Research In Anodes Materials Modified By Metal Oxide For Microbial Fuel Cells

Energy is the material basis for human survival and economic development.According to the existing energy structure,human beings are facing a serious energy crisis.The rapid development of economy and the acceleration of industrial production have made the problem of environmental pollution more and more prominent,especially the water pollution problem is constantly threatening human survival.With the intensification of energy crisis and water pollution,the utilization of sewage resources is a new way to solve the problem of water shortages and the development of renewable energy.Microbial fuel cells?MFCs?can use microorganisms to degrade organic substances in wastewater,convert chemical energy to electrical energy,and realize the utilization of wastewater.The anode material of the MFC is an important factor that affects its electrical performance,and it can be effectively improved by anode modification.This paper explored the modification of MFC anodes by using cheap tantalum capacitor materials MnO₂ and NiO.The effects of the modified anodes on the performance of elcetricity generation and methyl orange dye wastewater degradation of MFC were investigated.In addition,the performance of methyl orange dye wastewater degradation simultaneous elcetricity generation of MFC was also investigated.The specific research contents and conclusions are as follows:1.Preparation,characterization and electrochemical performance of MnO₂-CF anode:The MnO₂-CF anode was prepared by the constant potential electrodeposition method and its preparation conditions were optimized.The best preparation conditions were:The concentration of MnAc₂ deposition solution was 0.25 mol·L^-1,the deposition voltage was0.9 V,and the deposition time was 60 min.The SEM,XRD,surface contact angle and electrochemical test results of MnO₂-CF show that the surface of the electrode has been successfully loaded with MnO₂ particles with high purity and density.MnO₂-CF anode has the advantage of super hydrophilicity,good conductivity,capacitance and impedance performance.The maximum output voltage of MFC with MnO₂-CF anode?MnO₂-MFC?is558 mV,which is 27.6%higher than that of CF-MFC.The maximum power density is 667mW·m^-2,which is 5.2 times of CF-MFC,and the degree of anodic polarization of MnO₂-MFC is smaller.2.Preparation and characterization of NiO/MnO₂-CF and NiO/MnO₂-MFC performance:The core-shell NiO/MnO₂-CF electrode was prepared by a facile two-step hydrothermal method.SEM,XRD,contact angle and CV measurements show that the MnO₂layer grows tightly on the reticulated framework of NiO nanosheets and forms a NiO/MnO₂core-shell structure.MnO₂ exhibits a granular morphology and can increase the specific surface area of the electrode.The specific surface area of NiO/MnO₂-CF is 8.68 m²·g^-1,which is higher than those of CF,NiO-CF and MnO₂-CF electrodes.The NiO/MnO₂-CF electrode has excellent capacitance characteristics and super-hydrophilicity.Compared with CF,NiO-CF and MnO₂-CF anode MFCs,NiO/Mn O₂-CF anode MFC?NiO/MnO₂-MFC?has the maximum output voltage?652 mV?,the maximum power density(628 mW·m^-2),the smallest charge transfer internal resistance?11.7??,and the highest battery capacitance?8.87 mF?.The degree of anodic polarization is the smallest and the open circuit voltage is more negative.The above results are due to the best conductivity,capacitance and super-hydrophilic properties of the NiO/MnO₂-CF electrode.3.Performance of methyl orange wastewater treatment simultaneous power generation of NiO/MnO₂-MFC:The decolorization rate and COD removal rate of NiO/MnO₂-MFC respectively reaches 92.5%and,58.29%at 48h.The maximum output voltage is 327 mV,and the maximum power density reaches 510 m W·m^-2.The performance of methyl orange dyes treatment is stable.After 6 cycles of operation,the dye can be stably decolorized.The decolorization rate of each cycle can reach over 90%.NiO/MnO₂-MFC can produce electricity while stably treating dyes.4.Microbial community diversity analysis of biofilms on NiO/MnO₂-CF:The microbial community richness and diversity of the NiO/MnO₂–CF biofilm is the highest,indicating that NiO/MnO₂-CF has the highest biocompatibility,which is conducive to the enrichment of Geobacter.Therefore,NiO/MnO₂-MFC has the largest power generation performance and MO decolorization efficiency.5.Preparation and characterization of MnO₂@C-CF electrode and MnO₂@C-MFC performance:The MnO₂@C-CF electrode was prepared by hydrothermal method-dipping-pulling method-calcination.The SEM,XRD,contact angle and CV tests show that the carbon layer is uniformly and delicately wrapped on the surface of carbon fiber and urchin-like MnO₂ particles.The surface of the electrode has super-hydrophilicity.The MnO₂@C-CF electrode has high capacitance of MnO₂ and high electrical conductivity of carbon layer.Compared with CF,C-CF and MnO₂-CF anode MFCs.The MFC with MnO₂@C-CF anode?MnO₂@C-MFC?has the maximum output voltage?761 mV?,the highest maximum power density(1090 mW·m^-2),the minimum charge transfer resistance?10.4??,and the highest battery capacitance?7.74 mF?.The polarization degree is minimum and the open circuit voltage is more negative.The above results are due to high capacitance characteristics,high conductivity,and super-hydrophilicity of the MnO₂@C-CF anode.6.Performance of methyl orange wastewater treatment simultaneous power generation of MnO₂@C-MFC:The decolorization rate and COD removal of MnO₂@C-MFC respectively reaches 95.6%and 61.2%at 48h.The maximum output voltage is 660 mV,and the maximum power density reaches 728 mW·m^-2.The performance of methyl orange dyes treatment is stable.After 6 cycles of operation,the dye can be stably decolorized.The decolorization rate of each cycle can reach 95%or more in 48 hours.MnO₂@C-MFC can produce electricity while stably treating dyes.7.Influence factors of methyl orange wastewater treatment simultaneous power generation of MnO₂@C-MFC:The effects of open and closed circuit conditions,initial concentration of methyl orange,CH₃COONa concentration and initial pH of the anode compartment solution were investigated.The decolorization rate and the COD removal of methyl orange wastewater by closed circuit MFC were significantly higher than that of open circuit MFC.The decolorization rate and COD removal rate of methyl orange,the output voltage and power density of MnO₂@C-MFC all decreased with the increase of the initial concentration of methyl orange,increased with the increase of CH₃COONa concentration until they were basically stable.On the one hand,the number of microbes on MFC anode is certain.With the increase of initial concentration of methyl orange,the treatment ability of microbes has been fully played;Secondly,although the microorganism has a certain degree of tolerance as the concentration of methyl orange(10mg L^-1-30mg L^-1)is low,but methyl orange has certain inhibitory effect on electricigens activity as its concentration increases,the number of electrons required to broke chemical bonds increases,and thus the number of electrons transferred through the electronic circuit to the anode decreases;In addition,the number of electrons generated by the microbial catalytic oxidation of CH₃COONa increases with the increase of CH₃COONa concentration.Therefore,the degradation efficiency of methyl orange and the electricity generation efficiency of MFC increased.When the initial pH pH=7.00,the metabolic activity of the microorganism is the highest,and the MFC decolorization efficiency and simultaneous power generation are the best.The decoloration rate and COD removal rate of MnO₂@C-MFC respectively reaches 95.6%and 61.2%.Besides,the maximum output voltage is 660 mV,and the maximum power density reaches728 mW·m^-2.