Jun Yano

Poly(o‐phenylenediamine)‐Film‐Coated Electrode Having a Permselective Response to Halogenide Ions

A poly(o-phenylenediamine)(PoPD)-film-coated electrode had electrochemical responses only to two halogenide ions, I - and Br - , while it had no responses to other inorganic ions examined. In this case, the film was found to be permeable to the ions. The permeability of the ions was controllable by incorporating quinones into the film. Furthermore, the incorporation enhanced the permselectivity of the film to the halogenide ions

The kinetic difference between hydroquinone and Fe2+ in the electrochemical response of a polyaniline-film-coated electrode

Abstract The electrochemical response of a polyaniline (PANI) film to dissolved hydroquinone and Fe 2+ was examined. The PANI film electrocatalyzed the electrode reactions of not only Fe 2+ but also hydroquinone. The rotated disk voltammograms of both hydroquinone and Fe 2+ , which were oxidized-mediated by PANI films, were measured. The Koutecky-Levich plots obtained from the voltammograms of hydroquinone had no intercept, while those of Fe 2+ had finite intercepts. In order to examine what causes the difference, the measurements of the steady-state current-potential curves on a PANI pellet electrode and of the conductivity of the PANI pellet were carried out. Furthermore, the rates of the electrode reactions of hydroquinone and Fe 2+ on the PANI-film-coated electron were measured by a spectroscopic method. The respective results obtained led to the following: (1) the rate of electron self-exchange between the redox-active sites within the film for hydroquinone was much faster than for the Fe 2+ and (2) hydroquinone was strongly partitioned from the aqueous solution into the film.

Spectroscopic studies on the incorporation of polypyrrole into zeolite channels

A composite film consisting of polypyrrole (PPy) and Y-type zeolite particles has been formed by electrolyzing pyrrole in aqueous suspension of Y-zeolite. It is indicated from the XRD pattern that the PPy in the composite is located within the channel of Y-zeolite, in which the cationic PPy is in combination with the negative surface of Y-zeolite. ESR spectrum of the composite film exhibited the resonance signal characteristic of conducting polymer in a partially oxidized (polaron) form. The optical intensity of this spectrum was considerably smaller than that of pure PPy, suggesting that a certain portion of PPy in the composite is stabilized by the formation of bipolarons (diamagnetic). During the electrochemical polarization of the PPy/Y-zeolite composite-electrode, PPy is found to remain undetached in the zeolite channel, and the charge to be balanced by incorporation and exclusion of electrolyte cations into/from the composite.

Electrochemical separation of ionic compounds using a conductive stationary phase coated with polyaniline or polypyrrole film, and ion exchange properties of conductive polymers

Abstract We report here the separation of anionic compounds using a conductive stationary phase which consists of glassy carbon particles. The stationary phase was modified with polyaniline or polypyrrole film to add selectivity to the separation. At negative stationary phase potentials at which polyaniline was in the reduced form, anions were not retained on the column. When polyaniline was oxidized at potentials above 0.1 V vs. Ag|AgCl|sat.KCl|, the retention time of anions increased as a result of the formation of cationic sites in the film. Halide ions were separated successfully at 0.3 V, although carboxylic anions eluted exhaustively from the column with the least potential dependence of all the ions studied. When oxidatively treated carbon particles were used with polyaniline, an increase in retention time started at a potential much more negative than that at which film oxidation was observed. When the stationary phase was modified with polypyrrole, anions were irreversibly taken up in the film, and the anions inserted couyld be eluted after a negative potential perturbation.

Electrochemical Reduction of Carbon Dioxide on Dual‐Film Electrodes Modified With and Without Cobalt (II) and Iron (II) Complexes

Carbon dioxide has been electrochemically reduced to organic substances on dual-film electrodes modified with and without a metal complex. Polymethylpyrrole/molybdenum blue-modified electrodes yielded methanol, ethanol, and acetone as the reduction products. The substitution of the coated film by the Fe(II)-4,5-dih droxybenzene-1,3-disulfonate complex-immobilized polyaniline/Prussian blue led to the selective formation of lactic acid. Reaction products were found both in the solution and within the coated film, suggesting that the electroreduction of CO 2 takes place at active centers existing in the coated film and at the electrode/solution interface

Visible-light-assisted decomposition of H2O and photomethanation of CO2 over CeO2TiO2 catalyst

Abstract The reaction of CO2 and H2O over a CeO2TiO2 catalyst was performed with irradiation by visible light. The reaction products were H2, CH4 and O2. The initial rates of formation of H2 and O2 were 2.75 and 1.28 μmol h−1 g−1 respectively. The reaction proceeded through the stoichiometric photodecomposition of H2O followed by the methanation of CO2; however, some of the generated O2 was involved in the reoxidation of the reduced ceria or titanium oxide when a catalyst pretreated in H2 was used. The maximum yield of H2 was exhibited with highly dispersed 0.5wt.%CeO2TiO2.

Poly(o-phenylenediamine)-film-coated electrode: incorporation of o-benzoquinone and permselectivity of I– and Br–

A poly(o-phenylenediamine)(PoPD) film has an electroinactive potential range where the film itself is not redox active. Even within the range, the redox waves of I– and Br– were evident, while those of Fe2+, TI+ and Mn2+ were not observed. The respective Levich plots obtained from the voltammograms for the oxidation of I– and Br– showed that the film was permeable to I– and Br–. Thus, the film showed permselectivity of I– and Br–. The film also responded to several dihydroxybenzenes such as catechol in spite of its electroinactivity. In particular, the noteworthy behaviour in those responses was the following: (1) cathodic currents of benzoquinones, the products of oxidation of dihydroxybenzenes, were remarkably suppressed and (2) the anodic currents of dihydroxybenzenes as well as the redox currents of the film itself gradually decreased with repeated potential scans. Catechol was selected as being representative of dihydroxybenzenes and the mechanism of the behaviour was studied. Voltammetric and spectroscopic results regarding the effect of incorporation of o-benzoquinone in the film were obtained. The amount of o-benzoquinone incorporated was changed by the number of the potential cycles (N). The amount of I– and Br– permeating was, therefore, controllable by altering N. Furthermore, the permselectivity of I– and Br– was enhanced by enlarging N.

Electroreduction of CO2 to C2 and C3 compounds on bis(4,5-dihydroxybenzene-1,3-disulphonato) ferrate(II)-fixed polyaniline | prussian blue-modified electrode in aqueous solutions

Abstract Electrocatalytic reduction of CO2 has been performed using the bis(1,2-dihydroxybenzene-3,5-disulphonato)ferrate(II)-immobilized polyaniline | Prussian Blue-modified electrode in aqueous solutions. CO2 was reduced at a low overpotential under ambient condition, and lactic acid, together with C2 and C1 compounds, was obtained with the highest selectivity of about 88%. The most probable pathway of the reduction of CO2 is the stepwise hydrogenation by Hads. Adsorbed hydrogen atoms were generated by the catalytic reduction of H+ ions near the PAn | PB interface where the doping and undoping processes of K+ ions proceed simultaneously.

Electrocatalytic generation of C2 and C3 compounds from carbon dioxide on a cobalt complex-immobilized dual-film electrode

The electrocatalytic reduction of CO2 on a Prussian blue–polyaniline dual film electrode on platinum including immobilized 2-hydroxy-1-nitrosonaphthalene-3,6-disulfonatocobalt(II) in aqueous solution leads to the formation of lactic acid, ethanol, acetone and methanol at a low overpotential (–0.6 V vs. standard calomel electrode) under ambient conditions.