Computational Study Of Carbon Dioxide Electrochemical Reduction To Formic Acid By Single Atom Alloy In Solvent System

With the excessive consumption of fossil fuels,the increasing concentration of CO₂ in the atmosphere has caused people to worry about global warming and other environmental problems.Electrocatalysis is an effective method to improve the utilization of CO₂ conversion,close the carbon cycle and thus achieve the"double carbon"goal of our country.Among the electrocatalysts for CO₂ conversion reported so far,Bi and In metal materials have attracted much attention due to their unique catalytic performance of CO₂ reduction to HCOOH.In particular,the targeted conversion efficiency of Bi and In has become a focus of attention of researchers through alloying strategy.However,it is difficult to select catalysts by experimental method due to the large variety of alloys due to the adjustable properties of composition and composition.Therefore,theoretical and computational chemical methods provide an effective way to accurately regulate the atomic level of Bi and In alloys.Although researchers have reported the reaction mechanism of CO₂ reduction to HCOOH catalyzed by some Bi-based and In-based alloys through theoretical calculation methods,the following two key scientific problems still exist:（1）HCOOH has a strong hydrophilicity,but most of the current calculations are carried out In vacuum environment,resulting in inconsistent simulation results with the real situation.（2）The second metal type and Bi and In crystal surface have great influence on catalytic CO₂ reduction performance,but the reaction mechanism and structure-activity relationship are still unclear.Based on this,this paper carried out a systematic study on the electrocatalytic reduction of CO₂ to HCOOH by Bi-based and In-based monatomic alloys through density functional theory calculation.Firstly,this paper selected four Bi and In catalyst surfaces and proposed a set of correction parameters for aqueous solvent action,which was used to correct the solvation in CO₂ reduction reaction catalyzed by M₁Bi and M₁In（M=d-zone elements（Ti,Fe,Ni,Cu,Zn,Pd,Ag,Pt,Au）and p-zone elements（Ga,In,Sn,Sb,Pb,Bi））monatomic alloy.And then,this paper calculated the catalytic conversion mechanism of 49 single atom alloys,and screened out 4 candidate electrocatalysts for efficient reduction of CO₂ to HCOOH,which provided theoretical guidance for the experimental study of this reaction and the structural design of catalysts.Specific research contents are as follows:1.The role of water solvent in Bi and In electrocatalytic reduction of CO₂ to HCOOH reaction:The catalytic mechanism of Bi（001）,Bi（012）,In（101）and In（002）electric reduction of CO₂ in aqueous solvent system was studied by means of density functional and ab initio molecular dynamics,and the influence of aqueous solvent on the important intermediates in the process of CO₂reduction to HCOOH was revealed.The results showed that *OCHO and *COOH formed hydrogen bonds with water molecules in the solvent,weakened their adsorption on the catalyst surface,and then changed the reaction potential energy curve.The binding energy between water solvent and high exponent crystal plane is greater than that between water solvent and low exponent crystal plane,indicating that water molecule is beneficial to stabilize the reaction intermediates on high exponent crystal plane.The binding energy between water solvent and Bi surface is lower than that on In surface,indicating that Bi-based catalyst is more affected by solvation.Furthermore,a set of correction values of solvation energy was proposed for the calculation of CO₂ reduction reaction:*OCHO and*COOH are-0.28 eV and-0.36 eV on Bi（001）,Bi（012）,In（101）and In（002）,-0.30 eV and-0.38 eV,-0.24 eV and-0.35 eV,-0.26 eV and-0.37 eV,respectively.The solvation energy correction of*CO is-0.22 eV.Compared with the calculated results In the gas phase,the catalytic activity of Bi（001）and Bi（012）In reducing CO₂ to HCOOH in aqueous solvent system is improved,while In（101）and In（002）are slightly decreased.The potential energy control steps on the In（002）surface change from*+CO₂→*OCHO in the gas phase to*OCHO→HCOOH in the liquid phase,while the other three surface potential energy control steps remain unchanged.Compared with the side reactions of CO₂ reduction to CO and hydrogen evolution,the water solvent action did not change the selectivity of the four Bi and In surface catalytic CO₂ reduction,and HCOOH was still the dominant product.This work provides an essential set of solvation parameters for reasonable simulation of the mechanism of electrocatalytic CO₂ reduction.2.Calculation study on the electrocatalytic CO₂ reduction to HCOOH performance of M₁Bi and M₁In single atom alloy:By density functional theory method,based on the water solvent correction parameters proposed in this paper,The catalytic performance of 49 M₁Bi,M₁In monatomic alloy catalysts for electrocatalytic reduction of CO₂ to HCOOH was investigated.The calculation results show that the p-doped monatomic alloys have better thermodynamic stability than d-doped monatomic alloys.Compared with Bi（001）,In（101）and In（002）,the monatomic alloy based on Bi（012）has higher CO₂ reduction capacity.Compared with the low index surface,the high index of the crystal surface is beneficial to improve the selectivity of HCOOH products,that is,M₁Bi（012）is better than M₁Bi（001）,M₁In（002）is better than M₁In（101）.Considering the reduction of CO₂ to CO and the side reactions of hydrogen evolution,The single atom alloys with the best catalytic performance on the four crystal planes are Zn₁Bi（012）（U_L=-0.14 V）,Cu₁Bi（001）（U_L=-0.21 V）,Sb₁In（101）（U_L=-0.26 V）,Bi₁In（002）（U_L=-0.19 V）.ΔG（*OCHO）can be used as a descriptor for evaluating catalytic CO₂ reduction activity.Zn₁Bi（012）at the top of the volcanic curve has a moderate adsorption free energy（0.12 eV）.It has the lowest limiting potential of CO₂ reduction to HCOOH.This work provides theoretical support for the structural design of catalyst for CO₂ reduction to HCOOH single atom alloys.