First-principles Calculation Study On The Performance Of Defect-Regulated Two-dimensional Materials For Electrocatalytic Reduction Of CO₂

The excess carbon dioxide(CO2)emitted by the rapid consumption of fossil fuels has led to serious environmental problems such as the greenhouse effect and ocean acidification,forcing people to find effective ways to reduce the concentration of CO2 in the atmosphere.Among various methods,electrochemical reduction of CO2 to various high value-added chemical raw materials has been widely concerned as an effective way to reduce the concentration of CO2 in the atmosphere.However,CO2 molecule has excellent thermodynamic stability and a large number of reduction products,so it is necessary to find a catalyst with high activity and selectivity.Recently,two-dimensional(2D)materials,such as tungsten disulfide(WS2),nitrogen-doped graphene(C2N),and Graphyne(GY),have shown great properties.However,the process of electrochemical reduction potential in electrochemical catalysis due to their unique microstructure and excellent physicochemical of CO2 usually takes place on the surface of materials.Therefore,it is of great scientific significance and engineering application value to design defects and regulate properties of 2D material surface during catalyst design.In this paper,several typical 2D materials are taken as the research object.Starting from the design and regulation of defects on the base plane and edges of materials,the carbon dioxide reduction reaction(CO2RR)reactivity of these materials is studied.The innovative research results are as follows:(1)The edge structure of WS2 with W atoms exposed in the top layer was established by density functional theory.Through using WS2-xTM-y(x=1,2 or 3;y=1 or 2;TM=Zn,Fe,Co or Ni)models by doping TM atoms on the top layer of WS2,the effects of dopant species,doping concentration and adsorption site on their electrocatalytic activity were investigated.Among the models,the active site for CO2RR is the W atoms.The doping of TM atoms would affect the bond strength between W and S atoms.After the doping of TM atoms in WS2-2TM-1 ones,the electrical conduction of S atoms and the underlying W atoms can greatly be improved.Thus the catalytic activities can be significantly increased,in which the WS2-2Zn-1 model has the best catalytic activity.The limiting potential(UL)of the CO2RR to CO on WS2-2Zn-1 model is-0.51 V;and the Gibbs energy change(ΔG)for the adsorption of intermediates on WS22Zn-1 model are ΔG(COOH*)=-0.37 and ΔG(CO*)=-0.51 eV,respectively.Solvation correction showed that WS2-2Zn-1 could maintain good catalytic performance in a wide range of pH values.The present results may provide a theoretical basis for the design and synthesis of novel electrocatalysts with high performance for CO2RR.(2)Using density functional theory,a monolayer porous C2N supported transition metal trimers(3TM-C2N,TM=Mn,Mo,Ru,Ti)catalyst models were established for the reduction of carbon dioxide(CO2)to C1 product.The results show that the 3TM-C2N catalyst has a stable structure,which not only can effectively adsorb and activate CO2,but also has a good inhibition on hydrogen evolution(HER).The Gibbs free energy distribution shows that the paths of Ci production catalyzed by 3TM-C2N are different.Limit potential(UL)analysis showed that 3Mn-C2N showed the best catalytic performance in 3TM-C2N and the best selectivity for CH3OH and CH4,both of which were-0.44V.These findings not only provide theoretical basis for the experimental regulation of C2N-based catalysts,but also have guiding significance for the development of other efficient CO2RR electrocatalysts.(3)Based on first principles,the model of GY supported triatomic catalyst TM1TM2TM3@GY(TM=Mn,Fe,Co,Ni,Cu and Mo)was established,and the catalytic performance of TM1TM2TM3@GY catalyzing CO2 to produce CO products was systematically studied.The results show that TM1TM2TM3@GY catalyst has a stable structure,and the introduction of transition metal trimers can effectively improve the energy band structure and conductivity of catalysts.Among them,MnMoFe@GY and MnMoCu@GY show the best catalytic activity and CO2RR selectivity,and have a good inhibition on HER.MnMoFe@GY and MnMoCu@GY reduced CO2 to produce CO with UL of-0.73 and-0.36 V.The difference of geometric structure and electronic structure results in the difference of catalytic performance between MnMoFe@GY and MnMoCu@GY.The results show that the synergistic effect of Mn,Mo and Cu is the reason for the best catalytic performance of MnMoCu@GY.These findings not only provide theoretical basis for experimental regulation of GY-based catalysts,but also have guiding significance for the development of other efficient CO2RR electrocatalysts.