Nitrogen and oxygen co-doped graphene quantum dots with high capacitance performance for micro-supercapacitors

Abstract

The applications of carbon-based micro-supercapacitors (MSCs) based on the electrical double layer capacitance mechanism are usually limited by the extremely low specific capacitances and energy storage densities of carbon electrodes fabricated from less active, large-size carbon materials. As a promising alternative, high-activity N and O co-doped graphene quantum dots (N-O-GQDs) offer a combination of advantages, such as ultrasmall sizes, rich active sites, high hydrophilicity, and facile assembly into conductive carbon films. Here we report the facile electrophoresis construction of carbon-based MSCs for ultrahigh energy density storage using N-O-GQDs as the initial electrode material. The N-O-GQD MSCs show extremely high volumetric capacitances of 325 F cm−3 in H2SO4 due to their high pseudocapacitive activity, high loading density, and enhanced electrolyte wettingability ascribed to a large amount of doped nitrogen and oxygen functional groups. They deliver an ultrahigh volumetric energy density, superior to that of thin-film lithium batteries. Three connected all-solid-state N-O-GQD MSCs can light a red light--emitting diode. Furthermore, the pseudocapacitive MSCs maintain high power densities, and cycling stability owing to improvements in electrical conductivity and electrolyte penetration. The important results highlight the promising applications of high-activity nanographenes in on-chip power sources for driving diverse micro-devices.