Antibacterial Activity And Power Generation Of Microbial Fuel Cells With Graphene-modified Anodes

Microbial fuel cell(MFC), which has a great potential for simultaneous wastewater treatment and power generation, has become one of the emerging technologies in the field of environmental protection and energy recovery in recent years. At present, low power output and high cost are perceived as the two major bottlenecks in the commercialization of MFC. Moreover, the electrode materials play a crucial role in the electricity generation and cost of MFC. Recently, increasing attention is paid to graphene, a new revolutionary material with excellent physical and chemical properties, which has been successful applied for performance improvement of MFC. Additionally, the antibacterial activity of graphene has been confirmed by a certain number of studies, which obviously impact the electrochemical active bacterias in MFC. Hence, the goal of this study was to detectthe the interreaction of graphene-modified anodes(GMAs) and exoelectrogen, and answer whether graphene exhibits antibacterial effect on exoelectrogen, and to further investigate the impact of antibacterial activity on the output performance of MFC, providing fundamentals for the practical application of graphene.In this work, graphite oxide(GO) was successfully synthesized by improved Hummers method. XRD, Raman, TEM and AFM analyses demonstrated that GO was a lamellar structure with some crμmpled parts and lots of oxygen-containing functional group. GMAs with different amounts of graphene were obtained by cyclic voltammetric electrodeposition of 5, 20 and 40 potential cycles(5-G, 20-G and 40-G). Raman and FESEM analyses indicated that most of oxygen functionalities were removed and as-obtained graphene was uniform depositied on the surface of electrodes. Electrochemical measurements suggested that the charge transport property of the GMAs were much better than that of the bank electrode(BG).CV analyses showed that the electrochemical activity of all the GMAs were obviously lower than that of the BG after 5 h inoculation.With subsequent 13 h operation of the MFC, the electrochemical activity of 40-G increased to the value which was similar to that of the BG. Eventually, all the electrochemical activity of the GMAswere higher than that of the BG when the MFCs were operated for 30 days. CLSM testing showed the thickness of biofilm increased dramatically, with an increase in the operated time. GMAs displayed lower biofilm viability than BG after 5 h of bacterial cell growth. However, 18 h later, the viability of biofilm on the GMAs all increased, which were much higher than that of the BG. The change of electrochemical activity and biofilm viability with time during biofilm growth probably because, after the attachment of growing bacterial cells, biofilm matrix formed on the surface of the anodes, within a large amount of exoelectrogenic bacteria embedded in EPS which could protect the internal biofilm bacteria from antibacterial activity of graphene. At the same time, the biofilm bacteria might be able to transfer electron via electrically conductive bacterial nanowires or EPS that promoted long-range electron transfer.In order to clarify whether the antibacterial activity of GMAs had a negative effect on electricity generation, the performance of MFCs with different anode were evaluated. Compared with the BG, GMAs had lower overpotential and higher voltage generation and power density, with electricity stable time reduced by 27%. These results suggested that the antibacterial activity of graphene did not negatively affect electricity generation performance of the MFC, and the maximum power density of the MFC was increased with the deposited amount of graphene on the anode.