• 전기화학회지
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• 제6권2호
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• pp.158-160
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• 2003

We have reported to make nanostructured cobalt oxide electrode that have large capacitance over than 400 F/g (specific capacitance) and good cycleability. But, it had serious demerits of low voltage range under 0.5 V and low power density. Therefore, we need to increase voltage range of cobalt oxide electrode. We report here on the electrochemical properties of sol-gel-derived nanoparticulate cobalt xerogel in 1M KOH solution and aqueous polymeric gel electrolyte. In solution electrolyte, cobalt oxide electrode had over 250 F/g capacitance consisted of EDLC and pseudocapacitance. In gel electrolyte, cobalt oxide electrode had around 100 F/g capacitance. This capacitance was only electric double layer capacitance of active surface area. In solution electrolyte, potassium ion as working ion reacted with both of layers easily. However, In gel electrolyte, reacted with only surface-active layer. Itis very hard to reach resistive layer. So, we have studied on pretreatment of electrode to contain working ions easily. We'll report more details.

• Carbon letters
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• 제16권2호
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• pp.78-85
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• 2015

Activated carbons (ACs) were prepared by activation of coal tar pitch (CTP) in the range of $700^{\circ}C-1000^{\circ}C$ for 1-4 h using potassium hydroxide (KOH) powder as the activation agent. The optimal activation conditions were determined to be a CTP/KOH ratio of 1:4, activation temperature of $900^{\circ}C$, and activation time of 3 h. The obtained ACs showed increased pore size distribution in the range of 1 to 2 nm and the highest specific capacitance of 122 F/g in a two-electrode system with an organic electrolyte, as measured by a charge-discharge method in the voltage range of 0-2.7 V. In order to improve the performance of the electric double-layer capacitor electrode, various mixtures of CTP and petroleum pitch (PP) were activated at the optimal activation conditions previously determined for CTP. Although the specific capacitance of AC electrodes prepared from CTP only and the mixtures of CTP and PP was not significantly different at a current density of 1 A/g, the AC electrodes from CTP and PP mixtures showed outstanding specific capacitance at higher current rates. In particular, CTP-PP61 (6:1 mixture) had the highest specific capacitance of 132 F/g, and the specific capacitance remained above 90% at a high current density of 3 A/g. It was found that the high specific capacitance could be attributed to the increased micro-pore volume of ACs with pore sizes from 1 to 2 nm, and the high power density could be attributed to the increased meso-pore volume.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.53-54
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• 2002

New lubrication mechanism for nanomachine is proposed. This mechanism utilizes the effect of diffusive double layer observed in hydrophobic colloidal solution. Basic idea of the theory is inspired by the research for possible mechanism of bacterial flagellar motor In this study, formulation of this mechanism is achieved and numerical calculation is performed. It is shown that this mechanism can produce enough load capacitance. Furthermore not only capacitance to sustain driving force of flagellar motor

• 전기화학회지
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• 제16권2호
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• pp.65-69
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• 2013

전기이중층 커패시터용 활성탄의 정전 용량 향상을 위해 우레아를 이용해 활성탄 표면에 펩티드 결합을 유도하였다. 우레아 도입에 따른 활성탄은 소성과정을 거쳐 안정화되었으며, 전기화학적 특성을 순환전류 전압법을 이용하여 정전 용량을 관찰하고, 임피던스를 통해 저항 변화를 관찰하였으며, 충방전 평가를 통해 싸이클 성능을 관찰하였다. 결과적으로 질소성 작용기의 도입으로 정전 용량은 기존 탄소재에 비해 약 22.9%의 향상을 이루었으며, 저항 감소 및 우수한 싸이클 성능을 나타냄을 확인하였다.

• Advances in Energy Research
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• 제8권1호
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• pp.41-57
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• 2022

Electrochemical double-layer capacitors (EDLCs) based on solid polymer electrolytes (SPEs) have gained an immense recognition in the present world due to their unique properties. This study is about preparing and characterizing EDLCs using a natural rubber (NR) based SPE with natural graphite (NG) electrodes. NR electrolyte was consisted with 49% methyl grafted natural rubber (MG49) and zinc trifluoromethanesulfonate ((Zn(CF₃SO₃)₂-ZnTF). It was characterized using electrochemical impedance spectroscopy (EIS) test, dc polarization test and linear sweep voltammetry (LSV) test. NG electrodes were made using a slurry of NG and acetone. EIS test, cyclic voltammetry (CV) test and galvanostatic charge discharge (GCD) test have been done to characterize the EDLC. Optimized electrolyte composition with NR: 0.6 ZnTF (weight basis) exhibited a conductivity of 0.6 x 10^-4 Scm^-1 at room temperature. Conductivity was predominantly due to ions. The electrochemical stability window was found to be from 0.25 V to 2.500 V. Electrolyte was sandwiched between two identical NG electrodes to fabricate an EDLC. Single electrode specific capacitance was about 2.26 Fg^-1 whereas the single electrode discharge capacitance was about 1.17 Fg^-1. The EDLC with this novel NR-ZnTF based SPE evidences its suitability to be used for different applications with further improvement.

• Transactions on Electrical and Electronic Materials
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• 제8권4호
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• pp.174-177
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• 2007

We fabricated organic field-effect transistors (OFETs) based a fluorinated copper phthalocyanine ($F_{16}CuPC$) and copper phthalocyanine (CuPc) as an active layer. And we observed the surface morphology of the $F_{16}CuPC$ thin film. The $F_{16}CuPC$ thin film thickness was 40 nm, and the channel length was $50{\mu}m$, channel width was 3 mm. And we also fabricated the $F_{16}CuPc/CuPc$ double layer FET and with different $F_{16}CuPc$ film thickness devices. We observed the typical current-voltage (I-V) characteristics and capacitance-voltage (C-V) in $F_{16}CuPc$ FET and we calculated the effective mobility. From the double layer FET devices, we observed the higher drain current more than single layer FET devices.

• Journal of Electrochemical Science and Technology
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• 제8권1호
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• pp.1-6
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• 2017

The conductivity of the electrolyte used plays a critical role in the optimization of the performance of electrochemical double layer capacitors. However, when the difference in the conductivities of different electrolytes is not significant (only 10-20%), the conductivity has little effect on the capacitance. On the other, unlike the conductivity and viscosity of the electrolyte, the cation size directly influences the capacitance. Cyclic ions have a smaller effective radius than that of the corresponding acyclic ions because the acyclic alkyl groups have a greater number of conformational degrees of freedom, such as the rotational, bending, and stretching modes. Consequently, because of the smaller effective size of the cyclic ions, cells containing electrolytes with such ions exhibit higher capacitances than do those with their acyclic counterparts.

• 공업화학
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• 제10권6호
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• pp.822-827
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• 1999

본 연구에서는 에너지 밀도가 큰 초고용량 캐패시터를 제작하기 위한 기초 연구로서 활성탄소섬유의 물성과 유기 전해질의 특성이 초고용량 캐패시터의 전기화학적 특성에 미치는 영향을 조사하였다. 유기성 전해질의 경우는 이온의 크기가 수용성 전해질 보다 훨씬 크기 때문에 탄소전극의 세공크기에 많은 영향을 받으며, 용량을 발현할 수 있는 유효세공의 크기가 커야 한다는 것을 알 수 있었다. 혼합용매를 이용한 전해액의 조성은 큰 비축전용량과 빠른 충전속도, 그리고 낮은 ESR 및 방전전류의 세기에 대한 높은 비축전용량 유지성 등의 우수한 충방전 특성을 나타내는 것을 알 수 있었고, 전해질의 높은 이온전도도가 용량발현 및 자가방전 특성에 큰기여를 하고 있으며, 전해질 이온의 크기는 충전속도에 많은 영향을 미치는 것을 알 수 있었다.

• Carbon letters
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• 제22권
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• pp.70-80
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• 2017

Activated carbons (ACs) have been used as electrode materials of electric double-layer capacitors (EDLC) due to their high specific surface areas (SSA), stability, and ecological advantages. In order to make high-energy-density ACs for EDLC, petroleum pitch (PP) pre-carbonized at $500-1000^{\circ}C$ in $N_2$ gas for 1 h was used as the electrode material of the EDLC after KOH activation. As the pre-carbonization temperature increased, the SSA, pore volume and gravimetric capacitance tended to decrease, but the crystallinity and electrode density tended to increase, showing a maximum volumetric capacitance at a medium carbonization temperature. Therefore, it was possible to control the crystalline structure, SSA, and pore structure of AC by changing the pre-carbonization temperature. Because the electrode density increased with increasing of the pre-carbonization temperature, the highest volumetric capacitance of 28.4 F/cc was obtained from the PP pre-carbonized at $700^{\circ}C$, exhibiting a value over 150% of that of a commercial AC (MSP-20) for EDLC. Electrochemical activation was observed from the electrodes of PP as they were pre-carbonized at high temperatures above $700^{\circ}C$ and then activated by KOH. This process was found to have a significant effect on the specific capacitance and it was demonstrated that the higher charging voltage of EDLC was, the greater the electrochemical activation effect was.

• 한국전기전자재료학회논문지
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• 제31권2호
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• pp.112-116
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• 2018

Electric double layer capacitors (EDLCs) are promising candidates for energy storage devices in electronic applications. An EDLC yields high power density but has low specific capacitance. Carbon material is used in EDLCs owing to its large specific surface area, large pore volume, and good mechanical stability. Consequently, the use of carbon materials for EDLC electrodes has attracted considerable research interest. In this paper, in order to evaluate the electrochemical performance, graphene is used as an EDLC electrode with flake sizes of 3, 12, and 60 nm. The surface characteristic and electrochemical properties of graphene were investigated using SEM, BET, and cyclic voltammetry. The specific capacitance of the graphene based EDLC was measured in a 1 M $TEABF_4/ACN$ electrolyte at the scan rates of 2, 10, and 50 mV/s. The 3 nm graphene electrode had the highest specific capacitance (68.9 F/g) compared to other samples. This result was attributed to graphene's large surface area and meso-pore volume. Therefore, large surface area and meso-pore volume effectively enhances the specific capacitance of EDLCs.