Morphology controllable fabrication of arch-like covalent triazine framework nanosheets for high-rate and high energy density zinc-ion hybrid supercapacitors

Covalent triazine frameworks (CTFs) are a class of N-rich porous organic polymers with high chemical and thermal stabilities, showing enormous potential in Zn-ion energy storage devices. However, irregular block-shaped morphology of traditional CTFs hinders ion transport and electron transfer in frameworks and thus limits their specific capacity and rate-performance. Here, a morphology controllable fabrication strategy has been developed to prepare CTFs nanosheets using bisnitrile derivative-grafted hollow mesoporous SiO2 nanospheres (HMSN-CN2) as the precursor for the first time. After ZnCl2-mediated cyclotrimerization at the optimal temperature and removing HMSN template, arch-like O-bridged CTF nanosheets (namely, CTFO-NS-700) were successfully obtained. The arch-like 2D nanosheet morphology and hierarchically porous structure with an appropriate mesopore size (2–10 nm) effectively shorten the ion diffusion paths and reduce the ion migration barriers. The CN and COC groups offer abundant active centers for Zn-ion adsorption, which have been verified by ex-situ characterizations and theoretical calculations. As an advanced cathode for zinc-ion hybrid supercapacitors (ZHSCs), CTFO-NS-700 deliver a high capacity of 164.7 mAh/g (296.5F g−1) at current density of 1.0 A/g, superior-rate performance (retain 82.5 mAh/g, 148.5F g−1 at a high current density of 50 A/g), and a high energy density of 162.5 Wh kg−1, as well as long cycling life. In addition, CTFO-NS-700 based flexible ZHSCs also displays satisfactory capacity, excellent flexibility and nice anti-freezing property.