We have found an excellent CO tolerance at Pt anodes alloyed with the second metals in spite of the formation of Pt skin layer (ca. 1-2 nm in thickness) over the alloy surfaces due to the dissolution of the second metals and proposed a new mechanism for the catalysis. In this study, ATR-SEIRAS, coupled with CV measurement, was used to observe the oxidation process of adsorbed CO on the typical Pt-Fe alloy. The alloy anode exhibits a lower saturated coverage with CO than that of pure Pt. Linear CO is observed predominantly on the alloy electrode, differing from both of linear and bridged CO besides COOH on the pure Pt. The negative-shift of the wavenumber for the linear CO stretching and the broadening of the half-wave width at the alloy also indicate the weakening of metal-CO bonding and the increased mobility of the adsorbed CO, respectively. As a presumable effect of the electronic structure change at the Pt skin, the dissociation/oxidation of adsorbed water as well as a formation of adsorbed HOOH species are clearly observed beyond 0.6 V in the electrolyte solution without CO. The mechanism of CO tolerance at the Pt skin on top of the alloy surface with an increased d-band vacancy, proposed previously by us, is supported by the present SEIRAS data as the “detoxification mechanism”, featured by an increased mobility of the adsorbed CO with suppressed coverage.
Single phase stoichiometric spinel LiMn2O4 and oxygen defect spinel Li1+xMn2−xO4−z has been successfully prepared and its discharge capacity is discussed theoretically. This defect spinel shows discharge plateaus with equivalent capacity at ca. 4.4 and 3.2 V. It is proved that the discharge capacity at 3.2 V is tightly related to oxygen defect content, z, by the slope analysis.
The synthesis of manganese dioxide by spray pyrolysis has been investigated as a cathode material of lithium/manganese dioxide cell. Spraying solutions with Na/Mn ratios of 0.0-0.7 were prepared by mixing sodium acetate and manganese acetate. Sodium manganese composite oxides were obtained by spray pyrolysing the resulting solutions at 500℃. γ-MnO2 was formed by extraction of sodium ion from the composite oxides in nitric acid solution. The formation of α-MnO2 phase was observed with Na/Mn ratios of above 0.3. The powders were in a range of 0.5-2μm and the specific surface areas were 221-254 m2 g−1. The discharge capacities (281-283 mAh g−1) of the products obtained with Na/Mn ratios of below 0.3 were higher than that of electrolytic manganese dioxide (207 mAh g−1).
The electrocatalytic properties of a sintered ZnO electrode in electroreduction of CO2 were investigated in aqueous solutions of several potassium salts. The reduction product from CO2 was only CO (faradaic efficiency = 70% at −1.4 V vs. Ag-AgCl in 0.1 mol/dm3 KHCO3 solution) with a considerable amount of H2 as a byproduct. The ZnO was found to have a higher electrocatalytic activity for CO formation than metallic Zn, since the potential showing a maximal faradaic efficiency for CO formation was nobler by 200–250 mV than that of the Zn electrode. The partial current density for CO formation on the ZnO electrode in 0.1 mol/dm3 KH2PO4 solution was 10 to 50 times higher than that on a Zn foil electrode. The sum of the faradaic efficiencies for CO and H2 formation did not reach 100%, the difference from which was attributed to the faradaic efficiency for the reduction of the electrode itself. The metallic Zn thus formed on the electrode surface played no significant role in the electroreduction of CO2.
Ultrasonic effects on indirect electrolytic oxidation of n-butylamine with a tris (p-bromophenyl)amine redox mediator were investigated in comparison with mechanical stirring effects. The cyclic voltammogram of a mixture of the n-butylamine substrate and the mediator exhibited a typical catalytic anodic peak current for the indirect oxidation in silence without the stirring, while limiting currents were observed in silence and under irradiation with and without the stirring, respectively. The current was significantly increased under the irradiation. Influence of ultrasonic power, stirring speed and concentrations of the substrate and mediator on the current were experimentally and theoretically examined, and consequently it was suggested that (a) diffusion layer thickness of anode interface is significantly decreased by ultrasonic irradiation, (b) reaction rate constant of the mediator with the substrate is not affected, and (c) distance from the electrode surface to region of the reaction is also not influenced.
Cathode polarization is a major factor of voltage loss in molten carbonate fuel cells (MCFCs), and it is caused by oxygen reduction at the cathode. In order to clarify, the interaction between the molten carbonate and the cathode in MCFCs, we have attempted to develop the in situ micro observation using an environmental scanning electron microscope (E-SEM). We could directly observe the microscopic behavior of the molten carbonate on Au electrode together with the electrochemical measurement. In secondary electron images, we found that there is the thin film of molten carbonate on the electrode partially among the thick film. The thin film area on the electrode drastically changed with potential during the cyclic voltammetry. The thickness of the thin film was about 0.1 µm when the potential is negative to reference electrode. We suggested that the thin film might have strong relations to active area of the cathode reaction.
The theory of transient analysis by a channel flow triple electrode was derived. In the present electrode system, two serial collecting electrodes were located at the down-stream of the working electrode. Three dynamic collection efficiencies, which were complex numbers depending on the frequency, were measured for the compensations among the transient currents on the three electrodes, The amplitude of the dynamic collection efficiency was close to steady state collection efficiency in the low frequency range, and decreased with increasing frequency in the high frequency range, indicating that the collection system works as a low pass filter. The transient current of the working electrode, which emitted the ions, could be determined from the transient currents of the two collecting electrode by the calibration using dynamic collection efficiencies.
Electrochemical oscillatory phenomena were first observed on mercury electrodes (including a hanging mercury drop electrode (HMDE), and liquid and solid Hg-coated gold electrodes) in the redox reaction of the O2/O2− (superoxide ion) couple in quinoline media. The current oscillation occurred during the reoxidation process of the electrogenerated O2−. It was found that the observed oscillation is really irregular, complicated and affected by many experimental factors such as electrode substrate, concentration of O2− (and O2), the rate and range of potential scan in cyclic voltammetry. A probable explanation for the observed oscillation is given.
Spherical and hard carbon particles containing ZnO at highly dispersed state were prepared by carbonizing an ion-exchange resin exchanged by Zn2+ ion. The antibacterial activity of as-prepared samples was studied by measuring the change in electrical conductivity with the growth of Staphylococcus aureus. From XRD measurements of carbonized resins, ZnO of hexagonal type was detected in the exchanged resin and no graphite was observed. The antibacterial activity of samples dispersed with ZnO increased with the concomitant increase of powder concentration, but no activity of samples without ZnO was observed, irrespective of powder concentration. From the comparison of the antibacterial activity for the prepared samples, it was clarified that the activity decreased with increasing the carbonizing temperature of an ion-exchange resin. The pH value after dispersing the samples containing ZnO in physiological saline was approximately 5.6. In the case of the sample without ZnO, however, the value was 9.1.