Preparation And Electrocatalytic Properties Of Fe/Ni Doped Nitrogen Carbon Matrix Composites

The increasingly serious global fossil energy crisis and environmental pollution problems have intensified human demand for clean and sustainable energy,and new green energy conversion and storage devices such as fuel cells,electrolytic water devices and metal air batteries have developed rapidly.Electrochemical oxygen reduction（ORR）,oxygen evolution（OER）and hydrogen evolution（HER）catalyzed by precious metals such as platinum（Pt）,iridium（Ir）and Ruthenium（Ru）and noble metal oxides are the basis for the work of commercial fuel cells,electrolytic water and metal-air batteries.Precious metal catalytic materials have high cost,poor stability and easy poisoning,which have become the bottleneck of inhibiting the development of green and clean energy system.Transition metal materials with low price,wide source and special electronic structure are the most promising alternatives for precious metal catalysts.However,for practical applications,the catalytic activity and catalytic stability of transition metal materials still need to be improved.Nano-carbon materials have the characteristics of large specific surface area,stable structure and good electrical conductivity.The composite of nano-carbon materials and transition metal catalysts is an effective method to improve the catalytic activity and catalytic stability of transition metal materials.It is worth noting that the binding mode of transition metal catalyst with nano-carbon materials is one of the important factors that determine its catalytic activity and stability.Organic compounds have clear structure and rich functional groups.In this paper,suitable organic functional groups/compounds are selected and metal ions are complexed by non-covalent bonds to form nanocarbon material precursors.Or use organic functional groups for secondary complexation of transition metal clusters/nanocarbon composites to control the combination of transition metals and nanocarbon materials,improve the catalytic activity and catalytic stability of the materials,and establish a metal-air battery with excellent performance.The research mainly includes the following three aspects:1.Fe-C-N materials with homogeneous dispersion of Fe₃N and coated with porous nitrogen doped carbon nanoparticles were prepared by using organic/inorganic double templates combined with secondary high temperature pyrolysis.The synergistic effects of porous structure,carbon coating,uniform dispersion and nitrogen doping improve the catalytic activity,catalytic stability and anti-toxicity of the material.Fe-C-N-800 pyrolysis temperature of 800℃showed excellent ORR activity and anti-methanol and anti-SCN^-toxic properties in0.1 M KOH,0.5 M H₂SO₄and 0.5 M H₃PO₄solutions.In addition,the catalytic performance of OER is close to that of commercial oxyoxide（Ir O₂）.The excellent multifunctional catalytic performance,toxicity resistance and wide p H applicability lay the foundation for the practical application of transition metal catalysts.2.A fusion self-assembly method was developed to assemble the organic ligands rich in amino and hydroxyl groups into a eutectic mixture with metal ions.The eutectic mixture was pyrolyzed at high temperature to obtain the porous Fe-Ni-co-doped nitrocarbon-based nano-carbon catalyst（Fe-Ni-N-C）.The fusion self-assembly method is not suitable for solvent,which is beneficial to increase the complexation strength of organic ligand and metal ions,and also to increase the interaction between organic ligand molecules.Thanks to the melting self-assembly,the precursor obtained a hollow fissure bubble structure after thermal decomposition,and the size of Fe and Ni nanoparticles as low as sub-nanometer scale,which gives Fe-Ni-N-C excellent catalytic performance.The results show that the OER catalytic performance of Fe-Ni-N-C-900 at 900℃exceeds that of commercial Ir O₂.The half-wave potential of Fe-Ni-N-C-800 catalyzed ORR at 800℃is close to that of commercial Pt/C,and has high toxicity resistance and stability.The power density and capacity of the zinc air battery assembled by Fe-Ni-N-C-800 are as high as 647.78 m W·cm^-2and 1161.5 m Ah·g^-1,far exceeding that of the commercial Pt/C+Ir O₂-based zinc air battery(545.94m W·cm^-2and610.3m Ah·g^-1).3.High temperature pyrolysis of carbon precursors and transition metal salt complexes is the main method for preparing transition metal/nano-carbon composites.The aggregation of transition metal nanoparticles during high temperature pyrolysis is the main factor for the poor catalytic performance of the composites.To solve this problem,a novel approach was developed in this paper.Carbon nitride（CN）with abundant defects was used for secondary wet complexation with iron nanoparticles/carbon nanocomposites,which effectively improved the dispersion of Fe clusters in carbon matrix and formed a single atomic iron catalyst Fe（SAs）@C@CN-10,whose OER catalytic performance exceeded that of commercial Ir O₂.This opens up a convenient new way for the synthesis of monatomic catalysts.