The quartz crystal microbalance technique coupled with cyclic voltammetry (referred to as electrochemical quartz crystal microbalance (EQCM)) was employed to study the oxidation of BH4- on Au in alkaline media (0.1 M and 2 M NaOH, respectively) using a newly designed vertical cell to minimize the interference by evolved H-2. The electrode potential was scanned between -0.7 and 0.7 V vs. SHE with scan rates in the range of 0.01 V s(-1) and 1 V s(-1). The relative mass changes of the Au resonator-electrode were interpreted in combination with density functional theory (DFT) modeling and pertinent experimental results from the literature. The potential scan rate dependent mass change profiles revealed: i) weak adsorption of BH4- below -0.2 V leading to high anodic overpotential, ii) accumulation of reaction intermediates on the surface between approximately -0.2 V to 0.3 V (scan rate dependent), and iii) Au surface hydroxide and oxide assisted oxidation of BH4- and possibly of other active species present such as BH3OH- formed by hydrolysis. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.046301jes] All rights reserved.