Study On Structure-Activity Relationship Between Single-atom Ni-based Porous Carbon Spheres And Electrocatalytic CO₂ Reduction To CO

The single-atom catalysts have many advantages such as high atomic efficiency,good stability and excellent catalytic activity in electrochemical CO₂ reduction reaction,and have a wide application prospect.Development of transition metal catalyst compared with noble metal can effectively reduce the cost of catalyst preparation,which represented by Fe,Co,Ni single-atom catalysts in the CO₂ reduction into electricity CO reaction has good catalytic performance,but there are scattered single-atom easy to reunite,uneven phenomenon.It is necessary to have good structural stability,metal dispersion and excellent pore structure,and hollow porous carbon spheres can meet the above conditions,which is an ideal single-atom catalysts support.In this work,the support of single-atom catalysts was designed from multiple perspectives.In order to facilitate the dispersion of monatomic catalysts and mass transfer in the reaction process,the hollow porous carbon spheres（Ni-N/C）supported by monatomic Ni and doped with nitrogen were designed and constructed.The effects of different morphology and pore structure of Ni-N/C catalyst on mass transfer,metal activity number and electrochemical catalytic performance were investigated by using CO₂ reduction as a model reaction and N₂ physical adsorption,TEM,XRD,HRTEM and XPS characterization.The main contents of this thesis are as follows:（1）Four kinds of catalysts with different morphology and pore structure were designed by modified traditional St（?）ber method.The effect on the activity number of monatomic Ni and the difference in the performance of CO₂ electroreduction to CO were investigated.The catalysts were characterized by TEM,XRD,N₂ physical adsorption,ICP,HRTEM and spherical differential electron microscopy.The hollow and porous structure of the catalysts supported by monatomic Ni was proved to have large specific surface area and abundant pore structure,which was beneficial to the exposure of the active metal and mass transfer during the reaction process.The microporous structure of the catalyst plays a limited role in the pyrolysis process,which makes the metal Ni exist stably as a single-atom species.The results of electrocatalytic CO₂ reduction show that the hollow carbon spheres with rich micro-mesoporous structure Ni group show good catalytic activity and stability.In the wide potential range of-0.7～-1.0V,they show more than 90%Faraday efficiency and high current density,and have good stability.Meanwhile,it also showed good stability.After 5h stability test,the selectivity of CO is always above 90%.In this section,the relationship between the morphology and reactivity of hollow porous carbon spheres catalyst was elucidated.（2）Based on the improved St（?）ber method,Ni single-atom supported porous hollow carbon sphere catalysts with different wall thickness were designed by adjusting the hydrolysis time of silica source and the concentration of ammonia water in the reaction system.By TEM,SEM,N₂ physical adsorption and HRTEM characterization,it was proved that the carbon sphere was hollow structure with regular morphology,ultra-high specific surface area and abundant micromesoporous structure.In addition,all the catalysts show good electrocatalytic performance,with CO Faraday efficiency of more than 85%and high CO current density in a wide potential range.This method was applied to the preparation of Fe and Co single-atom catalysts,and the highly dispersed metal carbon spheres were successfully obtained.This section shows that the hollow porous carbon sphere can be used as an excellent carbon carrier for metal monatomic,and the preparation process is simple,providing ideas for the design of transition metal monatomic carbon carrier..