Influence of Sulfide on Oxygen Reduction Reaction in 3.5% Sodium Chloride Solution

Abstract

Different from the corrosion under anaerobic conditions, oxygen (O2) takes part in the cathodic reaction under aerobic conditions. Sulfate-reducing bacteria (SRB) have been regarded for many years as strictly anaerobic bacteria, but recently, they are found to be able to survive in the presence of O2, and how they affect the oxygen reduction reaction (ORR) has not been clear. In this study, the role of sulfide, a key inorganic metabolite of SRB, in ORR has been investigated on Q235 carbon steel electrode with cyclic voltammetry and electrochemical impedance spectroscopy. Three cathodic processes are recorded on cyclic voltammograms in O2-saturated 3.5% NaCl solution: ORR, iron oxides reduction and hydrogen evolution. The peak current of ORR decreases with the introduction of sulfide, and finally vanishes when the sulfide concentration is more than 0.5 mM. EIS reveals that sulfide leads to the disappearance of the feature of semi-infinite diffusion of ORR and the fitting results demonstrate that charge transfer resistance increases with increasing sulfide concentration. Therefore sulfide hinders the cathodic reduction of O2on Q235 carbon steel in 3.5% NaCl solution.