Preparation And Properties Of Surface Nitrogen Modified Perovskite Oxygen Electrocatalyst

This research subject of this thesis is about the new energy conversion and storage technologies,such as the metal-air battery,with a focus on the slow kinetics of oxygen reduction and evolution catalytic reaction processes.We dedicate to developing efficient and sustainable catalyst materials.Perovskite oxides are a kind of catalytic materials with tunable crystal structure and composition and possessing intrinsic high catalytic activity.In this work,we try to construct heterostructure and create more surface oxygen vacancies concentration to improve the catalytic activity through surface metal precipitation,nitrogen modification,and CN coating.The efficient electrospinning technology is mainly used to prepare the low dimensional nanotube and nanofiber structure perovskite oxide material richening surface pore structure,and the doped transition metal is precipitated on the surface of perovskite oxide under reducing atmosphere,accompanying with the production of oxygen vacancy.Surface N doping or CN coating induces the modification of the material surface electronic structure and improves the electronic conductivity,subsequently the improved electrochemical performance.The main research content and results are as follows.First,a Ba₂MnWO₆ double perovskite oxide material was prepared under reducing conditions,which was then used to prepare a BMW-N-C composite by heat-treating with a mixture of polyaniline and conductive carbon black.After CN modificaion,the particle size of the material became smaller,and the specific surface area increased to 633.3 m² g^-1.XPS characterization confirmed that the material was richened with pyridine nitrogen and the oxygen vacancies.We found that when the BMW:C:PANI composition ratio is 1:3:6,ORR activity under the BMW-N-C material has the best ORR activity with onset potential reach 0.902 V,half-wave potential is 0.779 V,the limit current density can reach 5.65 m A cm^-2 and the number of electron transfers is close to 4 in 0.1M KOH conditions.Moreover,the composite material showed better potentiostatic test stability,resistance to methanol poisoning,and high maximum power density as air catalyst in zinc-air batteries than that of commercial Pt/C material.Secondly,through consecutive electrospinning,reducing treatment and RT N₂ plasma treatment with various time and plasma intensity,we obtained a nano-composite catalyst P-r-PSCFN which has Co Fe alloy precipitation,nitrogen doping and oxygen-rich vacancies on the surface.P-r-PSCFN with 120s plasma-treated period gave the best OER activity,specifically,a featured over-potential at the current density of 10 m A cm^-2 of 351 m V and Tafel slope of 105.77m V dec^-1in 1M KOH electrolyte.The electrochemical impedance spectroscopy test C_dlcalculations confirmed that metal surface segregation and plasma treatment reduced the charge transfer resistance of the catalyst while increased the electrochemically active area.After N₂plasma treatment,the content of adsorbed oxygen on the material increased significantly,and subsequently provided with more active sites.In particular,the current density of P-r-PSCFN was improved in the 24-hour potentiostatic stability test,and at the same time,kept stable under cyclic voltammetry test for 5000 cycles indicating that the material has good practical catalytic application.Finally,La_0.8Sr_0.2Ti_0.65Fe_0.25Ni_0.1O₃（LSTFN）nanofibers were prepared by the classic electrospinning technology,which was subjected to high temperature urea modification to precipitate in situ Fe Ni nanoalloy and N-surface doping.The XPS characterization results confirmed that the N element was successfully doped,and the adsorbed oxygen content in the modified U-r-LSTFN material increased.The improved conductivity by the segregation of metal,combined with the electronic state through N doping and the generation of a large number of oxygen vacancies on the surface,improve the OER performance of the material.The OER activity test of synthetic materials in 1M KOH.The overpotential of U-r-LSTFN material with a characteristic current density of 10 m A cm^-2 is only 345 m V with a much improved charge transfer resistance and reaction kinetics,significantly lower than that of LSFTN material（426 m V）under the same operational condition.In a words,the electrocatalytic performance of surface nitrogen element modified perovskite oxides has been improved to a certain extent through compositing with CN material,N₂ plasma treatment and urea one-step reduction.The research results in this work will provide a certain basis/clue for modifying or revealing the high intrinsic activity of perovskite oxide materials.The developed nanocomposite material can also be referred to the development of practically efficient and stable new energy conversion and storage devices,not just metal-air batteries or electrolytic cells.