Two-dimensional Conductive MOFs Materials For Electrocatalytic Carbon Dioxide Reduction Reactions:a Theoretical Study

In recent years,the energy and environmental problems caused by the excessive burning of traditional fossil fuels have become increasingly serious,and it has become crucial to explore efficient energy conversion technologies for the sustainable use of renewable energy sources such as solar,wind,and tidal energy.Electrocatalytic carbon dioxide（CO₂）reduction reactions can convert CO₂ into fuel molecules or other valuable chemicals,which can effectively reduce atmospheric CO₂ concentration and re-establish a sustainable carbon cycle,and is an effective way to mitigate global warming and energy shortage.Typically,CO₂ is a highly stable and chemically inert linear molecule,so electrocatalytic CO₂ reduction requires a catalyst with high catalytic activity.Two-dimensional metal organic framework materials（2D-MOFs）with high specific surface area,rich pore structure,and flexible and controllable backbone structure are widely used in energy conversion and are excellent candidates for constructing efficient catalysts in recent years.In this thesis,via first principles calculation,we designed a class of two-dimensional metal-hexahydroxybenzene frameworks materials,namely M₃（C₆O₆）₂（M=Cr,Mn,Mo,Fe,Co,Ni,Cu,Ru,Rh and Pd）monolayers.A study of their structure,electrical properties and catalytic activity for CO₂ reduction reactions（CRR）was carried out.First,we explored the structural and electrical properties of the M₃（C₆O₆）₂ monolayers and compared the adsorption strength of CO₂ and*H on the catalyst surface to select the materials with the highest activation capacity for CO₂,followed by the investigation of their activity and selectivity as CRR catalysts.Due to the effective orbital interactions between the conjugated benzene rings and the MO₄ units,all ten 2D-MOFs structures exhibit metallic with good electrical conductivity,with the Mo₃（C₆O₆）₂ material exhibiting excellent catalytic activity and selectivity toward CO₂ and can reduce CO₂ to methane at a limiting potential of-0.67 V.The catalytic activity is better than of the traditional Cu（211）catalyst,which is promising to be an efficient CRR electrocatalyst material.Based on the above study,w we continued to explore the effects of axial hydroxyl coordination on the structure,electrical properties,and CRR catalytic ability of 2D-M₃（C₆O₆）₂materials.In contrast to the 2D-M₃（C₆O₆）₂ monolayers,the structure of Cu₃（C₆O₆）₂ monolayers was severely deformed after the addition of axial hydroxyl ligands due to their poor oxidation stability,While the other nine 2D-M₃（C₆O₆）₂ materials with the addition of axial hydroxyl ligands were structurally stable and exhibited good electrical conductivity.In addition,the selectivity of these nine materials for CO₂ adsorption was significantly improved after the addition of axial ligands.The calculated results showed that both Mo₃（C₆O₆）₂-OH and Ru₃（C₆O₆）₂-OH catalysts exhibited good CRR catalytic activity,and the reduction products were both methane with the limiting potentials of-0.47 and-0.53 V,respectively,and both were smaller than the limiting potential（-0.74 V）in the conventional Cu（211）catalyst.This indicates that the addition of axial ligands can effectively improve the CRR catalytic performance of 2D-M₃（C₆O₆）₂ materials.The addition of axial ligands to the active sites of catalysts is expected to be an effective method to modulate the catalytic activity of MOFs catalysts.