Catalytic Performance of Pt/Reduced Graphene Oxide Composites to Methanol Electrochemical Oxidation: Optimization of Mass-Specific Activity.

Series of catalysts made of Pt nanoparticles supported on reduced graphene oxides (Pt/RGO) were synthesized and tested in methanol oxidation reaction, aiming for optimizing the mass-specific activity of prepared Pt/RGO composites. The loading amount of Pt is controlled through setting different reaction time and determined precisely by atomic absorption spectrophotometer. The structure of Pt/RGO composites is characterized by X-ray diffraction, transmission electron microscopy and Raman spectroscopy. The electrochemical testing data reveal that the Pt/RGO-mass-specific activity, judged by current density and long-term stability, is maximized in the sample in which cooperation of the Pt loading amount and electrochemical active surface area (ECSA) per amount of Pt is best optimized. The performance of the catalyst with smallest Pt particles or highest Pt loading amount is dragged down by either too less Pt loading or poor ECSA per amount of Pt. The results in this research demonstrate that the mass-normalized activity of whole catalyst, which is associated with the anticipated power output per amount of catalyst, could be enhanced significantly by deliberate tuning of fabrication process.

Template-free synthesis and mechanistic study of porous three-dimensional hierarchical uranium-containing and uranium oxide microspheres.

A novel type of uranium-containing microspheres with an urchin-like hierarchical nano/microstructure has been successfully synthesized by a facile template-free hydrothermal method with uranyl nitrate hexahydrate, urea, and glycerol as the uranium source, precipitating agent, and shape-controlling agent, respectively. The as-synthesized microspheres were usually a few micrometers in size and porous inside, and their shells were composed of nanoscale rod-shaped crystals. The growth mechanism of the hydrothermal reaction was studied, revealing that temperature, ratios of reactants, solution pH, and reaction time were all critical for the growth. The mechanism study also revealed that an intermediate compound of 3 UO3 ⋅NH3 ⋅5 H2 O was first formed and then gradually converted into the final hydrothermal product. These uranium-containing microspheres were excellent precursors to synthesize porous uranium oxide microspheres. With a suitable calcination temperature, very uniform microspheres of uranium oxides (UO2+x , U3 O8 , and UO3 ) were successfully synthesized.