Preparation Of Catalyst Assisted By SiO₂ And Applications In Electrocatalytic Reduction Of CO₂

Carbon dioxide（CO₂）is the major greenhouse gas that can be converted into low-cost fuels and high value-added chemicals in order to solve problems such as global warming.Among many CO₂ conversion methods,the use of renewable energy to convert CO₂ has broad application prospects.As an important indicator of electrocatalytic CO₂ reduction reaction（CO₂RR）,the electrocatalytic system with high activity,high selectivity and high stability is an important factor for the application of CO₂RR.Among them,the confined effect of silicon dioxide（SiO₂）can reduce the surface energy of metal atoms and improve the stability of the catalyst.At the same time,Si doping can change the active sites and improve the performance of electrocatalytic CO₂ conversion.Therefore,in this thesis,a variety of catalysts were designed and prepared by using the auxiliary strategy of SiO₂,so as to control the active sites and inhibit the hydrogen evolution reaction（HER）,and a new route for preparing high value-added chemicals by CO₂ reduction were developed.The main research contents and innovations of this paper are as follows:（1）Si-Ni-CNTs-800,a Ni-based carbon nanotube catalyst doped with Si,was prepared by hydrothermal method assisted by SiO₂ coating,which was used for electrocatalytic reduction of CO₂ to prepare carbon monoxide（CO）.In an H-type electrolytic cell with 0.1M KHCO₃ solution as electrolyte,the Faraday efficiency(FE_CO)of the catalyst can reach98%at a potential of-0.9 V vs.RHE（Reversible Hydrogen Electrode）and a partial current density of 21.5 mA cm^-2,and it can be kept stable for at least 12 h.In addition,the Si-Ni-CNTs-800 electrode can achieve more than 90%FE_CO in a wide potential range（-0.6～-1.1 V vs.RHE）.The results show that the rich active sites of Ni-SiO_x in the catalyst are helpful to activate CO₂ to form CO*intermediates and inhibit HER,thus promoting the efficient conversion of CO₂ to CO.（2）Ultra-high-density Cu monoatomic catalyst(TWN-Cu_13.35-600-SAC)was prepared on thin-walled N-doped carbon nanotubes by using SiO₂ confined method,using hydrogen bonded organic framework（HOF）as carbon-based precursor,and was used for electrocatalytic CO₂ reduction to produce ethanol.The results show that the single atom loading of Cu in the catalyst can reach 13.35 wt%.The Faraday efficiency(FE_ethanol)and conversion frequency(TOF_ethanol)of ethanol produced by TWN-Cu_13.35-600-SACs can reach81.9%and 3.458 h^-1,respectively in an H-type electrolytic cell with 0.5 M Cs HCO₃ solution as electrolyte at-1.1 V vs.RHE potential.At the same time,the catalyst also showed high partial current density(35.6 mA cm^-2)and good stability（over 25 h）.Experimental research and density functional theory（DFT）prove that short-distance adjacent Cu-N₃ active sites can promote C-C coupling,which is beneficial to electrocatalytic reduction of CO₂ to ethanol.