Activity Modulation Of Non-Platinum Oxygen Electrocatalysts For Zinc-Air Batteries

In recent years,energy and environmental pollution issues have been widely concerned,and new energy conversion and storage devices have been vigorously developed.Among various new energy technologies,zinc-air batteries（ZABs）are known as one of the most promising green energy sources in the 21st century because of their abundant raw materials,high energy density,light weight,safety and environmental protection.The main bottleneck limiting the wide application of ZABs is the sluggish kinetics process of oxygen electrode reaction including oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）,and therefore seeking for high-performance oxygen electrocatalysts is a key challenge to achieve the large-scale commercial application of metal-air batteries.At present,the most widely used ORR and OER catalysts with the best activities in commercial applications are the precious platinum（Pt）and ruthenium（Ru）/iridium（Ir）based catalysts,respectively.However,these noble metals are scarce in the earth’s crust,expensive,and difficult to meet the simultaneous catalysis of oxygen reduction and oxygen evolution reactions,and which limit their application in rechargeable ZABs.Therefore,the design of inexpensive,efficient and stable bifunctional catalysts is the key to the rapid development of metal-air batteries.Recently,transition metal-based electrocatalysts derived from MOFs have received a lot of attention from researchers due to their excellent catalytic activity,low cost and excellent stability.In this dissertation,non-precious metal bifunctional catalysts with excellent performance are constructed by taking advantage of MOFs with adjustable structure and various modification methods.The main study contents are as follows:1.FeNi@ZIFs-8@PAN fibers were prepared by electrostatic spinning of Fe,Ni-embedded ZIF-8（FeNi@ZIF-8）-containing polyacrylonitrile（PAN）solution,and then carbon nanofibers（CNFs）-encapsulated Fe,Ni-embedded nitrogen-doped carbon（FeNi-NC）,named FeNi-NC@CNF-T（where T represents the pyrolysis temperature）were prepared by high-temperature pyrolysis of FeNi@ZIFs-8@PAN fibers.The effect of reaction conditions on electrocatalytic performance of the as-synthesized materials for ORR and OER was studied.The optimized FeNi-NC@CNF-900 showed excellent bifunctional electrocatalytic activity and stability in alkaline electrolyte.The zinc-air batteries assembled using FeNi-NC@CNF-900 as an air electrode catalyst exhibited better performance than Pt/C+Ru O₂-based batteries.2.Fe-embedded ZIFs-8 microspheres were synthesized by a facile microemulsion method.The Fe,Zn embedded nitrogen-doped carbon microspheres,itemed as Fe Zn/NC-T（where T stands for the pyrolysis temperature）,were then prepared by pyrolysis of Fe-embedded ZIFs-8 microspheres under inert atmosphere.The activity influencing laws of different components and pyrolysis temperature on electrocatalytic of the as-prepared catalysts was summarized.The optimized Fe Zn/NC-800-a（where a denotes for acid leaching）exhibited excellent bifunctional oxygen electrocatalytic activity and good stability.The Zn-air batteries assembled with Fe Zn/NC-800-a as the air electrode catalyst showed a peak power density of 137.5 m W cm^-2 and a long-term charge/discharge cycle stability with 200 h.3.The Fe,Ni embedded ZIF-8（FeNi@ZIF-8）with the lamellar structure was prepared by a simple liquid synthesis method.After carbonization of FeNi@ZIF-8,Ni₃Fe alloy nanoparticle-embedded N-doped bamboo-like carbon nanotubes,labelled as FeNi@NCNTs-T（where T denotes the pyrolysis temperature）.The effect of reaction conditions such as metal component and pyrolysis temperature on oxygen electrocatalytic performance of the as-synthesized materials was uncovered.The optimized FeNi@NCNTs-900 exhibited excellent electrocatalytic performance for both ORR and OER in alkaline electrolyte.The zinc-air batteries assembled with FeNi@NCNTs-900 as the air cathode catalyst outperformed the Pt/C+Ru O₂-based batteries in terms of peak power density,rate performance and long-term charge/discharge cycle stability.