Different methods used to form oxygen reducing biocathodes lead to different biomass quantities, bacterial communities, and electrochemical kinetics

Six biocathodes catalyzing oxygen reduction were designed from the same environmental inoculum but using three different methods. Two were formed freely at open circuit potential, two using conventional aerobic polarization at − 0.2 V/SCE and two by reversion of already established acetate-fed bioanodes. Observation of the biofilms by SEM and epifluorescence microscopy revealed that reversible bioelectrodes had the densest biofilms. Electrochemical characterization revealed two different redox systems for oxygen reduction, at − 0.30 and + 0.23 V/SCE. The biocathodes formed under aerobic polarization gave higher electrocalatytic performance for O2 reduction, due to production of the redox systems at + 0.23 V/SCE. Analyses of the bacterial communities on the biocathodes by 16S-rRNA pyrosequencing showed different selection (or enrichment) of microorganisms depending on the method used. This study highlights how the method chosen for designing oxygen biocathodes can affect the cathode coverage, the selection of bacterial populations and the electrochemical performance.