| Microbial fuel cells (MFCs) are devices which covert the chemical energy contained in wastewater into electrical energy using electrochemically active microorganisms. MFCs have drawn increasing attention as a promising technology for wastewater treatment and energy production. Single-chambered air-cathode MFCs are simple in structure and can absorb oxygen directly from the air, thus have a great potential for practical application. At present, large-scale industrial application of MFCs has not yet been realized due to three major restrictions:low power density, high construction cost and poor long-term stability. In this dissertation, the electrochemical performances of anode and air cathode in MFCs were enhanced by regulating the interface properties of electrode reactions. Results from this study will provide theoretical and technical support for improving the power density, reducing the construction cost, and improving the long-term stability of MFCs.To improve the electrochemical performance and reduce the treatment cost of anode materials, an efficient, low cost and environmental friendly method was developed for modifying carbon cloth anodes. Pretreatment of anodes with formic acid, isopropyl alcohol, hydrogen peroxide and sodium hypochlorite effectively reduced the contents of C-O and pyrrolic nitrogen/pyridine nitrogen groups. Therefore, the adherence and growth of exoelectrogenic bacteria on anode were promoted, and the electron transfer properties of anode biofilm were improved, which resulted in an 26.4%～43.6% improvement in the maximum power density of MFCs. Pretreatment of carbon cloth anodes with ultrasonic cleaning and anodic effluent of MFCs showed little pollution on the environment, and increased the power generation of MFCs by 23.3%-33.7%.To improve the oxygen reduction performance and water-pressure resistance performance of air cathodes, a novel stainless steel mesh air cathode was developed. In order to further improve the cathode performance, microwave radiation was employed to prepare catalyst layer instead of the traditional heating process. This method improved the three-phase interfaces for oxygen reduction of catalyst layer, increased the exchange current density of cathode, reduced the cathode internal resistance, and thus improved the maximum power density of MFCs by 15.6%～23.3%.To understand the reason for the poor long-term stability of air cathodes, the effects of soluble microbial products (SMP) on the electrochemical performance of air cathodes were studied. The physicochemical properties of SMP were characterized for the first time in MFC systems. It was found that the cathode biofilm SMP contained polysaccharides, proteins and humic acids, which have a large number of carboxyl, amino, hydroxyl and other functional groups, and the molecular size of SMP was less than 600 nm. The SMP produced by cathode biofilms diffused into the catalyst layer, which reduced the hydrophobicity of catalyst layer, increased the ohmic resistance of cathode, decreased the catalytic activity of the catalysts, and hindered the transportation of oxygen, H+ and OH- in the catalyst layer. Therefore, they increased the internal resistance of air cathode, thus reduced the electrochemical performance of air cathode and the power generation of MFCs.To improve the long-term stability of air cathode, we proposed a new method to restrain the cathode biofilm growth by incorporating enrofloxacin into the catalyst layer. The biofilm biomass on catalyst layer was reduced 60.2%, which greatly improved the stability of the electrochemical performance of air cathode. After 3 months of operation, the maximum power density of the MFCs with enrofloxacin treated cathodes did not decline, but the power generation of those with common cathodes dropped by 22.5%. |
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