Synthesis And Energy Storage Properties Of Three-dimensional Graphene/metal-organic Framework Derived Metal Oxides

The development of green energy and energy-saving technology has become one of the most important and most popular research topics in the world.It is a key problem to find and develop new electrode materials with high specific capacity,long cycle life and high conductivity.The research route of this paper includes:（1）Based on the inherent characteristics and merits of 3D Graphene Network（3DGN）（high conductivity,large surface area and high mechanical strength）and MOF(high specific surface area,large pore volume,small density,good stability,flexible channels.The 3DGN/MOF composites were fabricated by the in-suit self-assembly method.（2）The 3DGN/metal oxide（MOx）composites were prepared after the high-temperature treatment of 3DGN/MOF.The as-synthesized materials were characterized and analyzed,and the preparation parameters and controllable ways were also probed and optimized.（3）Based on the research of structures,physical properties,electrochemical properties and energy storage mechanism,the relationship between the composition,microstructure,conductivity,porosity and electrochemical properties of 3DGN/MOx composites was investigated.High performance electrode materials were obtained by adjusting and optimizing the structure and physical properties of materials.This work provides a new idea for the development of new type of electrode materials.The research contents are as follows:（1）The Mn-based MOF（Mn-BTC）crystals were grown on 3DGN via a solvothermal method.The free-standing flexible and porous 3DGN/Mn₂O₃ composite was prepared through the calcination of 3DGN/Mn-BTC precursors.3DGN/Mn₂O₃ composite was directly used as an electrode and has demonstrated remarkable electrochemical performances.The designed 3DGN/Mn₂O₃ electrode material exhibits a high specific capacitance of 471.1 F g^-1 at 0.2 A g^-1,good rate capability of 57.3% at 5 A g^-1 relative to the initial value at 0.2 A g^-1,and excellent long-cycle stability without decaying after 1800 charge-discharge cycles.（2）The Ni-based MOF（Ni-BTC）crystals were grown on a 3DGN substrate through a simple solvothermal method,and then a high-temperature calcination has resulted in the formation of a 3DGN decorated with NiO nanoparticles.The free-standing 3DGN/Ni O composite was employed as anodes for Li-ion battery,yielding a good electrochemical performances.After 50 cycles,the specific capacitance of 3DGN/NiO was 430 mAh g^-1 at 100 mA g^-1.When the current density was 250 mA g^-1,197 mAh g^-1 wasretented.Electrochemical results show that 3DGN/NiO electrode material is superior to pure NiO electrode material in the aspects of cycle stability and rate performance.（3）The Cu-based MOF（Cu-BTC）crystals were first uniformly grown on the surface of 3DGN substrate through a solution immersion method and then a subsequent thermal treatment isolated the formation of well-dispersed nanostructured CuO octahedras wrapped 3DGN.The free-standing 3DGN/CuO composite was utilized as binder-free anodes,yielding a high reversible gravimetric capacity of 409 mAh g^-1 at 100 mA g^-1,excellent cyclability with 99% capacity retention after 50 cycles and superior rate capability of 219 mAh g^-1 at 1600 mA g^-1.