Synthesis Of Highly Dispersed Copper Nanoparticles And Its Performance On Electrocatalytic Carbon Dioxide Reduction

Electrochemical CO₂ reduction reaction?eCO₂RR?is a promising research technique for catalytic reduction of greenhouse gas-carbon dioxide using electrical energy,which can convert CO₂ into long-chain organic compounds such as hydrocarbons and alcohols.However,the structure of CO₂ is stable and the mechanism of eCO₂RR is complicated,requiring the aid of a catalyst with high activity.In recent years,copper-based electrocatalysts are one of the most studied electrocatalysts due to their low cost and the ability to catalyze the production of long-chain organic compounds.The influence of chemical composition and physical structure is related to the adsorption and reaction pathway of reaction intermediates in the catalytic process,and has been discussed in detail both theoretically and experimentally.This dissertation discusses the scale distribution of copper nanoparticles,investigates the dispersion of different carbon-based aerogel materials on copper nanoparticles,and the preparation of efficient and stable eCO₂RR catalytic materials.The detailed research contents are as follows:?1?In this work,Cu²⁺was embedded into a polycondensation structure of resorcinol?R?and formaldehyde?F?via sol-gel polymerization,and the complex was subsequently calcined at high temperature to obtain copper nanoparticles-dispersed carbon aerogels?Cu/CA?.The samples underwent CO₂ activation followed by secondary activation under N₂ atmosphere at different temperatures.The final products obtained were labelled as Cu/CA-CO₂-N₂-T.The existence of highly dispersed Cu⁰ on the carbon aerogels was confirmed by XPS and HRTEM,which exhibited attractive activity towards electrochemical CO₂ reduction reaction?eCO₂RR?,forming carbon product in 0.1 M KHCO₃ aqueous media.Furthermore,the eCO₂RR product distribution varied under different samples.The sample activated under 700??Cu/CA-CO₂-N₂-700?with Cu loading of c.a.5.13 wt%showing remarkable CO faradaic efficiency?FE??75.6%?at-0.96 V?vs.RHE?.Further calcination led to more exposure of copper,and CO dimerization to C₂ product.The high selectivity toward CO by Cu/CA-CO₂-N₂-700 maybe attributed to the high defect density,large surface area,large pore size,and especially their excellent stability in maintaining the metallic nature of Cu component within the hydrophobic carbon aerogels during electrocatalysis,which further prevents the adsorption and reduction of*CO on the catalyst.?2?We demonstrated a rational fabrication of a novel silk fibroin-driven SF-Cu/CA,uniformly distributed in the porous carbon skeleton.We extracted silk protein from silkworm cocoons,add a small amount of copper salt,and use CO₂ gas as an acid catalyst to cause the formation of gels.After high-temperature calcination,the C,N and other heteroatoms in the silk fibroin reduced the metal and achieved high dispersion to obtain N-doped SF-Cu/CA carbon aerogel.The rich amino structure and?-sheet structure of the silk protein was responsible for the inherent N-doping during calcination.In order to improve the catalytic efficiency,a small amount of Zn salt was added as a pore-forming agent during the preparation of SF-Cu/CA,to produce a new catalyst denoted as SF-Cu/CA-1.The SF-Cu/CA-1 had a large specific surface area of935.1 m²g^-1 and the existence of abundant N species in SF-Cu/CA-1 increased the concentration of CO₂ on the surface of the catalyst.Furthermore,the porous structure of the catalyst accelerates the mass transfer of CO₂,and provides multiple desorption pathways for*CO intermediates,resulting in a higher CO yield of at-1.26 V?vs.RHE?,with CO yield as high as 80.03%.This study provides a practical and effective method for the synthesis of highly active eCO₂RR catalyst.?3?The production of syngas?a mixture of H₂ and CO?in eCO₂RR in an aqueous solution is one of the sustainable strategies for utilizing CO₂ in the atmosphere.Generally,when using single-component metal catalysts,such as Ag,Au or Zn for eCO₂RR,the voltage has a great influence on the selectivity,hence the composition of the synthesis gas changes greatly with voltage.This limits its range in the electrochemical production of synthesis gas applications.In this study,silk fibroin-derived CuAg nanoparticle aerogels with different molar ratios of Cu:Ag were synthesized.The catalyst obtained were marked as SF-CuAg/CA-N?N=20%,40%,60%,80%of copper?,and electrochemical measurements showed that the catalyst had an adjustable H₂/CO ratio of syngas.SF-CuAg/CA-20 had FE as high as81.85%at-1.46 V?vs.RHE?.SF-CuAg/CA-60 had a large voltage range and a controllable CO₂ reduction product in aqueous solution.SF-CuAg/CA-60 had an adjustable voltage range of over 500 mV with excellent stability.The SF-CuAg/CA-N composite material prepared in this study provides new possibilities for the design of electrochemical syngas catalysts.