Study On The Performance Of Cu Based Catalyst For Electrochemical Reduction Of CO₂ Based On Density Functional Theory

The burning of fossil fuels and excessive emissions of CO₂make energy and climate issues more and more concerned.Electrochemical reduction technology is one of the most effective solutions so far.However,many catalysts face the disadvantages of poor activity and low product selectivity,it is particularly important to select high-quality catalysts in the process of electrochemical reduction of CO₂.Cu-Sn bimetallic catalyst has the advantages of rich raw materials,high stability and good selectivity,and is the main research direction at present.However,many researchers only focus on the products of HCOOH and CO,and do not study the multi-electron transfer products.From the perspective of theoretical calculation,this topic mainly uses density functional theory to study the electrochemical reduction of CO₂to CH₃OH over Cu-Sn catalyst.The main research contents and conclusions of this paper can be summarized as follows:（1）Through Sn-doped Cu-based catalyst,five catalyst models of Cu（111）,1Sn@Cu（111）,2Sn@Cu（111）,3Sn@Cu（111）and 9Sn@Cu（111）are established and the mechanism of CH₃OH production by electric reduction of CO₂is studied.The charge analysis and structure optimization of the catalyst are carried out,and the adsorption energy of the intermediate and the activation free barrier and Gibbs free energy change of each reaction are calculated.The results showed that CO₂is more inclined to the formic acid（HCOO）salt path for the gradual reduction of CH₃OH over the catalyst surface with lower activation free energy barrier.The optimal reduction path of these five catalysts is,CO₂→HCOO→HCOOH→H₂COOH→CH₂O→CH₃O→CH₃OH.The activation free barriers for Cu（111）,1Sn@Cu（111）,2Sn@Cu（111）,3Sn@Cu（111）and 9Sn@Cu（111）are1.02,0.96,0.91,0.71 and 0.96 e V,respectively.Among the five catalysts,3Sn@Cu（111）has the highest catalytic activity in the reaction of electric reduction of CO₂to CH₃OH,and the elemental reaction of HCOOH+H→H₂COOH is the speed determining step,which is greatly improved compared with CO₂on pure Cu（111）.（2）In order to further increase the Cu-Sn ratio,three alloy catalyst models of Cu₃Sn（100）,Cu Sn（100）and Cu Sn₃（100）are established,and the mechanism of CH₃OH production by electric reduction of CO₂is studied on their surfaces.The projected density of states（PDOS）results of Cu₃Sn（100）,Cu Sn（100）and Cu Sn₃（100）catalysts show that the stability structure order of alloy catalysts is Cu₃Sn（100）>Cu Sn（100）>Cu Sn₃（100）.The results show that the optimal reduction path of the alloy model is consistent with the doping model,which is still CO₂→HCOO→HCOOH→H₂COOH→CH₂O→CH₃O→CH₃OH.The activation free barriers of Cu₃Sn（100）,Cu Sn（100）and Cu Sn₃（100）optimal path speed determination steps are 0.76,0.83 and 0.93 e V respectively,Cu₃Sn（100）shows the highest activity,and the speed determination step is CO₂+H→HCOO.However,the activity of the alloyed Cu₃Sn（100）catalyst is slightly lower than that of the doped3Sn@Cu（111）catalyst.（3）Based on the best path and catalyst in the above conclusions,two dominant solvent models of Water-solvated and H-shuttling are established to explore the effects of water molecule on Cu（111）and 3Sn@Cu（111）.Under the influence of dominant solvent model,the optimal path for the reduction of CO₂to CH₃OH by Cu（111）catalyst changes from H₂COOH→CH₂O+OH to CH₃O+H→CH₃OH,and the required activation free barrier decreases from 1.02 e V to 0.76 e V;the speed determining step of the optimal path for the electrochemical reduction of CO₂to CH₃OH by the 3Sn@Cu（111）catalyst has not changed,it is still HCOOH+H→H₂COOH,and the activation free barrier is reduced from 0.71e V to 0.59 e V.