Rotating ring-disc electrode (RRDE) voltammetry is applied for the in situ determination of hydroxy borohydride (BH3(OH)(-)) formation during borohydride (BH4-) electro-oxidation on a gold (Au) electrode in 6.0 M NaOH solution. The BH3(OH)(-) is detected at the ring electrode due to its further oxidation to BH2(OH)(2-) by maintaining its potential in the range of -0.800 to -0.600V vs. normal hydrogen electrode (NHE) while oxidizing BH4- on the disc electrode. The study reveals that the generation of BH3(OH)(-) increases if the anodic polarization of the disc electrode is increased. The RRDE ring-shielding experiments show that the electro-oxidation of BH4- Occurs over a wide potential range of -0.500 to 0.400V on the Au electrode under hydrodynamic conditions. Chronoamperometry is also used to study the BH3(OH)(-) oxidation in the potential range of -0.800 to -0.600V with 0.33 M NaBH4 in three different buffer solutions of pH 10.2, 11.0 and 11.70, respectively. The chronoamperometric studies indicate that the formation and stability of BH3(OH)(-) depends on the pH value. (c) 2008 Elsevier B.V. All rights reserved.