Oxygen Reduction Reaction Affected by Sulfate-Reducing Bacteria: Different Roles of Bacterial Cells and Metabolites.

Sulfate-reducing bacteria (SRB) were found to be capable of tolerating a certain amount of oxygen (O), but how they affect oxygen reduction reaction (ORR) has not been clear. The present work investigated the impact of SRB on ORR in 3.5 wt% sodium chloride solution with the cyclic voltammetry method. The addition of SRB culture solution hampered both the reduction of O to superoxide (O) and hydrogen peroxide (HO) to water (HO), and the influence of SRB metabolites was much larger than that of bacterial cells. Sulfide and extracellular polymeric substances (EPS), typical inorganic and organic metabolic products, had great impact on ORR. Sulfide played an important role in the decrease of cathodic current for HO reduction due to its hydrolysis and chemical reaction activity with HO. EPS were sticky, easy to adsorb on the electrode surface and abundant in functional groups, which hindered the transformation of O into O and favored the reduction of HO to HO.