Mechanisms Of Electrochemical Reduction Of CO₂ Over Metal Catalysts At Constant Potential

Since the industrial revolution,the massive use of fossil fuels has led to CO₂becoming a greenhouse gas with high levels in the air,causing a negative impact on global climate issues that cannot be ignored.Important issues such as carbon peaking and carbon neutrality are also set to solve the problem of excessive CO₂emissions.Electrocatalytic CO₂reduction can be driven by electricity to convert CO₂into small molecules of organic compounds such as HCOOH,CO,CH₄and C₂H₄by the action of a catalyst to achieve carbon sequestration.This process is very fast and under mild conditions,and produces organic small molecules with some economic value while consuming CO₂.However,the reaction mechanism of the process of CO₂electrocatalytic reduction is very complicated,and the reduction products and selectivity are affected by various aspects such as electrode potential,catalyst,p H,electrolyte,and pressure.Therefore,an in-depth study on the mechanism of CO₂electroreduction reaction can help to find highly selective electrocatalysts with low overpotential.Based on density functional theory（DFT）calculations,most of the theoretical research works have used the CHE model to investigate the thermodynamic aspects of the CO₂electrocatalytic reduction reaction.However,the original computational hydrogen electrode（CHE）model is a charge-neutral interfacial model that does not take into account the role of solvent effects and electrode potentials.After continuous development,solvent effects can be more appropriately considered into the CHE model,but there is still no more suitable approach for the introduction of electrode potential.The more common method of applied ions has good simulation effect but large computational resource requirement,while the method of controlled charge has small computational resource requirement but average simulation effect.In this thesis,we optimize the common applied ion method based on DFT calculations,reduce its demand on computational resources,and incorporate the electrostatic effect of electrode potential into the CHE model to form a new constant potential model（CHE+U）,and investigate the mechanism between the thermodynamic properties of CO₂electrocatalytic reduction and electrode potential under this constant potential model（CHE+U）,and compare it with the traditional CHE model（non-constant potential model）.the main studies include:（1）To investigate the mechanism of CO₂electrocatalytic reduction reactions on the surfaces of Cu,Ag,and Au metals（111）（100）（110）with high selectivity for the deep reduction products of CO or CO,which are common under the non-constant potential conventional CHE model,and to investigate the mechanism of CO₂electrocatalytic reduction reactions on the surfaces of Cu,Ag,and Au from the perspective of competition for key intermediates（*COOH and*HCOO）and from the perspective of the potential-limiting step of the decisive step theory.The reasons for the high selectivity of the deep reduction products of the three metals with CO or CO and to investigate the feasibility of Cu,Ag,and Au alloying strategies for improving the selectivity of CO deep reduction products.（2）To investigate the mechanism of CO₂electrocatalytic reduction reactions on the surfaces of Pb,Tl,and In metals with high selectivity for HCOOH products,which are commonly found under the non-constant potential conventional CHE model,and to investigate the reasons for the high selectivity of Pb,Tl,and In metals for HCOOH from the perspective of competition for key intermediates（*COOH and*HCOO）and from the perspective of the potential-limiting step of the decisive step theory.The reason for the consistency between the high selectivity of HCOOH products and the high overpotential of hydrogen precipitation on different metals is also investigated from the perspective of electrostatic interaction forces.（3）To investigate the mechanism of the CO₂electrocatalytic reduction reaction on Cu（100）surface at different electrode potentials under the constant potential CHE+U model,and to investigate the effect of electrode potential on the CHE model in terms of the adsorption structure of reactants and products and the degree of adsorption energy affected by electrode potential,as well as the degree of reaction free energy of key intermediates（*COOH and*HCOO）affected by electrode potential.The effect of electrode potential on the calculated results was investigated.