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PYUN, Su Il 대한금속재료학회(대한금속학회) 1999 METALS AND MATERIALS International Vol.5 No.1
In-situ spectroelectrochemical technique has been applied to investigate passivating surface film on porous carbon electrode and plasma enhanced chemical vapour deposited (PECVD) carbon film electrode in organic electrolytic solution consisting of ethylene carbonate (EC) and diethyl carbonate (DEC) solvent, and 1 M LiPF_6 and LiAsF_6. Water impurity with the concentration of 0 M, 0.02 M, 0.05 M, and 0.1 M Hz0 was added to 1 M LiPF_6-EC/DEC solution. In-situ Fourier transform infra-red (FTIR) spectra of the surface film on both electrodes with the constituents of ROCO₂Li, Li₂CO₃, and Li_xPF_y suggested that the reduction of EC to ROCO₂Li runs via a one-electron transfer pathway as a result of diffusion of water through the surface film, and then Li₂CO₃ formation proceeds simultaneously by the chemical reaction of ROCO₂Li with water. From the measured potential dependence of the amount of the salt reduction products, it is suggested that the surface film formed in 1 M LiPF_6-EC/DEC solution gives a poorer passivity as compared with that formed in 1 M LiAsF_6-EC/DEC solution, which is due to the considerable interference of LiPF_6 salt reduction with the compact sedimentation of ROCO₂Li on the electrode. In-situ FTIR spectra of the surface film showed that all the peak intensities of the three constituents significantly increase with increasing water content under application of the negative potentials with respect to open circuit potential (OCP). From these experimental results, the dependence of the passivity of the surface film on the carbon electrode on the water concentration of the electrolyte, as well as on the lithium salt type, was discussed in view of the salt and solvent reactivities.
PYUN, Su Il 한국부식학회 1999 Corrosion Science and Technology Vol.28 No.1
This article first explained the basic concepts of chemical diffusivity D~_(chem) and component diffusivity D_(comp) of cation(ion) in mixed conductor which are of great importance in the area of solid state electrochemistry and then introduced briefly such electrochemical methods to their determination as galvanostatic intermittent titration technique(GITT), potentiostatic intermittent titration technique(PITT) and electrochemical impedance spectroscopy(EIS). Finally this article summarised the results of the investigation on chemical and component diffusivities of lithium ion in Li_δV₂O_5, Li_(1-δ)MO₂(M=Ni,Co) and Li_(1-δ)Mn₂O₄, using those electrochemical techniques reported from our laboratory.
Pyun, Su-Il,Na, Kyung-Hwan,Go, Joo-Young,Park, Jin-Ju The Korean Electrochemical Society 2003 한국전기화학회지 Vol.6 No.3
The present work is concerned with characterization of surface roughness and inhomogeneity of four kinds of hot-rolled carbon steels in terms of the fractal dimension and the depression parameter by using image analysis method and electrochemical impedance spectroscopy, respectively. From the analysis of the 3D AFM image, it is realized that all the hot-rolled steel surfaces show the self-affine fractal property. The values of the fractal dimension of the hot-rolled steels were determined by the analyses of the AFM images on the basis of both the perimeter-area method and the triangulation method. In addition, the Nyquist plots were found to be depressed from a perfect semicircle form. From the experimental findings, the changes in the values of the fractal dimension and the depression parameter with chemical composition have been discussed in terms of the change in the value of hardness of base steel.