Woon-kie Paik

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.

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.

Electroactive counter anions in conducting polypyrrole: hexacyanoferrate and heteropolytungstate ions

Summary form only given. Hexacyanoferrate ions [Fe(CN) /sub 6/,z-(z=3,4) and heteropolytungstate ions [SiW/sub 12/O/sub 40/]/sup 4-/, [P/sub 2/W/sub 18/O/sub 62/]/sup 6-/ were doped into conducting polymers of pyrrole. The polymers exhibited reversible redox properties inherent to the anions in addition to those of the polypyrrole moiety, resulting in enhanced electrochemical charge storage capability which may have potentially useful applications. Whereas the hexacyanoferrate ions were labile toward exchange with anions in the electrolyte solutions in contact, the heteropolytungstate ions were retained in the polymer matrix without being ion-exchanged after repeated potential cycles in electrolyte solutions containing no heteropoly anions. Charge compensation on reduction was accomplished by cation insertion instead of releasing of the anions. Spin density of polymer with [Fe(CN) /sub 6/]/sup z-/ or [P/sub 2/W/sub 18/O/sub 62/]/sup 6-/ as measured by ESR was small indicating bipolaron formation accelerated by the anions bearing multiple charges.

Polypyrrole doped with heteropolytungstate anions

Abstract Electronically conducting polypyrrole doped with heteropolyrungstate anions [SiW 12 O 40 ] 4− , and [P 2 W 18 O 62 ] 6− were synthesized by electrochemical polymerization. The polymers exhibited reversible redox properties inherent to the heteropolyanions in addition to those of the polypyrrole moiety. The anions were retained in the polymer matrix without being ion-exchanged after repeated potential cycles in electrolyte solutions containing no heteropolyanions. Charge compensation on reduction was accomplished by cation insertion instead of releasing the anions. The spin density of the polymer with [P 2 W 18 O 62 ] 6− was small, indicating bipolaron formation accelerated by the polyanions. The polymers showed potentially useful properties.

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.

Ellipsometric studies on polypyrrole and polyaniline

Abstract Electropolymerized polypyrrole and polyaniline films were investigated during their growth and conversions by in situ threeparameter ellipsometry method. The optical properties of the polymers continuously changed with growth of the film and also on redox switching of the polymers. Both expansion and contraction in the thickness with oxidative doping were observed depending on the stage of polymerization.

Mechanism of the mercury beating heart: An experimental study of the electrochemical-mechanical oscillator

Abstract Detailed mechanism of oscillation of the “mercury beating heart” was investigated for the iron-triggered and the aluminium-triggered cases by probing the electrode potential, electrocapillarity and the shape of the mercury surface. Electrochemical reductions primarily of dissolved oxygen on the mercury surface and corrosion reactions of the active metals such as Fe or Al drove the potential of mercury alternately up and down. The range of potential oscillation was found to be on the positive side of the electrocapillary maximum of mercury in the case of Fe-triggered oscillation in acidic solutions, and on the negative side in the case of Al-triggered oscillation in basic solutions. The ultimate cause of the mercury oscillation was shown to be fluctuating surface charge density without involving a film-formation on the mercury surface or oxidation of mercury, at variance with some views in the literature.

An ellipsometric study on the early stage of passive film formation on nickel in acidic solutions

Abstract Ellipsometric transient measurements were made on the nickel surface in acidic solutions. An automatic ellipsometer built for transient three-parameter ellipsometric measurement including reflectance recording was used to determine the optical constants and thickness of the passive film as functions of time. The real and imaginary parts of the refractive index showed some change before reaching steady values after the potential was changed. There was, however, no discontinuous or drastic variation of the optical constants even in the early stage of passive film growth, within a second when the thickness change was rapid. Experimental results pertaining to the question of film transformation are discussed.

Self-Assembly Process of Organosulfur Molecular Layers on Gold: Electrochemical Mechanisms

Abstract Mechanism of adsorption process in the self-assembly of organosulfur monolayers on gold was probed by electrochemical measurements. While alkanethiols were found to adsorb on gold by an anodic process, disulfide molecules appeared to adsorb primarily by a cathodic process.

Properties of Polyphenylquinoxaline Acid Complex as an Electrode Material

Polyphenylquinoxaline (PPQ), known as an effective insulating coating material, became electronically conductive with desirable properties as an electrode material when complexed with strong protonic acids. Although the conductivity of PPQ-acid film was quite high (10 -4 to 10 -2 S cm -1 ), the complex lost the acid component to become almost insulating (10 -7 S cm -1 ) in weakly acidic or neutral solutions, or in the ambient atmosphere when the acid in the complex was volatile. The pK a values of the PPQ.H 4 4+ and PPQ.H 2 2+ complex were determined by the spectroscopic method to be about -6.1 and -2, respectively, indicating that the acid-base interaction between PPQ and an acid is very weak. The electrochemical oxidation and reduction of PPQ-acid are remarkably reversible in strong acid solutions. The storage charge density per unit volume of the protonated PPQ film electrode as measured by galvanostatic charging and discharging was quite large at about 125 mAh cm -3 between -0.1 and 0.1 V.