Analysis And Research On The Electricity Generation Performance Of Heteroatom-doped Metal-free Carbon Microbial Fuel Cell Cathode

The energy problem has increasingly become the main bottleneck restricting the economic development of the international community.The development of low-carbon and environmentally-friendly new energy has attracted worldwide attention.Microbial fuel cells?Microbial fuel cells,MFC?as a new type of battery technology,it can use domestic wastewater,industrial wastewater and other wastewater organic matter as raw materials due to the self-metabolism of electricity-producing microorganisms to complete the conversion from chemical energy to electric energy,achieving the goal of combining energy recovery and sewage purification.For a long time,due to the low power generation performance of MFCs,poor long-term operational stability,and high practical cost of cathode catalysts,it has limited the large-scale commercial application.Among them,the catalytic activity of the cathode catalyst is particularly important and is a key factor limiting its output electrical energy.In this article,improving the electricity production performance of MFCs and reducing the cost of cathode catalysts as the key point,the hetero atom-doped non-metallic porous carbon as the starting point,to preparing the cathode catalysts with high activity and low cost.The materials of structural characteristics were analyzed by XRD,XPS,BET,SEM and TEM.The electrocatalytic principle and activity of the materials were analyzed by electrochemical methods such as cyclic voltammetry?CV?,linear sweep voltammetry?LSV?,and rotating disk/ring electrode?RDE/RRDE?.In the experiment,the waste pomelo was used as the carbon source to reduce the experimental cost.Ammonium fluoride was used as the fluorine source and nitrogen source,zinc chloride is used as the cocatalyst.Different amounts of KOH were then added as an activator to the carbon support?1:1,1.5:1,2:1,2.5:1?.The nitrogen-fluorine co-doped metal-free porous carbon?NF-PGCs?catalyst was prepared by a two-step carbonization process?first step activation,second step carbonization?.For NF-PGCS composites,the doping of heteroatoms such as nitrogen and fluorine can produce synergistic effects,and the conductivity of the composites can be improved by adding co-catalysts,and the addition of a cocatalyst can increase its conductivity.In addition,the amount of different activators results in a porous structure on the surface,which can effectively increase the specific surface area and increase the active site of the oxygen reduction reaction.The CV and LSV tests were carried out separately,and the relationship between the porous structure of NF-PGCs materials and the oxygen reduction electrocatalytic activity was initially explored.NF-PGC-2 achieves maximum current density compared to Pt/C and follows the four-electron transfer kinetics.The NF-PGC-2 was assembled at the cathode of the MFCs and the maximum output power density was measured to be 1039.7 mW m^-2,which was higher than Pt/C.In order to improve the MFC production performance,the surface pore structure of the cathode catalyst is further improved based on the above experiment.Using the same biomass carbon source?pomelo peel?,immersed in a mixed solution of thiourea and ferric chloride,using solution evaporation and self-assembly method to introduce different amounts of SiO₂ template?0,0.25,0.5,0.75,1.0g?.After high temperature carbonization,a sulfur-nitrogen co-doped two-dimensional porous metal-free carbon catalyst?HP-SN-PGCs?was prepared by etching a template by an alkali solution.Due to heteroatom doping and abundant pore structure,HP-SN-PGCs material has higher catalytic effective component content,higher degree of graphitization,more carbon defects,faster mass transfer rate and good catalytic activity.When applied to the actual operation of MFCs,HP-SN-PGC-0.5 has maximum output voltage,power density(1161.13 mW m^-2)and small mass transfer internal resistance?19.3??.After 1800 hours of operation,the power density decreased by only 4.5%,and it has good power generation efficiency and long-term stability compared with Pt/C.The heteroatom-doped porous carbon materials prepared herein have good ORR catalytic activity and low cost.It has good application potential in substituting MFCS cathode platinum-based catalysts.