Synthesis Of Single Atom Catalysts By Electrochemical Method And Its Application Study

Single-atom catalysts(SACs)usually refer to catalysts in which isolated metal atoms are used as active centers dispersed on a support.This catalyst perfectly inherits the advantages of homogeneous catalysts and heterogeneous catalysts.With its 100%atomic utilization,well-defined and uniformly distributed active centers,high atomic activity,easy separation and recycling,and stability,in just a few years,single-atom catalyst has quickly become a new frontier in the catalysis and has aroused the research enthusiasm of many scientific researchers.Many synthesis strategies of single-atom catalysts have been developed,including wet-chemistry,pyrolysis routes,high-temperature atom capture method,etc.Various single-atom catalysts with excellent performance have also been synthesized,and then used in CO oxidation,water–gas shift reaction,selective hydrogenation and other organic reactions.However,limited by the synthetic methods and the choice of supports,the development of these catalysts in other fields has been relatively slow.For example,the support of traditional single-atom catalysts is usually metal oxide or carbon nitride and other materials with poor conductivity,which greatly limits the application of single-atom catalysts in the field of electrocatalysis.Therefore,in order to apply single-atom catalysts in more fields,it is urgent to develop a universal method for preparing single-atom catalysts,including different types of metal single atoms and support materials.Moreover,due to the inherent high surface free energy of single-atom catalysts,in order to avoid the occurrence of agglomeration,the weight loadings of single-atom catalysts is often very low,which leads to that sometimes the overall catalytic performance is not as good as that of nanoparticle catalysts.It is a fatal flaw for application of single-atom catalysts in industrial production.In order to break the shackles of the application of single-atom catalysts in certain fields and broaden its application in the field of catalysis,the research work in this thesis first constructed a single-atom catalysts with strong conductivity through electrochemical methods from the perspective of support modification,and then apply them in the field of electrocatalysis.After that,we further developed a cryo-electrochemical deposition method,which can not only prepare a series of metal single-atom catalysts universally,but also realize the preparation of three high-loadings noble metal single-atom catalysts.These three representative noble metal single-atom catalysts have shown excellent catalytic performance in the fields of classical electrocatalysis,photocatalysis and organic catalysis,respectively.The main content of this paper is mainly expanded from the following parts:Chapter 1:IntroductionThis chapter first introduces the basic concepts and development history of single-atom catalysts,and introduces in detail the commonly used characterization methods,main synthesis strategies and common applications in single-atom catalysts.Finally,it summarizes the basis of the topic selection,research content and research innovation of this thesis.Chapter 2:The design of partial nitridation on the Ni framework substrate to achieve the immobilization of Pt single atoms for electrocatalytic hydrogen evolution and photoelectrocatalytic water reduction in neutral electrolytesThis chapter proposes a new partial nitridation modification strategy.Through the coordination of the lone pair of electrons of the N atom and the unoccupied d orbital of the Pt atom,the single Pt atom is successfully anchored on the porous nickel foam with strong conductivity by electrochemical methods,which successfully gets rid of the limitation of the traditional weakly conductive support.The single-atom catalyst is successfully applied in the field of electrocatalysis,and high-efficiency electrochemical hydrogen evolution performance is realized in the neutral electrolyte.It is even integrated as a co-catalyst on the Cu₂O nanowire photocathode,and then applied to photoelectrocatalytic water reduction,exhibiting extremely high photocurrent density and good PEC conversion efficiency.Chapter 3:A universal method for preparing metal single-atom catalysts—cryo-electrochemical depositionAlthough in the previous chapter,we have successfully applied single-atom catalysts in electrocatalytic reactions by low-temperature nitridation modification on metal supports,and exhibited excellent catalytic performance,it is also noted that the single-atom catalyst obtained by this preparation method still has certain limitations.This preparation method still lacks effective strategy to limit the occurrence of inter-atom agglomeration during the preparation process,and the problem of low single-atom loadings still exists,which is not conducive to the practical application of single-atom catalysts.Therefore,in this chapter,we have developed a general synthesis strategy for high-loadings single-atom catalyst——cryo-electrochemical deposition.The freezing method can greatly inhibit the agglomeration between atoms,thereby ensuring that a high-loaded single-atom catalyst is obtained,and we can also directly control the single-atom loadings by controlling the amount of electricity during the electrochemical deposition process and regulate the distribution of single atoms to meet actual demands.Using this method,we have not only successfully prepared a series of single-atom catalysts containing various types of metal atoms,but also realized the immobilization of single-atoms on supports with different spatial dimensions,and more interstingly,these single-atoms can also interact with supports composed of different elements.In addition,the cryo-electrochemical deposition method can also allow us to prepare single-atom catalysts in which multiple metal atoms coexist,which is expected to exert effects in some complex tandem,cascade reactions or domino reactions.Chapter 4:Application of noble metal single-atom catalysts prepared by cryo-electrochemical deposition in electrocatalysis,photocatalysis and organic catalysis The versatility of the cryo-electrochemical depostion proposed in the previous chapter in the preparation of single-atom catalysts allows us to design the desired single-atom catalysts more easily and directly according to actual needs.In this chapter,in order to verify the practical value of this preparation method,three high-loading noble metal single-atom catalysts were prepared by cryo-electrochemical depositin method.They have shown excellent catalytic performance in classical electrocatalysis,photocatalysis and organic catalytic reactions.Moreover,for precious metals with scarce resources and high prices,the high atomic utilization of single-atom catalysts is of great significance for industrial processes that rely on precious metal catalysis.This synthesis strategy of cryo-electrochemical depositin is expected to help single-atom catalysts be applied in more fields,and may accelerate the process of industrial application of single-atom catalysts.