First-principles Study On The Adsorption And Reduction Properties Of Metal-doped Graphene For CO₂

Current energy consumption and installed capacity of power plants in China have resulted in a large amount of CO₂ emission,which seriously harms the environment and human’s health.In order to reduce the CO₂ emission,we can convert CO₂ into valuable chemicals,such as Formic acid.However,CO₂ itself has no energy content and is a very stable and non-reactive molecule,so the conversion of CO₂ to formic acid is challenging.Therefore,finding a highly active catalyst to promote the reaction is the key to solving the problem.Here,based on the first-principles principle and density functional theory,the adsorption characteristics of CO₂ under different types of graphene-based single atom catalysts（SACs）were studied,including 66 different catalysts adsorbing CO₂made up of selected 6 transition metals（Ti,V,Cr,Mn,Fe,Co）and 11 graphene substrates.The results showed that dsorption height and anchor bond length of metal atoms followed the order Ti>V>Cr>Mn>Fe>Co,and the binding energy of the catalyst followed the order Ti>V>Co>Fe>Mn>Cr.The binding energy of each catalyst was sufficient to meet the stability of the catalyst.When the catalyst is in a single vacancy configuration,there was a negative correlation between adsorption distance of CO₂ and the adsorption energy.Analysis of the electronic properties revealed that charge transfer occurred between CO₂ and the catalyst.CO₂ accepts electrons as the acceptors and metals Atoms and graphene substrates provide electrons as the donors.Analysis of EDD and DOS diagrams proved that CO₂ adsorbed on metal-doped graphene-based catalysts was the result of charge transfer and molecular hybridization.CO₂ could be activated by effective catalysts,promoting the subsequent reduction reaction.Then by comparing the bonding energy and adsorption energy,it was found that the Ti@DV-N4 catalyst showed excellent performance both in terms of stability and adsorption of CO₂.Besides,due to the absence of the double vacancy and the modification of nitrogen atom in the graphene substrate,Ti@DV-N4 maintained a strong activation effect on the CO₂ molecules.Therefore,Ti@DV-N4 was selected as the catalyst for the reduction of CO₂ to formic acid.Next,the CI-NEB calculation method was used to calculate the reduction reaction.The two reaction paths（PathⅠand PathⅡ）of the E-R mechanism were calculated and the corresponding structural parameters and energy changes were introduced in detail.The results showed that the reaction process can be divided into two stages,obtaining the intermediate product COOH^*and formic acid,respectively.By comparing the energy changes in each state of each reaction path,it was found that the cracking of hydrogen determined the speed of the entire E-R reaction.The reaction energy barriers of the two reaction paths were1.38.e V and 2.42 e V,respectively.Therefore,Path I was chosen to be the optimal path for the CO₂ reduction reaction.The research provides theoretical support through first-principle calculations for finding effective catalysts that can reduce CO₂ to formic acid.