Polypyrrole Electrodes Show Strain-Specific Enhancement of Photocurrent from Cyanobacteria

Abstract

Except for a limited number of exoelectrogens, most microbes of interest are surrounded by insulating membranes impairing an efficient extracellular electron transfer. This study focuses on the fabrication of a conductive polypyrrole (PPy) based coating for enhancing microbial charge extraction. The polymer deposition was characterized and optimized using a combination of potentiodynamic and potentiostatic measurements as well as scanning electron microscopy (SEM), energy dispersive X-Ray (EDX) analysis, and Raman spectroscopy. The electrodes were used to extract photosynthetic electrons from the cyanobacteria Synechocystis sp. PCC6803 and Synechococcus Elongatus PCC7942. The PPy electrode showed a six-fold increase in extracted photocurrent for Synechocystis under unmediated conditions compared to bare graphite electrodes. This enhancement was attributed to decreased resistivity and increased electroactive surface area of the PPy electrode. By contrast, Elongatus showed no substantial difference in photocurrent between the PPy and bare electrodes. A comparison of the zeta potential and adherence of the cells suggested more limited charge interaction of Elongatus cells with the PPy surface compared to the Synechocystis cells indicating a strain-specific enhancement of these electrodes.