Kotaro Ogura

Photoelectrochemical Behavior of Electrodeposited CuO and Cu2 O Thin Films on Conducting Substrates

Cuprous oxide has been prepared by the photoelectrochemical reduction of a CuO film formed on a conducting substrate by the anodic deposition from an alkaline solution of a Cu(II)-amino acid complex. Both copper oxide films thus prepared are found to be typical p-type semiconductors. The onset of the cathodic photocurrent due to the reduction of O 2 on CuO/ITO (ITO, indium tin oxide) and Cu 2 O/ITO electrodes give positive shifts of about 0.2 and 0.03 V, respectively, from the dark current rises. Optical bandgap energies of CuO films depend on the amino acids used, 1.56 (glycine), 1.40 (alanine), 1.38 (isoleucine), 1.38 eV (valine), and the value of Eg for the Cu 2 O film is 2.17 eV. The relationship between the flatband potential (V FB ) and the pH for CuO and Cu 2 O films are both linear with the slope of about -60 mV/pH in agreement with the Nernstian expression for the V FB of a semiconductor.

A New Humidity Sensor Using the Composite Film Derived from Poly(o‐phenylenediamine) and Poly(vinyl alcohol)

A composite film consisting of conducting poly(o-phenylenediamine) (PoPD) and insulating poly(vinyl alcohol) (PVA) has been prepared in a proportion which possesses satisfactory mechanical strength and characteristics favorable for a humidity senor. The electrical conductivity and PoPD content curves were measured, and it was found that the conductivity of the composite film rose sharply at about 0.1 volume percent (v/o) of the PoPD content, reaching a value of ∼10 -2 S cm -1 corresponding to that of PoPD itself. The change in conductivity was as large as four orders of magnitude, which was attributed to the formation of networks that ena le the insulating composite to reveal the electrical conduction. The conductivity of the composite film was linearly related to the humidity, extending from 2.5 x 10 -5 to 1.5 x 10 -1 S cm -1 between the dry and wet states. Measurements of the conductivity were not attended with hysteresis in the moistening or desiccating runs. The change in conductivity was caused by a shift of the equilibrium between the conducting and the insulating PoPD depending on the atmospheric humidity in which, e.g., in the drying process the reaction of the protonated and conjugated PoPD with the OH group of PVA occurred to form the insulating PoPD and a water molecule resulting in the decrease of the conductivity of the composite film.

The humidity dependence of the electrical conductivity of a solublepolyaniline–poly(vinyl alcohol) composite film

A humidity-sensitive composite film has been synthesized that consists of soluble polyaniline (PAn) and poly(vinyl alcohol) (PVA). PAn gave a percolation threshold where the electrical conductivity rose sharply at a volume fraction of 0.1%. This value is very small compared with that (about 5 vol%) reported in general for composite films consisting of conducting and non-conducting polymers, indicating that the two polymers used in this study were mixing completely. The conductivity of the PAn–PVA composite was proportional to the relative humidity, and the linearity was valid from 3×10–5 to 1.5×10–1 S cm–1 . The response time of the composite for the humidity change was 45 s and 9 min for moistening and desiccating steps, respectively. The conductivity of the composite film varied depending on the doping level of PAn, which was affected by the concentration of water molecules surrounding the conducting polymer. At high humidity, the PAn was in the form of an emeraldine salt, and transformed into a non-conducting base with decreasing environmental humidity.

Thermogravimetric/Mass and Infrared Spectroscopic Properties and Humidity Sensitivity of Polyaniline Derivatives/Polyvinyl Alcohol Composites

Humidity-sensitive polyaniline derivatives/polyvinyl alcohol (PVA) composites have been studied using thermogravimetric (TG)/mass (MS) and in situ Fourier transform infrared spectroscopy. The electrical conductivity of the poly(o-phenylenediamine) (PoPD)/PVA and poly(o-aminophenol) (PoAP)/PVA composites were linearly related with the atmospheric humidity, but there was no such linear relationship for the poly(m-phenylenediamine) (PmPD)/PVA and poly(o-toluidine) (PoTd)/PVA composites. The FTIR intensity at 3600 and 3200 cm -1 for the PoPD/PVA and PoAP/PVA composites decreased with a decrease of humidity, indicating a removal of water molecules from the composite. For the PmPD and PoTd composites, however, the involvement of water molecules in the drying and wetting stages was not pronounced. The TG/MS analyses suggested that the PoPD/PVA and PoAP/PVA composites have two types of water: one is weakly bound to the composite and equilibriates with the atmospheric moisture, and the other is strongly bound to the composite at the PVA unit and stays there even in a dry state (<130°C). Emphasis is laid on the role of these different types of water for the linear dependence of the conductivity on the atmospheric humidity

A Conductive and Humidity‐Sensitive Composite Film Derived from Poly(o‐phenylenediamine) and Polyvinyl Alcohol

Electrically conducting composite films have been prepared from the polymer solution of conducting poly o-phenylenediamine (PoPD) and nonconducting polyvinyl alcohol (PVA). This composite film showed a very low value of the percolation threshold (0.1 volume percent of the PoPD content) where the conductivity rose sharply. On the other hand, the conductivity of the prepared composite film was linearly related to the atmospheric humidity, extending from 2.5 x 10 -5 to 3.5 x 10 -1 S.cm -1 . The humidity-dependence of the conductivity was caused by the change in the acid-base equilibrium between the PoPD and PVA in the composite film.

Electrocatalytic behaviour of a poly(N-methylaniline) filmed electrode to hydroquinone

Poly(N-methylaniline) (PNMA) was prepared on a bare platinum electrode by electrooxidation of N-methylaniline in 1.0 mol dm−3 HCl. The PNMA film was more stable to anodic treatment than the polyaniline film. The electric conductivity of the PNMA film was potential dependent. High conductivity appeared only within the potential region where PNMA itself was redox-active. The PNMA filmed electrode showed redox response to dissolved hydroquinone whose redox current was evident within the potential region. Furthermore, the PNMA film behaved as an electrocatalyst for the electrode reaction of hydroquinone. The kinetics of the electrocatalytic reaction were investigated mainly using a rotating disc electrode. The experimental results obtained were analysed by the theory of Albery and Hillman, and the rate constant of the electron cross-exchange transfer between hydroquinone and the redox-active sites in the film (k) was determined and found to be 6.4 × 103m−1 s−1 at 20° C.

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

Spectroscopic and scanning tunneling microscopic characterization of virgin and recast films of electrochemically prepared poly(o-phenylenediamine)

It has been found that poly(o-phenylenediamine)(PoPD) electrochemically prepared shows considerable solubility in organic media and PoPD is most soluble in dimethyl sulfoxide (17.0 g dm−3). The spectroscopic, scanning tunneling microscopic and electrochemical characterization of the virgin and recast (reprocessed) films of PoPD has been studied, and the results compared. In both films, the anodic peak at −0.05 V vs. sce was responsible for the color change of the film from transparent yellow to red brown. However, the electrochemical reversibility of the recast film was much worse than that of the virgin film. This was attributed to the crowded stacking of the former polymer chains which prevented counter anions from being readily undoped.

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.

Electrochemical Deposition of Spinel-Type Cobalt Oxide from Alkaline Solution of Co2 + with Glycine

The electrochemical formation of spinel-type cobalt oxide has been presented in which the potentiostatic or potentiodynamic oxidation is performed with a Au or Pt electrode in a solution of high pH containing CoSO 4 and glycine. The electrochemical quartz crystal microbalance studies indicate that the electrodeposition of cohalt oxide proceeds through the electrochemical oxidation of a cobalt-glycine complex at high pH. The scanning electron microscopy morphology of the deposited film is very compact and quite similar to that of the cobalt oxide prepared by the sol-gel route, followed by the heat-treatment around 300°C. The constituent of the film is determined to be Co 3 O 4 from the electron probe microanalysis and X-ray diffraction measurement. The electric charge of 350 mC cm - passed at 1.0 V vs. Ag/AgCl in a solution of pH 10.5 containing 2 mM CoSO 4 + 20 mM glycine corresponded to the film thickness of 10 nm. The Co 3 O 4 -deposited Au electrode exhibits two reversible couples in an alkaline solution. The first observed at 0.120 V is attributed to the redox of CoOOH/Co 3 O 4 , and the second appearing at 0.476 V is equivalent to the CoO 2 /CoOOH couple.