E. Sato

New Types of Anodes for the Oxygen Evolution Reaction in Acidic Solution

New type of electrodes of IrO/sub 2//TiO/sub 2//Ti, where the TiO/sub 2/ films are prepared by the anodic oxidation accompanied by sparking and are porous, were tested as the anode for the oxygen evolution reaction in acidic solution. The IrO/sub 2//TiO/sub 2//Ti electrodes were prepared by thermal decomposition of IrCl/sub 4/ aqueous solution on the TiO/sub 2/ films. The resistivities of the electrodes themselves became zero by the thermal decomposition process to form IrO/sub 2/, if the TiO/sub 2/ films were prepared by the anodic oxidation accompanied by sufficient sparking. It was found that the catalytic activities of the IrO/sub 2//TiO/sub 2//Ti electrodes are higher than that of the IrO/sub 2//Ti electrode. The electrodes prepared at a calcination temperature lower than about 500/sup 0/C dissolved in the long-term test, although their surface areas were very large. The IrO/sub 2//TiO/sub 2//Ti electrodes prepared at 550/sup 0/ are very superior in their catalytic activity and their stability in the long-term test for the oxygen evolution reaction. The surface difference between the IRO/sub 2//TiO/sub 2//Ti and the IrO/sub 2//Ti electrodes is also discussed.

Oxygen evolution on SrFeO3 electrode

Abstract Oxygen evolution reactions on SrFeO3 were investigated in alkaline and acidic solutions. It was found that the catalytic activity for the oxygen evolution reaction in the alkaline solution is high. The following reaction steps (V)+Fe+2H2O→(O)+FeOH2+2H++2e− in acidic solution and FeOH+OH−→FeO−+H2O in alkaline solution are presumed to be rate-controlling in the anodic evolution of oxygen on SrFeO3 electrode, where (V) denotes oxygen vacancy on the electrode surface. The reaction mechanism and the catalytic property are discussed in connection to the band structure of the oxide.

Superconducting Y1−xLxBa2−yMyCu3−zNzOδ system with higher Tc than 77K

Abstract The Tc and the Jc at 77K of the oxides of the nominal composition of Y 1−x L x Ba 2−y M y Cu 3−z N z O δ (L,M:alkaline and alkaline earth metals, N:transition metal) whose Tc are higher than 77K, were measured. The alkaline and alkaline earth substituted oxides show the higher Tc than 77K in the ranges of x 2 Cu 3−z Ag z O δ in the nominal composition range of z

Electrochemical properties of the single crystal La0.7Pb0.3MnO3 electrode

Abstract Electrochemical properties of the single crystal La 0.7 Pb 0.3 MnO 3 were studied. This oxide is stable only at the anodic potential region in alkaline solution. It was found that the catalytic activities for the oxygen reduction and evolution reactions are relatively high due to the effect of the B site Mn cation on the oxide surface. However, the mechanisms of the oxygen reduction and evolution reactions are different from the case of La 1- x Sr x MnO 3 electrodes and it was presumed that these differences are assigned to the influence of the A site Pb cation in La 0.7 Pb 0.3 MnO 3 and that of the (100) crystal plane.

Photoelectrochemical properties of thermally oxidized TiO2

The photoelectrochemical properties of polycrystalline TiO2 prepared at high temperature and doped polycrystalline TiO2 with noble metals have been investigated. The polycrystalline TiO2 prepared at high temperature give a cathodic photocurrent as well as a visible light response. These phenomena can be explained by a model based on the d-band formed by the interstitial Ti ion in TiO2 lattice. The doped polycrystalline TiO2 with noble metals (Rh, Ru, Pt, Au) prepared at low temperature also show a cathodic photocurrent and a visible light response. These are based on the impurity band formed by the doping metals. It is judged that the impurity band is near the π* conduction band for the doped TiO2 with Rh, Ru and Pt, but is near the π valence band for the Au doped TiO2 in energy position. It is found that there exist overlap potentials of the anodic and cathodic photocurrents at the doped TiO2 with noble metals. This will provide evidence on the mechanism of the enhancement of the photocatalysis on TiO2 owing to the doping of noble metals.

Improvement of CaFe2O4 photocathode by doping with Na and Mg

The low conductivity of CaFe/sub 2/O/sub 4/ and the nonohmic contact in the CaFe/sub 2/O/sub 4//metal interface, which lead to only a small photocurrent, were improved by doping with Na and Mg. The oxides of the Ca/sub 1-x/Na/sub x/Fe/sub 2-y/Mg/sub y/O/sub 4/ system gave the high conductivity and the ohmic contact of the oxide/Pt-Pd interface, but very small photocurrent. It was judged from the measurement of the Seebeck coefficient that the hopping mechanism is dominant for the conduction of the oxides containing Na. The hopping level is presumed to bring about the ohmic contact and the very small photocurrent because of the small band bending. The CaFe/sub 2/O/sub 4//Na,Mg electrode, where one side of the surfaces was doped with Na and Mg and the interface of CaFe/sub 2/O/sub 4//Na,Mg/Pt-Pd was ohmic contact, gave a large photocurrent. Photoelectrochemical dissolution was observed for the CaFe/sub 2/O/sub 4//Na,Mg electrode in acidic solution but not in neutral solution. The mechanism of the dissolution is also discussed.

Protoelectrochemical properties of the single-crystal SrTiO3 doped in the surface region

Abstract The photoelectrochemical properties of the single crystal SrTiO 3 , doped in the surface region are studied. It is found that the doped SrTiO 3 with Cr, Co, Pt and Rh give a relatively large photoresponse to visible light. The dark anodic currents which will be due to the resonance tunnelling or hopping mechanism are observed at the doped electrodes with the above metal cations. Therefore, it is concluded that the visible light response is mainly attributable to the formed impurity levels and/or structure defetcs by the doping metal cations near the conduction band of SrTiO 3 . The above doped electrodes also bring the large cathodic photocurrent or the dark cathodic current due to the O 2 reduction, except for the Co doped electrode. This will show that the impurity levels act as the active site of O 2 reduction.

Anodic characteristics of SrFe0.9M0.1O3(M: Ni, Co, Ti, Mn) electrodes

Abstract Anodic characteristics of the substituted oxides, SrFe 0.9 M 0.1 O 3 (M: Ni, Co, Ti, Mn), were studied. It was found that the catalytic activities of the oxides substituted with Ni and Co ions for the oxygen evolution reaction are high in alkaline solution. The reaction mechanisms for the oxygen evolution reaction are proposed for all the substituted oxides under the assumption of Langmuirian adsorption condition. The current efficiencies of the anodic dissolution of the oxides were much higher in acidic solution than those in alkaline solution. The anodic dissolution is much suppressed by the substitution with Ni or Co ion in alkaline solution. Therefore, the oxides substituted with Ni and Co ions are most suitable as anode materials in alkaline solution. The anodic dissolution is based on the oxygen vacancy formed in the oxygen evolution process. The mechanism of the anodic dissolution of the oxides is proposed.

The properties of silver-tin alloy deposits from pyrophosphate bath

Abstract Properties of silver-tin alloys deposits from a pyrophosphate bath have been studied to obtain data for using as functional deposits. Cathode current efficiency and the throwing power tended to decrease in current density. The highest value of the throwing power was obtained at pH 9, no pH effect on current efficiency being found. Satisfactory deposits were gained at the total metal concentration of 40 gl −1 in the depositing bath, when tin content was 10 wt. % and hardness was Hv 186. The pH of depositing bath had a small effect on both composition and hardness of alloy deposits, however, the effect of cathode current density on them was remarkable. Increasing current density increased tin content of deposits and decreased hardness. The deposit of silver-tin (90/10) alloy had a different crystal structure from that of a metallurgical alloy and a smooth surface was obtained according to the SEM photographs. Then it was observed that alloying silver and tin minuted the crystal grain. This crystal fineness was found to mainly cause the increase of hardness. With respect to the electrodeposition of the silver-tin alloy from a pyrophosphate bath, electrodeposits with various crystal structure can be obtained by the electrolytic condition. Further, current efficiency, surface condition and properties were found to be controlled by the crystal structure of electrodeposit.

STM study of photoelectrochemical plating on p-type silicon electrodes

Abstract We succeeded in observing surface changes in p-type silicon in aqueous chloroplatinic acid solution under illumination or in the dark. The scanning tunneling microscope (STM) image obtained after cathodic polarization in the dark implies that the crystal growth of deposited platinum predominates over nucleation. However, the STM image obtained after cathodic polarization under illumination implies that nucleation predominates in the initial deposition. The explanation for this behavior is that electron transfer occurs at a relatively high overpotential under illumination, i.e. the charge transfer potential of the electron under illumination is higher than that in dark.