Research On Preparation And Performance Of MOF-Derived Non-Noble Metal Oxygen Electrode Catalysts

The growing demand for energy promotes the development of advanced energy storage and conversion devices.New energy devices such as metal-air batteries have good commercial prospects due to their high energy conversion efficiency and environmental friendliness.However,the oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）occurring at the oxygen electrode in these devices are kinetically sluggish,thus requiring catalysts to accelerate the reaction kinetics.The high cost and monofunctionality of noble metal catalysts severely limit the energy conversion efficiency of related devices.Therefore,the research of high-performance non-noble metal dual-function ORR and OER electrocatalysts has become a focus in recent years.Metal-organic frameworks（MOF）and their derivatives have been widely used in the preparation of highly efficient electrocatalysts due to their unique porous crystal structure and tunable chemical properties.In this paper,the structure optimization and morphology modulation of MOF-derived materials were carried out,and Fe Co-SNC and Co Ni-NC catalysts were synthesized.The advantages of the composition and structure of the as-synthesized catalysts were fully utilized to improve the ORR/OER catalytic performance,and microstructures of the materials and the correlative mechanisms of electrochemical performance enhancement were systematically studied.The main research contents are listed as follows:（1）To enhance the intrinsic activity of the active centers inside MOF-derived non-noble metal catalysts,Fe Co-SNC catalysts were prepared by elemental doping and controlled pyrolysis of the zeolite imidazolate framework（ZIF-8）.The characterization results show that the atomically dispersed Fe-Co bimetallic sites coordinating with N and S are embedded in the porous carbon matrix.Fe Co-SNC has efficient ORR and OER bifunctional catalytic activity due to the synergistic effect of Fe-Co bimetal sites and the electronic structure of N and S coordination.The half-wave potentials of Fe Co-SNC in alkaline and acidic media are 0.91 V and 0.78 V,respectively,with the OER potential of 1.56V at 10 m A cm^-2 and the oxygen potential difference of 0.65 V in alkaline medium.The liquid Zn-air battery assembled with Fe Co-SNC cathode catalyst achieves a maximum power density of 115.4 m W cm^-2.（2）To solve the problems of few exposed active sites and poor electron transport ability of bulk MOF materials,metal nanoparticles supported on hollow tubular nitrogen-doped carbon（Co Ni-NC）catalyst was synthesized by simple ligand exchange and pyrolysis carbonization methods.Through the rational control and design of the MOF precursor,the specific surface area of the Co Ni-NC catalyst reaches 1211.6 m² g^-1,resulting in more active sites on the surface of Co Ni-NC.Meantime,the hollow tubular structure facilitates electron transport.Electrochemical test results show that Co Ni-NC exhibits good ORR and OER catalytic activities.The half-wave potentials of Co Ni-NC in alkaline and acidic media are 0.84 V and 0.76 V,respectively.The OER potential is 1.62 V at 10 m A cm^-2 and the oxygen potential difference is 0.78 V in alkaline condition.The liquid Zn-air battery assembled with Co Ni-NC cathode catalyst achieves a maximum power density of 134.3 m W cm^-2,with excellent cycling stability.The all-solid-state Zn-air batteries assembled with Co Ni-NC as cathode catalyst achieves maximum power densities of 92.1 mW cm^-2.