Synthesis Of Atomic-scale Electrocatalysts Based On Functionalised Supports For The Study Of Their Catalytic Properties

The development of sustainable energy technologies to meet energy needs has led to research into the development of advanced functional nanocatalysts.Single-atom catalysts not only have maximum atomic efficiency,but also exhibit high activity and selectivity,which is due to quantum size effects,the large number of unsaturated coordination sites and the unique interaction between metal single atoms and supports.In addition,the increased understanding of the unique interactions between metal single atoms and supports has begun to revolutionise the development of traditional support-based metal catalysts,which has greatly contributed to the rise of single atoms catalysis.At present,much research has been devoted to the exploration of suitable supports for the loading of high-density metal single atoms,thereby effectively enhancing the number and stability of active sites.While the role of supports in electrocatalytic reactions have often been greatly neglected.Therefore,the selection and optimisation of functionalised supports with catalytic potential can effectively increase the interaction between supports and metal single atoms,which not only effectively stabilises metal single atoms,but also optimises the electronic and atomic structure of single atoms and supports,thus improving its electrocatalytic performance.In this paper,based on the search for suitable functionalised supports,the electronic and atomic structures of supports are further optimised using metal modification,doping,defect construction,morphology modulation and component optimization.All of these can increase the number of anchor sites and catalytic active sites on supports.Ultimately,support-based single-atom catalysts with excellent electrocatalytic performance were obtained.The influence of the interaction between functionalised supports and metal single atoms on the electrocatalytic performance is also further explored.The paper highlights the importance of functionalised supports in the synthesis of single-atom catalysts and their electrocatalytic applications.Details of the work are summarised as follows:（1）In view of the rich C and N coordination（e.g.pyridine nitrogen,pyrrole nitrogen and graphite nitrogen）of graphitic carbon nitride（g-C₃N₄）nanosheets,as well as the advantages of low cost,nontoxicity,specific trapping sites,large surface area,and good stability,Pt single atoms were successfully anchored on g-C₃N₄nanosheets（Pt/CN）for high-efficiency H₂O₂ synthesis.The Pt/CN with ultra-low platinum loadings（Pt:0.21 wt‰）exhibits high activity（the onset potential:～0.81 V vs.RHE）,selectivity（the selectivity of H₂O₂:98%）,and stability toward electrochemical H₂O₂ production.（2）Based on the previous work,transition metal single-atom catalysts based on g-C₃N₄ nanosheets（CNNS）were synthesized by a method similar to that used in research work（1）for efficient electrochemical H₂O₂ synthesis in 0.1 M PBS,in order to reduce the costs of production and deepen the understanding of the interaction between functionalized supports and single atoms.The optimization of CNNS using transition metal single atoms achieves the functionalization of CNNS and enhances the 2e^-ORR selectivity of supports.And the enhanced interaction between the transition single atoms and CNNS facilitates the activity（TM SA/CNNS）.In particular,the Ni_0.10 SA/CNNS exhibits the highest H₂O₂ selectivity（～98%）.The H₂O₂ production rate of Ni_0.10 SA/CNNS is～503 mmol g_cat^-1 h^-1,which is～14.6 times higher than that of CNNS(～34.4 mmol g_cat^-1 h^-1).In conclusion,all TM SA/CNNS showed significantly enhanced electrochemical performance,which provides more reference ideas for the preparation of H₂O₂ by 2e^-ORR.（3）To further investigate the effect of defects as well as doping on functionalised supports in atomic scale catalysts,this work constructed atomic scale Pd catalysts on oxygen vacancy-rich WO_x＿C nanowire networks.Through the carbon modification on tungsten oxide nanowires,the construction of oxygen vacancy and the loading of carbon organic substances are obtained,which effectively improves the OER activity and stability of the supports.And the strong interaction between supports and atomic-scale Pd is further enhanced,thus improving the activity and stability of the support-based metal catalyst.The Pd_1.54/WO_x＿C 1:1 has an overpotential of 19 m V vs.RHE at 10 m A cm^-2 and a Tafel slope of 50 m V dec^-1,which is comparable to the HER activity of commercial Pt-based catalysts.Also,the Pd_1.54/WO_x＿C 1:1 showed minimal loss of current density in tests with 24 h current time profile.The prepared Pd/WO_x＿C exhibits excellent catalytic activity and stability in acidic media,which provides a new strategy for the development of cost-effective and efficient HER electrocatalysts.（4）Based on the analysis of these results,it can be found that the use of nanomaterials with excellent catalytic activity as supports for the construction of single-atom catalysts can often be achieved with half the effort.Herein,the functionalisation of Fe Ni OOH supports（reducing the crystallinity of Fe Ni OOH and constructing ultrathin nanosheets）was achieved through component optimisation and morphology modulation to optimise their own OER activity and construct Pt single atoms catalysts.In particular,the low crystallinity and ultra-thin nanosheets can generate abundant unsaturated coordination sites and reactive sites,which lead to the solid binding of Pt single atoms.Meantime,the enhanced interaction between Pt single atoms and the ultra-thin Fe Ni OOH nanosheets with low crystallinity is used to further increase the activities of HER and ORR.Pt_2.08/Fe₁Ni₁OOH exhibits excellent OER performance,which have a low OER overpotential（1.43 V vs.RHE）at 10 m A cm^-2.Pt_2.08/Fe₁Ni₁OOH also shows enhanced the activity of both HER and ORR,the overpotential is 0.145 V vs.RHE（HER）and the half-wave potential is 0.8 V vs.RHE（ORR）.At the same times,Pt_2.08/Fe₁Ni₁OOH also exhibits excellent OER,HER and ORR stability,which can maintain 99.5%OER and 99%HER activity over 12 hours testing,respectively.And Pt_2.08/Fe₁Ni₁OOH maintains a conversion efficiency of 62%over 300 hours of cycling in zinc-air fuel cells.Based on this,the prepared single-atom catalysts exhibit excellent activities and stability of OER,HER and ORR,which provide a new idea for the construction of low-cost and efficient electrocatalysts.