Hirohisa Yamada

Effect of Agglomeration of Pt/C Catalyst on Hydrogen Peroxide Formation

Various amounts of 20 wt % Pt/C catalysts (56.7-5.7 μg c a r b o n cm - 2 ) were loaded on glassy carbon (GC) disk electrode, and the effect of agglomeration on hydrogen peroxide formation in oxygen reduction was investigated by the rotating ring-disk electrode technique. The formation of H 2 O 2 was enhanced with a decrease in agglomeration of Pt/C. Even in the operating potential range of polymer electrolyte fuel cell cathodes (0.6-0.8 V), 10% hydrogen peroxide was formed at 5.7 μg c a r b o n cm - 2 Pt/C loaded on GC. These results revealed that series two-electron reduction pathway, which is negligible on clean bulk Pt surface, does exist on Pt particles supported on carbon.

Effect of Core Size on Activity and Durability of Pt Core-Shell Catalysts for PEFCs

Pt/Au/C and Pt/Pd/C core-shell catalysts were prepared from Au/C and Pd/C cores with different core sizes using under potential deposition (UPD) of Cu, and the activity for oxygen reduction reaction and durability of the Pt/Au/C and Pt/Pd/C catalysts were investigated. Pt/Au/C and Pt/Pd/C core-shell catalysts showed higher mass activities than a commercially available Pt2.8nm/C catalyst, and hence they are promising for reducing the Pt usage in PEFCS. In potential cycling durability tests between 0.6-1.0 V, opposite effects of core size on were observed for Pt/Au/C and Pt/Pd/C. For Pt/Au/C, smaller cores gave high durability, whereas for Pt/Pd/C, larger cores gave high durability comparable with the Pt2.8nm/C.

Effects of type of reactor, crystallinity of SiC, and NF3 gas pressure on etching rate and smoothness of SiC surface using NF3 gas plasma

Polycrystalline β-SiC and single-crystalline 4H-SiC surfaces were etched by reactive ion etching (RIE) using NF3 gas plasma. A smooth surface was obtained on the polycrystalline SiC after RIE at NF3 gas pressures of 2 and 10 Pa for 10 min, and neither spikes nor pillars were formed on it. On the other hand, some pillars were formed on the single-crystalline SiC surface by RIE at NF3 gas pressures of 2 and 10 Pa. Though the absence of carbon-rich regions and SiOx on the outermost surface before etching was confirmed by x-ray photoelectron spectroscopy and Raman analysis, x-ray diffraction analysis revealed that graphite crystallites were present in the single-crystalline SiC bulk. It was concluded that the graphite crystallites acted as masks and the pillars grew up from the graphite crystallites in the single crystalline SiC during RIE.

Hydrogen Peroxide Formation as a Degradation Factor of Polymer Electrolyte Fuel Cells

Durability is one of the most important issues in commercialization of polymer electrolyte fuel cells (PEFCs). A long life over 90,000 hours (= 10 years) is required for PEFC stacks in the small-scale cogeneration systems; however, sufficient durability to meet this demand has not been established. Various mechanisms are being considered for the deterioration of the cell stacks during a long operation. Hydrogen peroxide formation, which is formed electrochemically or chemically during operation, is one of the potential deteriorating factors of PEFCs. In the present study, we investigated H2O2 formation as a degradation factor of PEFCs.