Influence of electrode surface charge on current production by Geobacter sulfurreducens microbial anodes

Positively charged electrode surfaces are thought to enhance electrostatic interaction with mostly negatively charged bacteria cell surface, thereby improving microbial fuel cell performance. In this work, electrostatic self-assembly of charged polymers was used to systematically modify the surface of indium tin coated electrodes. Evaluation was based on start-up time, maximum current, biofilm thickness and coulombic efficiency of microbial Geobacter sulfurreducens anodes. Coated electrodes were polarized to +0.1 V vs. SHE as biological duplicates. The thickest biofilms and in turn highest current density and shortest start-up time was achieved for negatively charged electrode surfaces like non-coated ITO or polystyrol sulfonate coated electrodes, while positively charged chitosan, negatively charged alginate and positively charged polyethylene imine, in the particular order, produced thinner biofilms, with less current and longer start-up time. This finding contradicted the initial hypothesis. Most experiments on electrode surface modifications are accompanied by an increase in available electrode surface which makes it difficult to extract solely the effect caused by the surface modification. Our study showed the importance of considering also factors other than the surface charge, e.g. potential interactions of the surface modification with the conditioning film and the medium, namely the attraction of cations by a negatively charged surface.