Increase In Electronic Conductivity Research Articles

Graphene Nanosheets Suppress the Growth of Sb Nanoparticles in an Sb/C Nanocomposite to Achieve Fast Na Storage

Presently, graphene incorporation is one of the most effective strategies to develop superior electrode materials for sodium‐ion batteries (SIBs). Herein, it is excitingly found that an incorporated graphene nanosheet in the preparation processes can not only completely protect all the Sb nanoparticles in an Sb/C composite from being inactivated, but also suppresses their growth to undesirable micrometer size. While there are still many exposed Sb particulates on the surface of pristine Sb/C microplates, the graphene‐incorporated Sb/C/G nanocomposite consists of uniform Sb nanoparticles of 20–50 nm, all of which have been protected by and wrapped in the mixed carbon network. When used as anode materials for SIBs, the Sb/C/G nanocomposite exhibits the best Na‐storage properties in terms of the highest reversible capacity (650 mA h g−1 at 0.025 A g−1), fastest Na‐storage ability (290 mA h g−1 at a high current density of 8 A g−1), and optimal cycling performance (no capacity decay after 200 cycles), in comparison to pristine Sb/C and pure Sb. It is further revealed that the much enhanced performance should originate from the improvement of Na‐storage kinetics and increase of electronic conductivity via comparing the electrochemical impedance spectra, and cyclic voltammetry profiles, as well as the polarization variation along with current densities.

Composite MWCNT/carbon xerogel-nafion electrode for energy storage

In this paper, we report the preparation and characterization (morphological, structural, surface, and electrochemical) of multiwalled carbon nanotube (MWCNT)/carbon xerogel (CX) electrodes prepared by mixing. This research proposes the hypothesis that the use of a hydrophilic binder (nafion) and the use of MWCNTs enhance electrode capacitance and conductivity. Electrochemical measurements in 2 M NaCl solution were performed. The advantage of adding multiwalled carbon nanotubes to the array of xerogel-nafion was studied through different electrochemical methods. It was validated that the greater carbon nanotube mesoporosity allows less compaction of the electrode, thus effectively increasing the specific area and therefore capacitance. Furthermore, we observed the increase in electronic conductivity reported in numerous studies, a fact that is true for iR drop measurement cycles in both galvanostatic charging and discharging. The carbon composite proved to be viable for energy storage.

Electrochemical behavior of zinc in KOH media at high voltage: Micro-arc oxidation of zinc

Electrochemical behavior of pure zinc was studied in alkaline KOH-based media over a large range of voltage (0–300V) in order to investigate the occurrence of the micro-arc phenomenon, responsible for the formation of “ceramic-like” oxide layer. According to electrolyte composition, three anodizing steps can be observed, first, a classical anodizing process at low voltage, a voltage range of micro-arc phenomenon with a more or less intense water oxidation, and a sharp current rise corresponding to an increase of electronic conductivity of “metal/oxide/electrolyte” interface.Both KOH concentration and presence of additives in the electrolytic bath control the micro-arc voltage range, and the composition of anodized layer. Nevertheless, the internal layer of the coating remains mainly constituted by crystallized ZnO, formed by a mechanism of solid-state diffusion of O2− under electric field. Despite the significant coating thickness (several microns), the electrochemical characterization of the corrosion behavior in NaCl electrolyte only shows a slight improvement of the performances of the zinc anodized in presence of additives in KOH electrolyte, compared to an untreated one.

Slurry electrodes for iron plating in an all-iron flow battery

Slurry electrodes are investigated in order to decouple the energy storage capacity from the power delivery capability in an all-iron flow battery. For the slurry electrode to perform effectively, the battery negative reaction must occur on the slurry particles at reasonably high current densities. Mathematical modeling is used to investigate the current distribution in a slurry electrode as a function of the slurry specific area and electrical conductivity in order to achieve >95% plating in the slurry electrode (not on the flat plate) at > 200 mA cm−2. From the mathematical modeling, MWCNTs are selected to demonstrate slurry electrode performance. The experimental performance of all-iron batteries charged using the MWCNT slurry electrodes is found to improve while increasing the battery state-of-charge. Two possible mechanisms contributing to this effect are an increase in electronic conductivity of the slurry and an increase in plating kinetics. After cycling the battery, <5% of the total battery charge was observed to have plated onto the current collector.

Surprisingly High Conductivity and Efficient Exciton Blocking in Fullerene/Wide-Energy-Gap Small Molecule Mixtures.

We find that mixtures of C60 with the wide energy gap, small molecular weight semiconductor bathophenanthroline (BPhen) exhibit a combination of surprisingly high electron conductivity and efficient exciton blocking when employed as buffer layers in organic photovoltaic cells. Photoluminescence quenching measurements show that a 1:1 BPhen/C60 mixed layer has an exciton blocking efficiency of 84 ± 5% compared to that of 100% for a neat BPhen layer. This high blocking efficiency is accompanied by a 100-fold increase in electron conductivity compared with neat BPhen. Transient photocurrent measurements show that charge transport through a neat BPhen buffer is dispersive, in contrast to nondispersive transport in the compound buffer. Interestingly, although the conductivity is high, there is no clearly defined insulating-to-conducting phase transition with increased insulating BPhen fraction. Thus, we infer that C60 undergoes nanoscale (<10 nm domain size) phase segregation even at very high (>80%) BPhen fractions.

Al-doped SnO2 hollow sphere as a novel anode material for lithium ion battery

SnO2 hollow spheres are doped with different contents of Al (1, 1.5, 2at.%) by a one-step hydrothermal reaction. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and Brunauer–Emmett–Teller (BET) are utilized to characterize the structures, components, chemical environments, morphologies and specific areas of the as-prepared samples. The investigation in cycling performances demonstrates that 1.5at.% Al-doped SnO2 hollow spheres exhibit the best cycling stability, with a specific capacity of 443mAhg−1 and coulombic efficiency of 99.1% after 50cycles at 0.1C, much higher than those of the pristine SnO2 hollow spheres and the other Al-doped samples. The improved electrochemical performances of Al-doped SnO2 hollow spheres are attributed to the increase of electronic conductivity and lithium ion diffusion coefficient, and therefore, enhance the reversible capacity and cycling properties.

Structure and electrochemical properties of Sc3+-doped Li4Ti5O12 as anode materials for lithium-ion battery

Spinel Li4Ti5−xScxO12(x=0, 0.05, 0.10, 0.15) anode materials were successfully synthesized by a facile solid state reaction. The structure, morphology and electrochemical performance in a broad voltage window were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge–discharge tests in sequence. Li4Ti4.95Sc0.05O12 material exhibits excellent cycling stability and rate capability in relevant lithium-ion batteries, which can retain a capacity of 138.6mAhg−1 after 80 cycles at 2C charge–discharge rate. This performance is much better than that of pristine Li4Ti5O12 (121mAhg−1), whose capacity fades seriously. The improved electrochemical performance of Sc3+-doped Li4Ti5O12 can be ascribed to the reduction of charge transfer resistance, increase of electronic conductivity, and fast lithium ion diffusion behavior. Hence, Li4Ti4.95Sc0.05O12 can be considered as an economical and potential candidate as anode material for power lithium-ion batteries.

First-principles study on the electronic structure of Ti-doped NbSe2

Layered transition metal dichalcogenides (LTMDs) have renewed interest as electronic materials, but the poor conductivities hinder their further development. Chemical doping can often significantly modify atomic structures and electronic functionalities of a wide range of materials and thus acts as one of the most effective ways to precisely tune material properties for technological application. Here, the geometries and band structures as well as the densities of states of pure NbSe2 and Ti-doped NbSe2 nanostructure are studied by employing the ab-initio plane-wave ultra-soft pseudo potential technique based on the density functional theory. We optimize the ground state of NbSe2 in the layered structure by using the generalized gradient approximation for the exchange-correlation potential. The computational structural parameters are in good agreement with experimental values within 2.5%. To investigate the stability of the doped system with changing the concentration of Ti atoms, 2×2×1 2H-NbSe2 supercells are taken into consideration. Meanwhile, we consider a total of three possible Ti-doping models: substitution, intercalation, and embedded model, and investigate the energy band diagrams, state densities and densities of partial wave state diagram before and after the doping. The results show that the energy electron density of states reaches a higher peak, and the band structure near Fermi level (EF) is changed obviously, resulting in the variations of the band gap and EF position and then the increase of electronic conductivity after doping. In addition, our calculations also predict that the electron transport properties can be enhanced by doping Ti and it can be regarded as a useful way to tailor electronic states so as to improve electron transport properties of 2H-NbSe2. Such a remarkable modification of electronic structure of 2H-NbSe2 by chemical doping offers an additional way of modulating performances of LTMDs and developing new electrical contact composite materials.

Effects of Cu doped ZnO diluted magnetic semiconductors on magnetic and electrical performance from simulation and calculation

At present, the effects on the magnetic and electrical properties of Cu heavily doped ZnO with the mole amount of Cu being in a range of 0.02778-0.16667 are rarely studied by first-principles. Therefore two models for Zn1-xCuxO supercells (x=0.02778, 0.03125) are set up to calculate the band structures and density of states by using the plane-wave ultrasoft pseudopotential based on the spin-polarized density functional theory. The calculation results indicate that the doped systems are degenerate semiconductors, and they are semimetal diluted magnetic semiconductors. As the doping amount of Cu increases, the relative concentration of free holes increases, the effective mass of holes decreases, the electron mobility decreases and the electronic conductivity increases. These results are validated again by the analysis of ionization energy and Bohr radius, and they are consistent with the experimental data. As the doping amount of single-Cu increases from 0.02778 to 0.0625, the volume of doping system decreases, the total energy increases, the stability decreases, the formation energy increases and doping is more difficult. As the same concentration and the different doping modes for double-Cu doped, the magnetic moment of doping system first increases and then decreases with the increasing of spacing of Cu-Cu; while the bonds of nearest Cu–O–Cu lie along the a-axis or b-axis, the magnetic moment of doping system disappears; while the bonds of nearest Cu–O–Cu lie along the c-axis, the Curie temperature reaches a temperature above room temperature. As the doping amount of double-Cu increases from 0.0625 to 0.16667, the total magnetic moment of doping system first increases and then decreases, while the bonds of nearest Cu–O–Cu lie along the c-axis. The calculation results are consistent with the experimental data.

Improving the performance of high voltage LiMn1.5Ni0.5O4 cathode material by carbon coating

In this work, the high voltage LiMn1.5Ni0.5O4 cathode material has been synthesized as octadecahedron crystals with a disordered spinel structure and has been coated with a carbon layer from two different precursors (sucrose and Xerogel carbon) to improve its performance in Li-ion batteries. The effect of carbon coating on the physical and electrochemical properties of the crystals has been evaluated using X-ray diffraction (XRD), Infrared (IR) and Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), elemental and surface area (BET) analyses and battery cycling at different charge/discharge rates and temperatures. It was found that the amount of carbon, present as a thin layer (5–10 nm) and estimated at <1 w.t.%, causes an increase in electronic conductivity with no effect on crystal structure. Battery results of the cathode material in half cells show that carbon coating greatly improves the discharge capacity, rate capability at room temperature and 60 °C as well as cycling stability. Moreover, the material coated from Xerogel carbon shows the highest capacity at 10 C rate and 60 °C.

Surfactant for Enhanced Rheological, Electrical, and Electrochemical Performance of Suspensions for Semisolid Redox Flow Batteries and Supercapacitors

AbstractA suspension of Li4Ti5O12 and of Ketjen black in a solution of 1 M lithium bis(trifluoromethanesulfonyl)imide in propylene carbonate is studied as the anolyte for semisolid redox flow batteries. The rheological behavior and electronic conductivity are studied both at rest and under shear flow. The electrochemical behavior is evaluated at rest as a function of the charge/discharge rates and of the thickness of the suspension in the electrochemical cell. The highly beneficial influence of the addition of a non‐ionic surfactant in the composition of the suspension is demonstrated. All practical properties are improved with respect to semisolid redox flow applications. The viscosity decreases, the electronic conductivity increases and is less affected by the shear flow, and the electrochemical performance is improved. Moreover, the suspension shows much better stability, so its performance is preserved over time.

Preparation of polypyrrole-coated CuFe2O4 and their improved electrochemical performance as lithium-ion anodes

CuFe2O4 network, prepared via the electrostatic spray deposition technique, with high reversible capacity and long cycle lifetime for lithium ion battery anode material has been reported. The reversible capacity can be further enhanced by coating high electronic conductive polypyrrole (PPy). At the current density of 100 mA·g−1, Li/CuFe2O4 electrode delivers a reversible capacity of 842.9 mAh·g−1 while the reversible capacity of Li/PPy-coated CuFe2O4 electrode increases up to 1106.7 mAh·g−1. A high capacity of 640.7 mAh·g−1 for the Li/PPy-coated CuFe2O4 electrode is maintained in contrast of 398.9 mAh·g−1 for Li/CuFe2O4 electrode after 60 cycles, which demonstrates good electrochemical performance of the composite due to the increase of electronic conductivity. The electrochemical impedance spectroscopy (EIS) further reveals that the Li/PPy-coated CuFe2O4 electrode has a lower charge transfer resistance than the Li/CuFe2O4 electrode.

Molybdenum Doping of Li4Ti5O12 in a Reducing Atmosphere for High-Power Lithium Ion Batteries

Li4Ti5O12 (LTO) is recognized as being one of the most promising anode materials for high power Li ion batteries; however, its insulating nature is a major drawback. In recent years, a simple thermal treatment carried out in a reducing atmosphere has been shown to generate oxygen vacancies for increasing the electronic conductivity of this material. Such structural defects, however, lead to re-oxidization over time, causing serious deterioration in anode performance. Herein, we report a unique approach to increasing the electronic conductivity with simultaneous improvement in structural stability. Doping of LTO with Mo in a reducing atmosphere resulted in extra charges at Ti sites caused by charge compensation by the homogeneously distributed Mo6+ ions, being delocalized over the entire lattice, with fewer oxygen vacancies generated. Using this simple method, a marked increase in electronic conductivity was achieved, in addition to an extremely high rate capability, with no performance deterioration over time.

Stabilization of Oxygen-deficient Structure for Conducting Li4Ti5O12-δ by Molybdenum Doping in a Reducing Atmosphere

Li4Ti5O12 (LTO) is recognized as being one of the most promising anode materials for high power Li ion batteries; however, its insulating nature is a major drawback. In recent years, a simple thermal treatment carried out in a reducing atmosphere has been shown to generate oxygen vacancies (VO) for increasing the electronic conductivity of this material. Such structural defects, however, lead to re-oxidization over time, causing serious deterioration in anode performance. Herein, we report a unique approach to increasing the electronic conductivity with simultaneous improvement in structural stability. Doping of LTO with Mo in a reducing atmosphere resulted in extra charges at Ti sites caused by charge compensation by the homogeneously distributed Mo6+ ions, being delocalized over the entire lattice, with fewer oxygen vacancies (VO) generated. Using this simple method, a marked increase in electronic conductivity was achieved, in addition to an extremely high rate capability, with no performance deterioration over time.

First-principles study of the electronic structure and NO2-sensing properties of Ti-doped W18O49 nanowire

The geometry and band structures as well as the density of states of Ti-doped nonstoichiometric W18O49 nanowire are studied by employing the ab-initio plane-wave ultra-soft pseudo potential technique based on the density functional theory. Meanwhile, the adsorption and NO2-sensing properties of the doped nanowire are analyzed by further calculating the adsorption energy, planar averaged charge density difference and atomic Mulliken charge population of the NO2/Ti-W18O49 nanowire adsorption system. The results reveal that Ti-doping modifies the electronic structure and then the gas sensitivity of W18O49 nanowire obviously. After Ti-doping, new electronic states are introduced and the band structure near Fermi level (EF) is changed obviously, resulting in the variation of the band gap and EF position and then the increase of electronic conductivity. The adsorbed NO2 molecule acts as a charge accepter to extract electrons from the conduction band of W18O49 nanowire, causing the gas-sensing response due to the conductivity change of the nanowire. NO2 adsorption on Ti-doped W18O49 nanowire can cause more electrons to transfer from nanowire to NO2 molecule than the case on pure W18O49 nanowire, theoretically suggesting the validity of Ti-doping that can improve the sensitivity of W18O49 nanowire. The population calculations on different gas molecules adsorbed on Ti-doped W18O49 nanowire further indicate the much good sensitivity and selectivity of the doped nanowire to NO2 gas.

Scalable enhancement of graphene oxide properties by thermally driven phase transformation

Chemical functionalization of graphene is promising for a variety of next-generation technologies. Although graphene oxide (GO) is a versatile material in this direction, its use is limited by the production of metastable, chemically inhomogeneous and spatially disordered GO structures under current synthetic protocols, which results in poor optoelectronic properties. Here, we present a mild thermal annealing procedure, with no chemical treatments involved, to manipulate as-synthesized GO on a large scale to enhance sheet properties with the oxygen content preserved. Using experiments supported by atomistic calculations, we demonstrate that GO structures undergo a phase transformation into prominent oxidized and graphitic domains by temperature-driven oxygen diffusion. Consequently, as-synthesized GO that absorbs mainly in the ultraviolet region becomes strongly absorbing in the visible region, photoluminescence is blue shifted and electronic conductivity increases by up to four orders of magnitude. Our thermal processing method offers a suitable way to tune and enhance the properties of GO, which creates opportunities for various applications.

Praseodymium and gadolinium doped ceria as a cathode material for low temperature solid oxide fuel cells

Mixed ionic electronic conducting praseodymium and gadolinium doped ceria (PrxCe0.95−xGd0.05O2−δ (0.15 ≤ x ≤ 0.40)) compositions have been studied as a cathode material for low temperature solid oxide fuel cells. Four compositions of PrxCe0.95−xGd0.05O2−δ (PCGO) have been prepared by varying the praseodymium content. Phase formation, thermal expansion, ionic conductivity, electronic conductivity, ionic transference number and electrochemical performance have been investigated. X-ray diffraction results indicate that PCGO samples crystallize in the fluorite structure, and the lattice volume decreases with increasing praseodymium content, x. The coefficient of thermal expansion increases with increasing x, and at x = 0.2 shows an optimum value of 12 × 10−6 K−1. Ionic transference number decrease while electronic conductivity increase with increasing x. It has been found that electronic contribution to the total conductivity is higher than ionic contribution for all compositions. The praseodymium doping with cerium dioxide introduces impurity bands within the ceria band gap and facilitates the electronic transition from valance band to conduction band through praseodymium impurity levels. The single cell with configuration, Pr0.2Ce0.75−xGd0.05O2−δ–Ce0.80Gd0.20O2−δ∥Ce0.80Gd0.20O2−δ∥NiO–Ce0.80Gd0.20O2−δ delivers a maximum power density of 98 mW cm−2 at 650 °C.

Accommodation of niobium and cerium variable valence cations in the crystal lattice of the Ln 2 3+ Ti 2 4+ O7 (Ln = Dy, Yb) pyrochlores

We have studied the accommodation of niobium and cerium variable valence cations in the Ln 2 3+ Ti 2 4+ O7 (3+/4+) (Ln = Dy, Yb) pyrochlores in air and in a 5% H2 + 95% Ar reducing atmosphere. The (Dy0.8Ca0.1Ce0.1)2Ti2O7 − δ and (Yb0.8Tb0.1Ca0.1)2[Ti1−x Nb x ]2O7 − δ (x = 0–0.3) oxygen ion conducting solid solutions were synthesized through coprecipitation followed by heat treatment in air for 4 h at temperatures of 1400 and 1550°C, respectively. According to X-ray photoelectron spectroscopy (XPS) data, the valence state of the niobium in the (Yb0.8Tb0.1Ca0.1)2[Ti1−x Nb x ]2O7 − δ (x = 0.05, 0.1) solid solutions is 4+ and, hence, isovalent niobium substitution for titanium takes place. During synthesis in air, the titanium sublattice of the (Yb0.8Tb0.1Ca0.1)2[Ti1−x Nb x ]2O7 − δ pyrochlores is stable when the Nb4+ content does not exceed 10% (x = 0.1). According to conductivity data for the high-conductivity material (Yb0.8Tb0.1Ca0.1)2[Ti0.95Nb0.05]2O6.9 at low oxygen partial pressures, there is no reduction of pentavalent niobium and no increase in electronic conductivity, which is supported by XPS results that only Nb4+ is present in the solid solution. In pyrochlore-like (Dy0.8Ca0.1Ce0.1)2Ti2O7 − δ synthesized in air at 1400°C, the dysprosium site contains both tri- and tetravalent cerium, as supported by conductivity measurements under reducing conditions. The Ce4+ + e → Ce3+ reduction process led to a change in the color and disintegration of the sample when the oxygen partial pressure was reduced. In the 3+/4+ A2B2O7 pyrochlores, variable valence cations on the A site (eightfold coordination) more readily participate in redox processes than do those on the B site (sixfold coordination).

Structural and electrical properties of La2–xSrxMo2O9–δ

Sr-doped La2Mo2O9 were prepared by solid state reaction and characterized by XRD, impedance spectroscopy and Hebb- Wagner polarization method. XRD patterns of the samples indicated that the solubility limit of Sr2+ in La2–xSrxMo2O9–δ was in the range of 7 mol.% to 7.5 mol.%, i.e., the maximum stoichiometric coefficient x in La2–xSrxMo2O9–δ was larger than 0.14 and less than 0.15. The cubic lattice parameter of La2–xSrxMo2O9–δ (0<x≤0.14) increased linearly with the content of dopant Sr2+ increasing and the relationship could be expressed as: a=0.7154+0.00451x (mm). The total conductivities of Sr-doped La2Mo2O9 were measured by impedance spectroscopy method in argon and air atmosphere, respectively. The results indicated that substituting Sr2+ for La3+ could suppress the first order phase transform of La2Mo2O9 and stabilize the cubic structure to room temperature, and the conductivities of Sr-doped La2Mo2O9 were more sensitive to the change of atmosphere than that of undoped La2Mo2O9. The conductivity variation of Sr-doped La2Mo2O9 with the dopant content exhibited similar trend in air and argon atmosphere, firstly decreased and then increased with the dopant content increasing, and a minimum value appeared at x=0.1. The electronic conductivities of Sr-doped La2Mo2O9 were measured using Hebb-Wagner polarization method in argon atmosphere. It could be found that Sr-doping caused the increase in electronic conductivity and decrease in oxide-ion transport numbers, but the conducting species were predominantly oxide ions. And the oxide-ion transport numbers of some Sr-doped La2Mo2O9 samples could also reach 0.99.

Effect of Lanthanum Additive on Electrical and Thermal Properties of Bismuth Sodium Titanate Ceramics

This work investigated the preparation and properties of (Bi0.5Na0.5)1–1.5xLaxTiO3 ceramics where x = 0, 0.05, 0.10, 0.15 and 0.20 mol fraction. The powders were fabricated by mixed oxide method and calcined at 800°C for 2 h. The ceramic pellets were prepared by uniaxial pressing method and being sintered at various temperatures ranging from 1150–1200°C for 2 h. Bulk densities, phase, electrical and thermal properties were also measured using various techniques. The result showed that all ceramic samples possessed high density and XRD patterns indicated that all ceramics had a main phase of BNT-based composition with rhombohedral (or pseudocubic) structure. The formation of secondary phase was found for sample containing La greater than 0.10 mol fraction. Electrical resistivity measurements at low frequencies indicated a decreasing trend with increasing La addition indicating an increase in electronic conduction. The dielectric constant and thermal conductivity measurements also showed the effects of charged defects induced by La addition and macro defects present by the formed second phase in this material system.