• The Korean Journal of Ceramics
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• v.5 no.4
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• pp.353-356
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• 1999

Highly proten-conductive elastic composites have been successfully prepared from $H_3PO_4$-doped silica gel and styrene-ethylene-butylene-styrene block elastic copolymer. In addition solid state electric double-layer capacitors have been fabricated using the composite as an electrolyte and activated carbon powders(ACP) hybridized with the composite as a polrizable electrode. The cyclic voltammogram of the electric double-layer capacitor fabricated demonstrated that electric charge was stored in the elecric double-layer at the interface between the polarizable electrode and the electrolyte. The value of capacitance of the capacitor was 10 F/(gram of total ACP), which was comparable to that of the capacitors using conventional liquid electrolytes.

• Journal of Hydrogen and New Energy
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• v.27 no.2
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• pp.176-181
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• 2016

Recent years, supercapacitors have been attracting a growing attention as an efficient energy storage, due to their long-lifetime, device reliability, simple device structure and operation mechanism and, most importantly, high power density. Along with the increasing interest in flexible/stretchable electronics, the supercapacitors with compatible mechanical properties have been also required. A eutectic gallium-indium (EGaIn) liquid metal could be a strong candidate as a soft electrode material of the supercapacitors because of its insulating surface oxide layer for electric double layer formation. Here, we report the electrochemical study on the charging/reaction process at the interface of EGaIn liquid metal and electrolyte. Numerical fitting of the charging current curves provides the capacitance of EGaIn/insulating layer/electrolyte (${\sim}38F/m^2$). This value is two orders of magnitude higher than a capacitance of a general metal electrode/electrolyte interface.

• Applied Chemistry for Engineering
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• v.24 no.2
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• pp.201-207
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• 2013

In this study, the surface of a phenol based activated carbon (AC) used as an electrode in an electric double layer capacitor was modified via boric acid treatment for the capacitance investigation. The effect of boric acid treatment on electrochemical performance was also investigated. The AC surface functional groups ratio of quinone-like (O=C) which is electrochemical active functional groups was increased after the boric acid treatment. And, boric acid treated AC showed an increase in the specific surface area, total pore volume, and micropore volume. In case of optimum boric acid treated AC, its specific capacitance increased by 20% in comparison to that of untreated AC. These results demonstrate that a boric acid treated carbon surface-based electric double layer capacitor electrode effectively enhances specific capacitance.

• Journal of Hydrogen and New Energy
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• v.29 no.6
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• pp.627-634
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• 2018

Gallium-based liquid metal, e.g., eutectic gallium-indium (EGaIn), is highly attractive as an electrode material for flexible and stretchable devices. On the liquid metal, oxide layer is spontaneously formed, which has a wide band-gap, and therefore is electrically insulating. In this paper, we fabricate a capacitor based on eutectic gallium-indium (EGaIn) liquid metal and investigate its cyclic voltammetry (CV) behavior. The EGaIn capacitor is composed of two EGaIn electrodes and electrolyte. CV curves reveal that the EGaIn capacitor shows the behavior of electric double-layer capacitors (EDLC), where the oxide layers on the EGaIn electrodes serves as the dielectric layer of EDLC. The oxide thicker than the spontaneously-formed native oxide decreases the capacitance of the EGaIn capacitor, due to increased voltage loss across the oxide layer. The EGaIn capacitor without oxide layer exhibits unstable CV curves during the repeated cycles, where self-repair characteristic of the oxide was observed. Finally, the electrolyte concentration is optimized by comparing the CV curves at various electrolyte concentrations.

• Journal of Applied Reliability
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• v.12 no.2
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• pp.67-78
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• 2012

An electric double-layer capacitor(EDLC) is an electrochemical capacitor with relatively high energy density, typically hundreds of times greater than conventional electrolytic capacitors. EDLCs are widely used for energy storage rather than as general-purpose circuit components. They have a variety of commercial applications, notably in energy smoothing and momentary-load devices, and energy-storage and kinetic energy recovery system devices used in vehicles, etc. This paper presents an accelerated degradation test of an EDLC with rated voltage 2.7V, capacitance 100F, and usage temperature $-40^{\circ}C{\sim}65^{\circ}C$. The EDLCs are tested at $50^{\circ}C$, $60^{\circ}C$, and $70^{\circ}C$, respectively for 1,750hours, and their capacitances are measured at predetermined times by constant current discharge method. The failure times are predicted from their capacitance deterioration patterns, where the failure is defined as 30% capacitance decrease from the initial one. It is assumed that the lifetime distribution of EDLC follows Weibull and Arrhenius life-stress relationship holds. The life-stress relationship, acceleration factor, and $B_{10}$ life at design condition are estimated by analyzing the accelerated life test data.

• Carbon letters
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• v.15 no.3
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• pp.192-197
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• 2014

A hierarchical pore structured novolac-type phenol based-activated carbon with micropores and mesopores was fabricated. Physical activation using a sacrificial silicon dioxide ($SiO_2$) template and chemical activation using potassium hydroxide (KOH) were employed to prepare these materials. The morphology of the well-developed pore structure was characterized using field-emission scanning electron microscopy. The novolac-type phenol-based activated carbon retained hierarchical pores (micropores and mesopores); it exhibited high Brunauer-Emmett-Teller specific surface areas and hierarchical pore size distributions. The hierarchical pore novolac-type phenol-based activated carbon was used as an electrode in electric double-layer capacitors, and the specific capacitance and the retained capacitance ratio were measured. The specific capacitances and the retained capacitance ratio were enhanced, depending on the $SiO_2$ concentration in the material. This result is attributed to the hierarchical pore structure of the novolac-type phenol-based activated carbon.

• Journal of the Korean Electrochemical Society
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• v.9 no.1
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• pp.10-18
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• 2006

This article is concerned with the overview of the activated carbon fibers. Firstly, this review provides a comprehensive survey of the overall processes for the synthesis of the activated carbon fibers from the carbonaceous materials. Subsequently, the physicochemical properties such as pore structures and surface oxygen functional groups of the activated carbon fibers were discussed in detail. Finally, as electrochemical applications of the activated carbon fibers to electrode materials for electric double-layer capacitor (EDLC), the electrochemical characteristics of the activated carbon fiber electrodes and the various methods to improve the capacitance and rate capability were introduced. In particular, the effect of pore length distribution (PLD) on kinetics of double-layer charging/discharging was discussed based upon the experimental and theoretical results in our work. And then we discussed in detail the applications of the activated carbon fibers to adsorbent materials for purification of liquid and gas.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.6
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• pp.502-507
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• 2007

The oxidation treatment of several carbon materials with a sodium chlorate and 70 wt.% of nitric acid, combined with heat treatment, were attempted to achieve an electrochemical active material with a larger capacitance. Among pitch, needle coke, calcinated needle coke and natural graphite, the structure of needle coke and calacinated needle coke were changed to the graphite oxide structure with the expansion of the inter-layer. On the other hand, the calcinated needle coke after oxidation and heating at $200^{\circ}C$ has exhibited largest capacitance per weight and volume of 29.5 F/g and 24.5 F/ml at the two-electrode system in the potential range of 0 to 2.5 V. The electrochemical performance of the calcinated needle coke was discussed with the phenomenon of the electric field activation and the formation of new pores between the expanded inter-layer at first charge.

• Korean Journal of Materials Research
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• v.32 no.5
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• pp.270-279
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• 2022

In this study, N/S co-doped carbon felt (N/S-CF) was prepared and characterized as an electrode material for electric double-layer capacitors (EDLCs). A commercial carbon felt (CF) was immersed in an aqueous solution of thiourea and then thermally treated at 800 ℃ under an inert atmosphere. The prepared N/S-CF showed a large specific surface area with hierarchical pore structures. The electrochemical performance of the N/S-CF-based electrode was evaluated using both 3-electrode and 2-electrode systems. In the 3-electrode system, the N/S-CF-based electrode showed a good specific capacitance of 177 F/g at 1 A/g and a good rate capability of 41% at 20 A/g. In the 2-electrode system (symmetric capacitor), the freestanding N/S-CF-based electrode showed a specific capacitance of 275 mF/cm² at 2 mA/cm², a rate capability of 62.5 % at 100 mA/cm², a specific power density of ~ 25,000 mW/cm² at an energy density of 23.9 mWh/cm², and a cycling stability of ~ 100 % at 100 mA/cm² after 20,000 cycles. These results indicate the N/S co-doped carbon felts can be a promising candidate as a new electrode material in a symmetric capacitor.

• Korean Journal of Metals and Materials
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• v.49 no.5
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• pp.419-424
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• 2011

Carbon nanotubes (CNTs) were directly synthesized on a copper (Cu) plate as a current collector by the catalytic thermal vapor deposition method for an electric double-layer capacitor (EDLC) electrode. The diameters of vertically aligned CNTs grown on the Cu plate were 20~30 nm. From cyclic voltammetry (CV) results, the CNTs/Cu electrode showed high specific capacitance with typical profiles of EDLCs. Rectangularshaped CV curves suggested that the CNTs/Cu electrode could be an excellent candidate for an EDLC electrode. The specific capacitances were in a range of 25~75 F/g with a scan rate of 10~100 mV/s and KOH electrolyte concentration 1~6 M, and were maintained up to 1000 charge/discharge cycles due to strong adhesion between the Cu substrate and the CNTs.