Effect Mechanism Of Electrospinning Metal-doped Carbon Fiber On Electrical Performance Of Microbial Fuel Cell

In order to respond to the call of the nation and accelerate the building of a green,pollution-free,sustainable and environmentally friendly society,it is ungently to explore the new energies.Microbial fuel cell（MFC）supports the conversion of electrical energy and chemical energy,and has significant development potential.Like restoring power from sewage and metabolizing pollutants.Unfortunately,the sluggish extracellular electron transfer（EET）between the microorganisms and the electrode interface impedes the broad industrialization MFCs.Although lots of previous works have reported that the anodes doped with metal compounds or composites can improve the output power of MFCs and the bioelectric catalytic activity of the anode,the role of metal doping in modifying the anode interface and the mechanism of directional metal modification of the anode interface on the EET process are not clear.This has guiding significance for the design and synthesis of high-efficiency anode materials with surface modification by substance doping.Therefore,tending to explore the mechanism of metal modified anode on the electrical performance of MFCs,two kinds of metal doped high-efficiency carbon nanofiber anodes were prepared by electrospinning technology.One is single metal doped carbon nanofiber and the other is duplex metal doped composite carbon nanofiber.They were applied to the anodes of MFCs inoculated with S.putrefaciens CN32.Under the aspects of morphological characteristics,surface characteristic analysis and electrochemical behavior measurements,the potential mechanism of enhancing the performance of electrogenic microorganisms and accelerating the rate of EET was studied.The main research contents and results are as follows:1.An innovative method for preparing a uniform iron ion-mixed carbon precursor by directly electrospinning iron-doped carbon nanofibers（Fe@CNF）is proposed.Via adjusting the doping concentration,the optimized Fe@CNF-20 anode exhibits greatly improved bio-electrocatalytic performance in MFCs,which delivers 8.67 times higher than that of the undoped CNF one.More importantly,results reveal that Fe-doping forms Fe₃C in anode,which not only greatly enhances the adsorption of electron mediator（flavin）,thus accelerating the mediation electron transfer（MET）between the substrate and electrogenic microorganisms,but also promotes the direct contact with proteins of cell membrane,resulting in strong direct electron transfer（DET）,thereby simultaneously boost both mediation and direct electrochemistry processes.A facile approach to synthesis of high-performance MFCs anode materials for concurrently strengthen both mediation and direct electron transfer rate while providing scientific insights in designs of efficient bioelectrochemical systems is furnished by this work.2.In daily life,copper,nickel and manganese are also well-known transition metals in addition to iron.Aiming to explore the role of different metal doped anodes in enhancing the performance of bioelectrocatalysis,iron doped,copper doped and nickel doped carbon nanofiber（Fe@CNF-20,Cu@CNF-20 and Ni@CNF-20）anodes were synthesized partly at the optimal doping concentration,which was 20 m M.And then the three materials were applied for MFC anodes of S.putrefaciens CN32.The results demonstrate that the doping of three metals can improve the bioelectric catalytic performance of MFCs,but there are differences between them.After morphology comparison,surface characteristic analysis and electrochemical behavior tests,it is found that due to surface of Fe@CNF-20 has special morphology and the formation of Fe₃C,leading to the better biocompatibility and the stronger electronegativity than other materials,which can improve the electrical performance of bacteria and the direct electrochemical（DEC）,so as to boost the bioelectrocatalysis efficiency of the anode.The maximum output power of Fe@CNF-20 is 641.96 m W m^-2,which is significantly higher than that of Ni@CNF-20(411.26 m W m^-2)and Cu@CNF-20(336.01 m W m^-2).This work proves that metal doping can modify the anode surface,but the effect of different metals is discrepant,which provides a reference for designing the high-efficiency anodes in the future.3.Since the doping effect of Cu and Ni is unsatisfactory,this work attempts to realize the synthesis of duplex metal doped nanofiber anodes through the addition of Fe for heightening the performance and regulation in DEC.Then compare the behavior of these composite anodes in bioelectric catalysis to elaborate the potential mechanism.Firstly,nickel-iron duplex metal doped carbon nanofibers were synthesized.By optimizing the doping concentration and proportion,the optimal doping conditions were determined.Secondly,copper-iron and copper-nickel doped composite anodes were prepared.The results exhibit that with the effective addition of Iron,the performance of copper doped and nickel doped carbon nanofiber anodes has been improved in varying degrees,while the performance of copper-nickel duplex metal doped anode is inapparently improved without addition of Iron.Among the three different materials,Ni Fe@CNF has a special morphology,the highest electronegativity,excellent biocompatibility and the existence of a large number of active sites,resulting in its maximum power density of 855.32 m W m^-2,which is evidently higher than other materials.Owing to the reasonable selection of metals for duplex metal doping,the efficiency of MET and DET can be improved at the same time.Because of the existence of active sites,the electronegativity is enhanced,which is conducive to the formation of bacterial biofilm and the adhesion of electrogenic microorganisms.And then it is instrumental in realizing the accumulation of FMN on the anode surface to form a reaction atmosphere with high electron mediator concentration,ensuring the rapid progress of EET.In this work,the potential mechanism of duplex metal doped composite anodes in EET and the regulation of DEC behavior were studied,which further confirmed the key role of anode interface modification in advancing the electrocatalytic activity of electrogenic microorganisms.