Microbial fuel cell with an azo-dye-feeding cathode.

Microbial fuel cells (MFCs) were constructed using azo dyes as the cathode oxidants to accept the electrons produced from the respiration of Klebsiella pneumoniae strain L17 in the anode. Experimental results showed that a methyl orange (MO)-feeding MFC produced a comparable performance against that of an air-based one at pH 3.0 and that azo dyes including MO, Orange I, and Orange II could be successfully degraded in such cathodes. The reaction rate constant (k) of azo dye reduction was positively correlated with the power output which was highly dependent on the catholyte pH and the dye molecular structure. When pH was varied from 3.0 to 9.0, the k value in relation to MO degradation decreased from 0.298 to 0.016 micromol min(-1), and the maximum power density decreased from 34.77 to 1.51 mW m(-2). The performances of the MFC fed with different azo dyes can be ranked from good to poor as MO>Orange I>Orange II. Furthermore, the cyclic voltammograms of azo dyes disclosed that the pH and the dye structure determined their redox potentials. A higher redox potential corresponded to a higher reaction rate.