The Study Of Theoretical Design Of CO₂ Capture And Targeted Conversion Catalysts By DFT

As a greenhouse gas,CO₂ is the"culprit"of aggravating global warming,which has brought many environmental problems.In order to slow down the growth rate of CO₂concentration in the atmosphere and actively respond to the carbon-neutral policy advocated by my country,it is crucial to study new carbon-containing gas enrichment technologies.Among them,capturing,storing,and separating CO₂ by controlling the applied electric field has proved to be an effective method for CO₂ recovery.Using electrocatalytic CO₂ reduction reaction（CRR）technology to convert CO₂ into chemical products with high added value,there have also been many experimental and computational studies.The study of CO₂ capture and reuse technology is beneficial to the sustainable development of renewable energy and environmental protection and is of great strategic significance to the sustainable utilization of resources.The choice of electrocatalyst has become a key condition restricting CO₂ conversion.With the improvement of computing resources and the application of theoretical calculation and simulation in catalyst design,density functional theory（DFT）based on first principles has now been adopted by a large number of researchers.The performance of the catalyst greatly saves the experimental cost and improves the safety of scientific researchers.Based on this,for CO₂capture and reduction,four 2-dimensional（2D）layered materials for CO₂ capture and a 2D material-based single-atom electrocatalyst for CO₂ reduction were investigated using DFT:（1）Using particle swarm optimization（PSO）crystal structure prediction methods and DFT,the two-dimensional material Bi_mC_n was investigated to obtain three structurally stable two-dimensional bismuth carbide materials,namely Bi C-α,Bi₂C-α,and Bi₂C-βmonomolecular layers.Calculations of cohesion energy,Born’s criterion,first-principles molecular dynamics simulations,and phonon spectroscopy show that all three 2D materials have good stability and the Bi C-αmonomolecular film has a graphene honeycomb structure similar to that ofβ-phase bismuth.Considering the spin-orbit coupling（SOC）effect,the hetero-ubiquitous（HSE06）results indicate that the Bi C-αand Bi₂C-βmonolayers are metallic,but Bi₂C-αhas a direct bandgap of 0.40 e V.The results of CO₂ adsorption on the three materials indicate that the Bi C-αand Bi₂C-αmonolayers have three stable adsorption sites,namely C2,the activation capacity of the CO₂ adsorbed molecules is in the order of T4 over T3 over C2.（2）The feasibility of the two-dimensional metallic material Si P₂ loaded with transition metal atoms as a CO₂RR electrocatalyst was investigated by DFT.The calculation results show that Si P₂ material is a metallic material with good electrical conductivity.The results of co-polymerization energy,mechanical shear modulus,molecular dynamics simulations,and phonon spectroscopy calculations indicate that the Si P₂ material is structurally stable and has structural anisotropy.CO₂ cannot be adsorbed on pure Si P₂ substrates,however,after the modification of transition metal atoms from Sc to Cu for Si P₂,we have successfully screened V@Si P₂ materials that can catalyze CO₂ under three constraints,including stable molecular dynamics,high migration potential of the metal atoms,and a suitable bandgap for electrocatalysts after doping.The reduction product of V@Si P₂ is HCOOH,with a potential decisive step（PDS）of*OCHOH→*+HCOOH,a limiting potential of-0.50 V（vs RHE）,and an overpotential of 0.75 V（vs RHE）.（3）The ability of BC₃ nanosheets to capture CO₂ under an applied electric field and their application in the separation and purification of CO₂/H₂/CH₄ was investigated using DFT.BC₃nanosheets are superhard materials that have long been successfully synthesized in the laboratory.The results show that the transition from physisorption to chemisorption of CO₂ can be achieved in the electric field range of 0.0060-0.0065 a.u.The adsorption/desorption of CO₂can be precisely controlled by turning the electric field strength of 0.0065 a.u.on/off,a reversible process.In addition,the selective adsorption of CO₂/H₂/CH₄ by BC₃ can be used to achieve gas separation and purification under different electric fields.（4）A novel two-dimensional monolayer biphosphorylated silicon compound Si P₂ has been successfully predicted using the PSO method.The results of cohesion energy,mechanical parameters,molecular dynamics simulations,and canonical phonon spectroscopy calculations demonstrate the structural stability.The strain has a strong influence on the energy band structure and optical properties of Si P₂,a high-performance CO₂ trapping material that can be used for effective activation and trapping of CO₂ with an adsorption energy of-0.45 e V.At a strain ratio of 9.5%,the conductivity of Si P₂ changes from semiconductor to metallic.（5）The adsorption and separation behavior of CO₂/CH₄/H₂ on the surface of a two-dimensional Al₂C material was investigated by DFT calculations.The applied electric field perpendicular to the surface of the Al₂C material caused a gradual change in the CO₂ adsorption state to chemisorption（change in adsorption energy from-0.29 to-3.61 e V）.The negative electric field does not affect the adsorption of CO₂.The external electric field can activate the C=O bonds in the adsorbed CO₂ state（up to 15%under an applied electric field of 0～0.005a.u.）.Only at an applied electric field of 0.0033 a.u.and temperatures above 525K/675K can either（a）CO₂ adsorption alone or（b）the adsorption/separation reaction of a CO₂/CH₄/H₂mixture proceed spontaneously.The controlled adsorption/desorption of CO₂ by Al₂C nanosheets can be easily carried out by switching the electric field strength at 0.003～0.0033a.u.Both processes are exothermic.The ability of Al₂C material per unit area to capture CO₂under an electric field decreases with the increasing CO₂ concentration,but it still has effective gas separation performance for CO₂/CH₄/H₂ separation.