Preparation Of Gold/Palladium Nanocatalyst And Its Electrocatalytic Performance For CO₂ Reduction

In recent years,the rapid development of industry and transportation has caused a large amount of fossil fuel consumption,resulting in severe environmental problems and the greenhouse effect,and restricting the sustainable development of social economy.As the main greenhouse gas component,the conversion of carbon dioxide into C₁ or C₂₊high-value products(such as CO,HCOOH,CH₄,C₂H₄ and C₂H₅OH,etc.)has attracted widespread attention from scholars.Therefore,the electrocatalytic reduction of carbon dioxide into value-added chemicals is one of the most challenging and fastest growing areas in the field of catalysis.In the system with potassium bicarbonate as the electrolyte,in addition to the target product,the hydrogen evolution reaction(HER)is the largest competitive reaction in the electrocatalytic reduction of CO₂ reaction(CO₂RR).Due to the high overpotential of CO₂RR,Highly active nano-catalysts are needed to electrocatalytically reduce CO₂.However,efficient electrocatalytic carbon dioxide reduction reactions rely on electrocatalysts with high activity,high selectivity and high stability.Doped oxide nanocatalysts have attracted much attention in the field of electrocatalytic CO₂RR due to their unique and easily adjustable nano-assembled structure,excellent stability and excellent electrocatalytic activity.However,the preparation of doped oxide nano-electrocatalytic CO₂ reduction catalysts with high selectivity,high activity and good durability is still challenging in theory and experiment.Based on the above considerations,this thesis prepared a highly active nanocatalyst with adjustable components through a simple synthesis method,and studied the relationship between the nanostructure,composition and crystal factors and the electrocatalytic CO₂ reduction performance.It provides experimental basis and theoretical reference for the preparation of highly selective and stable doped metal oxide gold/palladium-based alloy nanocatalysts.The main contents of the paper are as follows:1.Using L-glutamic acid as an additive and ethylene glycol as a reducing agent,a cubic hollow shell Pd_nCu_100-n nano-alloy catalyst supported by carbon nanotubes was synthesized at 160°C.The results of ICP-MS found that when the precursor n(Pd Cl₂):n(Cu Cl₂·2H₂O)is 1:1,the synthesized Pd₆₅Cu₃₅/MWCNTs is doped with a small amount of cuprous oxide nanoclusters,while the precursor n(Pd Cl₂):n(Cu Cl₂·2H₂O)were 1:3 and 3:1,the products were Pd₂₅Cu₇₅/MWCNTs alloy nanocatalyst and Pd₇₅Cu₂₅/MWCNTs alloy nanocatalyst.TEM,XRD and EDS-Mapping techniques show that the Pd₆₅Cu₃₅/MWCNTs nanocatalyst doped with a small amount of cuprous oxide nanoclusters has a hollow hexahedron with a large specific surface area;Cu,Pd,O and C are uniformly distributed in the cubic hollow nanocatalyst;The edge length is about 30 nm.Electrochemical test results show that the Pd₆₅Cu₃₅/MWCNTs catalyst doped with a small amount of cuprous oxide nanoclusters has excellent electrocatalytic CO₂ activity and good stability.At-0.845 V vs.RHE,the CO selectivity is 94%,and the activity is stable.The stability is better than Pd₂₅Cu₇₅/MWCNTs and Pd₇₅Cu₂₅/MWCNTs nano-alloy catalysts.Experimental analysis shows that the high performance of Pd₆₅Cu₃₅/MWCNTs doped with a small amount of cuprous oxide nanoclusters is mainly due to the synergy between doped Cu₂O and Pd Cu alloy catalysts to promote CO₂reduction of CO;while the activity of Pd₂₅Cu₇₅/MWCNTs and Pd₇₅Cu₂₅/MWCNTs alloy catalysts is mainly It comes from the synergy between Pd Cu alloys.2.On the basis of the cubic empty shell Pd_nCu_100-n nano-alloy catalyst supported by synthetic carbon nanotubes,in order to reduce the cost of the catalyst and improve the performance,the third metal element Co is introduced to synthesize the cubic empty-shell Pd_nCu_80-nCo₂₀ alloy nano-catalyst.The results of ICP-MS found that when the precursor n(Pd Cl₂):n(Cu Cl₂·2H₂O)is 1:1,the synthesized product is an alloy nanocatalyst doped with a small amount of Cu₂O nanoclusters Pd₄₀Cu₃₁Co₂₉/MWCNTs,and the other two component catalysts are respectively Pd₂₀Cu₆₀Co₂₀/MWCNTs and Pd₆₀Cu₂₀Co₂₀/MWCNTs nanoalloy catalysts.Tests such as TEM,XRD and EDS-mapping show that the synthesized catalyst is a hollow hexahedron with a size of about 45 nm.Cu,Pd,Co,O and C are uniformly distributed in the cubic hollow nanocatalyst.Electrochemical test results show that when Pd₄₀Cu₃₁Co₂₉/MWCNTs doped with a small amount of cuprous oxide nanoclusters are at-0.845 V vs.RHE,the Faraday efficiency of CO is 95%,and the selectivity and stability are better than those of Pd₂₀Cu₆₀Co₂₀/MWCNTs and Pd₆₀Cu₂₀Co₂₀/MWCNTs.Alloy catalyst.It has been analyzed that the excellent CO selectivity of Pd₄₀Cu₃₁Co₂₉/MWCNTs doped with cuprous oxide nanoclusters is due to the synergistic effect between doped Cu₂O and Pd Cu Co alloy,which is beneficial to the improvement of electrocatalytic CO₂ activity.However,the Pd₂₀Cu₆₀Co₂₀/MWCNTs alloy catalyst The performance of the Pd₆₀Cu₂₀Co₂₀/MWCNTs alloy catalyst comes from the synergy between Pd,Cu and Co.3.Ultrafine Au nanowire catalysts doped with different amounts of amorphous Pd O(named Au_30%-Pd O_cluster NWs,Au_50%-Pd O_cluster NWs and Au_60%-Pd O_cluster NWs,respectively)were synthesized by a mild thermal solvent method.TEM test results show that the diameter of the Au nanowire catalyst doped with amorphous Pd O is less than 5 nm.The Au-Pd O_cluster NWs nanocatalyst was characterized and electrochemically tested.When Au_60%-Pd O_cluster NWs is at-0.745 V vs.RHE,the Faraday efficiency of CO is 95%,and the selectivity and stability are better than Au_30%-Pd O_cluster NWs.And Au_50%-Pd O_cluster NWs.Further analysis showed that the high CO selectivity and stability of the ultrafine Au nanowire catalysts with different content of amorphous Pd O are mainly derived from the synergistic effect between the doped amorphous Pd O and the Au nanowire catalyst.In summary,in this paper,a series of doped metal oxide nanocatalysts with different morphologies,compositions and structures were prepared using simple and operable synthetic methods,and their electrocatalytic carbon dioxide reduction performance was studied,and the composition-structure-performance of different catalysts were discussed in depth.The relationship between them provides experimental guidance and theoretical basis for the next step in the design of electrocatalysts with better performance.