Controlled Synthesis And Electrocatalytic Performance Of Fe₃C（Co,Ni）/N/C-Based Bifunctional Electrocatalyst

With the continuous depletion of fossil fuels and the increasingly serious environmental pollution,it is urgent to find an alternative material.Direct alcohol fuel cells（DAFCs）can directly convert chemical energy into electrical energy through electrochemical methods.The process is not affected by the Carnot cycle,and the energy conversion efficiency is high.Therefore,fuel cells have potential applications in replacing fossil fuels.However,fuel cells also have some disadvantages.The reaction progresses are slow and it is difficult to meet the commercial demand.Therefore,it has become a hot research topic to seek high efficiency electrocatalysts.At present,the electrocatalysts for anodic alcohol oxidation and cathodic oxygen reduction reaction（ORR）,Pt and Pt-based materials are considered to be the most effective catalysts.However,Pt and Pt-based are short of resources,expensive,and are prone to alcohols oxidation intermediate products poisoning,which leads to the decrease of stability.Therefore,it is significance to research the high efficiency and low price non-Pt catalyst.In this work,the Fe₃C（Co,Ni）encapsulated by nitrogen doped carbon nanotubes non-Pt electrocatalysts have been studied（Fe₃C（Co,Ni）/N/C）.The electrocatalytic activity of ORR in alkaline environment was studied.A series of Fe₃C/N/C-based modifications were carried out.The bifunctional electrocatalysts were obtained by Pd nanoparticles and bimetallic Pd-M（M=Au,Ag,Cu）loading.The research contents are as follows:（1）Nitrogen doped carbon nanotubes coated iron carbide,cobalt and nickel were prepared by calcination method（Fe₃C@NCNTs,Co@NCNTs,Ni@NCNTs）.The morphology,crystal structure and component of the electrocatalysts were tested by using X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,high-resolution transmission electron microscopy（HTEM）,Brunner-Emmet-Teller（BET）and X-ray photoelectron spectroscopy（XPS）.The traditional three electrode system was used to test the electrochemical properties.They are cyclic voltammetry（CV）,linear sweep voltammetry（LSV）and electrochemical impedance spectroscopy（EIS）.The electrocatalytic activities of the three catalysts for ORR were investigated in alkaline conditions.The results show that the three electrocatalysts had good catalytic activity and stability for ORR,which is better than commercial Pt/C.（2）Based on the research of Fe₃C@NCNTs,Co@NCNTs and Ni@NCNTs,the Fe₃C@NCNTs was selected as the support.The Pd nanoparticles loaded on Fe₃C@NCNTs（Pd/Fe₃C@NCNTs）electrocatalyst was synthesized by photochemical reduction method.The morphology,crystal structure and component of the electrocatalysts were tested by XRD,SEM,TEM,HTEM and XPS were analyzed.After Pd loading,the microstructure and the charge transfer of the Pd/Fe₃C@NCNTs electrocatalyst was calculated by density functional theory（DFT）.The calculating results show that the charge transfer was enhanced in the Pd and Fe₃C@NCNTs complex region.This was beneficial to the electrochemical activity of the electrocatalyst.The electrocatalytic performance of the electrocatalyst for the oxidation of ethanol and ethylene glycol（EOR,EGOR）and ORR was investigated by electrochemical method.The results show that the Pd/Fe₃C@NCNTs electrocatalyst exhibited good electrocatalytic activity and stability for EOR,EGOR and ORR in the alkaline medium,which were better than commercial Pd/C and Pt/C.（3）The Pd-Cu,Pd-Ag,Pd-Au bimetallic nanoparticles were loaded the Fe₃C@NCNTs to form Pd-Cu/Fe₃C@NCNTs,Pd-Ag/Fe₃C@NCNTs,and Pd-Au/Fe₃C@NCNTs electrocatalysts.Then the crystal structure,morphology and component of the electrocatalysts were characterized by XRD,SEM,TEM,HTEM and XPS.The success of bimetallic loading was also proved.The results of electrochemical performance test exhibited that the three electrocatalysts had good electrocatalytic activity for the EOR and EGOR in alkaline medium.Moreover,they had good resistance to CO poisoning.The electrocatalytic activity of the Pd-Au/Fe₃C@NCNTs electrocatalyst was best in three electrocatalysts,which was better than that of commercial Pd/C.Compared with the Pd/Fe₃C@NCNTs electrocatalyst,the catalytic activity of these electrocatalysts for ORR had slight enhance in alkaline medium.In addition,different proportions of Pd-Au were investigated in the work.When the mass ration of Pd and Au was 2:1,the electrocatalytic activity of Pd-Au/Fe₃C@NCNTs electrocatalyst was best for EGOR.