Preparation And Oxygen Reduction Performance Of ZIF-derived Iron/Nitrogen Co-doped Carbon Materials

In the 21st century,human beings are facing two major challenges:energy crisis and environmental pollution.In recent years,new energy technologies,such as fuel cells and metal-air batteries have become the current research hotspot due to their advantages of high efficiency,cleanness and sustainability.The sluggish kinetics of oxygen reduction reaction（ORR）seriously restrict their practical applications.At present,Pt and Pt based materials have been used as commercial catalysts to accelerate ORR,but they have been plagued by such problems as scarcity,high cost,poor stability and anti-poisoning ability.Transition metal/nitrogen co-doped carbon based materials（M-N-C）are considered to be the most promising alternatives to Pt-based catalysts owing to their high activity,good stability,low cost and abundant synthetic precursors.Metal organic frameworks（MOFs）with high specific surface area,rich pores and diverse components provide a broad platform to design high-performance M-N-C electrocatalysts.In this paper,two different Fe-N-C electrocatalysts with excellent ORR performance have been prepared with Fe-doped zinc-based zeolite imidazole framework（ZIFs）as the precursors.The main research works are as follows:1.First,3D flower like ZnFe-ZIF precursor was synthesized by chemical doping approach in aqueous solution.Then,a hierarchical porous carbon material with Fe,N-codoped CNTs is obtained by one-step carbonization.Benefiting from advantageous structural features,sufficient active sites and effect doping,the optimal Fe-N-CNTs-12catalyst exhibits better ORR activity(E_1/2=0.89 V),stronger durability and CH₃OH/CO tolerance than commercial Pt/C in 0.1M KOH.In addition,it shows good approaching activity to Pt/C（0.78 V）and more robust stability in 0.5 M H₂SO₄.When utilized in the liquid zinc-air battery delivers a superior output performance(a peak power density of131.7 m W cm^-2 and energy density of 880 Wh kg^-1)and excellent discharge stability.Moreover,the possible practicability of the catalyst was further confirmed by the all-solid-state zinc air battery assembled with it.2.Fe doped ZIF-8 nanocrystals（～60 nm）were initially synthesized in water by wet chemical impregnation.Subsequently,Fe,N co-doped porous carbon containing carbon nanotubes was obtained by one-step pyrolysis.By virtue of proper Fe/N doping,rich carbon defects and good conductivity,the optimal Fe-N-C catalyst possesses outstanding activity（0.90 V）,excellent stability and methanol resistance in 0.1 M KOH,which are superior to commercial Pt/C.Besides,it also shows an exceptional ORR activity（0.792 V）in 0.5 M H₂SO₄,very close to Pt/C.When served as the air cathode catalyst in the primary battery,Fe-N-C-900 exhibits excellent discharge stability and rate performance.Furthermore,the Fe-N-C-900-based button battery delivers a maximum power density up to 178 m W cm^-2 and operates stably for at least 40 h at the current density of 5 m A cm^-2,which behaves obviously better than commercial Pt/C.