Maximum Conductivity Research Articles

Predicting of electrical conductivity for Polymer-MXene nanocomposites

The prediction of electrical conductivity in MXene nanosheet –polymer composites is a complex task that lacks a straightforward model. In this study, a model is proposed to predict the conductivity for the samples filled with MXene. Our proposed method takes into account various factors that influence the overall conductivity of the samples. The factors include the dimensions of MXene, volume fraction of MXene, percolation onset, tunnel distance, network fraction, and interphase thickness. The validity of the expressed method is examined using experimental data for several samples. Furthermore, an analysis of the relationship between the predicted conductivity and the parameters is conducted to confirm the reliability of the proposed methodology. The calculated outcomes from the proposed model exhibit a high level of accordance with the experimented conductivity of the samples. The maximum electrical conductivity of 16.1 S/m is achieved by the minimum tunneling distance of 1 nm, but the conductivity becomes very weak when tunneling distance in more than 11 nm.

Thermal control materials of carbon/SiO2 composites with a honeycomb structure.

Anisotropic composite thermal control materials show efficient thermal management ability, which can not only improve the heat flow in the direction of high thermal conductivity and prevent local overheating, but also reduce the heat flow in the direction of the low thermal conductivity and improve thermal insulation. In this paper, the anisotropic microstructure of natural wood (e.g. poplar) was used as a reference template. The filling of the SiO2 aerogel into the multi-layer pore structure and microtubule structure originally occupied by lignin was controlled by the process of the axial self-adsorption, limited sol-gel and natural drying. The anisotropic composite biomimetic thermal control materials were prepared by high temperature carbonization and the thermal control properties were evaluated. The anisotropic carbon/SiO2 (ACS) composite biomimetic thermal control material obtained after carbonization inherits the anisotropic microstructure. The axial thermal conductivity of the ACS composite biomimetic thermal control material is mainly determined by the thermal conductivity of the carbon composite microtubule structure. The SiO2 aerogel filled between carbon composite microtubules and the abundant axial microcracks endow the ACS composite biomimetic thermal control material with excellent radial thermal insulation performance. The maximum specific surface area of the ACS composite biomimetic thermal control material is 183 m2 g-1, and the maximum density is 517.8 ± 55.9 kg m-3. The maximum axial thermal conductivity of the ACS composite biomimetic thermal control material is 0.73 ± 0.07 W m-1 k-1, and the radial thermal conductivity is 0.28 ± 0.01 W m-1 k-1. The maximum ratio of the axial thermal conductivity to radial thermal conductivity of the ACS composite biomimetic thermal control material is 3.3.

Синтез углеродных нанотрубок с помощью СВЧ излучения для модификации эластомера с улучшенной электро- и теплопроводностью

The paper presents a method of microwave influence on ferrocene C10H10Fe and graphite to obtain multilayer carbon nanotubes (MWCNTs) — designed to improve the electrical and thermophysical properties of silicon-graphite elastomer (Silagerm 8020). Diagnostics and characterisation of the synthesised MWCNTs were carried out by energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. According to SEM data, it follows that the morphology of the synthesised MWCNTs has the form of filamentous formations intertwined in bundles with the diameter of individual MWCNTs from 40 to 60 nm and length up to several microns. At the same time, the surface of most of the MWCNTs is covered with a continuous layer of iron (Fe). The EDX method also confirmed the Fe and oxygen content on the surface of the MWCNTs. XRD method identified the presence of Fe in combination with carbon in the form of Fe3C iron carbide and pure Fe iron at 44.7°. The compound Fe3C, also referred to the active phase of Fe allowing the synthesis of MWCNTs. By increasing the concentration of MWCNTs in the elastomer, an increase in thermal conductivity with percolation transition was achieved at a concentration of 8 % MWCNTs. The maximum thermal conductivity of the nanomodified elastomer was 0.48 W/(m·°C), which corresponded to the mass concentration of MWCNTs equal to 8 wt.%. At the same time, the electrical conductivity of the composite, when the MWCNTs concentration was changed from 1 to 8 %, increased in the range from 4·10–5 to 2.4 cm·cm–1 and is also due to the percolation of MWCNTs in the elastomer matrix.

Vapor pressure deficit drives the mortality of understorey woody plants during drought recovery in the Atlantic Forest

AbstractQuestionDrought‐induced tree mortality has been documented in forests worldwide but the mechanisms related to drought recovery are still poorly understood. To better predict forest trajectories under future climate scenarios, it is essential to disentangle physiological mechanisms underlying plant mortality caused by El Niño droughts. Here, we assessed how vegetation structure, vapor pressure deficit (VPD), and functional traits interact to mediate tree mortality after a severe drought in a tropical forest.LocationMata das Flores State Park, an Atlantic Forest fragment in southeast Brazil.MethodsWe established 20 permanent plots with contrasting vegetation structure and topography. In each plot, we measured tree abundance and diameter at breast height (DBH) of every woody plant (1–10 cm diameter) at the end of the drought, and two years after the break of drought, to calculate mortality rates during drought recovery. Hydraulic (e.g., maximum stomatal conductance to water vapor, stomatal density, etc.) and economic traits (specific leaf area, wood density, etc.) were measured on the 10 most abundant species. We also measured local air temperature and air humidity using HOBO dataloggers in each plot to calculate the VPD.ResultsThe studied Atlantic Forest understorey did not recover from the 2014–2016 drought, in terms of tree mortality. Lower VPD, driven by big trees in the valley, protected understorey plants with acquisitive economic attributes and conservative hydraulic attributes against mortality. On the other hand, higher VPD, driven by smaller trees and higher stem density on the ridge and slope, increased the mortality of understorey plants with acquisitive attributes.ConclusionRidges represent the most important fraction of the Atlantic Forest and our results suggest this type of forest is at high climate risk due to global change. Altogether, our results highlight that valleys are microclimate refuges for understorey plants and might help mitigate drought impacts in tropical forest under forecasted climate changes.

Detection and photothermal inactivation of Gram-positive and Gram-negative bloodstream bacteria using photonic crystal biosensor and plasmonic core-shell.

Plasmonics and core-shell nanomaterials hold great potential to develop pharmaceuticals and medical equipment due to their eco-friendly and cost effective fabrication procedures. Despite these advancements, combating drug-resistant bacterial infections remains a global challenge. Therefore, this study aims to introduce a tailored theoretical framework for a one-dimensional (1D) photonic crystal biosensor (PCB) composed of (ZrO2/GaN)N/defect layer/(ZrO2/GaN)N, designed to detect Gram-positive and Gram-negative bloodstream bacteria employing the transfer matrix method (TMM). In addition, using the finite difference methods (FDM), the photothermal inactivation of bloodstream bacteria with plasmonic core-shell structures (FeO@AuBiS2) was explored using key factors such as light absorption, heat generation, and thermal diffusion. By incorporating six dielectric layers and contaminated blood into the proposed PCB, a maximum sensitivity of 562 nm per RIU was recorded, and using rod-shaped plasmonic core-shell structures, 5.8 nm-1 light absorption capacity and 152 K change in temperature were achieved. The maximum detection sensitivity, light absorption, heat conduction and heat convection capacity of the proposed 1D PCB and plasmonic core-shell show an effective approach to combating drug-resistant bacteria.

The shift current photovoltaic effect response in wurtzite and zinc blende semiconductors via first-principles calculations.

Recently, the search for materials with high photoelectric conversion efficiency has emerged as a significant research hotspot. Unlike p-n junctions, the bulk photovoltaic effect (BPVE) can also materialize within pure crystals. Here, we propose wurtzite and zinc blende semiconductors without inversion symmetry (AgI, GaAs, CdSe, CdTe, SiGe, ZnSe, and ZnTe) as candidates for achieving the BPVE and investigate the factors that affect the shift current. GaAs with a wurtzite structure exhibits the highest shift current value of 31.8 μA V-2 when spin-orbit coupling is considered. Meanwhile, the peak position of the maximum linear optical conductivity and shift current in the wurtzite structure is lower than that in the zinc blende structure. In addition, we also found that strong covalency within the same main axis group element significantly influences the shift current, exemplified by wurtzite SiGe, which exhibits 15.8 μA V-2. Our research highlights the importance of a smaller band gap, reduced carrier effective mass, and increased covalency in achieving a substantial shift current response. Ultimately, this study provides valuable insights into the interplay of the structural and electronic properties, offering directions for the discovery and design of materials with an enhanced BPVE.

Designing Self-Sustained Hydrogel Electrolytes for Aqueous, Transparent, and Flexible Batteries

The arrival of aqueous sodium-ion batteries has been an essential sustainable advancement in energy storage devices. The use of electrolytes based on polymeric hydrogel is emerging due to the facility in which they can be obtained as film, flexibility, and high ionic conductivity. Additionally, these electrolytes have a dual purpose by acting also as separators. This work deals with the preparation and characterization of hydrogels based on polyvinyl alcohol (PVA), sodium chloride (NaCl), and boric acid (H3BO3) to be used as electrolytes in transparent and flexible aqueous sodium-ion batteries. It was observed that lower amounts of NaCl yielded transparent and conductive gels, while increasing the amount of NaCl yielded translucent samples, due to the non-dissolved NaCl. The preparation, gelation step and electrode deposition were optimized to achieve the maximum transparency and conductivity. Subsequently, the selected electrolyte was applied in symmetric devices based on transparent nanocomposite films as electrodes. These devices demonstrated both high transparency and grand current rates. Furthermore, the performance of the electrolyte was verified in a flexible and symmetrical device, revealing an increased current, indicating improved electrode/electrolyte contact. This observation underscores the efficacy of hydrogels in enhancing device performance, particularly in flexible configurations.

In Silico Modeling and Validation of the Effect of Calcium-Activated Potassium Current on Ventricular Repolarization in Failing Myocytes.

The pathophysiological role of the small conductance calcium-activated potassium (SK) channels in human ventricular myocytes remains unclear. Experimental studies have reported upregulation of in pathological states, potentially contributing to ventricular arrhythmias. In heart failure (HF) patients, the upregulation of SK channels could be an adaptive physiological response to shorten the action potential duration (APD) under conditions of reduced repolarization reserve. In this work, we aimed at uncovering the contribution of SK channels to ventricular repolarization in failing myocytes. We extended an in silico electrophysiological model of human ventricular failing myocytes by including a representation of the SK channel activity. To calibrate the maximal SK current conductance (G SK), we simulated action potentials (APs) at different pacing frequencies and matched the changes in AP duration induced by SK channel inhibition or activation to available experimental data. The optimal value obtained for GSK was 4.288 μ S/ μF in mid-myocardial cells, and 6.4 μS/ μF for endocardial and epicardial cells. The simulated SK block-induced effects were consistent with experimental evidence. 1-D simulations of a transmural ventricular fiber indicated that SK channel block may prolong the QT interval and increase the transmural dispersion of repolarization, potentially increasing the risk of arrhythmia in HF. Our results highlight the importance of considering the SK channels to improve the characterization of HF-induced ventricular remodeling. Simulations across various scenarios in 0-D and 1-D scales suggest that pharmacological SK channel inhibition could lead to adverse effects in failing ventricles.

Proton conductivity of fluorite based rare earth titanates (LnxTi1-x)4O8-2x (Ln = Yb, Er, Ho, 0.667 ≤ x ≤ 0.765).

Solid solutions of rare earth titanates with high contents of rare earth oxides of up to 50-62% have been synthesized by the co-precipitation method and their structure, microstructure and conductivity in dry and wet air have been studied. Proton conductors have been found for the first time in solid solutions of rare earth titanates with a high content of Ln2O3 (>50%) with a nominal formula composition of (LnxTi1-x)4O8-2x (Ln = Yb, Er, Ho, 0.667 ≤ x ≤ 0.765). Among (LnxTi1-x)4O8-2x (Ln = Yb, Er, Ho, x = 0.684), (HoxTi1-x)4O8-2x (x = 0.684) showed the maximum conductivity in wet air. In this context, four additional compositions (HoxTi1-x)4O8-2x (x = 0.718, 0.734, 0.75, and 0.765) were synthesized in the holmium series. An increase in the holmium content leads to an increase in the proton transfer coefficients; at the same time, a more complex nature of the dependence of the conductivity under dry and wet atmospheres is observed. For the fluorite-like solid solution (HoxTi1-x)4O8-2x (0.701 ≤ x ≤ 0.765), the proton transfer coefficients were found to be ∼0.9 in the range of 200-450 °C. As the temperature continues to rise, the proton conductivity decreases quite sharply and the transfer coefficient becomes as low as 0.3 at 700 °C. The increase in proton conductivity in the Yb-Er-Ho series is associated with an increase in the hydrophilic properties of rare earth cations. In the (HoxTi1-x)4O8-2x (x = 0.667 ≤ x ≤ 0.765) series, the conductivity in wet air was ∼1 × 10-6 S cm-1 at 450 °C for most compositions. The conductivity of ceramics with x = 0.701 and 0.75 is about 2 times higher, which may be due to the optimal size of pyrochlore nanodomains in the fluorite matrix for x = 0.701 and the formation of pure fluorite for x = 0.75, respectively.

Impact of solution flow-rate on the microstructure and optoelectronic properties of Cu2ZnSnS4 thin films deposited via ultrasonic spray method

Cu2ZnSnS4 (CZTS) thin films were synthesized on glass substrates via ultrasonic spray pyrolysis method to investigate the influence of solution flow-rate on their physical properties. Solution flow-rate was varied in the range of 10–30 ml/h to analyse its impact on the films. XRD analysis revealed a kesterite phase with a preferred orientation along the (112) plane, which intensified with higher flow-rates. Additionally, structural investigations identified secondary phases of CuxS, Sn2S3, and Cu2SnS3 in the films prepared at a solution flow-rate of 25 ml/h. Raman spectroscopy confirmed the XRD analysis. SEM micrographs indicated compact growth with a slightly rough surface. UV–Vis spectroscopy demonstrated a significant decrease in transmittance, leading to a corresponding reduction in the bandgap value from 2.17 to 0.84 eV as the flow rate increased from 10 to 30 ml/h. The electrical conductivity analysis indicated p-type conductivity, with maximum conductivity value of 2.73 (Ω cm)−1 observed at a flow-rate of 20 ml/h.

On the influence of the coherence length on the ionic conductivity in mechanochemically synthesized sodium-conducting halides, Na3−xIn1−xZrxCl6

A decreasing coherence length with higher Zr content in ball milled Na3−xIn1−xZrxCl6 is observed, which leads to a negative correlation between the ionic conductivity and the material's coherence length.

Exploring Surfactant-Enhanced Stability and Thermophysical Characteristics of Water-Ethylene Glycol-Based Al2O3-TiO2 Hybrid Nanofluids

This study presents an empirical investigation into the impact of surfactant's enhanced stability and thermophysical characteristics of water-ethylene glycol (60:40) based Al2O3-TiO2 hybrid nanofluids. It aims to shed light on the nanofluid's behavior, mainly how surfactants affect its stability and thermal performance, thus contributing to advancements in heat transfer technology and engineering applications. The growing interest in nanofluids, which involves blending nanoparticles with conventional base fluids, spans diverse sectors like solar energy, heat transfer, biomedicine, and aerospace. In this study, Al2O3 and TiO2 nanoparticles are evenly dispersed in a DI-water and ethylene glycol mixture using a 50:50 ratio with a 0.1 % volume concentration. Three surfactants (SDS, SDBS, and PVP) are utilized to investigate the effect of the surfactants on hybrid nanofluids. The study examines the thermophysical characteristics of these hybrid nanofluids across a temperature range of 30 to 70 0C in 20 0C intervals to understand their potential in various industrial applications. The results show the highest stability period for nanofluids with PVP compared to nanofluids with surfactant-free and other surfactants (SDS, SDBS). The thermal conductivity is slightly decreased (max 4.61%) due to PVP surfactant addition compared to other conditions. However, the nanofluids with PVP still exhibit more excellent thermal conductivity value than the base-fluid and significantly reduced viscosity (max 55%). Hence, the enhanced thermal conductivity and reduced viscosity with improved stability due to PVP addition significantly impact heat transfer performance. However, the maximum thermal conductivity was obtained for surfactant-free Al2O3-TiO2/Water-EG-based hybrid nanofluids that reveal a thermal conductivity that is 17.05 % higher than the based fluid. Instead, the lower viscosity of hybrid nanofluids was obtained at 70 0C with the addition of PVP surfactant. Therefore, adding surfactants positively impacts Al2O3-TiO2/Water-EG-based hybrid nanofluids with higher stability, enhancing thermal conductivity and reducing viscosity compared to the based fluids. The results show that adding surfactants at a fixed volume concentration affects thermal conductivity at low temperatures and viscosity at high temperatures, suggesting that these fluids might be used as cooling agents to increase pumping power in industrial applications.

Borax cross-linked guar gum hydrogel-based self healing polymer electrolytes filled with ceramic nanofibers towards high-performance green energy storage applications

An inventive concept towards the implementation of green energy-storing devices is the synthesis of hydrogel-based gel electrolytes from biopolymers imbued with self-healing capabilities. However, these electrolytes have drawbacks, such as low mechanical stability due to inadequate cross-linking and limited ionic conductivity compared to synthetic polymers. This work develops and characterizes a flexible self-healing hydrogel polymer electrolytes (HPEs) based on guar gum (GG) hydrogel for use in energy storage devices. Hydrogel is prepared with silicon dioxide (SiO2) nanofibers dispersed into borax-bonding cross-linked guar gum. Propylene carbonate (PC) and diethyl carbonate (DC) in equal amounts and lithium perchlorate (LiClO4) are used as plasticizers and salt, respectively. It has been found that adding nanofibers to the hydrogel and spreading them there considerably increases the ionic conductivity as evaluated by ac impedance spectroscopy. When the nanofiber concentration is 5 wt% (wt%), the hydrogel electrolytes reach their maximum room temperature ionic conductivity of 4.3 × 10−3 S cm−1. XRD, FTIR, SEM, and XPS investigations are used to explain the enhanced conductivity caused by the dispersion of nanofibers. Nanofibers also improve the self-healing abilities of materials, as demonstrated by the fact that hydrogels loaded with 5 wt% nanofibers recover from deformation more quickly than hydrogels with lower nanofiber contents. Additionally, the dispersion of nanofibers enhances the hydrogel's mechanical and thermal properties. According to electrochemical investigations and linear sweep voltammetry (LSV) graphs, hydrogel electrolytes are stable up to 4.7 V. When compared to nanofiber-free hydrogels, nanofiber-integrated hydrogel electrolytes show more excellent interfacial stability. The developed self-healing hydrogel-based polymer electrolytes exhibit outstanding promise for a range of energy storage systems, opening the way for creating high-performance and environmentally friendly energy storage solutions.

Polypyrrole fabricated Laponite RD conductive nanocomposites: influence of grafting efficiency on structural and conductive properties.

In the present work novel conductive organic-inorganic nanocomposites were produced by grafting of pyrrole monomer onto silanized Laponite RD utilizing emulsion graft polymerization. Influence of some important factors like concentration of monomer, initiator and surfactant were investigated on grafting efficiency. Grafting of polypyrrole chains onto modified Laponite RD was verified by Fourier transform infrared spectroscopy (FT-IR). Scanning electron microscope (SEM) revealed the spherical particles of nanocomposite with average diameter of 271.5 nm. XRD pattern showed that molecular framework of pure polypyrrole almost remains same in nanocomposite. Surface area and pore volume of Laponite RD, measured by Brunauer-Emmett-Teller (BET) analysis, was also altered indicating effective grafting of polypyrrole chains onto modified substrate. Maximum grafting efficiency (%), determined gravimetrically, was 87.3% at monomer, initiator, and surfactant concentrations of 1.50, 1.00, and 0.50% respectively. Prepared nanocomposites with grafting efficiency of 87.3% have displayed maximum electrical conductivity of 0.23 × 10-2 Scm-1. These nanocomposites can be used for manifold applications like biomedical and energy storage devices.

Effect of the reinforcement phase on the electrical and mechanical properties of Cu–SWCNTs nanocomposites

In this research a pre-treatment of single-walled carbon nanotubes (SWCNTs) was performed to obtain Cu–SWCNTs composites by powder metallurgy technique. The SWCNTs were subjected to a chemical functionalization in acidic medium followed by a copper coating to improve their incorporation into the metal matrix. The results revealed a considerable inclusion of carboxyl, carbonyl and hydroxyl groups in the nanotubes, maintaining their structural integrity which was demonstrated by characterization using X-ray photoelectronic spectroscopy (XPS), scanning electron microscopy (SEM) and Raman spectroscopy techniques. The electroless process used allowed a complete reduction of copper sulfate to a metallic copper obtaining a suitable and homogeneous carbon nanotubes incorporation into the copper matrix. Microhardness measurements of the Cu–0.01 % SWCNT composite presented an improvement of 13 % compared with pure copper. Furthermore, this composite showed the best tribological properties obtaining a wear rate of 2.1 × 10−4 mm3/Nm, 18 % better than Cu, which was associated with the improved dispersion of the SWCNTs bundles into the matrix, and with a lower amount of surface defects. The maximum electrical conductivity obtained was 96 % IACS in the samples with the least amount of reinforcement phase which confirms their homogeneity into the copper matrix.

Effect of He diluted plasma on the deposition of flexible low-temperature polycrystalline silicon thin film

The growth of a low-temperature polycrystalline silicon (LTPS) thin film on a flexible polyethylene terephthalate (PET) substrate under the assistance of helium plasma has been examined in detail in this study. By utilizing the plasma enhanced chemical vapor deposition method, LTPS thin films are directly deposited on a PET substrate at a relatively low temperature (80 °C), and the variations in the morphology, structure, and electrical property of the samples with He flow are systematically characterized by performing a series of tests. The results show that the purely helium-diluted silane plasma has the function of inducing crystallization and fabricating the c-Si network. After optimizing the He flow rate to 600 SCCM, the LTPS thin film with the largest average grain size of ∼204.7 nm can be obtained, while the maximum dark conductivity (4.16 × 10−5 S/cm) is also achieved. Finally, a detailed discussion is presented to illustrate the growth mechanism of the LTPS thin film in He plasma.

Fabrication of electrically conductive interconnected microcellular thermoplastic elastomeric foam composite for absorption dominating electromagnetic interference shielding with ultra low reflection

AbstractThe elevated rates of electromagnetic radiation pollution, resulting from the growing need for wireless communication systems and electronic gadgets, have sparked interest in creating shielding materials that are lightweight, flexible, non‐corrosive, simply processable, and affordable. In this study, a collection of microcellular nanocomposites based on ethylene octane copolymer (EOC) were created utilizing Vulcan XC 72 conductive carbon black (VCB) by a dual mixing process involving both melt and solution mixing. A chemical blowing agent was utilized to induce the cellular architecture in the composite, resulting in its lightweight nature (maximum density of 0.65 g/cc). The composite foam, when loaded with 30 parts per hundred of volume (phr) of VCB, displays a conductive network and also achieves an electromagnetic interference (EMI) shielding efficiency of 23.2 decibels (dB), satisfying commercial requirements. Furthermore, the findings indicated that the composite's cellular structure significantly influences the absorption‐dominated EMI shielding mechanism with an absorption rate of 89%–94% and a specific shielding effectiveness of 194 dBcm2/g within the frequency range of 8.2–12.4 GHz (X band). The foam composite also demonstrated as a thermal management system, with a maximum thermal conductivity of 0.3 W/mK. As a result, this lightweight, easily processable, electrical conductive EOC/VCB polymer composite foams are projected to be used as EMI shielding materials in electronics, cars, and packaging.Highlights Fabrication of lightweight microcellular Carbon black‐loaded EOC composite Rheological, mechanical, and thermal properties of foam composites The cell density filled composites reduces by the cellular foam structures Carbon black pronouncedly enhanced the electrical conductivity of foam composite An absorption‐dominated shielding effectiveness with ultra‐low reflection.

Studies on sodium carboxymethyl cellulose + sodium triflate polymer electrolyte

AbstractThis paper presents the effect of salt concentration on the electrochemical, thermal, and structural properties of the solid polymer electrolyte (SPE) prepared with the polymer sodium carboxymethylcellulose (NaCMC) and the salt sodium triflate (NaCF3SO3). The electrolyte was prepared in the form of membranes using solution cast technique. Deionized water was used as a common solvent for both the precursor materials. The membranes were characterized using electrochemical impedance spectroscopy (EIS), Fourier‐transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), and differential scanning calorimetry (DSC). XRD results show reduction in crystallinity of the electrolyte with an increase in the salt concentration. The FTIR result confirms polymer‐salt interaction. The ionic conductivity of the electrolyte membrane was found to be dependent on the concentration of NaCF3SO3. The maximum ionic conductivity of the SPE membranes was observed to be 1 × 10−4 Scm−1 at room temperature (36°C). DSC results show an increase in glass transition temperature (Tg) with increasing salt concentration. The total ionic transference number of the highest conducting sample was found to be ~1, which shows that the conductivity of SPE membranes is predominantly due to the transport of ions.

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Development of Hydrophilic Oxide/Polymer Composite Membranes for Polymer Electrolyte Fuel Cells Operating at Wide Temperature Range

Toward the wide-spread use of heavy-duty vehicles (HDVs) operated by polymer electrolyte fuel cells (PEFCs) should approach the higher temperature around 120oC besides normal temperature (60-80oC). Commercial perfluorosulfonic acid-based electrolyte (PFSA, e.g. NafionⓇ) shows better proton conductivity with chemical stability in wide temperatures range, though decreases under low back pressure at 100~120 oC. In order to improve the proton conductivity at the higher temperature range, composite membrane of NafionⓇ with a hydrophilic filler of Ta doped TiO2 (Ta-TiO2) was synthesized. The Ta-TiO2 nanoparticles fillers with fused-aggregate network microstructure were synthesized by the flame method, and were crushed by wet mill(Star Burst, :Sugino Machine Limited CO.). The fillers were mixed with NafionⓇsolution (20 wt.%：D2020 Chemours Co.) by use of a rotary ultrasonic dispersing processor (500 rpm, 60 min. PR-1 :Thnky Co.), a planetary ball mill (500 rpm、30 min.：PULVERISETTE 6：FRITSCH Co.), and a defoaming processor (500 rpm、5 min.：HM-400W: Kyouritu Seiki). The dispersion solution was coated in hot air by use of a die coating system (die coater: Taku-Dai Mini-50: Daimon Co., Ltd.), and were hot-pressed (140 ℃ 3 min. TCMD-2.5:TOHO KOGYO co.) to form composite membranes (9 cm×9 cm ×25 µmt).The cross-sectional backscattered electron image BSE) of the composite membrane observed by scanning electron microscope (SEM, acceleration voltage 2 kV, SU9000: Hitachi High-Tech Co.) and transmission electron microscope (TEM, H-9500: Hitachi High-Tech Co.). The proton conductivity of the composite membrane was measured by the AC four-probe method. The current-voltage (IV) polarization curves of Single cells using the prepared composite membrane (membrane thickness: 25 µm) were measured at 80 ℃ 100% RH and 120 ℃ 20% RH, back pressure 50 kPaG.The obtained composite membranes were well flexibility with softness. The BSE images indicated that the high contrast images of Ta-TiO2 parties were uniformly dispersed in composite membrane. The higher magnified of the cross-sectional TEM images also showed that the hydrophilic surface of Ta-TiO2 adhered to the Nafion® without any air pores. The proton conductivity of the composite membrane at 80% RH increased with increasing Ta-TiO2 content and showed maximum value of 0.13 S cm-1at 3 wt%, and then decreased. The maximum proton conductivity was 1.3 times higher than that of Nafion®. The IV performance of the single cell using composite membrane kept same performance to that using Nafion® membrane at 80 oC 100% RH, and then improved at 120 oC 20% RH. The water content at 120 oC 20% RH kept higher value by the effect of hydrophilicity of the Ta-TiO2, which would be one of the reasons to enhance the cell performance at 120 oC 20% RH. Figure 1