Preparation And Properties Of Metal Organic Frameworks Derived Metal Oxides

Currently,with the rapid development of consume electronics and new energy devices,it is urgent to explore new battery system which has better rate performance,larger capacity and higher safety.Manganese oxides,due to its high theoretical specific capacity,low working potential,high stability and low price,has become one of the most potential material to replace the commercial graphite anode.However,the low conductivity and the extremely large volume change during recycling leads to the fast degradation of specific capacity.It is well known that synthesizing materials with hollow and porous structure could be an efficient solution to suppress the volume effects,as well boost the transfer of lithium ion,thus obtaining excellent electrochemical performance.Metal organic frameworks（MOFs）has been widely applied for hydrogen storage and electrocatalysis due to their special morphology,porous structure and superhigh specific surface area.Moreover,the metal oxides commendably maintain the morphology and structure of MOFs precursor after high temperature calcination.In this thesis,we facially synthesize manganese oxides by facially calcining the manganese based MOFs with special morphologies and structures.The manganese based MOFs are prepared by co-precipitation method at room temperature and their morphology and structure are subtly controlled by selecting different organic ligands.Finally,the as-prepared manganese oxides exhibit excellent electrochemical performance.The main research contents are as follows:1.The Mn-MOF microspheres are synthesized at room temperature by co-precipitation method with using 1,3,5-tricarboxylic acid as the ligand.Then the obtained Mn-MOF microspheres were calcined in muffle furnace and the hollow Mn₂O₃microspheres were finally obtained.The obtained Mn₂O₃ microspheres exhibit good electrochemical performance,with the first discharge capacity of 1341.2m Ah g^-1 at a current density of 500m A g^-1,and a capacity retention rate of 71.1%after 100 cycles.2.The Mn-MOF nanosheets are synthesized at room temperature by co-precipitation method with using terephthalic acid as the ligand.Subsequently,the prepared Mn-MOF nanosheets and the Mn-MOF microspheres prepared in 1 are calcined in an inert atmosphere to obtain Mn O/C composite materials with respective morphologies of Mn O/C nanosheets and Mn O/C microspheres.The Mn O/C microspheres still maintain the morphology of Mn-MOF microspheres,while the Mn O/C nanosheets have a loose layered and cross-linked structure.Although the two morphologies of Mn O/C composites exhibit excellent electrochemical performance,the Mn O/C nanosheets show even better.After 1000 cycles at a current density of 2000m Ag^-1,the specific capacity remains691.1m Ahg^-1,with a capacity retention rate of 96.3%.3.Two bimetallic MOFs,Ni-Mn-MOF and Zn-Mn-MOF,were respectively synthesized by co-precipitation method with using terephthalic acid as the ligand.Subsequently,the obtained Ni-Mn-MOF and Zn-Mn-MOF are respectively calcined in a muffle furnace and then the bimetal oxides of Ni Mn₂O₄ and Ni Mn₂O₄ are obtained.The morphology of Ni Mn₂O₄ is flaky,with a first discharge capacity of 2183.3m Ah g^-1 at a current density of 500m A g^-1.The obtained Zn Mn₂O₄ is a porous plate structure composed of nanoparticles with a first discharge capacity of 1790.2m Ah g^-1 at a current density of 500m A g^-1.