• Journal of Electrochemical Science and Technology
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• v.12 no.2
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• pp.237-245
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• 2021

Atomic layer deposition (ALD) enhances the stability of cathode materials via surface modification. Previous studies have demonstrated that an Ni-rich cathode, such as LiNi_0.8Co_0.1Mn_0.1O₂, is a promising candidate owing to its high capacity, but is limited by poor cycle stability. In this study, to enhance the stability of the Ni-rich cathode, synthesized LiNi_0.8Co_0.1Mn_0.1O₂ was coated with Al₂O₃ using ALD. Thus, the surface-modified cathode exhibited enhanced stability by protecting the interface from Ni-O formation during the cycling process. The coated LiNi_0.8Co_0.1Mn_0.1O₂ exhibited a capacity of 176 mAh g^-1 at 1 C and retained up to 72% of the initial capacity after 100 cycles within a range of 2.8-4.3 V (vs Li/Li⁺. In contrast, pristine LiNi_0.8Co_0.1Mn_0.1O₂ presented only 58% of capacity retention after 100 cycles with an initial capacity of 173 mAh g^-1. Improved cyclability may be a result of the ALD coating, which physically protects the electrode by modifying the interface, and prevents degradation by resisting side reactions that result in capacity decay. The electrochemical impedance spectra and structural and morphological analysis performed using electron microscopy and X-ray techniques establish the surface enhancement resulting from the aforementioned strategy.

• Corrosion Science and Technology
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• v.4 no.4
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• pp.121-129
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• 2005

Basic design concept of the future steel structure requires environmental compatibility and maintenance free capability to minimize economic burdens. Recent trends in alloy design for advanced weathering steel include addition of various alloying elements which can enhance formation of stable and protective rust layer even in polluted urban and/or high $Cl^{-}$ environment. The effects of Ca, Ni, W, and Mo addition on the corrosion property of Ca-modified weathering steel were evaluated through a series of electrochemical tests (pH measurement and electrochemical impedance spectroscopy: EIS) and structural analysis on rust layer formed on the steel surface. Ca-containing inclusions of Ca-Al-Mn-O-S compound are formed if the amount of Ca addition is over 25 ppm. Steels with higher Ca content results in higher pH value for condensed water film formed on the steel surface, however, addition of Ni, W, and Mo does not affect pH value of the thin water film. The steels containing a high amount of Ca, Ni, W and Mo showed a dense and compact rust layer with enhanced amount of ${\alpha}-FeOOH$. Addition of Ni, W and Mo in Ca-modified weathering steel shows anion-selectivity and contributes to lower the permeability of $Cl^{-}$ ions. Effect of each alloying element on the formation of protective rust layer will be discussed in detail with respect to corrosion resistance.

• Bulletin of the Korean Chemical Society
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• v.34 no.7
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• pp.2162-2166
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• 2013

The tailored surface modification of electrode materials is crucial to realize the wanted electronic and electrochemical properties. In this regard, a dexterous carbon encapsulation technique can be one of the most essential preparation methods for the electrode materials for lithium rechargeable batteries. For this purpose, DL-malic acid ($C_4H_6O_5$) was here used as the carbon source enabling an amorphous carbon layer to be formed on the surface of Si nanoparticles at enough low temperature to maintain their own physical or chemical properties. Various structural characterizations proved that the bulk structure of Si doesn't undergo any discernible change except for the evolution of C-C bond attributed to the formed carbon layer on the surface of Si. The improved electrochemical performance of the carbon-encapsulated Si compared to Si can be attributed to the enhanced electrical conductivity by the surface carbon layer as well as its role as a buffering agent to absorb the volume expansion of Si during lithiation and delithiation.

• Carbon letters
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• v.1 no.3_4
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• pp.170-177
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• 2001

Lithium intercalated carbon (LIC) are basically employed as an anode for currently commercialized lithium secondary batteries. However, there are still strong interests in modifying carbon surface of active materials of the anode because the amount of irreversible capacity, charge-discharge capacity and high rate capability are largely determined by the surface conditions of the carbon. In this study, the carbonaceous materials were coated with tin oxide and copper by fluidized-bed chemical vapor deposition (CVD) method and their coating effects on electrochemical characteristics were investigated. The electrode which coated with tin oxides gave the higher capacity than that of raw material. Their capacity decreased with the progress of cycling possibly due to severe volume changes. However, the cyclability was improved by coating with copper on the surface of the tin oxides coated carbonaceous materials, which plays an important role as an inactive matrix buffering volume changes. An impedance on passivation film was decreased as tin oxides contents and it resulted in the higher capacity.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1100-1103
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• 2003

One of the good ways to raise the rate of the electrochemical reaction is to broaden the effective surface area of the electrode by developing cylindrical nano-pores on the surfaces. The numerous pores of several nanometer in diameter can be used to enhance a specific faradaic reaction so that the nano-porous structure attract keen attention in terms of implication of new bio/chemical sensors, in which no chemical modification is involved. Amperometric glucose sensor is a representative example that needs the selective enhancement of glucose oxidation over the current due to physiological interferents such as ascorbic acid. The present paper reports how the ascorbic acid and glucose diffuse around the nano-porous surface by simulation study, for which 2D-FDM (Finite Difference Method) was adopted. The results of the simulation not only consist with those from electrochemical experiments but also reveal valuable potential for more advanced application of the nano-porous electrode.

• Journal of the Korean Ceramic Society
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• v.55 no.1
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• pp.21-35
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• 2018

Spinel $LiNi_{0.5}Mn_{1.5}O_4$ has received great attention as one of the most outstanding cathode materials for Li-ion batteries (LIBs) because of its high energy density resulting from the operating voltage of ~ 4.7 V (vs. $Li^+/Li$) based on the $Ni^{2+}/Ni^{4+}$ redox reaction. However, $LiNi_{0.5}Mn_{1.5}O_4$ is known to suffer from undesirable side reactions with the electrolyte at high voltage as well as Mn dissolution from the structure. These issues prevent the realization of the optimal electrochemical performance of $LiNi_{0.5}Mn_{1.5}O_4$. Extensive research has been conducted to overcome these issues. This review presents an overview of the various surface-modification methods available to improve the electrochemical properties of $LiNi_{0.5}Mn_{1.5}O_4$ and provides perspectives on further research aimed at the application of $LiNi_{0.5}Mn_{1.5}O_4$ as a cathode material in commercialized LIBs.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.20 no.2
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• pp.209-229
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• 2022

This work provided a review of three techniques-(1) spectrochemical, (2) electrochemical, and (3) spectroelectrochemical-for molten salt medias. A spectroelectrochemical system was designed by utilizing this information. Here, we designed a spectroelectrochemical cell (SEC) and calibrated temperature controllers, and performed initial tests to explore the system's capability limit. There were several issues and a redesign of the cell was accomplished. The modification of the design allowed us to assemble, align the system with the light sources, and successfully transferred the setup inside a controlled environment. A preliminary run was executed to obtain transmission and absorption background of NaCl-CaCl₂ salt at 600℃. It shows that the quartz cuvette has high transmittance effects across all wavelengths and there were lower transmittance effects at the lower wavelength in the molten salt media. Despite a successful initial run, the quartz vessel was mated to the inner cavity of the SEC body. Moreover, there was shearing in the patch cord which resulted in damage to the fiber optic cable, deterioration of the SEC, corrosion in the connection of the cell body, and fiber optic damage. The next generation of the SEC should attach a high temperature fiber optic patch cords without introducing internal mechanical stress to the patch cord body. In addition, MACOR should be used as the cell body materials to prevent corrosion of the surface and avoid the mating issue and a use of an adapter from a manufacturer that combines the free beam to a fiber optic cable should be incorporated in the future design.

• Corrosion Science and Technology
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• v.21 no.2
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• pp.111-120
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• 2022

To solve the corrosion problem of industrial equipment and other constructions containing metals, corrosion protection can be performed by using coating which provides a barrier between the metal and its environment. Coatings play a significant role in protecting irons and steels in harsh marine and acid environments. This study was conducted to identify an anti-corrosive epoxy coating for carbon steel composite with 0.1, 0.3, and 0.5 wt% concentrations of nanoparticles of SiO₂ using the dip-coating method. The electrochemical behavior was analyzed with open circuit potential (OCP) technics and polarization curves (Tafle) in 3.5 wt% NaCl and 5 vol% H₂SO₄ media. The structure, composition, and morphology were characterized using different analytical techniques such as X-ray Diffraction (XRD), Fourier Transform Infrared spectrum (FT-IR), and Scanning Electron Microscopy (SEM). Results revealed that epoxynano SiO₂ coating demonstrated a lower corrosion rate of 2.51 × 10^-4 mm/year and the efficiency of corrosion protection was as high as 99.77%. The electrochemical measurement showed that the nano-SiO₂ / epoxy coating enhanced the anti-corrosive performance in both NaCl and H₂SO₄ media.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2001.11a
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• pp.31-32
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• 2001

Recently, many of the current development in surface modification engineering are focused on multilayered coatings. Multilayered coatings have the potential to improve the tribological and corrosion properties of tools and components. By using cathodic arc deposition, $WC-Ti_{1-x}Al_xN$ multilayers were deposited on steel substrates. Wear tests of four multiplayer coatings were performed using a ball-on-disc configuration with a linear sliding speed of 0.1m/s, 5N load. The tests were carried out at room temperature in airby employing AISI 52100 steel ball ($H_v=848N$) of 11mm in diameter. Electrochemical tests were performed using the potentiodynamic and electrochemical impedance spectroscopy (EIS) measurements. The surface morphology and topography of the wear scars of tribo-element and the corroded specimen have been determined by using scanning electron spectroscopy (SEM). Also, wear mechanism was determined by using SEM coupled with EDS. Results have showed an improved wear resistance and corrosion resistance of the $WC-Ti_{1-x}Al_xN$ coatings.

• Journal of Electrochemical Science and Technology
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• v.15 no.3
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• pp.421-426
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• 2024

Ru dye (Z-907) is a crucial photosensitizing material in dye-sensitized solar cells (DSSCs). To enhance the utilization of Ru dye's photosensitizing properties in bulk heterojunction solar cells, a method was developed to synthesize phenyl-C61-butyric acid methyl ester (PCBM) nanoparticles that are chemically linked to Ru dye. PCBM contains a methoxy (-OCH₃) group, whereas Ru dye incorporates a carboxyl group (-COOH) within its molecular structure. By exploiting these complementary functional groups, a successful bond between Ru dye and PCBM was established through an anhydride functional group. The coupling of PCBM with Ru dye results in a modification of the energy levels, yielding lower LUMO (3.8 eV) and HOMO (6.1 eV) levels, compared with the LUMO (3.0 eV) and HOMO (5.2 eV) levels of Ru dye alone. This configuration potentially facilitates efficient electron transfer from Ru dye to PCBM, alongside promoting hole transfer from Ru dye to the conducting polymer. Consequently, the bulk heterojunction solar cells incorporating this Ru dye-PCBM configuration demonstrate superior performance, with an open circuit voltage (V_oc) of 0.62 V, short circuit current (J_sc) of 0.63 mA cm^-2, fill factor (FF) of 65.6%, and a photovoltaic conversion efficiency (η) of 0.25%.