Electrochemical oxidation of borohydride on platinum electrodes: The influence of thiourea in direct fuel cells

The electrochemical behaviour of sodium borohydride on a platinum electrode in the absence and presence of thiourea (TU) was investigated by cyclic voltammetry. In the absence of thiourea, several overlapping peaks associated with the hydrolysis of BH4− appear in the domain of hydrogen oxidation, i.e., in the potential range of −1.25 to −0.50 V versus Ag/AgCl. As a consequence of secondary reactions, the borohydride oxidation in 3 M NaOH solution shows a four to six-electron process, according to its concentration, in direct fuel cells. A conveyable TU/NaBH4 concentration ratio of 0.6 inhibits the delivery of hydrogen simultaneously with catalytic hydrolysis of BH4−. Thus, the coulombic efficiency in direct fuel cell discharge was increased showing an about eight-electron process for the oxidation of BH4−.