Noble Metal Palladium-based Nanostructured Catalysts And Their Electrocatalytic Performance For Ethanol Oxidation Reaction

Due to the irreversible consumption of non-renewable fossil energy and the need of environmentally friendly development concepts,high efficiency fuel cells（FCs）have become a research hotspot,and high performance nanocatatologists used in FC catalytic layers have also become the focus of research and exploration.Noble metal palladium（Pd）has been used in direct ethanol fuel cells（DEFCs）due to its excellent electrochemical performance in ethanol oxidation reaction.However,it has high cost,limited catalytic activity and poor anti-toxicity.The introduction of other metals can solve the problem of cost,also can produce a lot of defects,the surface active site exposure quantity increase.Moreover,the synergistic effect will lead to the decrease of the d-band center,which will also reduce the adsorption amount of toxic products,thus increasing the catalytic activity.Therefore,in this thesis,two kinds of alloy catalysts with different compositions and sizes of palladium-lead（Pd-Pb）nanoparticles and nano-dendrites were prepared by simple solvothermal method and lower temperature water bath method.Through the experience in the synthesis of palladium-lead（Pd-Pb）bimetallic alloy catalysts,the synthesis of palladium-manganese（Pd-Mn）and palladium-bismuth（Pd-Bi）catalysts was further investigated.The structures of these alloys were analyzed and their electrochemical properties were characterized under different conditions.（1）Different proportions of Pd（acac）₂ and Pb（acac）₂ were dissolved in N,N dimethylformamide（DMF）,cetyltrimethylammonium bromide（CTAB）and urea were added as the surfactant,and ascorbic acid（AA）was added as reducing agent.Pd-Pb alloy nanoparticles（NPs）with controllable content and size were synthesized by solvothermal method.With the increase of Pb doping,the XRD diffraction peaks of Pd₁₂Pb₁,Pd₉Pb₁ and Pd₆Pb₁ NPs shift to the left,because the larger Pb atom replaces the Pd atom,the lattice expands.With further increase of Pb content,Pd₃Pb₁NPs can be divided into ordered Cu₃Au type Pd₃Pb structure.Among these Pd-Pb NPs,Pd₉Pb₁ NPs have a relatively high current density(2620 m A mg^-1),and Pd₃Pb₁NPs has the best anti-toxicity and long-term stability,and the activity,anti-toxicity and cyclic stability of all alloy samples are better than that of commercial Pd/C catalysts commonly used in the market,which is closely related to their morphological characteristics and electronic structure.Analysis of its dynamics found that,the higher temperature and the higher KOH/C₂H₅OH concentration are conducive to the higher electrocatalytic activity of Pd-Pb NPs（2）Using low temperature water bath synthesis method,Pd Cl₂ and Pb Cl₂ as metal precursors,dissolved in Na Cl aqueous solution,adding sodium dodecyl sulfate（SDS）as surfactant,Na BH₄ alkali solution as reducing agent for water bath heating to obtain Pd-Pb bimetallic alloy catalyst with adjustable proportion of nano-dendritic structure（NDC）.The resulting products were named Pd₃Pb₁,Pd₆Pb₁,Pd₉Pb₁ and Pd₁₂Pb₁ NDC.With the increase of Pb,the XRD diffraction angle of the four groups of samples is shifted.The sizes of Pd₃Pb₁,Pd₆Pb₁,Pd₉Pb₁ and Pd₁₂Pb₁ NDC are 16.8nm,16.6 nm,16.4 nm,and 16.3 nm,respectively,and the larger Pb atoms replace Pd atoms,resulting in lattice expansion.Among these Pd-Pb NDC,the Pd₉Pb₁ NDC has a higher current density(1920 m A mg^-1)and a larger starting potential.At the same time,Pd₉Pb₁ NDC with the highest activity also had better anti-toxicity and cycling stability,with the current density remaining 85.2%after the completion of 300 cycles.Analysis of its dynamics also found that,the catalytic activity of the samples to ethanol can be improved under high temperature and high concentration of KOH/C₂H₅OH solution.（3）Based on the synthesis experience and method of the completed system,the synthesis of other less studied Pd-based bimetallic nanocatalysts such as Pd-Mn and Pd-Bi catalysts was attempted.Pd-Mn nanocatalysts were synthesized by low temperature water bath method with Pd（acac）₂ and Mn Cl₂ as metal precursors.Using Pd（acac）₂ and Bi（NO₃）₂·5H₂O as metal precursors,Pd-Bi alloy nano-catalyst was synthesized by solvothermal method.To characterize the structure performance at the same time,the Pd-Mn samples of the XRD diffraction peak shift to the left,and Mn atomic radius smaller,analysis of intermetallic compound may have been formed,Pd-Bi sample XRD diffraction peak shift to the left,the larger the Bi atoms replaced the Pd,lattice expansion.The current density of several samples in 1 M KOH+1 M C₂H₅OH was simply tested.Both samples have good catalytic performance,and the subsequent anti-toxicity improvement and other mechanisms need to be explored.