In-Hyeong Yeo

Conducting Polymer with Metal Oxide for Electrochemical Capacitor: Poly(3,4-ethylenedioxythiophene) RuO x Electrode

Electrodes made by depositing ruthenium oxide on conducting poly(3,4-ethylenedioxythiophene) (PEDT) were studied for their electrochemical and impedance properties. In acidic electrolytes the PEDT-RuO x composite electrodes exhibited large capacitance due to contributions from the double-layer capacitance and the faradaic capacitance. Optimization of the thickness of the conducting polymer film and the amount of ruthenium deposition was found necessary to realize large specific capacitance. The specific capacitance based on the combined mass of PEDT-RuO x was 420 F/g, and the specific capacitance based on the mass of RuO 2 was 930 F/g. The energy storage density of a capacitance cell constructed with a pair of PEDT-RuO x electrodes reached 27.5 Wh/kg when the cell was charged to 1.0 V. The impedance analysis of the composite electrode revealed that both the double-layer capacitance and the pseudocapacitance originating from both PEDT and RuO x contribute to large specific capacitance.

Spectroelectrochemical and electrochemical behavior of epinephrine at a gold electrode

Spectroelectrochemical and electrochemical behavior of epinephrine, adrenaline, at a gold electrode was studied with cyclic voltammetric and spectroelectrochemical techniques. Based on the analysis of a series of spectra obtained by in-situ spectroscopic measurements absorption bands of possible intermediates generated in the electrochemical oxidation of adrenaline could be assigned. Also, assignments of various peaks in the cyclicvoltammograms obtained in different pH conditions are not always in agreement with the past findings, especially the formation of dehydrated form of leucoadrenochrome is not likely to occur under acidic conditions. From the analysis of current voltage curves and simultaneously obtained absorption UV-Vis. spectra, it was able to assign the absorption characteristics of species generated. Adrenalinequinone (λ=380 nm) is formed in the first step of oxidation of adrenaline (λ=290 nm) followed by cyclization of the quinone product to produce leucoadrenochrome (λ=310 nm). The leucoadrenochrome is finally converted into adrenochrome (λ=470∼525 nm) chemically or electrochemically. Especially, derivative cyclic voltabsorptograms (DCVA) of a species obtained by measuring absorbance change with potential scans at a selected wavelength provide a new information on the oxidation of adrenaline.

A study on ion transports and growth of conducting polypyrrole with electrochemical quartz crystal microbalance

Abstract Growth of polypyrrole and ion exchange processes in the polypyrrole were investigated by an electrochemical quartz crystal microbalance for various eletrolytes. The polymer was deposited potentiodynamically or potentiostatically on a gold film electrode. The mass change associated with insertion and expulsion of ions in the polymer matrix with successive potential scans at the electrode and during the growth of the polymer were monitored in situ . The observation supports that insertion of anions into polymer matrix in CH 3 CN occurs for anodic polarization and expulsion of the same ion for cathodic polarizaiton. However, charge compensation occurs also by cations in aqueous electrolyte even when the polymer is composed of small dopant anions. Also, it is found that growth of polymer is much faster and induction period is much shorter in H 2 O than in CH 3 CN.

Electrocatalysis of Anodic Oxygen Transfer Reactions: Comparison of Structural Data with Electrocatalytic Phenomena for Bismuth‐Doped Lead Dioxide

X-ray structural data, O/sub 2/ evolution overpotentials, and rate constants are compared for anodic oxidation of Mn(II) and 2-thiophene carboxylic acid (2-TCA) at Bi-doped PbO/sub 2/ in 1.0M HClO/sub 4./ It is concluded that the rutile structure of pure {beta}-PbO/sub 2/ deposited anodically from 1.0M HClO/sub 4/ containing Pb(II) is retained even as the Bi(III) content is increased to Bi/Pb ..d.. ca. 0.7, i.e., mole fraction Bi = 0.4. There is no evidence of a new oxide phase being formed. Crystallites of the Bi-PbO/sub 2/ are deposited with an increasing preferential orientation of the 020-plane parallel to the Au substrate surface as the ratio Bi/Pb is increased. The kinetic results are discussed as a function of the enthalpy of transition between the two highest oxide phases for metal oxide electrodes.

Voltammetric Studies on the Palladium Oxides in Alkaline Media

The formation and stripping of palladium oxides on a palladium electrode in a 0.1M LiOH solution was studied by cyclic voltammetry. Cyclic polarization methods were used to form palladium oxides on the surface of the palladium electrode. Three different types of palladium oxides were found to be formed in alkaline solutions. A higher oxidation state of palladium oxide (PdO[sub 3]) can be formed (induced) on the surface of the electrode even at low anodic potential limit, 0.6 V (vs. SCE). Strong evidence that PdO[sub 3] can only be formed in a specific potential range is presented. From the voltammograms obtained after a long cyclic polarization time, the peak in the range of [minus]0.47 to [minus]0.60 V could be attributed to the reduction of dehydrated PdO.

Growth of lead dioxide on a gold electrode in the presence of foreign ions

Abstract The effects of added cations and anions on the nucleation and growth of lead dioxide were studied at a gold rotating disc electrode. The accumulation of electrodeposited lead dioxide in the presence of a high concentration of As(III) does not proceed because the chemical stripping rate of lead dioxide by As(III) is greater than its deposition rate. Among anions, sulfate and nitrate greatly enhance the rate of deposition of lead dioxide whereas phosphate decreases the rate of deposition. It is shown that the growth of PbO2 on the gold substrate is not a uniform process, but proceeds by preferential growth on specific sites on the surface of the substrate.

Ion transport in conducting polymers doped with electroactive anions examined by EQCM

Transport properties and stability of ionic species in films of conducting polymers polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDT) were examined by electrochemical quartz crystal microgravimetry (EQCM) experiments. The mobility of ions in these polymers were greatly affected by the mode of polymerization with which the polymer film was prepared, as well as by the structure of the ions. When the conducting polymers were doped with macrocyclic anions, phthalocyanine and porphyrin derivatized with sulfonate anionic groups, these anions were not expelled from the PPy or PEDT films by extensive potential cycles. Heteropolytungstate ions have partial mobility in the polymers and were expelled by negative potential sweeps applied to the films that were formed by electropolymerization at a constant potential or constant current. Polymer films formed with alternating potential programs showed drastically diminished permeability to anions. By forming a polymer film with cyclic potential sweeps or square wave potentials, it was possible to examine transport of other ions without complications due to the transport of the initial dopant ions.

Anodic detection in flow-through cells

Virtually all organic compounds and numerous inorganic compounds are predicted from thermodynamics to be oxidized at potentials accessible at commonly used solid electrodes in aqueous media by reactions which require transfer of oxygen from H2O to the oxidation products. These anodic reactions are usually kinetically inhibited because of their complexity. Progress is summarized to develop electrocatalytic processes for anodic detection in flowing aqueous solutions.Pulsed amperometric detection at Pt electrodes is applicable for the sensitive detection of the HCOH group in all alcohols, polyalcohols and carbohydrates, the nitrogen in amines, amino acids and aminoglycosides, and sulphur in most inorganic and organic compounds. Pure and doped lead dioxide electrodes are described for amperometric detection at constant potential.The voltammetric response of electrocatalysed oxygen-transfer reactions is dictated by the potential dependence of the process transferring oxygen from H2O to the electrode surface, so that attempts at voltammetric resolution of mixtures are not generally effective. The most useful analytical application of the electrocatalysed processes for mixtures is in the form of amperometric detection in liquid-chromatographic systems.

Identification of Two Luminescence Sites of Sr2SiO4:Eu2+ and (Sr,Ba)2SiO4:Eu2+ Phosphors

Europium activated strontium orthosilicate Sr2SiO4:Eu phosphors were prepared by a solid state reaction method using flux. Two emissions bands of blueish-green at 490 nm (SI) and of yellow at 560 nm (SII) were observed. The two emission bands are assigned to the 4f-5d transition of Eu ions in two different cation sites in α’-Sr2SiO4 orthorhombic lattices. The relative intensities of two emission bands and the efficient yellow-emission strongly depend on the fluxes used for the preparation process and the Eu concentration in the Sr2SiO4:Eu phosphors. The emission intensity of Eu was also increased especially for the SII site, by incorporating Ba into the lattice (BaxSr2-xSiO4).

Polypyrrole/thermally sensitive polyelectrolyte composite (I)

Abstract Polypyrrole (PPy) was prepared by electrochemical polymerization with the polyelectrolyte (PE) as a dopant. The PEs were copolymers of the water soluble polymers and 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS). The water soluble polymers were thermally sensitive poly( N -isopropyl acrylamide), P(NiPAAm) and thermally insensitive poly(acrylamide), P(AAm). The surface of PPy/PE film observed by SEM was smoother than that of PPy film doped with a monoelectrolyte. PPy/PE composites were fairly conductive, whose electrical conductivities measured by the four-probe method were in the range of 10 −1 to 10 −2 S/cm. The characteristics of cation and anion exchange during redox processes were investigated by applying potential from −0.8 to 0.5 V vs. an Ag/AgCl reference electrode to the PPy. The effect of temperature on the doping–dedoping behavior and mass change of PPy composites was investigated by potentiodynamic voltammetry and electrochemical quartz crystal microbalance (EQCM). The electrochemical activity of the PPy/PE gradually decreased with increasing temperature. PPy/P(NiPAAm/AMPS) showed much greater mass change with increasing temperature than PPy/P(AAm/AMPS), mainly because of a decrease in the degree of swelling of thermally sensitive moiety. This confirms that PPy/P(NiPAAm/AMPS) possesses temperature-dependent electrochemical activity, which indicates that it can be utilized for many attractive applications. The thermal volume transition temperature of PPy/P(NiPAAm/AMPS) was estimated from the slope change of mass decrease. The transition temperature of the oxidized state of PPy/P(NiPAAm/AMPS) was higher than that of the reduced state.