Thionine and ferric chelate compounds as coupled mediators in microbial fuel cells

Abstract The mediating effects of mixed mediator systems consisting of a series of ferric chelate compounds and thionine were studied in bio-fuel cells containing Escherichia coli. Significant increases in the coulombic output from the bio-fuel cells containing mixed mediators were observed compared with those obtained from the fuel cells containing single mediators. A correlation was observed between the cell voltage of a bio-fuel cell containing Fe(III)EDTA and thionine and the concentration of Fe(III)EDTA in the anode compartment, indicating that the concentration of the reduced form of ferric chelate was dominant in maintaining the cell voltage. The reduction of thionine by E. coli in the presence of Fe(III)EDTA, and that of Fe(III)EDTA by E. coli in the presence of thionine were measured. The results support a proposed mechanism involving a redox coupling reaction between Fe(III)EDTA and reduced thionine.