Properties Study Of Mini-Microbial Fuel Cells Using Polypyrrole-based Nanowires As Anode

A microbial fuel cell (MFC) is a new biological energy utilization technology, using microorganisms as catalysts, which can transform chemical energy storing in organics into electricity. It has broad application prospects with many advantages of vast raw material sources, mild reaction conditions, friendly environment and so on. The anode is one of the key factors to decide the performance of MFC since it is the place for bacteria attachment, organics oxidation and electron transfer. So it has an important academic significance and engineering application value to explore anodes’properties.Firstly, the project studied polypyrrole (PPy) nanowires and polypyrrole nanowires/graphene composites’properties. Using different characterization and analytical methods, surface morphology, microstructures and electrochemical properties of PPy nanowires and PPy nanowires/graphene composites were studied. The results showed that PPy nanowires had the diameter of about 140nm, length of about 5 u m, and in the PPy nanowires/graphene composites, graphene attached to the surface of the PPy nanowires. PPy nanowires/graphene composites had better electrochemical performance than that of PPy nanowires, which were more conducive for electronic transmissions. The properties of PPy nanowires/graphene composites were more excellent than those of PPy nanowires, such as electron transfer rate (0.104s’1), the charge transfer resistance (4.23 Ω cm-2) and electrode resistance (0.35 Q cm"2).Two 56-uL single-chamber miniature MFCs with these two kinds of materials as anodes were used to respectively investigate their performances. As a result, the mini-MFC using PPY nanowires/graphene composites as anode had higher power density (22.3 mW/m2) and open circuit voltage (710 mV), than those of the mini-MFC using PPy nanowires as anode (15.9 mW/m2,650mV). The performance of PPy nanowires/graphene composites is better than that of PPy nanowires/graphene composites. We also found that the anode of PPy nanowires/graphene composites has more microorganism than the anode of PPy nanowires. It means PPy nanowires/graphene composites were more suitable for microorganism’s attachment.The extracellular electron transfer mechanisms of the mini-MFCs were investigated based on PPy nanowires and PPy nanowires/graphene composites. There were two common extracellular electron transfer mechanisms:nanowire electron transfer mechanism and redox mediator electron transfer mechanism. Besides, extracellular electron transfer mechanism of mini-MFC using PPY nanowires/graphene composites as anode also has another mechanism:graphene electron transfer mechanism. The electron was passed to PPy nanowires through the graphene.