Preparation And Properties Of Colloidal Metal-Organic Frameworks

Metal-organic frameworks(MOFs)are a new type of porous material,constructed by linking metal cations or clusters with organic ligands through coordination bonds.Owing to their unlimited possibility to build new structures,they have diverse structures and properties.Over the past two decades,the design synthesis and performance studies on MOFs have been shown explosive growth.Novel structures,functional diversification of MOFs continue to emerge.Research focus has gradually from the initial synthesis,structural characterization to the practical application of development.At present,a novel application of MOFs in energy storage is of great concern,and its research in the field of electrochemical energy storage is still in its infancy.Therefore,this paper aims to explore the colloidal MOFs with different sizes and morphologies as electrode materials applying in electrochemical energy storage.In this thesis,Colloidal M-MOF-74 with different size and morphology were synthesized by the diverse methods and to explore its electrochemical properties as cathode materials of Li-O2 batteries.The main research work are as follows:(1)In this paper,MOF-74 crystals have been successfully prepared at room temperature.The effects of different metal salts and different alkaline additives on the size and morphology of MOF-74 were discussed.The synthesized products were characterized by XRD and SEM.The results show that the morphology and the crystalline form of the products were uniform when N-butylamine was used as the base additive.Alkaline additive is conducive to removing the protons and accelerating the coordination reaction,tending to form smaller crystals.Colloidal Co-MOF-74 was also synthesized by solvothermal conditions in this article.The effects of different acid additives,different cobalt salts,different concentrations of acetic acid and the amount of PVP on products were studied.The product was characterized by XRD and SEM,and the synthesis conditions of colloidal Co-MOF-74 were further optimized.(2)Based on the above research,we can control the size and morphology of the crystal by adjusting the solvent conditions.Aiming at the application of MOFs as cathode materials of Li-O2 in electrochemical energy storage,MOFs with different morphologies were selected as cathode materials for Li-O2 batteries,and their influences on the capacities were assessed.The nanofibers Co-MOF-74 delivers a high discharge capacity of 11350 mA h g-1 at a current density of 100 mA g-1,which is about five times higher than that capacity of the Li-02 battery without an MOF.The cycling and rate property of Li-O2 batteries with nanofibers Co-MOF-74 as the cathode materials were also investigated.The satisfactory electrochemical performances suggest that this nanofibers Co-MOF-74 is potentially promising for application as an efficient cathode materials for Li-O2 batteries.