Multiple Cathodic Reaction Mechanisms in Seawater Cathodic Biofilms Operating in Sediment Microbial Fuel Cells

In this study, multiple reaction mechanisms in cathodes of sediment microbial fuel cells (SMFCs) were characterized by using cyclic voltammetry and microelectrode measurements of dissolved oxygen and pH. The cathodes were acclimated in SMFCs with sediment and seawater from San Diego Bay. Two limiting current regions were observed with onset potentials of approximately +400mV(Ag/AgCl) for limiting currentI and -120mV(Ag/AgCl) for limiting currentII. The appearance of two catalytic waves suggests that multiple cathodic reaction mechanisms influence cathodic performance. Microscale oxygen concentration measurements showed a zero surface concentration at the electrode surface for limiting currentII but not for limiting currentI, which allowed us to distinguish limiting currentII as the conventional oxygen reduction reaction and limiting currentI as a currently unidentified cathodic reaction mechanism. Microscale pH measurements further confirmed these results.