Design Optimization Of Metal-Nitrogen-Carbon Catalysts For Electrocatalytic Oxygen Conversion

In today’s society,the serious fossil energy crisis and environmental pollution have threatened the sustainable development of human society,which is related to the national people’s livelihood and national security.To reduce the use of fossil energy and rely on electrocatalytic energy conversion equipment have become the current mainstream.Electrocatalytic energy conversion equipment is mainly limited by oxygen reduction reaction and oxygen evolution reaction kinetics.In order to improve the conversion efficiency,catalysts must be added to speed up the reactions.At present,Pt/C is recognized as the best catalyst for oxygen reduction reaction,Ru O₂ and Ir O₂ are the best catalysts for oxygen evolution reaction.However,the scarcity and high price of Pt,Ru and Ir limit their large-scale application.Therefore,it is imperative to prepare efficient and inexpensive non-noble metal electrocatalysts to accelerate oxygen reduction and oxygen precipitation reaction.In this paper,a series of cheap transition metal catalysts were prepared around the transition metal,and the activity of the materials in different types of electrocatalytic conversion reactions were improved through reasonable structural design.The main contents are as follows:（1）Iron-porphyrin was grown in situ on Ti₃C₂ nanosheets by porphyrin and ferrous chloride on MXene as the substrate to synthesize Fe NC/MXene lamellar composites.The catalysts were calcined at different temperatures to obtain Fe NC/MXene-X（X stands for calcination temperature,X=600,700,800℃）,in which the Fe NC/MXene-700 catalyst showed the best catalytic performance for oxygen reduction due to the synergistic effect of Fe₂O₃nanoparticles and Fe-N_x sites,and its stability and methanol resistance were superior to commercial Pt/C.The assembled Fe NC/MXene-700-based zinc-air battery had good performance.（2）Sandwich structure Co-N-C catalyst:A series of ZIF-67@MXene-X（X represents the reaction time,X=2,4,6）catalysts for the growth of ZIF-67 on both sides of MXene were prepared using Ti₃C₂-based MXene as growth template by controlling the reaction time.The process of ZIF-67 on the surface of MXene from small proppant to homogeneous nanocrystalline and then to complete dodecahedron was observed in detail by scanning electron microscope images.Among them,ZIF-67@MXene-4 catalyst is a typical sandwich structure with a transverse size of several hundred nanometers to several microns.When it is used in the oxygen evolution reaction,the required potential is only 1.60 V when the current density is 10m A·cm^-2.（3）Co-N-C biomass porous carbon nanomaterials:Inspired by the regulated morphology in the previous two parts,a series of hierarchical porous nano-materials with highly dispersed cobalt atoms were successfully prepared in this chapter by calcination using biomass orange peel as carbon source and Zn Cl₂ as salt template and activator.By using different content of Zn Cl₂ to regulate the ratio of microporous and mesoporous materials,including Co BPN-10 of microporous and mesoporous reach a state of balance,showing the most excellent ORR catalytic activity,high stability,and OER the catalytic performance is good,which is a kind of excellent bifunctional catalyst.The assembled by Co BPN-10 zinc air battery performance is excellent,the maximum power density can reach 114.7 m W·cm^-2,.