Hierarchical Porous M-N-C Nanomaterials Derived From MOFs As High-efficient Catalysts For Rechargeable Zn-air Battery

Zinc-air batteries（ZABs）are considered to be highly promising energy storage and conversion systems because of their high theoretical energy density,environmental safety,and the abundance of zinc resources in the earth.However,the slow reaction rates of the anode oxygen reduction reaction（ORR）and oxygen precipitation reaction（OER）limit the performance of zinc air batteries.Therefore,the development of efficient and stable bifunctional catalysts is a hot topic in zinc-air battery research.At present,the best catalytic performance of noble metal catalysts can only be used in the laboratory because of their scarce resources and high cost.Metal-nitrogen-carbon（M-N-C）catalysts are the most studied catalyst materials with catalytic performance comparable to noble metals.Meanwhile,with the development of flexible electronics,flexible energy storage devices are also greatly needed by the market.ZABs can be prepared as quasi-solid-state flexible batteries（FZABs）,which greatly expands the application scenario of zinc-air batteries（ZABs）.In this thesis,a series of M-N-C catalysts were prepared using metal organic framework（MOF）and its derivatives as precursors,and the relationship between catalyst composition,structure and electrocatalytic performance was investigated,as well as the catalytic mechanism.Meanwhile,a novel solid state gel polymer electrolytes（GPEs）were prepared and their performance was tested.The practical applications of catalysts and electrolyte films were further verified by assembling mold-type aqueous ZABs and solid-state FZABs.The main tasks are summarized as follows:1.Three Nitrogen-doped multipore-carbon supported Co nanoparticles catalyst materials（Co@NHPC-700,Co@NHPC-800,Co@NHPC-900）were innovatively prepared using one-dimensional rod-shaped Bio-MOF-1 as the base material by Co ion exchange and pyrolysis at three different temperatures of 700,800 and 900℃.The best performance of the catalysts prepared at 800°C was demonstrated by material characterization and electrochemical tests.The ORR and OER intermediate species were detected by advanced in situ Raman characterization,and the catalytic mechanism of the Co@NHPC-800 catalysts for ORR and OER was postulated to occur through the redox of Co（II）and Co（III）species.The prepared materials and noble metal materials were applied to water system and flexible zinc-air batteries.The performance of zinc-air batteries with Co@NHPC-800 as positive electrode was better than that of commercial catalyst Pt/C+Ru O₂.In this work,high efficiency ORR and OER catalysts were prepared,and the mechanism of catalysis was investigated,and their application prospects on ZABs were explored,providing new ideas for the synthesis of high efficiency bifunctional catalysts.2.Using Bio-MOF-1 as a template,in order to further improve the catalytic activity of catalyst OER,bimetallic Co and Ni ion exchange was introduced to prepare a nitrogen-doped multipore-carbon supported Co Ni nanoparticle catalyst（Co Ni-Co N₄-HPC-900）.The excellent ORR and OER catalytic activities of Co Ni-Co N₄-HPC-900were verified by physical characterization and electrochemical tests.The intermediate species of the reaction were detected by in situ Raman and X-ray absorption spectroscopy,and the reaction mechanism and the structure of the active site were speculated and clarified.Moreover,the specific reaction process and catalytic mechanism of Co Ni₃-Co N₄ as the active center were simulated by DFT calculation.FZABs and button ZABs were assembled using Co Ni-Co N₄-HPC-900 as the cathode catalyst,and the power density of the coin cells reached 27 m W cm^-2,which verified the broad application prospects of the catalyst materials.3.The commonly used GPEs membrane was modified by using green,renewable,and inexpensive biomass material-cotton-as the key base material.Cotton fiber was extracted by removing impurities.By using cotton fiber,KOH,and PVA,CF-PVA film with better performance was prepared.The contact angle,impedance,and corrosion tests were used to verify that the ionic conductivity and water retention of the membrane were improved,thereby improving the performance and runtime of quasi-solid FZABs.The precursor was obtained by in situ growth of ZIF-67 on cotton fiber as the base material.The Co-N-C@GCF-950 catalyst material was obtained by high-temperature carbonization under an inert atmosphere.Its excellent ORR performance was demonstrated by a series of characterizations and electrochemical tests.Finally,both the electrolyte membrane and catalyst materials were applied to FZABs to improve their performance and reduce their overall cost.This work demonstrated the potential of cotton fibers for multifaceted applications in FZABs and their contribution to environmental protection.