• Journal of the Korean Electrochemical Society
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• v.13 no.4
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• pp.223-234
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• 2010

In this review, the theory and applications of the complex capacitance analysis, which can be utilized in analyzing capacitor-like electrochemical systems, were summarized. Theoretically, it was suggested that the imaginary capacitance plots (Cim vs. log f) can provide a simple way to analyze electrochemical characteristics of capacitive systems, without complicated mathematical calculations. The usefulness of the complex capacitance analysis has been demonstrated by applying it to analyze EDLC characteristics of practical porous carbon electrodes, ionic conductivities inside small pores, and ionic resistances in the catalyst layers of polymer electrolyte membrane fuel cells.

• Journal of the Korean Electrochemical Society
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• v.6 no.4
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• pp.255-260
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• 2003

The complex capacitance analysis was performed in order to examine the potential-dependent EDLC characteristics of porous carbon electrodes. The imaginary capacitance profiles $(C_{im}\;vs.\;log\lf)$ were theoretically derived for a cylindrical pore and further extended to multiple pore systems. Two important electrochemical parameters in EDLC can be estimated from the peak-shaped imaginary capacitance plots: total capacitance from the peak area and $\alpha_0$ from the peak position. Using this method, the variation of capacitance and ion conductivity in pores can be traced as a function of electric potential. The electrochemical impedance spectroscopy was recorded on the mesoporous carbon electrode as a function of electric potential and analyzed by complex capacitance method. The capacitance values obtained from the peak area showed a maximum at 0.3V (vs. SCE), which was in accordance with cyclic voltammetry result. The ionic conductivity in pores calculated from the peak position showed a maximum at 0.2 V (vs. SCE), then decreased with an increase in potential. This behavior seems due to the enhanced electrostatic interaction between ion and surface charge that becomes enriched at more positive potentials.

• 한국전기화학회:학술대회논문집
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• 2003.10a
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• pp.55-55
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• 2003

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.9
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• pp.1626-1631
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• 2010

The characteristics of electric current for the voltaic cell are important for electric power applications. In this paper, an electrical equivalent model consist of three resisters and a capacitance for the Cu/NaCl solution/Zn electrochemical cell is proposed. The capacitance which exists in the Zn electrode/electrolytic interface increased according to Zn electrode area, but cannot affect almost in electric current. Complex impedance plot was used to analysis the interface effect for Zn/electrolyte. This result shows that the interface is similar with the electric transmission line. The short current measurements were conducted to investigate the effects of hydrogen peroxide, the watery sulfuric acid and NaCl aqueous solution. As the hydrogen peroxide increased, the electric current increased because the hydrogen gas being converted with the water. Also electric current increased significantly with increase of the hydrogen ion with the watery sulfuric acid and increased with increase of $Na^+$ ion and $Cl^-$ion in the NaCl electrolyte.

• Transactions on Electrical and Electronic Materials
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• v.8 no.3
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• pp.131-134
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• 2007

An $ITO/Alq_3/Al$ structure was used to study complex impedance of $Alq_3$ based organic light-emitting diodes. Equivalent circuit was analyzed in a device structure of $ITO/Alq_3/Al$ with a thickness layer of $Alq_3$ of 100 nm. The obtained impedance was able to be fitted using equivalent circuit model of parallel combination of resistance $R_p$ and capacitance $C_p$ with a small series resistance of $R_s$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.438-439
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• 2006

We have used ITO/$Alq_3$/Al structure to study complex impedance in $Alq_3$ based organic light emitting diode. Equivalent circuit was analyzed in a device structure of ITO/$Alq_3$/Al by varying the thickness of $Alq_3$ layer from 60 to 400nm. The impedance results can be fitted using equivalent circuit model of parallel combination resistance $R_p$ and capacitance $C_p$ with a small series resistance $R_s$.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.213-216
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• 2007

PEMFC의 전기화학적 반응은 촉매, 이오노머, 기공이 만나는 삼상계면에서만 일어나므로, 전극 구조의 최적화가 성능 향상 및 장기안정성 확보에 있어 매우 중요하다. 본 연구에서는 전극 미세구조를 실시간으로 분석하기 위해 임피던스 복소캐패시턴스법을 도입하고자 하였다. 즉, PEMFC의 양극에 질소를 공급하면 0.4 V 부근에서 전기이중층 형성 반응만이 일어나는 것을 확인하였으며, 이때 음극에는 수소를 공급하여 기준전극 및 반대전극으로 사용하였다. 측정된 임피던스를 복소캐패시턴스로 변환하고 허수부를 주파수에 대해 도시하면 피크 형태의 곡선이 얻어지는데, (1) 피크 면적은 전극/전해질의 계면면적, (2) 피크 위치는 이오노머 네트워크에 의한 수소이온 전도 특성, (3) 피크 폭은 다공성 구조의 균일도를 각각 나타내므로, 피팅 없이 직접적인 해석이 가능하다는 장점을 가진다. 반면, 기존의 Nyquist 도시법은 피팅에 의한 분석이 필요하며, 전극층의 불균일한 구조로 인해 단순한 등가회로 구성이 어려운 문제점을 가진다. 최종적으로, MEA 제작 조건 및 운전 조건을 변수로 하여 임피던스를 측정하고 복소캐패시턴스 분석을 수행하여, 퇴화 경로를 규명하고 운전 조건을 최적화하고자 하였다.

• Journal of the Korean Electrochemical Society
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• v.10 no.4
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• pp.252-256
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• 2007

A series of spherical porous carbons were prepared via resorcinol-formaldehyde (RF) sol-gel polymerization in the presence of cationic surfactant (CTAB, cetyltrimethylammonium bromide), wherein the carbon sphere size was controlled by varying the CTAB introduction time after a pre-determined period of addition reaction (termed as "pre-curing"). The sphere size gradually decreases with an increase in the pre-curing time within the range of 30-150 nm. The carbons possess two types of pores; one inside carbon spheres (intra-particle pores) and the other at the interstitial sites made by carbon spheres (inter-particle pores). Of the two, the surface exposed on the former was dominant to determine the electric double-layer capacitor (EDLC) performance of porous carbons. As the intra-particle pores were generated inside RF gel spheres by gasification, the pore diameter was similar for all these carbons, thereby the pore length turned out to be a decisive factor controlling the EDLC performance. The charge-discharge voltage profiles and complex capacitance analysis consistently illustrate that the smaller-sized RF carbons deliver a better rate capability, which must be the direct result of facilitated ion penetration into shorter pores.

• Journal of the Korean Ceramic Society
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• v.28 no.3
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• pp.179-188
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• 1991

The semiconducting BaTiO3 ceramics used in this study were sintered in the reducing atomosphere(hydrogen gas) and neutral atmosphere(nitrogen gas), then were heat-treated in air to vary defect concentrations. In this experiment, the correlations between the composition analysis and electrical characteristics of these samples were investigated. When the BaTiO3 ceramics were sintered in N2 atmosphere, it was observed that the Ba contents near the interface were lower than that of the grain center, and these samples showed superior PTCR effects. From analysis of the resistivities of grains and grain boundaries by CIRM(Complex Impedance Resonance Method), it was confirmed that the PTCR effects were caused by the resistivity of grain boundaries. And from measurement of the capacitance at each temperature, the samples sintered in N2 atmosphere show the increase of room temperature resistance and the decrease of capacitance as a result of the increase of the charge depletion layers. This phenomenon agrees well with the cation deficiencies in the analytical results.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.05a
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• pp.252-254
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• 2002

Metal oxides with high dielectric constants have the potential to expend scaling of transistor gate capacitance beyond that of ultrathin silicon dioxide. However, during deposition of most metal oxides on silicon, an interfacial region of SiOx is formed and limits the specific capacitance of the gate structure. We deposisted aluminum oxide and examined the composition of the interfacial layer by employing high-resolution X-ray photoelectron spectroscopy and X-ray reflectivity. We find that the interfacial region is not pure SiO$_2$, but is composed of a complex depth-dependent ternary oxide of $AlSi_xO_y$ and the pure SiO$_2$.