Unveiling the Mechanism of Enhanced Extracellular Electron Transfer by Polarity Inversion of Bioelectrodes

Polarity inversion from the bioanode to the biocathode enables a rapid formation of efficient biofilms for microbial electrochemical reduction. Though this approach has been widely adopted for various applications, the mechanism behind the enhanced extracellular electron transfer (EET) during the polarity inversion process remains unclear. Therefore, in this study, the succession pattern and electron transfer mechanism of the inverted denitrifying biocathode were investigated by continuously monitoring the electrochemical properties, denitrification dynamics, and biofilm characteristics. The results indicated that the highest current density of the biocathode after inversion from bioanode was twice that of the steady current density, and the dominant flora of the electrode biofilm shifted from Geobacter sp. to denitrifying bacteria (e.g., Shinella and Comamonas). The reversal polarity induced a decreasing content of cytochrome C, while iron-containing compounds were found to be responsible for an enhanced EET within the denitrification process. This study provides a deep understanding of the EET mechanism behind the electrode polarity inversion and is of great significance for the future development of biocathode applications.