Preparation Of Palladium Nanoflowers And Palladium-lead Nanowires And Their Electrocatalytic Performance

In the past decade,Pd and Pd-based catalysts have been shown promising applications such as fuel cell,oxygen reduction reaction,electrochemical biosensors and so on due to the excellent catalytic activity and relatively low price.Especially,they show a more desirable catalytic performance for ethanol electrooxidation in alkaline media.As we all know,the morphology and structure of catalysts have an important influence on the catalytic performance which can be enhanced by optimizing the morphology and structure as well as synergistic effect.Herein,we had synthesized Pd nanoflowers（Pd NFs）,PdPb nanoparticles（PdPb NWs）and PdPb nanoparticles（PdPb NPs）by different ways and characterized its structure and properties.（1）Pd NFs were prepared by a facile route with the assistance of carrageenan and the thorns can be tunable by adjusting the concentration of the reducing agent AA.XRD and TEM revealed that Pd NFs had a good crystallinity.Electrochemical data showed that Pd-AA60 possessed the largest ECSA among all the as-prepared samples which was beneficial to the maximum utilization of Pd atoms.Pd-AA60 exhibited the highest catalytic current density for the electrooxidation of ethanol while the Pd NFs with the thick thorns still retained 96%of the highest activity after 300 cycles due to the stable structure.（2）PdPb NWs with different ratio of Pd and Pb were prepared through hydrothermal method.The introduction of Pb was the key factor to successfully prepared 1 D nanowire.Pd₆₅Pb₃₅ have a large aspect ratio with a diameter of 3.5±0.4 nm and hundreds nanometers for length.HRTEM images revealed that there are a large number of convex and concave area and twin boundaries in Pd₆₅Pb₃₅.These lattice defects provided a lot of highly active sites for improving the electrooxidation of the ethanol.Moreover,the results of XPS showed that the presence of Pb atoms optimized the electronic structure of Pd then weaken the toxic intermediates adsorption onto the surface of the catalysts.This would be helpful for improving the antipoisoning abilities of the PdPb NWs.Electrochemical data revealed that Pd₆₅Pb₃₅ exhibited the highest catalytic current density about 3460 mA mg_Pd^-1 among all the samples which was about6.3 times higher than commercial Pd/C.In addition,all the PdPb NWs had the higher activities and stronger cycle stabilities than pure Pd.It was confirmed that the synergistic effect play a positive role in electrooxidation of ethanol.Further analysis found that Pd₆₅Pb₃₅ had a stable structure and optimized surface atomic arrangement,even in an acidic media for a long time it would keep high catalytic activity as well.（3）Carrageenan was used as capping agent to prepared PdPb NPs through a water bath method.The ratio of Pd and Pb show a big difference in morphology of nanoparticles.The preliminary characterization and analysis found that the PdPb NPs had a large size when the Pd content was high.Because of the low utilization of Pd atoms,the sample showed a poor catalytic performance.In contrast,when the Pb content was low,the synergistic effect was not obvious.It showed a little improvement in the catalytic performance.Meanwhile,we also researched the effects of KBr on as-prepared samples.As complexing agent,KBr can react with PdCl₂ to form stable[PdBr₄]^2-.This not only improves the solubility of PdCl₂,but also changes the rate of the reaction.The resulting smaller nanoparticles enhanced the catalytic activity.However,further research were necessary for choosing the optimal parameter to prepared high-effective catalysts.