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Electro-oxidation of borohydride on colloidal Os and Os-alloys (Os-Sn, Os-Mo and Os-V)

Pages: 243-249

Mohammed H. Atwana, Derek O. Northwood^*,a and Elod L. Gyenge^*,b

^aDept. of Mechanical, Automotive and Materials Engineering University of Windsor, 401 Sunset Avenue, Windsor, ON, Canada N9B 3P4
^bDept. of Chemical and Biological Engineering, The University of British Columbia, 2360 East Mall, Vancouver, BC, Canada V6T 1Z3

Received March 5, 2005 ; received in revised form February 20, 2006

Abstract: The electrochemical behaviour of sodium borohydride (NaBH4) in 2 M NaOH on supported colloidal Os and Os-alloys (i.e. Os-Sn, Os-Mo and Os-V) prepared by the Bönneman method was investigated. Cyclic voltammetry experiments on pure colloidal Os (i.e. 10, 20 and 30 %wt Os on carbon support with 30 μg cm^-2 metal load) showed peaks due to the OsO^2-₄ / Os and OsO^2-₅ / OsO^2-₄ redox couples in conjunction with a BH^-₄ oxidation wave. Furthermore, it was observed that the hyperosmate (OsO^2-₅ ) - osmate (OsO^2-₄) couple acts as a redox mediator of the BH^-₄ oxidation. The catalytic activity of colloidal Os toward BH^-₄ electro-oxidation has been shown by cyclic voltammetry, chronopotentiometry and chronoamperometry experiments, whilst the investigated Os-alloys were catalytically inactive. Chronopotentiometry experiments with a current step of 25 mA cm^-2 revealed that the 20 %wt Os gave the lowest anodic potentials, i.e. -0.73 V vs. Ag/AgCl, KClstd. Therefore, Os shows promise as anode electrocatalyst for direct borohydride fuel cells.

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