Synthesis Of Pd-based Bimetallic Alloy Nanocrystals And Their Electrocatalytic Performance For Ethanol

Palladium（Pd）has been widely used as an ideal anode catalyst for direct ethanol fuel cell（DEFC）due to its high catalytic activity for ethanol oxidation.However,its high cost and limited activity have always been the problems of precious metal catalysts.Lots of studies have shown that the synthesis of Pd based bimetallic alloy nanocatalyst by introducing another metal can effectively solve the above problems.Compared with pure Pd catalyst,the advantages of Pd based bimetal alloy nanocatalysts are mainly reflected in the following aspects.First,the introduction of another metal reduces the content ratio of Pd in the alloy catalyst,thus reducing the production cost of direct ethanol fuel cell.Secondly,the interdoping of different elements may cause a large number of defects in the catalyst,thus increasing the number of catalytic active sites exposed on the surface.Finally,the synergistic effect between the bimetals will reduce the d-band center of Pd and weaken the adsorption capacity of toxic products produced by incomplete oxidation of ethanol on Pd surface,thus enhancing the toxicity resistance of the catalyst.In addition,Pd-based one-dimensional materials have always been the focus of nanomaterials research because of their superior structural properties.Therefore,the preparation of high-performance palladium-based bimetallic alloy nanocatalysts with one-dimenstional structure morphologies and compositions has become a key research topic.In this paper,a series of palladium-silver（Pd-Ag）and palladium-lead（Pd-Pb）bimetallic alloy nanocatalysts with different metal ratios were synthesized by simple hydrothermal method by using different metal precursors and reducing agents,and their morphology and electrochemical behavior in different electrolyte solutions were systematically analyzed.（1）Palladium acetyl acetonate（Pd（acac）₂）was used as Pd source,silver nitrate（Ag NO₃）was used as the second metal source,ethylene glycol（EG）was used as reaction solvent,glucose and ethylene glycol were used as co-reductants,and four kinds of Pd-Ag NDC（Nano-Dendrite Crystal）alloy nanocatalysts with different palladium/silver content ratios were synthesized by simple hydrothermal method.TEM results showed the morphology of the as-made samples possess"wire"structures formed by interconnecting Pd-Ag alloy particles.The subsequent characterization results show that the size of the Pd-Ag NDC alloy nanocrystalline particles will change to some extent by regulating the amount of Ag components.In addition,the introduction of Ag also affects the charge transfer between nanoparticles,which improves the electrocatalytic performance of Pd-Ag NDC catalyst for EOR.Electrochemical test results show that Pd₅Ag₁ NDC possesses the highest EOR catalytic performance,and the peak current density can reach 1950 m A mg^-1.In addition,Pd₅Ag₁ NDC showed the strongest resistance to toxic intermediates produced by incomplete oxidation of ethanol in alkaline solution.After 300 cycles in ethanol/KOH solution,the peak current density of Pd₅Ag₁ NDC is 1605 m A mg^-1,which is 82.3%of the highest current density.Moreover,the catalytic performance,cycle stability and toxicity resistance of Pd₆Ag₁ NDC,Pd₄Ag₁ NDC and Pd₃Ag₁ NDC for ethanol are far superior to those of commercial Pd/C catalysts.This may be caused by the synergistic effect between Pd-Ag bimetals reduces the d-band center of Pd,optimizes the coordination structure of electrons,and improves the overall performance of Pd-Ag NDC catalyst.（2）A series of Pd-Pb alloy nanocatalysts with different element ratios were synthesized by one-step hydrothermal method using palladium chloride and lead chloride as metal precursors and sodium borohydride as reducing agent.TEM images show that Pd-Pb alloy is a network structure composed of nanowires.Electrochemical test results showed that Pd₆Pb₁ NNWs（Nanowire Networks）had the highest catalytic current density of 2344 m A mg^-1 for ethanol,which was 3.83 times that of commercial Pd/C catalyst.The catalytic current densities of Pd₈Pb₁ NNWs,Pd₄Pb₁ NNWs and Pd₃Pb₁ NNWs are 2174,1936 and1728 m A mg^-1,respectively.After 300 cycles,the activity of Pd₆Pb₁ NNW still retained92.9%of the maximum current density value,which was much higher than that of commercial Pd/C catalyst.After 5000 s timing current test,Pd₆Pb₁ NNWs showed excellent toxicity resistance.In addition,Pd₆Pb₁ NNWs catalyst was used as the experimental object,and it was found that the catalytic activity of Pd₆Pb₁ NNWs catalyst for ethanol oxidation reaction was improved with the increase of temperature,KOH and ethanol concentration.In addition,a series of Pd-Co and Pd-Cu alloys were synthesized by changing the precursors of the experimental process,which showed high activity for ethanol oxidation reaction,indicating that the synthesis pathway is also suitable for other metals.These findings provide a convenient way to synthesize alloy catalysts with high activity for ethanol,which provides strong information support for promoting the practical application of Pd based alloys.