Improved power generation using nitrogen-doped 3D graphite foam anodes in microbial fuel cells

The properties of the anode material and structure are critical to the microbial growth and interfacial electron transfer between the biofilm and the anode. In this paper, we prepared the nitrogen-doped 3D expanded graphite foam (NEGF) by simple, rapid and inexpensive methods of liquid nitrogen expansion and hydrothermal treatment from commercial graphite foil (GF). X-ray photoelectron spectroscopy confirmed the success of nitrogen doping on expanded graphite foam (EGF). Using cyclic voltammetry and electrochemical impedance spectroscopy, the NEGF and EGF electrode exhibited increased electrochemical active surface area and fast interfacial electron transfer ability than that of pristine GF, and NEGF electrode performed even better. Scanning electron microscopy revealed that NEGF and EGF possessed graphene-like structure and large surface area. MFCs equipped with NEGF or EGF anodes, respectively, achieved maximum power density of 0.739 and 0.536 W m−2, which was about 17.4 and 12.6 times larger than that of MFCs with GF anodes (0.0451 W m−2). The anode and cathode polarization curves further confirmed that the different anode other than the cathode was responsible for the advanced performance of MFCs. The morphology of the biofilm on three kinds of anodes proved the densest biofilm formed on NEGF anode. All the results indicated the synergistic effect of 3D graphene-like structure and N-doped surface on the performance of MFCs, which might provide special insights into designing simple and efficient route for anode construction to achieve promising electricity generation.