Tailoring Of Hierarchical Porous Carbon Anode For Improved Interfacial Electrocatalysis Of Shewanella Microbial Fuel Cell Anode

Microbial fuel cell(MFC)operates at normal temperature that can utilize a wide range of microorganisms as catalysts to treat sewage organic matter,heavy metal ions,etc.,and can be used as a biosensor to evaluate the toxicity of sewage.It is a promising environmental restoration technology.At this stage,the low output power density of MFC is difficult to drive most devices,and the high production cost of electrode materials greatly limits the application of MFC in industry.Among them,the sluggish kinetics of the microbial anode due to the slow interfacial electron transfer is the main obstacle that restricts its bioelectrocatalytic performance,making it difficult to increase the output power.In recent years,porous carbon materials have been widely used in MFC anodes,which has greatly improved the power generation performance of MFC.Through a review of previous studies,we found that the porous structure and surface properties of anode materials have a significant impact on the performance of MFC.However,the specific mechanism of porous structure and surface properties to promote interface electron transfer and its effect on Shewanella electrochemical behavior is not yet clear,which has guiding significance for the design of efficient anode materials.In this dissertation,polymers were used as precursors to fabricate hierarchical porous carbon electrodes via one-step carbonization.Through the variety of pore-forming agent and the adjustment of the polymer precursor ratio,different internal pore structures and with different surface nitrogen and oxygen ratio were obtained.The electrochemical behavior analysis of the anode was evaluated in a typical electricity-producing strain,Shewanella putrefaciens(S.putrefaciens)CN32 drived MFCs.The effects and possible mechanisms of pore structures and surface elements on interface electron transfer were investigated.The main research contents and results are as follows:(1)A cellulose-NaOH-urea mixture aerogel derived hierarchical porous carbon(CPC)is developed to promote the flavin based interfacial electron transfer.The porous structure of the CPC can be tailored via adjusting the ratio of urea in the cellulose aerogel precursor to obtain CPCs with different type of dominant pores.According to the electrocatalytic performance of different CPC electrodes,the CPCs with higher mesoand macropore area exhibit greatly improved flavin redox reaction.While,the CPC-9 with appropriate porous structure achieves highest power density in S.putrefaciens CN32 MFC due to larger active surface for flavin mediated interfacial electron transfer and higher biofilm loading.(2)Polyvinylpyrrolidone(PVP)was used as the precursor and sodium bicarbonate was used as a pore-forming agent to fabricate PVP-derived porous carbon(PPC)materials with different pore structures.The pore structure(micropores,mesopores and macropores)of porous carbon and the content of surface elements(nitrogen and oxygen)could be tailored through adjusting the content of sodium bicarbonate in the precursors.The experimental results show that the PPC-6 anode exhibits the best bioelectrocatalytic performance,which is higher than that of PPC-4(with higher micropore volume)and CPC-9(with higher mesopore volume).The reason could be that PPC-6 has larger effective pore area(pore size greater than 3 nm)and higher oxygen content,which promotes the number of adhered bacteria cells and thus enhances interfacial electron transfer and also increases catalytic current.As a result,the CPC-6 achieved best performance in S.putrefaciens CN32 MFC.In summary,the nanoporous structure mainly promotes the interfacial electron transfer process via small molecule mediators.The surface elements also have an important influence on the morphology and structure of the biofilm on the electrode surface,which also affects the directly extracellular electron transfer process.Effective regulation of the anode porous structure is an effective way to enhance the interfacial electron transfer,achieve efficient bioelectrocatalysis and improve the output performance of microbial fuel cells.