Saline catholytes as alternatives to phosphate buffers in microbial fuel cells

Highly saline solutions were examined as alternatives to chemical buffers in microbial fuel cells (MFCs). The performance of two-chamber MFCs with different concentrations of saline solutions in the cathode chamber was compared to those with a buffered catholyte (50 mM PBS). The use of a NaCl catholyte improved the CE to 43–60% (28% with no membrane) due to a reduction in oxygen transfer into the anolyte. The saline catholyte also reduced the membrane and solution resistance to 23 Ω (41 Ω without a membrane). The maximum power density of 491 mW/m2 (240 mM NaCl) was only 17% less than the MFC with 50 mM PBS. The decrease in power output with highest salinity was due to reduced proton transfer due to the ion exchange membrane, and pH changes in the two solutions. These results show that MFC performance can be improved by using a saline catholyte without pH control.