• Journal of the Korean Chemical Society
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• v.18 no.5
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• pp.373-380
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• 1974

Direct electrochemical preparation of periodate from iodide $(I^-{\to}{IO_4}^-)$ was investigated using a none-diaphragm cell and lead dioxide anode. The direct electrolytic conditions were combinations of the respectively results on the processes of iodate from iodide$(I^-{\to}{IO_3}^-)$, and periodate from iodate$({IO_3}^-{\to}{IO_4}^-)$ which were reported by the author, previously. The optimum condition was achieved when 1.0 M potassium iodide solution containing 0.5 g/l potassium dichromate as an anti-reducing agent was electrolyzed at anodic current density of $15{\AA}/dm^2$ and electrolytic temperature of $60^{\circ}C$. Under such a condition, the current efficiency was found to be 84 % at 98 % conversion of iodide to periodate. The explanation of electrode reaction was also given a consideration based on the polarization curves at lead dioxide anode in various electrolyte solutions.

• Korean Chemical Engineering Research
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• v.51 no.5
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• pp.540-544
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• 2013

During start up and shut down of a proton exchange membrane fuel cells (PEMFC), the performance and lifetime of PEMFC were reduced. In this study, effect of startup and shutdown were investigated in dead-end type PEMFC using oxygen as a cathode gas with polarization curve, impedance spectroscopy (EIS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Dummy load which eliminates residual hydrogen and oxygen during startup and shutdown operation should be applied to mitigated the degradation of PEMFC performance. At 50% relative humidity (RH) under the repetitive on/off cycling, the cell performance decayed faster than at 100% RH because of corrosion of the cathode carbon support. Water suppling into cell reduced the degradation rate of dead-end type PEMFC during start up and shut down cycling at 50% RH.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.3
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• pp.186-189
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• 2003

The role of excess Pb about the crystallization behavior and electrical properties in b(Zr$\sub$0.52/Ti$\sub$0.48/)O3(PZT) thin films has not been precisely defined. In this work, the effect of excess Pb content on the ferroelectric properties of these films was investigated. To analyze the effect, PZT films containing various amounts of excess Pb were Prepared. PZT thin films were deposited on the Pt/Ti bottom electrode by rf magnetron sputtering method and then they were crystallized by rapid thermal annealing (RTA). The experiment showed that all PZT films indicated perovskite polycrystalline structure with preferred orientation (111) and no pyrochlore phase was observed. As higher excess Pb was included, the films showed that value of leakage current shift from 2.03${\times}$10$\^$-6/ to 6.63 ${\times}$ 10$\^$-8/A/cm$^2$ at 100kV/cm, and value of remanent polarization shift from 8.587 ${\mu}$C /cm$^2$ to 4.256 ${\mu}$C/ cm$^2$. Electrical properties of PZT thin film affected by Pb excess content of target were explained to be caused of defect among space charges and defect grain boundaries.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.1
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• pp.61-69
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• 2013

Polymer exchange membrane (PEM) fuel cells have multifunctional properties, and bipolar plates are one of the key components in these fuel cells. Generally, a bipolar plate has a gas flow path for hydrogen and oxygen liberated at the anode and cathode, respectively. In this study, the influence of iodine applied to a bipolar plate was investigated. Accordingly, we compared bipolar plates with and without iodine coating, and the performances of these plates were evaluated under operating conditions of $75^{\circ}C$ and 100% relative humidity. The membrane and platinum-carbon layer were affected by the iodine-coated bipolar plate. Bipolar plates coated with iodine and a membrane-electrode assembly (MEA) were investigated by electron probe microanalyzer (EPMA) and energy-dispersive x-ray spectroscopy (EDS) analysis. Polarization curves showed that the performance of a coated bipolar plate is approximately 19% higher than that of a plate without coating. Moreover, electrochemical impedance spectroscopy (EIS) analysis revealed that charge transfer resistance and membrane resistance decreased with the influence of the iodine charge transfer complex for fuel cells on the performance.

• Korean Chemical Engineering Research
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• v.54 no.2
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• pp.181-186
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• 2016

Recently, there are many efforts focused on development of more economical non-fluorinated membranes for use in PEMFCs (Proton Exchange Membrane Fuel Cells). In this study, characteristics of sulfonated Poly(ether ether ketone) (sPEEK) were compared according to degrees of sulfonation (DS), relative humidity, cell temperatures at PEMFC operation condition. I-V polarization curve, hydrogen crossover, electrochemical surface area, membrane resistance and charge transfer resistance were measured. sPEEK membrane showed high performance at high DS, high temperature and high relative humidity, in particular, performance of sPEEK membrane decreased largely due to low ionic conductivity at low DS and low relative humidity.

• Transactions on Electrical and Electronic Materials
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• v.6 no.2
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• pp.51-56
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• 2005

Ferroelectric Bi$_{3.35}$Sm$_{0.65}$Ti$_{3}$O$_{12}$(BSmT) thin films were synthesized using a sol-gel process. Bi(TMHD)$_{3}$, Sm$_{5}$(O$^{i}$Pr)13, Ti(O$^{i}$Pr)4 were used as the precursors, which were dissolved in 2­methoxyethanol. The BSmT thin films were deposited on Pt/TiO$_{x}$/SiO$_{2}$/Si substrates by spin­coating. The electrical properties of the thin films were enhanced using rapid thermal annealing process (RTA) at 600 $^{circ}$C for 1 min in O$_{2}$. Thereafter, the thin films were annealed from 600 to 720 $^{circ}$C in oxygen ambient for 1 hr, which was followed by post-annealed for 1 hr after depositing a Pt electrode to enhance the electrical properties. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze the crystallinity and surface morphology of layered perovskite phase, respectively. The remanent polarization value of the BSmT thin films annealed at 720 $^{circ}$C after the RTA treatment was 35.31 $\mu$C/cmz at an applied voltage of 5 V.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.3
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• pp.198-203
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• 2013

Dye-sensitized solar cells (DSSCs) based on titanium dioxide ($TiO_2$) have been extensively studied because of their promising low-cost alternatives to conventional semiconductor based solar cells. DSSCs consist of molecular dye at the interface between a liquid electrolyte and a mesoporous wide-bandgap semiconductor oxide. Most efforts for high conversion efficiencies have focused on dye and liquid electrolytes. However, interface engineering between dye and electrode is also important to reduce recombination and improve efficiency. In this work, for interface engineering, we deposited semiconducting ferroelectric $BiFeO_3$ with bandgap of 2.8 eV on $TiO_2$ nanoparticles and nanotubes. Photovoltaic properties of DSSCs were characterized as a function of thickness of $BiFeO_3$. We showed that ferroelectric $BiFeO_3$-coated $TiO_2$ electrodes enable to increase overall efficiency of DSSCs, which was associated with efficient electron transport due to internal electric field originating from electric polarization. It was suggested that engineering the dye-$TiO_2$ interface using ferroelectric materials as inorganic modifiers can be key parameter for enhanced photovoltaic performance of the cell.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.817-820
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• 2004

The $Sr_{0.7}Bi_{2.6}Ta_2O_9$(SBT) thin films are deposited on Pt-coated electrode($Pt/TiO_2/SiO_2/Si$) using a RF magnetron sputtering method. The ferroelectric properties of SBT capacitors with annealing time were studied. In the SEM images, Bi-layered perovskite phase was crystallized at 10min and grains largely grew with annealing tune. SBT thin films are transformed from initial amorphous phase to the fully formed layer-structured perovskite. During the annealing process at $750^{\circ}C$, we found that an fluorite-like stage is formed after 3min. In the XRD pattern, the SBT thin films after 3min annealing time had (105) orientation. The ferroelectric properties of SBT capacitor with annealing time represent a favorable properties at 60 min. The maximum remanent polarization and the coercive electric field with 60 min are $12.40C/cm^2$ and 30kV/cm, respectively. The leakage current density with 60min is $6.81{\times}10^{-10}A/cm^2$.

• Bulletin of the Korean Chemical Society
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• v.19 no.6
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• pp.661-666
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• 1998

Active reaction sites and electrochemical O2 reduction kinetics on La_{1-x}Sr_xMnO_{3+{\delta}} (x=0.1-0.4)/YSZ (yttria-stabilized zirconia) electrodes are investigated in the temperature range of 700-900 ℃ at $Po_2=10^{-3}$-0.21 atm. Results of the steady-state polarization measurements, which are formulated into the Butler-Volmer formalism to extract transfer coefficient values, lead us to conclude that the two-electron charge transfer step to atomically adsorbed oxygen is rate-limiting. The same conclusion is drawn from the $Po_2$-dependent ac impedance measurements, where the exponent m in the relationship of $I_o$ (exchange current density) ∝ $P_{o_{2}}^m$ is analyzed. Chemical analysis is performed on the quenched Mn perovskites to estimate their oxygen stoichiometry factors (δ) at the operating temperature (700-900 ℃). Here, the observed δ turns out to become smaller as both the Sr-doping contents (x) and the measured temperature increase. A comparison between the 8 values and cathodic activity of Mn perovskites reveals that the cathodic transfer coefficients $({\alpha}_c)$ for oxygen reduction reaction are inversely proportional to δ whereas the anodic ones $({\alpha}_a)$ show the opposite trend, reflecting that the surface oxygen vacancies on Mn perovskites actively participate in the $O_2$ reduction reaction. Among the samples of x= 0.1-0.4, the manganite with x=0.4 exhibits the smallest 8 value (even negative), and consistently this electrode shows the highest ${\alpha}_c$ and the best cathodic activity for the oxygen reduction reaction.

• Journal of Ocean Engineering and Technology
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• v.28 no.4
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• pp.356-362
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• 2014

Wear and corrosion of the engine parts surrounded with combustion chamber is more serious compared to the other parts of the engine because temperature of the exhaust gas in a combustion chamber is getting higher and higher with increasing of using the heavy oil of low quality. Therefore, an optimum repair weldment as well as an available choice of the base metal for these parts are very important to prolong their lifetime in a economical point of view. It reported that there was an experimental result for repair weldment on the forged steel which would be generally used with piston crown material, however, it is considered that there is no study for the repair weldment on the cast steel of piston crown material. In this study, four types of electrodes such as 1.25Cr-0.5Mo, 0.5Mo Inconel 625 and 718 were welded with SMAW and GTAW methods on the cast steel which would be generally used with piston crown material. And the corrosion properties of weld metal, heat affected zone and base metal were investigated using electrochemical methods such as measurement of corrosion potential, anodic polarization curves, cyclic voltammogram and impedance etc. in 35% $H_2SO_4$ solution. In the cases of Inconel 625, 718, the weld metals and base metals exhibited the best and worst corrosion resistance respectively, however, 1.25Cr-0.5Mo and 0.5Mo indicated that corrosion resistance of the base metal was better than the weld metal. And the weld metal welded with electrodes of Inconel 625 revealed the best corrosion resistance among the electrodes, and Inconel 718 followed the Inconel 625. Hardness relatively also indicated higher value in the weld metal compared to heat affected zone and base metal. In particular, Inconel 718 indicated the highest value of hardness compared to other electrodes in the heat affected zone.