Electron Conduction Path Research Articles

Preparation of needle-like .ALPHA.-Fe2O3 particles and influences of their morphology on the electrochemical behavior in all-solid-state lithium batteries

Needle-like α-Fe2O3 particles with the length of 2 µm and the width of 250 nm were prepared by thermal decomposition of β-FeOOH and the electrochemical performances in the all-solid-state cells were examined. The cell using needle-like particles with acetylene black as a conductive additive showed the first discharge capacity of about 700 mAh g−1 at the current density of 0.064 mA cm−2. The lithium ion and electron conduction path of the electrode was improved by using vapor grown carbon fiber as a conductive additive. The needle-like α-Fe2O3 particles were compared with α-Fe2O3 spherical particles; the suitability for the active material of all-solid-state batteries was investigated.

Synthesis of Pd nanowire networks by a simple template-free and surfactant-free method and their application in formic acid electrooxidation

Abstract A large volume of Pd nanowire networks with lengths of a few tens of nanometers are synthesized successfully by the inherent self-assembly process with the stabilizing effect of sodium citrate. The Pd nanowire networks exhibit a superior electrocatalytic activity for formic acid oxidation. The specific area activities of Pd nanowire at 0.1 V calculated from the forward-scan currents were 1.38 mA cm−2, which is 97% higher than that obtained from Pd nanoparticle or peanut-like structures (0.70 mA cm−2). The mechanism of the significant enhancement of the catalytic activity of Pd nanowire network can be due to the unique surface characteristics and effective electronic conduction path within the Pd nanowire networks.

ZnO / TiO 2 nanonetwork as efficient photoanode in excitonic solar cells

An innovative nanonetwork composed of TiO2 nanoparticles and single-crystalline ZnO nanowires is demonstrated as efficient photoanode in excitonic solar cells. Such architecture benefits of the capability of high sensitizer loading offered by the nanoparticles and of the direct conduction path for electrons guaranteed by the nanowires. The combination of these features leads to improved light absorption, electron photogeneration, and charge collection. The nanonetwork was implemented in a dye-sensitized solar-cell architecture demonstrating threefold enhancement of the efficiency with respect to a nanowire photoanode of the same thickness. Cell efficiency of 1.6% was obtained in 1.5 μm thick nanonetwork.

Growth behavior of nanocrystalline diamond films on ultrananocrystalline diamond nuclei: The transmission electron microscopy studies

Micron-crystalline diamond (MCD) films with a unique microstructure were synthesized using a modified nucleation and growth process, in which a thin layer of ultrananocrystalline diamond (UNCD) was used as nucleation layer for growing diamond films in H2-plasma. Thus obtained (MCD)UNCD diamond films consist of nanosized diamond clusters (∼10 nm in size) surrounding the large diamond grains (∼300 nm in size), exhibiting better electron field emission (EFE) properties than the conventional diamond materials with faceted grains. The EFE of these (MCD)UNCD films can be turned on at E0=11.1 V/μm, achieving EFE current density as large as (Je)=0.7 mA/cm2 at 25 V/μm applied field, which can be attributed to the presence of large proportion of UNCD grains lying in between the MCD grains, forming an electron conduction path and thus facilitating the EFE process. Transmission electron microscopy examinations reveal that such a unique microstructure was formed by agglomeration and coalescence of the nanosized UNCD grains.

Effect of fabrication methods of bifunctional catalyst layers on unitized regenerative fuel cell performance

In order to understand the origins of performance variations in unitized regenerative fuel cells (URFCs), bifunctional catalyst layers (BCLs) fabricated with two different methods, i.e., ink deposition on membrane or GDL, were designed in this paper. The performances of the two different methods were evaluated, and their reaction dynamics were measured by electrochemical impedance spectra. The different BCLs, caused by the different preparation processes, were found to influence the fuel cell performance. The cell potentials of the URFCs using platinum sprayed onto the gas diffusion layer (GDL) are above 0.100 V higher than those with platinum sprayed onto the membrane at 800 mA cm −2 in fuel cell (FC) mode. The mass transport resistances of the URFCs at different operation modes were also compared. It was proved that the platinum layer formed by applying platinum onto the GDL could prevent the cell from water flooding in FC mode. However, it was found that the cell performance changed slightly in water electrolysis mode with different BCLs. The electron conduction path was also found to be hindered by an IrO 2 agglomerate, which led to a decrease in cell performance. The highest and lowest round-trip efficiencies of the URFC with different BCLs were 42.1% and 22.3%, respectively, at 800 mA cm −2.

The effect of coating crystallization and substrate impurities on magnetron sputtered doped LaCrO 3 coatings for metallic solid oxide fuel cell interconnects

For IT-SOFC metallic interconnects, surface coating is effective for reducing Cr poisoning of the cathode and controlling scale growth. In this work, LaCrO 3 and doped LaCrO 3 coatings were deposited by magnetron sputtering on SS446 and Crofer 22 APU substrates. The crystallization process was studied by means of X-ray Diffraction (XRD) during the annealing of the sputter coated samples in ambient and reducing environments. The formation of intermediate phases when annealed in air, LaCrO 4 and La 2CrO 6, results in vacancy formation upon subsequent transformation to the LaCrO 3 phase and thus a decreased oxidation resistance. While the avoidance of an intermediate phase change when the coatings are initially annealed in a reducing environment leads to dense and compact coatings. This confirmed both by XRD and by scanning electron microscopy (SEM) of coating cross-sections. Crofer 22 APU alloys with various silicon and aluminum levels are deposited with doped LaCrO 3 coating to study substrate impurity effects on coating properties. It was found that silicon content in the substrates leads to increased ASR of the coatings. In addition, long term annealing in air shows that aluminum impurities in the substrate can lead to the formation of alumina at substrate grain boundaries, which in turn leads to enhanced Mn migration at the grain boundaries. Increased manganese concentrations at the film/grain boundary interface in coated samples produces larger than normal amounts of (Mn,Cr) 3O 4 spinel in these regions, which cracks the coating and reduces the ASR value due to extra electronic conduction path. A similar mechanism is not observed in a low Al/Si alloy.

Study of nanostructural behavior and transport properties of BaTiO3 doped vanadate glasses and glass–ceramics dispersed with ferroelectric nanocrystals

Abstract Nanostructural behavior and electrical properties of BaTiO 3 -(100− x )V 2 O 5 glasses (where x =35, 40, 45 and 50 mol%) and their corresponding nanocrystalline glass–ceramics were studied. Scanning electron microscopy (SEM) of quenched glasses, confirm the amorphous nature of the glasses present. Also, the overall features of X-ray diffraction (XRD) confirm the amorphous nature of the present glasses. Transmission electron micrograph (TEM) and XRD of the corresponding heat treated sample indicate nanocrystals with a particle size of 20–35 nm. It was found that density ( d ) increases gradually with the increase of the BaTiO 3 content in the nanocrystalline glass–ceramics. It is observed that the conductivity of the nanocrystalline glass–ceramics is higher than that of the corresponding glassy phase. The high conductivity of these nanocrystalline glass–ceramics is considered to be due to the presence of nanocrystals with a particle size of 20–35 nm. This is attributed to the formation of extensive and dense network of electronic conduction paths which are situated between V 2 O 5 nanocrystals and on their surface. The electrical conductivity of this system can be fitted with Mott's model of nearest neighbor hopping at high temperature. From the best fits, reasonable values of various small polaron hopping (SPH) parameters are obtained. From dielectric permittivity of the as-cast glass samples, no ferroelectric behavior can be observed. Also, the dielectric permittivity ( e ) values of these glasses are found to be very high compared to familiar vanadium containing glasses. By annealing the glass system around 450 °C for 1 h in air, nanocrystalline BaTiO 3 phase precipitates and the corresponding nanocrystalline glass–ceramics showed average broad peak around 352 K in the dielectric permittivity ( e ). It is interesting to note that pure nanocrystalline BaTiO 3 phase with average particle size less than 100 nm also shows ferroelectric phase transition around this temperature as predicted from the dielectric permittivity measurements. This observation of these glass–ceramics nanocrystals can be utilized to control BaTiO 3 particle size and hence transition temperature by proper adjustment of annealing time and BaTiO 3 content. Such a feature can be used for industrial applications where the shape of the application article is a necessary requirement.

固体電解質中の電子伝導経路に関する第一原理計算：原子スイッチ動作機構の理解に向けて

As a first step to clarify the microscopic working mechanism of atomic switches using solid electrolytes, we have examined electronic states and electron transport properties of Ag-Ag2S-Ag and Cu-Ta2O5-Pt systems using standard density functional theory and novel non-equilibrium Green's function method. In both the systems, we found that the bridge structures consisting of excess Ag or Cu in the middle solid electrolyte layer work as electronic conduction paths. In Cu-Ta2O5-Pt, we also found that O vacancy is much less effective for the enhancement of electronic conduction than excess Cu.

Enhanced Rate Capabilities of Nanobrookite with Electronically Conducting MWCNT Networks

Nanostructuring of intercalating electrode materials is a promising strategy in advanced lithium ion batteries with advantages of fast rate capabilities, high energy density, and excellent cycle life. However, the interparticle contact resistance caused by the easy aggregation of nanomaterials limits the electronic conduction paths and thereby reduces the power density. Herein, nanocomposites were formed by synthesizing brookite-type, TiO2 nanoparticles attached to carbon nanotubes with surfaces that had been functionalized with a cationic surfactant, cetyltrimethylammonium bromide (CTAB). The specific capacity of the nanobrookite composite incorporating carbon nanotubes was estimated to be approximately 3-fold greater than that of pure nanobrookite mechanically mixed with conventional carbon black. Furthermore, this composite electrode offers an outstanding rate capability with good capacity retention via the combined benefits of the decrease in interparticle contact resistance and one-dimensional (1D) e...

Investigation on Crystal and Electronic Structures and Oxide Ionic Conduction Path by Neutron and Synchrotron X ray Diffractions, and Oxygen Nonstoichiometry of LaGaO3 - Based Oxide Ionic Conductors

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Effects of pretreatment and post-annealing on the field emission property of diamond-like carbon grown on a titanium/silicon substrate

Diamond-like carbon (DLC) films were deposited on titanium/silicon substrates with the help of the microwave plasma chemical vapor deposition (CVD) method with Ar, H 2, and CH 4 as a mixed gas source. Titanium/silicon substrates were polished by diamond powder and etched by hydrogen (H 2) plasma, prior to deposition. After deposition, rapid thermal annealing (RTA) was used as a post-treatment. The effects of hydrogen plasma pretreatment and RTA post-treatment on the electron field emission characteristics of the DLC films was examined and correlated by Raman scattering, average surface roughness, and surface morphology. It is found that both treatments can improve the field emission characteristics of DLC films. However, RTA post-treatment demonstrates a more pronounced effect on the enhancement of field emission than does the hydrogen plasma pretreatment. This improvement is attributed in part to the increase in surface roughness resulting from sp 2 clustering formed during the RTA. The tips of these sp 2 clusters provide plenty of efficient emission sites on the surface of the DLC films. Another reason for this improvement is the graphene-like layers formed during the RTA, which provide efficient conduction paths for electrons to move through the DLC films. The field emission characteristics of CVD deposited on DLC films can be greatly enhanced by appropriate pretreatment and post-treatment, leading to promising applications for cold cathodes.

High-throughput studies of Li1−xMgx/2FePO4 and LiFe1−yMgyPO4 and the effect of carbon coating

A two-dimensional sample array synthesis has been used to screen carbon-coated Li(1−x)Mgx/2FePO4 and LiFe(1−y)MgyPO4 powders as potential positive electrode materials in lithium ion batteries with respect to x, y and carbon content. The synthesis route, using sucrose as a carbon source as well as a viscosity-enhancing additive, allowed introduction of the Mg dopant from solution into the sol–gel pyrolysis precursor. High-throughput XRD and cyclic voltammetry confirmed the formation of the olivine phase and percolation of the electronic conduction path at sucrose to phosphate ratios between 0.15 and 0.20. Measurements of the charge passed per discharge cycle showed that the capacity deteriorated on increasing magnesium in Li(1−x)Mgx/2FePO4, but improved with increasing magnesium in LiFe(1−y) MgyPO4, especially at high scan rates. Rietveld-refined XRD results on samples of LiFe(1−y)MgyPO4 prepared by a solid-state route showed a single phase up to y=0.1 according to progressive increases in unit cell volume with increases in y. Carbon-free samples of the same materials showed conductivity increases from 10−10 to 10−8Scm−1 and a decrease of activation energy from 0.62 to 0.51eV. Galvanostatic cycling showed near theoretical capacity for y=0.1 compared with only 80% capacity for undoped material under the same conditions.

Electrochemical and anticorrosion performances of zinc-rich and polyaniline powder coatings

In this work, hydrochloride polyaniline (PANI-Cl) powder was incorporated as a conductive pigment into powder zinc-rich primer (ZRP) formulations in order to enhance the electronic conduction paths between zinc particles inside the coating and the steel substrate (i.e. percolation). Coatings were applied onto steel substrates and immersed in a 3% NaCl solution at ambient temperature. The protective properties and electrochemical behaviour of coatings were investigated by monitoring the free corrosion potential versus time and by using EIS. It was found that corrosion potential remains cathodic and constant for a long time up to 100 days of immersion. From EIS results, it was shown that the coatings exhibit larger impedance values than those observed with liquid or other zinc-rich powder formulations containing carbon black. From Raman spectroscopy results, it may be proposed that zinc particles in contact with PANI-Cl pigments were passivated. Other zinc particles remain still active which ensures the cathodic protection of the substrate. Moreover, coatings exhibit good barrier properties.

Design of Thin-Layered Membrane Electrode Assenbly Prepared by Sputtering Method for Direct Methanol Fuel Cells

Superior performance of direct methanol fuel cells (DMFCs) may be obtained by localized catalyst loading on reaction sites and reduction of charge transfer and diffusion resistances. These may be realized by thin-layered membrane electrode assemblies (MEAs) for which new component materials and a new catalyzed method are used. In this study, gas diffusion electrodes consisted of sputter-deposited Pt as a catalyst layer and "carbon silk" as a diffusion layer are evaluated as cathodes for DMFCs. A cathode prepared by sputter-deposited Pt on spreading the mixture of Nafion, carbon and butyl acetate (NCB) solution showed an increase in current density and mass activity for the oxygen reduction reaction. Consequently, effects of NCB on cathodic polarization are explained by supplying protonic and electronic conduction paths to electrochemically inactive Pt with oxygen diffusion path. Mass activities using NCB were found about five times higher than a sputter-deposited Pt Cathodes without NCB

Study the effect of conductive fillers on a secondary Zn electrode based on ball-milled ZnO and Ca(OH) 2 mixture powders

The active materials of the secondary Zn electrode containing a mixture powder of zinc oxide (ZnO) and calcium hydroxide (Ca(OH) 2) powders were prepared by a ball-milled method. The characteristic properties of active materials of ball-milled ZnO + Ca(OH) 2 mixture powders were examined by scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) system, X-ray diffraction (XRD) analysis, and micro-Raman spectroscopy. The prepared Zn powder electrodes were by using the ball-milled active materials powder +2 wt.% highly electronic conductive fillers, i.e., nano-copper or carbon nanotubes (CNTs) powder. The electrochemical properties of the secondary Zn electrodes without and with the conductive fillers were studied by using cyclic voltammetry (CV) and galvanostatic charge/discharge tests. It was found that the charge/discharge properties of the secondary Zn electrode could be improved when the nano-sized conductive fillers were added into the electrode. In fact, it may be due to the formation of a better electronic conduction path in the electrode matrix. In particular, it was found that the best electrochemical properties were the secondary Zn electrode with 2 wt.% nano-copper fillers. According to the results, it is demonstrated here that the CV method is a quick technique to effectively evaluate the performance of a secondary Zn electrode.

Microstructure Control Using Impregnation of LSM in a Thin Porous Electrolyte Layer

A high performance LSM/ScSZ composite cathode was prepared by a novel fabrication method where LSM/ScSZ in the form of solid particles was impregnated in a porous electrolyte layer with a thickness of approximately 5-10μm. In the proposed method, a porous ScSZ electrolyte structure is first fabricated on a dense ScSZ electrolyte, and LSM powder in slurry is then printed on this surface structure. Since this surface layer is very thin and has appropriate electrolyte pore structure, LSM particles can be effectively impregnated. SEM observation has revealed that the impregnated LSM forms electronic conduction paths on the porous electrolyte structure without severe blockage of channels for gas phase diffusion, thus confirming the successful impregnation. The prepared cathode actually showed a significant improvement in polarization performance. Also, a cathode structure model is discussed by considering the effect of surface roughening and layer thickening for the interface between LSM/electrolyte

Metallic State in a Lime−Alumina Compound with Nanoporous Structure

We report a metallic state in a nanostructured porous crystal 12CaO x 7Al2O3 by incorporating electrons in the inherent subnanometer-sized cages, in which a three-dimensionally closely packed cage structure acts as an electronic conduction path. High-density electron doping ( approximately 2 x 10(21) cm(-3)), which was achieved by a thermal treatment in Ti metal vapor at approximately 1100 degrees C, induces homogenization of the cage geometry to a symmetric state, resulting in an insulator-metal transition with a sharp enhancement of the electron drift mobility from approximately 0.1 to 4 cm(2) V(-1) s(-1). The results provide an approach for the realization of electroactive functions in materials composed only of environmentally benign elements by utilizing the appropriate nanostructures.

Performance of sputter-deposited platinum cathodes with Nafion and carbon loading for direct methanol fuel cells

One of the difficulties for a direct methanol fuel cell (DMFC) is low catalyst utilization efficiency because a certain amount of Pt loading is inactive as the catalyst. Sputter-deposited Pt electrodes are expected to improve mass activities for oxygen reduction reaction (ORR) compared with those prepared by a conventional method. Meanwhile, mass activities of sputter-deposited Pt cathodes for the ORR decreased with an increase in amount of Pt loading. In this study, the loading of protonic and electronic conductors to improve mass activities of sputter-deposited Pt electrode were investigated as cathodes for DMFCs. Cathodes prepared by spreading the mixture of Nafion, carbon and butyl acetate (NCB) solution on sputter-deposited Pt showed an increase in current densities and mass activities for the ORR. These may suggest an increase in catalyst active sites. Moreover, results of AC impedance analysis showed a decrease in charge transfer resistance and an increase in double layer capacitance for a sputter-deposited Pt cathode with NCB spread. Consequently, effects of NCB on cathodic polarization were explained by supplying protonic and electronic conduction paths to electrochemically inactive Pt with the oxygen diffusion path maintained. Mass activities were found about fifteen times higher than a Pt/C cathode prepared by a conventional method.

Synthesis and oxygen permeation properties of 75 mol% Ce0.75Nd0.25O1.875–25 mol% Nd1.8Ce0.2CuO4 composite

An oxygen-permeable composite constituted to oxide ionic conductor phase (Ce0.75Nd0.25O1.875) and oxide electronic conductor phase (Nd1.8Ce0.2CuO4) was prepared using the acetate pyrolysis method. Based on electrical conductivity measurements, total electrical conductivity of 75 mol% Ce0.75Nd0.25O1.875–25 mol% Nd1.8Ce0.2CuO4 composite material was governed by the electronic conduction paths. With respect to the oxygen permeation properties, the results showed that oxygen permeation properties were unexplainable by a simple composite rule using the electrical transport properties of the bulk Ce0.75Nd0.25O1.875 and the bulk Nd1.8Ce0.2CuO4.

Control of a Surface Photochemical Process by Fractal Electron Transport Across the Surface: O2 Photodesorption from TiO2(110)

The photodesorption of O(2) from TiO(2)(110) has been found to exhibit fractal kinetic behavior. The rate coefficient for photodesorption is measured throughout the entire experiment and is shown to decrease by a factor of approximately 100 over a time period of approximately 250 s. A model is proposed in which the electrons associated with O-vacancy defects on the surface percolate from vacancy site to vacancy site via the filled orbitals at these sites to neutralize photoproduced holes. This electron percolation, causing electron-hole recombination, reduces the efficiency of charge transfer between a photoproduced hole and an O(2)(-)(a) species localized at a vacancy defect site, causing the rate of O(2) photodesorption to follow a fractal rate law. We postulate that the fractal electron conduction path across the surface is one-dimensional.