Analysis Of Self-Mediated Extracellular Electron Transfer Of Bacteria Cells Based On Nanostructured Anode

Microbial fuel cells (MFCs) are device that use microbes as catalysts to convert chemical energy from the organic substrate into electricity. As a new type of fuel cells with high energy conversion efficiency, mild operation conditions and low cost substrates, microbial fuel cells (MFCs) have attracted substantial attention from research organizations. Microbial fuel cells (MFCs), an appealing clean energy technology that combines electricity generation and wastewater treatment, has attracted great research interests. However, due to the higher anode overpotential made it power output has been at a low level, to solve the bottleneck problem, is very crucial to improving the electron-transfer efficiency between the microbes and the electrode. This research object is Shewanella putrefaciens, through the synthesis of nanomaterials with three-dimensional and multi-layer hole structure to increase the reaction activity area of flavin molecule on the electrode surface to improve the battery performance. Only by improving the nanostructured of anode materials for improving the efficiency of interfacial electron transfer is very limited, In this work, a carbon nanotube microbial powder electrode is developed to analyze the self-excreted electron shuttles of microbial. The specific conclusions are as follows:In this work, an iron decorated rGO with hierarchical porous structure is developed via freeze-drying assisted hydrothermal method. In this work, the iron/nitrogen doped graphene aerogels with hierarchical porous structure is developed via freeze-drying assisted hydrothermal method and ammonium ferrous sulfates as iron and nitrogen source. A series of physical characterization results show that this material not only has higher specific surface area, but also with a hierarchical porous structure over distributed pore sizes of 10-20μm and the mesoporous structure of below 10nm. The iron/nitrogen doped graphene aerogels can provide the largest specific surface area and the best three-dimensional reticulated porous structure when the mass ratio of graphene oxide and ammonium ferrous sulfate is around 10:1, and this material will provide more active reaction centers when applied in the electrochemical reaction. The electrocatalytic behavior analysis results show that the material will deliver the highest peak current and the smallest charge transfer resistance when it was provided with a best physical structure. Thus, this material will significantly increase the discharge current density and power density when used as Shewanella putrefaciens MFC anode.As the development of microbial fuel cells (MFCs), the self-mediated extracellular electron transfer behavior has attracted more attention. However, as concentration of the self-generated electron shuttles is quite low especially in non-metal-reducing bacteria cell cultures and the concentration is often various during the discharging process of microbial fuel cells (MFCs), it is very important to develop a method to quantitatively investigate the self-generated electron shuttles. In this work, Shewanel/a putrefaciens CN32 as the mode strain, three-dimensionally hierarchical nano materials are fabricated as anodes for enhancing microbial fuel cells (MFCs) performances through increasing the electro-active reaction area of flavins. Comparison of real-time monitoring flavins endogenously secreted from Shewanella putrefaciens CN32 cells, the result shows that only CNT powder microelectrode rather than glassy carbon electrode (GCE) and carbon cloth electrode can be adequate for real-time monitor because of the low concentration of flavins. The redox peak potential of flavins detected by CNT powder microelectrode is in agreement with previous reports. During the discharge process of microbial fuel cells (MFCs), the concentration of flavins was positive correlated to the out-put current density, which reached to the maximum value when the current reached to the maximum stable output. Interestingly, even if the detectable concentration of flavins subsequently decreased, the out-put current density could maintain its maximum value for a long time. In addition, the concentration of flavins in the area far away from anode was found to be larger than that in the area near anode, which might be resulted from the strong adsorption of flavins on anode.To further explore the cellular-based mechanisms behind the direct electrochemical behaviour of E. coli and Pseudomonas aeruginosa, a detailed investigation was conducted into the relationship between electrochemical behaviour and time.When real-time monitoring the anode compartment of E. coli K12 MFC, the redox peak potential of detected electroactive substance is consistent with that of flavins (-0.45 V, vs SCE), indicating that the molecular structure of electroactive substance may be similar to flavins. In the anode compartment of Pseudomonas aeruginosa MFC, an obvious redox peak potential was also appear at -0.45 V (vs SCE) rather than that of pyocyanine, indicating that there are other metabolin participated in bacterial extracellular electron transfer. All the results demonstrates that powder microelectrode is an effective technology for real-time monitoring the change of anode compartment of MFC, which is conducive to analyze the behavior of autocrine electron mediators by bacteria in anode compartment, thereby offer new evidences for deeply explain the mechanism of bacterial self-mediated extracellular electron transfer. This work provides a new platform for on-line analysis of self-mediated extracellular electron transfer behavior of bacteria cells in a running MFC.In summary, novel mesoporous and macroporous structure of the iron/nitrogen-doped graphene anodic materials were synthesized and microelectrodes to detect anolyte electron mediator was developed to enhance the power density of MFCs. This work offers new approaches for improvement of MFC performance and solid evidence of the direct electrochemistry of the bacteria in microbial fuel cells (MFCs). This research indicates the strong potential to improve microbial fuel cells (MFC) performance by the use of nanomaterials. The investigation of the direct electrochemistry of there modes strain cells advances the fundamental knowledge regarding the electron-transfer process between cells and the electrode, providing scientific insight into the electrochemistry of the bacteria in microbial fuel cells for increased power output.