Study On The Surface Electron Reconstruction Of Transition Metal Catalysts And CO₂ Electrocatalytic Reduction Mechanism

CO₂ exists in the atmosphere as a metabolite of life activities and industrial by-products,and mainly comes from the fields of thermal power generation,automobiles,building materials,metallurgy,chemical industry and other fields.At the same time,CO₂ is also the main form of carbon participating in the material cycle in nature.In recent years,with the development of industry,a large amount of CO₂gas has been emitted,leading to a sharp rise in the atmospheric CO₂ concentration,which has caused a series of environmental problems such as the greenhouse effect.The use of electrical energy generated by non-stable renewable energy sources such as wind energy,solar energy,and tidal energy to convert CO₂ into high-value-added chemicals（CO,methane,formic acid,methanol,hydrocarbons,etc.）to reduce the concentration of CO₂ and achieve resource utilization.At the same time,it can promote the circulation of carbon resources and stores electrical energy in high-energy-density carbon-containing fuels,which can not only convert CO₂ on a large scale,reducing the concentration of CO₂ in the atmosphere,but also effectively store electrical energy.It is a clean,environmentally friendly and sustainable development Methods.With the research and development in the field of electrocatalytic conversion of CO₂,the following problems have been highlighted:（1）high reaction potential and energy consumption;（2）low selectivity of high value-added products;（3）low reaction current density and reaction rate;（4）The reaction mechanism is complicated,and the precise regulation of electrocatalytic reduction of CO₂ cannot be achieved.Therefore,the development of new high-efficiency electrocatalysts and in-depth reseach the reaction mechanism are the keys to solving the above problems.Based on the existing literature,Co atmos with low overpotential as the active component,a series of Co-based catalysts have been prepared by constructing high-concentration oxygen vacancies,multiple active centers and surface electron reconstruction.The structure-activity relationship with the electrocatalytic reduction of CO₂ was explored,and the mechanism of electrocatalytic reduction of CO₂ was explored in order to improve the catalytic activity and selectivity of electrocatalytic CO₂into liquid products.The main research contents and conclusions are as follows:（1）Study on electrocatalytic reduction of CO₂ to formic acid on Co₃O₄-CeO₂/LGC catalyst electrodeCo₃O₄-CeO₂/LGC electrocatalyst with oxygen vacancies was prepared by adding Co₃O₄ into CeO₂/LGC.Co₃O₄ can promote the escape of CeO₂ lattice oxygen to form oxygen vacancies,thereby improving the effective adsorption of CO₂ on the surface of Co₃O₄-CeO₂/LGC.DFT calculations show that the electron density at the edge of the valence band of CO₂*（Co₃O₄）₃-CeO₂ is significantly higher than that of CO₂*CeO₂ or CO₂*Co₃O₄ due to the reconstruction of the electronic state between Co₃O₄ and CeO₂.When CO₂ molecules are adsorbed near（Co₃O₄）₃-CeO₂ oxygen vacancies,due to the special electronic structure of（Co₃O₄）₃-CeO₂,they can effectively bond with CO₂molecules,and electrons can be quickly transported to form highly active sites.According to the calculation of the free energy,it was found that the optimal path of CO₂RR on the Co₃O₄-CeO₂/LGC catalyst was CO₂→CO₂*→COOH*→HCOOH.Experimental results showed that the Faraday efficiency of formic acid on the Co₃O₄-CeO₂/LGC catalyst electrode was 3.3 times and 44.1 times of that on the Co₃O₄/LGC and CeO₂/LGC catalyst electrodes,respectively.On the Co₃O₄-CeO₂/LGC catalyst electrode,the maximum production rate of formic acid was 1.6mmol·m^-2·s^-1·C^-1·mg^-1（-0.75 V vs.RHE）.At the same time,under the condition of-0.75 V vs.RHE for 45 h,the selectivity of formic acid was not significantly reduced,indicating that the Co₃O₄-CeO₂/LGC catalyst possessed good stability.（2）Study on electrocatalytic reduction of CO₂ to formic acid by nanocluster CoO_x/ZrO₂-GICs catalystCo（OH）₂/ZrO₂-GICs precursors were treated by N₂-cold plasma activation to prepare nano-cluster CoO_x/ZrO₂-GICs catalysts.N₂-cold plasma treatment can promote the formation of CoO_x clusters on ZrO₂-GICs carriers.Increasing Co²⁺content on the surface of CoO_x clusters can effectively reduce the*CO₂^δ-generation energy barrier and promote the chemical adsorption of CO₂ on the catalyst surface.At the same time,theπ-π*bond formed by the insertion of ZrO₂-GICs into the compound contributes to the formation of*OCHO,thereby improving the selectivity of formic acid.At-0.35 V vs RHE,the Faraday efficiency of CO₂RR into formic acid on CoO_x/ZrO₂-GICs catalyst electrode was as high as 98.4%,the current density was-8.2 m A·cm^-2,and it has high catalytic stability（lifetime>60 h）.（3）Study on the electrocatalytic reduction of CO₂ to low carbon alcohols with Ag-Co₃O₄-CeO₂/LGC catalyst with multiple active sitesAg-Co₃O₄-CeO₂/LGC composite catalysts with multiple active sites were prepared by introducing transition metals and their oxides（Ag,Co,and Ce）on the surface of low-graphitized carbon（LGC）.Ce active sites with oxygen vacancies can effectively enhance the adsorption of*CO₂^δ-and intermediate states（*CO and*CHO）,reducing the adsorption of H⁺,thereby inhibiting HER and promoting the CO₂RR reaction.On the Co³⁺active site,*CO₂^δ-is reduced to*COOH,and then the*COOH is gradually reduced to methanol.At the same time,*COOH on Co³⁺overflows to the Ag atom,further reducing*COOH to ethanol.At low potential（-0.85 V vs.RHE）,the total Faraday efficiency of low-carbon alcohols was as high as 77.6%（23.4%methanol,54.2%ethanol）,and the Faraday efficiency was not significantly reduced after 60 hours of continuous reaction,indicating that the catalyst possessed good catalytic stability.（4）Study on electrocatalytic reduction of CO₂ to ethanol by H₂-cold plasma activated AgCo surface in situ alloy catalystAg-Co PBA MOF precursors were activated by H₂-cold plasma to prepare AgCo surface alloy catalysts.At room temperature,H₂-cold plasma can promote Ag/Co₃O₄in-situ alloying to form AgCo surface alloys with a depth of 0.5 to 1 nm.The introduction of Co atoms into the surface of{111}Ag can reduce the formation energy barrier of*CO₂^δ-and reduce the reaction overpotential.Electron restructuring occurs on the surface of the AgCo in-situ alloying,forming a carbonyl pool"CO*Ag",which is favorable for the adsorption of CO,thereby improving the coverage of CO*on the catalyst surface,and promoting the formation of*OC-CO*by the C-C coupling reaction.At-0.80 V（7.4 m A/cm²）,the Faraday efficiency of CO₂RR into CH₃CH₂OH on the catalyst is as high as 72.3%,and it has good stability（>48 h）.