Extracellular Electron Transfer Mechanism Of Promoted Anode In Microbial Fuel Cells

Microbial Fuel Cell (MFC) was restricted for practical application with its Low power output, improving anode performance has become a critical step to solve this problem. The efficiency of electron transfer in anode of MFCs, especially in the process of biological membrane to the electrode, was thought to be an important factor limiting anode performance. In this study, anode electrode was modified with nano iron oxides film to improve electron transfer efficiency and much evidence was developed to explain the mechanism"how did anode decorated with metal oxides accelerate electron transfer process". Meanwhile, influence the capacitance characteristic of electrode material itself played on gaining higher transfer efficiency was also discussed. This study can be helpful for understanding the extracellular electron transfer mechanism and developing new methods to enhance total MFC power generation.The results showed that the iron oxide addition can greatly promote the anode current generation, which can obtain a 4 to 6 times higher biological current compared to unmodified anode, following by great decrease of internal resistance and enhancement of open voltage of anode; CV scanning results showed that a positive liner relation was obtained between current generation and absorbed Fe²⁺ concentration which was generated by microbe in reducing iron oxides at its surface. Fe²⁺ generation was directly related to the types, the crystallinity, the concentration, the crystal structure, form of iron oxides and the iron reduction ability of bacteria as well. It results that higher iron reductive ability of bacteria, higher specific crystal surface and lower crystallinity can be beneficial to accelerate the process. Therefore, iron oxide-Fe3 +/iron oxide-Fe2 + in the anode surface was proved to be a key role of the electronic shuttle. Iron oxides instead of electrode become favorable electron receptor for bacterial extracellular electron carrier. While anode was decorated with iron oxides Through electrochemical modification, the MFCs can obtain as high as 1500 mW·m^-2 power density (8 times higher than undecorated anode) and lower internal resistance which was result of greatly increase of biomass and Fe²⁺ concentration in electrode surface. This founding provided direct evidence to electronic shuttle role Fe²⁺ has paid on electron transfer process. Meanwhile, the layer of RuO2 and PPY/AQS were modified on electrode respectively through electrochemical modification to explore the key role of capacitance of electrode materials paid on power generation improvement. Results show that, the RuO2 and PPY/AQS modified anode can obtain 5 times and 16 times power generation respectively as cooperated to undecorated anode, the maximum power reached up to 3000 mW·m^-2; It was followed by enhancement of microbes electrochemical activity and decrease of battery internal resistance as well, which provided evidence of a substantial improvement in electron transfer between the cells and the anode; a liner positive relation was gained between electric capacity and power generation, namely the larger the capacity, the higher power density and the better electronic transfer efficiency. Therefore, electron could possibly be transferred to electrode via rapid process of charging and discharging on the surface and in the capacitance material, instead of choosing electrode as directly electronic receptor. These results provided a new mechanism of extracellular electronic transfer.