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Abstract: A series of polypyrrole (PPY)-modified carbon-supported Co(OH)2 catalysts [Co(OH)2-PPY-C] with different types of carbon supports and the PPY and Co(OH)2 contents are synthesized to investigate the effect of the Coic>x and h name="dbnd" />Nh name="dbnd" /> sites on the oxygen reduction reaction (ORR). X-ray photoemission spectroscopy results reveal that the Coic>x and h name="dbnd" />Nh name="dbnd" /> sites dominate the four- and two-electron transfer ORR, respectively. The carbon support and the PPY and Co(OH)2 contents of the catalysts determine the distribution of the Coic>x and h name="dbnd" />Nh name="dbnd" /> sites. The competition between these two sites determines the overall electron number of the ORR. A direct borohydride fuel cell using an optimal Co(OH)2-PPY-C as the cathode catalyst exhibits a maximum power density of 550mWcm−2 at 80°C. [Copyright &y& Elsevier]

Abstract: An amorphous Fe-based catalyst supported on polypyrrole-modified carbon nanotubes is synthesized by a chemical method. The microstructure, surface composition and morphology are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The synthesized amorphous Fe-based catalyst is composed of amorphous FeOOH and microcrystalline Fe2O3. Compared with a crystalline FeOOH catalyst, the amorphous Fe-based catalyst demonstrates higher electrocatalytic activity toward the oxygen reduction reaction (ORR), due to its amorphous structure and large specific surface area. It is considered that amorphization of transition metal compounds could be one of the methods used to improve their catalytic activity toward the ORR. [ABSTRACT FROM AUTHOR]

Abstract: Carbon-supported Co(OH)2 and Ni(OH)2 catalysts are prepared to examine the mechanism of oxygen reduction reaction (ORR) on hydroxide catalysts. ORR via the 4-electron transfer pathway on a hydroxide undergoes oxidation of hydroxide by O2 to form oxyhydroxide, followed by electrochemical reaction of oxyhydroxide to regain hydroxide. β-Ni(OH)2 has the same crystal structure and lattice parameters as β-Co(OH)2, but it exhibits a poorer catalytic activity toward ORR than β-Co(OH)2 at a low temperature. The poor catalytic activity of Ni(OH)2/C can be attributed to the difficulty in Ni(OH)2 oxidation and the slow kinetics of NiOOH electroreduction to Ni(OH)2. The catalytic activity of the Ni(OH)2/C catalyst is significantly improved through elevating the operation temperature because Ni(OH)2 oxidation to NiOOH and NiOOH electroreduction are improved at a high temperature. A model of ORR via the 4-electron transfer pathway on transition metal hydroxides is suggested and discussed. [Copyright &y& Elsevier]