Highly microporous carbon with nitrogen-doping derived from natural biowaste for high-performance flexible solid-state supercapacitor

Highly microporous carbon material with nitrogen doping has been synthesized via a facile one-step approach by employing natural biowaste miscellaneous wood fibers derived hydrochar as precursor and melamine as nitrogen source respectively. The added melamine not only results in the incorporation of some nitrogen into the carbon framework but also increases the specific surface area of carbon material. Such resultant N-doped microporous carbon possesses the functionalized nitrogen doping (1.75 at. %), a large specific surface area (∼1807 m² g^-1) and abundant highly interconnected micropores. Benefiting from the synergistic effect of high specific surface area, well-developed pore size distribution and functionalized groups, this carbon material delivers a high specific capacitance of 345 F g^-1 at 0.5 A g^-1, an excellent capacitance retention with 270 F g^-1 at up to 30 A g^-1, and a remarkable cycle ability with 91.3% retention after 10,000 cycles at 5.0 A g^-1. Based on it, the as-developed flexible symmetric solid-state supercapacitor delivers a high energy density of 7.92 W h kg^-1 at the power density of 250 W kg^-1. Evidently, this work provides a facile and cost-effective route for functionalized natural biowaste-based carbon materials and further opens up a way for highly value-added recycling of biowaste-like materials.