The Synthesis And Electrochemical Performance Of Carbon-supported Cobalt-based Oxides Composite For Oxygen Reduction Reaction And Zinc-air Battery

With the rapid development of the economy,the increasing awareness of environmental protection and the contradiction between the exponential growth of energy demand,people’s research on new energy storage materials has received extensive attention.Among various energy storage technologies,rechargeable metal air batteries and fuel cells have the greatest potential for use in next-generation electric vehicles and hybrid vehicles.The zinc-air battery is a semi-fuel cell that uses metal zinc instead of hydrogen as a fuel.Due to the high energy density,friendly environment,low production cost,stable charge and discharge voltage,high safety and reversible charge and discharge of zinc-air batteries,a large number of researchers are interested in developing zinc-air battery,so as to rapidly promote the industrialization and commercialization of zinc-air battery.Although zinc-air battery still needs to be improved in electrolyte,zinc electrode and other technologies,the most critical technology of zinc-air battery is to design efficient air electrode,and the most critical material of air electrode is efficient oxygen reduction（ORR）electrocatalyst.Therefore,the development of electrocatalysts with high activity,low cost,good stability and simple preparation process is the key to promote zinc-air batteries to replace low-efficiency and high-pollution energy storage equipment on the market.At present,the reason for restricting the large-scale commercial application of zinc-air batteries is that the electrocatalyst is required to reduce the overpotential of the reaction in the process of discharging oxygen reduction reaction with slow dynamics.Platinum（Pt）and its alloys are considered to be the most efficient ORR catalysts,but their high cost,scarcity and lack of durability hinder their successful implementation.Therefore,it is meaningful and challenging to develop non-precious metal ORR catalysts with high stability and low cost,which have the same performance as platinum based materials.In order to solve these drawbacks of zinc-air battery,it mainly focuses on excessive metal oxide materials,effective compounding of rare earth element materials and carbon-based materials,nitrogen co-doping technology,nanomaterial morphology and structure control,catalytic active sites and synergistic catalysis.Fundamental research such as mechanism,through different characterization techniques,determines the similarity or commonality under the highly active composite electrocatalyst,and provides theoretical basis and new way for the preparation of high-efficiency and low-cost non-precious metal catalysts.The main research contents are as follows:（1）.A simple and efficient method for the preparation of LaCoO₃/CNTs-2 catalyst by high-energy ball milling has been developed as a high-efficiency oxygen reduction catalyst for zinc-air batteries.The electrocatalytic activity of LaCoO₃ is significantly enhanced by high-energy ball milling with CNTs,comparable to commercial Pt/C catalysts,with a slope potential of 0.73 V vs.RHE and a limiting current density of 4.3 mA cm².A large amount of active oxygen(O₂^2-/O^-)and oxygen vacancies in carbon nanotubes in LaCoO₃.Due to the synergistic effect between LaCoO₃ and CNTs,LaCoO₃/CNTs-2 favors the four-electron pathway of the oxygen reduction reaction.In addition,a zinc-air battery using LaCoO₃/CNTs-2 as a positive electrode catalyst can provide a stable,high-discharge platform.Therefore,the introduction of defective carbon nanotubes is an effective strategy for regulating the electrocatalytic activity of LaCoO₃,which will extend to other 3D transition metal oxide based perovskite materials in energy applications.（2）.Cobalt oxides（Co₃O₄）/carbon（C）,as popular materials for catalyzing the oxygen reduction reactions（ORR）of metal-air batteries,still needs to be enhanced to meet the requirements of next-generation metal-air batteries.Herein,we adopt the CeO₂ as a strong ORR promoter to fabricate the bicentric Co3O₄-CeO₂/Co-N-KB catalyst via a one-step hydrothermal method.The results indicate that this novel catalyst has good endurability and exhibits an half-wave potential of 0.8 V（vs.RHE）and a limiting current density of 6.1 mA cm^-2,which is close to that of Pt/C.Additionally,the Zn-air battery using the Co₃O₄-CeO₂/Co-N-KB as cathode catalyst could provide stable and high discharge platforms.This remarkable performance is attributed to the bicentric structure for catalysis,the oxygen storage capacity of CeO₂,the doping effect of nitrogen,and the graphene-like structure of carbon support.This work offers a new viewpoint on synthesizing the catalysis with favorable bicentric structure for metal-air batteries.