Rationally exfoliating chitin into 2D hierarchical porous carbon nanosheets for high-rate energy storage

Two-dimensional (2D) carbon nanomaterials with hierarchical porous structure and heteroatoms doping are highly desirable in the fields of energy storage because of their rich active surface and open ion diffusion channels. However, the scalable preparation of carbon materials simultaneously possessing ultrathin 2D feature and hierarchical pores remains a considerable challenge. Herein, a facile one-step method to massively fabricate 2D porous chitin nanosheets (coded as PCNs) via a phytic acid assisted top-down exfoliation of bulk chitin under hydrothermal treatment was presented. Subsequently, 2D carbon nanosheets with extra-thin thickness (3.6 nm), well-defined hierarchical porosity, high specific surface area (855 m²·g^-1), as well as abundant self-doped heteroatoms (N, O, P) were fabricated by carbonizing the PCNs, and was named as HPCNs. The as-obtained HPCNs demonstrated remarkable electrochemical performance as electrode material for supercapacitors. The symmetric supercapacitors (SSCs) based on HPCNs exhibited a high specific capacitance of 79 F·g^-1 (316 F·g^-1 for single electrode) in 6 M KOH aqueous electrolyte solution, as well as a remarkable energy density of 23.8 W·h·kg^-1 by using 1 M Li₂SO₄ as electrolyte. It is also demonstrated that HPCNs/PCNs hybrid dispersions can be used as inks to fabricate conductive films and energy devices with high strength and superior flexibility. This work paves a new avenue for the economical and large-scale synthesis of 2D hierarchically porous carbon materials for energy storage related applications.