Design And Synthesis Of Iron-Doped Carbon Electrocatalysts For Oxygen Reduction Reaction

With the rapid consumption of coal,oil and natural gas,energy shortage and environmental pollution have become urgent issues to be solved.As novel energy storage device,fuel cell can directly transform chemical energy to electric energy.In addition,fuel cell is universally admired for it’s high energy conversion density and low pollution.However,the sluggish kinetics of their cathodic oxygen reduction reaction（ORR）have seriously influenced their extensive commercial development,which need bulk electrocatalysts to reduce the overpotential.Currently,Pt-based materials have demonstrated prominent electrocatalytic activity toward the ORR,but their scarce abundance and poor stability severely hamper their widely practical applications.Based on the above problems,we focus on the rationality and practicality to develope a series oxygen reduction electrocatalysts with low-cost and high-performance to replace the Pt-based electrocatalytic materials.The mian research contents are as follows:Firstly,a MOF precursor with stacking structure was designed and synthesized by ball milling method,and then N-doped carbon materials coupled with Fe₃O₄ and Fe₂C（BM-Fe@NC-120）were prepared by calcining the as-prepared mental organic framework（MOF）precursor under high temperature.We investigated the effect of ball milling time on the MOF structure and the results demonstrated that the MOF structure gradually appeared with the increase of grinding time.The optimal ball milling time was 120 min,which gave a superior ORR performance with 0.80 V half-wave potential and-5.08 m A cm^-2 limiting current density.Secondly,a SiO₂ templating strategy was applied to prepare a highly active Fe-N_xanchoring nitrogen-doped porous carbon material（ISA-Fe-NC-7）.We explored the effect of SiO₂ amount on the final structure.The results revealed that embedded silica could not only help construct porous structure of the carbon material,but also prevent the agglomeration of Fe atoms and advantageous for forming Fe-N_x active sites.Thus,it is a reasonable strategy to synthesize iron and N co-doped carbon electrocatalysts.The ISA-Fe-NC-7 sample exhibited superior ORR performance with half-wave potential of 0.85V,which exceeded 20%Pt/C.Furthermore,88%of its limiting current density was remained after 10 h i-t stability test in0.1M KOH solution,which indicating the outstanding stability.Finally,owing to the defect engineering of carbon,an N and P co-doped iron-based porous defective carbon material electrocatalyst was designed.By utilizing the electron-withdrawing effect of N,metal organic complexes were directly connected to defects carbon matrix.As the results revealed,the porous and defective structure of carbon effectively promoted proton transport and the formed Fe-N_x sites is highly active,thus improving the oxygen reduction reaction performance.In 0.1 M KOH solution,the prepared sample exhibited a half-wave potential of 0.83 V and limiting current density of-5.74 m A cm^-2.