In Situ Growth Of Carbon Nanotubes And Their Modified Composite Materials For Electrogenesis In Microbial Fuel Cell

In this paper, carbon felt (CF) was selected as substrate to make new material. According to chemical vapor deposition method, carbon nanotubes (CNTs) were grew on the surface of CF. Herein we refer to this composite as a (CNTs/CF). It was also used as the main material which further modification based on. All of the modified composite materials characterized via Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), Energy Dispersive X-ray (EDX) and Fourier Transform Infrared Spectrometer (FTIR), and their electrochemical performance tested by Cyclic Voltammetry (CV) and Electrochemical Impedance spectra (EIS). Then they were set as the anode of microbial fuel cell (MFC) for investigation of electrogenesis.The external of experiment circuit linked 2500 Ω resistance to computer with data acquisition frequency of 1000 Hz. The actual volume of anolyt was 120 mL. The effective surface area of anode was 25 cm2 and that of cathod was 45 cm2, respectively. Atholyte consisted of phosphate buffer system (pH=7) and 50 mmol·L-1 K3[Fe(CN)6]. The optimal operation conditions of reactor were determined at pH value of 7, temperature of 38℃ and anodic initial COD concentration about 1500 mg·L-1, according to the influence of different temperature and concentration to COD removal. In addition, the electricity production level and anodic substrate concentration would fall significantly, then keep in a low value because the MFC ran continuously for a week. In order to restore microbial activity and production capacity, anodic nutrient solution replaced once every 7 days for the study of MFC electricity generation in a microbial intermittent cycle.Totally,5 kinds of modified electrodes were prepared based on the main material in this paper. Including CNTs/CF pretreatment by polyvinyl alcohol (PVA), nanometer of ZnO or nanometer of SnO2 doped CNTs/CF, and in situ polymerization of aniline with or without adding the grapheme (G) on CNTs/CF. Our data suggest that the modified electrode showed greater performance on electrical production and electrochemical property compared to CNTs/CF. The GPANI composite electrode achieved power density up to 165.89 mW m-2, the highest voltage of 0.687 V, the average voltage of 0.4 V, the apparent resistance of 206 Ω, COD removal rate nearly 81%, coulomb efficiency about 5.7%. Cyclic voltammogram show wider current response to voltage and weak redox properties. According to the analysis of equivalent circuit fitting from Nyquist curve, its internal resistance and charge transfer resistance were estimated to be approximately 2.5 Ω and 18.9 Ω, indicating graphene can enhance capacitive property. Moreover, the other electrodes also reflected great comprehensive feature. In conclusion, modified electrodes based on its large specific surface area, lower internal resistance, interfacial area and high conductivity, provide more space for microbial adhension and improve electron transfer efficiency. In addition, benefiting from the excellent compatibility, microorganism grow faster and release more electrons, meanwile, facilitating electron transfer from exoelectrogens to anode and thereby further improving the MFC electrogenesis performance.