Nano-materials Modification Of Electrodes For Performance Improvement In Microbial Fuel Cell

Energy and water supply are two of the biggest challenges facing humanity in thecoming decades. In comparison with conventional fuel cells and waste treatment equipment,microbial fuel cells (MFC) are promising clean energy sources for simultaneous wastetreatment while harvesting electricity, which have been greatly developed in recent years.Currently, MFC is still in its infant and its future is filled with many challenges. Toeffectively apply MFC in commercial and practical application, challenges including lowerpower output and high cost have to be tackled first. As the optimization of material andconfiguration, ohmic resistance was sharply decreased. As a result, activation resistanceoriginated form the electrode reactions became the main limiting factor of the power outputimprovement. The high cost mainly resulted from the noble metal cathode, which used foroxygen reduction reaction. Developing an efficient and cost-effective cathodic electrocatalystor using biocathode instead of noble metal electrocatalyst was the solutions.In this study, modification of the carbon anode material was used to increase the electrontransfer between the anode and the biocatalyst, thus improving anode performance. To lowerthe cost of cathodes and simultaneously improve oxygen reduction reaction, non-noble metalsand biocathode (self-regeneration, low cost, sustainability) have been investigated as cathodiccatalysts. For biocathode, several commonly used biocathode materials were tested andcompared. Moreover, modification of the biocathode was used to increase its performance.Some innovative findings have been found as follows:(1) A novel mesoporous carbon (MC) modified carbon paper has been constructed usinglayer-by-layer self-assembly method and is used as anode in an air-cathode single-chambermicrobial fuel cell (MFC) for performance improvement. Using cyclic voltammetry (CV) andelectrochemical impedance spectroscopy (EIS), we have demonstrated that the MC modifiedelectrode exhibits a more favorable and stable electrochemical behavior, such as increasedactive surface area and enhanced electron-transfer rate, than that of the bare carbon paper. TheMFC equipped with MC modified carbon paper anode achieves considerably betterperformance than the one equipped with bare carbon paper anode: the maximum powerdensity is81%higher and the startup time is68%shorter. CV and EIS analysis confirm thatthe MC layer coated on the carbon paper promotes the electrochemical activity of the anodicbiofilm and decreases the charge transfer resistance from300to99. In addition, the anodeand cathode polarization curves reveal negligible difference in cathode potentials butsignificant difference in anode potentials, indicating that the MC modified anode other thanthe cathode was responsible for the performance improvement of MFC. In this paper, we have demonstrated the utilization of MC modified carbon paper to enhance the performance ofMFC.(2) To develop an efficient and cost-effective cathodic electrocatalyst for microbial fuelcells (MFC), carbon nanotubes (CNTs) coated with manganese dioxide using an in-situhydrothermal method (in-situ MnO2/CNTs) have been investigated for electrochemicaloxygen reduction reaction (ORR). Examination by transmission electron microscopy showsthat MnO2is sufficiently and uniformly dispersed over the surfaces of the CNTs. Using linearsweep voltammetry, we determine that the in-situ MnO2/CNTs are a better catalyst for theORR than CNTs that are simply mechanically mixed with MnO2powder, suggesting that thesurface coating of MnO2onto CNTs enhances their catalytic eactivity. Additionally, amaximum power density of210mW m2produced from the MFC with in-situ MnO2/CNTscathode is2.3times of that produced from the MFC using mechanically mixed MnO2/CNTs(93mW m2), and comparable to that of the MFC with a conventional Pt/C cathode (229mWm2). Electrochemical impedance spectroscopy analysis indicates that the uniform surfacedispersion of MnO2on the CNTs enhanced electron transfer of the ORR, resulting in higherMFC power output. The results of this study demonstrate that CNTs are an ideal catalystsupport for MnO2and that in-situ MnO2/CNTs offer a good alternative to Pt/C for practicalMFC applications.(3) The choice of the cathode material is crucial for every bio-cathode microbial fuel cell(MFC) setup. The commonly used biocathode materials, Graphite felt (GF), carbon paper (CP)and stainless steel mesh (SSM) were compared and evaluated in terms of current density,power density, and polarization. The maximum current density and power density of the MFCwith GF-biocathode achieved350mA m2and109.5mW m2, which were higher than that ofthe MFC with CP-biocathode (210mA m2and32.7mW m2) and the MFC withSSM-biocathode (18mA m2and3.1mW m2). The polarization indicated that thebiocathode was the limiting factor for the three MFC reactors. Moreover, cyclic voltammetry(CV) showed that the microorganisms on the biocathode played a major role in oxygenreduction reaction (ORR) for GF-and CP-biocathode but SSM-biocathode. Electrochemicalimpedance spectroscopy suggested that GF biocathode performed better catalytic activitytowards ORR than that of CP-and SSM-biocathode, also supported by CV test. Additionally,the MFC with GF-biocathode had the highest Coulombic Efficiency. The results of this studydemonstrated GF was the most suitable biocathode for MFC application among the threetypes of materials when using anaerobic sludge as inoculums. (4) A novel carbon nanotubes (CNTs) coated stainless steel mesh (SSM) electrode hasbeen fabricated by a simple and scalable process and is used as biocathode in microbial fuelcell (MFC) for performance improvement. Examination by scanning electron microscopeshows that CNTs are uniformly distributed over the surface of the SSM, thus forming athree-dimensional network structure. The MFC with CNT-SSM biocathode achieves highermaximum power density (147mW m2), which is49times larger than that (3mW m2)produced from the MFC with bare SSM biocathode. Moreover, cyclic voltammetry shows thatthe microorganisms on the CNTs-SSM biocathode plays a major role in oxygen reductionreaction (ORR), and the CNT-SSM biocathode performes better catalytic activity toward ORRthan that of SSM biocathode. Additionally, the MFC with CNTs-SSM biocathode has higherCoulombic Efficiency than that of MFC with bare SSM biocathode. In this study, wedemonstrate that the use of CNTs-SSM offers an effective mean to enhance the electricity ofbiocathode MFC.