A universal KOH-free strategy towards nitrogen-doped carbon nanosheets for high-rate and high-energy storage devices

Abstract

In this work, we report a universal KOH-free strategy to fabricate two-dimensional nitrogen-doped carbon nanosheets from edible oil residues. The saponification process and novel mild activators are introduced for the first time to optimize the microstructure of the nitrogen-doped carbon nanosheets. The resulting carbon nanosheets present a high specific surface area (2470 m² g⁻¹), wide pore size distribution (0.5–60 nm), and high nitrogen content (4.96%). As electrode materials for supercapacitors, the as-prepared nitrogen-doped carbon nanosheets exhibit a high specific capacitance of 340 F g⁻¹ at a current density of 0.5 A g⁻¹ and retain a high capacitance of 282 F g⁻¹ at a very high current density of 50 A g⁻¹, with no capacitance attenuation seen after 20 000 charge/discharge cycles in 6.0 M KOH electrolyte. The as-fabricated carbon nanosheet-based symmetric cell manifests a maximum energy density of 55.5 W h kg⁻¹ at the power density of 369 W kg⁻¹ and retains a high energy density of 32.3 W h kg⁻¹ at 6180 W kg⁻¹ in 1.0 M LiPF₆ electrolyte. Experimental results reveal that this study provides an efficient and universal strategy for novel pre-treatment and KOH-free activation of nitrogen-doped carbon nanosheets with high specific surface area for high-rate and high-energy supercapacitors.