The Study Of Microbially Reduced Graphene Oxide Modified Anode And Biofilm Characteristics For A High-performance Microbial Fuel Cell

Microbial Fuel Cell has attracted much attention in the field of Energy and Environment Engineering and now is one of the biggest concerns about renewable energy which is potential commercial.Through microbial activity,it can be used to degrade organic matterand generate electricity at the same time,anddoes not produce any secondary pollution.Many studies have shown that the electrode materials of Microbial Fuel Cell,especially the anode material,is one of the key to the battery performance and cost control.Graphene,which was successfully through mechanical exfoliation in 2004,was widely seen as a potential material could trigger technology revolution.Its high stability,high strength,high conductivity,high specific surface area,high carrier mobility,good biological adaptability determine that it could be the perfect modifucation material for the battery electrodes.At present,the main preparation methodsfor graphene are CR?Chemical Reduction?and CVD?Chemical Vapor Deposition?.Both of these two preparation methods require strict experimental conditions and introduce toxic substances,which could harm the MFC systems.In order to improve the shortcomings mentioned above,some studies reported that some kinds of bacteria could reduce GO to graphere through its catalysis reaction,and tried to modified electrode by microbially reduced graphene oxide.To complete the research system,it is a huge necessity to analysis the anodic biofilm characteristics,the influential factors in mrGO modification,the infulence of mrGO modification on the electrons transfer,the variety of mrGO and anodic biofilm in long-term running.In this work,we used the synthesis method called Improved Hummers to prepare the graphite oxide,and then prepare the graphene oxide dispersion through ultrasonic treatment and centrifugation.Graphene oxide dispersion was added into Microbial Fuel Cell reactor and after 200 hours of MFC operation,we characterized the anodic material by Scanning Electron Microscope?SEM?,Raman Spectroscopy?Raman?,X-Ray Diffraction?XRD?and X-Ray Rhotoelectron Spectroscopy?XPS?and so on.We confirmed that this preparation method of microbial reduction graphene?mrGO?was feasible and mrGO was found on the surface of the anode.We also Confirmed that the structure of mrGO on anode surface was like a three-dimensional scaffold which contained many irregular cavities.After 3-5 Electricity Production Cycles?EPCs?,a large number of microbial adhered on surface of the three-dimensional structure and in the cavernous structure of mrGO.We confirmed that the type of contact between microbial and mrGO was directly physical contact and no any nanowire was found between them.Through analysis of Nyquist atlas for mrGO modified anode,we discovered that mrGO couled reduce the electricity trasfer impedance of anode effectively and improve electrochemical activity.In study of battery performance and operation condition of mrGO modified anode,two MFC operation modes were adopted:condition of limiting substrate and conditio-n of non-limiting substeate.In the condition of limiting substrate,the maximum power density of mrGO modified anode MFC was 1140.6 mWm^-2,which was 65.3%higher than bare anode MFC.At the same time,the electrochemical impedance for mrGO modified andoe was 52.6%less than the bare anode.In the condition of non-limiting substrate,the maximum power density of mrGO modified anode MFC was 1600.6 mWm^-2,which was 70.1%higher than bare anode MFC.We also studyied the influence of GO dispersion concerntration,active sludge inoculation and glucose concentration on the battery performance of the mrGO modified anode MFC.The study obtained th-e optimum concerntration and volume for these three influence factors:GO concentration=1 mgm L,Volume of active sludge inoculation=0.125 mLmL^-1,Glucose concentrati-on=500 mgCODL^-1.We studied the anodic biofilm evolution and viability during in situ preparation of a graphene/exoelectrogen composite biofilm electrode.In the intial stage of the MFC operation,for mrGO modified anode,the total protein of biofim was 47.25%lower than which for bare anode and this demonstrated that mrGO produced antimicrobial activity to anodic biofilm.After 3 Electricity Production Cycles?EPCs?,completely reduction of GO was comfirmed.At this period,the biofilm thickness of mrGO modified anode was up to 29.44?m,which was40.02%higher than the bare anode.We also discover that the fluctuation of biofilm biomass for mrGO modified anode was smaller than the bare anode and the biofilm viability was in good agreement for thees two anodes,of which the viability ratio was more than 92.0%.The results of Genetic Sequensing based on 16s rRNA were compared for the mrGO modified anode biofilm.We discovered that in the formation process of mrGO modified anode,the proportion of the Poteobacteria was 62.2%-92.1%more than the bare-anode MFC and it became the dominent bacteria in phylum level for anodic biofilm.In Genus level,the proportion of Escherichia?typical electrogenesis bacteria?was up to 30.0%for anodic biofilm at the 2nd EPC and it became the domint bactia.In addition,the proportions of Geobacterand Shewanellawere both increased significantily,which demonstrated that mrGO could improve the inrichment of the electrogenesis bacteria.In this work,we analyzed the influence of mrGO on the electron transfer for mrGO modified anode through CV testing,anodic polarization testing and coulombic efficiency testing.The method and mechanism of electrons transfer were also analyzed.The result showed that,in the initial stage of MFC operation,the anode without modification obtained a stronger electric current in the redox reation.After 200 hours operation,mrGO modified anode obtained a stronger electric response,as the anode potential reached-0.5 V,the current density for mrGO modified anode was 0.24 mAcm^-2,by 118.2%more than bare-anode.Meanwhile,the electron transfer impedance for mrGO modified anode was 20.4%lower than bare-anode.the Coulombic Efficiency was promoted and the COD removal efficiency was closed to each other.At this period,bacteria on the mrGO modified anode used extracellular pigment protein and flavins as mediators to transfer the electrons to the surfurce of anode,and its electronchemical activity increased greatly.We tested the stability of the output voltage and power density of the mrGO modified anode MFC in a long-term running?92 d?and confirmed that the maximum power density and output voltage for mrGO modified anode raised by 66.3%and 27.2%respectively,compared to the MFC with shorter runing time.Result of the test also showed that afrer long-term running,mrGO reduced the activation overpotential of the electrochemical reaction occured on anode and promoted the electron transfer rate.The Coulumbic Effifiency and COD removal efficiency were both improve significantly,which demonstrated mrGO could enhance the electron transfer ability from substrate to surface of anode.With the results of mrGO's characterization,the reduction of GO were stable the long-term running.The weight of mrGO adhered on the surface of anode also increased,which indicated the fixation of mrGO onto anode was improved.