The electrochemical oxidation of BH4 − in 2M NaOH on Pt and Au (i.e. catalytic and non-catalytic electrodes, respectively, for BH4 − hydrolysis accompanied by H2 evolution) has been studied by cyclic voltammetry, chrono-techniques (i.e., potentiometry, amperometry, coulometry) and electrochemical impedance spectroscopy. In the case of Pt the cyclic voltammetry behaviour of BH4 − is influenced by both, the catalytic hydrolysis of BH4 − yielding H2 (followed by electrooxidation of the latter at peak potentials between −0.7 and −0.9V versus Ag/AgCl, KClstd) and direct oxidation of BH4 − at more positive potentials, i.e., between −0.15 and −0.05V. Thiourea (TU, 1.5×10−3 M) was an effective inhibitor of the catalytic hydrolysis associated with BH4 − electrooxidation on Pt. Therefore, in the presence of TU, only the direct oxidation of BH4 − has been detected, with peak potentials between −0.2 and 0V. It is proposed that TU could improve the BH4 − utilization efficiency and the coulombic efficiency of direct borohydride fuel cells using catalytic anodes. The electrooxidation of BH4 − on Pt/TU is an overall four-electron process, instead of the maximum eight electrons reported for Au, and it is affected by adsorbed species such as BH4 − (fractional surface coverage ∼0.3), TU and possibly reaction intermediates.