Syntheses, Characterizations And Energy Storage Performances Of Transition Metal Oxides Based On MOF

Carbon material is common commercial electrode material. However, the theoretical capacity is lower. In order to meet the demand of high power and high energy resource, developing a new generation of lithium-ion battery electrode materials and ultracapacitors is urgency. 3d transition metal oxide is the best candidate material, however the electrical conductivity is very poor and structural collapse happened caused by volume expansion/contraction during cycle process. It is hoped to prepare hollow structured electrode material or nanostructured porous material for solving the above mentioned problems. The research results are as follows:?1? In a simple solvothermal strategy, preparing a cobalt-based precursor by adjusting the amount of pyrazine, we obtain twin hemispherical structures and flower novel flower-like morphology. By thermal decomposition of the precursor, we prepared Co₃O₄ porous material with the original morphology. Porous Co₃O₄ with twin hemispherical and flower-like structures were obtained with the assistance of PVP by adjusting the amount of pyrazine. The results of nitrogen adsorption-desorption indicate the BET surface area?22.6 m2·g-1? of twin hemispherical Co₃O₄ structures is lower than that?33.3 m2·g-1? of flower-like Co₃O₄ structures. However, the pore size of twin hemispherical Co₃O₄ structures is smaller, which is centered at about 2.5, 4.0 and 20.0 nm. As lithium-ion battery anode electrode materials, the initial discharge capacity of twin hemispherical and flower novel flower-like porous Co₃O₄ nanostructures are 1325.5 and 1243 mAh g-1, respectively. After, 90 cycles, the reversible capacities still retain 470.3 and 529.2 mAh g-1. As supercapacitor electrode materials, the specific capacitances of twin hemispherical and flower novel flower-like porous Co₃O₄ nanostructures are 96.9 F g-1, 103.7 F g-1, respectively. After 1000 cycles, the specific capacitance still retains 93.5 F g-1?101.7 F g-1, respectively. Therefore, the porous Co₃O₄ nanomaterials with twin hemispherical and flower-like structures exhibit excellent electrochemical performances, which may be attributed to the smaller particle size and compact porous structures with suitable pore size.?2? In a simple solvothermal system, [CoZn?BTC??NO3?]?2H2O??0.5DMF? was synthesized by controlling the reaction conditions, such as surfactant, solvent, and reaction temperature, etc. Then, the porous ZnO/Co₃O₄ polyhedrons with the diameter of 100 ?m were prepared by further calcination at 400 oC for 30 minutes, which were assembled by nanoparticles about 20 nm. The BET specific surface area was calculated to be 37.2 m2 g-1?As lithium-ion battery anode electrode materials, the first discharge and charge specific capacity are 1092.6 mA h g-1?612 mA h g-1, respectively. As supercapacitor electrode materials, at a current density of 0.5 A g-1, the specific capacity of the porous ZnO/Co₃O₄ polyhedrons was 106.7 F g-1, which still retained 102.7 F g-1 aftern 1000 cycles. Therefore, the porous ZnO/Co₃O₄ polyhedrons as electrode materials exhibit excellent cycling performances.?3? In a simple solvothermal method, we changed the reaction conditions, and added a surfactant cetyltrimethyl ammonium bromide?CTAB?. Finally, we obtained nano-MOF [ZnNi?BTC??NO3??1.6H2O?]?0.4DMF? and porous Zn O/NiO microspheres by further calcination. Porous ZnO/NiO microspherical structures have been devised and prepared successfully via a solid-state conversion process of heterobimetallic MOF. Electrochemical data illuminated that the first discharge and charge specific capacity is 1092.6 mA h g-1,612 mA h g-1 as lithium-ion battery electrode materials. As supercapacitor electrode materials, the specific capacitance of ZnO/NiO micro-spheres is 143.7 F g-1 for the first cycle at a current density of 1 A g-1, and still retains 140.0 F g-1 after 2000 cycles. It exhibits better cycling stability, which is attributed to be double metal oxide, high specific surface area and high porosity.