Chemically activated graphite enhanced oxygen reduction and power output in catalyst-free microbial fuel cells

In search of a cost effective cathode material for microbial fuel cells (MFCs), graphite was chemically treated with H3PO4, HNO3, ZnCl2, urea or melamine, and the effect of chemical activations on the oxygen reduction reaction (ORR) was examined. The performance of MFCs with activated graphite as the catalyst-free cathodes was then compared to those with untreated graphite. Results suggested that H3PO4 and HNO3 activations could improved ORR, showing the highest ORR activity in graphite treated with 14.62 M H3PO4 for 12 h at 30-50 °C. MFCs with H3PO4 and HNO3 activated graphite cathodes generated maximum power densities (7.9 W/m3 and 6.5 W/m3, respectively) 2.4 and 1.8 times higher than that of the untreated control. The chemical activation process involves just a simple immersion step, and it does not require heating, electrochemical process or expensive chemicals. Therefore, it is a highly cost-effective approach to improve the performance of MFCs. We recommend an in-situ modification of graphite cathodes in scale-up MFCs with either H3PO4 or HNO3 to optimize MFCs' various industrial applications.