Nitrogen Electrochemical Reduction Performance Of Highly Dispersed Transition Metal Atoms On Nanoporous Graphene

Ammonia is an indispensable source of nitrogen to sustain the life of an organism.As an alternative to the high-energy Haber-Bosch process,electrocatalytic reduction of N₂ to produce ammonia has the advantages of mild reaction conditions,low energy consumption,and easy product purification.Therefore,the development of highly efficient NRR catalysts is of great significance.Based on the catalyst design,this paper uses density functional theory（DFT）,and explores the stability and NRR catalytic performance of highly dispersed metal catalysts on porous graphene with the help of transmission electron microscope（TEM）electron microscopy.The specific research contents are as follows:（1）Modified carbon material on the surface of nanoporous gold,heat treated to melt and evaporate gold to form nanoporous graphene.On the nanoporous graphene,a large number of stable Au single atoms,as well as relatively stable diatomic pairs and triatomic clusters in some regions were observed by electron microscopy.The electronic structure analysis based on DFT shows that the defect changes the electronic structure of the graphene surface atoms,which is a main reason for the stable combination of Au single atoms and atomic clusters with nanoporous graphene.In addition,the theoretical calculation results also show that the curvature also has an effect on the stability of the atoms.The smaller the curvature,the stronger the fixation effect on the Au atoms,and the calculated diatomic pair and triatomic cluster configurations also agree well with electron microscopy results.This work made it clear that the nanoporous graphene supported transition metal monoatomic and diatomic structures can exist stably,which laid the foundation for the subsequent design of monoatomic and diatomic catalysts.（2）A single-atom transition metal was supported on nitrogen-doped porous graphene to construct a monoatomic NC catalyst for NRR.Through DFT calculations,using Gibbs free energy of N₂,N₂H and NH₂ as descriptors,Fe and Ag single-atom NC catalysts with high NRR catalytic activity and selectivity were selected.The calculation results of the reaction free energy of different paths showed that the potential energy determination step（PDS）of the two catalyst is*N₂ hydrogenation to*NNH.Electronic structure analysis shows that the reason for the high NRR catalytic performance is that the d orbital of the single atom of the transition metal interacts with the p orbital of*N₂,and the charge of the metal atom is transferred to*N₂ to promote the activation of the N₂ molecule,making the NRR reaction easier Proceed to obtain high catalytic performance.（3）A binuclear atom NC catalyst was further designed.Using descriptors to calculate,it is found that the Mo single atom is too strongly adsorbed to the intermediate*NH₂,which is not conducive to the final desorption.While the Fe single atom is too weakly adsorbed to*N₂H,which is not conducive to the first step hydrogenation of nitrogen.After the formation of diatoms,the above problems are significantly improved,and DFT calculations show that the stability of diatomic catalysts is generally higher than that of monoatomic catalysts,so the performance and stability of Mo and Fe binuclear atom catalysts for NRR are superior to single atom catalyst.The electronic structure analysis shows that the reason for the improvement of the catalytic performance after the formation of the diatomic catalyst for Mo atoms is the negative shift of the state density,and the reason for the improvement of the catalytic performance for the formation of the diatomic catalyst for Fe atoms is that the state density moves toward the Fermi level.