Inhibitory Effect of Sulfur–containing Compounds on Anodic Oxidation of Borohydride

Abstract

Inhibitory effect of sulfur–containing compounds on anodic oxidation of borohydride was investigated. The linear sweep voltammetry technique revealed that sulfur compounds such as thiosulfate and sulfide inhibited anodic oxidation of borohydride not only on a platinum surface but also on a glassy carbon surface which had less catalytic activity of borohydride electro–oxidation. Through electrochemical impedance spectroscopy, it was confirmed the charge transfer resistance of borohydride oxidation at the electrode surface increased in the presence of sulfur compounds, but the capacitance of the electric double layer at the surface did not depend on sulfur compounds and their concentration. The degree of inhibition by each sulfur compound on the electro–oxidation of borohydride in the presence of electrodes and its spontaneous oxidation in the absence of electrodes was similar. Thus the sulfur compound inhibitive influence on borohydride oxidation occurred without adsorbing onto the surface of the electrode. The anodic oxidation of borohydride was suppressed to less than 1/10 of the exchange current in the case of thiosulfate and sulfide. Sulfur compounds inhibited anodic oxidation of hydrazine and dimethylaminoborane as well, while the effect of each sulfur compound varied from that of borohydride.