Tadayoshi Sakata

Electrochemical Reduction of Carbon Dioxide on Various Metal Electrodes in Low‐Temperature Aqueous KHCO 3 Media

Electrochemical reduction was investigated on 32 metal electrodes in aqueous medium. The current efficiency of reduction on Ni, Ag, Pb, and Pd increases significantly with lowering the temperature. The ratio of reduction products are also changed by lowering temperature. Potential dependence of and on an Hg electrode supports the electron transfer mechanism for production. Formation of methane and ethylene is observed on almost all metal electrodes used, although the efficiency is mainly very low except for Cu. A periodic table for reduction, which is drawn based on the dependence of reduction products on various metals, suggests the existence of a systematic rule for the electrocatalytic reduction of on metal surfaces.

Photocatalytic decomposition of gaseous water over TiO2 and TiO2—RuO2 surfaces

Abstract Hg-lamp irradiation of TiO 2 powders mixed with RuO 2 leads to the continuous production of hydrogen and oxygen from gaseous water at room temperature. The rate of hydrogen evolution per 100 mg TiO 2 —RuO 2 and 20 h was 11 μmole at a steady state. A mechanism of water decomposition over TiO 2 is proposed from the dependence of the reactivity on the surface treatments.

Heterogeneous photocatalytic production of hydrogen and methane from ethanol and water

Xe lamp irradiation of various TiO2 photocatalysts suspended in an ethanol-water mixture can produce hydrogen, methane and acetaldehyde at room temperature. The quantum yield of hydrogen production was increased greatly by supporting metals or metal complexes on the TiO2 surface, amounting to 38% for a Pt-TiO2 photocatalyst. A mechanism of the photocatalytic reactions is discussed.

Electrochemical reduction of carbon dioxide under high pressure on various electrodes in an aqueous electrolyte

Abstract The electrochemical reduction of CO 2 at a pressure of 30 atm on various electrodes at large current densities (163–700 mA cm −2 ) in an aqueous KHCO 3 solution and the cathodic voltammograms obtained were investigated. The electrocatalytic activities of various electrodes for the electrochemical reduction of CO 2 under high pressure conditions were clarified. The main products on Ag, Au, Zn, Pb and In electrodes were formic acid and/or CO, as at CO 2 pressures of 1 atm. The total current density on the cathodic voltammograms of those metal electrodes increased with increasing CO 2 pressure. On group 8–10 metals, such as Fe, Co, Rh, Ni, Pd and Pt, the main reduction products were formic acid and/or CO under high pressure, whereas under 1 atm CO 2 hydrogen was formed by reduction of water. In these cases, the total current density changed only slightly with increasing CO 2 pressure. By comparing the electrocatalytic activities of various electrodes at a CO 2 pressure of 30 atm with those at a CO 2 pressure of 1 atm, the electrodes were classified into four groups. On Rh, Ag and Pd electrodes, the maximum partial current densities for CO 2 reduction under 30 atm were 237 mA cm −2 , 383 mA cm −2 and 397 mA cm −2 respectively. The reduction of CO 2 at large current densities could be accomplished at high pressures.

Spectral sensitization of a TiO2 semiconductor electrode by CdS microcrystals and its photoelectrochemical properties

Abstract CdS microcrystals were deposited on TiO2 and ZnO semiconductors and photoelectrochemical properties were studied from the viewpoint of semiconductor sensitization. The photocurrent of a CdSTiO2 photoelectrode was caused by photoinduced electron transfer in the direction from CdS to TiO2. The photoelectrochemical properties of CdSTiO2, such as a flat band potential, were found to be strongly influenced by those of CdS as sensitizer. The quantum yield of the photocurrent amounted to 30%. A photoelectrochemical solar cell composed of CdSZnO and polysulphide solution was studied.

Photochemical diode model of Pt/TiO2 particle and its photocatalytic activity

The photocatalytic properties of a powdered semiconductor loaded with metal catalyst are discussed using a photochemical diode model. The rate of hydrogen evolution depends on particle size and correlates with irreversibility of oxidation of reactants. Only a small amount of Pt (smaller than 1/100 monolayer on TiO2) is required to produce a remarkable effect on photocatalytic activity.

Design of Alloy Electrocatalysts for CO 2 Reduction III . The Selective and Reversible Reduction of on Cu Alloy Electrodes

Many Cu alloys have been studied for electrocatalytic activity of reduction in aqueous solution. Anomalously low overpotentials with highly selective Cu alloy catalysts have been seen for the reduction of to, , or . Cu‐Ni alloys produce and selectively at reversible potentials and Cu‐Sn and Cu‐Pb produce and with an enhanced reaction rate at the reversible potentials of formation. Other alloy catalysts such as Cu‐Zn, Cu‐Cd, or Cu‐Ag also exhibit behaviors distinct from those of the elemental metals. The results reported here indicate further possibilities for the development of powerful new electrocatalysts for the reduction of .

Photocatalytic hydrogen production from liquid methanol and water

Xe-Lamp irradiation of TiO2 powders mixed with a Pt, Pd, RuO2, or rhodium complex, leads to the efficient production of hydrogen from liquid methanol and water at room temperature.

Room‐temperature preparation of the highly crystallized luminescent CaWO4 film by an electrochemical method

Highly crystallized polycrystalline film of single‐phase CaWO4 has been prepared on a tungsten substrate at room temperature in an alkaline solution containing calcium ions by an electrochemical method with the current density of 1 mA/cm2. This film showed blue emission (456 nm wavelength) with excitation light (254 nm wavelength) at room temperature.

Electrochemical reduction of high pressure CO2 at Pb, Hg and In electrodes in an aqueous KHCO3 solution

The electrochemical reduction of CO2 under high pressure in an aqueous solution at metal electrodes with high overpotentials for hydrogen evolution such as Pb, Hg and In was studied. When the electrolysis was conducted under high pressure CO2, HCOOH was formed with faradaic efficiencies of almost 100%, even at high current densities (∼ 200 mA cm−2). The maximum partial current density of HCOOH formation amounted to 560 mA cm−2 at the In electrodes under 60 atm of CO2. On the other hand, it was found that CO could form as the main reduction product of CO2 at Pb and In electrodes, at which HCOOH has previously been believed to be the main product under 1 atm of CO2. The selectivity for CO formation depended on the electrode potential. The less negative were the potentials, the higher was the faradaic efficiency of CO formation.