Chemically Activated Graphite Used As The Electrode Materials In Microbial Fuel Cells

Microbial fuel cells (MFCs) are considered to be the very popular and promising bio-electrochemical reactors using the catalysis of microorganisms to recover electrical energy from wastewater as well as to remove organics in wastewater. In this study, the surface characteristics of graphite activatied chemically (phosphoric acid, nitric acid, carbamide, melamine or zinc chloride as surfactants) and the feasibility of activated graphite-granule as the anode and cathode in MFCs were investigated by the means of electrochemistry and analytical chemistry.The oxygen reduction reaction (ORR) on graphite cathode can be influenced by chemical activation. The graphite activated by phosphoric acid (H3PO4) and nitric acid (HNO3) exhibits great electrocatalytic activity for ORR. The variation of species and quantity of surface function groups of graphite activatied chemically has been found. The oxygen-containing functional groups of graphite activated by H3PO4 and HNO3 have increased while the phosphorus-containing functional groups were introduced in the former. The nitrogen-containing functional groups of graphite activated by carbamide and melamine were introduced. The surface wettability and specific surface also changed to a certain degree.The power generation performance and COD elimination ratio of MFCs with graphite activated chemically were investigated. The MFC with graphite activated by H3PO4 as cathode (P-cathode) generated a maximum power density (7.92W/m3),2.4 time higher than the MFCs with the untreated graphite cathode, and the ratio of COD elimination obviously increased, which could be resulted from the significant increment of the species and quantity of surface function groups and the improvement of surface wettability. Therefore, phosphoric acid is an excellent surfactant to activate graphite using as cathodic materials in MFC.The graphite activated chemically using as anodic materials improved the MFCs' performances. It's indicated that the graphite activated by melamine, carbamide and zinc chloride used as MFCs'anodic material respectively could improve MFCs'power density and outputs as well as decrease internal resistance to improve the MFCs'performance. MFC with graphite activated by melamine as anode achieved the maximum power generation (0.442W/m3),26.8% more than the untreated one. The reason improving MFCs'performance might be that the introduction of nitrogen-containing functional groups can increase the efficiency of electron transfer from the bacteria to the anode surface and the enhancement of surface wettability can raise adhesion of bacteria.