Theoretical Study On Electrocatalytic CO₂ Reduction With Transition Metal Atoms Embedded In Porphyrin Molecular Catalyst

As people’s lives become more dependent on fossil fuels,the amount of carbon dioxide emissions in the atmosphere has increased year by year,leading to increasingly prominent environmental problems in today’s society,which has aroused the interest of many experts and scholars.Among them,the electrocatalytic reduction of CO₂is considered to be a more effective method to solve this problem.This method can not only reduce the emission of CO₂in the atmosphere,but also convert it into an energy carrier for reuse.In the past few decades,the research and development of electrocatalysts have produced products with different selectivity and activity.At present,most of the research is to convert carbon dioxide into high value-added products,such as C1 products including carbon monoxide（CO）,formic acid（HCOOH）,methanol（CH₃OH）,methane（CH₄）and C2 products including ethanol（CH₃CH₂OH）and ethylene（C₂H₄）.In order to improve the conversion rate of products,many scholars mainly focus on metal nitrogen carbon（MNC）molecular catalysts,while porphyrins molecular catalyst is one of the better representatives.Therefore,porphyrin-based catalysts become one of the ideal materials to improve the CO₂conversion rate and product selectivity.In this paper,the electrocatalytic reduction of CO₂with transition metal embedded in porphyrin molecular catalyst is systematically studied theoretically.The main contents are as follows:1.Electrocatalytic CO₂reduction reaction（eCO₂RR）is a promising technology for the conversion of waste CO₂into raw materials or synthetic fuels for the chemical industry.The development of a catalyst with high activity and selective electrocatalytic reduction of carbon dioxide is the difficulty and focus of the practical application of this technology.The electrocatalytic reduction of CO₂over porphyrin molecular catalys（PMC）with metal atom M as the active center（M/PMC,M=Fe,Os and Ru）is studied by using density functional（DFT）calculations.Calculations show that the use of Fe/PMC catalyst to generate methane requires the smallest limiting potential,and the optimal path obtained is:*+CO₂+8H⁺→C*OOH+7H⁺→C*O+6H⁺→*CHO+5H⁺→CH₂O*+4H⁺→CH₃O*+3H⁺→CH₃O*H+2H⁺→*CH₃+H⁺→*+CH₄.At the same time,the relationship between metal and M/PMC is analyzed by using density of states.Based on further studies on the activity and selectivity of electrocatalytic CO₂catalysts,it provides a theoretical basis for the rational design of porphyrin molecular catalysts for electrocatalytic CO₂reduction and their applications in high-performance equipment.2.Studies have shown that hybridization of d orbitals of transition metals and porbitals of non-metal atoms or the use of materials such as metal carbides and nitrides is a very promising method.By exploring the adsorption energy and the corresponding reaction free energy of the intermediate in the process of electrocatalytic CO₂reduction with transition metal embedded porphyrin catalysts（Rh/PMC and Ir/PMC）,the correlation between the catalyst and the reaction is obtained,and the best path to form methane is indicated.By comparing the energy changes of the respective reactions of Rh/PMC and Ir/PMC,the limiting steps for the formation of CH₄by the two catalysts are obtained.The results showed that the embedded transition metal affected the structure and catalytic activity of e CO₂RR intermediates.By comparison,it is found that Rh/PMC is more effective in carrying out e CO₂RR.The catalyst model is predicted using the d-band center,and a model with higher accuracy is obtained.In this study,the d-band values of the two catalysts are compared with E_F,and the catalyst with better catalytic activity is obtained.This conclusion provides a design guide for the development of efficient transition metal-embedded porphyrin molecular catalysts that enable CO₂reduction to clean energy.3.With the increase in the use of fossil fuels worldwide,carbon dioxide emissions are increasing day by day.By converting carbon dioxide（CO₂）into new fuels by electrocatalysis,this not only alleviates the increasingly serious environmental problems,but also provides new energy for people’s lives.To this end,the reduction of CO₂to C1products（CH₄）and C2 products（CH₃CH₂OH）is studied by imbedding transition metal dimer into porphyrin molecules（Rh Cu/PMC and Rh Rh/PMC）as catalysts.The limiting steps for the two catalysts to form CH₄and CH₃CH₂OH are determined by all reaction pathways.The calculation of density functional shows that Rh Cu/PMC（limiting potential:-0.11V）is superior to Rh Rh/PMC（limiting potential:-0.93V）in electrocatalysis of CO₂to CH₄,in which the conversion of*CHO to CH₂O*is the limiting step.Compared with Rh Rh/PMC catalyst,the limiting potential of Rh Cu/PMC for CH₃CH₂OH production is lower（Rh Cu/PMC is-0.46V,Rh Rh/PMC is-0.55V）.By studying the mechanism and reaction energy,it is obtained that Rh Cu/PMC has good selectivity for the formation of CH₃CH₂OH.This work mainly studies the process of electrocatalytic reduction of CO₂,and further explore the influence of more effective catalyst on its reduction process.This study can provide a reference for the design of metal dimer-embedded porphyrin molecular catalysts,and provide a theoretical basis for obtaining electrocatalytic CO₂reduction with higher activity and selectivity.