• Title/Summary/Keyword: graphite oxide

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Improvement of Cathode Reaction of Vanadium Redox Flow Battery by Reforming Graphite Felt Electrode Using Cobalt Oxide (바나듐 레독스 흐름전지 양극 반응 향상을 위한 코발트 산화물 전극 개질법 연구)

  • Park, Jeongmok;Ko, Minseong
    • Journal of the Korean institute of surface engineering
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    • v.52 no.3
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    • pp.180-185
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    • 2019
  • The demands to improve the performance of the vanadium redox flow battery have attracted an intense research on modifying the carbon-based electrode. In this study, the surface of graphite felt was reformed, using cobalt oxide. The cobalt oxide was implanted into graphite felt during hydrothermal and two step heat treatments. The cobalt was deposited by hydrothermal method and the two step heat treatments made lots of holes on the graphite felt surface which is called as porous surface. The porous surface acts as an electrochemically active site for the cathodic reaction of vanadium redox flow battery. The reformed electrode shows the electrochemically improved performance compared with the pristine electrode.

Chemical Reaction between Aluminium and graphite Crucible During the Fabrication of Spherical Monosized Al particles

  • Kwon, Hansang
    • Journal of Powder Materials
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    • v.25 no.2
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    • pp.99-103
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    • 2018
  • Spherical monosized pure aluminum (Al) particles are successfully fabricated by the pulsated orifice ejection method (POEM). The surface reaction between Al and the graphite crucible is investigated by analysing the microstructure and chemical composition of the materials. No significant chemical reaction occurs between Al and the graphite owing to the crystalline Al oxide (${\gamma}-Al_2O_3$) layer generated in the initial state. The ${\gamma}-Al_2O_3$ layer is clearly observed in all regions between the Al particles and graphite via transmission electron microscopy and confirmed by the selected area diffraction pattern. The morphology of the ${\gamma}-Al_2O_3$ layer perfectly follows the surface morphology of the graphite crucible, which showed nanoscale roughness. This implies that molten Al could not directly contact graphite even though the surface of the crucible became rough to some extent. However, this passivation phenomenon allowed the successful fabrication of monosized pure Al particles. Therefore, POEM is a useful process at least to manufacture monosized pure Al particles.

Preparation and Characterization of Reduced Graphene Nanosheets via Pre-exfoliation of Graphite Flakes

  • Meng, Long-Yue;Park, Soo-Jin
    • Bulletin of the Korean Chemical Society
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    • v.33 no.1
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    • pp.209-214
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    • 2012
  • In this work, the reduced graphene nanosheets were synthesized from pre-exfoliated graphite flakes. The pristine graphite flakes were firstly pre-exfoliated to graphite nanoplatelets in the presence of acetic acid. The obtained graphite nanoplatelets were treated by Hummer's method to produce graphite oxide sheets and were finally exfoliated to graphene nanosheets by ultrasonication and reduction processes. The prepared graphene nanosheets were studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). From the results, it was found that the preexfoliation process showed significant influence on preparation of graphite oxide sheets and graphene nanosheets. The prepared graphene nanosheets were applied to the preparation of conductive materials, which yielded a greatly improved electrical resistance of $200{\Omega}/sq$.

Effect of Microwave Irradiation on Exfoliation of Graphene Oxide (마이크로파 조사가 산화그래핀의 화학적 박리에 미치는 효과)

  • Lee, Jae-Hee;Hwang, Ki-Wan;Jeong, Young-Hoon;Kim, Eui-Tae
    • Korean Journal of Materials Research
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    • v.23 no.12
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    • pp.708-713
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    • 2013
  • Graphene oxide has been synthesized by microwave-assisted exfoliation of graphite oxide prepared by modified Hummers method. Graphite was oxidized in a solution of $H_2O_2$ and $KMnO_4$ at $65{\sim}80^{\circ}C$, followed by 10 % $H_2O_2$ solution treatment at $80{\sim}90^{\circ}C$. The graphite oxide was exfoliated under microwave irradiation of 1 kW and was reduced to graphene effectively by hydrazine hydrate ($H_4N_2{\cdot}H_2O$) treatment. The exfoliation of graphene oxide was significantly affected by the microwave irradiation on (heating)/off (cooling) period. An on/off period of 10 s/20 s resulted in much more effective exfoliation than that of 5 s/10 s with the same total treatment time of 10 min. This can be explained by the higher exfoliation temperature of 10 s/20 s. Repetition of the graphite oxidation and exfoliation processes also enhanced the exfoliation of graphene oxide. The thickness of the final graphene products was estimated to be several layers. The D band peaks of the Raman spectra of the final graphene products were quite low, suggesting a high crystal quality.

The Cycling Performance of Graphite Electrode Coated with Tin Oxide for Lithium Ion Battery (리튬이온전지용 주석산화물이 도포된 흑연전극의 싸이클 성능)

  • Kang, Tae-Hyuk;Kim, Hyung-Sun;Cho, Won-Il;Cho, Byung-Won;Ju, Jeh-Beck
    • Journal of the Korean Electrochemical Society
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    • v.5 no.2
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    • pp.52-56
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    • 2002
  • Tin oxide was coated on graphite particle by sol-gel method and an electrode with this material having microcrystalline structure for lithium ion battery was obtained by heat treatment in the range $400-600^{\circ}C$. The content of tin oxide was controlled within the range of $2.25wt\%\~11.1wt\%$. The discharge capacity increased with the content of tin oxide and also initial irreversible capacity increased. The discharge capacity of tin oxide electrode showed more than 350 mAh/g at the initial cycle and 300 mAh/g after the 30th cycle in propylene carbonate(PC) based electrolyte whereas graphite electrode without surface modification showed 140 mAh/g. When the charge and discharge rate was changed from C/5 to C/2, The discharge capacity of tin oxide and graphite electrode showed $92\%\;and\;77\%$ of initial capacity, respectively. It has been considered that such an enhancement of electrode characteristics was caused because lithium $oxide(Li_2O)$ passive film formed from the reaction between tin oxide and lithium ion prevented the exfoliation of graphite electrode and also reduced tin enhanced the electrical conduction between graphite particles to improve the current distribution of electrode.

Effect of Magnesium Nanoparticles on Graphite Oxide for Hydrogen Storage Behaviors (마그네슘입자가 담지된 그라파이트 옥사이드의 수소저장거동)

  • Lee, Seul-Yi;Park, Soo-Jin
    • 한국신재생에너지학회:학술대회논문집
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    • 2011.05a
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    • pp.157.2-157.2
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    • 2011
  • In this work, we prepared Mg nanoparticles loaded graphite oxide (Mg-G) as a function of Mg content in order to investigate hydrogen storage behaviors. The structure and morphology of the Mg-G samples were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The textural properties of the samples were evaluated using $N_2$/77 K adsorption isotherms. The hydrogen adsorption capacities were investigated at 298 K/10 MPa. As a result, the hydrogen adsorption capacities of the Mg-G were enhanced with increasing the Mg content. Therefore, it was found that the presence of Mg on graphite surfaces created hydrogen-favorable sites, resulting in enhancing the hydrogen adsorption capacity.

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EnhAnced Electric Double Layer Capacitance of New Poly Sodium 4-tyrenesulfonate Intercalated Graphene Oxide Electrodes

  • Jeong, Hye-Gyeong
    • Proceedings of the Korean Vacuum Society Conference
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    • 2013.08a
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    • pp.287.2-287.2
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    • 2013
  • We synthesized a new composite of poly sodium 4-styrenesulfonate intercalated graphene oxide for energy storage devices by controlling oxidation time in the synthesis of graphite oxide. Specific capacitance was improved from 20 F/g of the previous composites to 88 F/g of the new composite at the current density of 0.3 A/g. The capacitance retention was 94% after 3000 cycles, indicating that the new composites of high cyclic stability, prominent performance as electric double layer capacitor, and even low resistance could be an excellent carbon based electrode for further energy storage devices.

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Control of size and physical properties of graphene oxide by changing the oxidation temperature

  • Kang, Dong-Woo;Shin, Hyeon-Suk
    • Carbon letters
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    • v.13 no.1
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    • pp.39-43
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    • 2012
  • The size and the physical properties of graphene oxide sheets were controlled by changing the oxidation temperature of graphite. Graphite oxide (GO) samples were prepared at different oxidation temperatures of $20^{\circ}C$, $27^{\circ}C$ and $35^{\circ}C$ using a modified Hummers' method. The carbon-to-oxygen (C/O) ratio and the average size of the GO sheets varied according to the oxidation temperature: 1.26 and 12.4 ${\mu}m$ at $20^{\circ}C$, 1.24 and 10.5 ${\mu}m$ at $27^{\circ}C$, and 1.18 and 8.5 ${\mu}m$ at $35^{\circ}C$. This indicates that the C/O ratio and the average size of the graphene oxide sheets respectively increase as the oxidation temperature decreases. Moreover, it was observed that the surface charge and optical properties of the graphene oxide sheets could be tuned by changing the temperature. This study demonstrates the tunability of the physical properties of graphene oxide sheets and shows that the properties depend on the functional groups generated during the oxidation process.

Chemically Modified Graphenes: Chemistry and Applications

  • Park, Sung-Jin
    • Proceedings of the Korean Vacuum Society Conference
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    • 2011.02a
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    • pp.8-8
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    • 2011
  • During the last half decade, chemically modified graphene (CMG) has been studied in the wide range of applications, such as polymer composites, energy-related materials, sensors, 'paper'-like materials, field-effect transistors (FET), inks, actuators, and biomedical applications due to its excellent electrical, mechanical, and thermal properties. Chemical modification of graphene oxide, which is generated from graphite oxide, which is produced by simple oxidation of graphite, has been a promising route to achieve mass production of CMG platelets via their colloidal suspensions. Graphene oxide contains a range of reactive oxygen functional groups, which renders it a good candidate for use in the aforementioned applications (among others) through chemical functionalizations. In this presentation, I will discuss my recent research activities on the fundamental chemistry of graphite oxide, as well as novel applications based on CMGs. Topics will include the chemical structure of CMGs and colloidal suspensions of CMG platelets, as well as a wide variety of applications.

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A Study on the Preparation and Purification Characteristics of Graphene Oxide by Graphite Type (흑연 종류에 따른 산화 그래핀의 제조 및 정제를 통한 특성연구)

  • Jeong, Kyeom;Kim, Young-Ho
    • Clean Technology
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    • v.27 no.2
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    • pp.132-138
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    • 2021
  • Research is being conducted on graphene to provide graphene having both excellent physical as well as electrical properties in addition to unique physical properties. In this study, Hummer's method, which is a representative method for chemical exfoliation, was applied in order to investigate the possibility of the mass production of high-quality graphene oxide. Three types of graphite (graphite, crystalline graphite, and expanded graphite) were used in the preparation of graphene oxide with variations in the amount of potassium permanganate added, reaction temperature, and reaction time. Then a Fourier transform infrared spectroscopy (FT-IR), a Raman spectrometer, and a transmission electron microscope (TEM) were used to measure the quality of the prepared graphene oxide. Of the three types of graphite used in this experiment, crystalline graphite showed the highest quality. The prepared graphene oxide was then purified with an organic solvent, and an analysis conducted using energy dispersive X-ray spectroscopy (EDS). From the results of the residual values, we were able to confirm that both acid wastewater and wastewater were best purified using cyclohexane. The method for manufacturing graphene oxide as well as the method of purification using organic solvents that are presented in this study are expected to have less of an environmental impact, making them environmentally friendly. This makes them suitable for use in various industrial fields such as the film industry and for heat dissipation and as coating agents.