Theoretical Study On The Catalytic Performance Of Two-dimensional Carbon-based Materials Supported Transition Metals For Nitrogen Reduction Reaction

Ammonia is an indispensable raw material for industrial and agricultural production.But the current industrial production method Haber-Bosch process requires strict reaction conditions and emits large amounts of CO₂.In contrast,electrochemical nitrogen reduction reactions are very promising as nitrogen reduction reactions with the advantages of environmental friendliness and low energy consumption.However,it is still challenging to find a stable,active and selective catalyst.Meanwhile noble metal catalysts play a key role in electrochemical energy conversion and storage technology for nitrogen reduction reactions（NRR）.However,their scarcity and cost severely hinder their large-scale commercial application.Loading transition metal atoms onto the carrier surface in a dispersed form can effectively enhance the utilization of catalytically active atoms and thus reduce the cost of electrochemical ammonia reduction.How to enhance the catalytic activity and atom utilization of catalysts has been a major challenge for both academia and industry.Based on the above reasons,in Chapter 3 we systematically investigated the adsorption energyΔE（N₂*）,ΔG（N₂*→N₂H*）andΔG（NH₂*→NH₃*）of 23 transition metal single atoms doped with GY,which are three key NRR parameters affecting the catalyst activity.We selected six promising transition metal（TM）atoms（Ti,V,Cr,Mn,Ru,Os）doped to GY for detailed NRR investigation,and found that Mn-GY is with good NRR activity and selectivity with an onset potential of 0.42 e V.The results of this study provide guidance for the application of TM-GY in the field of electrocatalytic NRR.In chapter 4 we systematically investigated the effect of metal-free（MF）single atom doping of GY on the structure and electronic structure.Fourteen models of GY doping by seven metal-free atoms（B,N,O,F,P,S,Cl）were calculated.N₂ can only be adsorbed and activated on the B-substituted sp-C doped GY model.It has an over-potential of 0.47 e V and a rate-limiting step for the adsorption of N₂.The results and data in this chapter will help to understand the NRR catalytic performance of metal-free doped GY.In Chapter 5 we systematically investigated the NRR catalytic performance of six transition metal atoms co-doped with metal-free atom B on GY,including the adsorption energy ofΔG（N₂*）,ΔG（N₂H*）,andΔG（N₂H*）on N₂.We screened the NRR performance of Os-B-GY catalysts as superior to that of Os-GY and B-GY.We also calculated his energy band and total density of states,projected density of states before and after adsorption of N₂,spin density,differential charge analysis,Bader charge transfer,COHP for Os-B-GY,which showed that Os-B-GY,with good electrical conductivity during end-on adsorption of nitrogen,can promote charge transfer,thus facilitating the adsorption and activation of reaction intermediates.The optimal path for its reaction is the distal path with an over-potential position of 0.35 e V,and the decisive step is NH₂*→NH₃*.The results of this study provide guidance for the application of TM-B-GY in the field of electrocatalytic NRR and promote the experimental and theoretical development of ammonia synthesis from nitrogen.The experimental results of the above systematic study can provide useful guidance for the design of novel and efficient NRR electrocatalysts.