• 제목/요약/키워드: Electrochemical Impedance

검색결과 896건 처리시간 0.025초

Conversion of a Constant Phase Element to an Equivalent Capacitor

  • Chang, Byoung-Yong
    • Journal of Electrochemical Science and Technology
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    • 제11권3호
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    • pp.318-321
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    • 2020
  • Here I present a formula which converts a constant phase element (CPE) to its equivalent capacitor. Electrochemical impedance spectroscopy is capable of resolving a complex electrochemical processes into its faradaic and non-faradaic elements, and the non-faradaic process is frequently described as a CPE in place of a capacitor due to the non-ideality. Being described as a capacitor, the non-faradaic element provides information by its capacitance, but a CPE cannot provide a physical meaning. In order to solve the problem, the CPE has been dealt with as an equivalent capacitor of which the capacitance provides practical information. Succeeding the two methods previously suggested, a new conversion method is suggested in this report. While the previous ones manipulate only the CPE, the new method takes both the CPE and its related resistor into account for conversion. By comparing the results obtained by the three methods, we learn that the results are nearly the same within tolerable ranges, and conclude that any of the method choices is acceptable depending on the conditions of the system of interest.

Optical Interferometry as Electrochemical Emission Spectroscopy of Metallic alloys in Aqueous Solutions

  • Habib, K.;AI-Mazeedi, H.
    • Corrosion Science and Technology
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    • 제2권6호
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    • pp.277-282
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    • 2003
  • Holographic interferometry, an electromagnetic method, was used to study corrosion of carbon steel, aluminum and copper nickel alloys in NaOH, KCI and $H_2SO_4$ solutions respectively. The technique, called electrochemical emission spectroscopy, consisted of in-situ monitoring of changes in the number of fringe evolutions during the corrosion process. It allowed a detailed picture of anodic dissolution rate changes of alloys. The results were compared to common corrosion measurement methods such as linear polarization resistance measurements and electrochemical impedance spectroscopy. A good agreement between both data was found, thus indicating that holographic interferometry can be a very powerful technique for in-situ corrosion monitoring.

Novel State-of-Charge Estimation Method for Lithium Polymer Batteries Using Electrochemical Impedance Spectroscopy

  • Lee, Jong-Hak;Choi, Woo-Jin
    • Journal of Power Electronics
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    • 제11권2호
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    • pp.237-243
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    • 2011
  • Lithium batteries are widely used in mobile electronic devices due to their higher voltage and energy density, lighter weight and longer life cycle when compared to other secondary batteries. In particular, a high demand for lithium batteries is expected for electric cars. In the case of the lithium batteries used in electric cars, driving distance must be calculated accurately and discharging should not be done below a level that makes it impossible to crank. Therefore, accurate information on the state-of-charge (SOC) becomes an essential element for reliable driving. In this paper, a novel method for estimating the SOC of lithium polymer batteries using AC impedance is proposed. In the proposed method, the parameters are extracted by fitting the measured impedance spectrum on an equivalent impedance model and the variation in the parameter values at each SOC is used to estimate the SOC. Also to shorten the long length of time required for the measurement of the impedance spectrum, a novel method is proposed that can extract the equivalent impedance model parameters of lithium polymer batteries with the impedance measured at only two specific frequencies. Experiments are conducted on lithium polymer batteries, with similar capacities, made by different manufacturers to prove the validity of the proposed method.

A Review of Ac-impedance Models for the Analysis of the Oxygen Reduction Reaction on the Porous Cathode Electrode for Solid Oxide Fuel Cell

  • Kim, Ju-Sik;Pyun, Su-Il
    • 전기화학회지
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    • 제8권2호
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    • pp.106-114
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    • 2005
  • This article covers the theoretical ac-impedance models for the analysis of oxygen reduction on the porous cathode electrode f3r solid oxide fuel cell (SOFC). Firstly, ac-impedance models were explained on the basis of the mechanism of oxygen reduction, which were classified into the rate-determining steps; (i) adsorption of oxygen atom on the electrode surface, (ii) diffusion of adsorbed oxygen atom along the electrode surface towards the three-phase (electrode/electrolyte/gas) boundaries, (iii) surface diffusion of adsorbed oxygen atom m ixed with the adsorption reaction of oxygen atom on the electrode surface and (iv) diffusion of oxygen vacancy through the electrode coupled with the charge transfer reaction at the electrode/gas interface. In each section for ac-impedance model, the representative impedance plots and the interpretation of important parameters attributed to the oxygen reduction reaction were explained. Finally, we discussed in detail the applications of the proposed theoretical ac-impedance models to the real electrode of SOFC system.

직접탄소 연료전지에서 고체 탄소 연료에 따른 전기화학 임피던스 비교 연구 (A Comparative Study on Electrochemical Impedance Analysis of Solid Carbon Fuels in Direct Carbon Fuel Cell)

  • 조재민;엄성용;이광섭;안성율;김덕줄;최경민
    • 한국수소및신에너지학회논문집
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    • 제25권6호
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    • pp.620-628
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    • 2014
  • Direct Carbon Fuel Cell(DCFC) is one of new power generation that the chemical energy of solid carbon can be converted into electrical energy directly. At the high temperature, the electrochemical reaction of the carbon takes place and the carbon reacts with oxygen to produce carbon dioxide as followed overall reaction ($C+O_2{\rightarrow}CO_2$). However, in case of using the raw coals as a fuel of DCFC, the volatile matter containing carbon, hydrogen, and oxygen produces at operating temperature. In this study, the electrochemical reaction of Adaro coal was compared with Graphite. This work focused on the electrochemical reaction of two kinds of solid carbon by Electrochemical Impedance Spectroscopy(EIS). The EIS results were estimated by equivalent circuit analysis. The constant phase element(CPE) was applied in Randle circuit to explain an electrode and fuel interface. The correlation between the fuel characteristic and electrochemical results was discussed by elements of equivalent circuit of each fuel.

Monitoring of Corrosion Rates of Carbon Steel in Mortar under a Wet-Dry Cyclic Condition

  • Kim, Je-Kyoung;Kang, Tae-Young;Moon, Kyung-Man
    • 전기화학회지
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    • 제10권3호
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    • pp.179-183
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    • 2007
  • The corrosion behavior of metal covered with mortar under a wet-dry cyclic condition were investigated to apply for the measurement of corrosion rates of reinforcing steel in concrete structure. The carbon steel in mortar having t=3 mm cover thickness was exposed to the alternate condition of 6 h immersion in chloride containing solution and 18 h drying at $25^{\circ}C$ and 50%RH. The electrochemical phenomena of a carbon steel and mortar interface was explained by an equivalent circuit consisting of a solution resistance, a charge transfer resistance and a CPE(Constant Phase Element). The corrosion rates were monitored continuously during exposure using an AC impedance technique. Simultaneously, the current distribution over the working electrode during impedance measurement was analyzed from the phase shift, $\theta$, in an intermediate frequency. The result showed that corrosion rate monitoring using an AC impedance method is suitable under the given exposure conditions even during the drying period when the metal is covered with the wetted mortar.

Borate 완충용액에서 니켈 회전원판전극의 부식과 부동화 (Corrosion and Passivation of Nickel Rotating Disk Electrode in Borate Buffer Solution)

  • 김연규
    • 대한화학회지
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    • 제57권5호
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    • pp.533-539
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    • 2013
  • 변전위법과 전기화학 임피던스 측정법을 이용하여 borate 완충용액에서 니켈 회전원판전극의 전기화학적 부식과 부동화를 연구하였다. Tafel 기울기, 임피던스, 회전원판전극의 회전속도, 그리고 부식전위와 부식전류의 pH 의존성으로부터 니켈의 부식과 부동화 반응 메커니즘과 환원반응에서의 수소 발생 반응구조를 제안하였다. EIS data로부터 등가회로를 제안하였으며 산화반응의 영역별로 전기화학적 변수들을 측정하였다. 부동화 반응에 의하여 생성된 $Ni(OH)_2$ 산화피막은 전기장의 영향을 받는 탈수반응에 의해 NiO로 전환되는 것으로 보인다.

Effects of the Polarization Resistance on Cyclic Voltammograms for an Electrochemical-Chemical Reaction

  • Chang, Byoung-Yong
    • Journal of Electrochemical Science and Technology
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    • 제6권4호
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    • pp.146-151
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    • 2015
  • Here I report an electrochemical simulation work that compares voltammetric current and resistance of a complex electrochemical reaction over a potential scan. For this work, the finite element method is employed which are frequently used for voltammetry but rarely for impedance spectroscopy. Specifically, this method is used for simulation of a complex reaction where a heterogeneous faradaic reaction is followed by a homogeneous chemical reaction. By tracing the current and its polarization resistance, I learn that their relationship can be explained in terms of rate constants of charge transfer and chemical change. An unexpected observation is that even though the resistance is increased by the rate of the following chemical reaction, the current can be increased due to the potential shift of the resistance made by the proceeding faradaic reaction. This report envisions a possibility of the FEM-based resistance simulation to be applied to understand a complex electrochemical reaction. Until now, resistance simulations are mostly based on equivalent circuits or complete mathematical equations and have limitations to find proper models. However, this method is based on the first-principles, and is expected to be complementary to the other simulation methods.

Relative Comparison of Cathode Polarizations in Solid Oxide Fuel Cells Using the Spreading Concept in AC 2 Point Impedance Spectroscopy

  • Lee, Byung-Kook;Kim, Eui-Hyun;Hwang, Jin-Ha
    • 한국세라믹학회지
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    • 제50권2호
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    • pp.163-167
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    • 2013
  • A modified two-point impedance spectroscopy technique exploits the geometric constriction between an electrolyte and a cathode with an emphasis on semispherical-shaped electrolytes. The spatial limitation in the electrolyte/electrode interface leads to local amplification of the electrochemical reaction occurring in the corresponding electrolyte/electrode region. The modified impedance spectroscopy was applied to electrical monitoring of a YSZ ($Y_2O_3$-stabilized $ZrO_2$)/SSC ($Sm_{0.5}Sr_{0.5}CoO_3$) system. The resolved bulk and interfacial component was numerically analyzed in combination with an equivalent circuit model. The effectiveness of the "spreading resistance" concept is validated by analysis of the electrode polarization in the cathode materials of solid oxide fuel cells.

교류 임피던스기법을 이용한 철근부식 측정에 관한 실험적 연구 (Electrical Impedance Spectroscopy(EIS) Measurements to Evaluate Corrosion of Steel/Concrete System)

  • 정시영;김병국;최완철
    • 한국콘크리트학회:학술대회논문집
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    • 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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    • pp.659-662
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    • 2005
  • Electrochemical impedance spectroscopy (EIS) has been extensively used to try to evaluate the corrosion state of the steel/concrete system. This technique is attractive because, in theory, used in a wide range of frequencies, it can give detailed information about the mechanisms and kinetics of the electrochemical reactions. Impedance measurements were performed using potential control and measuring the corresponding current response. One-year-old southern exposure test. specimens were used in the current study. The effectiveness of corrosion inhibiting additives was evaluated. The corrosion current densities estimated by impedance measurements were confirmed by those determined using linear polarization techniques. The purpose of this study was to evaluate the long-term-performance potential of the corrosion inhibitors in chloride contaminated reinforce concrete.

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