• Korean Journal of Materials Research
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• v.33 no.10
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• pp.430-438
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• 2023

In this study, we synthesized pH-controlled resorcinol-formaldehyde (RF) gels through the polymerization of two starting materials: resorcinol and formaldehyde. The prepared RF gels were dried using an acetone substitution method, and they were subsequently carbonized under nitrogen atmosphere to obtain carbon xerogels (CX_Y) prepared at different pH (Y). The carbon xerogels were utilized as active materials for coin-type organic supercapacitor electrodes to investigate the influence of pH on the electrochemical properties of the carbon xerogels. The carbon xerogels prepared at lower pH (CX_9.5 and CX_10) exhibited sufficient particle growth, with a three-dimensional network of particles during the RF gel formation, resulting in the development of abundant mesopores. Conversely, the carbon xerogels prepared at higher pH (CX_11 and CX_12) retained densely packed structures of small particles, leading to pore collapse and low specific surface areas. Consequently, CX_9.5 and CX_10 showed high specific surface areas, and provided ample adsorption sites for the formation of electric double layers with electrolyte ions. Moreover, the three-dimensional particle network in CX_9.5 and CX_10 significantly enhanced electrical conductivity. The presence of well-developed mesopores in these materials further facilitated the effective transport of electrolyte ions, contributing to their superior performance as organic supercapacitor electrodes. This study confirmed that pH-controlled carbon xerogels are one of the promising active materials for organic supercapacitor electrodes. Furthermore, we concluded that pH during RF gel formation is a crucial factor determining the electrode performance of the carbon xerogels, highlighting the need for precise pH control to obtain high-performance carbon xerogel electrodes.

• Bulletin of the Korean Chemical Society
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• v.35 no.5
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• pp.1343-1348
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• 2014

A cholesterol-bridge-naphthopyran dyad (NP-MCB) was designed and synthesized. NP-MCB can readily self-assemble into gels under ultrasound-radiation in several organic solvents and the formed gels easily transfer to solution by heat. This reversible process can be repeated many times. Scanning Electron Microscopy results showed that the morphologies of all formed xerogels in different solvents have fibrillar microstructure. The gels formation was due to energy and pressure afforded by the ultrasonic process, resulting in formation of molecular hydrogen bonding and molecular aggregation. NP-MCB displayed the normal photochromism both in solution and gel states. The kinetic results confirm that the colored merocyanine in gels show a slower fading speed than that in solution due to the compact aggregation of NP-MCB molecules in gels. The xerogel film formed in polar gelling solvent had large surface wettability than that in nonpolar gelling solvent.

• Journal of the Korean Electrochemical Society
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• v.6 no.2
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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.

• Journal of Sensor Science and Technology
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• v.16 no.1
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• pp.77-83
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• 2007

Nanoporous silica aerogels with various surface modifiers were prepared by ambient drying process. Tetraethylorthosilicate (TEOS) were used a raw material. Ambient drying process for various surface modifier was studied in the point of view of a crack-free monolith and thin films and low cost. Various kinds of surface modifiers like as hexamethyldisilazane (HMDSZ), trimethlychlorosilane (TMCS), methlytriethoxylsilane (MTES), and methlytrimethoxysilane (MTMS) were studied in order to enhance hydrophobicity for the silica aerogel. Surface modified aerogels were evaluated by FT-IR, TG, BET, SEM and wetting angle measurement. Homogeneous and crack-free aerogels were obtained by modifying the HMDSZ and the TMCS. However silica xerogel was obtained when modified with MTMS, MTES.

• Bulletin of the Korean Chemical Society
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• v.35 no.12
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• pp.3465-3474
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• 2014

Porous silica particles are the most prevailing raw material for stationary phases of liquid chromatography. During a long period of time, various methodologies for production of porous silica particles have been proposed, such as crashing and sieving of xerogel, traditional dry or wet process preparation of conventional spherical particles, preparation of hierarchical mesoporous particles by template-mediated pore formation, repeated formation of a thin layer of porous silica upon nonporous silica core (core-shell particles), and formation of specific silica monolith followed by grinding and calcination. Recent developments and applications of useful porous silica particles will be covered in this review. Discussion on sub-$3{\mu}m$ silica particles including nonporous silica particles, carbon or metal oxide clad silica particles, and molecularly imprinted silica particles, will also be included. Next, the individual preparation methods and their feasibilities will be collectively and critically compared and evaluated, being followed by conclusive remarks and future perspectives.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.93-96
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• 2001

We have reported to make nanostructured cobalt oxide electrode that have large capacitance over than 400F/g (specific capacitance) and good cycleability. But, It had serious demerits of low voltage range under 0.5V 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 than 250F/g capacitance consisted of EDLC and pseudocapacitance. In gel electrolyte, cobalt oxide electrode had around l00F/g capacitance. This capacitance was only surface EDLC. In solution electrolyte, potassium ion as working ion reacted with both of layers easily. However, In gel electrolyte, reacted with only surface-active layer. Its very hard to reach resistive layer. So, we have studied on pretreatment of electrode to contain working ions easily. We'll report more details.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.93-96
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• 2001

We have reported to make nanostructured cobalt oxide electrode that have large capacitance over than 400F/g (specific capacitance) and good cycleability. But, It had serious demerits of low voltage range under 0.5V 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 than 250F/g capacitance consisted of EDLC and pseudocapacitance. In gel electrolyte, cobalt oxide electrode had around 100F/g capacitance. This capacitance was only surface EDLC. In solution electrolyte, potassium ion as working ion reacted with both of layers easily. However, In gel electrolyte, reacted with only surface-active layer. Its very hard to reach resistive layer. So, e have studied on pretretmetn of electrode to contain working ions easily. We'll report more details.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.101-102
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• 2006

금속을 도핑 함으로써 전기전도도가 향상될 것으로 생각되는 산화바나듐 나노선에 대하여 열처리 전후의 전기적 특성을 비교하였다. sol-gel 방법으로 만들어진 산화바나듐 xerogel($V_{1.66}Mo_{0.33}O_5{\cdot}nH_2O$)을 $Si_3N_4$ 절연막이 성장된 Si기판위에 분산시키고 Ti/Au으로 전극을 증착한 후 열처리 한 것과 하지 않은 두 시료의 전류-전압특성을 비교 분석하였다.

• Bulletin of the Korean Chemical Society
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• v.19 no.3
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• pp.328-332
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• 1998

Anionic ring-opening polymerization of 3,4-[(dimethylsilyl)isopropyl]benzo-1,1-dimethyl-1-silacyclopentene in the presence of n-butyllithium and HMPA in THF at - 78 ℃ afforded poly[3,4-(dimethylsilylisopropyl)benzo-1,1-dimethyl-1-silapentene]. The characteristic Si-H stretching frequency in the IR is observed at 2100 cm-1. The polycarbosilane has been modified by chloroplatinic acid catalyzed addition of styrene to the polycarbosilane SiH units. Molecular weights and thermal properties of the polymers were compared. The sol-gel polymerization of 3,4-[(dimethoxysilyl)isopropyl]benzo-1,1-dimethoxy-1-silacyclopentene in the presence of aqueous HCl or NaOH in THF resulted in a cross-linked polysiloxane. The xerogel has a low surface area of 13-14 m2/g and is stable up to about 400 ℃ with only 5% weight loss under a nitrogen atmosphere.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.3
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• pp.219-225
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• 2000

The spinel structured $LiMn_2O_4$was obtained by two consecutive heat treatment on xerogel; the first heat treatment was at $150^{\circ}C$ and the second at $350^{\circ}C$ was obtained by sol-gel process using an aqueous solution of lithium hydroxide and manganese acetate. The synthesized $LiMn_2O_4$ by the sol-gel process showed a discharge capacity of 88~56 mAh/g after 15 cycles in Li/lM $LiClO_4$(in PC)/$LiMn_2O_4$at a current density of 0.25 mA/$\textrm{cm}^2$ and the voltage ranged 3.5 V to 4.3 V. For the second heat treatment above $350^{\circ}C$, $Mn_2O_3$was formed as a by-product during the synthesis of $LiMn_2O_4$. The heat treatment at $500^{\circ}C$, for example, showed a lower discharge capacity 81~47 mAh/g, after the 15 charge/discharge cycles. The lower capacity was due to the increment of $Mn^{3+}$ ion and this phenomenon was in agreement with the Jahn-Teller distortion.