Yongsug Tak

Microporous Carbon Nanoplates from Regenerated Silk Proteins for Supercapacitors

Novel carbon-based microporous nanoplates containing numerous heteroatoms (H-CMNs) are fabricated from regenerated silk fibroin by the carbonization and activation of KOH. The H-CMNs exhibit superior electrochemical performance, displaying a specific capacitance of 264 F/g in aqueous electrolytes, a specific energy of 133 Wh/kg, a specific power of 217 kW/kg, and a stable cycle life over 10000 cycles.

Electrocatalytic activity of Cu electrode in electroreduction of CO2

The electrocatalytic activity of Cu electrode in the electrochemical reduction of carbon dioxide (CO2) was investigated. Electroreduction mechanism of CO2 was studied by the adsorption/desorption behaviors of reacting species by using an in-situ electrochemical quartz crystal microbalance. (EQCM) and the surface changes measured by ex-situ SEM, AES, and XRD analysis. During cathodic reduction of CO2 on Cu, the adsorption of amorphous carbon was observed. After electrolysis time of 1 h at constant cathodic potential, the poisoning of amorphous carbon resulted in the decrease of the faradaic efficiency for the formation of hydrocarbons such as CH4 and C2H4. On the other hand, the potential modulation method caused the change of the surface structure of copper, i.e. the formation of cuprous oxide (Cu2O). This structural change prevented the adsorption of amorphous graphite and the constant production rate of methane was obtained in long-term electrolysis.

Radio-Frequency Magnetron Sputtering Power Effect on the Ionic Conductivities of Lipon Films

gas atmosphere with different radio-frequency magnetronsputtering power from 80 to 160 W with 20 W step increase. Lipon films deposited at lower sputtering power showed higher ionicconductivities than the films deposited at higher sputtering power. The results of impedance measurements showed that nitrogenincorporation into the glass structure increased the ionic conductivity and this nitrogen content in the Lipon films increased as thesputtering power decreased. In addition, the Auger electron spectroscopy depth profile showed that the increased nitrogen contentin the Lipon films was not the result of the target surface poisoning effect but the result of reactive incorporation of nitrogen.© 2001 The Electrochemical Society. @DOI: 10.1149/1.1420926# All rights reserved.Manuscript submitted May 29, 2001; revised manuscript received September 21, 2001. Available electronically November 8,2001.

Electrodeposition of PbO2 onto Au and Ti substrates

The electrodeposition of lead dioxide (PbO2) onto Au and Ti substrates was anodically executed at 65°C and the electrochemical characteristics and the mechanism in the PbO2 films deposition were investigated by the using an in-situ electrochemical quartz crystal microbalance, cyclic voltammogram, and chronoamperometry experiments. An X-ray diffractometer and scanning electron microscope were also used for investigation of the formed lead dioxide films onto both substrates. Considering the experimental and theoretical mass/charge ratios, PbO2 deposition on Au by applying constant potential was in excellent agreement with the theoretical value, while relatively higher values of the mass/charge ratio due to film hydration were found when Ti was used as substrate. Analysis of X-ray diffractometer and scanning electron microscope show different film structures on each substrate, especially the additional hydration of the lead dioxide film deposited on Ti leads to some structural effects, identified as Sky-Lotus PbO2.

Electrodeposition of Cu2O Nanowires Using Nanoporous Alumina Template

We first electrodeposited highly ordered Cu 2 O nanowires using a home-made alumina template. Home-made nanoporous alumina templates were prepared by a two-step anodization method and selective removal of aluminum substrate by bromine solution. Chronopotentiometry (i.e., constant current method) of -0.5 mA/cm 2 was applied to deposit compact Cu 2 O nanowires without disconnection into the honeycomb shaped pores of a home-made nanoporous alumina membrane. Analyzing morphological observations by scanning electron microscopy and transmission electron microscopy, we observed that the diameter of Cu 2 O nanowire was ca. 57 nm and the length was 4 μm demonstrating an aspect ratio of 70. X-ray diffraction structural analysis indicated that Cu 2 O(200) was preferentially formed compared with other Cu 2 O crystalline phases which may be due to an adjusted solution pH 9.

Electrodeposition of ZnO on ITO electrode by potential modulation method

We report the effect of the concentration of hydroxide ion adsorbed (OHad) on indium tin oxide ~ITO! in the electrodeposition of zinc oxide ~ZnO! by potential modulation method. We found that by applying an optimal constant potential of 20.72 V, X-ray diffraction ~XRD! peak intensity of crystalline phase indicating ZnO ~100! and ZnO ~101! deposited in oxygen containing solution was significantly higher than that of ZnO formed in oxygen free solution. ZnO was islanding on ITO substrate in an oxygen free solution, while uniform ZnO underwent bulk deposition with higher growth rate due to higher concentration of OHad resulted from dissolved oxygen. Thus, morphological images were in good agreement with the crystal structural analysis. In pulsed potential method, several ZnO peaks in ex situ XRD analysis were obtained on ITO substrate as optimal cathodic potential of 20.72 V for 5 s was superimposed on off-time of 5 s at open-circuit potential in each cycle. When relatively shorter cathodic time of 1 s was applied, however, we did not obtain any XRD peak of ZnO, because it might be due to the lack of the critical concentration of OHad to form ZnO on the surface.

Electrochemical characterization of polymer actuator with large interfacial area

Abstract Actuating and electrochemical behaviors of nafion-based electrode were strongly dependent on the interfacial area between the electrode and the polymer electrolyte. A replication method was utilized to manufacture a large surface-area composite actuator. Measurement of double layer charging and scanning electron microscopy indicated that the interfacial area could be greatly increased by replication method. Larger interfacial area induced a better bending performance of ionic polymer metal composite (IPMC) (the magnitude of IPMC increased about 50% at 3 V). The surface resistance of IMPC and the effects of cations on IPMC were investigated with constant current experiment, cyclic voltammetry and electrochemical impedance spectroscopy (EIS).

Novel electroactive, silicate nanocomposites prepared to be used as actuators and artificial muscles

Reported herein is a newly developed nanocompositing technique that can provide an effective process tool to optimize the desirable properties of the base ionic polymer materials to be used as effective electroactive polymer (EAP) actuators and artificial muscles. We developed polymer nanocomposite (PNC) materials that incorporate clay-based layered silicates. The clay-based layered silicates were intercalated within the polymer matrix of perfluorosulfonate ionomer. A certain clay, Montmorillonite (MMT), was selected as an effective clay and was modified by a cationic surfactant in order to lower its surface energy significantly. This process gave rise to a favorable intercalation of Montmorillonite within the galleries. The obtained XRD patterns prove that the silicate layers are intercalated in a continuous polymer matrix. Such a polymer nanocomposite shows significantly improved structural and electrochemical behavior and, thus, can be successfully used as the effective base material of EAP actuators and artificial muscles.

Nickel oxalate nanostructures for supercapacitors

Herein, we describe a facile method to produce nickel oxalate nanostructures by chemical reaction of oxalic acid and a nickel foil in various organic solvents and water. Grass-like structures consisting of nickel oxalate are produced by the chemical reaction within 30 min for all solvents. Interestingly, nickel oxalate nanowires can be produced by the addition of a small amount of water in certain solvents. Annealing of nickel oxalate structures leads to formation of nickel oxide structures with a slight morphological change. Compositions of the nanostructures are investigated by TEM and FT-IR analyses. In addition, the supercapacitance of the nickel oxalate nanostructures is characterized, and the results show that they are superior to that of nickel oxide nanostructures.

Cobalt oxide preparation from waste LiCoO2 by electrochemical–hydrothermal method

Abstract Cobalt ions, extracted from waste LiCoO 2 by using a nitric acid leaching solution, are potentiostatically transformed into cobalt hydroxide on a titanium electrode and cobalt oxide is then obtained via a dehydration procedure. In linear sweep voltammetry, distinct cathodic current peak is observed and indicates that hydroxide ions are formed near the electrode via the electroreduction of dissolved oxygen and nitrate ions give rise to an increase in the local surface pH of the titanium. Under appropriate pH conditions, island-shaped cobalt hydroxide is precipitated on the titanium substrate and heat treatment of the cobalt hydroxide results in the formation of cobalt oxide.