Synthesis Of Noble Metal Catalyst Based On High-boiling Solvent System And Application In Electroreduction Of CO₂

The increase of greenhouse gas emissions,especially carbon dioxide emissions,has caused many bad impacts in environment,climate and ecology,recently.Therefore,the recycling of carbon dioxide needs to be developed urgently.Researchers found that electrochemical reduction of carbon dioxide can not only reduce the concentration of carbon dioxide,but also be able to convert CO₂ into fuels,and it has broad application prospects.Researchers further found that metal nanoparticles with controlled surface structure,high surface area and electrochemical activity are ideal electrode materials for the electrochemical reduction of carbon dioxide.Based on these points,we discussed the electrochemical reduction of carbon dioxide by metal nanoparticles.In this dissertation,the preparation methods of"pyramid"Pd nanoparticles and PdCu alloy are mainly proposed and discussed.The structures and properties of these two kinds of electrocatalysts synthesized are characterized here.Major results are summarized as follows:1.Noble metal materials have been demonstrated as excellent catalysts in electrochemical reduction of carbon dioxide."Pyramid"Pd was synthesized based on the preparation of catalyst in aqueous phase,and discussed the electroreduction performance of carbon dioxide of the Pd NPs.Here,we mainly discussed the catalytic properties of Pd nanoparticles of electrochemical reduction of carbon dioxide.The traditional solvent has been changed by us and expanding it to"green solvent"ionic liquid.Because of the high boiling point,conductive property,the fixation of carbon dioxide and other characteristics of the ionic liquid.We have adjusted the reaction temperature and surface stabilizer,polyvinylpyrrolidone?PVP?as the morphology stabilizer,and ionic liquid coated"pyramid"Pd nanoparticles were successfully synthesized by us when the temperature was 100?C.The catalyst has been tested to show excellent performance of electrochemical reduction of carbon dioxide.The ionic liquid adhered to the surface of the Pd nanoparticle,has an excellent impact in decreasing the surface resistance of the catalyst and an increase in the concentration of carbon dioxide adsorbed on the catalyst.The peak potential of electrochemical reduction of CO₂ is only-0.82 V in 0.5 mol/L KHCO₃.2.Although the morphology and the composition of PdCu alloy nanoparticles are remained as a challenge,PdCu alloy nanoparticles are the ideal materials for the electrochemical reduction of carbon dioxide.We have succeeded in synthesizing PdCu alloy with a relatively broad composition by analyzing the disadvantages of existing synthesis schemes and redesigning schemes.Here,we have adopted hot-injection method,oleylamine as the solvent with high-boiling point,limiting the copper source,and adjusting the ratio of copper components.After that,we have further discussed the influence of PdCu ratio and time on the electrochemical reduction of CO₂.CuCl₂ was finally determined as copper precursor by a series of controlled experiments.According to the PdCu ratio of 1:2 and the reaction time of 8h,the PdCu alloy was synthesized,and the peak of electrochemical reduction of CO₂was-0.8 V finally.These results have shown that the catalyst synthesized under this condition can expose more active sites,making the potential of the electrochemical of CO₂ more positively and enhancing the durability of the catalyst.Even if the use of Pd has been reduced,it can also achieve the same catalyst efficiency by a relatively low cost compared with our previous synthesis of Pd.