Complex Impedance Spectra Analysis of SnO_2-glaze Composites

SnO2-glaze composites were prepared by Sb-doped SnO2 and SiO2-CaO-Al2O3-B2O3 glaze. The composites changed from an electrical insulator to a conductor as the SnO2 content increased from Owt% to 90 wt% . The complex impedance spectra of the fabricated composites were investigated in the frequency range of 100Hz-40 MHz and three kinds of typical shape of complex impedance spectra were recorded and analyzed. The ,spectrum is quite close to the model of conduction via nonohmic contactiug when the SnO2 content is relatively low, In high loading region, the spectrum shows the conduction pattern through ohmic contact chains . In the moderate loading region, the model is a mixture of the above two models. Equivalent circuit of the composite changes from resistor-capacitor circuit to resistor-inductor circuit as the content of SnO2 increases.

Electrochemical impedance spectra of V_2O_5 xerogel films with intercalation of lithium ion

Vanadium pentoxide xerogel films used for lithium rechargeable batteries were prepared from crystalline c-V2O5 by melt quenching method,then the electrochemical process of lithium intercalation into vanadium pentoxide xerogel films was simulated with an equivalent circuit model, which was derived from the mechanism of electrode reactions. Measured electrochemical impedance spectra at various electrode potentials were analyzed by using the complex non-linear least-squares fitting method. The results show that impedance spectra consist of 2 high-to- medium frequency depressed arcs and a low frequency straight line. The high frequency arc is attributed to the absorption reaction of lithium ions into the oxide film, the medium frequency arc is attributed to the charge transfer reaction at the vanadium oxide/electrolyte interface and the low frequency is characterized by a straight line with a phase angle of 45° corresponding to the diffusion of lithium ion through vanadium oxide phase. The experimental and calculated results are compared and discussed focusing on the electrochemical performance and the state of charge of the electrode. Moreover, the high consistence of the fitted values of the model to the experimental data indicates that this mathematical model does give a satisfying description of the intercalation process of vanadium pentoxide xerogel films.

Anticorrosion performance of the coating/metal system by electrochemical impedance spectra

In order to investigate the anticorrosion performance of the organic coating/metal system, electrochemical impedance spectra （EIS） were measured in the 3.5wt% NaCl solution, the chemical component and the formation of corrosion products scale were analyzed by laser Raman microspectroscopy, and the pattern of the organic coating/metal system was observed by scanning electron microscopy （SEM）. The characteristics and the delamination process of the organic coating/metal system were investigated systematically, and the emphases were on the transportation of the corrosive medium and the changes of the coating/metal interface. The results show that the impedance decreases at the initial immersion, then increases at the middle-immersion, and again decreases at last, which is related to the corrosion products scale. The concentration of Cl in the coating, which destroys the corrosion products scale, increases with the immersion time.

Investigations on the Sensing Mechanism of Humidity Sensors Based on Poly(4-vinylpyridine)/carbon Black Composite by AC Impedance Spectra

1 Results Investigations on the sensing mechanism is important for understanding the electrical responses of humidity sensors to humidity change,and could provide guidelines for the design and synthesis of humidity sensitive materials with desirable properties.In this work,the sensing mechanism of humidity sensors based on quaternized poly(4-vinylpyridine) (PVP)/carbon black (CB) composite[1] was studied by measuring their AC impedance spectra at various humidities at room temperature.Under low humidity...

Electrochemical behaviors of tantalum in anhydrous ethanol containing hydrogen sulfate ions

The electrochemical behaviors of Ta in tetrabutylammonium hydrogen sulfate（TBAHS） ethanol solutions were studied using potentiodynamic polarization,cyclic voltammetry,potentiostatic current time transient and impedance techniques.The results revealed that no active-passive transition is presented in the cyclic voltammogram,and the anodic current density increases with the increase of solution temperature,TBAHS concentration,potential scan rate and water content.The apparent activation energy is about 43.389 kJ/mol and the dissolution process is diffusion-controlled.Potentiostatic measurements showed that the current density gradually decays to a steady value when the potential is low;however,when the potential is higher than a certain value,the current density initially declines to a minimum value and then increases gradually.The resistance of passive film decreases with increasing potential,and inductive loops are presented when the potential is higher than 2.0 V.

Electrochemical characterization of ion selectivity in electrodeposited nickel hexacyanoferrate thin films

The ion selectivity of electrodeposited nickel hexacyanoferrate （NiHCF） thin films was investigated using electrochemical impedance spectroscopy （EIS） and cyclic voltammetry （CV）. NiHCF thin films were prepared by cathodic deposition on Pt and Al substrates. EIS and CV curves were determined in 1 mol/L （KNO3＋C5NO3） and 1 mol/L （NaNO3＋CsNO3） mixture solutions, which were sensitive to the concentration of Cs^＋ in the electrolytes. Experimental results show that all Nyquist impedance plots show depressed semicircles in the high-frequency range changing over into straight lines at lower frequencies. With increasing amounts of Cs^＋, the redox potentials in CV curves shift toward more positive values and the redox peaks broaden; the semicircle radius in corresponding EIS curves and the charge transfer resistance also increase. EIS combining CV is able to provide valuable insights into the ion selectivity of NiHCF thin films. 2008 University of Science and Technology Beijing. All rights reserved.

Effectiveness of inhibitors in increasing chloride threshold value for steel corrosion

This investigation was aimed at evaluating the effectiveness of corrosion inhibitors in increasing the chloride threshold value for steel corrosion. Three types of corrosion inhibitors, calcium nitrite （Ca（NO2）2）, zinc oxide （ZnO）, and N,N＇-dimethylaminoethanol （DMEA）, which respectively represented the anodic inhibitor, cathodic inhibitor, and mixed inhibitor, were chosen. The experiment was carried out in a saturated calcium hydroxide （Ca（OH）2） solution to simulate the electrolytic environment of concrete. The inhibitors were initially mixed at different levels, and then chloride ions were gradually added into the solution in several steps. The open-circuit potential （Ecorr） and corrosion current density （lcorr） determined by electrochemical impedance spectra （EIS） were used to identify the initiation of active corrosion, thereby determining the chloride threshold value. It was found that although all the inhibitors were effective in decreasing the corrosion rate of steel reinforcement, they had a marginal effect on increasing the chloride threshold value.

Passivation Mechanism of 316L Stainless Steel in Oxidizing Acid Solution

The compositions and the chemical valence states of elements of 316L stainless steel passive film formed in the oxidizing acid solution were studied by X-ray Photoelectron Spectroscopic (XPS) analysis. The electrochemical polarization curve was measured. The passivation process in the oxidizing acid solution was studied by AC impedance technology. The results indicated that the stable compounds layer was formed on the surface of the sample and the adsorption was the main step in the nitrite solution during passivation process. The catalysis passivation mechanism was put forward according to the experimental results. During passivation process, the water molecule was adsorbed on the surface of the sample at first in the oxidizing acid solution. The oxidizer in the solution played a role as catalyst. The oxide and hydroxide, which could be changed each other and finally formed stable passive film, were generated from adsorbing intermediate under the catalytic action. The mathematical models for predicting the steady polarization curve and the AC impedance spectra at certain conditions have been obtained. The passivation mechanism of 316L stainless steel in the oxidizing acid solution can be interpreted by the catalysis passivation mechanism.

Low Temperature Preparation of Ceria Solid Solutions Doubly Doped with Rare-Earth and Alkali-Earth and Their Properties as Solid Oxide Fuel Cells

A series of solid electrolytes, (Ce 0.8 Ln 0.2 ) 1- x M x O 2-δ (Ln= La, Nd, Sm, Gd, M:Alkali earth), were prepared by amorphous citrate gel method. XRD patterns indicate that a pure fluorite phase is formed at 800 ℃. The electrical conductivity and the AC impedance spectra were measured. XPS spectra show that the oxygen vacancies increase owing to the MO doping, which results in the increase of the oxygen ionic transport number and conductivity. The performance of ceria based solid electrolyte is improved. The effects of rare earth and alkali earth ions on the electricity were discussed. The open circuit voltages and maximum power density of planar solid oxide fuel cell using (Ce 0.8 Sm 0.2 ) 1-0.05 Ca 0.05 O 2- δ as electrolyte are 0.86 V and 33 mW·cm -2 , respectively.

Ionic Conductivity of Nano-LaF_3 Bulk Material at Room Temperature

Nanocrystalline powder of LaF3 was synthesized by a method of direct precipitation from water solution. Particle size and shape of LaF3 nanocrystalline powder was analysed with TEM. Particles were mainly spherical with narrow particle size distribution （10 20 nm）. The average particle size analysed with XRD is 16.7 nm. Nano-LaF3 bulk material was prepared by compacting the powder to 1 GPa at room temperature and a vacuum of 10^-4 Pa. The ionic conductivity of nano-LaF3 bulk material was studied with complex impedance spectra at room temperature. The ionic conductivity of nano-LaF3 bulk material （1 × 10^-5 S·cm^-1 ） at room temperature is significantly increased compared to that of single crystal LaF3 （1 × 10^-6 S·cm^-1）. A special phenomenon was observed firstly time that the ionic conductivity increased gradually with multiple testing in result of relaxation.

Structural and electrical properties of single crystalline and bi-crystalline ZnO thin films grown by molecular beam epitaxy

C-oriented ZnO epitaxial thin films are grown separately on the a-plane and c-plane sapphire substrates by using a molecular-beam epitaxy technique. In contrast to single crystalline ZnO films grown on a-plane sapphire, the films grown on c-plane sapphire are found to be bi-crystalline; some domains have a 30~ rotation to reduce the large mismatch between the film and the substrate. The presence of these rotation domains in the bi-crystalline ZnO thin film causes much more carrier scatterings at the boundaries, leading to much lower mobility and smaller mean free path of the mobile carriers than those of the single crystalline one. In addition, the complex impedance spectra are also studied to identify relaxation mechanisms due to the domains and/or domain boundaries in both the single crystalline and bi-crystalline ZnO thin films.

Features of the Conductivity of the Ag8Ge1-xMnxTe6 Solid Solutions

Samples of Ag8Ge1-xMnxTe6 solid solutions with different manganese content (x = 0, 0.05, 0.1, 0.2) were prepared by fusing and further pressing their powders under the pressure of 0.6 GPa. In addition of Mn atoms to the Ag8GeTe6 compound leads to compression of their lattice. All p-type samples acquire a high resistance below the transition at temperatures of 180 - 220 K. The electrical conductivity of all compositions in the range of 220 - 300 K increases due to hopping mechanism, and at temperatures T > 320 K, a semiconductor characteristic is observed. By studying impedance spectra of samples, it was established that at 80 K solid solutions behave like a homogeneous dielectric material. At high temperatures and frequencies of an external electric field, a significant role of grain boundaries in conductivity was revealed. The dielectric anomaly occurring at low frequencies is also associated with an effect that manifests itself in the grain boundary.

自组装FeRu双金属纳米催化剂在可逆固体氧化物电池中实现高效稳定的CO-CO_(2)相互转化

本文报道了一种适应于高效稳定的CO-CO_(2)相互转化的可逆固体氧化物电池(RSOC)相变燃料电极.该燃料电极由FeRu双金属纳米催化剂和Ruddlesden-Popper相Pr_(0.8)Sr_(1.2)Fe_(1-x-y)Ru_(x)Mo_(y)O_(4)氧化物复合而成(FeRu@PSFRM).固体氧化物燃料电池(SOFC)模式时,单电池800℃时的最大输出功率密度可以达到170 W cm^(-2);而在固体氧化物电解池(SOEC)模式下,800℃、1.3 V时电解池的电解电流密度达到-0.256 A cm^(-2).在SOFC-SOEC循环测试过程中,RSOC中CO-CO_(2)相互转化过程经历了“活化-稳定-衰退”三个明显阶段.幸运的是,性能衰退的燃料电极可通过“原位氧化-还原”处理实现性能再生,有效提升该电池的使用寿命.研究结果表明,原位脱溶形成的FeRu@PSFRM材料是一种极具应用潜力的燃料电极候选材料,以期实现高效稳定的CO-CO_(2)相互转化.

Formation Characteristic of CO_2 Corrosion Product Layer of P110 Steel Investigated by SEM and Electrochemical Techniques

Formation characteristic of CO2 corrosion product layer on the surface of P110 steel was investigated in simulated oilfield environment using massqoss experiment, potentiodynamic polarization curve, impedance spectroscopy, and SEM micrograph analysis. Samples of different times up to 240 h were tested during exposure. Corrosion product was primarily composed of Fe（Ca, Mg）（CO3 ）2, which was distinguished by two layers. With an increase in the exposure time, the charge transfer resistance and polarization resistance increased progressively, the uniform cor- rosion rate decreased, and the corrosion reaction was controlled by the diffusion process instead of the activation process. All phenomena were attributed to the formation of the protective corrosion product layer. More compact and lower porosity of the layer made it more difficult to transfer and diffuse through the corrosion product layer for the charges and ions. Similar results were obtained bv electrochemical test and mass-loss experiment.

Low temperature preparation and fuel cell properties of rare earth doped barium cerate solid electrolytes

The solid electrolytes, BaCe0.8Ln0.2O2.9(Ln: Gd, Sm, Eu), were prepared by the sol-gel method. XRD indicated that a pure orthorhombic phase was formed at 900°C. The synthesis temperature by the sol-gel method was about 600°C lower than the high temperature solid phase reaction method. The electrical conductivity and impedance spectra were measured and the conduction mechanism was studied. The grain-boundary resistance of the solid electrolyte could be reduced or eliminated by the sol-gel method. The conductivity of BaCe0.8Gd0.2O2.9 is 7.87 × 10-2 S· cm-1 at 800°C. The open-rireuit voltage of hydrogen-oxygen fuel cell using BaCe0.8Gd0.2O2.9 as electrolyte was near to 1 V and its maximum power density was 30 mW· cm-2.

Structure and electrical properties of (1-x)BaTiO_3+(x)La_(2/3)-Sr_(1/3)MnO_3 composites

Liquid-phase sintering method was used to prepare BaTiO3 powders and the struc- ture and electrical properties of （1-x）BaTiO3-]-（x）La2/3Srl/3Mn03 （LSMO） compos- ites were investigated. The results of X-ray diffraction showed that the prepared BaTiO3 powders were pure and fine, indicating that sintering temperature was effec- tively lowered when the NaC1 sintering aid was added. X-ray diffraction patterns of （1-x）BaTiO3＋（x）La2/3Srl/3Mn03 （LSMO） composites showed that LSMO and BaTiO3 phases were coexistent and no other phases were detected. The impedance spectra showed that the resistance of grain boundaries for LSMO-doped samples was suppressed. The resistivity-temperature measurements showed that room- temperature resistivity of the composites was lowered from insulator for pure BaTiO3 ceramic to 103 ~.m for the x----0.3 sample. The sample of x_〈0.2 showed the positive temperature coefficient （PTC） effect whereas the x=0.3 sample exhibited PTC effect at temperatures below 68 ~C and then negative temperature coefficient （NTC） effect at temperatures above 68 ~C. The related mechanism has been elucidated.

Chemical composition and Mott-Schottky analysis of passive film formed on G3 alloy in bicarbonate/carbonate buffer solution

The chemical composition and semi-conductive properties of passive film on nickel- based alloy （G3 alloy） in bicarbonate/carbonate buffer solution were investigated by Auger electron spectroscopy （AES）, X-ray photoelectron spectroscopy （XPS）, elec- trochemical impedance spectra （EIS） and Mott-Schottky plot. AES and XPS results showed that the passive film appeared double-layer structure, in which the inner film was composed of nickel oxide, the mixed nickel-chromium-molybdenum-manganese oxides were the major component of the outer film. The electrochemical results revealed that the factors including frequency, potential, time, temperature and pH value can affect the semi-conductive property, the doping densities decreased with increasing potential and pH value, prolonging time and decreasing temperature. According to the above results, it can be concluded that the film protection on the substrate was enhanced with increasing potential and pH value, prolonging time and decreasing temperature.

Investigation on Electronic Property of Passive Film on Nickel in Bicarbonate/Carbonate Buffer Solution

The electronic properties of passive film formed on nickel in bicarbonate/carbonate buffer solution were studied by electrochemical impedance spectra （EIS） and Mott-Schottky plot. The film composition was analyzed by X-ray photoelectron spectroscopy （XPS）. The results showed that passive film exhibited p-type semi-conductive character, and the acceptor density （NA） decreased with increasing potential, prolonging time, decreasing temperature, increasing pH value and decreasing chloride/sulfur ions concentration. The transfer resistance and film resistance increased with the above factors changing. XPS results showed that passive film was composed of NiO and a little amount of Ni2O3.