C₂N-graphene Supported Single-atom Catalysts For CO₂ Electrochemical Reduction Reaction:A DFT Study

With the development of the global economy,the demand for energy is increasing,and the emission of carbon dioxide（CO₂）in the atmosphere is increasing.Ideally,the amount of carbon dioxide produced and consumed on Earth is dynamically balanced to keep the amount of carbon dioxide in the atmosphere stable.However,as human industrial activity intensifies,this balance has gradually been broken,and more and more carbon dioxide has caused problems such as global warming.In order to effectively alleviate the"greenhouse effect"and reduce the content of CO₂ in the atmosphere,the recovery and conversion of CO₂ is one of the important ways.In the prior art,CO₂ electrochemical reduction reaction is a new technical means for large-scale synthesis of high value-added small molecules and fuels（for example:CO,methane,methanol,formic acid,formaldehyde,etc.）at room temperature and mild conditions.Density functional theory（DFT）calculation of the new graphene-supported metal monoatomic M@C₂N electrocatalytic activation of CO₂ inert bond to obtain CO₂ electrochemical reduction reaction mechanism,rate limiting step,reaction Gibbs free energy potential energy map,Information on structure-effect relationships and electronic structures.This paper will clarify the intrinsic catalytic activity of the metal monoatomic active site and screen out the best single-atom catalyst for the target product,providing a theoretical basis for the bottom-up,rational and efficient design of CO₂ electrocatalytic cathode catalytic materials.The main results were as follow:（1）A single layer of p（2×2）C₂N graphene model was established,which has 12 metal monoatoms M（M=Ti,Mn,Fe,Co,Ni,Cu,Ru,Rh,Pt,Ag,Pd and Au）.In the C₂N graphene,the cyclic density functional theory（DFT）method was used to study the electrocatalytic reduction of CO₂ by M@C₂N single atom catalyst（SAC）.The results show that the binding strength of M monoatoms and N atoms supported in the pyridine（N6）cavity is moderate,and neither M atoms diffuse to form metal nanoclusters due to weak bonding,nor is the bonding too strong.Lead to catalyst poisoning.At the same time,AIMD calculations show that M@C₂N exhibits high stability under conditions of 500K,and M monoatoms do not form dimers（M₂）or trimers（M₃）.（2）Moreover,by introducing solvation effect,zero energy and entropy effect to obtain Gibbs free energy reaction potential energy surface,key information such as reaction path,potential determining step（PDS）and target product of different M single atoms are determined.The results of DFT study show that the vast majority of SAC can promote the activation of O=C=O inert bond and the subsequent protonation step,where*COOH→*CO→*CHO is the main way to produce methanol and methane,*OCHO→*HCOOH→*CHO is a secondary route for the production of methanol and methane.At the same time,It is found that*CO+H⁺+e^-→*CHO is most likely to be the potential determining step and breaking the scaling relation of*CO and*CHO binding on M@C2N SACs.In general,among twelve metals screened,M@C2N SACs where M=Ti,Mn,Fe,Co,Ni,Ru are identified to be effective in catalyzing CO2 RR with lowered overpotentials（0.58V⁰.80V）.