Hajime Kusaba

H2S Poisoning of Solid Oxide Fuel Cells

The influence of H 2 S fuel impurity on power generation characteristics of solid oxide fuel cells (SOFCs) has been analyzed by measuring cell voltage at a constant current density, as a function of H 2 S concentration, operational temperature, and fuel gas composition. Reversible cell voltage change was observed around 1000°C, while fatal irreversible degradation occurred at a lower operational temperature, at a higher H 2 S concentration, and at a lower fuel H 2 /CO ratio. Sulfur tolerance of SOFCs was improved by using Sc 2 O 3 -doped ZrO 2 instead of Y 2 O 3 -doped ZrC 2 as electrolyte and/or as electrolyte component in the anode cermets. It has been found that H 2 S poisoning consists of at least two stages, i.e., an initial cell voltage drop within a short time period to a metastable cell voltage, followed by a gradual larger cell voltage drop. Possible H 2 S poisoning processes are discussed.

Oxygen-sorptive and -desorptive properties of perovskite-related oxides under temperature-swing conditions for oxygen enrichment

Abstract A group of A- and/or B-site partially substituted strontium cobaltites was investigated for oxygen-sorptive properties under temperature-swing conditions in air. The cobaltites with perovskite structure desorbed and absorbed significant amounts of oxygen quickly as well as reversibly on heating or cooling in the temperature range between 300 and 1000 °C, while those with brownmillerite or 2H-BaNiO 3 structure either lacked oxygen-sorptive properties or showed retarded oxygen sorption with hysteresis, respectively. Under temperature-swing cycles between 300 and 550 °C at a heating or cooling rate of 30 °C/min, SrCo 0.4 Fe 0.6 O 3− δ showed the largest mass change of 0.96%, or sorption and desorption of 7 cm 3 oxygen (STP)/g oxide among the perovskite-type oxides tested. This result appears to indicate the potential of a new oxygen enriching method coupled with a temperature-swing technique.

Low-cost catalysts for the control of indoor CO and PM emissions from solid fuel combustion.

Cu-Mn based mixed oxide type low-cost catalysts have been prepared in supported form using mesoporous Al(2)O(3), TiO(2) and ZrO(2) supports. These supports have been prepared by templating method using a natural biopolymer, chitosan. The synthesized catalysts have been characterized by XRD, BET-SA, SEM, O(2)-TPD and TG investigations. The catalytic activity for CO as well as PM oxidation was studied, in a view of their possible applications in the control of emissions from solid fuel combustion of rural cook-stoves. The trend observed for the catalytic activity of the synthesized catalysts for CO oxidation was ZrO(2)>TiO(2)>Al(2)O(3) while for PM oxidation it was observed to be TiO(2)>ZrO(2)>Al(2)O(3). The effect of CO(2), SO(2) and H(2)O on CO oxidation activity was also investigated, and despite partial deactivation, the catalysts show good CO oxidation activity. An effective regeneration treatment was attempted by heating the partially deactivated catalysts in presence of oxygen. Redox properties of TiO(2) and ZrO(2) and their structure appeared to be responsible for their promotional activity for CO and PM oxidation reactions. These unordered mesoporous materials could be useful for such reactions where mass transfer is more important than shape and size selectivity.

Preparation and Electrochemical Activities of Pt–Ti Alloy PEFC Electrocatalysts

Titanium is one of the most stable materials, remaining undissolved under strongly acidic polymer electrolyte fuel cell (PEFC) conditions. Nanocrystalline Pt-Ti alloy electrocatalysts with a catalyst grain size of several nanometers have been successfully prepared by the colloidal and sol-gel method, characterized by X-ray diffraction, field-emission scanning electron microscope, scanning transmission electron microscope, energy-dispersive X-ray analysis, and X-ray photoelectron spectroscopy. Electrochemical activities were evaluated by current-voltage characteristics measurements using membrane electrode assemblies for humidified H 2 fuels with or without 100 ppm CO, cyclic voltammetry, and CO-stripping voltammetry in 0.1 M HClO 4 . Pt-Ti alloy electrocatalysts exhibited higher electrochemical performance than pure Pt catalyst, i.e., higher activity for oxygen reduction reactions and improved CO tolerance.

Synthesis and characterisation of the six-membered cyclopalladated complexes of 2-benzylbenzothiazole

Abstract The six-membered cyclopalladated complex di- μ -acetato-bis[2-(2′-thiazolylmethyl)phenyl- C 1 , N ]dipalladium(II), [{Pd( μ -O 2 CMe) ( η 2 -bbt)} 2 ] ( η 2 -bbt = 2-(2′-thiazolylmethyl) phenyl- C 1 , N ), has been prepared by the reaction of palladium(II) acetate and 2-benzylbenzothiazole. Its di-μ-halogeno analogues [{Pd( μ -K) ( η 2 -bbt)} 2 ], synthesised by the metathetical reaction with LiCL or NaX, undergo bridge-splitting reactions with some pyridine derivatives and thallium(I) acetylacetonate to yield corresponding mononuclear cyclopalladated complexes. The cyclopalladated feature and the six-membered structure have been confirmed by the 1 H NMR spectra of the mononuclear pyridine complexes. Temperature-dependent 1 H NMR spectra have been observed for [{Pd( μ -O 2 CMe) ( η 2 -bbt)} 2 ] and [Pd(acac) ( η 2 -bbt)] and are attributed to inversions of acetato bridges and the boat-formed six-membered ring, respectively.

Temperature-swing based oxygen enrichment by using perovskite-type oxides

A family of partially substituted strontium cobaltites were examined for the oxygen-sorptive properties under temperature-swing conditions in air to explore the feasibility of the new oxygen-enriching method.

Nanostructured PEFC Electrode Catalysts Prepared via In-situ Colloidal Impregnation

Nanostructured Platinum-based electrode catalysts were prepared via in-situ colloidal impregnation for polymer electrolyte fuel cells. Crystallite size, grain size, and distribution of Pt nanoparticles on carbon support materials were characterized by XRD, TEM, high-resolution FESEM, and STEM. Effective surface area and kinetically-controlled current density of Pt electrode catalysts were analyzed by cyclic and hydrodynamic voltammetry using rotating disk electrodes. PEFCs with these electrode catalysts were also prepared and their I-V characteristics were examined at 80°C. We have succeeded to develop Pt electrode catalysts with a diameter of a few nm, supported on carbon nanofibers with different structures (including herringbone-type fibers, platelet-type fibers, and highly-conductive vapor-grown fibers), carbon nanotubes, as well as carbon black. The dependencies of nanostructure and electrochemical properties on crystallographic structure of carbon support materials and preparation conditions of electrode catalysts are analyzed and discussed. Nanostructural design of PEFC electrode catalyst layers using carbon nanofibers as catalyst supports and electrode fillers is also discussed.

High Temperature PTC Thermistor Using Ba Cobaltite

It was found that partially Fe-substituted Ba cobaltite, BaCo0.7Fe0.3O3-δ, shows sharp PTC behavior at temperature above 850 °C. As revealed by XRD measurements, the PTC behavior is accompanied by phase transformation between hexagonal perovskite structure (low temperature) and cubic one (high temperature).