Preparation Of Pd-based Catalysts And Their Electrocatalytic Performance For Ethanol Oxidatio

Energy crisis and environmental pollution are two major problems in the world today.Fuel cells are developing rapidly under this background.However,the development of fuel cells is limited by some factors such as poor durability,high cost and insufficient fuel supply infrastructure.Among,the storage and transportation of large-scale hydrogen is a huge difficulty.Compared with hydrogen,ethanol has attracted much attention due to its wide raw materials and safe transportation and storage.Thus,direct ethanol fuel cell（DEFC）has been studied by more and more researchers with a simple configuration system,light weight and high power generation efficiency.Nevertheless,the anodic ethanol oxidation reaction（EOR）process of DEFC is complex,the C-C bond is difficult to break,and the reaction kinetics is slow.At present,Pd is one of the most widely studied anode catalysts in DEFC.But it remains a rare noble metal.The introduction for a broad technological use would lead to an irreversible rise in its market price,and pure Pd catalyst is difficult to meet the needs of practical application.Therefore,the construction of efficient DEFC anode catalysts based on Pd has an important research value.In this paper,3D hierarchical Pd Ag alloy nanosheets,surface nitridation Pd Cu alloy nanosheets and Pd nanosheets with rough surface were synthesized respectively,and morphology and structure of catalysts were characterized and analyzed.At the same time,the electrocatalytic activity,stability and anti-toxic ability were studied and explored.The main contents are as follows:（1）3D hierarchical defected Pd Ag alloy nanosheet catalysts were prepared by CO reduction method with about 7 atomic layers.It is found that the appropriate molar ratio of Pd/Ag precursor plays an important role in constructing the novel structure.For EOR,the peak current density of the optimized Pd₇Ag₃ NS/C is up to 9365.9 m A mg_Pd^-1,which stays ahead of Pd₃Ag NS/C,Pd₅Ag₃ NS/C and Pd NS/C catalysts.At the same time,Pd₃Ag NS/C catalyst also possesses enhanced electrochemical stability.The highly enhanced catalytic mechanism of Pd₇Ag₃ NS/C catalyst is mainly attribute to the introduction of an appropriate amount of Ag element,which optimize the binding energy of Pd and accelerate charge transfer.Moreover,3D hierarchical interconnected ultra-thin nanosheets structure promotes mass transfer and accelerates reaction kinetics as a stable skeleton,alleviating Ostwald ripening and reducing total surface free energy to achieve high electrochemical stability.In addition,abundant atomic vacancies and twin defects are recognized as active sites to highly improve catalytic performance,especially peak current density.（2）A novel catalyst,surface nitridation Pd Cu nanosheets,was prepared by a simple nitrogen plasma treatment.It was found that its ECSA is up to 179.1 m² g_Pd^-1 and mass activity is up to 12.8 A mg_Pd^-1 for EOR.In addition,compared with the other four control samples,the stability of N-Pd₆₀Cu₄₀ NS is also significantly improved.The enhancement mechanism of N-Pd₆₀Cu₄₀ NS is mainly attributed to the synergistic effect between the introduction of Cu and surface nitridation,which reduces the R_ct and enhances the anti-toxicity ability.Among,surface nitridation modifies the electronic structure of Pd,reduces the d-band center of Pd,and weakens the bonding between Pd and CO,making CO easier to desorb or further oxidize,so as to improve catalytic activity and anti-CO poisoning ability of N-Pd₆₀Cu₄₀ NS catalyst.Simultaneously,the strengthening stability of N-Pd₆₀Cu₄₀ NS catalyst may be due to the existent N-Pd bonds,which makes structure more stable.（3）Pd nanosheets catalyst with rough surface was synthesized by a step-by-step method.Hydrogen peroxide plays an important role in the formation of rough surface.Electrochemical tests showed that compared with Pd NS,the prepared RS-Pd NS catalyst exhibits highly enhanced catalytic activity as a EOR catalyst,with ECSA up to 43.75 m²g_Pd^-1 and mass activity up to 4000 m A mg_Pd^-1.The enhanced catalytic activity should be attributed to the unique rough surface structure,which provides a large surface area/volume ratio and rich atomic edges and steps as active sites to improve the catalytic activity of catalyst.Meanwhile,it also provides an effective channel for rapid mass transfer,reduces the charge transfer resistance,and greatly promotes the reactants to enter the inner surface of the electrode to accelerate the reaction kinetics.