Rational Design And Intensive Study Of Cathode Electrode For High Specific Energy-density Zn-air Battery

Nowadays,the increasing demand for fossil energy the environmental problems have greatly restricted the sustainable development of society.Therefore,the development of clean and efficient alternative energy sources and the establishment of a sustainable energy development system are the first problems to be solved in modern society.Reducing reliance on fossil energy depends on the development of new energy conversion and storage devices.Zinc-air batteries are expected to be the energy source for next-generation mobile wearable devices due to their higher specific energy density and lower price.In recent years,studies have found that the efficiency and performance of zinc-air batteries are mainly limited by the reaction kinetics of air electrodes.At present,commercial precious metals such as Pt/C,Ru O₂,etc.are generally used as air electrode catalysts to reduce energy consumption during the reaction,and to reduce the reaction barrier in order to increase the efficiency of the chemical reaction.However,precious metal catalysts generally have problems,such as high prices and low reserves,which limits their large-scale commercial applications.Therefore,research and development of inexpensive metal catalysts,non-metallic air electrode catalysts have important significance for the wide application of zinc-air batteries.This paper mainly uses metal-free and low-cost metal catalysts to do three things in the light of the problems of today’s air electrodes:（1）Ligand-regulated thermal in situ pyrolysis ZIF-8 Preparation of nitrogen and phosphorus double-doped mesoporous-microporous carbon framework materials for oxygen reduction and oxygen evolution catalysts:metal-organic framework（MOF）as precursor Nanocomposite nanomaterials doped with various elements and various morphologies.However,due to the poor stability of the ligand of MOF and the easy agglomeration of the metal center,the application of the air electrode of the metal air battery is still limited.Therefore,this part works by modifying the ZIF-8 by controlling the end-burning temperature and the ligand type by using the zeolitic imidazolate skeleton（ZIF-8）as a precursor stencil.During high-temperature calcination,the metal zinc in ZIF-8 sublimes to form vacancies,and the ligand carbonizes to form a nitrogen-phosphorus double-doped porous carbon skeleton.At the same time,through the strong coordination of the ligand tripolyphosphazene,Maximum retention of the structure of the precursor.In addition,the doping of phosphorus can further enhance the intrinsic activity of the material and reduce the Gibbs free energy of the reaction.Under the condition of an alkaline electrolyte,excellent oxygen reduction（ORR）and oxygen evolution（OER）reactivity are simultaneously exhibited,thereby achieving high-efficiency charge-discharge performance of the zinc-air battery.This part of the work provides a research idea for the construction of modified MOF-based multifunctional electrocatalysts.（2）Conjugated organic framework-carbon nanotube composite precursor Preparation of nitrogen and phosphorus double-doped zinc-air battery cathode material:Conjugated organic framework（COF）structure has porous,ordered and other structural characteristics,but the less active sites are the main disadvantages which limit its utilization in electrocatalytic conversion reactions.The conjugated organic framework（COF）material was coated on the carbon nanotubes as a catalyst precursor by means of solvothermal polymerization.The nitrogen and phosphorus were successfully doped by controlling the calcination temperature of the raw material ligand during the reaction.Experiments have shown that the metal-free catalyst has more pore structure and can increase the immersion ability of the electrolyte.At the same time,the nitrogen,phosphorus dual-doped graphite coating formed by calcination was verified by the combination of experiments and DFT calculation.The synergistic effect between the pyridinic nitrogen and the P-C bond was obtained,and the active site of the catalyst was greatly increased,thereby improving the oxygen reduction performance of the catalyst.This catalysts exhibite excellent performance which even over the precious metal Pt/C catalysts in zinc-air battery air electrodes.This part of the work expands the application of COF materials in electrochemical conversion,and in-depth investigation of the potential of COF materials in the application of air electrodes in zinc air batteries.（3）In this part,amorphous iron borate nanosheets are used as self-powered water splitting and reversible zinc-air battery multi-function electrodes.Recently,stability and low cost multi-functional catalysts are in high demand for advanced energy conversion and storage equipment,but on the market,the transition metal based air electrode catalyst only has a single catalytic effect and cannot be simultaneously applied to electrolyzed water and air battery electrode reaction.In view of the above situation,this part of the work successfully prepared a self-supporting amorphous iron borate catalyst by one-step solvothermal method.The catalyst has high specific activity and mass activity,many catalytic active sites and strong activity,and can be simultaneously applied to hydrogen evolution reaction（HER）,oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）.Two series connected zinc-air batteries that consisting of the self-supporting catalyst can illuminate a 2.5 V LED lamp for more than 20 hours.The Faraday efficiency of the electrocatalytic self-power water splitting device can reach 93.2%,and the oxygen can be collected over 74 m L in 4 hours.Overall,this part of the work provides a way of thinking for the preparation of transition metal-based multifunctional catalysts and exploring new energy supply methods.