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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]

Abstract: Hydrolysis of sodium borohydride NaBH4 is a promising method for on-board hydrogen supply for fuel cells. In this study, the hydrolysis reaction was studied by starting with solid NaBH4 rather than aqueous borohydride solutions, and adding less amount of water in an attempt to explore the maximum hydrogen generation capacity. It was found that hydrogen could be liberated at very high rates and over than 90% conversion rates were achieved when the mole ratio of water to sodium borohydride was not less than 4:1. The final hydrogen generation capacity was achieved as high as 6.7wt%. Materials such as CoCl2 or cobalt powder were found to be effective as the catalysts for the hydrolysis reaction at such reaction conditions. A large heat effect due to the exothermic reaction and a low melting point of NaBO2·4H2O led to the acceleration of hydrogen generation at the latter part of the hydrolysis process. It is thus promising to utilize these reaction conditions to achieve high hydrogen generation capacity by proper system design. [Copyright &y& Elsevier]

Abstract: Borohydrides, a group of compounds with large hydrogen contents, can generate hydrogen readily by their hydrolysis reaction. In this study catalysts based on nickel and cobalt were developed to accelerate the hydrolysis reaction for hydrogen generation. Catalysts in four forms were tested for each metal: fine metal powder, metal salt, metal boride and Raney metal. It was found that the hydrolysis reaction was primary a zero-order reaction under the catalysis of these catalysts. Although cobalt showed higher catalytic activity than nickel in most cases, Raney Ni exhibited almost the same activity as the Raney Co. Among four chemical forms for nickel, Raney Ni demonstrated the best performance. Moreover, Raney catalysts made from alloys of nickel and cobalt showed even higher activity. The reaction on Raney metals was also characterized by a slowdown in hydrogen generation rate at low borohydride concentrations because of a mass transfer limitation. [Copyright &y& Elsevier]

Abstract: A direct hydrazine fuel cell using H2O2 as the oxidizer has been developed. The N2H4/H2O2 fuel cell is assembled by using Ni–Pt/C composite catalyst as the anode catalyst, Au/C as the cathode catalyst, and Nafion membrane as the electrolyte. Both anolyte and catholyte show significant influences on cell voltage and cell performance. The open-circuit voltage of the N2H4/H2O2 fuel cell reaches up to 1.75V when using alkaline N2H4 solution as the anolyte and acidic H2O2 solution as the catholyte. A maximum power density of 1.02Wcm−2 has been achieved at operation temperature of 80°C. The number of electrons exchanged in the H2O2 reduction reaction on Au/C catalyst is 2. [Copyright &y& Elsevier]

Abstract: A polypyrrole modified carbon-supported cobalt hydroxide (Co(OH)2-PPY-C) has been prepared by the impregnation-chemical method and used as the electrode catalyst in a direct borohydride fuel cell (DBFC). The microstructure of Co(OH)2-PPY-C has been characterized by X-ray diffraction and transmission electron microscopy. The cell performance and short-term performance stability of the DBFC using the Co(OH)2-PPY-C as catalysts have been investigated. A maximum power density of 83mWcm−2 has been achieved at 0.6V under ambient conditions. The Co(OH)2-PPY-C catalyst demonstrates a smaller value of polarization than the carbon-supported Co(OH)2 catalyst. Results from electrochemical impedance spectrum analysis confirm that the polypyrrole addition to the cathode effectively decreases its resistance. During operation of the DBFC using Co(OH)2-PPY-C as catalyst, the Co(OH)2 tends to be converted into CoHO2. [Copyright &y& Elsevier]