Publications by authors named "Doo-Hwan Jung"

10 Publications

  • Page 1 of 1

The Effect of Oxygen Content in Binderless Cokes for High-Density Carbon Blocks from Coal Tar Pitch.

Materials (Basel) 2021 Apr 7;14(8). Epub 2021 Apr 7.

Fuel Cell Laboratory, Korea Institute of Energy Research (KIER), Daejeon 34129, Korea.

High-density carbon blocks are much lighter than metals and have excellent mechanical properties and are one of the materials garnering attention to replace existing metal parts. In this study, a binderless coke was produced by changing the flow rates of nitrogen and air as a carrier gas during heat treatment of coal tar pitch and using this, a green body was formed at 150 MPa and carbonized to produce a high-density carbon block. We express the binderless coke produced in this way by N10A0, N7A3, N5A5, N3A7, N0A10 according to the ratio of nitrogen and air, and in the case of carbon block, we have added CB in front of it. We then considered the effect of oxygen content in the binderless cokes on the optical, chemical, and mechanical properties. It was observed that the produced binderless cokes develop into a dense mosaic structure with a small particle size as the air flow rate increased. To survey the change in oxygen content of the produced binderless coke, O1s and C1s regions were measured using X-ray photoelectric spectroscopy (XPS), and O1s/C1s was calculated. The O1s/C1s ratio steadily increased as the air flow rate increased, and in the case of N0A10, it increased about twice as much as that of N10A0 to 11.20%. β-resin has a very large effect on the mechanical strength of the carbon block in addition to air in the pitch. And in the case of CB-N0A10, it shows the best mechanical strength with a density of 1.72 g/cm, bending strength of 87 MPa, and shore hardness of 93 HSD.
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http://dx.doi.org/10.3390/ma14081832DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8067829PMC
April 2021

Surface oxidation of petroleum pitch to improve mesopore ratio and specific surface area of activated carbon.

Sci Rep 2021 Jan 14;11(1):1460. Epub 2021 Jan 14.

Fuel Cell Laboratory, Korea Institute of Energy Research (KIER), Daejeon, 34129, Republic of Korea.

In this study, surface oxidation of petroleum pitch was performed to enhance the thermal stability, specific surface area, and mesopore ratio of activated carbon. The oxygen uptake of the pitch by surface oxidation has a strong influence on the formation of the specific surface area and pore size of activated carbon. It was confirmed that the oxygen uptake from the surface to the inner side of the surface oxidized pitch was the highest at the temperature of 330 °C (IP330-AC), with a mesopore ratio of 63.35% and specific surface area of 1811 m g. The oxygen content of the surface oxidized pitch increased proportionately with the mesopore ratio in activated carbon. The specific surface area and mesopore ratio of IP330-AC were respectively 163% and 487% higher than those of petroleum-based commercial activated carbon (A-BAC), and 102% and 491% higher than those of coconut-based commercial activated carbon (P60).
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http://dx.doi.org/10.1038/s41598-020-80784-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7809199PMC
January 2021

Mechanical and electrical properties of MCMB/Chopped carbon fiber composite with different bead size.

Sci Rep 2019 May 8;9(1):7065. Epub 2019 May 8.

Department of Advanced Energy and Technology, Korea University of Science and Technology, 102 Gajeong-ro, Yuseong-gu, Daejeon, 305350, Republic of Korea.

The carbonization and graphitization of carbon/carbon (C/C) composites prepared from mesocarbon microbeads (MCMB) and chopped carbon fiber (CCF) have been studied with a wide range of temperatures, CCF contents and MCMB sizes. Three different sizes of MCMB were prepared with coal tar pitch at three temperatures, 420, 430 and 440 °C, and identified as about 12.8, 16.0 and 20.1 µm, respectively. Each size of MCMB was mixed with CCFs at ratios of 2, 4, 6 and 8 wt. % and formed into block shape. After carbonization at 1200 °C, carbonized C/C blocks (CCBs) were graphitized at 2000, 2400 and 2800 °C. The CCB prepared with CCF content of 2 wt. % and an MCMB size of 16.0 µm exhibited the highest flexural strength of about 151 MPa. The graphitized C/C block (GCB) with CCF content of 2 wt. %, which was graphitized at 2000 °C showed the highest flexural strength of about 159 MPa.
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http://dx.doi.org/10.1038/s41598-019-43480-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6506510PMC
May 2019

Manufacture of high density carbon blocks by self-sintering coke produced via a two-stage heat treatment of coal tar.

Heliyon 2019 Mar 19;5(3):e01341. Epub 2019 Mar 19.

Advanced Energy and System Engineering, University of Science and Technology (UST), 217 Gajeong-ro, Yuseong-gu, Daejeon, 34113 Republic of Korea.

High-strength and high-density carbonized carbon blocks from self-sintering coke were manufactured using coal tar and two-stage heat treatments (1 and 2 stage treatments). First, the molecular weight distribution of the refined coal tar was controlled through a pressured heat treatment (1 stage treatment). Second, the 1 stage heat-treated coal tar (1S-CT) was treated using a delayed coking system (2 stage treatment) to become the self-sintering coke. Finally, carbon blocks were molded from 2 stage heat-treated coke (2S-C) and carbonized at 1200 °C for 1 h. Through rapid decomposition of the high molecular weight components in the coal tar at 360 °C in the 1 stage treatment, the molecular weight distribution of coal tar was confirmed to be controllable by the 1 stage treatment. Swelling during carbonization was observed in carbon blocks manufactured from 2S-C containing more than 15 wt% of volatile matter from 150-450 °C. The optimum conditions of the two-stage heat treatments were confirmed to be 300 °C for 3 h and 500 °C for 1 h. The highest density and flexural strength of the carbonized carbon blocks manufactured from 2S-C were 1.46 g/cm and 69.2 MPa, respectively.
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http://dx.doi.org/10.1016/j.heliyon.2019.e01341DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6430006PMC
March 2019

Improving the mechanical properties of a high density carbon block from mesocarbon microbeads according to oxidative stabilization.

Sci Rep 2018 Jul 23;8(1):11064. Epub 2018 Jul 23.

Advanced Energy and System Engineering, Korea University of Science and Technology, Yuseong-gu, Daejeon, 305350, Republic of Korea.

In this study, a high density carbon block without binder was manufactured by mesocarbon microbeads (MCMB) from coal tar pitch. To develop the high density carbon block without a binder, MCMBs were oxidized at different levels of temperature. To verify the effect of oxygen content in the carbonized carbon block (CCB), an elementary analysis (EA) and X-ray photoelectron spectroscopy (XPS) were performed. The morphological and mechanical properties of the CCBs were investigated by using scanning electron microscopy (SEM), a shore hardness test, and a flexural strength evaluation. The results revealed that the oxygen content increased with stabilization temperature and the physical properties of the CCBs were considerably improved via oxidative stabilization. Small cracks between MCMB particles were observed in the CCBs that were stabilized over 250 °C. From the results of this study, the CCB from MCMBs stabilized at 200 °C for 1 h showed optimum mechanical properties and high density.
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http://dx.doi.org/10.1038/s41598-018-26971-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6056457PMC
July 2018

Methanol-Tolerant Platinum-Palladium Catalyst Supported on Nitrogen-Doped Carbon Nanofiber for High Concentration Direct Methanol Fuel Cells.

Nanomaterials (Basel) 2016 Aug 15;6(8). Epub 2016 Aug 15.

Fuel Cell Research Center, Korea Institute of Energy Research (KIER), Daejeon 305-343, Korea.

Pt-Pd catalyst supported on nitrogen-doped carbon nanofiber (N-CNF) was prepared and evaluated as a cathode electrode of the direct methanol fuel cell (DMFC). The N-CNF, which was directly synthesized by the catalytic chemical vapor deposition from acetonitrile at 640 °C, was verified as having a change of electrochemical surface properties such as oxygen reduction reaction (ORR) activities and the electrochemical double layer compared with common carbon black (CB). To attain the competitive oxygen reduction reaction activity with methanol tolerance, the Pt and Pd metals were supported on the CB or the N-CNF. The physical and electrochemical characteristics of the N-CNF-supported Pt-Pd catalyst were examined and compared with catalyst supported on the CB. In addition, DMFC single cells using these catalysts as the cathode electrode were applied to obtain I-V polarization curves and constant current operating performances with high-concentration methanol as the fuel. Pt-Pd catalysts had obvious ORR activity even in the presence of methanol. The higher power density was obtained at all the methanol concentrations when it applied to the membrane electrode assembly (MEA) of the DMFC. When the N-CNF is used as the catalyst support material, a better performance with high-concentration methanol is expected.
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http://dx.doi.org/10.3390/nano6080148DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5224627PMC
August 2016

Designing an ultrathin silica layer for highly durable carbon nanofibers as the carbon support in polymer electrolyte fuel cells.

Nanoscale 2014 Oct 8;6(20):12111-9. Epub 2014 Sep 8.

Fuel Cell Research Center, Korea Institute of Energy Research (KIER), Daejeon, 305-343, Republic of Korea.

A critical issue for maintaining long-term applications of polymer electrolyte fuel cells (PEFCs) is the development of an innovative technique for the functionalization of a carbon support that preserves their exceptional electrical conductivity and robustly enriches their durability. Here, we report for the first time how the formation of a partially coated, ultrathin, hydrophobic silica layer around the surfaces of the carbon nanofiber (CNF) helps improve the durability of the CNF without decreasing the significant electrical conductivity of the virgin CNF. The synthesis involved the adsorption of polycarbomethylsilane (PS) on the CNF's sidewalls, followed by high temperature pyrolysis of PS, resulting in a highly durable, conductive carbon support in PEFCs. The Pt nanoparticles are in direct contact with the surface of the carbon in the empty spaces between unevenly coated silica layers, which are not deposited directly onto the silica layer. The presence of a Pt nanoparticle layer that was thicker than the silica layer would be a quite advantageous circumstance that provides contact with other neighboring CNFs without having a significant adverse effect that deeply damages the electrical conductivity of the neighboring CNF composites with the silica layer. Furthermore, the ultrathin, hydrophobic silica layer around the surfaces of the CNF provides great potential to reduce the presence of water molecules in the vicinity of the carbon supports and the ˙OH radicals formed on the surface of the Pt catalyst. As a result, the CNF with a 5 wt% silica layer that we prepared has had extremely high initial performance and durability under severe carbon corrosion conditions, starting up with 974 mA cm(-2) at 0.6 V and ending up with more than 58% of the initial performance (i.e., 569 mA cm(-2) at 0.6 V) after a 1.6 V holding test for 6 h. The beginning-of-life and end-of-life performances based on the virgin CNF without the silica layer were 981 and 340 mA cm(-2) at 0.6 V, respectively. The CNF having a silica layer had long-term durability which was superior to that of the virgin CNF.
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http://dx.doi.org/10.1039/c4nr04293jDOI Listing
October 2014

Electrocatalytic effects of carbon dissolution in Pd nanoparticles.

Langmuir 2012 Feb 9;28(7):3664-70. Epub 2012 Feb 9.

Fuel Cell Research Center, Korea Institute of Energy Research, 71-2 Jang-dong, Yuseong-gu, Daejeon 305-343, Korea.

Highly dispersed Pd nanoparticles were prepared by borohydride reduction of Pd(acac)(2) in 1,2-propanediol at an elevated temperature. They were uniformly dispersed on carbon black without significant aggregation. X-ray diffraction showed that carbons from the Pd precursor dissolved in Pd, increasing its lattice parameter. A modified reduction process was tested to remove the carbon impurities. Carbon removal greatly enhanced catalytic activity toward the oxygen reduction reaction. It also generated an inconsistency between the electronic modifications obtained from X-ray photoelectron spectroscopy and the electrochemical method. CO displacement measurements showed that the formation of Pd-C bonds decreased the work function of the surface Pd atoms.
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http://dx.doi.org/10.1021/la2042668DOI Listing
February 2012

Innovative polymer nanocomposite electrolytes: nanoscale manipulation of ion channels by functionalized graphenes.

ACS Nano 2011 Jun 6;5(6):5167-74. Epub 2011 May 6.

Department of Chemical & Biomolecular Engineering (BK21 program), KAIST, Daejeon 305-701, Republic of Korea.

The chemistry and structure of ion channels within the polymer electrolytes are of prime importance for studying the transport properties of electrolytes as well as for developing high-performance electrochemical devices. Despite intensive efforts on the synthesis of polymer electrolytes, few studies have demonstrated enhanced target ion conduction while suppressing unfavorable ion or mass transport because the undesirable transport occurs through an identical pathway. Herein, we report an innovative, chemical strategy for the synthesis of polymer electrolytes whose ion-conducting channels are physically and chemically modulated by the ionic (not electronic) conductive, functionalized graphenes and for a fundamental understanding of ion and mass transport occurring in nanoscale ionic clusters. The functionalized graphenes controlled the state of water by means of nanoscale manipulation of the physical geometry and chemical functionality of ionic channels. Furthermore, the confinement of bound water within the reorganized nanochannels of composite membranes was confirmed by the enhanced proton conductivity at high temperature and the low activation energy for ionic conduction through a Grotthus-type mechanism. The selectively facilitated transport behavior of composite membranes such as high proton conductivity and low methanol crossover was attributed to the confined bound water, resulting in high-performance fuel cells.
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http://dx.doi.org/10.1021/nn2013113DOI Listing
June 2011

Direct synthesis and structural analysis of nitrogen-doped carbon nanofibers.

Langmuir 2009 Jul;25(14):8268-73

Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka 816-8580, Japan.

Carbon nanofibers containing a range of nitrogen contents of 1-10 atom % were directly synthesized by catalytic chemical vapor deposition over nickel-based catalysts at 350-600 degrees C using acetonitrile and acrylonitrile. The nitrogen content was controlled by careful choice of the reaction conditions. The N-doped carbon nanofibers showed herringbone structure with 20-60 nm diameter. X-ray photoelectron spectroscopy was applied to examine the chemical state of nitrogen in carbon nanofibers. Structural features of N-doped carbon nanofibers were examined in X-ray diffraction and electron microscopy. The mechanism for nitrogen including the structure of carbon nanofibers through the catalysis was discussed on the basis of the results.
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http://dx.doi.org/10.1021/la900472dDOI Listing
July 2009