Mediating Effects of Redox Dyes and Ferric Chelates in Microbial Fuel Cells Using E. Coli

Potential measurements were made with microbial fuel cells for the conversion of chemical energy to electrical energy through the catalytic action of Escherichia coli, using Methyl Red and two different Ferric Chelates (EDTA and MES). A good mediator should be easily reduced and oxidized, and facilitate the transfer of electrons during the respiratory process of the bacteria without killing it. The setup of the cell consisted of two chambers separated by a semi-permeable membrane with inlets and outlets for N2 gas to remove oxygen and maintain anaerobic conditions during the voltage measurements. The bacteria were dissolved in the ferric chelate solution mixed with phosphate buffer at ph 7.00 and were placed at the anode compartment. At the cathode compartment a 0.1 M K3Fe(CN)6 solution was placed. Each compartment was filled with 20 mL of the correspondent solutions. Carbon cloth of 2cm x 4cm served as electrodes in both compartments, and 10 µmol of glucose were added as fuel in the anodic half-cell. In our preliminary studies, among the four mediators already studied we observed that EDTA is the best mediator, followed by Methyl Red. In the other hand, MES has the lowest coulombic output, which makes it a poor mediator.