Ultrathin Nitrogen-Enriched Hybrid Carbon Nanosheets for Supercapacitors with Ultrahigh Rate Performance and High Energy Density

Two-dimensional carbon nanosheets are promising materials as supercapacitor electrodes for high-efficiency energy storage. Herein, a simple strategy is engineered to configure ultrathin nitrogen-enriched hybrid carbon nanosheets (HCNSs) with a thickness of approximately 3.6 nm using graphene oxide as a structure-directing agent and nano-CaCO3 as an in-situ-activated agent. The polydopamine synthesized in situ on the graphene oxide sheet surface is used as a nitrogen-rich carbon precursor, leading to the formation of nearly transparent nitrogen-enriched HCNSs under an electron beam. Benefiting from the nitrogen-enriched species (8.92 wt % N content), highly exposed electroactive sites and fast ion/electron transport arising from the porous and ultrathin nanosheet structure, the HCNS electrode exhibits remarkably enhanced electrochemical characteristics with a high specific capacitance of 227 F g−1 at 0.5 A g−1 and superior rate capability (70 % capacitance retention at 100 A g−1) in 6 m KOH electrolyte. More importantly, it delivers a high energy density of 86.6 W h kg−1 at a power density of 111 W kg−1 in a 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid electrolyte. This study might shed new light on the configuration of nitrogen-enriched and ultrathin 2D carbon nanomaterials for high-efficiency energy storage/conversion devices.