Graphite anode surface modification with controlled reduction of specific aryl diazonium salts for improved microbial fuel cells power output.

International audienceGraphite electrodes were modified with redn. of aryl diazonium salts and implemented as anodes in microbial fuel cells. First, redn. of 4-aminophenyl diazonium is considered using increased coulombic charge d. from 16.5 to 200 mC/cm2. This procedure introduced aryl amine functionalities at the surface which are neutral at neutral pH. These electrodes were implemented as anodes in "H" type microbial fuel cells inoculated with waste water, acetate as the substrate and using ferricyanide redn. at the cathode and a 1000 Ω external resistance. When the microbial anode had developed, the performances of the microbial fuel cells were measured under acetate satn. conditions and compared with those of control microbial fuel cells having an unmodified graphite anode. We found that the max. power d. of microbial fuel cell first increased as a function of the extent of modification, reaching an optimum after which it decreased for higher degree of surface modification, becoming even less performing than the control microbial fuel cell. Then, the effect of the introduction of charged groups at the surface was investigated at a low degree of surface modification. It was found that neg. charged groups at the surface (carboxylate) decreased microbial fuel cell power output while the introduction of pos. charged groups doubled the power output. SEM revealed that the microbial anode modified with pos. charged groups was covered by a dense and homogeneous biofilm. Fluorescence in situ hybridization analyses showed that this biofilm consisted to a large extent of bacteria from the known electroactive Geobacter genus. In summary, the extent of modification of the anode was found to be crit. for the microbial fuel cell performance. The nature of the chem. group introduced at the electrode surface was also found to significantly affect the performance of the microbial fuel cells. The method used for modification is easy to control and can be optimized and implemented for many carbon materials currently used in microbial fuel cells and other bioelectrochem. systems. [on SciFinder(R)