Application Performance Of Three Dimensional Carbon Material Anodes In Microbial Fuel Cells

With the increase of human activities,the demand for energy is also increasing.The consumption of fossil energy has prompted the world to look for potentially cheap and clean renewable energy technologies.Microbial fuel cells(MFCs)use microorganisms to degrade organic substances in wastewater,and recover the energy stored in them by electrical energy,effectively combining sewage treatment and energy recovery technologies,and are considered to be a very promising new energy technology.In recent years,with the efforts of researchers,MFCs have achieved great breakthrough in the ability to recover energy from renewable resources.However,the lower output power and the cost of expensive electrode materials are still the main challenges that limit the scale-up and practical production applications of MFCs.Anode is the main place where the electricity-generating microorganisms oxidize organic substrates and transport electrons in MFCs,the properties of which are closely related to the electricity-generating performance of MFCs.Among the current used anode materials,three-dimensional(3D)carbon material anodes with good biocompatibility and high specific surface area have great advantages in enriching microorganisms and recovering electrons,and are favored by researchers.First,this subject used 3D phenolic carbon felt with low-cost and high specific surface area as the anode,and achieved high power generation performance through heat treatment at different temperatures.Then,different chemical modification treatments were carried out on the phenolic carbon felt to explore the electrical performance of the modified phenolic carbon felt anode.Finally,in order to further reduce the intrinsic resistance of the anode material,we used mesophase pitch-based carbon foam with high-conductivity and ultra-large pores as the anode,and deeply analyzed the relationship between its intrinsic properties and the performance of MFCs,and discussed its application value in MFCs,to provide a reference for the amplified research of MFCs.The main results achieved in this thesis are as follows:(1)First,we used phenolic carbon felt(PCF)as the anode material,the effect of anode material properties obtained under different preparation conditions on the electrical performance of MFCs was studied.By carbonizing the phenolic fiber felt at 700,800,900,1000 and 1400℃,we find that the anode of the phenolic carbon felt carbonized at 900℃(PCF-900)has the most excellent power generation performance,and its maximum power density is up to 2600 mW/m2.XPS test results show that PCF-900 has many hydrophilic functional groups,which could increase the hydrophilicity of the material and promote the enrichment of electro-producing bacteria.And the strong hydrogen bonding between the phenolic hydroxyl group and the outer membrane of bacteria is conducive to the transfer of electrons.In addition,the Zeta potential results show that the surface of PCF-900 has the strongest electropositivity and the strongest electrostatic attraction with electricity-generating microorganisms,which is conducive to the formation of biofilms and electron transfer.This shows that PCF-900 has the best biocompatibility and electricity generation performance,and is an efficient anode material.Also this is the first time that phenolic carbon felt is used as the anode material of MFCs.(2)Then,in order to further increase the specific surface area and surface electropositive functional groups of PCF-900,the PCF-900 anode was further chemical activated and NH3 modification,and it is found that both modification methods were not conducive to improving the electrical performance of the phenolic carbon felt(PCF)anode.The results show that the phenolic activated carbon felt(PACF)obtained by chemical activation has a specific surface area is up to 2159.83 ml/g,and its pore structure is mainly micropores,which increases its resistivity.And compared with PCF-900,the Zeta potential of PACF anode is negatively shifted,which weakens the electrostatic attraction between PACF and microbial and increases the resistance of electron transport,causing the maximum power density of PACF-MFC to decrease to 1620 mW/m2.Besides,the modification of PCF-900 with NH3 shows that the electrochemical performance of the modified PCF anode also decreased.SEM and resistivity analysis show that NH3 modified PCF has different degrees of etching and pore-forming effects on its surface.Although the surface roughness is improved,the resistivity is also significantly reduced.In addition,XPS and Zeta potential show that after NH3 treatment,the N element doped on the surface of the PCF is mainly pyrrole-N,which is negatively charged.The pyrrole-N would reduce the surface electrical properties of the material and increase the resistivity of the material,thus weakening the attractive force between the anode surface and the microbial,increasing the energy loss during the electron transfer process,so that the power generation capacity of MFCs decreases.Therefore,other effective modification methods need to be developed to further improve the electrical performance of phenolic carbon felt anodes.(3)To further investigate the effect of the intrinsic resistance of the anode material on the electrical performance of MFCs,a novel carbon material,high-conductive 3D graphitized mesophase pitch-based carbon foam(GMCF)was used as the anode of MFCs,and the electrical performance of mesophase pitch-based carbon brush(MCB)and carbon felt(CF)anode are compared.The results show that the GMCF anode has a staggered macropore and through-hole structure,providing broad habitat for microorganisms,and the developed ligament structure makes it highly conductive and could effectively improve the electron transfer rate.By analyzing the electrical performance of the three anodes,it is found that the GMCF anode exhibits excellent electrical performance.When the external resistance is 1000 Ω,the maximum output voltage of GMCF-MFC is 0.59 V,which is higher than MCB-MFC(U=0.56 V)and CF-MFC(U=0.5 V).And the maximum power density of GMCF-MFC reached 1800 mW/m2,which is 1.33 and 2.65 times of MCB-MFC and CF-MFC,respectively.Therefore,highly conductive carbon foam could be used as a high-performance anode material,and has great application potential in amplified MFCs.