Design,Preparation,and Application Of Ag/Lu-N-C Materials In Electrocatalytic Carbon Dioxide Reduction

The electrocatalytic CO₂ reduction reaction（CO₂RR）utilizes clean and renewable energy sources such as solar power,wind energy,and tidal energy to convert CO₂into high-value chemicals,providing a sustainable carbon-neutral pathway for energy storage.However,the CO₂RR process is complex with multiple product pathways,making the design and preparation of efficient CO₂RR catalysts a focus and challenge of research.Metal-nitrogen-carbon（M-N-C）catalysts have been widely studied due to their high surface area,good stability,tunable electronic structure,and high conductivity.However,the high-temperature preparation process of M-N-C catalysts inevitably leads to the coexistence of atomically dispersed metal-nitrogen coordination（M-N_x）sites and internal carbon/nitrogen（C/N）defect sites.In most previous studies,these two active sites have often been independently discussed.This independent approach to CO₂ catalytic sites design does not reflect the true nature of the entire catalytic process,limiting a deep understanding of the M-N-C electrocatalytic process and the development of more efficient electrocatalysts.Therefore,in this study,two types of Ag/Lu-N-C catalysts were obtained by introducing low-coordinated,low-Tammann temperature transition metal Ag and high-coordinated,large atomic radius rare-earth Lu into nitrogen-doped porous carbon（N-C）matrices.Through a comprehensive combination of experimental and theoretical simulations,the relationship between M-N_x sites and intrinsic defect sites in the two Ag/Lu-N-C catalysts was revealed.Based on this,the mechanism of cation-enhanced CO₂electrocatalytic performance of the Ag-N-C catalyst was elucidated by controlling the interfacial microenvironment of the catalyst.The main findings of this paper are as follows:1.The Ag-N-C electrocatalyst was designed and synthesized,and the conformation relationship between defect sites and Ag-N_x sites in Ag-N-C materials was discussed,and the CO₂RR performance was studied.The obtained results revealed the pyrolysis creation of edge-hosted Ag-N₃ site with adjacent N-defect was thermodynamically favorable in Ag-N-C,through the selective C/N-Ag and C-N bond cleavage.The DFT calculation showed that the K⁺cations in a KHCO₃ electrolyte was apt to fall into the N-defect sites of Ag-N-C,which electrostatically anchored HCO₃^-anions,thus facilitating the adsorption of CO₂ species on single Ag atoms.This synergistic effect promoted the generation of bicarbonate intermediates and*COOH species for the efficient production of CO with high Faraday efficiency up to 95.21%.2.The Lu-N-C electrocatalyst was designed and synthesized,and the conformation relationship between defect sites and Ag-N_x sites in Ag-N-C materials was discussed,and the CO₂RR performance was studied.The experimental and simulation tests were conducted and revealed that the formation of a Lu–N₆ structure site with an individual defect is thermodynamically favorable in Lu–N–C.The high atomic number and mass of Lu and the strong coordination capacity of its atoms result in a good CO₂RR performance of the Lu–N–C catalyst with a Faradaic efficiency（FE）of up to 95.1%and a current density of 18.2 m A cm^-2 for CO production.Furthermore,using KHCO₃ electrolytes facilitates the fall of the K⁺cations into the defective sites of Lu–N–C,enabling better CO₂capture and activation,which increases the catalyst conductivity for Lu–N–C.Moreover,remarkable current density(124 m A cm^-2)and FE（90%）were obtained for CO production using this catalyst in a flow cell.3.In this study,CO₂RR experiments in KHCO₃ solution were conducted using Ag-N-C（Ag-N-C-700,Ag-N-C-800）catalysts with varying defect densities.It was observed that the Ag-N-C-800 catalyst,which had a higher defect density,exhibited better electrocatalytic activity.Experimental and theoretical simulations revealed that the porous carbon and nitrogen materials exhibited an adsorption effect on K⁺ions,which improved the random distribution of K⁺ions on the electrode surface.This,in turn,reduced the coverage of protons at the interface kinetically.Additionally,by jointly regulating the surface microenvironment of the catalyst through the influence of cations on the charge of the external Helmholtz layer,CO₂RR was promoted to produce CO products.By investigating the effect of different cations on the electrocatalytic performance of the catalysts,it was found that Ag-N-C had the strongest limitation on Cs⁺ion,and Cs⁺had the most significant enhancement effect on the electrocatalytic performance.In summary,this thesis presents a systematic evaluation of high-performance M-N-C catalysts,which were obtained by regulating metals with different coordination energies,namely low coordination Ag and high coordination Lu.By combining experimental and theoretical analyses,we established the conformational relationship between M-N_x sites and defect sites in the M-N-C.Through exploring the mechanism of enhancing M-N-C electrocatalytic performance by regulating cation species,we revealed the M-N-C electrocatalytic process.This study provides a basis for guiding and designing high-performance M-N-C catalysts and opens up new avenues for research in this field.