| Microbial fuel cell（MFC）,one of the advanced environmental biotechnology,can efficiently finish wastewater treatment and simultaneously achieve energy from the electricity generation.Therefore,developing MFC technology is important for water treatment.As the main place for biofilm formation and extracellular electron transfer（EET）,electrode is one of the important factors that determine the performance and cost of MFC.Also,the development of cheap and accessible electrodes is the key factor to promote the sustainable energy.In recent years,natural biomass materials such as loofah,kapok and cocoon have been successively prepared into MFC electrodes,and higher electricity generation capacity was obtained.However,the electrode materials from natural biomass have defects in macroscopic configuration,microscopic morphology,catalytic properties and material sources.Therefore,new and efficient electrode materials from natural biomass sources need to be developed to further promote the sustainable development of MFC.In view of aforementioned issues,two natural biomass materials（spirogyra and basswood）based on the criteria of macroscopic configuration,microscopic morphology,and catalytic performance were selected as the raw materials for MFC electrode preparation.The spirogyra and basswood were prepared into three-dimensional porous carbon electrodes and their physical and chemical properties were analyzed in detail.The electricity generating capacities and EET mechanism of MFC with those electrodes were also investigated.The results are summarized as follows:（1）Spirogyra,a biological material with a wide range of sources,was used to prepare high performance electrode material of MFC.Its physicochemical characterizations,MFC performance and EET mechanism were studied in detail.The ribbon carbon fibers were synthesized with good electrical conductivity,highly wrinkled surface and uniform carbon nanoparticles by optimizing the preparation process.Furthermore,the 3D carbon electrode was constructed by means of assembly of water fiber and successfully applied in MFC.The maximum output voltage of the sponge electrode MFC（pure bacteria）is about 335±20 mV,which is 1.5 times and 2.5times higher than the carbon felt electrode（CF）and carbon cloth electrode（CC）in MFC,respectively.The maximum power density and mass power density of miscible MFC of soil-carbon electrode were attained up to 2385 mW/m2 and 53.2 mW/g,which were significantly better than the electrodes of other natural biomass materials.Further study found that due to the high specific surface area and biological compatibility of the fiber,when compare with the traditional electrode,the number of cells in the electrode biofilm was significantly increased compared with the traditional electrode;On the other hand,due to the special micro-nano structured materials were helpful to enhance the surface of the fiber,the efficient interaction between the fiber and the cell surface were enhanced electron transfer efficiency between the cell and electrode could be realized.Therefore,the performance of sponge electrode in MFC is much higher than other natural materials or commercial carbon electrode,which indicates that spirogyra can be used as a better new natural electrode material.（2）Based on the natural 3D macroporous structure of basswood,the electrode materials with high mechanical strength,good electrical conductivity and 3D graded porous structure were prepared with natural basswood,and their electrocatalytic properties and mechanism in MFC were studied.In this study,through optimization of pretreatment conditions,H2O2-HAC hydrothermal reaction method combined with high-temperature carbonization technique was selected to prepare basswood material into three-dimensional porous carbon electrode.This electrode structure is formed by cross-linking mesopores of different sizes,it contains many micropores in the inner wall of these mesopores,resulting in the connection between pores,which is helpful to increase the specific surface of the material,and enhance the extracellular electron transfer efficiency of the microorganisms.Therefore,3d basswood electrode greatly improves the performance of MFC compared with traditional commercial carbon electrode:The maximum current density of MFC mixed with bacteria reaches around5800 mA/m2,and exhibited maximum power density of 3040 mW/m2,which is about2.3 times and 1.8 times higher than the carbon cloth and carbon felt electrode respectively.At the same time,basswood has good mechanical strength and processing properties.Therefore,basswood were utilized as a effective electrode in MFC.（3）In order to improve the performance of three-dimensional electrodes made from natural materials,the effects of different modification methods on the electricity generation ability of basswood carbon electrode in MFC were studied in this paper.Throughout the comparative study of modified electrodes,it is found that the modification of basswood electrode with graphene can effectively improve the catalytic activity of the electrode and significantly enhance the electricity generation in MFC.The maximum power density was 3.2 times higher than that of unmodified linden wood electrode.The three-dimensional structure of the self-assembled graphene and Shewanella complex wrapped around the linden wood electrode not only increased the specific surface area of the electrode,but also the loose structure was conducive to the substrate diffusion and the enrichment of flavin-like electron mediators.After reduction by Shewanella,which exhibits good electrical conductivity and enhanced the transfer efficiency between cells and electrodes. |
