Assemble 2D redox-active covalent organic framework/graphene hybrids as high-performance capacitive materials

Graphene and two-dimension covalent organic frameworks (2D COFs) with a redox-active skeleton are promising potential capacitive materials for energy storage applications. However, their tendency to form thick laminates severely limits electron transfer and ion diffusion. Herein, we demonstrate graphene hybrids assembled by mixing 2D COFs and reduced graphene oxide (rGO) nanosheets to address their problems effectively. Electrochemical analysis shows that the two different 2D nanosheets prevent their restacking into thick laminates. Electrically conductive rGO nanosheets provide fast electron paths, while 2D COFs with abundant mesopores make graphene surface and redox-active sites in COFs accessible to electrolyte ions. The optimized hybrid containing 30 wt% COFs delivers a high gravimetric capacitance of 599 F g−1, much higher than the pristine rGO (203 F g−1) and COFs (110 F g−1). It also exhibits excellent rate capability with over 80% capacity retention when the charging/discharging current density increases by 40 times. This mixing strategy of different types of 2D nanosheets by hydrothermal assembly can be further extended to various graphene hybrids containing COFs and other 2D materials, creating a wide range of novel carbon composite materials for fundamental research and applications.