Design Of Doped Metal Organic Frameworks Derivative As Cathode Catalysts For Lithium-carbon Dioxide Batteries

In the context of carbon neutrality and carbon peak,to solve various intractable problems caused by energy crisis and greenhouse effect,it is urgent to develop clean and renewable energy to replace traditional fossil fuels.Li-CO₂ batteries has attracted extensive attention due to its high theoretical energy density and the ability to fix CO₂,which is expected to become an appealing energy storage technology.However,the low actual energy density and the inferior reversibility caused by the poor CO₂adsorption capacity of the cathode catalysts and the high thermodynamic stability of the discharge product limit the practical application and development of Li-CO₂ batteries.Cathode catalysts with great catalytic performance are beneficial to improve the reaction kinetics,reversibility,and cycle life of the batteries.Metal-organic framework（MOF）has been widely applied in the field of CO₂ catalysis with the advantages of adjustable compositions,porous structure,and high specific surface area.In this thesis,metal-organic framework（MOF）derivatives were used as cathode catalysts for Li-CO₂ batteries,and the catalytic performance was further enhanced by doping single atoms.The specific experimental contents and test results are listed as follows:（1）Zeolitic imidazolate framework-L nanosheets were synthesized by a simple hydrothermal method and grown on carbon cloth to form nanosheet arrays（Zn Co ZIF-L/CC）.Then it was converted into porous carbon nanosheets（Co-NPs NC/CC）with great electrical conductivity by a subsequent annealing treatment at high temperature.Next,the carbon cloth was immersed in Ru Cl₃ solution while the Ru Cl₃ was adsorbed in the pores of the carbon nanosheets,and the Ru single atom was successfully introduced into the materials（Co Ru@NC/CC）by further pyrolysis.Through X-ray diffraction analysis,X-ray photoelectron spectroscopy analysis,X-ray absorption fine structure analysis and other related physical characterization,it was confirmed that Ru exists in the form of single atoms in the catalyst.In addition,the discharge products after charge and discharge process of the Li-CO₂ batteries using Co Ru@NC/CC as a cathode catalyst were characterized and analyzed by field emission scanning electron microscopy tests,Raman spectroscopy and other related characterization tests.The discharge product proved to be Li₂CO₃ was uniformly deposited on the surface of the carbon nanosheets,and the batteries exhibited excellent reversibility.In the electrochemical performance test,Ru atoms had greatly improved the reversibility and cycle performance of the batteries.Co Ru@NC/CC provided a low overpotential of 0.71 V,a high discharge capacity of 18522.75μAh cm^-2 at a current density of 100μA cm^-2,and an excellent cyclability over 400cycles at a current density of 600μA cm^-2.（2）Zeolitic imidazolate framework-L nanosheets doping of a small amount of different nitrates were synthesized and grown on carbon cloth（Co M ZIF-L/CC,M=Cr,Fe,Cu,Ni,Mn）.After annealing treatment at high temperature,it was converted into single atoms doped carbon nanosheets（SA M-Co NC/CC）,In the electrochemical performance test,it was concluded that the active sites of Cr atoms could effectively reduce the overpotential,promote the decomposition of discharge products,and enable the materials to exhibit the best catalytic activity by comparing the properties of five transition metal single atoms doped materials.Compared with Co-based carbon nanosheets（Co/NC/CC）,Co Cr@NC/CC used as the cathode electrocatalyst with great cycle life and reversibility exhibited a low overpotential of 0.77 V,and stable cyclability over 387 cycles and 357cycles at the current density of 200μA cm^-2 and 400μA cm^-2,respectively.