Bipolar Charge Storage in a Nanoporous Amorphous Tetrazine-based Covalent Organic Framework for High-Voltage Symmetric Supercapacitors

This work demonstrates the fabrication of a suitably designed tetrazine-based nanoporous amorphous covalent organic framework (Tz-DMA-TFP-COF) as an electrode material for supercapacitors. The amine precursor, tetrazine-based diamine, Tz-DMA [4,4′-(1,2,4,5-tetrazine-3,6-diyl)bis(2,6-dimethylaniline)], was condensed with TFP (2,4,6-triformylphloroglucinol). The COF was comprehensively characterized using Fourier-transform infrared (FTIR), solid-state C13 NMR (CP-MAS), thermogravimetric analysis (TGA), Powder X-ray diffraction (PXRD), FE-SEM, High-Resolution Transmission Electron Microscopy (HRTEM), and Brunauer–Emmett–Teller (BET) analyses, which confirmed the completion of the polymerization. Microscopic analysis revealed that Tz-DMA-TFP-COF is a fibrous nanoporous material. The BET isotherm further supported its porous morphology, with a high BET surface area of 227 m2/g and pore volume of 0.513 cm3/g. Furthermore, Tz-DMA-TFP-COF was employed as an electrode material for a symmetric supercapacitor, representing a fascinating example of a tetrazine-based covalent organic framework with intrinsic bipolar electrochemical behavior. This specific combination in the COF creates a highly ordered porous structure with multiple redox-active sites that can function at both positive and negative potentials. For three-electrode setups at a current density of 0.8 A/g, a Cs of 571.80 ± 33.51 F/g was found, with a Coulombic efficiency (CE) of 105.62 ± 8.9%, an energy density (Ed) of 316.31 ± 18.45 Wh/kg, and a power density (Pd) of 796.61 ± 0.29 W/kg. While the calculated values of Cs, Ed, and Pd for the device are 121.22 ± 5.38 F/g, 66.63 ± 3.04 Wh/kg, and 791.49 ± 1.24 W/kg, respectively, at 0.8 A/g. The COF exhibited excellent cycling stability (100%) even after 4000 cycles. Thus, these results indicate that Tz-DMA-TFP-COF is a promising electrode material for next-generation supercapacitors, combining high energy and power densities with outstanding stability.