Three-dimensional Graphene-based Porous Composites:Synthesis And Electrochemical Performance Application

Graphene, with large specific surface area, excellent electrical conductivity and high chemical stability, has been considered as an ideal carbon material for a variety of applications including electronics, energy storage/conversion, biology, environment, etc. However, the strong aggregation and restacking of graphene sheets poses a barrier to obtain naturally single graphene layer which seriously hamper the practical applications of graphene. The three-dimensional (3D) macroscopic frameworks built up by graphene sheets, such as graphene papers, aerogels or foams, can not only mitigate the effect of aggregation and restacking between graphene sheets, but also provide highly interconnected channels for the transportation of charge carriers, which are appealing for the energy storage and conversion devices.(1) Herein, Hierarchically porous hybrids with strongly coupled nitrogen doped porous carbons and graphene aerogel (NPC-GA) were fabricated by the solid oxidation polymerization and carbonization of m-phenylenediamine (mPD) on the interconnected macroporous frameworks of GA. As a result, hierarchically porous hybrids can provide more storage sites and short transport paths for electrolyte ions, and enhance the overall conductivity of the electrode. By adjusting the time of the pyrolysis temperature, the specific surface areas and nitrogen content of NPC-GA can be controlled, which further manifest influences on the electrochemical performance of the hybrids. In three-electrode system, the NPC-GA electrode shows ultra-high capacitance of 608.3 F g-1 at 0.1 A g-1 in 1 M H2SO4. More importantly, the all-solid-state flexible supercapacitor delivers superior energy density (12.4 WhKg-1) and power density (2432 W Kg-1) as well as excellent cycling stability (92% specific capacitance retention after 10000 cycles). These exciting results suggest that a low-cost and environmentally friendly design of electrode materials can be further applied to fabricate high performance electrode materials for various energy devices.(2) Three-dimensional hybrids of cobalt oxide (Co3O4) and graphene frameworks are fabricated via a facile hydrothermal self-assembly process. By adjusting the time of the hydrothermal treatment, the morphologies of the Co3O4 components can be modified from rods to nanoparticles, which further manifest influences on the electrochemical performance of the hybrids. As the anode in lithium ion battery, the hybrid loaded with spherical Co3O4 nanoparticles exhibits the highest reversible capacity of 1148 mA h g-1 at 100 mA g-1 for 100 cycles among the three samples. Even at a high current density of 5000 mA g-1, its reversible capacity is still kept at 600 mA h g-1, outperforming the reported hybrids of Co3O4 and graphene. The outstanding electrochemical behavior was attributed to the 3D frameworks with mesopores, macropores and large surface area, which not only prevented the ?-? stacking of graphene and the agglomeration of Co3O4 nanoparticles, but also facilitated fast ion and electron transport in 3D pathways.