Facile preparation of N-doped porous carbon nanosheets derived from potassium citrate/melamine for high-performance supercapacitors

[Display omitted] •A facile method for N-doping onto interconnected porous carbon nanosheets is propose.•Stepwise thermal annealing is advantageous over direct thermal annealing in improving the N-doping efficiency.•The nanosheets are favorable for the fast ion movement and increasing the wettability of the electrolyte.•A maximum specific capacitance of 350F g−1 was achieved at 1 A g−1 in a three-electrode test. Nitrogen (N)-doped porous carbon nanosheets have attracted research attention owing to their effective structure for fast ion diffusion and pseudocapacitive properties in supercapacitors. However, to synthesize N-doped porous carbon nanosheets while maintaining their original shape requires complicated multistep processes such as plasma and arc-discharge methods. Herein, we propose a facile and effective method for N-doping into interconnected porous carbon nanosheets that preserves their original structure with a stepwise thermal annealing using melamine as N-doping source. The stepwise thermal annealing is advantageous to improve N-doping efficiency into the carbon matrix compared to direct thermal annealing method owing to the condensation of melamine. As-synthesized N-doped carbon nanosheets with interconnected and porous structure exhibits high specific surface area and N-doping contents, which favorable for the fast ion movement, adsorption, and increasing the wettability of the electrolyte. The electrochemical performance shows a maximum specific capacitance of 350F g−1 at 1 A g−1 in a three-electrode test. Moreover, a fabricated symmetric full-cell device using an optimized N-doped carbon electrode demonstrates a long-term durability over 10,000 cycles and a maximum energy density of 16.1 Wh kg−1.