Microwave Absorption Studies on Superparamagnetic Conducting Nanocomposites as Signal Coating Materials

In this paper, preparation and characterization of superparamagnetic nanoparticles and their polymer composites prepared by varing doping level of conducting polymer and their microwave absorption studies at radar system in 8–12 GHz frequency range have been discussed. These composites are conducting polymers have been widely used because of their lower density as well their good environmental stability as in the case of polyaniline (PAN). In the present work, in situ polymerization of aniline was carried out in the presence of 30 mole% Fe₃O₄ nanoparticles to synthesize polyaniline/Fe₃O₄(PAN/Fe₃O₄) composites in epoxy resin matrix. The composites, thus synthesized have been characterized by infrared (IR) spectroscopy and X-ray diffraction. The morphology of these composites was studied by scanning electron microscopy. The measurement of % absorption was carried out in X and K band microwave region.     

Polystyrene-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite solid polymer electrolyte for lithium secondary battery

In a common salt-in-polymer electrolyte, a polymer which has polar groups in the molecular chain is necessary because the polar groups dissolve lithium salt and coordinate cations. Based on the above point of view, polystyrene [PS] that has nonpolar groups is not suitable for the polymer matrix. However, in this PS-based composite polymer-in-salt system, the transport of cations is not by segmental motion but by ion-hopping through a lithium percolation path made of high content lithium salt. Moreover, Al₂O₃ can dissolve salt, instead of polar groups of polymer matrix, by the Lewis acid-base interactions between the surface group of Al₂O₃ and salt. Notably, the maximum enhancement of ionic conductivity is found in acidic Al₂O₃ compared with neutral and basic Al₂O₃ arising from the increase of free ion fraction by dissociation of salt. It was revealed that PS-Al₂O₃ composite solid polymer electrolyte containing 70 wt.% salt and 10 wt.% acidic Al₂O₃ showed the highest ionic conductivity of 9.78 × 10^-5 Scm^-1 at room temperature.     

Electrospinning of poly(vinylpyrrodine) template for formation of ZrO2 nanoclusters for enhancing properties of composite proton conducting membranes

Nanosized ZrO₂ clusters were prepared by electrospinning a poly(vinylpyrrodine) (PVP)/ZrO₂ mixture for calcination to remove PVP template and sizing. The morphological, chemical, structural, and thermal resistance changes during preparation stages were investigated using scanning electron microscope, energy-dispersive X-ray spectroscopy, transmission electron microscope, X-ray diffraction, and thermogravimetric analysis. The obtained ZrO₂ clusters were used for preparation of nanocomposite membranes by dispersion in 2,6-pyridine polybenzimidazole (2,6-Py-PBI) matrix at 5?wt% content followed by phosphoric acid (PA) doping. The ZrO₂ nanoclusters were found to be uniformly distributed in 2,6-Py-PBI/PA matrix leading to a remarkable increase in the PA doping level and proton conductivity of the obtained composite membrane.     

Studies on proton conductivity of polyimide/H3PO4/imidazole blends

A new anhydrous proton conducting material based on polyimide(PI)/H₃PO₄/imidazole(Imi) Blends was prepared. FTIR spectrum shows the existence of hydrogen bonds between protonated and unprotonated imidazole units. The addition of phosphoric acid can accelerate the degradation process of PIs, while the addition of imidazole in PI/H₃PO₄ blends can improve their chemical oxidation stability enormously. The proton conductivity of PI/H₃PO₄ blends increases significantly with increasing content of imidazole. Proton conductivity of PI/xH₃PO₄/yImi membranes increases with increasing temperature and content of phosphoric acid. The experimental results show that it is possible to significantly improve the operating temperature of PEM fuel cell system by replacing water with imidazole as proton solvent in the polymer membrane. Hydrogen bond seems to play an important role in the proton conductivity of this system. The decrease of proton conductivity of imidazolium phosphate shows in some degree that the interaction between imidazole and phosphoric acid is not the main reason for the conductivity increment of imidazole doped PI/H₃PO₄ system.     

Effect of propylene carbonate on the ionic conductivity of polyacrylonitrile‐based solid polymer electrolytes

Solid polymer electrolyte membranes consisting of polyacrylonitrile (PAN) as a host polymer, ammonium nitrate (NH₄NO₃) as a complexing salt, and propylene carbonate (PC) as a plasticizer were prepared by a solution casting technique. An increase in the amorphous nature of the polymer electrolytes was confirmed by X‐ray diffraction analysis. A shift in the glass‐transition temperature of the PAN/NH₄NO₃/PC electrolytes was observed in the differential scanning calorimetry thermograms; this indicated interactions between the polymer and the salt. The impedance spectroscopy technique was used to study the mode of ion conduction in the plasticized polymer electrolyte. The highest ionic conductivity was found to be 7.48 × 10^?3 S/cm at 303 K for 80 mol % PAN, 20 mol % NH₄NO₃, and 0.02 mol % PC. The activation energy of the plasticized polymer electrolyte (80 mol % PAN/20 mol % NH₄NO₃/0.02 mol % PC) was found to be 0.08 eV; this was considerably lower than that of the film without the plasticizers. The dielectric behavior of the electrolyte is discussed in this article. A literature survey indicated that the synthesis and characterization of ammonium‐salt‐doped, proton‐conducting polymer electrolytes based on PAN has been rare. The use of the best composition membrane (80 mol % PAN/20 mol % NH₄NO₃/0.02 mol % PC) proton battery was constructed and evaluated. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41743.     

Anhydrous proton conductivity of KHSO4–H3PW12O40 composites and the correlation with hydrogen bonding distance under ambient pressure

Anhydrous proton conductive KHSO₄–H₃PW₁₂O₄₀ (KHS–WPA) composites were successfully synthesized using mechanochemical treatment. 95KHS·5WPA (mol%) composite, for example, showed very high anhydrous proton conductivity of 1.3 × 10⁻² to 2.4 × 10⁻³ S cm⁻¹ in a temperature range from 160 °C to 80 °C under ambient pressure. Chemical interactions via ion-exchange and hydrogen bond between KHS and WPA were confirmed from structural studies. Furthermore, the anhydrous proton conductivity of the KHS–WPA composites was well correlated with their estimated hydrogen bonding distance, indicating that reduction of the hydrogen bonding distance in the KHS–WPA composites is significant in the proton hopping to achieve anhydrous high proton conductivity.     

Plasticized chitosan-PVA blend polymer electrolyte based proton battery

This paper focused on the transport studies of PVA-chitosan blended electrolyte system and application in proton batteries. The electrolytes were prepared by the solution cast technique. In this work, 36 wt.% PVA and 24 wt.% chitosan blend doped with 40 wt.% NH₄NO₃ exhibited the highest room temperature conductivity. The conductivity value obtained was 2.07 × 10⁻⁵ S cm⁻¹. EC was then added in various quantities to the 60 wt.% [60 wt.% PVA-40 wt.% chitosan]-40 wt.% NH₄NO₃ composition in order to enhance the conductivity of the sample. The highest conductivity obtained was 1.60 × 10⁻³ S cm⁻¹ for the sample containing 70 wt.% EC. The Rice and Roth model was applied to analyze the conductivity enhancement. The highest conducting sample in the plasticized system was used to fabricate several batteries with configuration Zn//MnO₂. The open circuit potential (OCP) of the fabricated batteries was between 1.6 and 1.7 V.     

Electrochemical promotion of catalysis controlled by chemical potential difference across a mixed ionic-electronic conducting ceramic membrane – an example of wireless NEMCA

A La_0.6Sr_0.4Co_0.2F_0.8O₃ mixed ionic electronic conducting (MIEC) membrane was used in a dual chamber reactor for the promotion of the catalytic activity of a platinum catalyst for ethylene oxidation. By controlling the oxygen chemical potential difference across the membrane, a driving force for oxygen ions to migrate across the membrane and backspillover onto the catalyst surface is established. The reaction is then promoted by the formation of a double layer of oxide anions on the catalyst surface. The electronic conductivity of the membrane material eliminates the need for an external circuit to pump the promoting oxide ion species through the membrane and onto the catalyst surface. This renders this “wireless” system simpler and more amenable for large-scale practical application. Preliminary experiments show that the reaction rate of ethylene oxidation can indeed be promoted by almost one order of magnitude upon exposure to an oxygen atmosphere on the sweep side of the membrane reactor, and thus inducing an oxygen chemical potential difference across the membrane, as compared to the rate under an inert sweep gas. Moreover, the rate does not return to its initial unpromoted value upon cessation of the oxygen flow on the sweep side, but remains permanently promoted. A number of comparisons are drawn between the classical electrochemical promotion that utilises an external circuit and the “wireless” system that utilises chemical potential differences. In addition a ‚surface oxygen capture’ model is proposed to explain the permanent promotion of the catalyst activity.     

Polyacrylonitrile‐based proton conducting membranes containing sulfonic acid and tetrazole moieties

Proton conducting membranes based on polymers containing sulfonic acid and tetrazole moieties were developed. Successful syntheses of poly(acrylonitrile‐co ‐styrene sulfonic acid) (PAN‐co ‐PSSA), poly(acrylonitrile‐co ‐5‐vinyl tetrazole) (PAN‐co ‐PVTz), and poly(acrylonitrile‐co ‐5‐vinyl tetrazole‐co ‐styrene sulfonic acid) (PAN‐co ‐PVTz‐co ‐PSSA) were confirmed by ¹H‐nuclear magnetic resonance spectroscopy, elemental analysis, and Fourier transform infrared spectroscopy. Two approaches were performed to study the effects of molar ratio of sulfonic acid to tetrazole and tetrazole content on membrane properties. In the first approach, PAN‐co ‐PSSA was blended with PAN‐co ‐PVTz at three molar ratios. The second approach focused on PAN‐co ‐PVTz‐co ‐PSSA membranes with various tetrazole contents. PAN‐co ‐PSSA membrane was also prepared. All solution‐cast membranes were hydrolytically stable, except for PAN‐co ‐PVTz‐co ‐PSSA with 71% tetrazole. Surface morphologies of blend membranes were studied using scanning electron microscopy, and no phase separation was observed. Water uptake was shown to increase with increasing tetrazole. All membranes exhibited high thermal stability (up to 250 °C) and high storage moduli. Proton conductivity was found to depend significantly on relative humidity. The influences of sulfonic acid to tetrazole ratio and tetrazole content on proton conduction were observed and discussed. A maximum proton conductivity of 7.1 × 10^?3 S/cm at 26 °C was obtained from PAN‐co ‐PSSA membrane. In addition, all tested membranes showed relatively good oxidative stability after treatment in Fenton's reagent. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45411.     

Cs2.5H0.5PWO40/SiO2 as addition self-humidifying composite membrane for proton exchange membrane fuel cells

In this paper, we first reported a novel self-humidifying composite membrane for the proton exchange membrane fuel cell (PEMFC). Cs_2.5H_0.5PWO₄₀/SiO₂ catalyst particles were dispersed uniformly into the Nafion^® resin, and then Cs_2.5H_0.5PWO₄₀-SiO₂/Nafion composite membrane was prepared using solution-cast method. Compared with the H₃PWO₄₀ (PTA)_, the Cs_2.5H_0.5PWO₄₀/SiO₂ was steady due to the substitute of H⁺ with Cs⁺ and the interaction between the Cs_2.5H_0.5PWO₄₀ and SiO₂. And compared with the performance of the fuel cell with commercial Nafion^® NRE-212 membrane, the cell performance with the self-humidifying composite membrane was obviously improved under both humidified and dry conditions at 60 and 80 °C. The best performance under dry condition was obtained at 60 °C. The self-humidifying composite membrane could minimize membrane conductivity loss under dry conditions due to the presence of catalyst and hydrophilic Cs_2.5H_0.5PWO₄₀/SiO₂ particles.     

Electrochemical preparation and characterization of V2O5/polyaniline composite film cathodes for Li battery

Vanadium pentoxide/polyaniline (V₂O₅/PANi) composite films were prepared by a two-step electrochemical method and evaluated for their application in lithium batteries. As a first step the PANi film was potentiodynamically grown in an acid solution containing aniline monomer, and secondly vanadium oxide was oxidatively deposited on the polyaniline film in a temperature controlled VOSO₄ solution. The increased current efficiency obtained with the larger anodic current in the high temperature solutions results in high contents of V₂O₅ in the composites, even if the oxidative dissolution of PANi also occurs. The large value of the diffusion coefficient estimated from the cyclic voltammograms for the composite film provides evidence for the synergistic effect of the conducting polymer and the inorganic composite. The cell exhibited excellent cycle stability with a high charge storage capacity. The large increase in the specific capacity for the composite film prepared in this work demonstrates that the conducting polymer in the composite acts as a binding and conducting element by contributing its electroactivity. The V₂O₅/PANi composite film cathodes show a large specific capacity (ca. 270 mAh/g) and improved cyclability with an extremely small amount of capacity fading (ca. 3.4%) during repeated charge/discharge cycles.     

Preparation and Characterisation of Proton Exchange Membranes Based on Crosslinked Polybenzimidazole and Phosphoric Acid

Crosslinked polybenzimidazole (PBI) was synthesised via free radical polymerisation between N‐vinylimidazole and vinylbenzyl substituted PBI. The degree of crosslinking increases with increasing content of the crosslinker. The phosphoric acid doping behaviour, mechanical properties, proton conductivity and acid migration stability of crosslinked PBI and linear PBI are discussed. The results show that the acid doping ability decreases with increasing degree of crosslinking of PBI. The introduction of N‐vinylimidazole in PBI is beneficial to its oxidation stability. The mechanical stability of crosslinked PBI/H₃PO₄ membrane is better than that of linear PBI/H₃PO₄ membrane. The proton conductivity of the acid doped membranes can reach ∼10^–4 S cm^–1 for crosslinked PBI/H₃PO₄ composite membranes at 150 °C. The temperature dependence of proton conductivity of the acid doped membranes can be modelled by an Arrhenius relation. The proton conductivity of crosslinked PBI/H₃PO₄ composite membranes is a little lower than that of linear PBI/H₃PO₄ membranes with the same acid content. However, the migration stability of H₃PO₄ in crosslinked PBI/H₃PO₄ membranes is improved compared with that of linear PBI/H₃PO₄ membranes.     

Structure, transport properties and interfacial stability of PVdF/HFP electrolytes containing modified inorganic filler

Gel polymer electrolyte membranes composed of poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) and surface modified aluminum or titanium oxide were prepared according to the so-called Bellcore process. Modifications were done by impregnating ceramic powder with 1-8% sulphuric acid aqueous solutions. Filler grain size varied from 10 to 12 μm. The membranes were conditioned in liquid electrode—1 mol/l LiClO₄ in PC.The ionic conductivity of polymer membrane increased by more than one order of magnitude upon the addition of filler into polymer host. For electrolyte membrane containing modified aluminum or titanium oxide, the interfacial resistance is stable in time as opposed to unmodified gel electrolytes. An increase in lithium transference number is observed upon the addition of filler. Lithium transference number also increases with the fraction of acidic surface groups.     

Effect of Pore Structure on Proton Conductivity and Water Uptake in Nanoporous TiO<Subscript>2</Subscript>

This paper reports on an investigation involving water content, water properties and proton conductivity in nanoporous TiO₂ materials fabricated through sol-gel processing techniques. TiO₂ nanoparticles having a primary particle diameter of less than 5 nm are packed into xerogels at room temperature and at 50^∘C. The resulting xerogels are fired at temperatures of 200, 300 and 400^∘C to alter the structural properties of these materials. Further alteration in the surface chemistry of the pore walls of these materials are made by equilibrating these porous wafers at pH 1.5 and 4.0 using nitric acid. Porosity, pore size, and surface area are evaluated with nitrogen adsorption techniques. Water content is calculated using data from thermogravimetric methods and water adsorption isotherms. Proton conductivity is measured using impedance spectroscopy. Of all variables affecting water content, water structure, and proton conductivity, the pH of pre-equilibrating the fired xerogels is the most important. However, porous structures of TiO₂ arising from the open packing of nanoparticles, that have less tortuosity, are substantially different in the uptake of water with relative humidity than samples obtained from the close-packing of these same particles regardless of firing temperature. Also, the material with the smallest pore size (a close-packed structure fired at 200^∘C) has the highest proton conductivity when measured between 20–60% relative humidity making this system the most favorable in terms of proton exchange membrane systems. Lastly, it is interesting to note that the density of water in these pores can vary between 1.2 and 1.6 g/l which is different than the 1.0 g/l of bulk water. This result likely comes from a combination of surface charge and surface roughness that affects the structure of interfacial water. These findings have importance not only for proton exchange membrane systems but also for other membrane technologies, cements, sensors, fabrication of wetting surfaces and in other areas that might benefit from the use of nanoporous materials.     

Hydrodesulfurization of Dibenzothiophene Over Ni-Mo Sulfides Supported by Proton-Exchanged Siliceous MCM-41

Strong acid sites on the surface of mesoporous MCM-41 were generated by ion-exchanging siliceous MCM-41 with dilute HNO₃ solution (0.5 M). The XRF determination indicates that most of the sodium cations contained in MCM-41 can be removed by the proton exchange, and dealuminization was observed during the proton exchange. The acidity of the mesoporous materials was characterized by means of NH₃-TPD and the Hammett indicators. It is revealed that new strong acid sites (-5.6 > H₀ > -8.2) were generated after the first 2 h of ion exchange and that the following ion exchanges had little effect on the acidic properties. XRD patterns of the mesoporous materials indicate that the structure of siliceous MCM-41 was improved by HNO₃ ion exchange. When Ni-Mo sulfides were supported on the prepared solid acid (H⁺-MCM-41), high performance in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) was observed. However, the HDS activity was decreased while the selectivity of biphenyl (BP) was increased, when H⁺-Si-MCM-41 was ion exchanged with Na₂CO₃ aqueous solution. TPR profiles of the supported Ni-Mo oxides reveal that the acidic properties of the supports greatly influence the hydrogenation activities of the bimetallic oxides. The high performance of H⁺-MCM-41-supported Ni-Mo catalysts may be attributed to the enhanced hydrogenation activity. The introduction of Na cation into the support led to the decrease of the HDS activity due to the poor hydrogenation ability of the supported bimetallic oxides. The HDS activity is well correlated with the low H₂ consumption temperature in the TPR profiles.     

Partitioning of U(VI) and Eu(III) between Acidic Aqueous Al(NO3)3 and Tributyl Phosphate in n‐Dodecane

Abstract

The preferred approach to removing Al from Hanford tank sludges, based on aqueous alkaline leaching, often does not achieve complete success. Previous laboratory investigations on the treatment of Hanford tank sludge simulant samples indicate that an acidic scrub can enhance the dissolution of Al from various sludge matrices. If acidic leaching was deployed to enhance removal of tank waste residues, the resulting acidic Al(NO₃)₃ leachate solution could contain measurable amounts of solubilized transuranic elements and so would demand treatment prior to disposal. In this study, a liquid‐liquid extraction system for the decontamination of the HNO₃/Al(NO₃)₃ aqueous leachate by contact with 60% v/v tributyl phosphate (TBP)/n‐dodecane organic solution has been examined. The partitioning of U and Eu between the TBP phase and solutions of varying [HNO₃] and [Al(NO₃)₃] containing small amounts of Cr or ascorbic acid have been investigated._. The results indicate that >99% of both species could be removed from the aqueous phase using such a process.     

Effect of nano-porous Al2O3 on thermal, dielectric and transport properties of the (PEO)9LiTFSI polymer electrolyte system

Thermal, electrical conductivity and dielectric relaxation measurements have been performed on (PEO)₉LiTFSI+10 wt.% Al₂O₃ nano-porous polymer electrolyte system. It is observed that the conductivity enhances substantially due to the presence of the filler particles with different surface groups. The highest enhancement is found for the filler particles with acidic groups followed by basic, neutral, and weakly acidic. The results reveal that the filler particles do not interact directly with poly(ethelene) oxide (PEO) chains indicating that the main chain dynamics governing the ionic transport has not significantly affected due to the filler. The results are consistent with the idea that the conductivity enhancement is due to the creation of additional sites and favourable conduction pathways for ionic transport through Lewis acid-base type interactions between the filler surface groups and the ionic species. This is reflected as an increase in the mobility rather than an increase in the number of charge carriers. A qualitative model has been proposed to explain the results.     

CHITOSAN-BASED FUEL CELL MEMBRANES

Chitosan complex membranes are prepared and characterized at room temperature. They are expected to be used as proton exchange membranes. The studied membranes are cross-linked membranes with sulfuric acid; salt-complexed membranes with lithium nitrate; cross-linked and salt-complexed membranes; plasticized and salt-complexed membranes; cross-linked, plasticized, and salt-complexed membranes; and doped membranes with sulfuric acid. A fixed amount of ethylene carbonate is used as plasticizer. It is found that the ion exchange capacity and hydrogen gas permeability of all membranes is better than that of Nafion membranes. However, their proton conductivities are worse than Nafion membranes. It can be stated that ethylene carbonate does not improve conductivity. An optimum amount of lithium nitrate salt can enhance conductivity. The formation of a sulfate group in cross-linked membranes is necessary for proton conduction. The proton conductivities of 4%cross-linked and 50%LiNO₃ membrane before and after acid doping are (3.11±0.40) × 10^?2 and (6.64±0.11) × 10^?2 S cm^?1, respectively. That of Nafion is (8.02±1.19) × 10^?2 S cm^?1.     

Ionic Conductivity and Discharge Characteristic Studies of PVA-Mg(CH3COO)2 Solid Polymer Electrolytes

Ion conducting solid polymer electrolytes based on a polymer polyvinyl alcohol (PVA) complexed with magnesium acetate (Mg(CH₃COO)₂) were prepared by solution cast technique. Various experimental techniques, such as XRD, DSC, composition-dependent conductivity, temperature-dependent conductivity, and transport number measurements are used to characterize these polymer electrolyte films. The transference number data indicated the dominance of ion-type charge transport in these polymer electrolyte systems. An electrochemical cell with the configuration Mg/(80PVA + 20Mg(CH₃COO)₂)/(I₂ + C + electrolyte) has been fabricated and its discharge characteristics were studied. The Open Circuit Voltage (OCV) is 1.84 V.     

A new anhydrous proton conductor based on polybenzimidazole and tridecyl phosphate

Most of the anhydrous proton conducting membranes are based on inorganic or partially inorganic materials, like SrCeO₃ membranes or polybenzimidazole (PBI)/H₃PO₄ composite membranes. In present work, a new kind of anhydrous proton conducting membrane based on fully organic components of PBI and tridecyl phosphate (TP) was prepared. The interaction between PBI and TP is discussed. The temperature dependence of the proton conductivity of the composite membranes can be modeled by an Arrhenius relation. Thermogravimetric analysis (TGA) illustrates that these composite membranes are chemically stable up to 145 °C. The weight loss appearing at 145 °C is attributed to the selfcondensation of phosphate, which results in the proton conductivity drop of the membranes occurring at the same temperature. The DC conductivity of the composite membranes can reach ∼10⁻⁴ S/cm for PBI/1.8TP at 140 °C and increases with increasing TP content. The proton conductivity of PBI/TP and PBI/H₃PO₄ composite membranes is compared. The former have higher proton conductivity, however, the proton conductivity of the PBI/H₃PO₄ membranes increases with temperature more significantly. Compared with PBI/H₃PO₄ membranes, the migration stability of TP in PBI/TP membranes is improved significantly.