Chronopotentiometric Investigation of Borohydride Oxidation at a Gold Electrode

Sodium borohydride (NaBH(4)) presents interesting options for electrochemical power generation acting either as a hydrogen source or an anodic fuel for direct borohydride fuel cells. Though there have been several papers concerning electrochemical determination of relevant thermodynamic and kinetic parameters to the borohydride (BH(4)(-)) system, there are many basic aspects that have not yet been systematically studied. This paper reports chronopotentiometric studies of the electro-oxidation of BH(4)(-) at a gold electrode in 2 M NaOH solutions at temperatures ranging from 25 to 65 degrees C. Gold displays a rather good BH(4)(-)oxidation activity, and the overall oxidation process is shown to be irreversible involving a number of exchanged electrons close to the theoretically expected value of 8. For the specific potential and concentration ranges observed, the results suggest that the rate-determining step is an irreversible, diffusion-controlled, one-electron oxidation step for which several key kinetic parameters (alpha, k(s), and E(ct)(0)) are calculated. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3256136] All rights reserved.