Electrooxidation of borohydride on a polycrystalline platinum electrode modified with Bi species

Abstract

Surface analysis techniques (XPS and SEM) and electrochemical measurements (cyclic voltammetry) were employed to study borohydride oxidation on a polycrystalline Pt electrode modified with irreversibly adsorbed Bi species in an aqueous alkaline medium containing 0.05 M NaBH4 and 1 M NaOH. X-ray photoelectron spectroscopy revealed the presence of metallic Bi and Bi-oxychloride / hydroxide / oxide on the Pt surface after various immersion times of Pt electrode into a BiCl3 modifying solution in concentrated hydrochloric acid under open-circuit conditions. The Bi-modified polycrystalline Pt electrode exhibited an outstanding electrocatalytic activity for BH4– oxidation with hydrogen oxidation highly suppressed implying the inhibition of borohydride hydrolysis reaction. A considerable gain of the current on the Bi-modified polycrystalline Pt electrode can be explained by a gradual conversion of Bi-oxychloride and Bi-hydroxy / oxy surface species into higher valent Bi-oxygenated surface species along with borohydride oxidation. It is supposed that the presence of hydroxylated Bi species on the top of the modifying layer may imply that they act as a donor of hydroxyl species, providing their higher availability on the Bi-modified polycrystalline Pt surface for borohydride oxidation.