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 nano -spheres (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 C--N and C-O-C 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.