• Journal of the Korean Ceramic Society
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• v.39 no.6
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• pp.523-527
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• 2002

LiMn$_2$O$_4$ compounds were synthesized by calcining a mixture of LiOH and MnO$_2$(CMD) at 47$0^{\circ}C$ for 10 h and then calcining again at $650^{\circ}C$ to 90$0^{\circ}C$ fur 48 h in air with intermediate grinding. All the synthesized samples exhibited XRD patterns for the cubic spinel phase with a space group Fd3m. The lattice parameter increased gradually as the sintering temperature rose. The electrochemical cells were charged and discharged fur 20 cycles at a current density 300$\mu$A/$\textrm{cm}^2$ between 3.5 V and 4.3 V. The voltage vs. discharge capacity curves for all the samples showed two plateaus. The LiMn$_2$O$_4$ sample calcined at 90$0^{\circ}C$ had the largest first discharge capacity. This sample exhibited the best crystallinity, had relatively large lattice parameter and had relatively large particles with rectatively homogeneous size. All the samples showed good cycling performances. Among all the samples, the LiMn$_2$O$_4$ calcined at 85$0^{\circ}C$ had relatively large first discharge capacity and very good cycling performance. The addition of excess LiOH and the mixing in ethanol considered to help the formation of the more LiMn$_2$O$_4$ phase per unit weight sample and the more stable LiMn$_2$O$_4$phase. These led to the larger discharge capacities and the better cycling performances. The cyclic voltammograms fur the second cycle of the LiMn$_2$O$_4$ samples showed the oxidation and reduction peaks around 4.05 V and 4.18 V and around 4.08 V and 3.94 V, respectively. The larger first discharge capacity of the sample calcined at the higher temperature is related to the larger lattice parameter.

• Journal of the Korean Electrochemical Society
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• v.12 no.3
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• pp.263-270
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• 2009

Carbon felt surface was modified by heat or acid treatment in order to use for the electrode of a redox-flow battery. Polymers on the surface of carbon felt was removed and oxygen-containing functional group was attached after the thermal treatment of carbon felt. Thermal treatment was better for the stability of the carbon structure than the acid treatment. Oxygen-containing functional group on the thermally treated carbon felt at 500$^{\circ}C$ was confirmed by XPS and elementary analysis. BET surface area was increased from nearly zero to 96 $m^2/g$. Thermally treated carbon felt at 500$^{\circ}C$ showed lower activation polarization than the thermally treated carbon felt at 400$^{\circ}C$ and the acid-treated carbon felt in the cyclicvoltammetry and polarization experiments. The thermally treated carbon felts at 400$^{\circ}C$ and 500$^{\circ}C$ and the acid-treated carbon felt was applied for the electrode to prepare vanadium redox flow battery. Voltage efficiencies of charge/discharge were 86.6%, 89.6%, and 96.9% for the thermally treated carbon felts at 400$^{\circ}C$ and 500$^{\circ}C$ and the acid-treated carbon felt, respectively.

• Journal of the Korean Electrochemical Society
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• v.12 no.4
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• pp.329-334
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• 2009

This study is to develop a fuel cell system applicable to an in situ NMR (Nuclear magnetic resonance) diagnosis. The in situ NMR can be used in real time monitoring of various reactions occurring in the fuel cell, such as oxidation of fuel, reduction of oxygen, transport phenomena, and component degradation. The fuel cell for this purpose is, however, to be operated in a specifically designed tubular shape toroid cavity detector (TCD), which constrains the fuel cell to have a tubular shape. This may cause difficulties in effective mass transport of reactants/products and uniform distribution of assembly pressure. Therefore, a new flow field designed in a particular way is necessary to enhance the mass transport in the tubular fuel cell. In this study, a tubular-shaped close-type flow field made of non-magnetic material is developed. With this flow field, oxygen is effectively delivered to the cathode surface and the produced water is readily removed from the membrane-electrode assembly to prevent flooding. The resulting DMFC (direct methanol fuel cell) outperforms the open-type flow field and exhibits $36\;mW/cm^2$ even at room temperature.

• Journal of the Korean Electrochemical Society
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• v.12 no.1
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• pp.47-53
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• 2009

In this study, highly ordered AAO (Anodic Aluminum Oxide) with nanopores was prepared by commercial grade Al substrate containing 3.5 wt.% impurities through two step anodizing method. Nanopores of prepared AAO arrays were used as templates for preparing nanofiber. $TiO_2$ was deposited by using DP (deposition-precipitation) method into AAO pores to grow nanofiber. Au particles were loaded on this $TiO_2$ nanofiber which was grown vertically. Prepared 2 wt.% $Au/TiO_2$ nanofiber was characterized by XRD, SEM and Raman. The crystal structure was analyzed by the XRD. SEM was used to observe pore size and pore wall thickness. Photocatalytic activity of co-oxidation was compared with $TiO_2$ and $Au/TiO_2$ nanofiber on AAO arrays.

• Applied Chemistry for Engineering
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• v.18 no.5
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• pp.522-526
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• 2007

Structural features and electrochemical performances of cokes pyrolized from oxidized cokes were examined, and compared with KOH-activated coke. Needle cokes ($d_{002}=3.5{\AA} $), having a graphene layer structure, were changed to a single phase of graphite oxide after oxidation treatment with an acidic solution having an $NaCLO_3$/needle coke composition ratio of above 7.5, and the inter-layer distance of the oxidized coke was expanded to $6.9{\AA} $ with increasing oxygen content. After heating at $200^{\circ}C$, the oxidized coke was pyrolized to the graphene layer structure with inter-layer distance of $3.6{\AA} $. However, the change of the inter-layer distance of the needle coke was not observed in the KOH activation process. On the other hand, an intercalation of electrolyte ions into the pyrolized coke, observed at first charge, occurred at 1.0 V, in which the value was lower than that of KOH-activation coke. The cell capacitor using pyrolized coke exhibited a lower internal resistance of $0.57{\Omega}$ in 1 kHz, and a larger capacitance per weight and volume of 30.3 F/g and 26.9 F/ml at the two-electrode system in the potential range 0~2.5 V than those of the cell capacitor using KOH-activation of coke. This better electrochemical performance may be associated with structure defects in the graphene layer derived from the process of the inter-layer expansion and shrinkage.

• Korean Chemical Engineering Research
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• v.43 no.1
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• pp.9-15
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• 2005

In order to know the electrochemical decomposition characteristics of ammonia to nitrogen, this work has studied several experimental variables on the electrolytic ammonia decomposition. The effects of pH and chloride ion at $IrO_2$, $RuO_2$, and Pt anodes on the electrolytic decomposition of ammonia were compared, and the existence of membrane equipped in the cell and the changes of the current density, the initial ammonia concentration and so on were investigated on the decomposition. The performances of the electrode were totally in order of $RuO_2{\approx}IrO_2>Pt$ in the both of acid and alkali conditions, and the ammonia decomposition was the highest at a current density of $80mA/cm^2$, over which it decreased, because the adsorption of ammonia on the electrode surface was hindered due to the evolution of oxygen. The ammonia decomposition increased with the concentration of chloride ion in the solution. However, the increase became much dull over 10 g/l of chloride ion. The $RuO_2$ electrode among the tested electrodes generated the most OH radicals which could oxidized the ammonium ion at pH 7.

• Journal of the Korean Applied Science and Technology
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• v.31 no.1
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• pp.44-49
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• 2014

We were investigated by cyclic voltammetry to the stability through the electrochemical characteristics of phospholipid(L-${\alpha}$-phosphatidylethanolamine, LAPE) monolayer LB films. LAPE monolayer LB films was deposited by the LB method on the indium tin oxide(ITO) glass. The electrochemical properties was measured by cyclic voltammetry with a three-electrode system in 0.5 N, 1.0 N, 1.5 N and 2.0 N $KClO_4$ solution. The measuring range is continuously oxidized to 1650 mV, with an initial potential of -1350 mV was reduced. Scanning rates of 50, 100, 150, 200, and 250 mV/s was set. As a result, LB monolayer films of LAPE was appeared on irreversible processes by the oxidation current from the cyclic voltammogram. Diffusion coefficient (D) of LAPE was calculated 195, 15.9, 5.75, 1.38 and $0.754cm^2s^{-1}{\times}10^{-9}$ at 0.01 N, 0.05 N, 0.10 N, 0.15 N and 0.20 N $KClO_4$ solutions, respectively.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.6
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• pp.291-298
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• 2016

Electrochemical water treatment process as a useful treatment method for the removal of non-degradable matter has been consistently studied for several decades. Key process of electrochemical water treatment are oxidation reaction from an anode and reduction from a cathode. In this study, the effect of pre-treatment methods in the insoluble electrode manufacturing process for the water treatment has been evaluated for the life time of electrode The results of this study showed that pre-treatment methods of a base metal such as surface roughness, clean method and interlayer formation influenced to life time of electrode when the same condition (catalyst electrode layer coating method and material system) was applied for pre-treatment methods. This study was conducted by using $IrO_2/Ti$ electrode In the test of sand-blasting process, an electrode manufactured by using sanding media of different sizes resulted in the most effective electrode life time when the size of alumina was used for $212{\sim}180{\mu}m$ praticle size (#80). The most effective method was considered using arc plasma in the additional roughness control and cleaning process, sputtering method to form Ta type interlayer formation process.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.80-85
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• 2019

Vanadium dioxide is a well-known metal-insulator phase transition material. Lots of researches of vanadium redox flow batteries have been researched as large scale energy storage system. In this study, vanadium oxide($VO_x$) thin films were applied to cathode for lithium ion battery. The $VO_x$ thin films were deposited on Si substrate($SiO_2$ layer of 300 nm thickness was formed on Si wafer via thermal oxidation process), quartz substrate by RF magnetron sputter system for 60 minutes at $500^{\circ}C$ with different RF powers. The surface morphology of as-deposited $VO_x$ thin films was characterized by field-emission scanning electron microscopy. The crystallographic property was confirmed by Raman spectroscopy. The optical properties were characterized by UV-visible spectrophotometer. The coin cell lithium-ion battery of CR2032 was fabricated with cathode material of $VO_x$ thin films on Cu foil. Electrochemical property of the coin cell was investigated by electrochemical analyzer. As the results, as increased of RF power, grain size of as-deposited $VO_x$ thin films was increased. As-deposited thin films exhibit $VO_2$ phase with RF power of 200 W above. The transmittance of as-deposited $VO_x$ films exhibits different values for different crystalline phase. The cyclic performance of $VO_x$ films exhibits higher values for large surface area and mixed crystalline phase.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.134-134
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• 2010

Fuel cell is a device that directly converts chemical energy in the form of a fuel into electrical energy by way of an electrochemical reaction. In the anode for a high temperature fuel cell, nickel or nickel alloy has been used in consideration of the cost, oxidation catalystic ability of hydrogen which is used as fuel, electron conductivity, and high temperature stability in reducing atmosphere. Most MCFC stacks currently operate at an average temperature of $650^{\circ}C$. There is some gains with decreased temperature in MCFC to diminish the electrolyte loss from evaporation and the material corrosion, which could improve the MCFC life. However, operating temperature has a strong related on a number of electrode reaction rates and ohmic losses. Baker et al. reported the effect of temperature (575 to $650^{\circ}C$). The rates of cell voltage loss were 1.4mV/$^{\circ}C$ for a reduction in temperature from 650 to $600^{\circ}C$, and 2.16mV/$^{\circ}C$ for a decrease from 600 to $575^{\circ}C$. The two major contributors responsible for the change in cell voltage with reducing operation temperature are the ohmic polarization and electrode polarization. It appears that in the temperature range of 550 to $650^{\circ}C$, about 1/3 of the total change in cell voltage with decreasing temperature is due to an increase in ohmic polarization, and the electrode polarization at the anode and cathode. In addition, the oxidation reaction of hydrogen on an ordinary nickel alloy anode in MCFC is generally considered to take place in the three phase zone, but anyway the area contributing to this reaction is limited. Therefore, in order to maintain a high performance of the fuel cell, it is necessary to keep this reaction responsible area as wide as possible, that is, it is needed to keep the porosity and specific surface area of the anode at a high level. In this study effective anodes are prepared for low temperature MCFC capable of enhancing the cell performance by using zirconium hydride at least in part of anode material.