Oxygen Evolution Behavior Research Articles

An Electrochemical Study on the Anodic Oxygen Evolution on Oxide Film Covered Titanium

Anodic oxygen evolution reaction on titanium oxide film and its affect on the surface and bulk properties of the film is an important subject in the Ti-based studies and applications. In this work, the behavior of oxygen evolution and some other related electrode processes occurring at anodically grown films on titanium were investigated within a relatively wide potential range by electrochemical measurements in perchloric acid solution. For the formation of the oxide film, three potential regions (two passive regions and the film breakdown region) were selected. The changes both in surface properties (mainly caused by oxygen evolution) and in bulk properties (mainly caused by increased potential) were taken into account for the observed different oxygen evolution behavior. The origin of a cathodic current peak at revealed in cyclic voltammograms was attributed to the reduction of the oxygen atoms adsorbed/absorbed at the oxide film surface, which were generated during anodic oxygen evolution. The flatband potential for the anodically formed titanium oxide films in was estimated as . With the semiconducting energy band structure models constructed for the Ti/oxide film/ electrode system, both the different behavior for anodic oxygen evolution on the titanium oxide films formed at different potentials and the electron transfer processes for the electrochemical reactions observed in this work were further interpreted.

Reduction Behavior of CeO2−ZrO2 Solid Solution Prepared from Cerium Zirconyl Oxalate

CeO2−ZrO2 solid solutions were prepared by means of thermal decomposition of cerium zirconyl oxalate in an argon flow at 1273 K followed by oxidation at 673−873 K in air. The reduction behavior of the obtained CeO2−ZrO2 powders was investigated and compared with the samples prepared by the other methods already reported to yield CeO2−ZrO2 powders with high redox activity. The CeO2−ZrO2 samples prepared from the oxalate showed excellent reduction behavior, despite their very low surface areas. The reason for the excellent oxygen evolution behavior of the powders was discussed, from the viewpoints of the structure and the preparation process, and was attributed to both the appearance of a cubic phase with a different oxygen arrangement and the reduction by carbon formed in the sample preparation process.

Hydrophobic effect of PTFE‐modified Ru0.3Ti0.7O2 electrodes on oxygen evolution in alkaline solution

The hydrophobic effects of PTFE‐modified Ru0.3Ti0.7O2 electrodes on oxygen evolution are explored in this study by investigating contact angle, morphology and electrochemical characteristics. The hydrophobicity of electrodes is measured by the contact angle of the PTFE‐modified Ru0.3Ti0.7O2 electrodes. The morphologies of electrodes with various amounts of PTFE are observed by using a scanning electron microscope (SEM) and an atomic force microscope (AFM). The effects of PTFE‐content on the electrochemical characteristics of PTFE‐modified electrodes are evaluated by the measurements of voltammetric charge, polarization and ac‐impedance. The behavior of oxygen evolution and the performance of electrodes depende significantly on the hydrophobicity of PTFE‐modified electrodes. The electrode prepared from a dipping solution with 21.1 vol% PTFE have the best performance in terms of the largest number of active sites and the highest site activity. The variation in performance of electrodes for oxygen evolution with PTFE‐content is related to the variation in active site dispersion, morphology and bubble behaviors of the electrode.

自動車排ガス用助触媒CeO<SUB>2</SUB>-ZrO<SUB>2</SUB>系粉末の酸素放出特性と状態図

CeO2-ZrO2 powders with various ZrO2 compositions, which were prepared by co-precipitation, were subjected to an evolved-oxygen gas-analysis. The samples were heated from 373 to 1323 K in Ar+H2+H2O gas mixtures. A closed-system oxygen analyzer developed by one of the authors was used to establish a constant ratio of H2/H2O and also detect the oxygen evolved from the samples. After the amount of evolved oxygen was recorded as a function of temperature, the samples were oxidized at 873 K in O2 gas, then the 2nd deoxidation run continued by heating again from 373 K. The heating-deoxidation run was repeated three times, and the following conclusions were derived. (i): For CeO2 powders, a peak on the JO-T-t curve (1) was observed around 1073 K, and did not shift even on the 2nd and 3rd heating-deoxidation runs. (ii): On the 1st heating-deoxidation run, as the content of ZrO2 was increased, a peak appeared around 873 K and became higher; the sub-catalyst at low temperatures was improved monotonously with the addition of ZrO2. (iii): After the deoxidation and successive oxidation, the shapes of JO-T-t curves (2) and (3) were essentially different from those of the 1st run. This came from the appearance of cubic φ′ phase, (Ce2Zr3O10?), which had not been reported previously. (iv): By analyzing the JO-T-t curves, two kinds of qualitative phase diagrams of the ZrO2-CeO2-CeO1.5 ternary system were established. The evolution behavior of oxygen from ZrO2-CeO2 powders could be explained on the basis of the phase diagrams; it was proved that the oxygen evolution behavior of ZrO2-CeO2 powders at low temperatures as sub-catalyst is the best in the composition range of ZrO2: 45∼65 mol% after the appearance of the φ′ phase.It was inferred that oxygen vacancies played a part in the growth of φ′ phase, and therefore similar experiments were undertaken with the powders of XCe⁄XZr=2⁄3 doped with CaO. (v): When it was annealed at 1773 K for 50 h, almost a single phase of tetragonal φ was obtained. The φ phase turned to φ′ phase once deoxidized and successively oxidized. (vi): The structure of φ′ was approximated by a pyrochlore, though there was no oxygen vacancies; Zr and Ce atoms may take regular arrays. (vii): The grain of the powders became fine through the phase transitions: φ→pyrochlore→φ′, and the evolution rate of oxygen became fastest, along with a change in the phase diagram. (viii): Through the phase transitions, CeO2-ZrO2 powders with ZrO2, 45∼65 mol% possess a regeneration property as automotive exhaust sub-catalysts, and may be durable at higher temperatures. (ix): Through the present investigation, it was demonstrated that the evolved-oxygen gas-analysis utilizing the closed-system oxygen analyzer with high sensitivity is highly effective for the evaluation of ternary phase diagram related to oxides and also the detection of plausible compounds.

An alternative mathematical approach to the analysis of photosynthetic oxygen evolutiont

Whereas a linear four-step mechanism around a closed path has been used to interpret the kinetic behavior of oxygen evolution in higher plant photosynthesis, a straightforward successive difference analysis of published and original data shows that a more dynamical interpretation overcomes many of the inadequacies of simple kinetic models.