High Performance Microbial Fuel Cell Anode Materials Based On Nano-carbon Material And Conductive Polymer

With the increasingly serious environmental problems and energy crisis, microbial fuel cell(MFC) has attracted domestic and foreign researchers as a new wastewater treatment and energy recovery technologies. MFC directly converts chemical energy to electrical energy by harnessing the metabolism of exoelectrogens, microorganisms that can mediate extracellular electron transfer(EET). Therefore, MFC has a great potential for a broad range of applications, such as wastewater treatment and bioremediation with concomitant energy production. However, low power output remains one of the main obstacles for their widespread practical applications.In MFC, development of anode materials, which can directly affect the bacterial attachment, substrate oxidationand electron transfer, is a key factor for the MFC performance and cost-effectiveness. This paper focuses on the MFC new anode material. In this study, the use of two kinds of carbon material, including graphite felt and carbon cloth, as MFC anode substrate material, and the effect of different composites modified anode how to influence on the electrical properties of the mediator-free dual-chamber MFC inoculated Shewanella Putrefaciens SDMCC(S. Putrefaciens)210239. The results provide an easy scale-up, simple and controllable method for the preparation of high-performance and low-cost MFC anodes, and the main research contents and conclusions are as follows:(1)In the first experiment, macroporous graphite felt(GF) as the base material, Polyaniline(PANI) was electropolymerized on the surface of macroporous graphite felt(GF) followed by the electrophoretic deposition of carbon nanotube(CNT), denoted as CNT/PANI/GF. The CNT/PANI/GF material was characterized by scanning electron microscopy(SEM) technique, static water contact angle measurement, and electrochemical cyclic voltammetry(CV) technique. CNT adsorption conditions were optimized, using UV-Vis spectrophotometry to determine the loading of CNT was proposed. The effect of PANI and CNT modification on the MFC power output was investigated. In addition, the EET mechanisms of the exoelectrogen in transferring their electrons to the MFC anode were explored by viewing the surface morphology of the anode material and measuring CVs of the anode medium after MFC power output.SEM images show that for CNT/PANI/GF material, graphite felt smooth surface of the carbon fiber was completely covered with rough PANI, and CNT was attached or embedded into irregularly PANI layer. By the static water contact angle measurement, confirming PANI modified graphite felt surface becomes more hydrophilic. Electrochemistry measurements indicate that attachment of CNTs greatly enhances the electrical conductivity and the effective surface area of the PANI/GF material. The optimum CNT adsorption conditions were determined, the best time was 30 min and concentration was 125μg mL-1, furthermore, the load amount of different CNT concentration was calculated, and when the CNT concentration was 125μg mL-1, the value of CNT load amount was 412μg cm-3, and basically reached saturation. At the optimum conditions of CNT modification, the CNT/PANI/GF MFC attained a stable maximum voltage of 342 mV across an external resistor of 1.96 k? constant load, and a maximum power density of 257 mW m-2, increased by 343% and 186%, compared to that of the pristine GF MFC and the PANI/GF MFC, respectively. These results indicated the modification of PANI make GF surface covered with coarse PANI film, more conducive to the further modification of CNT and the adhering of exoelectrogen, then CNT adsorption on the surface of the PANI may not only to enhance the anode electrical conductivity, and can also act as the role of the nanowire, enhancing the EET of the exoelectrogen, thereby improving the output power of MFC. SEM images of the CNT/PANI/GF anodes collected at the stage of stable MFC voltage output show that the S. Putrefaciens were attached tothe anode surface through the numerous cilia, besides, no obvious redox waves were observed in the CV of the MFC anode medium. From these results, it can be proposed that the MFC EET mechanisms include direct electron transfer and indirect electron transfer through electrically conductive pili.(2) In the second experiment, with carbon cloth(CC) as the base material, modified polypyrrole(PPy) by dipping method, and electrodeposition on CNT, obtained CNT / PPy / CC anode. In the process of synthesis of PPy, Agar(AG) and chitosan(CS) were used as additive respectively,denoted as PPYAG and PPYCS. And the modification conditions of PPy were optimized. The differences of PPYAG and PPYCS modified CC electrode was evaluated. At the same time, the output voltage of the CNT / PPYAG / CC MFC and CNT / PPYCS / CC MFC were compared. The role of PPy and CNT modification on the MFC power output was studied.The results show that the stability of CNT/PPYCS/CC electrode is better than CNT/PPYAG/CC electrode. At the optimum conditions of PPy modification, The CNT/PPYCS /CC MFC obtained a maximum voltage of 230 mV(at the constant-load mode with an external resistance of 1.96 k?) and a maximum power density of 201mWm-2, significantly higher than those of the MFC constructed from CNT/PPYAG/CC anode, 176 mV and 61 mW m-2 respectively, for the maximum voltage and the maximum power density,and the MFC constructed from bare CC anode, 59 mV and 10 mW m-2 respectively, for the maximum voltage and the maximum power density. The result shows that PPYCS contains positively charged CS can occur electrostatic adsorption of negatively charged CNT, so that more CNT can be adsorbed on the PPYCS /CC anode, further improving the electrical conductivity, increasing the output power of MFC.