Sang-Eun Bae

Characteristics of methanol oxidation on Pt-Ru catalysts supported by HOPG in sulfuric acid

Abstract The details of the preparation and characterization of co-deposited Pt–Ru catalysts supported by highly oriented pyrolytic graphite are presented. The Pt–Ru catalysts were prepared by changing applied potentials in chloroplatinic and ruthenium solution of 20 mM , respectively. Electrocatalytic activity for methanol oxidation reaction of Pt–Ru catalysts prepared by applying a potential of −0.25 V was better than that of catalysts prepared at other applied potentials. This indicates that there is an optimum potential for electrodeposition of Pt and Ru. The activation energy of Pt–Ru catalysts is calculated as 38 and 47 kJ / mol in the 0.3 and 0.4 V , respectively. To investigate the stability of Pt–Ru catalysts, Ru stripping on Pt–Ru and Ru/Pt disk electrodes was investigated by changing the cycling numbers of cyclic voltametry and holding time at constant potential, respectively. The peak potential of methanol oxidation is shifted to high potential by increasing the cycling numbers and holding time. Shifts of peak potential are discussed in terms of the oxidation pathway of CO adsorbed on the surface of Pt–Ru catalyst. The particle size of Pt–Ru catalyst measured by SEM is about 75 A and the range of particle size measured by STM is from 35 to 110 A .

Oxidation State Shift of Uranium during U(III) Synthesis with Cd(II) and Bi(III) in LiCl–KCl Melt

Synthesis of U 3+ with Cd 2+ or Bi 3+ was investigated in a LiCl―KCl eutectic melt at 500°C by using cyclic voltammetry (CV) and ultraviolet-visible (UV-vis) spectroscopy. CV results showed that the equilibrium potentials of the species are larger in sequence of U 0/3+ < Cd 0/2+ < U 3+/4+ < Bi 0+/3+ . UV-vis spectroscopy results exhibited that U 3+ was directly produced in the eutectic melt containing Cd 2+ . In BiCl 3 , U metal was oxidized to U 4+ by Bi 3+ , and then U 4+ was reduced to U 3+ by additional U. From these results, the reaction mechanisms taking place during the synthesis are proposed.

Electrooxidation of methanol on ruthenium oxide layer supported by basal plane graphite in acid media

Abstract The electrooxidation of methanol on ruthenium oxide layer supported by basal plane graphite (BPG) in acid media was investigated by cyclic voltammetry and X-ray photoelectron spectroscopy. A simple electrodeposition method of ruthenium oxide layer on BPG electrode was established in this study. Ruthenium oxide layer, which was prepared by a simple electrodeposition method in acidic ruthenium chloride solution, stable in the potential range between −0.3 and 0.9 V vs. saturated calomel electrode (SCE) but stripped at high potential range between 1.0 and 1.7 V . According to XPS analysis, the layer presented more than two different peaks, which showed the oxidation states of ruthenium between Ru (2+) and Ru (4+). A peak current of 260 μA at 1.0 V was observed for the electrooxidation of methanol on ruthenium oxide layer.

Electropolymerization of Pyrrole Applied to Biosystem

We have been investigating electropolymerization of pyrrole in aqueous electrolyte solutions in acidic as well as in neutral conditions by in situ electrochemical quartz crystal oscillator method, where resonant frequency and resonant resistance can be monitored simultaneously with current-voltage measurements during electropolymerization of pyrrole. The properties of thin PPy films prepared on electrode surfaces depended strongly on the experimental variables of electrode potentials applied, solution pH, kinds and quantity of supporting electrolytes, added chemicals, and the mode of electrochemical method employed. We are applying our experience gained on electropolymerization of pyrrole to immobilizing biomolecules onto electrode surfaces to develop a biosensor system. In this work, we wish to present the results on electrochemical monitoring on electropolymerization of pyrrole in the presence of DNA and albumin in different electrochemical conditions. Additionally we will summarize our investigations on the miniaturization of biomolecules/PPy composites by means of scanning tunneling microscopy.

Polypyrrole patterns formed during electropolymerization of pyrrole at gold surfaces in potassium chloride electrolyte solutions

Abstract Electropolymerization of pyrrole in the aqueous electrolyte solutions of potassium chloride was investigated by means of chronoamperometric, in situ electrochemical quartz crystal oscillator and optical microscopic methods. Polypyrrole patterns of one dot, two dots and three dots of triangle were successfully formed at gold electrode surfaces in aqueous solutions of pyrrole and were confirmed ex situ by optical microscopy. Further development of the technique and possible applications are discussed.

Electrochemical Behavior of UCl 3 and GdCl 3 in LiCl-KCl Molten Salt

Electrochemical behaviors of and were investigated in LiCl-KCl eutectic molten salt by using various electrochemical techniques. The electrodeposition and dissolution currents for uranium show the maximum at -1.51V and -1.35V, respectively while, for gadolinium,at -2.15V and -1.9V, respectively. In case of LiCl-KCl molten salt containing both of and , the peak potential of electrodeposition of gadolinium shifts to more positive potential than in the solution without . The potentials in chronopotentiometric data suddenly dropped to negative value as soon as the reduction currents were applied and became constant at the potential around which the and are electrodeposited. The results of normal pulse voltammetry (NPV) and square wave voltammetry show that those methods can be used to qualitatively analyze the elements in the melts. Especially, the differentiation of NPV result was found to be useful for the separation of the peaks of which potentials are close each other.

EC-STM Studies on Electrochemical Preparation of Si(111)-H Surfaces

Electrochemical scanning tunneling microscopy was employed to study the evolution of surface morphology during electrochemical preparation of Si(111)-H from Si(111) oxide. Anodic dark current of cyclic voltammogram in 0.2M solution (pH 4.7) decreased as the number of cycles increased and remained nearly constant after the second cycle. Then, the Si(111) oxide was entirely stripped, which was followed by H termination on the Si(111) surface. Hydrides at kink and step sites were etched more rapidly than on the terrace, which remained triangle pits with [112] oriented steps where existed stable monohydride. Then, triangle pits deepened. During chronomamperometry at 0.4V anodic dark current shoulder appeared and decreased slowly, indicated the stripping of Si(111) oxide and the formation of stable (112) oriented steps with monohydride. Additionally, the etching mechanism of Si(111)-H in 0.2M solution at +0.4V was discussed.