Thermally rearranged (TR) HAB-6FDA nanocomposite membranes for hydrogen separation

Thermally rearranged (TR) polymers exhibited a good balance of high permeability and high selectivity. For this purpose HAB-6FDA polyimide was synthesized from 3,3 dihydroxy-4,4-diamino-biphenyl (HAB) and 2,2-bis-(3,4-dicarboxyphenyl) hexafluoro propane dianhydride (6FDA) by chemical imidization. Initially, the sample was modified from pure polymer to silica nanofiller doped polymer membrane. Further the modification was done by thermal rearrangement reaction at 350 °C temperature. This modification causes a mass loss in polymer structure and therefore enhances the fractional free volume (FFV). The gases used for the permeation test were H₂, CO₂, N₂ and CH₄. Selectivity was calculated for H₂/CO₂, H₂/N₂ and H₂/CH₄ gas pairs and plotted in the Robeson's 2008 upper bound and compared with reported data. The transport properties of these gases have been compared with the unmodified membrane. Permeability of all the gases has increased to that of unmodified polymer membrane. Thermally rearranged polymer nanocomposite exhibits higher gas permeability than that of silica doped and pure polymer. Also the selectivity for H₂/CO₂ and H₂/N₂ gas pairs exceeds towards Robeson's upper bound limit. It crosses this limit dramatically for H₂/CH₄ gas pair. Polymer nanocomposite can be utilized to obtain high purity hydrogen gas for refinery and petrochemical applications.     

Enhanced performance of DMFC prepared by 10Cu/CeO2 catalyst and nanocomposite SPVA membranes with layer-by-layer coating of polyacrylic acid and chitosan

In the present study, TiO₂ nanoparticles are used as inorganic nanofiller material to prepare nanocomposite proton exchange membrane (PEM). Sulfonated polyvinyl alcohol (SPVA) is synthesized by 4-formylbenzene-1,3-disulfonic acid disodium salt hydrate and water. The cross-linking reaction is performed by glutaraldehyde. These membranes were then dip coated with polyacrylic acid and chitosan alternately and one layer-by-layer (LBL), two LBL and three LBL membranes were prepared. The chemical structure evaluation of SPVA membrane is performed using FTIR. The direct methanol fuel cell (DMFC) catalysts of 10Cu/CeO₂ and 10 Pt-10 CeO₂/C were prepared by reduction reaction and hydrothermal technique. Thus obtained material was spin coated on 2 × 2 cm² carbon paper to prepare catalyst anode/cathode. The morphology, size, and purity of catalyst particles are analysed by SEM, UV–visible spectroscopy, FTIR and EDS. Electrochemical analysis is also done to test the performance. Results show that Cu/CeO₂ catalyst shows excellent catalysis towards methanol oxidation, which is better than 10 Pt-10 CeO₂/C particles. The 10Cu/CeO₂ catalyst gives peak voltage of 915 mV for infinite resistance, which is higher than the reported value of the conventional 20 Pt/C catalyst (810 mV).     

Fast mass and charge transport through electrically aligned CNT/polymer nanocomposite membranes

This work represents the properties of electrically aligned carbon nanotubes (CNT)/polycarbonate (PC) nanocomposites towards the development of hydrogen gas separation membranes. A fraction (0.1 weight %) of CNTs synthesized by chemical vapour deposition method have been dispersed homogeneously throughout PC matrix by ultrasonication. The alignment of CNT in PC matrix has been accomplished by applying an external electric field of 1250 V/cm during solution casting. These nanocomposites have been studied by gas permeation, electrical, and dielectric constant measurements. Gas permeability measurements obtained here that electrically aligned nanocomposite membranes can be used as good hydrogen separating media. I–V characteristics and dielectric constant shows the enhancement in conductivity and permittivity of these nanocomposites. Overall experimental results exhibit here that alignment of CNTs in polymer matrix shows the dramatic improvement in mass and charge transport properties. Copyright © 2016 John Wiley & Sons, Ltd.     

Nanofiller incorporated poly(vinylidene fluoride–hexafluoropropylene) (PVdF–HFP) composite electrolytes for lithium batteries

Composite polymer electrolyte (CPE) membranes, comprising poly(vinylidene fluoride–hexafluoropropylene) (PVdF–HFP), aluminum oxyhydroxide (AlO[OH]_n) of two different sizes 7 μm/14 nm and LiN(C₂F₅SO₂)₂ as the lithium salt were prepared using a solution casting technique. The prepared membranes were subjected to XRD, impedance spectroscopy, compatibility and transport number studies. Also Li Cr_0.01Mn_1.99O₄/CPE/Li cells were assembled and their charge–discharge profiles made at 70 °C. The incorporation of nanofiller greatly enhanced the ionic conductivity and the compatibility of the composite polymer electrolyte. The film which possesses a nanosized filler offered better electrochemical properties than a film with micron sized fillers. The results are discussed based on Lewis acid–base theory.     

Palladium composite membrane fabricated on rough porous alumina tube without intermediate layer for hydrogen separation

A thin palladium composite membrane without any modified layer was successfully obtained on a rough porous alumina substrate. Prior to the fabrication of palladium membrane, a poly(vinyl) alcohol (PVA) layer was first coated onto the porous substrate by dip-coating technique to improve its surface roughness and pore size. After deposition of palladium membrane on the PVA modified substrate, the polymer layer can be completely removed from the composite membrane by heat treatment. The microstructure of the palladium composite membrane was characterized in detail using SEM, EDXS and XRD analysis. Permeation measurements were carried out using H₂ and N₂ at temperatures of 623 K, 673 K, 723 K and 773 K. The results indicated that the hydrogen permeation flux of 0.238 mol m^?2 s^?1 with H₂ separation factor α(H₂/N₂) of 956 for the as-prepared palladium membrane was obtained at 773 K and 100 kPa. Furthermore, the good membrane stability was proven during the total operation time of 160 h at the temperature range of 623 K–773 K and gas exchange cycles of 30 between hydrogen and nitrogen at 723 K.     

Quaternized poly(vinyl alcohol)/alumina composite polymer membranes for alkaline direct methanol fuel cells

The quaternized poly(vinyl alcohol)/alumina (designated as QPVA/Al₂O₃) nanocomposite polymer membrane was prepared by a solution casting method. The characteristic properties of the QPVA/Al₂O₃ nanocomposite polymer membranes were investigated using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), micro-Raman spectroscopy, and AC impedance method. Alkaline direct methanol fuel cell (ADMFC) comprised of the QPVA/Al₂O₃ nanocomposite polymer membrane were assembled and examined. Experimental results indicate that the DMFC employing a cheap non-perfluorinated (QPVA/Al₂O₃) nanocomposite polymer membrane shows excellent electrochemical performances. The peak power densities of the DMFC with 4 M KOH + 1 M CH₃OH, 2 M CH₃OH, and 4 M CH₃OH solutions are 28.33, 32.40, and 36.15 mW cm⁻², respectively, at room temperature and in ambient air. The QPVA/Al₂O₃ nanocomposite polymer membranes constitute a viable candidate for applications on alkaline DMFC.     

Hydrogen storage properties of magnesium nanotrees investigated by a quartz crystal microbalance system

We report enhanced low temperature hydrogen storage properties of magnesium “nanotrees” fabricated by glancing angle deposition (GLAD) method. The arrays of nanotrees and conventional thin films of elemental Mg have been deposited directly onto gold coated unpolished quartz crystal substrates. Mg nanotrees were about 15 μm in height, 10 μm by 1 μm in lateral size, and were composed of “nanoleaves” of about 20 nm in thickness, 2 μm length, and 1 μm width. Hydrogen absorption and desorption properties of Mg nanotrees and thin films were investigated using a quartz crystal microbalance (QCM) testing system that is capable of measuring weight changes with a nanogram sensitivity. QCM absorption tests were performed at temperatures 100, 200, and 300 °C under 30 bars of H₂ pressure. Measurements revealed that Mg nanotrees can absorb hydrogen at significantly higher weight percentage (wt%) and faster rates compared to conventional Mg films under similar conditions. Hydrogen storage of Mg thin film was observed to be at 0.02, 0.30 and 3.91 wt% (weight percentage), while it reached to 1.26, 3.75, and 5.86 wt% for nanotrees at temperatures 100, 200, and 300 °C, respectively, after 150 min. In addition, the results of desorption experiments show that Mg nanotrees can start to release hydrogen at temperatures as low as 100 °C at a rate of 0.11 wt% (vs. 0.01 wt% for thin film at the same temperature) with desorption rates reaching to 1.05 wt% at 200 °C (0.26 wt% for thin film) and 2.57 wt% at 300 °C (1.45 wt% for thin film), which are considerably lower desorption temperatures compared to previously reported values for bulk Mg (>300 °C). The enhancement in hydrogen absorption and desorption properties of Mg nanotrees is believed to originate from their thin and isolated nanoleaves that also have an improved oxidation resistance property.     

Preparation and characterization of multi-walled carbon nanotube/PBNPI nanocomposite membrane for H2/CH4 separation

By combining organic polymers normally used to make membrane filters with inorganic substances, multi-walled carbon nanotube (MWCNTs), an extraordinary ability to separate H₂ from CH₄ was developed in this study. A series of MWCNTs/PBNPI nanocomposite membrane with a nominal MWCNTs content between 1 and 15 wt% were prepared by solution casting method, in which the very fine MWCNTs were embedded into glassy polymer membrane. Detailed characterizations, such as morphology, thermal stability and crystalline structure have been conducted to understand the structures, composition and properties of nanocomposite membranes. The results found that this new class of membrane had increased permeability and enhanced selectivity, and a useful ability to filter gases and organic vapours at the molecular level.     

PVDF-HFP/PET/PVDF-HFP composite membrane for lithium-ion power batteries

In this study, a novel polymer electrolyte composite membrane is successfully fabricated using electrospinning and solution casting. The composite membrane comprises two microporous poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) layers plus an intermediate quaternary ammonium-containing SiO₂ nanoparticles modified polyethylene terephthalate (PET) nanofibrous nonwoven to form a sandwiched PVDF-HFP/PET/PVDF-HFP composite, which is employed as a separator for lithium-ion batteries (LIBs). The properties of the PET composite membrane are compared with those of commercial PE separator, such as the morphologies, physical properties, and electrochemical performances. According to our results, the composite membrane demonstrates superior thermal stability (thermal shrinkage ～8%), electrolyte-philicity (contact angle ～2.9°), electrolyte uptake and retention (282%, 74%), and ionic conductivity (～10^?3 S cm^?1). The separators are assembled into Li/LiFePO₄ cells for electrochemical tests, showing that the PET composite membrane cells exhibit higher capacities than those with the PE separator at 0.2–10C both at 25 °C and 55 °C. The discharge capacity retention and coulombic efficiency of the PET composite membrane cells at 1C/1C for 200 cycles can be respectively enhanced about 20% and 2% at 55 °C as compared to the PE separator cells. These results demonstrate that our prepared PET composite membrane is highly promising for LIB applications.     

Water-stable crosslinked sulfonated polyimide–silica nanocomposite containing interpenetrating polymer network

Sulfonated polyimide (SPI) interpenetrating polymer network (IPN) (IXSPI)–silica (SiO₂) nanocomposite membranes were fabricated as proton conducting solid electrolytes for fuel cells. Urethane acrylate non-ionomers (UANs) were used as dispersants to homogeneously distribute nanosized SiO₂ and, simultaneously, as crosslinkers to induce IPN structure formation. IXSPI–SiO₂ nanocomposite membranes showed high proton conductivity and hydrolytic stability, and low methanol permeability as compared with those of pristine SPI. Interestingly, the casting solvent for membrane fabrication influenced membrane performances, especially proton conductivity. In particular, dimethyl sulfoxide exhibited a strong interaction with sulfonic acid groups in the polymer matrix, which hindered them from spontaneously releasing protons and reduced the proton conductivity and electrochemical performances of the resulting membranes. Crosslinkers with long polyethylene oxide chains also contributed to improved proton conductivity and increased single cell performances.     

Fabrication of TiN inverse opal structure and Pt nanoparticles by atomic layer deposition for proton exchange membrane fuel cell

A titanium nitride (TiN) inverse opal structure was fabricated on carbon paper as a support of Pt for application in proton exchange membrane fuel cell (PEMFC). Polystyrene spheres with different diameters were coated on carbon paper by spin coating in multilayers as a template. Titanium dioxide (TiO₂) thin film was then deposited on the template by atomic layer deposition (ALD). The TiN inverse opal structure was fabricated by direct nitridation of TiO₂ in flowing ammonia atmosphere at above 800 °C. Platinum nanoparticles were then deposited uniformly on TiN by ALD. The performances of PEMFC using Pt@TiN@carbon paper composite as electrodes were examined. The homemade electrodes showed at least 13 times higher platinum specific power density than commercial E-Tek electrodes.     

Free-standing SnO2/MWCNT nanocomposite anodes produced by different rate spin coatings for Li-ion batteries

Free standing SnO₂/multiwalled carbon nanotube (MWCNT) nanocomposite anode materials were prepared for Li-ion batteries by sol–gel technique. Firstly, SnO₂ precursor sols were synthesized after removing chloride ions. Then the sols coated on MWCNT buckypapers, which used as substrates to form nanocomposite electrodes by spin coating method. Sintered nanocomposite structures were then characterized by field emission gun-scanning electron microscopy (FEG-SEM), energy dispersive X-ray spectrometer (EDS), and X-ray diffraction (XRD) analyses. Electrochemical tests were performed for the produced electrodes, assembled as CR2016 cells. The effect of spin rate on the anode capacity was investigated. Coating on the MWCNT buckypapers was thought to use as mechanical support to prevent electrode failure and prevented the formation of cracks of the sol–gel thin film on the MWCNT surfaces. The results showed beneficial effects to prevent mechanical disintegration and subsequent anode pulverization of SnO₂ anodes because of huge volume increase during lithium intercalation. The results indicated that the nanocrystalline SnO₂/MWCNT composites are suitable for applying as an anode electrode for Li-ion batteries to increase electrochemical energy storage performance.     

Potential of sodium alginate/titanium oxide biomembrane nanocomposite in DMFC application

A proton exchange membrane was synthesized consuming a sodium alginate biopolymer as the matrix and titanium oxide as the nanofiller. The titanium oxide content varied from 5 to 25 wt%. The biomembrane nanocomposite performs better than the pristine sodium alginate membrane based on liquid uptake, methanol permeability, proton conductivity, ion exchange capacity, and oxidative stability outcomes. The unique properties of sodium alginate and titanium oxide lead to outstanding interconnections, thus producing new materials with great characteristics and enhanced performance. The highest proton conductivity achieved in this study is 17.3 × 10^‐3 S cm^‐1, which performed by SAT5 (25 wt%) membranes at 70°C. An optimal content of titanium oxide enhances the conductivity and methanol permeability of the membrane. Additionally, the hydrophilicity of pure sodium alginate is greatly reduced and achieves a good liquid uptake capacity and swelling ratio. The characteristics of the SA/TiO₂ biomembrane nanocomposite were determined with field emission scanning electron microscope, Fourier transform infrared, X‐ray diffraction, thermal gravimetric analysis/differential scanning calorimetry, and mechanical strength analysis.     

Nucleate Pool Boiling Heat Transfer of Hydro-Fluorocarbon Refrigerant R134a on TiO2 Nanoparticle Coated Copper Heating Surfaces

ABSTRACT

Pool boiling heat transfer performance of hydro-fluorocarbon refrigerant R-134a on titanium dioxide (TiO₂) nanoparticle coated surface is experimentally studied in the article. The test surfaces, viz, 100 nm, 200 nm and 300 nm thick TiO₂ nanoparticle coated surfaces over 100 nm thin film surface are used in this experimentation. The surfaces are synthesized and fabricated by simple and cost-effective electron beam evaporation method. The test surfaces were characterized by scanning electron microscope and atomic force microscope to uncover the formation of crystalline structure on coated surfaces. These surfaces are utilized in pool boiling test rig using refrigerant R134a at 10°C saturation temperatures. The result indicated that a maximum of 87.5% augmentation in the boiling heat transfer has been achieved by higher thickness of TiO₂ coated surface than the bare copper surface. In addition, the incipience wall superheat is reduced for higher thickness coated surface. The augmentation of heat transfer coefficient might be the reason for increase in micro/nano-porosity, active nucleation site density and surface area of the heating surface. It is observed that with the increase of sub-cooling temperature of liquid, the bubble departure diameter was reduced while the heat transfer coefficient has been increased.     

Double core-shell of Si@PANI@TiO2 nanocomposite as anode for lithium-ion batteries with enhanced electrochemical performance

A unique double core-shell structure of Si@PANI@TiO₂ nanocomposite is synthesized by a simple in-situ growth method. The two shells of polyaniline (PANI) and TiO₂, hand in hand, play a key role to improve the electrochemical performance: First, the flexible properties of polyaniline (PANI) effectively accommodate the volume change of Si during the cycling. Second, the good mechanical feature of TiO₂ can maintain the structural integrity and attenuate the volume expansion of Si cores. Finally, both of polyaniline and the lithiated TiO₂ enhance the conductivity of Si, which promotes the electrons transport. Resulting in the Si@PANI@TiO₂ double core-shell nanocomposite exhibits remarkable synergy in large, reversible lithium storage, delivering a reversible capacity as high as 1027 mAh g^?1 after 500 cycles and a superior rate capacity of 640 mAh g^?1, at a current of 500 and 4000 mA g^?1, respectively. This excellent cycling and high-rate capability can be ascribed to the unique and well-designed double core-shell structure with the synergistic effect between polyaniline (PANI) and TiO₂.     

High performance ceramic nanocomposite fuel cells utilizing LiNiCuZn-oxide anode based on slurry method

A multi-oxide material LiNiCuZn-oxide was prepared through a slurry method as an anode for ceramic nanocomposite fuel cell (CNFC). The CNFCs using this anode material, LSCF as cathode material and a composite electrolyte consisting of CaSm co-doped CeO₂ and (NaLiK)₂CO₃ produced ～1.03 W/cm² at 550 °C due to efficient reaction kinetics at the electrodes and high ionic transport in the nanocomposite electrolyte. The electrochemical impedance spectroscopy revealed low ionic transport losses (0.238 Ω cm²) and low polarization losses (0.124 Ω cm²) at the electrodes. The SEM measurements revealed the porous microstructures of the composite materials at electrode and the dense mixture of CaSm co-doped CeO₂ and (NaLiK)₂CO₃. The Brunauer-Emmett-Teller (BET) analysis revealed high surface areas, 4.1 m²/g and 3.8 m²/g, of the anode and cathode respectively. This study provides a promising material for high performance CNFCs.     

Facile fabrication and optimization of bowl-like ZnO/CdS nano-composite thin films with hierarchical nanopores and nano-cracks for high-performance photoelectrochemistry

A special nano-structured composite ZnO/CdS thin film with hierarchical nanopores and nano-cracks has been synthesized by a facile two-step method for the first time, in which both loadings of ZnO and CdS are optimized. We first fabricated the hierarchical nanoporous ZnO thin film through rapid gas/liquid interface assembly and layer-by-layer transfers of bowl-like ZnO nanoparticles for thirteen times. The ZnO nanobowls are prepared by a simple solution chemical reaction without using any templates. After annealing, the assembled ZnO film is sensitized with CdS nanoparticles by successive ionic layer adsorption and reactions for six cycles. Nano-cracks form for the ZnO/CdS nano-composite film by calcination, which is due to the different thermal expansion behavior between the ZnO film and the CdS layer. The facilely optimized ZnO/CdS films can serve as a promising photoanode in a photoelectrochemical cell, and it can generate a saturated photocurrent density as high as 7.8 mA cm^?2 at ?0.9 V (vs. Hg|Hg₂SO₄|saturated K₂SO₄) under visible light illumination of 100 mW cm^?2 in an aqueous solution of 0.5 M Na₂S, corresponding to a solar-to-electricity conversion efficiency of 6.6%.     

Enhanced photoelectrochemical hydrogen evolution at p-type CuBi2O4 photocathode through hypoxic calcination

Uniform p-type CuBi₂O₄ thin film was prepared through a spin coating method on fluorine-doped tin oxide (FTO) coated glass substrate, with a subsequent hypoxic post-annealing process under semi-sealed condition to enhance its photoelectrochemical efficiency for hydrogen evolution reaction. Compared to CuBi₂O₄ specimen annealed in open-air environment, the semi-sealed annealed CuBi₂O₄ photocathode presents a remarkable improvement in cathodic photocurrent, from 0.42 mA/cm² to 0.7 mA/cm² at 0.25 V_RHE. X-ray photoelectron spectroscopy study revealed that the electronic structure of CuBi₂O₄ film was significantly modified during the post-annealing process and higher carrier concentration was obtained through Mott-Schottky measurement on semi-annealed CuBi₂O₄. We also demonstrate that the synthesized CuBi₂O₄ film with a thin overlayer of sputtered TiO₂ can retain good stability and efficiency as a photocathode. This work provides insights into the mechanism of the high efficiency CuBi₂O₄ photocathode achieved from the unique post-annealing treatment.     

Enhanced ionic conductivity of yttria-stabilized ZrO2 with natural CuFe-oxide mineral heterogeneous composite for low temperature solid oxide fuel cells

We report for the first time that the commercial yttrium stabilized zirconia (YSZ) nanocomposite with a natural CuFe-oxide mineral (CF) exhibits a greatly enhanced ionic conductivity in the low temperature range (500–600 °C), e.g. 0.48 S/cm at 550 °C. The CF–YSZ composite was prepared via a nanocomposite approach. Fuel cells were fabricated by using a CF–YSZ electrolyte layer between the symmetric electrodes of the Ni_0.8Co_0.2Al_0.5Li (NCAL) coated Ni foam. The maximum power output of 562 mW/cm² has been achieved at 550 °C. Even the CF alone to replace the electrolyte the device reached the maximum power of 281 mW/cm² at the same temperature. Different ion-conduction mechanisms for YSZ and CF–YSZ are proposed. This work provides a new approach to develop natural mineral composites for advanced low temperature solid oxide fuel cells with a great marketability.     

Synthesis of MoS2 nanoparticle deposited graphene/mesoporous MnOx nanocomposite for high performance super capacitor application

The present study deal with the fabrication of low cost nanocomposite based electrodes based on Nickel foam binder free substrate for supercapacitor applications. The composition of nanocomposite is molybdenum sulphide nanoparticle/graphene coated on mesoporous manganese oxide. The first step is to involve the preparation of mesoporous manganese oxide by non-ionic surfactant assisted method. In the second stage is to deposit the reduced graphene on mesoporous manganese oxide in the presence of ultrasonic irradiation followed by addition of known quantity of commercial MoS₂ nanopowder (particle size below 90 nm). The manganese oxide based nanocomposite is showing porous architecture with graphene sheet formation together with MoS₂ nanoparticle deposition. N₂ adsorption-desorption Isotherm curves for MoS₂ nanoparticle (NP) modified graphene oxide/meso-MnO₂ and pure meso-MnO₂ displayed type IV isotherm with improved surface area values. The reduced graphene oxide (graphene) and MoS₂ exist in the form of glassy flaky morphology as well as tubular/needle shapes are obtained after the deposition process in the final nanocomposite. The orderly arranged and anchored nano-sized mesoporous manganese oxide nanocomposites are showed increased specific capacitance (up to 527, 727 and 1160 F/g) and continuous cyclic stability.