N/O-functionalized ultrathin carbon nanosheets for zinc-ion hybrid capacitors

2D carbon materials have outstanding electrical properties and rich anchoring sites, and can be used as zinc ion storage electrodes. However, it remains a formidable challenge to fabricate these materials with tunable composition by a simple synthesis strategy. Herein, folic acid-derived N/O-functionalized ultrathin carbon nanosheets are synthesized via the activation effect of nano-ZnO template. The as-fabricated FACN-800 exhibits extremely thin thickness (similar to 1.6 nm), hierarchically porous structure and rich N/O heteroatoms (14.9 at.% of N and 8.4 at.% of O), which is conducive to accelerate ion transport and provide additional active sites for Zn-ion storage. Thus, the optimized FACN-800 based aqueous zinc-ion hybrid capacitor delivers excellent zinc-ion storage capabilities with high specific capacity (163.6 mAh g(-1) at 0.1 A g(-1)), admirable energy density (130.8 Wh kg(-1)) and ultralong cycle stability (90.3 % capacity retention over 40,000 cycles) and FACN-800 has a specific surface area of 554.3 m(2) g(-1). Moreover, a series of ex-situ measurements and DFT theoretical calculations further elucidate the electrochemical mechanism between zinc ion storage and N/O dopants.