• Journal of Electrochemical Science and Technology
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• v.11 no.3
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• pp.291-309
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• 2020

Chromium was electrodeposited from deep eutectic solvents-based Cr³⁺ electrolytes on HB-pencil graphite electrode. Factors influencing the electrochemical behavior and the processes of Cr nucleation and growth were explored using cyclic voltammetry and chronoamperometry techniques, respectively. Cr³⁺ reduction was found to occur through an irreversible diffusion-controlled step followed by another irreversible one of impure diffusional behaviour. The reduction behavior was found to be greatly affected by Cr³⁺ concentration, temperature, and type of hydrogen bond donor used in deep eutectic solvents (DESs) preparation. A more comprehensive model was suggested and successfully applied to extract a consistent data relevant to Cr nucleation kinetics from the experimental current density transients. The potential, the temperature, and the hydrogen bond donor type were estimated to be critical factors controlling Cr nucleation. The nucleation and growth processes of Cr from either choline chloride/ethylene glycol (EG-DES) or choline chloride/urea (U-DES) deep eutectic solvents were evaluated at 70℃ to be three-dimensional (3D) instantaneous and diffusion-controlled, respectively. However, the kinetics of Cr nucleation from EG-DES was found to be faster than that from U-DES. Cr nucleation was tending to be instantaneous at higher temperature, potential, and Cr³⁺ concentration. Cr nuclei electrodeposited from EG-DES were characterized at different conditions using scanning electron microscope (SEM). SEM images show that high number density of fine spherical nuclei of almost same sizes was nearly obtained at higher temperature and more negative potential. Energy dispersive spectroscopy (EDS) analysis confirms that Cr deposits were obtained.

• Journal of the Korean Electrochemical Society
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• v.2 no.2
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• pp.61-65
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• 1999

A new treatment of $LiV_3O_8$ has been proposed for improving its electrochemical behavior as a cathode material for secondary lithium batteries. Lithium trivanadate, $LiV_3O_8$, can be prepared in a finely dispersed form by dehydration of aqueous lithium trivanadate gels. The ultrasonic treatment method for Liv30s has been examined in comparison with $LiV_3O_8$ prepared by solutionmethod. The ultrasonically treated products in water were characterized by XRD (X-ray diffractometry), TGA (thermogravimetric analysis) and SEM (scanning electron microscopy). These measurements showed that the ultrasonic treatment process of aqueous $LiV_3O_8$ caused a decrease in crytallinity and considerable increased in specific surface area and interlayer spacing. The product, ultrasonically treated in water for 2 h, showed a high initial discharge capacity and was charge-discharge cycled without large capacity loss. The ultrasonic treated Liv30s can improve not only the specific capacity, but also the cycling behavior

• Journal of Electrochemical Science and Technology
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• v.8 no.3
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• pp.197-205
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• 2017

Lead dioxide thin films were electrodeposited on nickel substrate from acidic lead nitrate solution. Current efficiency and thickness measurements, cyclic voltammetry, AFM, SEM, and X-ray diffraction experiments were conducted on $PbO_2$ surface to elucidate the effect of lead nitrate concentration, current density, temperature on the morphology, chemical behavior, and crystal structure. Experimental results showed that deposition efficiency was affected by the current density and solution concentration. The film thickness was independent of current density when deposition from high $Pb(NO_3)_2$ concentration, while it decreased for low concentration and high current density deposition. On the other hand, deposition temperature had negative effect on current efficiency more for lower current density deposition. Cyclic voltammetric study revealed that comparatively more ${\beta}-PbO_2$ produced compact deposits when deposition was carried out from high $Pb(NO_3)_2$ concentration. Such compact films gave lower charge discharge current density during cycling. SEM and AFM studies showed that deposition of regular-size sharp-edge grains occurred for all deposition conditions. The grain size for high temperature and low concentration $Pb(NO_3)_2$ deposition was bigger than from low temperature and high concentration deposition conditions. While cycling converted all grains into loosely adhered flappy deposit with numerous pores. X-ray diffraction measurement indicates that high concentration, high temperature, and high current density favored ${\beta}-PbO_2$ deposition while ${\alpha}-PbO_2$ converted to ${\beta}-PbO_2$ together with some unconverted $PbSO_4$ during cycling in $H_2SO_4$.

• Journal of the Korean Chemical Society
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• v.35 no.4
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• pp.374-378
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• 1991

The electrochemical reduction behavior of Bilirubin (BR) in phosphate buffer (pH 7.8) solution was studied by DC polarography, differential pulse polarography, cyclic voltammetry and controlled potential coulometry. In DC polarogram, two reduction waves of BR were found. The half wave potentials of two reduction waves were -1.32 and -1.51 volts vs. Ag/AaCl respectively. The current type of 1st reduction wave was diffusion-controlled and the 2$^{nd}$ reduction wave was diffusion current containing a little kinetic current. The electrochemical reduction process of BR at each reduction step was all irreversible. The prewave appeared at lower concentration than 3.4 ${\times}$ 10$^{-4}$M, this prewave was identified as adsorption prewave. And the number of electron transfered in reduction steps, n$_{app}$ was two for the 1st reduction step and one for the 2$^{nd}$ reduction step.

• Journal of Electrochemical Science and Technology
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• v.1 no.2
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• pp.85-91
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• 2010

We have studied the origin of an additional plateau of $Li_{4+x}Ti_5O_{12}$ (LTO) observed at 0.7 V (vs. Li/$Li^+$). Some LTO has to be discharged down to below 1.0 V forming two-stage plateau (1.5 V and 0.7 V) in order to obtain most of capacity while others could achieve the same level of capacity at higher potential (1.0 V vs. Li/$Li^+$) forming one plateau (1.5 V). The particle size effect has been investigated as a possible reason of this. The 0.7 V plateau was gradually elongated with increasing the particle size. The structural variations and kinetic behaviors during discharge were carefully examined by in-situ XRD technique and OCV measurement. According to structural and electrochemical verifications, the kinetic limitation of $Li^+$ insertion is responsible primarily for the two-stage plateau which is related to the particle size of LTO rather than the formation of new intermediate phase during discharge. Herein, we propose a possible reaction model to elucidate this abnormal behavior of LTO below 1.0 V (Li/$Li^+$).

• Corrosion Science and Technology
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• v.8 no.1
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• pp.27-39
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• 2009

Non metallic composite materials, for example, GECM(graphite epoxy composite material) show high specific strength because of low density. These kinds of non metallic composite materials improved the structural effectiveness and operation economics. However, if these materials contacted several metals, corrosion can be arisen since non metallic composite materials have electrical conductivity. This paper dealt with galvanic corrosion between graphite epoxy composite material and several metals. Base on the electrochemical galvanic corrosion test between GECM and metals, corrosion current of carbon steel and aluminium increased with time but corrosion current of stainless steels and titanium decreased and galvanic potential increased. This behavior shows the galvanic corrosion depends upon the presence of passive film. Also, galvanic effect of GECM coupled with ferrous alloys and non-ferrous alloys was lower than that of 100% graphite, which is attributed to lower exposed area of graphite fiber in the GECM than apparent area of the GECM specimen used for the calculation of galvanic current in this work.

• Journal of the Korean institute of surface engineering
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• v.46 no.6
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• pp.271-276
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• 2013

The demand for stainless steel is continuously increasing with the development in offshore industry due to its excellent corrosion resistance characteristics. However, it suffers cavitation-erosion in application of high rotating fluid and the damage accelerates in combination with electrochemical corrosion because of Cl-ion in sea water. This paper investigated the complex damage behavior for 431 stainless steel, that is one of martensite stainless steels, through the hybrid test in sea water. Various experiments were carried out, including potential measurement, anodic/cathodic polarization experiment and Tafel analysis. Surface morphology was observed and damage depth was analyzed by SEM and 3D microscope after each experiment, respectively. The results revealed that more active potential was observed under cavitation condition than static condition due to breakdown of passive film and activation of charge transfer, and that higher corrosion current density was obtained under cavitation condition due to synergistic effect of corrosion and erosion.

• Journal of the Korean Electrochemical Society
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• v.17 no.1
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• pp.26-29
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• 2014

The corrosion behavior of stainless steel 304 (SS 304), titanium, nickel and aluminium is studied by immersion and anodic polarization tests in non-aqueous electrolytes. Tetraethyl ammonium tetrafluoroborate is used as a supporting electrolyte in the three kinds of solvents. The immersion test shows that chemical corrosion rate in propylene carbonate-based electrolyte is lower than those in acetonitrile- or ${\gamma}$-butyrolactone-based electrolytes. Surface analyses do not reveal any corrosion product formed after the immersion test. In the anodic polarization tests, a higher concentration of supporting electrolyte gives a higher current density. In addition, a higher temperature increases the current density in the active region and reduces the potential range in the passive region. SS 304 shows the highest corrosion potential while Al shows the lowest corrosion potential and the highest current density in all studied conditions. Based on the conducted corrosion tests, the corrosion resistance of metal substrates in the organic solvents can be sorted in descending order as follows: SS 304 - Ti - Ni - Al.

• Bulletin of the Korean Chemical Society
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• v.27 no.3
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• pp.403-406
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• 2006

The surface structure and electrochemical behavior of self-assembled monolayers (SAMs) formed by aromatic thiols on Au(111) were investigated by scanning tunneling microscopy (STM) and cyclic voltammetry. Benzenethiol (BT) forms disordered phases on Au(111) which are composed of many bright domains, while benzyl mercaptan (BM), with a methylene unit between the aromatic group and sulfur atom, forms twodimensional ordered SAMs on Au(111). In addition, two phase-separated domains consisting of disordered and ordered phases were observed in binary SAMs formed from a 1 : 1 mixed ethanol solution of BT and BM. From STM and CV measurements, we found that the blocking efficiency of aromatic thiol SAMs coated on an Au(111) electrode for an electron transfer reaction decreases as the structural order of the SAMs increases. Molecular-scale STM and CV results obtained here will be very useful in designing functional SAMs for further applications, such as the improvement of corrosion passivation of Au(111) on an aromatic thiolmodified Au(111) surface.

• Bulletin of the Korean Chemical Society
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• v.29 no.6
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• pp.1229-1232
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• 2008

The surface structure, electrochemical behavior, and wetting property of self-assembled monolayers (SAMs) formed by dioctyl diselenide (DODSe) on Au(111) were investigated by scanning tunneling microscopy (STM), cyclic voltammetry (CV), and contact angle measurements. In contrast to the formation of well-ordered SAMs by octanethiol on Au(111), the SAMs formed by DODSe have a disordered phase and many unusual vacancy islands (VIs). In addition, the formation of DODSe SAMs is largely influenced by the solution concentration used. DODSe SAMs formed in 5 $\mu$ M and 50 $\mu$ M solutions have two mixed domains consisting of missing-row ordered phases and disordered phases, while DODSe SAMs formed in 1 mM and 5 mM solutions have only disordered phases with an abnormally high VI fraction of 22-24%. We also found that the wetting property and electrochemical behavior of DODSe SAMs on Au(111) are markedly influenced by the formation of ordered SAMs and the density of VIs.