Study On The Modification Of Air-cathode Catalyst In Microbial Fuel Cells

In recent years,as a hot research topic,microbial fuel cells(MFCs)have been shown to be a substitute for green energy,energy-saving and efficient waste water treatment methods.MFCs powered by microbes with sustainable and clean characteristics,and they can effectively catalyze the degradation of a series of organic substrates under natural conditions.Although air-cathode MFC has been proved to have the most potential for large-scale application,its electrical performance remains a bottleneck.Graphene is widely used in supercapacitors,sensors,lithium batteries and other fields due to its unique structural characteristics,which make it have better electrical,chemical and mechanical properties than other carbon materials.The radius of nitrogen atom is similar to that of the carbon atom and has a higher electronegativity than the carbon atom.Nitrogen-doped graphene can effectively regulate its energy band structure and improve its electrochemical performance.In particular,the electrocatalytic activity and durability of graphene composite catalyst can be improved by synergistic effect between graphene and Fe-N.Therefore,more and more researchers devote themselves to the study of the modification of graphene.However,there are so many reports with different reference states about the application of various graphene in MFCs,having made it hard to compare and interpret their catalytic performance among these systems.Therefore,it is imperative to explore the differences of the catalytic properties of different types of graphene doped with iron and nitrogen.In this thesis,the effects of mixing ratio of Fe-N complex and carbon matrix material,kinds of doped graphene,carbonation holding time on the micromorphology and catalytic performance of the catalyst are discussed.The results are as follows:(1)X ray diffraction(XRD)test results show that with the increase of Fe-N content,the crystallization peak of Fe3C and FeNx is more obvious,the strength is higher and the crystallization is better.The electrochemical performance test results show that when the mixing ratio of Fe-N and carbon matrix is 4:1,the catalytic performance is the best.(2)High conductive graphene(HCG),high active graphene(HAG)and single-layer graphene(SLG)were dope by Fe-N compound,and the crystal particles in the catalysts were observed by using scanning electron microscope(SEM)and transmission electron microscope(TEM).In addition,the carbon tubes with a diameter of 0.1-1μm were formed on the graphene layer of the Fe-N doped single graphene(Fe-N/SLG)catalyst.The results of electrochemical performance test also show that F has the best performance,and the maximum power density of MFC is 1210 mW/m2 when the stability is reached.X-ray photoelectron spectroscopy(XPS)was used to compare the types and contents of elements on the surface of the catalysts,and the reasons for the difference in the catalytic properties of different graphene types were obtained.(3)when the holding time is 90～180min,the morphology of cluster carbon tube is the best.The results of TG mass spectrometry(TG-MS)further confirm the mechanism of cluster carbon tube generation and disappearance.The catalytic properties of cathode catalysts for oxygen reduction reaction(ORR)have been measured by rotating ring disk electrode technique(RDE).The transfer electron number of these catalysts has been calculated by K-L equation.It is found that the ORR reaction mechanism of the catalysts is a 4-electron dominated process.In addition,this thesis use Fe doped polyamic acid(PAA)as cathode catalyst for the first time,and the effects of different structure of PAA,carbonation temperature and holding time on the structure and performance of Fe-PAA as cathode catalyst were studied.The results are as follows:(1)Fe doped the PAA prepared by the consendation of PMDA(pyromelliticdianhydride)/p-PDA(p-phenylenediamine)has better catalytic performance.(2)Although PAA contains nitrogen,the doping of Fe can effectively improve its catalytic activity.When the carbonization temperature is 800 ℃ and the holding time is 90min,there is a better catalytic perfoemance,and the maximum power density and electron transfer number of oxygen reduction are 984±29mW/m-2 and 3.55 respectively.PAA itself contains nitrogen elements and is easy to prepare,which greatly reduces the preparation cost and improves the preparation efficiency.It is of great significance to realize the commercialization of MFC and the expansion of practical applications.