Preparation Of Iron-doped Carbon-based Materials And Investigation Of Their Electrocatalytic Properties

The burning of fossil energy brings serious environmental pollution problems,and fossil energy is a non-renewable energy,which forces people to find new energy systems.Oxygen reduction reaction(ORR)is a reaction process involving 4 electron transfers.It is a half-reaction of clean and efficient new energy conversion devices such as fuel cells and metal-air batteries.However,it is slow in reaction kinetics,which seriously restricts the development of these new energy conversion devices.To date,Pt based catalysts are still the most commonly used commercial catalysts for ORR,but they are not stable enough,expensive,and have limited reserves on earth.The transition metal and nitrogen-doped carbon material(M-N-C)is a very promising non-noble metal ORR catalyst with high catalytic activity and higher stability than Pt/C catalyst.Herein,we used two-dimensional zeolitic imidazolate frameworks(ZIFs)as precursors,introduced different iron(Fe)sources,designed a reasonable preparation method,and finally obtained two different Fe-based nitrogen-doped porous carbon materials.These materials have achieved high-performance ORR catalysis,and preliminary explored the mechanism of its catalytic reaction.The main research contents are as follows:(1)ZIF-L@ZIF-8 material with yolk-shell(yolk@shell)structure was prepared,and 5,10,15,20-tetraphenylporphyrin iron(FeTPP)was successfully introduced into ZIF-L@ZIF-8 containing zinc and cobalt.The FeTPP loaded ZIF-L@ZIF-8 was obtained.After pyrolysis at high temperature,the prepared FeCo bimetallic nitrogen-doped porous carbon material(FeCo-C/N)exhibits good ORR catalytic activity,with a onset potential of 0.946 V and a half-wave potential of 0.864 V,which is comparable to commercial Pt/C catalysts.The zinc-air battery assembled with FeCo-C/N catalyst showed good charge/discharge performance and stability,and its power density reached 397.25 mW cm-2,which is one of best non-precious metal ORR catalysts in the reported zinc-air battery.(2)The method of confined space-controlled two-dimensional ZIF-L is used to prepare a Fe-based nitrogen-doped porous carbon material(Fe-C/N)with a leaf-like two-dimensional morphology.Iron acetylacetonate was added to the Zn-ZIF-L synthesis system,and the Fe-loaded ZIF-L material was prepared as a precursor.Through the method of coating mesoporous silica(mSiO₂),the high temperature pyrolysis of the two-dimensional ZIF-L in a confined space is realized,and a Fe-based nitrogen-doped porous carbon material(Fe-C_/N).The Fe-C/N catalyst has good ORR catalytic performance and good stability in alkaline media,and its half-wave potential reaches 0.907 V,which is much better than that of commercial Pt/C catalyst.