Fabrication Of Nanoporous Carbon Fiber Materials For Promoted Anodic Interfacial Electron Transfer In Microbial Fuel Cells

Microbial Fuel Cell?MFC?is a device that can convert the chemical energy of the organic matter directly into electrical energy by microbial catalyst.The slow interfacial electronic transfer between the electrode and the microbial cells is one of the major obstacles to the catalytic performance of the anode.In recent years,various porous electrode materials,especially the ones with nano-structure units,have been applied to MFC anode to promote the interface electron transfer between electrodes and microorganisms,significantly improving the electrical performance of MFC.However,the MFC anode interface electron transfer process involves not only multiple extracellular electron transfer pathways of microbial cells,but also the morphology and distribution of electroactive biofilms on the electrode surface and the micro-nano structure of the electrode surface.Understanding the specific mechanism of nanoporous and macroporous structures promoting interfacial electron transfer will help to gradually clarify the mechanism of nanostructured anode interfacial electron transfer and provide a theoretical basis for the design of new electrode materials.The electrostatic spinning technique is applied to prepare a variety of nanoporous carbon fiber materials through the choice of nanoparticle template and the regulation of its ratio to polyacrylonitrile precursor.A carbon fiber network with different internal pore structures and inter spaces was constructed.The typical electricity production strain-Shewanella putrefaciens CN32 is used here and the electrochemical behavior of anodic interfacial electron transfer process is investigated to understand the possible mechanism of different pore structures promoting interfacial electron transfer.The main research contents and results are as follows:?1?Three kinds of porous carbon fiber materials with different structures have been synthesized by using PAN as precursor,ZnO nanoparticles as pore-forming template,N,N-dimethylformamide?DMF?as solvent.The final products were obtained through oxidation,carbonization and post-treatment process.Then,the developed materials were used as anode materials in Shewanella putrefaciens CN32 MFC to investigate the effect of pore structure on electron transfer at the electrode interface.It is difficult for ZnO nanoparticles to be uniformly dispersed in the the precursor solution of electrostatic spinning.However,compared with the non-porous carbonized PAN fibers,the adsorption amount of flavin mediators on the porous carbon fiber electrode surface is increased.Moreover,it has a large catalytic current and a high output power density in CN32 MFC.It is concluded that the introduction of nano-sized pore structure on PAN precursor can promote the interfacial electron transfer of carbon fiber electrode,but it is necessary to find specific nano particles that can be evenly dispersed in it as a template to form a uniformly distributed nano-pore structure.?2?On the basis of the previous study,zeolitic imidazolate framework-8?Zeolitic imidazolate framework-8?was selected for which was a widely used MOF as porous carbon template that can be synthesized under ambient temperature and pressure and can be easily vaporized during the carbonization process.To understand the effects of marcopores between fibers and the nanopores on the fibers to the interfacial electron transfer between the bacteria cells and the porous carbon fiber electrode,ZIF-8 was introduced into the electrospinning precursors,and three kinds of nanoporous carbon fiber?MPCF?materials with different structures were obtained by adjusting the mass fraction of the ZIF-8 template in the precursor.With the increase of ZIF-8 content in the precursor,the obtained MPCF fiber diameter,fiber gap?macropore?and nanopores volume are increased.The large number of nanopores promoted the flavin based interfacial electron transfer and the presence of macropores increased the bacterial loading amount.However,too large macro pores between broad fibers can impede the formation of biofilms,resulting in a lack of effective interfacial electron migration.The experiment showed that the MPCF-2 anode with appropriate pore size and nanopore volume achieves the best power output performance.The maximum power density of the anode in CN32 MFC is997±467 mW m^-2,which is 10 times higher than that of the carbon electrode.To sum up,the nano-sized pore structure mainly promotes the interfacial electron transfer process based on small molecular mediators,while the macropore structure has an important influence on the morphological structure of the electrode surface biofilm,and consequently affects the direct extracellular electron transfer process.Tailoring the porous structure of the anode is an effective way to accelerate the electron transfer at the electrode interface,realizing efficient bioelectrocatalytic reaction and improve the output efficiency of the microbial fuel cell.Owing to the facile fabrication process and relative low cost,this electrospun nanoporous carbon fiber electrode could be a promising candidate for high-performance MFC.This work will also provide some insights to the design of nanoporous fiber based electrode for MFC or other bioelectrochemical system devices.