Akira Saji

Effect of CO2 pressure on photocatalytic reduction of CO2 using TiO2 in aqueous solutions

Abstract The photocatalytical reduction of CO 2 at high pressure was investigated using TiO 2 suspensions in water and caustic solution. An increase in CO 2 pressure significantly accelerated the CO 2 reduction in both water and the caustic solution. The major reduction products are liquid phase products such as acetic acid and alcohols, and gaseous products such as methane, ethane and ethylene were also observed as a minor portions.

Photocatalytic reduction of CO2 using TiO2 powders in liquid CO2 medium

Abstract The photocatalytic reduction of CO2 was investigated using TiO2 powders in liquid CO2 medium. The TiO2 powders with liquid CO2 medium were illuminated in a stainless steel vessel. After reducing CO2 pressure to the ordinary state, purified water was added to the vessel containing the TiO2 powders without air contamination. No gaseous reduction products were observed and formic acid was exclusively obtained in the aqueous solution. It seems that formic acid is produced through the protonation of the reaction intermediates on the TiO2 powders with purified water.

Electrochemical reduction of CO2 on Au in KOH + methanol at low temperature

The electrochemical reduction of CO2 in KOH + methanol electrolyte was investigated with a gold electrode at −25, −15, 0 and 15°C. The main products from CO2 were carbon monoxide and formic acid. The current efficiency for CO formation was larger than that for formic acid formation. In general, the formation efficiency for CO increased as the temperature decreased, however in contrast, hydrogen formation decreased. The selectivity of CO2 reduction over H2 evolution was ameliorated by decreasing temperature. From the Tafel plot study, a sufficiently high mass transfer of CO2 to the electrode was confirmed even in the low temperature region. Consequently, it was found that temperatures of less than 0°C were effective for the suppression of hydrogen formation on the Au electrode in the KOH + methanol electrolyte.

Electrochemical reduction of CO2 at an Ag electrode in KOH-methanol at low temperature

Abstract The electrochemical reduction of CO 2 in 0.1 M KOH-methanol electrolyte with a silver electrode was investigated at 248, 258 and 273 K. The main products from CO 2 were carbon monoxide and formic acid. A predominant formation of CO from CO 2 on Ag electrode in the methanol electrolyte was found. The formation efficiency of CO increased at relatively negative potential as temperature decreased, however in contrast, hydrogen formation decreased. The selectivity of CO 2 reduction over H 2 evolution was ameliorated by lowering temperature. From the Tafel plot study, a sufficiently high mass transfer of CO 2 to the electrode was confirmed even in low temperature region. Consequently, it was found that low temperature was extremely effective for the depression of hydrogen formation on Ag electrode in the KOH-methanol.

Electrochemical Reduction of C02 on Cu in 0.1 M KOH-Methanol

The electrochemical reduction of carbon dioxide in 0.1 M KOH-methanol electrolyte was investigated with a copper electrode at −30, −15, 0, and 15°C. The main products from carbon dioxide by electrochemical reduction were carbon monoxide, formic acid, ethylene, and methane. Under the optimum experimental conditions, 56% Faradaic efficiency carbon monoxide, 23% formic acid, and 10% methane were produced from carbon dioxide by electrochemical reduction. The best ethylene formation (12%) was obtained at −2.2 V and 0°C.

Preparation of a Ag-Doped Bi-Sr-Ca-Cu-O Bulk Sample by the Floating-Zone Method

Bulk samples with nominal composition of Bi2Sr2CaCu2Oy doped with 0, 10 and 20 weight % Ag were prepared by the floating-zone method at growth rates of 2 mm/h and 5 mm/h. Ag-doping seems to slightly enhance Jc, while annealing is very effective for Jc enhancement. From preliminary ac susceptibility measurements, the Jc enhancement by annealing is considered to be due to improvement of the weak link between superconducting grains. The 10% Ag-doped sample grown at 2 mm/h possessed Jc of 5360 A/cm2 at 77 K under zero magnetic field after annealing.

Contact Resistance and V-I Characteristics in a Ag-Doped Bi-Sr-Ca-Cu-O Superconductor

Contact resistance and V-I characteristics were investigated in Ag-doped and undoped Bi-Sr-Ca-Cu-O bulk samples prepared by the floating-zone method. In undoped samples, with increasing current pulse width, rapidity of voltage rise in V-I characteristics increases and Jc decreases. The contact resistance is nonohmic and temperature dependence is semiconductorlike. In a Ag-doped sample, rapidity of voltage rise and Jc are not influenced by pulse width, and deviation of Jc among samples is small. The ohmic contact resistance has metallike temperature dependence, and its value is less than 1/500 of that in an undoped sample.

Rapid Synthesis of the YBa2Cu3Ox Film on Metal Substrate by Chemical Vapor Deposition Technique

A new chemical vapor deposition technique has been developed for rapid (max. 24 µm/h) formation of the oxide superconductor film on a metal substrate. In this system, blended β-diketonate chelates of source materials were slowly fed to the vaporizer with carrier gas. The source gas from the vaporizer and O2 gas were introduced into the reactor. We realized a superconducting YBCO thin film that had a Tc=87 K on a Hastelloy C-276 substrate.

Ag-Doped Bi-Sr-Ca-Cu-O Superconductor Prepared by Floating Zone Method

Ag-doped Bi2Sr2CaCu2Oy bulk samples were prepared by floating zone (FZ) method aiming at enhancement of critical current density (Jc) and lowering of contact resistance at current terminal. It was found that Ag particles tend to be elongated along the growth direction, and be trapped in the oxide grains. Jc value was not significantly affected by Ag-doping up to 10%, but the contact resistance at current terminal was lowered to about 1/1000 that of undoped sample.

Preparation of Bi-Sr-Ca-Cu-O Thin Films by Chemical Vapor Deposition

We report on the Bi-Sr-Ca-Cu-O film formation on MgO(100), SrTiO3(100) and LaAlO3(100) by MOCVD using Bi(C6H5)3, Sr(DPM)2, Ca(DPM)2 and Cu(DPM)2 as source materials. The XRD pattern for the films prepared on MgO(100) showed the high Tc phase with the c-axis oriented normal to the substrate surface, whose Tc zero was 75K. On the other hand, the XRD pattern for the films prepared on SrTiO3(100) and LaAlO3(100) showed the mixture of the high Tc and low Tc phases. The Tc zero of 79K on SrTiO3(100) and 82K on LaAlO3(100) were higher than that on MgO(100).