Synthesis Of Pd-based Binary Electrocatalysts Using PdO Hydrothermal Method And Investigation Of Their Electrocatalytic Properties

An important advantage of anion-exchange membrane direct alcohol fuel cells（AEM DAFCs）is that the kinetics of both alcohol anodic oxidation and oxygen cathodic reduction in alkaline media become much faster than in acidic media,making it possible to use non-platinum and low-cost metal catalysts.Among different types of fuel cells,direct methanol and ethanol fuel cells have attracted the interest of more researchers,their high energy density,low pollution emissions,and easy-to-transport liquid fuels,which make them easier to use as energy substitutes.But there are still some issues that hinder the expansion of the battery,the most important of these is the cost of the catalyst.In this paper,the palladium catalysts were modified by doping,that is,using lower-cost metals as co-catalysts to explore the electro-oxidation properties of the synthesized catalysts for methanol and ethanol.The specific experiment contents are as follows:（1）For the first time,the electrocatalytic performance of the pyrolysis products of the mixture including PdO+PdCl₂+MWCNTs was investigated.And in this work,three kinds of catalysts were prepared by using a very simple method of pyrolysis.The prepared catalysts were thoroughly characterized by using XRD and TEM.XRD patterns substantially indicated that after the pyrolysis process new substances of metallic Pd were produced.TEM images proved that some nanoparticles with a size less than 20nm were immobilized on the surface of MWCNTs after the pyrolysis process.The results of the electrochemical experiments verified that catalyst a,i.e.,the pyrolysis products of the mixture including PdO+PdCl₂+MWCNTs,showed the best electrocatalytic activity for MOR among all the synthesized catalysts.Showing the fact,that the electrocatalytic activity of catalyst a（the pyrolysis product of the mixture containing PdO+PdCl₂+MWCNTs）was much better than other catalysts,and it was the major contribution of this work,which implied that PdCl₂ could probably be employed as an additive agent to promote the electrocatalytic ability of a Pd-based catalyst.（2）In the present work,five kinds of composites were produced by a very facile method of pyrolysis,in which the influence of atomic ratio of Pd to Ni on both the physicochemical properties and the electrocatalytic activities of the resultant catalysts was systematically investigated.Physical characterization results indicated that both the composition and morphologies of the synthesized catalysts were remarkably affected by the atomic ratio of Pd to Ni.Electrochemical results（CV,CA,EIS,etc.）showed that addition of additive NiO can improve the catalytic activity of the system.However,when excessive Ni O is added,the reaction sites of fresh Pd atoms will be seriously blocked,thus the adsorption of ethanol molecules and further oxidation will be affected.catalyst b,which was the pyrolysis product of the mixture with an atomic ratio 1 to 1（Pd/Ni）,exhibited the best electrocatalytic activity among all the prepared catalysts.（3）We used a new composite catalyst,namely multi-walled carbon nanotubes（MWCNTs）supported palladium and lead catalysts（expressed as Pd_xPb_y/MWCNTs）.Using PdO,PbO and MWCNTs as starting materials,hydrothermal method was used to prepare materials.We have demonstrated through XRD,EDS and other characterizations and there will be a small amount of Pd nanoparticles after pyrolysis,and achieve the best effect by adjusting the amount of Pb incorporated into the metal.The electrocatalytic activity of the obtained catalyst in ethanol solution was mainly detected by electrochemical tests such as CV,CA and EIS.Electrochemical measurements showed that the EOR peak current on the Pd₁Pb₁/MWCNTs catalyst was almost 9 times larger than the Pd-free catalyst,and the initial potential of the EOR decreased by about 100 m V.（4）Multi-walled carbon nanotubes supported palladium and iron composite catalysts were prepared by hydrothermal method using Fe₂O₃ as additive,and the effects of different molar ratio of Pd/Fe on the catalytic performance of EOR in alkaline environment were discussed.The formation of metal Pd particles can be confirmed by XRD and EDS,and the metal Pd particles attached around the multi-walled carbon nanotubes can be visually observed through SEM and TEM images.Under alkaline conditions,we performed electrochemical tests such as cyclic voltammetry（CV）,chronoamperometry（CA）and electrochemical impedance spectroscopy（EIS）on all prepared catalysts.We also discussed the changes in current after many cycles,and the results proved that the catalyst prepared by pyrolysis at150℃shows good stability.The b-catalyst Pd₁Fe₁/MWCNTs composite catalyst with the atomic ratio of 1:1 has the highest stable current and the best catalytic activity in EOR.