 × 10^− 8 cm²/s are obtained. Finally, it is observed that the insertion of a thin TiN layer (40 nm) between gold and titanium acts as an effective diffusion barrier up to 400 °C.     

Preparation of new proton exchange membranes using sulfonated poly(ether sulfone) modified by octylamine (SPESOS)

Sulfonated poly(arylene ether sulfone) (SPES) has received considerable attention in membrane preparation for proton exchange membrane fuel cell (PEMFC). But such membranes are brittle and difficult to handle in operation. We investigated new membranes using SPES grafted with various degrees of octylamine. Five new materials made from sulfonated polyethersulfone sulfonamide (SPESOS) were synthetized with different grades of grafting. They were made from SPES, with initially an ionic exchange capacity (IEC) of 2.4 meq g⁻¹ (1.3 H⁺ per monomer unit). Pristine SPES with that IEC is water swelling and becomes soluble at 80 °C, its proton conductivity is in the range of 0.1 S cm⁻¹ at room temperature in aqueous H₂SO₄ 1 M, similar to that of Nafion^®. After grafting with various amounts of octylamine, the material is water insoluble; membranes are less brittle and show sufficient ionic conductivity. Proton transport numbers were measured close to 1.     

Electrophoretic technique for hydrothermal synthesis of NaA zeolite membranes on porous α-Al2O3 supports

Uniform and dense NaA zeolite membranes were prepared on the α-Al₂O₃ support by electrophoretic technique. The membrane morphology and membrane thickness were investigated by XRD, SEM and pervaporation properties for dehydration of 95 wt.% isopropanol/water mixture at 343 K, respectively. Under the action of the applied electric field, the negatively charged zeolite particles could migrate to the support surface homogenously and rapidly, forming uniform and dense membranes in a short time. High quality NaA zeolite membrane, with a separation factor (water/isopropanol) of 3281 and a flux of 1.24 kg/m² h, could be prepared by electrophoretic technique with the electrical potential of 1 V. The formation mechanism of zeolite membrane in the electric field is discussed.     

A DNA‐Threaded ZIF‐8 Membrane with High Proton Conductivity and Low Methanol Permeability

Natural biomolecules have potential as proton‐conducting materials, in which the hydrogen‐bond networks can facilitate proton transportation. Herein, a biomolecule/metal–organic framework (MOF) approach to develop hybrid proton‐conductive membranes is reported. Single‐strand DNA molecules are introduced into DNA@ZIF‐8 membranes through a solid‐confined conversion process. The DNA‐threaded ZIF‐8 membrane exhibits high proton conductivity of 3.40 × 10^?4 S cm^?1 at 25 °C and the highest one ever reported of 0.17 S cm^?1 at 75 °C, under 97% relatively humidity, attributed to the formed hydrogen‐bond networks between the DNA molecules and the water molecules inside the cavities of the ZIF‐8, but very low methanol permeability of 1.25 × 10^?8 cm² s^?1 due to the small pore entrance of the DNA@ZIF‐8 membranes. The selectivity of the DNA@ZIF‐8 membrane is thus significantly higher than that of developed proton‐exchange membranes for fuel cells. After assembling the DNA@ZIF‐8 hybrid membrane into direct methanol fuel cells, it exhibits a power density of 9.87 mW cm^?2 . This is the first MOF‐based proton‐conductivity membrane used for direct methanol fuel cells, providing bright promise for such hybrid membranes in this application.     

Annealing effect on the performance of RuO2–Ta2O5/Ti electrodes for use in supercapacitors

The preparation of RuO₂–Ta₂O₅/Ti electrodes, by dip-coating, for use in supercapacitors was investigated. The stability and specific capacitance of the electrodes annealed at various temperatures was examined. The results show that highly stable electrodes with a specific capacitance of 170 F g RuO₂⁻¹ were obtained at approximately 250 °C, while electrodes with a lower capacitance (130 F g RuO₂⁻¹) were obtained at 300 °C. The annealing time needed to obtain a stable RuO₂–Ta₂O₅/Ti electrode at various temperatures correlates well with the Arrhenius’ law: with the activation energy (E) of the annealing reactions for the electrodes being estimated as 73.5 kJ mol⁻¹. SEM images of the electrodes show the coating films to have rough surface morphology with cracks 2–6 μm in width. XRD data indicate that the coating films obtained are composed of crystalline RuO₂ and amorphous tantalum oxide.     

Hydrogen permeability and effect of microstructure on mixed protonic-electronic conducting Eu-doped strontium cerate

The hydrogen permeability of SrCe^0.95Eu^0.05O^3−δ was studied as a function of temperature, hydrogen partial pressure (P^H2) gradient, and water vapor partial pressure (P^H2O) gradient. The effect of the microstructure on hydrogen permeability through a 1.72 mm thick membrane was investigated. The ambipolar conductivity calculated from hydrogen permeation fluxes showed the same P^O2 and P^H2 dependence as the electronic conductivity, for the experimental conditions. The small grained membrane showed higher hydrogen permeability when compared with the larger grained membrane over the entire temperature range investigated.     

Synthesis of Fe/SiO2 composite particles and their superior electromagnetic properties in microwave band

Fe/SiO₂ composite particles were synthesized by hydrogen reduction of Fe₂O₃/SiO₂ precursor, which was prepared by sol-gel method. A reduction temperature higher than 600 °C is required for the complete conversion of Fe₂O₃ to Fe. Fe/SiO₂ composite particles exhibit superior complex permittivity and permeability in the microwave band. A reflection loss higher than − 70 dB as well as a broad absorption band can be simultaneously obtained for Fe/SiO₂-based coatings about 2 mm in thickness, suggesting that the Fe/SiO₂ composite particles are a promising candidate for high performance electromagnetic absorption materials.     

Research on the hot deformation behavior of Ti40 alloy using processing map

The deformation behavior of a Ti40 titanium alloy was investigated with compression tests at different temperatures and strain rates to evaluate the activation energy and to establish the constitutive equation, which reveals the dependence of the flow stress on strain, strain rate and deformation temperature. The tests were carried out in the temperature range between 900 and 1100 °C and at strain rates between 0.01 and 10 s⁻¹. Hot deformation activation energy of the Ti40 alloy was calculated to be about 372.96 kJ/mol. In order to demonstrate the workability of Ti40 alloy further, the processing maps at strain of 0.5 and 0.6 were generated respectively based on the dynamic materials model. It is found that the dynamic recrystallization of Ti40 alloy occurs at the temperatures of 1050-1100 °C and strain rates of 0.01-0.1 s⁻¹, with peak efficiency of power dissipation of 64% occurring at about 1050 °C and 0.01 s⁻¹, indicating that this domain is optimum processing window for hot working. Flow instability domains were noticed at higher stain rate (≥1 s⁻¹) and stain (≥0.6), which located at the upper part of the processing maps. The evidence of deformation in these domains has been identified by the microstructure observations of Ti40 titanium alloy.     

Effect of blending ratio on pervaporative separation of 1,4-dioxane/water mixtures through PVA-PEI membranes

Blend membranes were made by mixing aqueous solutions of hydrophilic polymers poly(vinyl alcohol) (PVA) and polyethyleneimine (PEI) in different ratios for investigating the separation of 1,4-dioxane/water azeotropic mixture by pervaporation (PV). Water forms azeotrope at 18 wt% concentration with 1,4-dioxane. The resulting membranes were characterized by FTIR to verify the interaction between the homopolymers, wide-angle X-ray diffraction (WAXD) to observe the effect of blending on crystallinity and thermal gravimetric analysis (TGA) to investigate the thermal stability. Sorption studies were carried out to evaluate the extent of interaction and degree of swelling of the blend membranes in pure liquids as well as binary mixtures. The effect of blend composition ratio on membrane parameters such as flux and selectivity was analyzed. An increase in PVA content in the blend caused a reduction in the flux and an increase in selectivity. Among the blends tested in the study, the 5:1 PVA/PEI blend membrane showed the highest separation factor of 44.01 and exhibited a flux of 0.733 kg/m² h 10 μm for azeotropic feed composition at ambient temperature (30 °C).     

Oxygen permeation and electrical transport of Gd1−xPrxBaCo2O5 + δ dense membranes

Double-perovskite Gd_1−xPr_xBaCo₂O_5 + δ membranes showed appreciable oxygen permeability at moderate temperatures. The overall oxygen permeation process of GdBaCo₂O_5 + δ was found to be controlled mainly by the bulk diffusion step with the membrane thickness larger than 0.8 mm, and the limitation by oxygen surface exchange came into play at reduced thickness of 0.8 mm. The electrical conductivity measurement showed Gd_1 - xPr_xBaCo₂O_5 + δ samples possessed a semiconducting behavior at a wide temperature range below 300 °C and a metallic behavior at 300-850 °C with a high conductivity of nearly 10³ S cm^− 1.