Boosting the energy storage densities of supercapacitors by incorporating N-doped graphene quantum dots into cubic porous carbon

Abstract

Hierarchical N-doped porous carbon has been prepared by assembling N-doped graphene quantum dots (N-GQDs) onto a carbonized metal–organic framework (cMOF-5) and used as an electrode material for supercapacitors. In this hierarchical composite structure, cMOF-5 provides an effective cubic porous framework with a large specific surface area and good electrical conductivity, while N-GQDs play an important role in enhancing the pseudocapacitive activity and improving the surface wettability of the electrode. Therefore, the N-GQD/cMOF-5 composite electrode material exhibits an outstanding specific capacitance of 780 F g⁻¹ at 10 mV s⁻¹ in a three-electrode system. Moreover, the composite electrode assembled in symmetric supercapacitors also displays a high specific capacitance of 294.1 F g⁻¹ at 0.5 A g⁻¹, excellent rate capacity and remarkable cycling stability with 94.1% of the initial capacitance retained after 5000 cycles at 5 A g⁻¹. When used as the positive electrode, the N-GQD/cMOF-5//AC asymmetric supercapacitor exhibits an energy density of 14.4 W h kg⁻¹ at a power density of 400.6 W kg⁻¹, while the capacitance retention after 5000 cycles reaches 90.1%. The current N-GQD/cMOF-5 composite electrode paves a feasible avenue to improve the capacitive performances of supercapacitors by constructing heteroatom-doped, hierarchically porous carbon architectures.