Construction Of 3D Macroporous Carbon-based Anode And Its Application For Microbial Fuel Cells

Microbial fuel cells(MFCs)can simultaneously realize sewage treatment and electric energy recovery by using microorganism as catalyst,so it has potential application value.Since the discovery of the phenomenon of biological current in1911,the research of MFCs has experienced a slow development in the past century and a rapid development in the past 15 years.A lot of progress has been made in reactor configuration,electrode materials,microorganism and bioelectrochemistry.However,MFCs still face some bottlenecks such as low power density and extracellular electron transfer(EET).The properties of anode,as an attachment of electroproducing bacteria,not only affects the growth of biofilm,but also the electron transfer rate from bacteria to anode,thus affecting the performance of the whole system.Therefore,the design of high efficient three dimensional(3D)anode materials is one of the core of improving the performance of MFCs and energy conversion.In order to improve the interaction between carbon-based anode and microorganism,several porous carbon-based anode materials were designed and prepared in this paper.The rapid enrichment of electroproducing microorganisms was realized,and the influence of structure,composition and interfacial property of different materials on promoting microbial EET was investigated.The specific content of the study is as follows:By using cheap and easily available bread as the raw material of electrode,the hetero-atom(nitrogen,phosphorus and sulfur)doped porous carbon foams(abbreviated as NPS-CFs)were obtained by a facile calcination method.Chemical composition and physical characteristics of the as-prepared products were characterized by scanning electron microscope(SEM),transmission electron microscope(TEM),nitrogen adsorption stripping tester(BET),X-ray photoelectron spectrometer(XPS),X-ray powder diffraction(XRD),Raman spectrometer(Raman),and so on.The influence of calcination temperature on microstructure and chemical composition of calcination was also studied systematically.The results show that the porous carbon foam obtained by carbonization at 1000 ~o C(NPS-CF-1000)has the largest specific surface area,abundant pore structure,optimal doping,excellent mechanical strength and good biocompatibility.In order to efficiently control the distribution of microorganisms in the anode materials,a noval 3D ordered porous carbon(abbreviated as 3D-OPC-x)was prepared by self-assembly using a hard plate method.In addition,in order to further promote electron transfer between microorganism and electrode,conductive PANI is further introduced into 3D ordered porous carbon structure.Macroscopic spatial structure and microscopic pore size distribution,chemical composition and physical properties of 3D-OPC-x and 3D-OPC-900/PANI anode materials were studied by means of SEM,TEM,XRD,Raman,BET,XPS and atomic force microscope(AFM).The results demonstrated that 3D-OPC-x and 3D-OPC-900/PANI anode materials have ordered and interconnected 3D structure,excellent conductivity and good biocompatility.The effects of structure,chemical composition and interfacial properties of carbon-based anode materials on start-up time,power density,internal resistance of MFCs,and voltammetric behavior of microorganism were investigated.NPS-CFs,3D-OPC and 3D-OPC-900/PANI show a fast start-up and high power density.Compared with NPS-CFs,the introduction of conductive polyaniline in 3D-OPC-900/PANI has a“siphon effect”on adhesion of electroproducing microorganisms,and the battery starts after 2-3 days of inoculation.Compared with the conventional carbon electrode,the starting period is shortened by 67%.At the same time,thanks to reasonable and effective nanostructure design,3D-OPC-900/PANI composite anode shows excellent bulk power density and voltage,superior to commercial carbon cloth(CC)and NPS-CFs.Above results indicated that 3D-OPC-900/PANI could achieve the rapid enrichment of electroproducing microorganisms and show excellent performance.The voltammetric behavior of biofilms on anode showed that the peak current of the NPS-CF-1000,3D-OPC-900 and 3D-OPC-900/PANI anode is proportional to the scanning rate,indicating that the redox reaction of MtrC on these anodes is subject to the surface-absorbed reactant-controlled process.However,the peak current of the biofilm on the surface of the CC anode is linear with the square root of the scanning rate,suggesting that the redox reaction of OmcA is subject to a diffusion-controlled process.Above results showed that NPS-CFs,3D-OPC and 3D-OPC-900/PANI electrodes have better contact with microbial membrane and facilitate extracellular electron transfer between electroactive bacteria and electrode via direct electron transfer through the redox active cytochrome proteins on the bacterial outer membrane.Using NPS-CFs and 3D-OPC-900/PANI as anode,the removal of organic matter by microorganism was achieved,and COD removal rate was 64.9% for NPS-CF and 68.9% for 3D-OPC-900/PANI based MFCs,respectively.At the same time,MFCs equipped with NPS-CFs anodes could successfully drive the actual device-the electromagnetic toy,while For the first time,the HIT sequence LED lights were successfully lit with MFC equipped with 3D-OPC-900/PANI.The effects of chemical composition and interfacial properties of carbon-based anode materials on the amount of biomass,the microbial community structure and biocompatibility of the biofilmwere investigated.The results show that the chemical composition and physiochemical properties of carbon-based anode affect the microbial community structure.Compared with NPS-CFs and 3D-OPC anode,3D-OPC-900/PANI anodes are more benefitful the enrichment of the electroactive bacteria.At the same time,SEM studies confirmed the presence of nanowires in3D-OPC-900/PANI anode biofilms.In addition,the results of the confocal laser scanning microscopy(CLSM)show that the NPS-CFs,3D-OPC and3D-OPC-900/PANI anode has good biocompatibility compared with commercial carbon cloth.