The Preparation Of Porous Graphitic Biochar As Efficient Oxygen Reduction Catalyst In Microbial Fuel Cells

At present,energy and environmental problems are becoming more and more serious,and the development of environmentally friendly renewable energy is highly urgent.The emergence of microbial fuel cells（MFC）technology provides new methods and ideas for wastewater treatment.Oxygen reduction reaction（ORR）at the cathode is a crucial factor that restricts MFC’s performance and commercial application.ORR contains four-electron and two-electron transfer reaction pathways,among which the four-electron transfer pathway will produce a lower overpotential,thereby improving the performance of MFC.Although the noble metal platinum（Pt）-based catalyst is currently considered a highly active cathode ORR catalyst,its high cost significantly limits its wide application.Therefore,exploring low-cost and high-performance cathode ORR catalysts to replace Pt-based materials is essential to promote the commercial application of MFC.Among various cathode ORR catalysts,carbon materials have become the current research focus of ORR catalysts due to their advantages in terms of low cost,large specific surface area,flexible porous structure and high conductivity.As a common carbon material precursor,biomass-based carbon materials have the advantages of sustainability,environmental friendliness,and adjustable physical and chemical properties.The porous structure of carbon materials and the degree of graphitization are the key factors that affect their electrocatalytic performance.However,the relationship between the two is often mutually restrictive.How to balance the relationship between the two and prepare porous graphitic biomass carbon as an ORR catalyst through a simple and effective method is of great significance.In response to the above problems,this paper starts from the cost,preparation method and electrocatalytic performance of the catalyst,using cheap mangosteen shells and eggplant biomass as carbon source and nitrogen source precursors,through simple impregnation treatment,and then high-temperature carbonization,successfully prepared Porous graphitic biomass carbon material.Through the structure and morphology characterization,electrochemical performance test of the materials,and application in MFC cathode to investigate the actual electricity generation performance,the main research results are as follows:（1）Using mangosteen shell as the carbon source and nitrogen source precursor,the nitrogen self-doped porous graphite biomass carbon material was prepared by a two-step impregnation method,in which KOH was used to improve the specific surface area and pore structure of the material and Co Cl₂ was used to increase the catalyst’s The degree of graphitization is followed by high-temperature pyrolysis to prepare the catalyst.The study found that the mangosteen shell porous graphite carbon（MPC-800）catalyst prepared by carbonization at 800℃has the largest specific surface area and reasonable pore structure distribution,which increases the active sites of ORR,and the high degree of graphitization improves the charge transportability.The MPC-800 catalyst exhibits high electrocatalytic performance in the electrochemical test.The initial potential and half-wave potential measured in the RRDE test are 0.150 V and-0.091 V（vs Ag/Ag Cl）.Using MPC-800catalyst for MFC cathode,the MPD obtained is 240 m W/m²,higher than the MPD（220m W/m²ï¼‰produced by MFC with Pt/C cathode catalyst.（2）Using K₃[Fe（C₂O₄）₃].3H₂O as the"activation-graphitization"dual-function catalyst,a one-step impregnation method followed by pyrolysis was used to prepare eggplant-derived porous graphitic biomass carbon materials.The optimal preparation conditions are that the mass ratio of K₃[Fe（C₂O₄）₃].3H₂O and eggplant is 2:1,and the pyrolysis temperature is 800℃.The eggplant-derived porous graphitic carbon（EPGC-800-2）material prepared under these conditions shows high specific surface area,well-developed pore structure and reasonable distribution,and a high graphitization degree.The EPGC-800-2 catalyst exhibits high ORR activity with a more positive ORR peak potential and more significant ORR peak current in CV tests.The exchange current density i₀ is 2.14×10^-4 A/cm².In the RRDE test,the onset potential and half-wave potentials are 0.153 V and-0.205 V（vs Ag/Ag Cl）,respectively,shows a four electron transfer pathway in the ORR process.MFC with EPGC-800-2 cathode catalyst obtains the highest MPD（667 m W/m²ï¼‰,which was higher than the MPD（621 m W/m²ï¼‰produced by the Pt/C cathode catalyst MFC,and also exhibits higher stability than Pt/C cathode catalyst MFC in long-term operation.（3）The structural performance and economic analysis of MPC-800 and EPGC-800-2 catalysts have been carried out.It shows that when MPC-800 and EPGC-800-2 catalysts are used as MFC cathode catalysts,they have the advantages of simple preparation,low price and cost-effectiveness.High performance,in which the preparation process of EPGC-800-2 catalyst is green and safe,and more efficient,which helps to improve the commercial application of MFC.