Mechanistic Study Of CO₂ Reduction To Ethylene Catalyzed By Cu/Cu₂O Loaded Fluorine-Modified Graphene

Electrocatalytic reduction of CO2(CO2RR)coupled with renewable energy power is an emerging technology for effective CO2 conversion and production of high valueadded platform compounds.Ethylene is one of the most demanded chemical products in the world,thus it is important to realize the synthesis of ethylene in a mild,environmentally friendly,and energy-saving way.The large electronegativity and small atomic radius of the F atom create unique physicochemical properties.Fluorine-modified copper catalysts are expected to improve CO2RR performance and ethylene selectivity,but the specific correlation between the modification pattern and reaction activity and selectivity remains to be investigated in depth.In addition to the modification of active species such as metals and oxides,the design of the support and the cluster-support interactions in cluster-loaded catalysts require detailed study.Herein,based on the framework of density functional theory,this work constructs the fluorine-modified Cu and Cu2O surfaces and explores the electronic structure of the catalyst surface,such as electronic density of states,differential charge density,and vibrational frequency.The energy analysis on the adsorption and important steps of key intermediates were also performed.Based on the previous results,the cluster-loaded catalytic system was constructed,Cu and Cu2O clusters were loaded on the fluorine-modified graphene surface,and the interaction between the surface and clusters and electronic properties were investigated to probe the key steps and products of CO2 reduction and summarize the energy pathway diagram.It was found that the modification of F on the F-Cu(111)surface enhanced the adsorption of*CO and improved the electron transfer from the surface to the reaction intermediates.The presence of both Cu0 and oxidized Cuδ+ species on the modified Cu surface facilitated the product selectivity of C2 products.The introduction of F species also promoted the formation of*CHO,the hydrogenation product of*CO,due to the enhanced*CO adsorption.By comparing the energy diagrams and products of the different hydrogenation paths,it was found that the F-Cu surface was more selective for C2H4.In addition,the F-modified Cu2O surface exhibited higher activity than Cu2O surface.The coupling of*CO on the F-Cu2O surface was less likely to occur,whereas increasing the hydrogenation of the intermediate was more favorable for the subsequent C-C coupling.In order to investigate the synergistic catalytic effect of carbon-based support with good electrical conductivity on the CO2RR process,the catalytic system with active species loaded graphene was constructed.The Cu clusters with different atomic numbers(Cux,x=1-8)were modeled,where the average binding energy and second-order energy difference of the Cu4 magic cluster in the gas phase were higher,indicating the more tightly-bounded Cu atoms.The introduction of F strengthened the interaction between Cu4 and graphene surface,promoted the electron transfer of Cu clusters,futher activated the graphene surface,and established favorable conditions for the subsequent reaction.The top site of Cu cluster(Cu4 top)is the dominant site for intermediate adsorption and the coupling of two*CO molecules(energy barrier of 1.823 eV)due to the undercoordinated environment.Cu2O-FDG surface was constructed in the same way as the Cu-FDG surface.Although it is relatively facile for the activated CO2 on the surface of Cu2O-FDG to generate*CO,the weaker binding ability of Cu2O clusters on the graphene surface makes it difficult for further coupling of*CO molecules to generate C2 products after the hydrogenation,which may require larger size of Cu2O clusters loaded on the FDG surface to enhance the adsorption stability of the clusters.