Cathode Modification In Microbial Fuel Cells Using Tourmaline And Bentonite

Recently, environment pollution and energy shortages have become very serious, which affect the development of economy and human life significantly. Microbial fuel cells (MFCs) can directly produce electricity from biodegradable waste materials. Since MFC has extensive fuel, mild reaction conditions and high energy conversion efficiency, it has been regarded as a promising technology. However, MFC also has some disadvantages, for example, low electricity producing efficiency and output power. Additionally, many factors can affect the performance of MFC, such as inoculated microorganisms, anode substrate, catalytic performance of cathode, proton exchange membrane and so on. Catalytic performance of cathode is one of the main factors during the operation period. The cathode mainly used precious metals, such as Pt, as its catalyst, while, Pt is very expensive and it will affect catalytic performance after long-term operation. Recent research results show that the cathode with microbes as catalyst could catalyze cathode reaction (generally for oxygen reduction). Biological cathode has high catalytic performance. The microbes will constantly reproduce under the adequate ability of biofilrn nutrition condition, which can guarantee the continuous catalytic. In addition, the microbes can also degrade pollutants during breeding period. Therefore, looking for a kind of cathode material with high conductivity, good biological adaptability and biological catalysis has become a hot topic in the study of microbial fuel cells. Focusing on the chosen of biological cathode electrode materials, the main work in this study is listed as follow.(1) In chapter2and3, the electrochemical method was used to modify the graphite electrode. Scanning electron microscopy (SEM), energy spectrum (EDS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to characterize the microstructure and electrochemical properties of the modified electrode. The graphite electrode modified by both tourmaline and polyaniline, the one that only modified by polyaniline and the unmodified electrode (acted as control) were used as the biological cathode materials of MFC (regarding as reactor1,2and3). The maximum output voltages of reactor1,2and3were0.20±0.005V,0.26±0.005V and0.37±0.005V respectively when the external resistance was800Ω, and the highest output power density of reactor1,2and3were54mW/m2,138mW/m2,266mW/m2respectively. Cyclic voltammetry curves showed that reductive current of reactor3was the highest one among the others, indicating that the cathode of reactor3had the strongest catalytic activity. The results demonstrated that tourmaline was a suitable bio-cathode material to modify graphite electrode.(2) In chapter4and5, PTEF and bentonite were used to modify the carbon cloth electrodes, and PTFE acted as binder. The SEM, EDS, CV and linear sweep voltammetry (LSV) were used to characterize the microstructures and electrochemical performance. The carbon cloth electrode (acted as control), unilateral bentonite modifying carbon cloth electrode and bilateral bentonite modified carbon cloth electrode were used as cathode materials of air cathode MFC (regarding as reactor1,2and3). When the external resistance was1000Ω, output voltages of reactor1,2and3were0.048V,0.095V and0.056V, respectively, and the output power density of reactor1,2and3were12mW/m2,33mW/m2,17mW/m2respectively. The results of voltage, polarization curve, power density and other electrochemical parameters showed that the reactor2possessed the best peformance. The results indicated that bentonite modified carbon cloth could improve oxygen adsorption ability of the cathode, the cathode catalytic properties, consequently, enhance the performance of the air cathode MFC.