Current-time Curves Research Articles

LiCl-KCl 용융염 내에서 10 g 규모의 Zircaloy-4 폐 피복관 처리를 위한 전기화학적 용해 연구

C LiCl-KCl molten salts to confirm the feasibility of the electrorefining process for the treatment of hull wastes. In the results of measuring the potential-current response using a stainless steel basket filled with oxidized Zircaloy-4 hull specimens, the oxidation peak of Zr appears to be at -0.7 to -0.8 V vs. Ag/AgCl, which is similar to that of fresh Zircaloy-4 hulls, while the oxidation current is found to be much smaller than that of fresh Zircaloy-4 hulls. These results are congruent with the outcome of current-time curves at -0.78 V and of measuring the change in the average weight and thickness after the electrochemical dissolution process. Although the oxide layer on the surface affects the uniformity and rate of dissolution by decreasing the conductivity of Zircaloy-4 hulls, electrochemical dissolution is considered to occur owing to the defect of the surface and phase properties of the Zr oxide layer.Keyword: Zircaloy-4, Hull wastes, Molten salts, Zr oxide, Dissolution, Electrorefining

Preparation and Electro-Catalytic Performance of Pt-Ag/C as Electro-Reduction Catalysts for H<sub>2</sub>O<sub>2</sub>

Using impregnation-chemical reduction method, we prepared Pt/C and Pt-Ag/C nano-catalysts. Both of them are with the same platinum content. The composition of the two catalysts was analyzed by XRD technique. The electrochemical performance was studied by cyclic voltammetry and current-time curve. The results show that: the existence of Ag in the Pt-Ag/C catalyst makes Pt crystallinity decreased; compared with Pt/C, Pt-Ag/C has a higher reductive peak current. In addition, both catalysts show the excellent catalytic stability.

Synthesis and Characterization of Zinc Oxide Nanostructured by Electrochemical Deposition Method

Zinc Oxide (ZnO) nanostructured was successfully synthesis by electrochemical deposition method. In this paper present the ZnO nanorods growth in a zinc nitrate/hexamethylenetetramine solution at 90°C with different potential applied. The effect of the growth process was investigated by the cyclic voltametric curve and the current-time curve. The structural of ZnO nanorods evidence that it has single crystalline, a wurtzite crystal structure with markedly preferential orientation along (001) direction was measured x-ray diffraction. The observation of ZnO nanorods was measured on field emission scanning electron microscopy that diameter of ZnO rods were below than 100 nm sizes. Uv-Vis spectrophotometer used to determine the transparency of ZnO nanorods through the UV light. The ZnO nanorods show the average transmittance (<90%) for all potential applied. The piezoelectric property of ZnO nanorods were measuring connected with two electrodes to the metal contact on the film that was driven by an ultrasonic wave. The piezoelectric output current was gained and characteristics curve have been illustrated for different voltage with constant driving frequency of ultrasonic wave at 40 kHz.

Improving the Stability and Ethanol Electro‐Oxidation Activity of Pt Catalysts by Selectively Anchoring Pt Particles on Carbon‐Nanotubes‐Supported‐SnO2

AbstractTo improve the stability and activity of Pt catalysts for ethanol electro‐oxidation, Pt nanoparticles were selectively deposited on carbon‐nanotubes (CNTs)‐supported‐SnO2 to prepare Pt/SnO2/CNTs and Pt/CNTs was prepared by impregnation method for reference study. X‐ray diffraction (XRD) was used to confirm the crystalline structures of Pt/SnO2/CNTs and Pt/CNTs. The stabilities of Pt/SnO2/CNTs and Pt/CNTs were compared by analyzing the Pt size increase amplitude using transmission electron microscopy (TEM) images recorded before and after cyclic voltammetry (CV) sweeping. The results showed that the Pt size increase amplitude is evidently smaller for Pt/SnO2/CNTs, indicating the higher stability of Pt/SnO2/CNTs. Although both catalysts exhibit degradation of electrochemical active surface area (EAS) after CV sweeping, the EAS degradation for the former is lower, further confirming the higher stability of Pt/SnO2/CNTs. CV and potentiostatic current–time curves were recorded for ethanol electro‐oxidation on both catalysts before and after CV sweeping and the results showed that the mass specific activity of Pt/CNTs increases more than that of Pt/SnO2/CNTs, indicating that Pt/CNTs experiences more severe evolution and is less stable. The calculated area specific activity of Pt/SnO2/CNTs is larger than that of Pt/CNTs, indicating SnO2 can co‐catalyze Pt due to plenty of interfaces between SnO2 and Pt.

Synthesis and Electron Transfer Properties of Metal Complex Oligomer Wires with an Inherent Potential Gradient on Gold Electrode

Abstractπ‐Conjugated bis(terpyridine)metal (M(tpy)2) oligomer wires were prepared by surface coordination programming such that they displayed an inherent potential gradient along the wire through the chain of metals and bridging ligands. The electron transfer properties of these wires were examined. Heterometal complex wires prepared in the sequence Au(111)‐Co(tpy)2‐Fe(tpy)2‐ferrocene (Fc); that is, Au‐[Aazo‐1CoLH‐1FeTFc] ((Aazo)2 = bis((4‐(4′‐2,2′;6′,2″‐terpyridyl)phenylazo)phenyl)disulfide, LH = bis(terpyridyl)‐p‐phenylene), displayed a rate constant, ket, for electron transfer at the terminal Fc moiety that was twice that obtained from wires prepared in the sequence electrode‐Fe(tpy)2‐Co(tpy)2‐Fc, Au‐[Aazo‐1FeLH‐1CoTFc]. This suggested that the oxidation reaction at the terminal Fc moiety was mediated by electron transfer via Co(tpy)2 more efficiently than via Fe(tpy)2. Metal complex wires with an inherent potential gradient based on the heteroligand combination were synthesized using bis(4‐(4′‐2,2′;6′,2″‐terpyridyl) phenyl)disulfide, (AH)2, or bis(4‐(4′‐5,5″‐difluoro‐2,2′;6′,2″‐terpyridyl)phenyl)disulfide, (AF)2, as anchoring ligands and bis(terpyridyl)‐p‐phenylene, LH, or bis(terpyridyl)‐tetrafluoro‐p‐phenylene, LF, as bridging ligands. Potential step chronoamperometry (PSCA) measurements of the redox reaction of Au‐[AH‐1FeL1‐2FeLF] and Au‐[AF‐1FeLF‐2FeLH] revealed only small differences in the current–time curves, indicating that the electron self‐exchange between the Fe(tpy)2 units in a wire was faster than electron transfer between an electrode surface and the adjacent Fe(tpy)2 units. Fast electron self‐exchange suppressed the expected rectification behavior of the wire, despite the presence of a potential staircase within the wire.

Electrolytic coloration and spectral properties of hydroxyl-doped potassium bromide single crystals

Hydroxyl-doped potassium bromide single crystals are colored electrolytically at various temperatures and voltages by using a pointed cathode and a flat anode. The characteristic OH− spectral band is observed in absorption spectrum of uncolored single crystal. The characteristic O−, OH−, U, V2, O2−−Va+, ML1, F and M spectral bands are observed simultaneously in absorption spectra of colored single crystals. Current–time curve for electrolytic coloration of hydroxyl-doped potassium bromide single crystal and its relationship with electrolytic coloration processes are given. Production and conversion of color centers are explained.

Porous alumina membranes with branched nanopores as templates for fabrication of Y-shaped nanowire arrays

Porous anodic alumina membranes with Y-branched and double-branched nanopores were fabricated by the stepwise reduction of anodizing potential during the second step of anodization carried out in 0.3 M oxalic acid. The process of nanoporous layer formation and influence of anodizing parameters on structural features of as-obtained anodic aluminum oxide (AAO) membranes were discussed in detail. The pore rearrangement process occurring after the potential decrease was investigated on the basis of the current density vs. time curves, and results were correlated with the field-emission scanning electron microscope images of the pore bottoms taken after different anodizing durations. It was found that the reorganization of nanopores begins after 600 and 500 s from the time of the potential reduction to 42 and 30 V and the process seems to be completed after about 900 and 800 s, respectively. The through-hole AAO membranes were used as templates for the fabrication of gold and polystyrene nanowires via electrochemical deposition and simple immersing in the polymer solution, respectively. The arrays of hierarchically branched nanowires were synthesized, and the dimensions of nanowires were consistent with the shape and structure of used AAO templates.

Activated direct electron transfer of nanoAu bioconjugates of cytochrome c for electrocatalytic detection of trace levels of superoxide dismutase enzyme

A novel amperometric biosensor for the detection of trace levels of superoxide dismutase enzyme is developed with the use of nanoAu bioconjugates of cytochrome c (Cyt c). NanoAu particles of finite size were synthesized by borohydride reduction in the presence of alkanethiols having COOH and OH end groups. The nanoAu particles were characterized by transmission electron microscopic analysis, and the mean size of the nanoparticles is determined to be 2.96nm diameter. The heme protein, Cyt c, is bound to the nanoAu particles, and the resulting nanoAu bioconjugates are investigated by cyclic voltammetric and rotating-disk voltammetric experiments. Cyt c has become electrodically reactive by binding with the nanoAu particles, and Cyt c-bound nanoAu particles exhibited a reversible, mass-transport limited electron-transfer reaction. Reversible redox peaks are observed with the formal redox potential of +0.05V (vs. Ag|AgCl) at bare GC and also at Au|alkanethiolate monolayer electrodes. Cyt c is highly reactive to superoxide radical, and electrocatalytic oxidation of superoxide occurs at the applied potential of +0.15V in the presence of the nanoAu bioconjugates. Steady state current–time curves show a sharp increase in the anodic current to the generation of superoxide radical and attain a plateau in ca. 6min. The structure and morphology of the alkanethiolate layer at the nanoAu-Cyt c interface tremendously influences the electrocatalytic current for superoxide. The electrocatalytic current observed for superoxide radical varied sharply by the presence of superoxide dismutase. From the dependence of the electrocatalytic current for superoxide on the concentration of superoxide dismutase, a low-detection-limit of as low as 0.25UmL−1 (∼50ngmL−1) has been established.

Electrostatic Attachment of Ferrocene Monolayer to a Gold Electrode for Use as Ascorbic Acid Sensor

A new ascorbic acid electrochemical sensor was made by electrostatic assembly of ferrocene polymer monolayer on the surface of gold electrode which modified with negatively charged alkanethiol. Cyclic voltammetry and current-time curve were employed to investigate the electrochemical characteristics of the sensor. The ferrocene monolayer modified electrode exhibit excellent electrocatalytic response to the oxidation of ascorbic acid. The anodic overpotential was reduced by about 180 mV compared with that obtained at a bare gold electrode in cyclic voltammetry. Under the optimal conditions, the linear range of the sensor response to ascorbic acid was from 0.05 to 1 mM and the detection limit was 2.710-5 M. The sensor possesses simple preparation, fast response and good electrochemical stability.

Electrodeposition of ZnO from DMSO solution: influence of anion nature and its concentration in the nucleation and growth mechanisms

The influence of the anion nature and its concentration in the electrodeposition of ZnO onto a gold electrode from dimethylsulfoxide (DMSO) solutions was studied. Voltammetric experiments revealed important changes in the zinc oxide electrodeposition process depending on the employed anion as electrolyte. From chronoamperometric experiments, the corresponding current-time curves were fitted with different nucleation and growth mechanism models. The analysis of these results showed changes from an instantaneous to a progressive growth when the solution composition was changed from ZnCl2 to ZnCl2 + LiCl. The change of the mechanism is associated to the adsorption of chloride ion on the active sites of the electrode surface when LiCl is present in the solution.

Researches on current distribution and plate conductivity of valve-regulated lead-acid batteries

A cell with tall plates was simulated by two cells and the controlled voltage with time was successfully used to measure the response current–time curves. It indicates that the current in the upper part of the plate is much higher than that in the lower part in early stage of the discharge, but in late stage, it is reversed, especially at high discharge rates. The upper part of the plate has higher capacity and deeper depth of discharge (DOD) so that the active mass degrades and sheds more quickly in cyclic applications. In the initial discharge, the lead sulfate formed at positive plates produces the internal stress and enhances the electric connection among the active mass particles. But the positive active mass only contributes a little to the conductivity of plates. The negative active mass with a bit shrinking but no passivation has better conductivity than the expanded active mass. The higher ohmic polarization of the active mass appears at higher discharge rates, in the upper part of the plates, in the late stage of the discharge, in aged battery, especially for negative plates.

Low-temperature electrolytic coloration and spectral properties of sucrose crystals

Sucrose crystals are colored electrolytically at low temperatures and various voltages by using a pointed cathode and a flat anode. Caramels, carbonyl compounds, glycosylamines and free radicals are produced in colored sucrose crystals. No obvious characteristic absorption band in UV and visible wavelength regions is observed in absorption spectrum of uncolored sucrose crystal. Intense characteristic absorption bands of glycosylamines, carbonyl compounds and caramels are observed in absorption spectra of colored sucrose crystals. Production of caramels, carbonyl compounds, glycosylamines and free radicals are explained. Current–time curve for electrolytic coloration of sucrose crystal and its relationship with electrolytic coloration process are given.

Low-temperature electrolytic coloration and spectral property of ammonium alum crystals

Ammonium alum crystals are colored electrolytically using a pointed cathode and a flat anode at low temperatures and under various voltages. SO3−, SO2− and O3− hole-trapped centers are produced in colored ammonium alum crystals. Characteristic absorption bands of SO3−, SO2− and O3− hole-trapped centers are observed in absorption spectra of colored ammonium alum crystals. Production and conversion of hole-trapped centers are explained. Current–time curves for electrolytic coloration of ammonium alum crystal and their relationship with electrolytic coloration process are given.

Electrochemical migration behavior of Ag-plated Cu-filled electrically conductive adhesives

The electrochemical migration (ECM) behavior of the electrically conductive adhesives (ECAs) filled with pure Ag powder or Ag-plated Cu composite powder with varied Ag:Cu ratios was investigated under the condition of applying constant voltage and distilled water environment. ECM resistance was determined from the current-time curves. The microstructure and composition of ECM dendrite products were analyzed by SEM/EDS and XRD. It was found that the ECM resistance of Ag-plated Cu composite powder-filled ECAs was evidently higher than that of pure Ag powder-filled ECAs. The Ag:Cu ratio of composite powder in ECAs had notable influence on ECM resistance, which was enhanced with the decrease of Ag:Cu ratios. The composition of dendrites formed between cathode and anode during ECM process was not uniform for Ag-plated Cu-filled ECAs. An ECM inhibiting mechanism of Ag-plated Cu composite powder was proposed according to analysis of the electrochemical impedance spectroscopy, Tafel plot and dendrite composition.

Electrochemical synthesis and characterization of conducting copolymers of biphenyl with pyrrole

AbstractCopolymer films of biphenyl and pyrrole were synthesized by electrochemical polymerization. The influence of the applied potential used for the electropolymerization on the structure, morphology, electrical conductivity, and stability of the films was examined. From the analysis of the current–time curves, it was found that the growth of the copolymer films starts immediately. The films were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis, X‐ray diffraction analysis, and scanning electron microscopy–energy‐dispersive X‐ray analysis, and their electrical conductivity (σ), energy gap (Eg), and electrochemical stability were also determined. Based on the results, the copolymers were classified into three groups. The first includes the (PP‐PPy)0.80 copolymer synthesized at the lowest potential Eox (0.80 V), having the highest ratio R (R = 0.35) of quinoid to benzenoid rings (calculated from FTIR), the highest value of σ (σ = 0.9 S/cm), the lowest Eg (Eg = 1.20 eV), and has compact morphology. The second group concerns the copolymers synthesized at higher potential (0.82 up to 0.86 V), having lower R (∼ 0.20), lower σ (below 0.4 S/cm), higher Eg (∼ 1.35 eV), and they are less compact with many pores. The third group includes the copolymers synthesized at even higher applied potential (0.88 and 0.90 V), having even lower R values (∼ 0.10), significantly lower σ (∼ 10−3 S/cm), even higher Eg (∼ 1.70 eV), and they are very porous. The applied potential during electropolymerization strongly affects the properties of the synthesized copolymers. Because of the combination of high conductivity, low energy gap, and partial solubility with significant electrochemical stability, these new copolymers are attractive candidates for many applications. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Novel amperometric assay for drug–DNA interaction based on an inhibitory effect on an electrocatalytic activity of DNA–Cu(II) complex

A novel strategy of amperometric assay for drug–dsDNA interactions was developed based on an inhibitory effect of antimararial drug (quinacrine) on an electrocatalytic activity of DNA–Cu(II) complex. In this method, a DNA–Cu(II) complex immobilized DNA/polyallylamine(PAA) polyion complex membrane was used as a sensing element. The electrocatalytic activity of a DNA–Cu(II) complex for hydrogen peroxide reduction was reversibly inhibited by electron blocking effect of quinacrine–dsDNA interaction and this inhibitory effect was amplified by the hydrogen peroxide reduction. This phenomenon was utilized for development of a novel amperometric biosensor for DNA-binding drug. From the amperometric current–time curves, the response time of the sensor to 20μM quinacrine was obtained about 20s, and the detection limit of the quinacrine was found to be 10μM estimated to a signal-to-noise ratio of 3.0. Based on the change of steady-state catalytic current, the kinetic analysis of drug–dsDNA interaction can be done in a similar manner of enzyme inhibition, and the binding constant of the quinacrine with DNA can be calculated. This measurement method would be useful for screening of wide variety of DNA-binding drugs and highly toxic pollutants.

Research on Short-Circuit Current of Marine AC Power System Based on Combined Programming

Based on the combined programming for VB, Excel and MATLAB, the paper makes research on short-circuit current of marine AC power system. This method can not only draw precise calculations, but also has the function of making short-circuit current time curve. And it opens up a new way to study the short-circuit current.

Forming efficiency of porous anodic oxide and formation mechanism of nanopores

Porous anodic alumina (PAA) and porous anodic TiO2 nanotubes have received considerable attention because of their applications in a number of fields. The formation mechanisms of nanopores and nanotubes in these porous anodic oxides, however, have remained unclear until now. The interactions between porous structural features and current-time transients in anodizing process cannot be successfully explained. Based on the mechanism of dielectric breakdown of the compact anodic alumina (CAA), the differences and internal relations in their forming processes between CAA and PAA are contrasted in detail. From this innovative standpoint, according to the divergence of PAA and CAA in their current-time curves (or voltage-time curves), two essential causes which induce the decrease of the forming efficiency of oxide in the anodizing process, that is, the generation of the electronic current and the oxygen evolution, are presented in the paper. The evidences of the round hollows within the CAA films, show that the regularly embryo pores result from the oxygen bubbles. According to the aluminum anodizing in the mixed-electrolyte, the results show that once oxygen evolution stopping, the pore growth must be stopped, and the pores must be sealed by the above compact oxide. A novel composite film of the anodic oxide is presented. All of the above conclusively show that in the forming process of PAA, an appropriate magnitude of electronic current ensures the oxygen evolution and the pores formation, an appropriate magnitude of ionic current ensures the oxide formation and growth of pore walls.

基于ZnS量子点与聚合物混合层的有机双稳态器件的记忆特性及其载流子传输机制

A write-once-read-many-times(WORM) bistable device was prepared,in which ZnS quantum dots doped poly-4-vinyl-phenol(PVP) layer was sandwiched between ITO anode and Al cathode.Current-voltage(I-V) curves showed a switching characteristic with a large ON / OFF ratio of 10 4.The electrical bistability properties and charge-transport mechanisms were discussed in detail based on I-V characteristics.The conduction mechanisms in both ON-and OFF-states were discussed in terms of different theoretical models.The data-retention characteristics of the current-time(I-t) curve exhibited permanent retention ability at ambient conditions.

A nonenzymatic glucose sensing platform based on Ni nanowire modified electrode

Glucose detection is very important for the diagnosis and management of diabetes, and nonenzymatic glucose sensors have attracted considerable attention due to their excellent stability, high sensitivity, and so on. Herein, a sensitive, cost-effective nonenzymatic glucose sensor using ultralong Ni nanowire (NW) modified glassy carbon electrode is presented. The current–time curve shows that the catalytic oxidation current is linearly dependent on glucose concentration in the range from 1 μM to 5 mM with a correlation coefficient 0.994, and a sensitivity of 367 μA mM−1 cm−2. The relative standard deviation is 3.7% for 8 successive measurements for 1 mM glucose. After 2-weeks storage in air at room temperature, the signal for 1 mM glucose maintains 97.2% of its initial value. What is more, the present Ni NW-based electrochemical sensing platform can successfully be used to detect glucose in human serum with satisfactory results.