Cathode performance will gradually decrease during long-term operation of microbial fuel cells (MFCs)

to answer why cathode performance decrease is of significant for practical application of MFCs. In this paper

nickel foam air-cathodes were used in a MFC to search the reason causing the degradation. It was found that power density of MFC with a nickel foam air-cathode was 22% less for after 4 months operation than for after 1 week operation. Electrode polarization curves measured showed that cathode performance degradation was the main reason leading to decrease in power density. At -0.2 V (vs Ag/AgCl)

current density of a new cathode was 12.3 A·m-2

and decreased to 4.2 A·m-2 after 4 months operation. Cathode performance decreased with increase of operation time

which showed mainly in the high current range [>-0.05 V (vs Ag/AgCl)]. Scanning electron microscope (SEM) images indicated that there was no biofilm on cathode surface

implying that the decrease of oxygen diffusion rate through cathodes was the main reason causing the decrease of cathode performance. From energy dispersive spectrometer (EDS) measurement it was found that there was phosphate precipitation inside the cathode after 4 months operation. These results indicated that salt precipitation increased with increase of operation time could clog micro-pores of cathode and decreased oxygen diffusion rate

leading to degradation of cathode performance.