Synthesis And Electrochemical Characterization Of Palladium-based Bimetallic Nanocrystalline Catalysts

In recent years,Pd-based catalysts have become more and more widely explored and applied in the field of ethanol oxidation,and Pd-based materials play an important role in anode catalysts for direct ethanol fuel cells（DEFCs）.There is now a lot of research that has proven that by introducing another non-precious metal into the precious metal Pd,many positive effects can be gained.Pd-based materials have many advantages,first of all,it will reduce the cost of catalyst use and reduce the use of precious metals to a certain extent.Secondly,the doping of dissimilar elements can cause more point,line and surface defects on the surface of the catalyst,which leads to an increase in the number of effective catalytic active sites at the catalyst interface.Third,there is a synergistic effect between the two metals,which changes the d-band center of Pd,which in turn improves the resistance and stability of the catalyst.Sn and Ag,which are common in life,were selected as the second introduced metals.In this thesis,several simple hydrothermal synthesis methods were designed,and a series of Pd-based bimetallic catalysts were successfully prepared by adjusting the selection and proportion of precursors,surfactants and reducing agents,as well as changing the reaction conditions,and the morphological structure and electrocatalytic performance of these different types of bimetallic catalysts were characterized and analyzed.（1）Pd-Sn NSAs with different bimetallic ratios were synthesized using palladium acetylacetone（Pd（acac）₂）,dihydrate and stannous chloride（Sn Cl₂·2H₂O）as precursors and cetyltrimethylammonium chloride（CTAC）as surfactants.It can be clearly seen from TEM images that Pd-Sn NSAs gradually become fluffy from the assembly of nanoparticle clusters as the molar ratio of Pd-Sn precursor gradually increases from 1:1,2:1 to 4:1,forming nanoclusters formed by folding and stacking nanosheets.The introduction of Sn element and the formation of the assembly enhanced its catalytic activity for the electrooxidation of ethanol.The electrochemical test results showed that Pd₂Sn₁ NSAs（Pd:Sn molar ratio is 2:1）had the highest catalytic current density of 2346 m A mg^-1 for ethanol,About 3.7 times that of commercial Pd/C counterparts,and exhibited the strongest resistance to toxic intermediates resulting from incomplete oxidation of ethanol in alkaline solutions.（2）Pd_xSn_y nanoparticles（NPs）were prepared by an oil-bath-based method,with Pd Cl₂and Sn Cl₂·2H₂O as precursors,L-ascorbic acid（AA）as a reducing agent for metal ions in the precursor,and a surfactant modified to cetyltrimethylammonium bromide（CTAB）.Among the three alloys,Pd₂₀Sn₂₄（x/y=0.83）NPs have a higher peak current density(2018m A mg^-1)for ethanol oxidation reaction（EOR）,which is about 3.2 times that of commercial Pd/C.Due to the different coordination environment and the change of the d-band center of Pd,the alloyed Pd_xSn_y NPs have a positive effect on all steps of the electrocatalytic reaction and have a positive effect on improving the catalytic efficiency.In addition,Pd₂₀Sn₂₄ NP have excellent toxicity resistance,lower reaction barrier and better long-term stability.In addition,by replacing the second metal with Ag,the Pd-Ag alloy is obtained,which still has high catalytic activity for ethanol oxidation reaction,which indicates that the preparation method is also suitable for other metals.