Synthesis And Electrochemical Properties Of Metal Doped Flexible Porous Carbon Nanofibers

In the electrochemical energy storage system,the zinc-air battery has the advantages of high theoretical energy density,simple structure,and complete product recovery,and has broad application prospects.During the charging and discharging process,the oxygen reduction（ORR）reaction and oxygen evolution reaction（OER）of the air cathode determine the energy utilization efficiency of the zinc-air battery.The currently commercialized cathode catalyst materials are precious metal catalysts,which have low inventory in nature,high cost,and unstable performance,which limits the commercial development of their zinc-air batteries.Therefore,designing low-cost,high-efficiency cathode catalysts to replace precious metals is the key to breaking through the commercialization of zinc-air batteries.Porous carbon nanofibers have the advantages of high specific surface area and stable performance,and can be used as catalysts or catalyst carrier materials.However,its intrinsic catalytic activity is poor,the preparation process is complicated,and it pollutes the environment.In response to the above problems,this paper uses a green,environmentally friendly,economical and convenient electrospinning synthesis method to prepare flexible porous carbon nanofiber non-precious metal catalyst materials.By adjusting the structure of carbon-based materials,the specific surface area and defect structure of carbon-based materials are increased;Combining the synergistic effect of metal atoms to build a special microstructure provides new ideas for the development of efficient and stable catalysts.The main research contents of this paper are as follows:1.Using polyvinylpyrrolidone（PVP）as a carbon source and polytetrafluoroethylene （PTFE）as a pore former,combined with electrospinning technology and heat treatment to synthesize flexible porous carbon nanofibers.Explore the effects of changing the content of pore formers and carbonization temperature on the microscopic morphology,pore size distribution,graphitization defects,and oxygen reduction activity in alkaline electrolytes of PCNFs.The results showed that after 2h of carbonization at 900℃,PCNFs formed part of the graphite crystal plane,and PCNFs-2:1 showed the largest bending angle.The specific surface area of the PCNFs-2:1sample is as high as 322.4 m²·g^-1,the CV curve has an obvious oxygen reduction peak,the oxygen reduction activity half-wave potential is 0.706V,and the initial test voltage of the assembled zinc-air battery is 1.029V,charge and discharge The life span is 110h.2.The oxygen reduction half-wave potential of the above porous carbon-based catalyst has not yet reached the level of commercial Pt/C.This chapter is based on the above-mentioned porous carbon-based materials,by doping transition metal copper atoms to improve the reaction activity of the catalyst.To study the effect of adding different content of Cu salt on the catalytic activity of porous carbon-based non-metallic catalysts.The results show that after carbonization at900°C,the specific surface area is 336.5 m²·g^-1,and the CV curve has both a reduction peak and an oxidation peak.When 1mmol of Cu salt was added,the catalyst showed the best oxygen reduction activity,the half-wave potential reached 0.793V,the Tafel slope was 113m V·dec^-1,and the electron transfer number reached 3.9.In alkaline electrolyte,Cu@PCNF has better stability than Pt/C,and the initial voltage reaches 1.296V after being assembled into a zinc-air battery.3.By doping bimetal salt ions to control the microstructure of carbon-based catalysts,we found that after 900°C carbonization,electronegative F ions anchor Cu and Co ions on the carbon fiber to form a bimetallic heterostructure.The high-resolution microscope observed that the metal particles have a layered structure inside,which can well avoid the agglomeration of metal particles.The prepared Cu/Co F₂@PCNF has an oxygen reduction half-wave potential of 0.84V,which is better than the commercial Pt/C catalyst（0.83V）,and the electron transfer number is 3.94.The Tafel slope is 113m V·dec^-1,which is lower than the 127m V·dec^-1 of Pt/C.After testing 1000 cycles of CV cycle,the catalyst activity only lost 0.1m V,while the Pt/C activity loss reached 33m V.The initial voltage of the zinc-air battery is as high as 1.468V,and the battery’s charge-discharge life span reaches 130h.