Synthesis Of Carbon-based Catalysts And Their Performance For CO₂ Electroreduction

In recent years,with the constant development of industrialization and urbanization in the world,the temperature of the earth has raised faster and faster due to the excessive CO₂emissions,which is seriously affecting the ecological balance of nature and the living conditions of human beings.Therefore,it is very important to control the emission of CO₂ and reduce the concentration of CO₂ in the atmosphere.Because of the simple process,mild reaction conditions and high conversion efficiency,electrocatalytic reduction of CO₂ has gradually become a hotspot in the field of energy conversion research.For further promoting the development of the basic research of electrocatalytic reduction of CO₂,designing the electrocatalysts with high selectivity and activity has been more and more important.Carbon-based materials have been widely used in the field of electrochemistry due to many advantages,such as the wide sources,high conductivity and stable structure.On this basis,through the method of heteroatom doping,the researchers have prepared a variety of nitrogen doped carbon catalysts and metal,nitrogen co-doped carbon catalysts,which have showed an excellent catalytic performance.However,the quantitative contribution of the active centers is fundamentally elusive.Therefore,in this paper,by the method of covalent bonding,the elements of N,Ni were introduced into carbon materials,and the nitrogen-doped carbon materials and nickel,nitrogen co-doped carbon materials were prepared,realizing the functionalization of the graphene oxide.The relationship between the density of activity site of pyridine nitrogen and nickel nitrogen and the catalytic activity of the catalyst was quantitatively analyzed by means of XPS.The main research contents and results are as follows:?1?The N-doped carbon catalysts with different N contents were synthesized using the graphene oxide,ethanediamine and 4,4'-bipyridine as precursors,through a same functionalization process,we found that the precursors with benzene ring have a better nitrogen-doping result,the N contents have a marked improve.In this paper,by testing the performance of the CO₂RR,with 2.4 times increase of the nitrogen content,the CO Faradaic efficiency and current density both showed an order of magnitude increase in the potential range from-0.6 to-1.2 V vs RHE.By analyzing the existence form of nitrogen group,the results show that for the non-metallic nitrogen doped carbon materials,the increase of contents of pyridinic nitrogen and pyrrolic nitrogen in the material is beneficial to improve the Faraday efficiency and partial current density of the product CO.At the potential of-1.1V?vs.RHE?,the contribution of 1 at%pyridinic or pyrrolic nitrogen to the catalytic activity of the materials was close to 3.5 mA m^-2.?2?Using the triethylenediamine nickel complex as nickel and nitrogen sources.By different functionalization processes,the two types of model catalyst were obtained on the basis of graphene oxide.?I?the first type of model catalyst with nickel nitrogen carbon structure?Ni-N-C?.?II?the second type of model catalyst with Ni-N-C coated by nitrogen-doped carbon layer.The difference of surface area between the model catalysts indicated that the combination of Ni²⁺and carbon materials prefers at defect sties or edge sites.The HAADF-STEM and XANES show the atomic dispersion of nickel species.DFT calculations confirm that the Ni-N-C₃ site is likely the active site of Ni-N-C catalyst.By analyzing the relationship between the chemical composition of each model catalyst surface and the catalytic performance of the material,the results show that the contribution of Ni-N structure to the catalytic activity is 60 times of pyridine nitrogen structure,and the introduction of Ni species can significantly improve the catalytic activity of the materials.The content of Ni-N structure has 1.3 times increase and the activity of the material nearly has 2 times increase by covering the carbon layer and impregnating with nickel.